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Pump-action Rainbow Write-up

A few things different from the original
homemade writeup rainbow spring pumpaction

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#1 Naturalman7

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Posted 17 July 2014 - 03:38 PM

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Begun January 24, 2014

Disclaimer: I did not want to anger any admins so instead of creating a new post for each section and making an interactive table of contents, I just broke it up into a few different sections due to image posting limits.


Is there a limit to the number of links allowed in a post? I'm not unfamiliar with post formatting, but for some reason, some things don't like to work right.


Read photos from left to right, top to bottom. Thank you Zorns Lemma for helping me with regex.

 

Rainbow


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This writeup for a Rainbow Pump will address common points of failure and pitfalls, include a McMaster parts list, extensive photos and instructions, diagrams and cutting templates. This is an 'Open Source' homemade design based on Ryan's original Rainbow Pump. However, this one requires slightly fewer steps and is also slightly cheaper. I would have focused on a pump-action plusbow writeup instead, but I feel like due to their greater cost, difficulty to make, and similar performance, a pump-action Rainbow is better. I saw numerous +bows used during 'geddon, and they all seemed similar in most ways to a pump-action Rainbow. Because there is already a very good write-up (although old), this writeup will not go super in depth on the things that are similar, but will focus on the things that are different. Much of this information is repeated from my other write ups. If you’ve read those, you’ll encounter repeat information. If you haven’t read them, I’d recommend you do. They have some information that isn’t repeated. Without further delay, here it is:




 

Pump-action Rainbow Blaster


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Table of Contents

-Overview and Cost
-Templates
-Tools
-Diagrams
-Procedure - Linked
--Machining Pieces
---Side Plates
---Handle Pieces
---Catch Circles
--Handle
---Handle Assembly
--Catch
---Cut
---Drill and Tap
---Assemble
--Plunger Rod
--Main Body - Linked
---Measuring
---Cutting, drilling, and Milling
---Tapping
---Catch
---Reattach Handle
---Back to Plunger Rod - Linked
--Priming Slide
---Slot in Priming Slide
---Access Hole
---Half Pipe
--Back to the Blaster
--Sheath and Stock
--Front Bushing - Linked
--Modified Stock
-Errors
-Plunger Rod Breakage




Overview and Cost
Ryan’s original blaster used a PVC inter coupler piece that I didn’t think was the most efficient thing. That’s the main difference and is what this blaster is based upon.

The blaster seen in this write up cost $44.55. Omitting the optional nylon washers would reduce the cost ~$0.38. An opaque blaster would bring the cost down a further $25.00, but would make assembly difficult. Changing the seal piece would reduce the price an additional $4.00. I anticipate the cheapest this blaster could be produced is ~$15.00.

The cost of materials to build one of these blasters is $180.00. This is not the cheapest possible. This is likely the best raw materials cost to produce the cheapest per blaster cost.




Templates

Rainbow Catch Templates.jpg
Rainbow Catch Templates.pdf
Rainbow Catch Templates.idw
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Tools
• Drill
• Scroll saw
• Screw drivers – ph2 for #6 and #8 screws
• Tapping sets (#6-32, #8-32)
• Dremel disks for cutting (diamond cutting wheels are best) and/or a jigsaw or mill
• Hacksaw or other tool for cutting sections of PVC such as pipe cutters or rotational cutters
• 7/64” drill bit for #6-32 tapping
• Drill bit for string pass-through (7/32” works for a 3/16” string, if the ends are whipped well)
• 5/32” for #6 pass-through holes
• Drill bit for screw driver to fit through (7/16” fits my drill/driver ¼” adaptor)
• 3/8” bit for slots (or anything around ¼” should work.
• 3/16” bit for metal rod (or whatever sized rod you want to use)
Recommended
• Drill press
• Hole-saw – 1-3/8”
• Sanding belt
• Dremel sanding wheel, sand paper, files
• Hammer
• Pliers
• Something long and skinny to move the plunger rod. Also something to place behind the plunger rod to hold it in place.
• A screwdriver that fits in the hole for the priming rod can be used as a temporary priming handle




McMaster Parts List/Materials List

Clicking the image will take you to the google drive shared excel sheet. The photo file can be found on flickr.
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• 2x Small Washers for catch (#6 x 3/8" Washers)
• 9x #6-32 x 1/2” Machine Screws
• #6-32 x 1-1/4" Machine Screw
• 7x #6-32 x 3/4" Machine Screws
• #6-32 Nylon Insert Lock Nut
• #8-32 x 1.25” Machine Screw
• 1-¼” PVC Tee
• 1”- ½” PVC Bushing
• ~19.5 sq in of 1x8x2 Poplar Board
• ~20” of 3/16” Braided Polyester Cord
• 3/16” x 1-1/4” Fender Washer Metal washer for base of plunger head (or Ryan Mc#’s plunger head assembly)
• 2” of 3/16” Diameter Steel Rod for priming rod
• 15” of 8663K15 Black Delrin® Acetal Resin Rectangular Bar, 3/8" Thick x 3/8" Width or 3/8” Square Nylon Rod
• Catch spring (I’ve got no part numbers for you. I’ve collected all sorts pen springs and such that I use. Just find something that looks like it’ll work, and it should.)
• 17.75” of 9245K51 Clear PETG Tube, 2" OD, 1-3/4" ID or 1.5” Thinwall PVC (the higher the PSI, the better)
• Main Power Spring. I use [k26]’s (McM #9637K26) Compression Spring Spring-Tempered Steel, 11" L, .844" OD, .08" Wire
• 11/64” of 8585K14 Impact-Resistant Polycarbonate Round Tube, 1" OD, 7/8" ID, Clear
• ~14 sq in of 8574K43 Impact-Resistant Polycarbonate Sheet, 1/4" Thick, 12" x 24", Clear (catch) – clear is cheaper than tinted
• ~6.75 sq in of 8574K41 Impact-Resistant Polycarbonate Sheet, 1/8" Thick, 12" x 24", Clear (side plates)
• 24” x 49035K86 Std-Wall (Schedule 40) Clear PVC Unthrd Pipe 1-1/4" Pipe Size or standard opaque PVC. The thicker walled, the better.
• 9” of 49035K28 Std-Wall (Schedule 40) Clear PVC Unthrd Pipe 2" Pipe Size or opaque 2” PVC
• Skirt seal – McMaster part #9562K46 Stretch-Fit Rotary-Shaft Ring Seal 1" Shaft Diameter, 0.95" to 1.07" Shaft Diameter
• 6x 92311A146 Type 18-8 SS Cup Point Socket Set Screw 6-32 Thread, 3/8" Length
Optional
• 1-1/4" PVC Endcap or 45 elbow and 2” of 1-1/4” PVC
• 9x 90295A075 Nylon 6/6 Flat Washer #6 Screw Size, .140" ID, .313" OD, .057"-.067" Thk




Diagrams


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Edited by Aeromech, 23 November 2015 - 02:51 AM.

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#2 Naturalman7

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Posted 17 July 2014 - 03:41 PM

Seriously though. This forum is weird. The last two photo's links were freaking out, and when I fixed them, the next photo immediately before them broke. When fixed, the next one broke and so on.

Procedure

Machining Pieces
You can either machine each piece before starting, or machine each as you go. I prefer to machine each as I go, unless mass producing any piece. But for clarity’s sake, I’ll just have you do it now until you’re more familiar with how to make each piece.

Apply the sticker templates to the polycarbonate on the indicated thicknesses. There are protective sheets on the polycarbonate. Glue or, if printed on adhesive backed paper, stick the templates on the polycarbonate. The rectangle side plates are the only pieces that need to be 1/8” thick. I’ve theorized using the 1/8” thick polycarbonate for the rear catch circle which may be possible. All other pieces are ¼” thick polycarbonate. The rectangle handle piece, trigger, and main handle piece are all for 1” wood – with a ¾” nominal thickness.

The easiest way to machine the pieces is to first drill all the holes on the faces of the pieces. Drill the holes as marked. Then, use a table saw to cut the square rectangles, cut the front wood handle piece, and cut the wood main handle piece. The wood trigger is easiest to cut on a scroll saw. The catch pieces, circles and catch plate, are also easiest to do on a scroll saw. However, I’ve recently found using a hole-saw and turning it down on a lathe is easiest for the circles.

Each piece has little quarks that I’ve come across.


Side Plates
Drill and cut the side plates out of 1/8” polycarbonate. ¼” thick polycarbonate is useable and would be an easy option due to ¼” polycarbonate being also required for other parts of the blaster. The easiest way to machine these pieces is to cut them on a table saw and drill the holes with a drill press. Either drill all holes on the handle side plates 5/32”, or drill the middle hole 7/64” and tap for #6-32. If tapped, this allows the trigger screw to tighten or loosen on the trigger. I find that, depending on how the handle wood pieces are sanded, the side plates could end up being too tight on the trigger to allow it to rotate freely. This can be resolved by sanding the trigger smaller or increasing the gap between the side plates by adjusting the trigger screw. You’ll want to sand all the edges and corners down so that it’s comfortable – more on this later.

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Handle Pieces
Drill and cut the forward handle piece, trigger, and handle. It is often easier to drill the pieces before cutting, because there’s more material to hold onto while drilling. However, the order isn’t important. All the holes are 7/64” except for the trigger which is a pass through for a #6 screw - 5/32”. The forward piece and handle are easiest done on a table saw and the trigger is easiest to cut out on a scroll saw. When the main handle is cut, drill the two holes on top. The holes in top of the main handle are easiest done in a drill press vise where the holes will be straight and the base of the handle will be flush. These, as well as all the holes drilled, should be centered and straight. Otherwise, your handle or other pieces could be ridiculously crooked and may cause friction, the screws to not align, or other problems. When the pieces are drilled and cut, sand them down. Smooth down edges and sand the trigger and handle so they are comfortable to use. I use Ryan’s original templates, but I remade them with more detailed markings.

Only one of the top 7/64” holes in the forward wood handle piece is needed. The other hole, if used, interferes with the function of the blaster. Modification of some of the pieces may remove redundancy, but the templates were borrowed from Ryan and the parts I’ve mass produced are also interchangeable with my Rainbow Pump blasters. I will add this to the customization section.

The trigger’s flat top prevents the trigger from over traveling forwards. If the hole is drilled too high or the top cut is too low, than the trigger will be allowed to move forwards, which may be a minor undesired feature.

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Catch Circles
The catch circles are easiest to first drill the two 7/64” holes in each circle, then to cut them out with a hole-saw, and then to finally lathe them down so they fit in 1.25” PVC. However, if you’d like the practice or are good with a scroll saw, than it would be faster to simply attempt to cut the circles with it. If done with a scroll saw, it’s easier to drill a pass through hole for the scroll saw blade in the center of circles to cut out the square holes. I like the perfect roundness of lathes, but a scroll saw is faster and, with skill, is just as easy to make round. However, if cut with a scroll saw, it may be necessary to sand the edges down so that it fits smoothly into PVC.

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The catch plate is easiest to just cut out on a scroll saw after drilling a center hole. After all the pieces are drilled and cut, thread a scroll saw blade through the pieces and cut the square holes. I find it’s easiest to start the cuts diagonal first, and then square out the holes. Here are some pictures to clarify.

Drill the center hole.

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Cut diagonally.

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Shave out the inside of the squares.

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Then clean it up.

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You’ll want to make sure that all the pieces are smooth and sanded well. They need to be able to slide across each other freely.

Also, while making each piece of the catch, you’ll want to make sure that the square holes fit the Delrin rod and that at each step, the catch fits in the PVC body or you’ll have to sand it down again.

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Plunger Head Circle
The easiest piece to machine is the circle of polycarbonate for the front of the plunger head. I find that this piece should be as wide as possible, but still allow the plunger head to fit into the PVC plunger tube. More on this later.

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Handle

Handle Assembly
After the pieces are cut and all the holes are drilled, assemble the handle. Assemble the handle with eight #6-32 x ½” screws. Tighten well – I like my handles to not have any wiggle. I use nylon washers because I think they look nice and you wind up with a lot of extra washers from making a +bow. Omitting these washers reduces the cost of the blaster by ~$0.38. However, I’ve also noticed that the handle may be thinner than the 1” that these two screws would require and that the washers give a larger margin of error in the thickness of the wood or length of the screws. This is also another reason one may want to use ¼” thick side plates instead of 1/8”. Also, Ryan’s original guide was incorrect in the parts list and wording of his guide. He said to use ¾” long screws to assemble the handle which are far too long to work. It would work if you used wood with 1” nominal size, but most 1” woods have an actual thickness of ¾”. Sand down the edges of the handle.
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Catch

Cut
I know I’ve said some of this before, but here’s where it’s important.

Cut, drill and tap all the catch pieces. It’s easier to drill the two 7/64” holes in the catch circles before cutting anything out. Cutting the pieces out is pretty self-explanatory, but it took me a few tries to cut circles and such perfectly on a scroll saw. I’ve found the easiest way to make the catch circles was to find a hole-saw and cut the templates out, then widdle it down on a lathe until it fit easily in the main body. The catch assembly and pieces should fit in the 1.25” PVC freely. One of the common pitfalls is machining the catch pieces. There’s quite a bit of margin of error, but the process can be made easier through a little bit of practice and technique. Just go slow and steady is the key. I find the easiest way to cut the square holes are to thread the blade through the center hole of the hole saw, cut diagonally across the squares, then ‘carve’ out the rest of the hole. Continuously test fit the 3/8” square Delrin rod into the catch pieces. For the catch plate, drill a pass through hole for the scroll saw blade, then cut the square hole.



Drill and Tap
Drill a 7/64” hole centered through the bottom of the catch plate and tap it for #6-32. Also tap the holes in the catch circles #6-32. Make sure the holes in the catch circles are straight, otherwise, if you’ve originally made the circles perfectly sized, the misaligned holes could cause the circles to no longer fit. With all the work done on the catch, debur and sand all the edges and holes in the catch pieces so they are smooth.

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When I had originally printed out templates, they included diagonal holes for the screws to attach the catch to the main body. You can either drill and tap these in one of the catch circles, or simply wait to drill and tap them later – which would likely be easier, but I’ve done it successfully with either way.

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Assemble

With the catch plate as a guide, assemble the catch with two #6-32 x ¾” screws with a quarter inch gap between the circles. The catch plate should slide freely in between the circles.

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On the first Rainbow’s I made, I simply drilled the templates, cut the circles, and rounded them out on a table belt sander instead of a lathe. Using a table sander gave the advantage of being able to easily sand the catch circles as a whole piece, if needed.

When the catch is assembled, it should still slide into the PVC easily. If the holes are misaligned and the catch is lopsided at all, hitting it with a touch of the sander can straighten it out to fit in the PVC again.

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Plunger Rod

At this point, I like to make the plunger rod next. This will determine the draw length, placement of catch, and steel priming rod.

Cut the section of 3/8” square Delrin to length.

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Then, mark the center of one end of the Delrin – which will be called the plunger rod (PR) from now on.

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I like to use a #8 sized screw for the front of the plunger (or plunger head/PH) because its wider diameter helps keep the PH centered. Drill a 9/64” pilot hole approximately one inch deep into the Delrin and tap it #8-32. Keeping the hole drilled and tapped centered will assist in making the air seal as perfect as possible.

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Create another ¼” polycarbonate disk that fits onto the top of the rotary shaft ring seal (if you haven't already). More about this in the next paragraph. This info was repeated from the machining section and this is where it applies.

Then, assemble the plunger head as pictured. A 1.25” x .25” metal fender washer acts as the spring rest and supports the skirt seal, the rotary shaft ring seal creates the air seal, the small section (11/64”) of 1” OD 7/8” ID tubing keeps the skirt seal from buckling inward on itself and ruining the air seal, and the polycarbonate disks in front squishes the skirt seal which seals the two holes in the top of the skirt and compresses the skirt which flares it outward, which helps the seal. I’ve found that making this piece as perfect as possible goes a long way to making the seal perfect. The front polycarbonate disk flares the seal outward and presses it into the walls of the PVC body. Without the tubing piece, the skirt seal sometimes buckles inwards and causes one side of the skirt to not seal probably. With a proper polycarb disk on top combined with a tubing piece of the right height, the seal is perfect and low friction. If the plunger head when lubricated has too much friction in the PVC, take down the OD of the polycarb disk slightly and retest fit it. This method seems to create a 100% seal perfectly, every time.

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Edited by Naturalman7, 17 July 2014 - 06:06 PM.

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#3 Naturalman7

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Posted 17 July 2014 - 03:44 PM

Main Body

Measuring
Take the complete plunger rod, section of 1.25” PVC, and 1” x ½” PVC reducer bushing and lay them out to measure the dimensions of the blaster. Give the plunger rod half an inch of free space in front of it – this gives the string stop room for error when it flexes and stretches a little before keeping the plunger head from impacting the front bushing, or the priming rod from impacting the priming slide or slots in main body.

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Layout all the components, measure, and mark the key points. I could provide measurements, diagrams, and such for the blaster, but they vary depending on draw length, spring used, personal preferences, etc. So, for all the measuring and marking, it’ll be done by measuring with the actual parts.


Figure out what spring you want to use. You’ll need to adjust the design to whatever it is you’re using. Take into account the length and pre-compression. The spring will change the length of PVC, the length of plunger rod, position of catch and subsequently the handle. I was thinking about creating some sort of program to calculate all the recommended dimensions based on inputting different spring and draw preferences.

The key points are where the catch and handle need to attach.

A [k26] spring with a half inch of pre-compression needs a total of 10.5” from the front spring stop, to the rear spring stop – which in this case is the PH and front of the catch assembly.

Mark the rear of the PH and 10.5” away.

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Then mark where the catch needs to be. The mark in the middle of the catch is where the catch screw will be.

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Line up the mark in the middle with the trigger.

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With the handle in the correct position, mark the back of the handle and make a second mark. This mark will determine the thickness of the back of the priming slide. This part’s only stress is returning to the forward position and smacking into the handle. This isn’t a huge concern and I’ve found that the cleaner the cut of the priming slide makes the slide stronger. I’ve tried 160psi PVC pipe with a ½” thick rear priming slide section. However, the cut was not rounded at the corners and the PVC was too thin and it broke. The pipe Ryan used in his original guide is much thicker than 1.25” TW PVC and is much stronger, so if you used the clear tube it would be stronger. I’ve used a ½” thick rear section with 200psi TW PVC and it has worked out just fine. So with this in mind, measure the distance you’d like for the rear section of your priming slide and mark it on the main body.

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Accounting for the same room for flex as with the front bushing, add half an inch to the draw length and measure that from the second mark. In this example, this blaster has 6.25” of draw, so the next mark is 6.75” from the second mark by the handle. If you’re also accounting for the width of the drill/mill bit, add ¼” length to these marks. These marks will be for the priming slots.

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With the marks measured out, I like to measure the circumference into eighths with one line on the words which will be the bottom. I measure the PVC into eighths with a marking jig.

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I continue the marks all the way down the body of the blaster by using a three sided ruler.

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With the circle jig, measure 1/8” past the marks made for the front of the catch assembly and mark on each diagonal side for attaching the catch assembly. Hopefully the plethora of pictures will clarify any confusion of my random jumbling. You'll want to place the screws to attach the catch 1/8" from the 10.5" mark.

On the west and east sides (the sides perpendicular to the handle/bottom), I measure and mark half an inch from the front. These will be for two screws to attach the front bushing when the time comes. I put them here because it is just before the wider end of the bushing. It makes it easier to seal the front bushing, and creates indentation of the bushing inwards so that the fit of any ½” PVC into the bushing is much tighter. I’ll elaborate more on this later.

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With the bottom of the body identified, line up the handle again with the trigger and mark where each of the holes are in the handle to attach the handle to the main body.

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Make the marks from the priming slots on the west/east sides. Measure ¼” wide rectangles for each slot on each slide.

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Continue drawing the rectangles on each side. Here, I also compensated for the ¼” diameter bit. If the measurements are correct and the lines straight, I won’t be drawing rectangles in the future – as it is unnecessary if cutting the slots with a mill.

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If your first set of marks for the handle were not on the right side of the blaster, this is also where I would use the quartering jig to make the marks around the circumference of the body.

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Copy the marks of the four handle hole marks to the opposite side, the top.

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And copy the marks for the catch to the bottom.

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This is marking the 1/8" mark from the 10.5".

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The completed markings:

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Double check all the measurements and markings are correct. The components laid out:

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Cutting, drilling, and Milling

When the marks for everything has been confirmed, proceed with the cutting, drilling, and/or milling of the body.

I used a ¼” milling bit to cut the slots. It works well, but requires going slow and making sure the body doesn’t slide, move, or bend funkily. Other methods are using mason twine, a dremel, scroll saw, or jig saw. I find the easiest methods are (from easiest to most difficult) milling, Dremeling, jig sawing, scroll sawing, or mason twining.

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With the slots cut, drill each of the holes needed in the bottom of the blaster for the handle and catch. Drill each one 7/64”, then widen the middle one to #6 pass through 5/32”. The holes should all line up with the handle.

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Flip the body over and drill four 7/16” holes mirrored where the holes for the handle are. They should be marked on the body. 7/16” is for passing a screw driver through, but a smaller hole would work if your screw driver is smaller. Just so you know, I messed up on the marking and accidentally drilled an extra hole – just another reason why I emphasize measuring and marking excessively.

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Tapping

Tap each of the 7/64” holes in the bottom of the blaster #6-32.

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Catch

Take the catch, which should fit into the body, insert it with the threaded side of the screws to the front. If you’re wondering, the flat side of the catch will act as the rear spring rest. The spring will rest on the flat side of the catch.

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Align the catch plate over the 5/23” pass through hole in the bottom.

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Assemble the catch spring into the blaster and tighten it down so the catch stays in position.

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Then, with a 7/64” bit, drill all the way through the body and catch circle on the diagonal sides. In order to keep the catch centered properly when drilling the holes, I like to hold the position of the catch with small drill bits.

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With the holes drilled, now here there are a few choices. If you chose to drill and tap the holes in the catch circle before this step, you can simply take #6 x ½” screws, insert them into the holes to kind of ‘cut’ the threads into the PVC and the polycarbonate and I’ve found that works, or remove the catch and tap the PVC and polycarbonate. If you did not drill and tap the catch circle before, you can remove the catch from the body and tap the holes. Or, simply tap the holes through the catch. Either way, put threads into the PVC and catch. You will need to push the catch out of the PVC with something long and skinny. An issue I’ve found is that #6 set screws have such a small drive size that too much friction can strip them. Make sure you can drive set screws to hold the catch in, but that they aren’t too tight or else you’ll never be able to get them out again. After inserting #6 x ½” screws and removing them again, or threading the catch while it’s in the main body, the threaded holes should be loose enough to drive set screws into.

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Attach the catch with four #6 x 3/8” set screws and add the catch spring assembly – a #6-32 x ¾” machine screw, two small washers, and the catch spring. I don’t know why people always use two washers, but it depends on the size of the catch spring and the pass through hole. The washers keep the spring from getting stuck in the hole if the spring is too small OD, and keeps the spring on the head of the screw if the spring is too wide OD.

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Now is a good time to remove the sharpie marks on the blaster.

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Make sure the 3/8” Delrin still fits in the assembled and attached catch. Lube the plunger head and if it’s tight, it should now fit easier when lubed.

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Reattach Handle
With the trigger lined up with the catch, the holes in the handle should also line up.

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I like to make sure everything is measured as precisely as I can so there’s also a lot of handle attaching and reattaching.

Attach the handle with four #6-32 x ¾” machine screws. Putting screws into the top and through the bottom can be tricky at the least without practice/technique. Trying to drill the screws into the PVC with them wobbling and always dropping into the PVC can be very frustrating.

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It’s easiest to attach the screws by holding the blaster upside down and starting the screws partially into the body.

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Make sure that the trigger is oriented properly, and not angled when you attach the handle.

This
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Not this

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When the screws are held into the body, I like to press the handle against the body and tighten the front most screw first, then the rear most, and finally the middle two. It doesn’t matter if the screws are done like this, but I like to do it this way. I like a system.

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Edited by Naturalman7, 17 July 2014 - 10:56 PM.

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#4 Naturalman7

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Posted 17 July 2014 - 03:49 PM

Back to Plunger Rod

With the handle attached, lay the rest of the components to double check the measurements. With the bushing flush to the front and a half an inch of leeway, figure out where the steel priming rod and string stop need to be. Mark the priming rod .5” from the start of the slots and mark the string stop at the end. I like to place it at least .5” from the end, but it could be placed closer if desired, but don’t. I’d say just don’t put it too close to the end, and account for the width of the hole.

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I put the string stop .5” from the end and the priming rod 1.25” from the end.

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Drill the string stop hole in the arbitrary top of the plunger rod and aim to put it in the middle of the width of the rod. Use a bit wide enough to fit the string you use. I use a 11/64” bit for my 3/16” string because the melted ends of string are more often than not wider than the string itself. Maybe it’s just because I don’t have a ton of experience with sealing ends of rope. Anyway, just use whatever bit you want that works. Just keep it smaller than the width of the rod.

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Drill the hole for the priming rod in the side of the plunger rod. Drill the hole the same size, or even a tiny bit smaller than the diameter of the rod. I use a 3/16” priming rod and a 3/16” hole.

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Make sure the string fits in the rod when the holes are done.

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Priming Slide

Next, is the priming slide. Before we get into machining, let’s talk materials – to sum up what I said before: I used Ryan’s original write ups tube. It’s nice, clear polyester. You can use regular 1.5” thinwall PVC, but you may have to adjust your cuts or measurements if you use a very low PSI. I’ve used 200PSI without problems, and the polyester is even thicker.

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Whatever material you choose, cut it to length. It helps to make at least one of the cuts square for the priming side so the blaster is primed evenly, but it’s just a minor detail. The length you choose affects how large of a priming grip you’ll have. I gave myself several inches. Keep in mind that you’ll have to cut a half pipe so that your loading mechanism can stick out the top. This will, of course, affect the feel and placement of the handle. If your hands are large, you may have problems, but I find that it just takes some getting used to. If you use an actual priming handle mounted on the bottom (more on that later), you can get away with a shorter priming slide. Using a maverick handle, one can completely eliminate the need for a half pipe.



Slot in Priming Slide
With the priming slide lined up with the end at the start of the slot, mark the handle and front of the PVC. The handle mark should be the same distance from the end of the priming slide as the distance measure behind the handle as before – 5/8”.

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Measure the width of the handle; it'll be slightly wider than 1" if you used the wood and 1/8” side plates. The priming slide needs to fit around the handle. Another important note: cut the slot slightly wider – on the outside edge of the marks. If you use 160PSI Thinwall PVC, you’ll have to be extra precise and cut the slot as perpendicular as possible. I’ve run into the problem of the priming slide’s wall getting pinched between the handle and PVC and stopping the slide from moving. If you make the handle and slide well enough, that pinching should be prevented. If you can, just use something thicker. Depending on how thick and strong and how clean the cut is on the priming slide, the 5/8" distance can be decreased.

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Measure and mark the width of the handle on the priming slide – round up if you can.

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Move the slide to the rear position, measure and mark the front of the handle.

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Extend the marks and draw a rectangle. Scribbled means cut away.

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To make sure everything is entirely measured and marked correctly before cutting, remove the handle to prepare for the slide. I like to keep the screws in the body to make it easier to reattach the handle later. Drill out the screws part way, then manually unscrew the rest of the way to make sure you don’t accidentally remove the screws.

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Also remove the catch spring.

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The slide should line up nicely. I also extended the front mark around the circumference.

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Using fancy tools…

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Cut out the slot. Try making the cuts clean and round the corners a little. Easiest ways are milling->jigsaw->Dremel. If Dremeling, use a diamond cutting wheel – they work great. I don’t find any issues with Dremeling PVC. It’s super messy, but diamond wheels work well. If a regular reinforced cutting wheel is used, I find regular wheels, for one, break quite often and melt both PVC and polyester releasing odors and melted pieces of plastic. A diamond wheel, on high speed, and using sufficient pressure can cut polyester and polycarbonate without melting it, releasing odors, or making a huge mess. A Dremel is, in my experience, probably the best option.

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I’ve found a jigsaw works quite well, granted is slightly messy, but with PVC it’s a lot less messy than a Dremel. You have to use a Dremel or a drill bit to start the blade. Hold the piece in your hand and a vice and it cuts extremely quick and straight. A skilled Dremel user could cut just as straight or quick, but not as clean.

I’ve milled a polyester priming slide once. It worked fairly well, but unless one has ‘fancy tooling’, it is quite difficult and is simply easier with a jigsaw or a Dremel.

The cut slot.

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Make sure the priming slide slot fits. With the catch spring and handle screws in the body, line up the handle and make sure there’s enough clearance around the handle when the handle is pressed against the PVC.

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Access Hole
Next, we’ll need to add access to the handle screws from the top. Make sure the slide is in the forward position.

Mark where the first hole is and then drill another screw driver pass through hole with the bit that was used previously.

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This is that hole. It provides access to the handle screws.

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If you don’t attach the handle to make the mark for the hole and if you don't realize the slide is rotated, your measuring and marking will be off. If so, just drill another hole or widen it. Just make sure your screw driver can pass through.

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Half Pipe
In the method mentioned before, attach the handle through the hole in the priming slide and the main body.

The back of the slide should line up with the start of the slot.

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With the slide in the forward most position, mark to cut a 'half pipe' to allow the wye or other loading mechanism to stick out the top. With the slide edge marked, remove the handle and slide once more. If you don’t mark the slide when the handle is attached, the half pipe may not properly be ‘half’.

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Remove the handle again and slide and mark the half pipe out. I then like to make the corners rounded for comfort and aesthetics by using a 1/2" diameter circle to mark the rounded corners.

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After the priming slide half pipe is all marked, cut it out and round the corners. The easiest way for this that I've found is a Dremel. A jigsaw is probably not precise enough, I haven't tried yet with the mill, but I suspect that milling may actually be easier than Dremeling.

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After the slide is cut out, round it out, sand the edges, and debur it all. I use scissors if there’s a lot of deburring to do, and then use a Dremel small sanding wheel.

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If you don't use a diamond wheel, you'll have cuts that look like this and you'll have to do a lot more deburring to remove all the melted chunks of plastic.
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After the slide is finished and smoothed, don’t forget to clean out any debris.


Remove any sharpie marks with rubbing alcohol and place it back onto the blaster. The front should be all nice and the PVC body should be flush with the priming slide.

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Back to the Blaster

Sand the handle edges down if you want to and haven't yet. It'll be much more comfortable if you do – even a little bit.

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Also, sand down the forward points on the handle. You’ll definitely want to if your handle is too small or your hand is too big.

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The rest of the blaster will be assembled as pictured.

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At this point, you can reinsert the plunger rod. Test the seal, and if you don’t already know your spring’s compression details, you can also insert a spring, compress the spring and gauge where the catch notch needs to be. Don't forget to lube the PH before you put it in. It'll be a tight fit going into the tube, but even tighter coming out if you don't lube it up.

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Measure how much draw you'd like and cut the notch in the plunger rod. With a pre-compressed length of 10.5" and 6.25" of draw, doing some math puts the catch notch 4.25" from the front. Don't cut the notch any more than half way through the Delrin. I like to cut a four sided shape into the notch. Half way down, .25" across, and 45 degrees up. I find this easiest done with a scroll saw, but simple hacksaw skills also work - but less precise. Whatever dimensions you use, keep in mind the thickness of the catch plate and catch circles. You’ll have to account for the added ½” in your measurements.

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This notch was cut too deep. Don't cut your notch like this. It will break. If it does, a viable solution can be found later.

Insert a temporary priming device and test out your catch.

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Primed - without the spring.

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The compressed length should be what you anticipated.

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Return the rod to the forward position. With the priming rod returned to the forward position (1/2” away from the priming slide and front of slot) there should be 1/2" of room in front of the plunger head plus the bushing.

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You can also test the seal, too, with the temporary priming rod.

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Add the spring and push the plunger to engage the catch. With any luck, it’ll work.

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String Stop and Priming Rod

With the blaster primed, add the string. I find ~20” is plenty long. You can always cut off the excess.

Due to the notch cut into the Delrin, the rod will likely be angled. Thread the string through one side and down the other.

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Cut a 2" long priming rod out of 3/16" steel and clean up the edges. The rod should be tight.

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Put it into the priming rod. I’ve found it easiest to hammer in the rod with something under the plunger rod. 1/2" PVC or 3/4" wood is good. Hammer it in. If you hammer the rod in too much, you can pull it back through. The rod should be centered, especially if it’s tight. If it’s loose, it’ll be self-centering, but it’s always better to try to be precise. It should line up with the priming slide. If you hammer the rod in too much, you can pull it back through.

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Sheath and Stock

Whatever you use as your sheath, the PVC tee should fit inside it. It'll be the stock. It doesn't need to be super strong, or clear, or anything specific.

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Mark a short distance on either side and drill more holes for the string.

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Depending on the draw length, preference and such, cut a length of pipe for the sheath. I used 9".

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Thread the string through the sheath and place the sheath on the blaster.

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A quick note, I like all the words to be on the bottom, check that before doing anything permanent.

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With the tee attached, drill a 1/8" hole and add a #6-32 x 1/2" machine screw to hold the back together.

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Thread the string through the tee. Make sure the strings aren't tangled up.

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Tie a knot in one of the ends of the strings.

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Deprime the blaster while holding one string so that it doesn’t get stuck in the blaster. Thread the string, gauge the leeway, and tie another knot. The knot will tighten up and move further down the string, so tie the knot a little higher than you think you’d need.

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With the blaster primed, you can adjust the knots.

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You can see the ~1/2" of leeway. Unprimed.

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Primed

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Edited by Naturalman7, 19 July 2014 - 02:00 PM.

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#5 Naturalman7

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Posted 17 July 2014 - 03:51 PM

Front Bushing

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The last, and arguably the most important step of a Nerf blaster is the front seal. There are a few different ways to create this seal. One involves plumber’s goop and tape of some sort.

Some say you can just hammer the bushing in the front. I've found that if you do this, it either isn't rigid enough to not move when pushed or hit on the front, or too tight and it cracks and breaks the clear PVC. Opaque PVC is stronger and doesn't crack.

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The ID of this PVC was 1.335". I'm working on figuring out exactly what difference between the PVC and bushing needs to be to not crack the PVC.

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A regular PVC bushing has an OD of 1.375" which is a bit too large.

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Either sand down the lip of the bushing or have it stick out.

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Wrap the base of the bushing in packing tape (or electrical tape, but I’ve found packing tape to be better).

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It should fit snug and you can test the fit as you wrap it.

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Once it's tight enough, you can cut it from the tape roll.

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Use a sharp knife to trip the excess tape. If you can ream it at an angle like pictured, it makes it easier to insert. Otherwise, the tape can get caught on the edge of the PVC.

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Apply goop around the entire circumference of the bushing and insert it into the PVC.

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Make sure as much of the excess goop is applied to the bushing. You can apply the excess goop to the front seam of the bushing and PVC. It's a small detail, but as I said, I like my system.

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The mark at the front of the PVC is for attaching the front bushing. I used calipers to figure out exactly where I wanted to put the screws.

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I used a 7/64" bit to drill pilot holes. However, I made sure to drill the pilot holes only 3/8" deep, just enough to fit a set screw. I marked the bit 3/8" down.

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I used calipers to figure out exactly where I wanted to put the screws, marked it, and drilled 7/64" pilot holes. Then tap #6-32. Or, instead of tapping, 'cut' threads by inserting a #6-32 x 3/8" screw and removing it repeatedly. Either way, make sure you can put two set screws into the front bushing without stripping them.


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Before inserting the set screws, apply good into the holes to make sure they’re sealed. Repeat for as many screws as you like.

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The Finished Blaster

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Modified Stock
Spoiler





Errors
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Plunger Rod Breakage
Spoiler





Finished Blaster (Gallery)
Spoiler

Edited by Naturalman7, 17 July 2014 - 11:04 PM.

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#6 Naturalman7

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Posted 17 July 2014 - 03:54 PM

Reserved. Just in case.
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#7 Naturalman7

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Posted 17 July 2014 - 03:57 PM

Also reserved. Also just in case.




Does anyone else think the gap between the pictures would look better if they were wider?


Questions, comments, flames, please post...

Edited by Naturalman7, 17 July 2014 - 09:06 PM.

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#8 KaneTheMediocre

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Posted 18 July 2014 - 02:40 AM

This writeup seems really nice. Everything seems clear to me, the photos have enough context in them that I can tell what you're doing and why, although that may be because I'm already familiar with the RBP design. I also like your use of the spoiler buttons to parenthesize extra information that isn't core to the writeup.

I would suggest a small modification to the traditional Rainbow catch to make these easier to produce--Thicker bushing plates! If the circles in front and behind the catchpiece were 1/2" thick, getting tapped holes in the edges would be much easier, and if you wanted to drill and tap at assembly you might even get away with opaque PVC. You still need to get the gap between the bushing plates line up with the hole for the catch screw, but once you have that you don't need to be very exact with the holes that hold the catch bushings.

Ryan and I tried to refine the design to not require the rear slots, but never came up with a satisfactory solution due to plunger rod rotation problems. With your square plunger rods, that isn't a problem at all! Basically the trick that we tried (and failed to implement reliably) was to

1. Eliminate the slotted 1 1/4 tube entirely (In your case, the plunger tube would just end a little bit past the handle)
2. Put a bushing inside the rear of the priming tube that allows the plunger rod to pass. In our case this was trivial because the plunger rod was round, but you will either need a square hole or a hole that's oversize by at least 1.41.... one and a half times. In your case with a 3/8" square plunger rod, that means at least 9/16".
3. Add a bushing or really anything that you can attach to the back of the plunger rod that's significantly larger in size than the aforementioned bushing in the priming tube
4. Add a grommet or other padding between the back of the priming tube bushing and the front of the aforementioned widget. This replaces the string stop--It will still end the travel with a longitudinal tension rather than compression force on the plunger rod, but without having to muck about with string.

The not-entirely-fatal flaw with this plan to eliminate machining is that now the 2" stock tube can only attached right behind the handle on the underside where the priming tube is cut away. That area is probably zero as you have the blaster dimensioned now, but adding a bit of length to the slot in the priming tube and the plunger tube will add that much real estate to work with--More will get you a sturdier stock, but will increase the OAL length and distance between the stock and the handle by that much more. I don't think that the stock wobble is that big of a deal because you aim by holding the handle and priming grip--the stock can pretty much wobble wherever without affecting that. That said, wobble may eventually lead to breaking off the chunk of plunger tube that's affixed to the 2" stock tube, so I'd give that at least 2".

I realize that even very small changes basically require you to re-write the whole thing, since pretty much every length in the blaster will change, and all the photos become wrong, etc. So I'm not expecting you to rewrite these instructions even if you like the aforementioned changes. But, if you plan to continue experimenting with refining the design to be easier, those are a couple ideas to try.
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#9 Naturalman7

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Posted 18 July 2014 - 10:44 AM

Thank you for the feedback, I really appreciate it. Not having the slots would be nice, and I can't say I've tried what you're proposing before. I can simply rewrite the affected sections and add a spoiler for the method. I'll add it to the list of changes I need to make on my write-ups.

I've successfully made an opaque RB style blaster with only 1/4" plates and had no difficulty. Using thicker plates would be easier, but I didn't find using 1/4" plates difficult (especially when 'pre-drilling' the plate) and 1/2" poly is more than twice as expensive and 1/4".

After a few more write-ups (if there's any more time left before October), I will look into this 'new method' and start with CAD.
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#10 Langley

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Posted 18 July 2014 - 10:53 AM

Jeez. I think you've submitted about a third of the total contest submissions.

Disclaimer: I did not want to anger any admins so instead of creating a new post for each section and making an interactive table of contents, I just broke it up into a few different sections due to image posting limits.


If it is for a write-up, you're always welcome to post as many times in a row as you need to in the beginning of the thread. Currently, this is the only way to break a writeup into sections that can be linked to from a table of contents.
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#11 Naturalman7

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Posted 18 July 2014 - 09:00 PM

Alright. Breaking up a write-up isn't too practical for a step-oriented write-up, but a section-oriented one would benefit from it.
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