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Nesting PVC/CPVC/Thin Wall Questions


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#1 HotShotAzn

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Posted 17 January 2014 - 10:16 AM

This is my third day of working on my daughter's aabow replica and I'm sure will be my third visit to HD for more supplies.

For the life of me, I can not figure out how people are nesting PVC/CPVC pipe together. On the aabow youtube video, 1/2" CPVC was nested inside 3/4" CPVC. That's not possible, at all, with the stuff I got. I tried using Kane's method and still, no idea how they are nesting their PVC.

I did manage to nest 1/2" EMT into 1/2" thin wall, then tried to nest that into regular 3/4" PVC (since ID should be bigger). Nope. Had to bore it out with a spade bit. I think this contributed to structural rigidity because I f'd that one up and had to start over.

I've gone to a few different stores because I figure sizes vary but still, I am not seeing how nesting is possible. Even in the aabow youtube video, the 1/2" PVC had to be wrapped with electrical tape because it was THAT MUCH smaller than the ID of the 3/4" PVC.

At this point, I am considering nesting the regular 1/2" PVC into bored out 3/4" and calling it a day. I'm just wondering if I'm missing something?
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#2 shmmee

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Posted 17 January 2014 - 10:36 AM

Most hardware stores have 1/2" pvc in 6' lengths. As odd as it may seem - these 6' pieces are thicker walled than the longer pieces. That's the stuff we use for nesting cpvc into (for adapting 1/2" pvc fittings to 1/2" cpvc (barrels and such). It will help to bevel both ends slightly and pound the cpvc in with a hammer, but it's a tight fit that won't come apart unless you want it to.

Sorry, I can't give you any guidance for 1/2" cpvc into 3/4" cpvc that does sound kinda wacky though.

Good luck with your AAbow!

Edited by shmmee, 17 January 2014 - 10:38 AM.

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#3 HotShotAzn

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Posted 17 January 2014 - 10:41 AM

Most hardware stores have 1/2" pvc in 6' lengths. As odd as it may seem - these 6' pieces are thicker walled than the longer pieces. That's the stuff we use for nesting cpvc into (for adapting 1/2" pvc fittings to 1/2" cpvc (barrels and such). You'll have to bevel both ends and pound the cpvc in with a hammer, but it's a tight fit that won't come apart unless you want it to.

Sorry, I can't give you any guidance for 1/2" cpvc into 3/4" cpvc that does sound kinda wacky though.


I bought 10' because it was cheaper than 6'. Go figure.

So you are actually nesting 1/2" CPVC into 1/2" PVC in order to use the PVC pipe fittings. Interesting. I didn't realize the two actually would fit. Most of the websites I've seen show that the OD of both pipes are 0.84". Even the 1/2" CPVC I have at home is between .82" - .84".

Even the ID of the 3/4" PVC is .80, so not sure how that would fit.

Edited by HotShotAzn, 17 January 2014 - 10:43 AM.

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#4 MAV13

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Posted 17 January 2014 - 10:51 AM

That's odd, all of the 1/2" CPVC I've seen is 5/8" OD, which can then be nested in 1/2" PVC after boring a small piece out with a 5/8" spade bit.

Although, if I may make a suggestion, try CaptainSlug's SNAP-7 Microbow instead of the Aabow. Its easier to make and it performs much better.
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#5 Meaker VI

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Posted 17 January 2014 - 11:19 AM

The PVC/CPVC you're using are pipes, which means that the ID's aren't consistent at all. I've dug through one pile of 1/2" CPVC and found some that fit my darts great for spring-blasters, some great for air-blasters, and some not at all. Usually if I'm nesting, I try to nest 1/2" CPVC into 1/2" 200-PSI PVC (thinwall) since it's easier for me to find.

I made model for figuring out which pipes fit where, I think it goes like this:
1/2" CPVC fits into
1/2" (sometimes/bored out Sch.40, otherwise 200-psi) PVC fits into
1/2" PVC coupler/fitting fits into
1" 200-psi PVC fits into
1.25" PVC (1" PVC also fits, but doesn't hold anything useful) fits into
1.25" PVC Coupler/fitting fits into
2" PVC

Needless to say, the world of plastic pipe is complex, rather than delve into the complexity just take nubs of the pipe you want to use and try to fit it into the pipe the store has available. As the others have mentioned, the shorter lengths of pipe they sell are usually more consistent. And you can sometimes find different qualities of pipe in the plumbing supply, plumbing drainage, irrigation, and electrical aisles.
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#6 ck32

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Posted 17 January 2014 - 11:24 AM

If your 1/2 in. CPVC is 5/8 in. OD then you could get a 5/8 spade bit. Drill out what ever you want to nest the 1/2 in. CPVC inside of, and solvent weld them together. This method works just as well as hammering them together, with out the struggle of actually hammering them together.

Edited by ck32, 17 January 2014 - 11:26 AM.

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#7 azrael

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Posted 17 January 2014 - 12:28 PM

You can try ordering off McMaster. Their 5/8" OD and 1/2" ID butyrate tubing is really consistent. It's perfect for my darts.
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#8 HotShotAzn

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Posted 17 January 2014 - 12:36 PM

Although, if I may make a suggestion, try CaptainSlug's SNAP-7 Microbow instead of the Aabow. Its easier to make and it performs much better.


CaptainSlug's? Or Did you mean Carbon's?

I asked my daughter which design she liked better and she liked the aabow because the barrel was inline versus offset. She shoots a compound when the weather is nice and is used to lining up her shots accordingly.

Physics wise, how does Carbon's perform better? I looked at the design and agree that it is simpler to make. However, with the air outlet being offset, you would think the air reduces in force because it has to redirect. My plunger -> barrel is direct.

The 1 1/4" plunger tube fits over the 3/4" TEE. In the 3/4" TEE, I added a 3/4" to 1/2" reducer, a stub of 1/2" thinwall and have 1/2" EMT going all the way out the other end of the TEE as the barrel. This seals well enough that I make stock arrows fishtail because of the power. But, if I could use Carbon's method and redirect the barrel back inline (think like a detour in traffic), than I will go this route.

I will tell you that Carbon's design gives me the most piece of mind for the bow arms. I've already broken two TEEs by having two piece bow arms and the stress on the ports. It worries me when my daughter draws it back that an arm is going to come off and smack her.

Edited by HotShotAzn, 17 January 2014 - 01:00 PM.

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#9 andtheherois

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Posted 17 January 2014 - 01:53 PM

Sift through 1/2: PVC conduit. It's ID is super inconsistent. I have a few 6ft lengths that all perfectly fit 1/2" cpvc. It just takes a bit of checking.
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#10 MAV13

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Posted 17 January 2014 - 01:58 PM

Yeah, I meant Carbon, its been a while since I've looked at homemades haha.

On mine I used a cross instead of the tee with the Cpvc elbow. Not a ton more dead space that way because of the bow arms filling up the cross and you can then have the barrel inline.

Edited by MAV13, 17 January 2014 - 01:59 PM.

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#11 HotShotAzn

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Posted 17 January 2014 - 02:14 PM

On mine I used a cross instead of the tee with the Cpvc elbow. Not a ton more dead space that way because of the bow arms filling up the cross and you can then have the barrel inline.


Are you talking about Kane's method? Tried that too. Inline aiming but still, separate bow arms. Man, this first bow is costing me a fortune in parts. The second and third bow will help even out :)

This is what I'm thinking. I'll apologize now for the crude drawing. Airflow is right to left. "T" is the TEE. Air is directed around and barrel is inline. Would this result in too much loss air pressure?


_____________      _______________
BARREL       |  T |  <-  <-   <-
___________  |  T |   _____________
           | |  T |  |  
           | |____|  |
           |_________|

Edited by HotShotAzn, 17 January 2014 - 02:16 PM.

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#12 MAV13

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Posted 17 January 2014 - 02:31 PM

Not Kane's method, a Snap-7 with a cross, bow arms run through the cross and air moves through the other holes of the cross from the plunger tube to the barrel. Its much simpler that way, at a cost of a bit more dead space. Bow arms are still one piece and everything else remains the same.
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#13 HotShotAzn

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Posted 17 January 2014 - 02:36 PM

Not Kane's method, a Snap-7 with a cross, bow arms run through the cross and air moves through the other holes of the cross from the plunger tube to the barrel. Its much simpler that way, at a cost of a bit more dead space. Bow arms are still one piece and everything else remains the same.


When I first saw Kane's method, I had thought that he did the exact same thing as you...let the air pass around the bow arms and I was going to go with this exact same process. Should have trusted my instinct.

I think I will go with this route. Few questions:

1) What is your cross size and bow arm size? Did you purposely oversize your cross to let more air go around the bow arms?
2) What kind of range should I expect?
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#14 MAV13

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Posted 17 January 2014 - 02:49 PM

If i remember correctly, its 1.25" plunger tube -> 1.25" coupler -> 1.25" to 1" reducing bushing -> 3/4" cross. The cross seats in the reducing bushing perfectly, its airtight with solvent weld. The arms go through 3/4" to 1/2" reducing bushings that have had the inner ridge sanded out to allow a tight fit around 1/2" PVC for the arms (be careful sanding these, you want it to be as airtight as possible). Then on the front of the cross is another unsanded 3/4" to 1/2" reducing bushing. You could probably reduce down to a 1/2" cross but 3/4" is probably the optimal balance of airflow to deadspace.

Here's an old picture of mine before I redid the tape and made a hopper. Notice the wire for the bow arms runs through the handle, don't do that. Drill a hole through your plunger rod such that the wire hits the back of the plunger tube to provide a bit of cushion. Actually I think this is when I still had CPVC bow arms as well. They work but they are weaker and they deform faster than PVC, may be better for your daughter though, PVC is a fairly hefty draw.
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Edited by MAV13, 17 January 2014 - 10:45 PM.

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#15 HotShotAzn

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Posted 17 January 2014 - 03:52 PM

Thanks so much, this is going to be super easy now. I am going to try 1/2" bow arms for my daughter and I think I might try a 1" cross with 3/4" bow arms for myself. I toyed with the idea of even using a 1" cross with 1/2" bow arms to maximize air flow.

I went to the CPVC section and I don't think what I was sold is CPVC as the tubes here are way different than what I have at home...and a lot more expensive. That would account for the nesting question. I found some 5' blue pex though and will use as the barrel, nested inside whatever it happens to fit.
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#16 HotShotAzn

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Posted 19 January 2014 - 11:32 AM

Side question about PVC and structural strength.

If a hole is drilled into the PVC, I am assuming the PVC loses some structural strength, correct? How much?

One of the current bows I have is using 3/4" arms. I am thinking of drilling a 5/8" hole for 6" of PEX to go from one end of the cross to another. Obviously use reducer bushings in both sides of the cross to get a seal. That way, I would effectively reduce dead space, account for any leaks in the arms, and allow for direct plunger.

Edited by HotShotAzn, 19 January 2014 - 11:34 AM.

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#17 MAV13

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Posted 19 January 2014 - 10:10 PM

3/4" PVC is strong stuff, it should be fine. Most of the stress will be on the junction between the arms and the bushings anyhow.
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#18 KaneTheMediocre

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Posted 20 January 2014 - 07:48 PM

5/8" hole through 3/4" PVC doesn't sound that bad. Sealing it up as you propose does work well--I did something similar with a 1 1/4" cross and 1" PVC on a few PACs. I found it difficult to put together, but much easier than trying to seal around the thru-hole with goo.

I'd like to know what discrepancies exists between the tubes I'm buying and the tubes you're buying. I'm particularly concerned because mcmaster sells CPVC pipe in the same sizes as PVC pipe, but the stuff I buy follows a different pipe size system shared with copper pipe. I don't even know the name of the pipe size standard the stuff I call "CPVC" follows, but my approximate dimensions of the tubes used here are:

1/2" CPVC Pipe: ~.485 ID .625 OD
1/2" EMT Conduit ~.622 ID, ~.71 OD
1/2" Thinwall PVC Pipe: ~.72 ID, .840 OD
3/4" CPVC Pipe: ~.72 ID, .875 OD

The 1/2" x 3/4" bushing is a mass produced pipe fitting (mcmaster 4880K313) built to fit 1/2" pipe on the ID, and imitate 3/4" pipe on the OD so it fits in 3/4" pipe fittings. So it should be .840" ID x 1.05 OD. That particular piece should fit fine without any machining.

Getting thinwall 1/2" PVC pipe and 3/4" CPVC pipe to fit over the EMT can be difficult, and I have to check at the hardware store before I buy it. It didn't sound like those bits were problematic for you though.
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#19 HotShotAzn

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Posted 21 January 2014 - 10:13 AM

Kane -

I'll measure what I have when I get home for comparison. I got my parts from three different places (Aces, Home Depot, and a mom and pop hardware store) which probably accounts for the vast difference in sizes. Lesson learned though...check multiple pieces for fitment before leaving the store.
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