105 replies to this topic

[merlinski]

Well with a spring, the spring constant (stiffness) is not an average. If a spring has stiffness 13 lbs/in, then compressing it 1 inch would take 13 pounds, compressing it 2 inches would take 26 pounds, etc. until you got to compressing it 8.5 inches, which would take 110.5 pounds of pressure. You can't really sum up the total force exerted over the range of motion because it's a vector quantity that's determined by the position. The figure of 120 lbs refers to the force exerted by the spring at the moment when it is compressed those 8 inches.

My guess is that the force exerted by the spring doesn't follow the equation F=kx, where k is the stiffness and x is the displacement. It probably is determined by the integral of k with respect to dx, where k is a function of x (k=k(x)). I'm just not sure how the stiffness varies as a function of displacement.

Edited by merlinski, 30 May 2005 - 05:58 PM.

[boltsniper]

F=kx just an approximation. Like you said, spring stiffness is a function of dispacement as well. It is quite good for linear springs though. As stated in the M16 milspec manual, the minimum spring constant for the action spring is 10 lbs/in for reliable operation. You can look it up if you like. I don`t feel like sifting through hundreds of pages of milspecs just to prove it.

120 pounds is high. It was a lapse of judgement on my part not to use some common sense and think about it before I posted that. The actual value is well under 100 pounds just by playing with it and comparing the pull to some known weight objects. Keep in mind though its not a dead weight. By the time you have the spring fully comressed and the force bulds you have a lot of inertia on your side. It is reasonably hard to hold the spring fully compressed.

What I`m failing to understand here is the relevance of this argument. The gun was completed when that was posted. I didn`t use that value when designing or building the rifle. I made a dumb mistake. It happens. It happened because I was just posting quickly and not putting much thought into it.

Thanks for catching it, but lets not make this a huge issue. Remember the title of this topic.

[merlinski]

I'm not nitpicking, I'm trying to determine the loads placed on different components of the design in order to make sure that some of the modifications I'm looking at will work. This stuff is still in the theoretical stage, but I'll post more about it once I'm confident that the design will work and have something concrete to back the idea up.

[Jakethesnake]

Call me stupid but......bolt on your excel spreadsheet writeup your measurements are in inches right? Well some of the pieces measure 6.3",7.2" 9.7" etc. How can you measure that way if inches are not based on multiples of ten. Shouldn't it be 1/2" 1/4" 1/8" 1/16" 1/32" etc. I know I'm probably missing something really obvious so please don't flame me for asking such a simple question but I don't understand, please help me!

[flamebo388]

That got me a little confused too, just estimate the right length, it doesn't make that much of a difference if your off a tiny bit.

[boltsniper]

Call me stupid but......bolt on your excel spreadsheet writeup your measurements are in inches right? Well some of the pieces measure 6.3",7.2" 9.7" etc. How can you measure that way if inches are not based on multiples of ten. Shouldn't it be 1/2" 1/4" 1/8" 1/16" 1/32" etc. I know I'm probably missing something really obvious so please don't flame me for asking such a simple question but I don't understand, please help me!

Typically, drawings are done with dimensions in decimal form. Makes it less cluttered, easier to read, easier to enter into a computer, etc. On the excel worksheets I set 10 squares to an inch, to get the best resolution I could, making each square 1/10th of an inch. I used an engineering scale, which is in tenths of an inch, to measure the parts. This is probably foreign to most of you who are only familiar with typical inch fraction scales.

You can approsimate the length of most of the parts. Nothing has a high enough tolerance that it needs to be exactly the length specified. Some parts could and problebly would vary quite a bit from the drawings depending on your gun. Just use a fraction scale and approximate where the length will be. Remember 0.5" = 1/2" , 0.75" = 3/4" , 0.125" = 1/8" , etc

[Jakethesnake]

Alright thanks a bunch, that helps, and also I searched all over and couldn't find a place where you mentioned getting music wire. Just a "music" store? hmm, where'd you get yours at? Again, thanks.

[flamebo388]

Ace hardware, mine was made by K&S metals, but I couldn't find the size bolt used because his was in fractions and all I saw was decimals, so I grabbed the brass that was supposed to slide over and found the right size. The music wire should be in the same area as the brass tubing and all that good stuff.

Edited by flamebo388, 04 June 2005 - 11:57 AM.

[boltsniper]

Any hobby shop will have it and most hardware stores. Music stores don`t have it. It's called music wire because it is the same hardened steel that guitar strings and such are made from. Other than that there is no connection to music. Some brands have give it in decimal and others in fraction. The sizes are usually the same whether fraction or decimal. Just difference in notation.

[Jakethesnake]

Bolt, correct me if I'm wrong but I think there's an error with your measurements on your spreadsheet write up, you have the butt of the stock made out of 1" pvc, and it says to cut it to 1" in length? I think that's a typo or something, anyways I'm not too worried about it but just letting ya know.

[boltsniper]

Good eye. I forgot to change the value when I was copying and pasting. The measurement is correct in the parts list and I have changed it on the drawing. I`ve added a good amount of other details and fixed some other typos/errors.

[Jakethesnake]

Bolt, when you modified the T-joints to be angled like that did you use halfed sections of pvc to extend the sleeves? I'm trying to figure out how you got them that long and that's the only way but wouldn't pvc be smaller than the T-joint because the joint is meant to slide over the 1 1/4" pvc.

edit I see how the pvc can fit inside of the T-joint, it's kinda hard to explain but I got that, but did you use pvc to extend the joint to hold the clip?

Edited by Jakethesnake, 09 June 2005 - 12:20 PM.

[flamebo388]

He use two couplers on each side of the mag well, so one goes over the upper reciever and the other makes that half of the mag well, then just make a second one for the other side, if this is confusing I'm sure bolt has a pic of couplers after cutting and before gluing.

[Jakethesnake]

No, I got that, but the T-joints only are like 2 inches long, It looks like his T-joints are reaching down like 3-4 inches where the mag enters into the T-joints.

[flamebo388]

I'm pretty sure his are just longer, mine are kinda short too.

[Jakethesnake]

How many tries did it take you flamebo to get that damn bolt action constructed, I'm working on mine, but I'm afraid I might have to re-do it.

[flamebo388]

The bolt itself I had to make twice, I miss drilled the ejector hole and went through the side of the bolt face. The slots for the bolt handle and spring catch took one try with a few touch ups later because it wasn't locking properly and it wasn't cocking consistently.

[Jakethesnake]

I've taken the real "bolt action" out of it's casing and I think I'm going to just drill the hole for the pin that keeps the carbon rod in there. That way I don't have to guess as to where the casing begins and starts.

edit Alright Flame, since boltsniper seems to be gone. How did you make the T- in the wire where the crank is. I tried supergluing a little piece on the side but it doesn't work. Bending a T in it wouldn't work either, from the pictures you can't really tell how bolty constructed it, what did you do there?

Edited by Jakethesnake, 11 June 2005 - 12:23 PM.

[Jakethesnake]

Ok, I know I'm double posting, but I found a place online that sells AR-15 action springs for like 4 bucks or something. Here's the link http://www.brownells.....16/M4 SPRINGS

Problem is, I don't want to order from here, and then realize I should have spent $15 for the one that bolt has. Can anyone tell me if this spring will work, bolt, maybe flamebou can help out. Many thanks in advance.

[boltsniper]

Ok, I know I'm double posting, but I found a place online that sells AR-15 action springs for like 4 bucks or something. Here's the link http://www.brownells.....16/M4 SPRINGS

Problem is, I don't want to order from here, and then realize I should have spent $15 for  the one that bolt has. Can anyone tell me if this spring will work, bolt, maybe flamebou can help out. Many thanks in advance.

That`ll work just fine. Jusr be sure you get a rifle length or A2 spring.

Edited by boltsniper, 20 June 2005 - 10:15 AM.

[jon]

Hey Bolt,
I hate to bring up an old subject, but how DID you angle and extend the T-joints? I'm having trouble figureing this one out. I dont understand flamebo's explanation could you put a pic? If you make one just for a pic, I'll be your best friend also I would sent you the total three bucks for the materials via mail. It would really help if you could tell us what was the angle you angled it at too. that way I can make the clip at the right angle.

[Ballman]

Hey bolt, could we get a cose up shot of inside the mag-well? Thats the only thing I truely don't understand.

[boltsniper]

The two magwell pieces are made from two separate pieces of PVC bonded together. I cut the two pieces from 1/1/4" T-joints because there are longer than couplers, but you could use to couplers and obtain the same result. The angle isn`t that important. I raked the magazine to some arbitrary angle that I thought looked good. Just make it a few degrees. You don`t have to angle it at all. I did it so that the the shells would have a nose up attitude at the top of the magazine to help feeding. I doubt you would have any jamming issues if you left the magazine vertical though. The vertical magazine would/does look kinda unnatural though.

here are the pics requested:

[Ronster]

Sorry to post on an old subject, but....
Bolt, I am making my FAR and dont see how the extractor works.
Does it grab the shell before it goes into the chamber or when it does go into the chamber?
Cause when I put the shell in the chamber and slide the bolt up, the extractor has no room to catch on the rim of the shell.
What am I doing wrong?

P.S. I have a video of me sticking the shell in the chamber and sliding the bolt up but I dont know how to add videos on to a post...

[boltsniper]

The extractor shouldn`t be rigidly attached to the bolt. I don`t know if this is the case with your's but that is kind of what it sounds like. The claw passes over the rim of the shell as it is pushed inthe chamber. You also need to have room in your receiver for the extractor to expand out as it passes over the shell rim. I don`t know if I can help much more without a picture.

To post your video you need to host it somewhere and then link it in your post. If its not too big you can email it to me and I`ll host it for you. I`d love to see it