14 replies to this topic

[Buffdaddy]

I apologize if this seems unnecessary, but while things such as barrels, springs, etc all have dedicated threads, plunger tube materials are left out.

PVC and polycarb have proven reliable. What about materials like acrylic? Just looking for advice on what other plastics could withstand the force of a primary-type homemade.

[nisaburo]

I have used acrylic for plunger tube replacements before. It broke pretty quickly, not a catastrophic failure with flying shards but it cracked around the the coupler after a few rounds. This was without a significant spring upgrade.

[Daniel Beaver]

I've used acrylic a couple times. It breaks.

[Doom]

As others have said, acrylic is brittle, so it is a poor plunger tube material. However, you might find that acrylic is good to quickly find stress concentrations in a test gun.

Any strong and ductile plastic would work. PVC and polycarbonate are two affordable options. Thinner aluminum would be a good choice as well (if you don't dent it).

[Buffdaddy]

Thanks for the input. The tubing seemed way too cheap to be usable, so I wanted to check first.

Right now, I'm playing with nylon and various plastic tubular pieces from under the sink (that part of plumbing). Polypropylene tubing seems ok, as long as you get the smooth inside.

[Zorns Lemma]

These are from McMaster. Clear box indicates no or poor rating and full circle indicates strong rating.




For even more detailed information: http://www.mcmaster....218/8574KAC.pdf

Tensile strength and impact strength are portions to note for plunger tubes, although depending on how your design only one might be relevant for the tube in question.

Nylon is extremely good at not exploding; the issues I've experience are that it isn't always circular and deforms at thin walls (vs polycarbonate) and that machining it is a nightmare.

Edited by Zorn's Lemma, 07 March 2013 - 12:00 AM.

[Daniel Beaver]

Nylon is extremely good at not exploding; the issues I've experience are that it isn't always circular and deforms at thin walls (vs polycarbonate) and that machining it is a nightmare.

It's sort of ridiculous how good it is for certain applications (plunger rods). But that burning plastic smell...

PVC has a poor impact rating?

[Buffdaddy]

It's sort of ridiculous how good it is for certain applications (plunger rods). But that burning plastic smell...

PVC has a poor impact rating?

That surprised me, too, considering we build 3/4 of our homemades with it. Then again, we usually aren't using really thin walled PVC for our plunger tubes, are we? High tensile strength for the PT + lots of material on the coupler in front = few issues.

[DartSlinger]

*plastics chart*

Here is another plastics chart from McMaster, but this one has numbers instead of circles.

Machining it is a nightmare.

What exactly makes it a nightmare to machine? Does it melt at high cutting speeds?

PVC has a poor impact rating?

Here is an excellents article about the strength of PVC.

[Zorns Lemma]

Here is another plastics chart from McMaster, but this one has numbers instead of circles.

Yes, I linked that as "additional reading." The circles are better because no one has a context for roughly what the numbers correspond to, or even how they are measured so as to know whether big numbers or small numbers are preferred.

From my experience lathing, milling, and cutting nylon on a saw, it doesn't "shave" very nicely in any direction perhaps due to high abrasion resistance, so it just melts into strands and goop causing your tooling to either stall (scroll saw) or your part to shit itself (lathe).

Compare that to HDPE which is also abrasion resistant, but machines smoothly taking off little scrapes of material at a time, the way wood or aluminum machines. It also is better resistant to vibrations so it doesn't catch itself in the tooling and sometimes try to run away unlike Polycarbonate.

Keep in mine I am not an tooling expert and these are entirely subjective experiences. YMMV.

Also, on the topic of PVC having poor impact strength:



When you use PVC as a plunger tube and just have the plunger head stopped by a bolt running through the PVC, that force is translated mostly into lateral forces and thus tests the ductility and tensile strength of the material.

In the FAL-2 I built for Tornadostrike integration, the PVC slams against other elements repeatedly due to poor priming grip design.

Edited by Zorn's Lemma, 07 March 2013 - 02:32 PM.

[Birch]

I know this is not really a alternative plastic, but I have used it and found it to be much easier than its normal size. I am thinking of 1 1/4 THINWALL pvc. It has the same outer diameter as regular pvc, but is exactly 1 1/2 inches on the inside. This means that you don't have to make a superlative head, just a washer sandwich. Link: http://flexpvc.com/c...C-PIPE-Class200

This also adds a lot of extra volume to springers made with it. A snap carbine with 5 in. of draw can use a hopper suitable for my snapbow, yet still shoot a little farther. If you are wondering, they both have k26s and great seals. This means that you can use shorter draw blasters like the aforementioned snap carbine, yet still get very competitive results.

Edited by Birch, 08 March 2013 - 06:56 PM.

[lech]

I know this is not really a alternative plastic, but I have used it and found it to be much easier than its normal size. I am thinking of 1 1/4 THINWALL pvc. It has the same outer diameter as regular pvc, but is exactly 1 1/2 inches on the inside. This means that you don't have to make a superlative head, just a washer sandwich. Link: http://flexpvc.com/c...C-PIPE-Class200

This also adds a lot of extra volume to springers made with it. A snap carbine with 5 in. of draw can use a hopper suitable for my snapbow, yet still shoot a little farther. If you are wondering, they both have k26s and great seals. This means that you can you shorter draw blasters like the aforementioned snap carbine, yet still get very competitive results.

In Australia we use a product called 32mm Class 12 PVC, It fits into 1 1/4" SCH40 fittings and has a thin wall, I believe its very similar to your thinwall PVC. It has a perfect seal with 32mm red rubber bathplugs. We use this material for TS plunger tubes, homemades, etc. with great success.

Extra volume does not always translate to extra power. Up to a certain point, yes, but there could be a lot of other factors at play in your blasters (friction on plungerhead/rod, weight of plunger rod, barrel length, spring compression, etc.) I've made Nite Rifles that are identical except one has a wider plunger tube and roughly double the volume, yet they shoot the same.

[Birch]

In Australia we use a product called 32mm Class 12 PVC, It fits into 1 1/4" SCH40 fittings and has a thin wall, I believe its very similar to your thinwall PVC. It has a perfect seal with 32mm red rubber bathplugs. We use this material for TS plunger tubes, homemades, etc. with great success.

Extra volume does not always translate to extra power. Up to a certain point, yes, but there could be a lot of other factors at play in your blasters (friction on plungerhead/rod, weight of plunger rod, barrel length, spring compression, etc.) I've made Nite Rifles that are identical except one has a wider plunger tube and roughly double the volume, yet they shoot the same.

I do see your point on extra volume does not translate to extra range, but what I was trying to prove is that it can use a hopper, which is driven by volume AND power. It might also be that because I am using a washer sandwich, there is less friction (which is definitely true) than with the snapbow.

I see your point with the night finder rifles, but the one with the larger plunger tube has more fiction, does it not?

Edited by Birch, 08 March 2013 - 07:03 PM.

[lech]

I see your point with the night finder rifles, but the one with the larger plunger tube has more fiction, does it not?

Yep, it probably has a marginally heavier plunger head as well. My point is that there's a lot of variables to take into account, not just volume, which most homemades have way more than enough of anyway.

[KaneTheMediocre]

I know this is not really a alternative plastic, but I have used it and found it to be much easier than its normal size. I am thinking of 1 1/4 THINWALL pvc. It has the same outer diameter as regular pvc, but is exactly 1 1/2 inches on the inside. This means that you don't have to make a superlative head, just a washer sandwich. Link: http://flexpvc.com/c...C-PIPE-Class200

This also adds a lot of extra volume to springers made with it. A snap carbine with 5 in. of draw can use a hopper suitable for my snapbow, yet still shoot a little farther. If you are wondering, they both have k26s and great seals. This means that you can use shorter draw blasters like the aforementioned snap carbine, yet still get very competitive results.

1.5" sch80 PVC also has a nominal 1.5" inner diameter, so if you really need the 1.5" actual ID but want more strength (and weight), there's that. It will probably also stay much more round than the thin wall.