3D printed throw weights

Whisper said:
Since I make my own weights with a 3-D printer I have an accuracy of 0.4 mm. Less if a 0.1 nozzle is used. So I haven’t needed wadding. The fit is tight enough that I actually have to use a tamping rod to push the weight to the bottom of the tube. When I initially made my first shot it was with a commercial throw bag at 16 ounces. It was a very tight fit so I could forgo the wadding.
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The inside of most PVC is not that precise, a bit of cloth wadding would make up for inconsistency in the barrel. My 12 ounce bag fits fairly snug in a 1.5” barrel and my 16 ounce bag is a really snug fit, both Weaver bags. But even having chamfered the muzzle, the bags are already showing some wear on the edges from barrel friction. A bit of cloth wadding would create a better seal and take the wear from rocking down the barrel. Cloth is cheaper than a throw weight…

I just haven’t experimented with it yet. I might be able to do it with the 12 ounce bag in the 1.5” barrel, but I’m not sure I could with the 16 ounce. A 2” barrel would require either some thick cloth or a sabot type round. My experiments took on a delay because of extenuating circumstances, hopefully in a week or two I can re-visit things. Only way to see what actually works best is to experiment, right?
 
LBF said:
The inside of most PVC is not that precise, a bit of cloth wadding would make up for inconsistency in the barrel. My 12 ounce bag fits fairly snug in a 1.5” barrel and my 16 ounce bag is a really snug fit, both Weaver bags. But even having chamfered the muzzle, the bags are already showing some wear on the edges from barrel friction. A bit of cloth wadding would create a better seal and take the wear from rocking down the barrel. Cloth is cheaper than a throw weight…

I just haven’t experimented with it yet. I might be able to do it with the 12 ounce bag in the 1.5” barrel, but I’m not sure I could with the 16 ounce. A 2” barrel would require either some thick cloth or a sabot type round. My experiments took on a delay because of extenuating circumstances, hopefully in a week or two I can re-visit things. Only way to see what actually works best is to experiment, right?
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I use a digital microcaliper to measure the barrel. Actually I’m a perfectionist so I measure everything. Lol I personally found the 16 oz commercial throw bag fit perfectly in my one and a half inch barrel. I made my barrels replaceable. They just screw off and I can screw another one on. So if they start to wear I’ll just replace them

Good luck with your experiments let me know how you made out.
 
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Whisper said:
I use a digital microcaliper to measure the barrel. Actually I’m a perfectionist so I measure everything. Lol I personally found the 16 oz commercial throw bag fit perfectly in my one and a half inch barrel. I made my barrels replaceable. They just screw off and I can screw another one on. So if they start to wear I’ll just replace them

Good luck with your experiments let me know how you made out.
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The white plumbing PVC (schedule 40) seems to not be very smooth inside, so unless you bore it, it’s a little inconsistent. The gray schedule 80 electrical is more precise and smooth, but I’m not sure how well it can be mated to schedule 40 white since fitting selection for schedule 80 is pretty minimal. Of course, eventually I want to move to a metal launcher of some type, or at least a metal pressure chamber and valve. This plastic work is more to figure out what works and what doesn’t.

I made my first launcher entirely modular. I can add on to the pressure chamber, I can change the valve, and I can change the barrel. Everything screws together. My second smaller launcher the pressure chamber and valve are fixed, but the barrel can be changed. So far barrel wear seems to be nonexistent, but bag wear exists. Theoretically, the inside of the barrel should be smooth enough, although bumpy, that there shouldn’t be much wear, but the edges of my bags indicate otherwise
 
LBF said:
The white plumbing PVC (schedule 40) seems to not be very smooth inside, so unless you bore it, it’s a little inconsistent. The gray schedule 80 electrical is more precise and smooth, but I’m not sure how well it can be mated to schedule 40 white since fitting selection for schedule 80 is pretty minimal. Of course, eventually I want to move to a metal launcher of some type, or at least a metal pressure chamber and valve. This plastic work is more to figure out what works and what doesn’t.

I made my first launcher entirely modular. I can add on to the pressure chamber, I can change the valve, and I can change the barrel. Everything screws together. My second smaller launcher the pressure chamber and valve are fixed, but the barrel can be changed. So far barrel wear seems to be nonexistent, but bag wear exists. Theoretically, the inside of the barrel should be smooth enough, although bumpy, that there shouldn’t be much wear, but the edges of my bags indicate otherwise
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You’re right there’s a very little selection of fittings for schedule 80. I’m sorry you’re having friction problems with your throw bags. I guess that’s the benefit of printing my own, when they wear out I just replace them. Like you I made my launcher to completely disassemble. The primary reason was for transportation and parts replacement. The only exception being the pressure chamber. So I can remove the Schrader valve and pressure gauge, etc as needed. I personally have not found a need to switch to metal. The one I have is already heavy enough. What throw bags are you using? Are they leather or cloth?
 
Vapour smoothed. Feels good. Testing next.

I’m sure I’m going to next make a 14oz with some design improvements with the TPU (green) part.
 

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Whisper said:
Vapour smoothed. Feels good. Testing next.

I’m sure I’m going to next make a 14oz with some design improvements with the TPU (green) part.
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Well now I know RTV sealant is the wrong adhesive. So I have to find another flexible adhesive that’ll work with these polymers or the next option is a using a mechanical fit which means a complete design modification. So it’s Back to the drawing board. :-/

Anybody here have any experience in adhesives and or solvents?!
 
Before it came apart it was flying well. moving through the bush well. I sent it right through a tangle of brambles and scrub brush and It didn’t get tangled coming out. The dead blow shots I made against the bole shows that that part needs tweaking though. Definitely could use more weight though.
 
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DSMc said:
Throw line is expensive for sure, but I believe that is from the small market base that it covers. It does, however, last a long time in the field and is specifically designed for the task.
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I agree. It lasts long enough that it really isn't that expensive.
 
Whisper said:
You’re right there’s a very little selection of fittings for schedule 80. I’m sorry you’re having friction problems with your throw bags. I guess that’s the benefit of printing my own, when they wear out I just replace them. Like you I made my launcher to completely disassemble. The primary reason was for transportation and parts replacement. The only exception being the pressure chamber. So I can remove the Schrader valve and pressure gauge, etc as needed. I personally have not found a need to switch to metal. The one I have is already heavy enough. What throw bags are you using? Are they leather or cloth?
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It’s not a huge friction problem, but eventually it could wear the bags prematurely. Like you, I’m just kind of experimenting. Seems like there’s been little innovation with this stuff, like they came up with throw bags and a giant slingshot and someone made a high pressure air launcher and everyone decided that was adequate. I would imagine a shorter barrel would yield less friction wear on bags, but my whole goal was to be able to lower the pressures required and a longer barrel is better for that. Or so is my working theory based on other air cannons.

I haven’t tried a 2‘ barrel yet, but I’m going to say that it may have a negative impact on performance. Might be fine for shorter distances, but part of the whole thing with a launcher is to be able to accurately reach beyond what can be easily hand thrown. With a lower pressure, I think you need a longer barrel to achieve full velocity. I kind of expected to see the 3’ barrel I made to require increased pressure for the same results and was kind of surprised to see that it didn’t, so I could be wrong, but the flip also could be true where a longer barrel could provide greater height, so my testing thus far of the 4’ barrel, I may not have yet found it’s limits.

My big cannon I put a threaded fitting on the bottom of the pressure chamber with the idea that I could extend the pressure chamber to continue to lower the required pressure. Of course, when 40 psi will put my 12 ounce weight 100’ up, I’m not sure how much lower the pressure really needs to be.

I’m currently using the like canvas Weaver bags. Would like to experiment with other throw weights at some point. Need to take care of a few things so I can get back to testing.
 
Whisper said:
Well now I know RTV sealant is the wrong adhesive. So I have to find another flexible adhesive that’ll work with these polymers or the next option is a using a mechanical fit which means a complete design modification. So it’s Back to the drawing board. :-/

Anybody here have any experience in adhesives and or solvents?!
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Urethane would probably be my choice to try, but I’ll second the idea of talking with 3m and Lock-tite. Maybe even Sika since they make a lot of Urethane and similar products
 
LBF said:
Urethane would probably be my choice to try, but I’ll second the idea of talking with 3m and Lock-tite. Maybe even Sika since they make a lot of Urethane and similar products
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I’ve used gorilla glue (urethane) to great success with ABS. My only concern is the flexibility of the TPU not playing nice with the gorilla glue. 3M has a very good spray adhesive I may try at least it’ll retain some flexibility.
 
Whisper said:
I’ve used gorilla glue (urethane) to great success with ABS. My only concern is the flexibility of the TPU not playing nice with the gorilla glue. 3M has a very good spray adhesive I may try at least it’ll retain some flexibility.
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Apparently 3M is reporting that they are backed up pretty bad for inquiries so I’m anticipating a delay before they get back to me.
 
Whisper said:
3M suggests this flexible epoxy DP100 Plus. 47$ For 50ml. Ouch >-:-<
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Unfortunately some of the really good adhesives are expensive. The question would be, how many weights on average could you assemble with one 50ml pack? If it only gets you like 2, then it’s not really worth it, but if it gets you 50, then it’s less than a dollar a weight.
 
LBF said:
Unfortunately some of the really good adhesives are expensive. The question would be, how many weights on average could you assemble with one 50ml pack? If it only gets you like 2, then it’s not really worth it, but if it gets you 50, then it’s less than a dollar a weight.
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Well at this point I think it’s probably impossible to tell that until I try the product. I don’t know how viscous it is or if I will need to use key slots (hollows to hold glue) to increase surface area. I tried looking at other manufacturers flexible epoxies and they’re all expensive.
 
My next attempt will be with urethane adhesive ( Gorilla glue). I’ve also add key slots to the design at the adhesive site and Will be incorporating a special (read: secret) material internally to aid in the dead blow effect. I’ve also modified the TPU surface area for greater energy disposition. There is also going to be a metal tie in point as the paracord from previous models was prone to wear. Adding That should be interesting to try and incorporate.
 
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