First Piston......please comment
Hi,
This is my first piston. 2 leftover 6mm acrylic disks bolted together with a M10 bolt, with a 3mm thick rubber disk on top of one of them. I haven't epoxied it together though, so the thing can be taken apart again.
It fits pretty tight in the tee. I will probably go add O rings sometime in the future, but I think I'd rather get the piston right first than to dabble with equalization holes and O rings. That said I have not finished making the pilot valve system yet, so no tests yet.
Please give your comments & suggestions on the thing, esp how it can be improved. I'm sure the pros like Ragnarok and JSR would have something to say.
Again, please understand that I live in Singapore, which has the strictest rules, plus my brother is a policeman, so I don't dare try it out for myself at home for fear of accidents.......
This is my first piston. 2 leftover 6mm acrylic disks bolted together with a M10 bolt, with a 3mm thick rubber disk on top of one of them. I haven't epoxied it together though, so the thing can be taken apart again.
It fits pretty tight in the tee. I will probably go add O rings sometime in the future, but I think I'd rather get the piston right first than to dabble with equalization holes and O rings. That said I have not finished making the pilot valve system yet, so no tests yet.
Please give your comments & suggestions on the thing, esp how it can be improved. I'm sure the pros like Ragnarok and JSR would have something to say.
Again, please understand that I live in Singapore, which has the strictest rules, plus my brother is a policeman, so I don't dare try it out for myself at home for fear of accidents.......
- Attachments
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- The piston from the rear. I forgot to add another rubber disk to the back. The beige thing is my hand. You can't see the nuts from this angle.
- 2.JPG (15.32 KiB) Viewed 1700 times
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- The piston from the side view. From left to right, nutt + washer, rubber disk, 6mm acrylic disk, UPVC JIS AE 3" pipe, 6mm acrylic disk, washer + bolt head.
- 1.JPG (15.7 KiB) Viewed 1700 times
Wow, I'm a professional.limbeh wrote:I'm sure the pros like Ragnarok and JSR would have something to say.
That looks like a good start, although the brittle acrylic might not fare well under the forces incurred by the valve's operation, so be careful when you're testing it.
Remember that the forces on the pistol will be transferred by compressive forces along the length of the piston, so if you haven't already, I'd recommend making sure there are nuts on the bolt which can cope with compression loads as well as tension loads.
Of course, if the piston's interior isn't entirely airtight, these problems will be lessened by some balancing pressures inside the piston.
Good start - now test it!
Does that thing kinda look like a big cat to you?
If it fits snug but friction free in the tee, you should be good. With the bolt holding things together, you probably won't need to epoxy everything together. Just make sure it is air tight from the rear to barrel opening and the sealing face is flush with your rubber seal.
Looks like a good design!!
Edit: Yes, Rag is a professional...
Looks like a good design!!
Edit: Yes, Rag is a professional...
Thanks all.
Some further data on the piston
Snug = yes
Airtight = no. Quite a good number of places which air can leak out from.
Friction free = No. Seems quite resistant to moving.
Intended usage = < 120psi. Not very high compared to some of you.
I'll post the pictures of the thing in the tee, when my policeman bro isn't around. More nuts will be added once I get them.
Thanks once again.
Limbeh
Some further data on the piston
Snug = yes
Airtight = no. Quite a good number of places which air can leak out from.
Friction free = No. Seems quite resistant to moving.
Intended usage = < 120psi. Not very high compared to some of you.
I'll post the pictures of the thing in the tee, when my policeman bro isn't around. More nuts will be added once I get them.
Thanks once again.
Limbeh
120 psi can be a lot in a larger cannon. Anything above about 150 is more getting into the preserve of smaller, metal launchers.
I'd be surprised to see a larger 200 psi PVC cannon, put it that way.
But enough of my semantics.
I'd be surprised to see a larger 200 psi PVC cannon, put it that way.
I'm probably more of an expert or adept, but not so far as a master or authority - professional sounds wrong, as I'm not making a profession out of it.starman wrote:Edit: Yes, Rag is a professional...
But enough of my semantics.
Does that thing kinda look like a big cat to you?
Airtight to the barrel opening is a requirement and resistant to moving isn't good. However, it sounds like you are very close to making this work right. Be very careful not to take too much away in freeing the movement. Use some fine sand paper to take ever so small amounts from the edges.limbeh wrote:Airtight = no. Quite a good number of places which air can leak out from.
Friction free = No. Seems quite resistant to moving.
Intended usage = < 120psi. Not very high compared to some of you..
120 psi is a lot for this size cannon.
- jackssmirkingrevenge
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It looks like a sturdy and relatively lightweight way to make a piston and should work well in practice. Shame it isn't airtight though, you could save yourself some dead volume, plus air leaking from the piston into your pilot volume could deacrease the efficiency of your piloting. Also, it's a little long, however I'm thinking in coaxial terms so if it's made for a tee I imagine it's as short as you can make it.
hectmarr wrote:You have to make many weapons, because this field is long and short life
- VH_man
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didnt i just post in this? whered it go?
anyway, Nice piston, im semi-envious.
The only problem i see is the fact that Lexan is not very impact resistant, and may shatter upon its impact with the rear of the piston housing.
Try it anyway tho, and if it breaks, well then... now you know! and if it doesnt, well then WOHOO! Its what spudding is all about.....
anyway, Nice piston, im semi-envious.
The only problem i see is the fact that Lexan is not very impact resistant, and may shatter upon its impact with the rear of the piston housing.
Try it anyway tho, and if it breaks, well then... now you know! and if it doesnt, well then WOHOO! Its what spudding is all about.....
Actually, 120psi is stretching it quite a bit. I'm using a normal, unmodded bicycle pump here, and I highly doubt that the thing could get me beyond 100psi. Must add the 20% safety margin
- Attachments
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- This is a picture of the cannon. Barrel diameter 3" JIS AE, tee size 4" JIS AW, pilot valve is JIS 1/2" ball valve.
- Cannon.JPG (22.7 KiB) Viewed 1656 times
- jrrdw
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Pro what? is my question!pros like Ragnarok and JSR
The disk on each end look bigger in diameter then the piston body. I for-see a problem with the sealing disk catching the cylinder while opening, piston tipping and so forth.
For your sake I hope I'm wrong because the above sernerio will cause catastrophic failure at 100psi....
- ALIHISGREAT
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thats a nice looking piston (i'm not gonna repeat everything everyone has already said)
but you could do with some more chamber volume if you want to have decent power.
but you could do with some more chamber volume if you want to have decent power.
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- jackssmirkingrevenge
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Agreed, especially if you're not using high pressure. Unless of course noise is a factor and you want to keep things quiet, in which case you're on the right trackALIHISGREAT wrote:you could do with some more chamber volume if you want to have decent power.
hectmarr wrote:You have to make many weapons, because this field is long and short life
jackssmirkingrevenge wrote:Agreed, especially if you're not using high pressure. Unless of course noise is a factor and you want to keep things quiet, in which case you're on the right trackALIHISGREAT wrote:you could do with some more chamber volume if you want to have decent power.
Correct guess. Given my circumstances, noise is not a good thing.
jrrdw was correct in that the disk would catch the cylinder while moving back. Operationally, not too bad a problem, it just means that I can't fire with the cylinder pointing downwards.
Ideally, I would go try for the best possible / foolproof cannon, but I can well put up with the inconvenience for the time being until I make a better one.
- jackssmirkingrevenge
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Can't you just trim the disk a little? I don't see the problem, nor the relevance of the launcher's orientationlimbeh wrote:jrrdw was correct in that the disk would catch the cylinder while moving back. Operationally, not too bad a problem, it just means that I can't fire with the cylinder pointing downwards.
hectmarr wrote:You have to make many weapons, because this field is long and short life
No problem trying. I have plenty of spare acrylic sheet and disks, leftovers from a school project.jackssmirkingrevenge wrote:
Can't you just trim the disk a little? I don't see the problem, nor the relevance of the launcher's orientation
The problem is that a large part of the piston overhangs out over the cylinder. So the front part of the piston does "drop" into the cylinder - and the part of the disk sticking out hits the rear wall of the cylinder.
But then and again, that can wait - constructing the pilot valve and getting it to work is the headache now on my side.............I lack the experience in that aspect.