Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 75 users online :: 4 registered, 0 hidden and 71 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Small coaxial

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
Sponsored 
  • Author
    Message

Unread postAuthor: MrCrowley » Fri Oct 26, 2007 10:53 pm

With the seam issue, what I did was...

Jam it in a vice, then with one hand hold a set square (to make sure the ruler is straight in comparison with the piston) and then using a dremel with a small cylinder tool bit, I dremeled a small groove into the piston.

It fits perfectly in the pipe's seam.

BTW I'm up in Auckland

NZ Spudfiles Members:
shud_b_rite - Auckland
Battlemonkey - Hamilton
nz_cannons - Nelson
MrCrowley(me) - Auckland
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: rixth » Fri Oct 26, 2007 11:01 pm

Yeah my current piston is a Coconut Cream can (250ml) that fits PERFECTLY in 50mm PN12 PVC, but not in the steel pipe. I've cast one out of hot glue now, just waiting for it to harden. How long should a piston be?

I've thought about getting a file and removing the first few cm of seam.

I must say though, I'm worried about the schedule 10 thing... (see my last post on page 2).

Oh, and I'm in Masterton =(

Edit: ahh! My piston is stuck inside the PVC I formed it in, I hit it as hard as I could (expecting it to just pop out) and it would not budge. Meh! Guess I'll buy more glue, and make another one, this time inside a paper sleeve or something.
  • 0


rixth
Specialist
Specialist
 
Posts: 47
Joined: Thu Nov 02, 2006 1:35 pm
Reputation: 0

Unread postAuthor: rixth » Fri Oct 26, 2007 11:38 pm

MrCrowley,

Just flicked through your instructable, saw you're using a deoderant can piston, well, I can testify that Rexona for Men cans fit PERFECTLY in 2"/50mm pipe. Plus, the end is curved in so it cups the barrel.

So yes, plan now is file the seam out of the pipe (only for 10cm), and make a 75mm long piston out of a Rexona can.
  • 0


rixth
Specialist
Specialist
 
Posts: 47
Joined: Thu Nov 02, 2006 1:35 pm
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Fri Oct 26, 2007 11:44 pm

rixth wrote:How long should a piston be?


The piston doesn't need to be longer than the width of the chamber, and if you can put in a lightweight core in the middle to reduce weight - have a look at my tutorial, it's writted for epoxy casting but the same principles apply.

ahh! My piston is stuck inside the PVC I formed it in, I hit it as hard as I could (expecting it to just pop out) and it would not budge. Meh! Guess I'll buy more glue, and make another one, this time inside a paper sleeve or something.


First of all you should be casting it directly in the pipe you're using as a chamber, and secondly, did you lube the sides of the pipe well first?
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: MrCrowley » Sat Oct 27, 2007 12:09 am

Just use some silicon spray or cooking spray when casting hot glue pistons, they'll pop right out.

JSR you should write a how-to on how to minimize pilot volume to your standards :P
  • 0

Last edited by MrCrowley on Sat Oct 27, 2007 12:31 am, edited 1 time in total.
User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: rixth » Sat Oct 27, 2007 12:21 am

Ok, so piston size:
- as long as the chamber is wide
- how far should it travel?l Is 10mm enough? The barrel is 20mm.

Am I going to weaken the pipe by grinding out the seam? (see picture)
  • 0

Attachments
_MG_7375.jpg

rixth
Specialist
Specialist
 
Posts: 47
Joined: Thu Nov 02, 2006 1:35 pm
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Sat Oct 27, 2007 12:25 am

Am I going to weaken the pipe by grinding out the seam?


Of course you're not making it any stronger but it shouldn't influence the amount of pressure it can take, especially as it's only for a small section.

rixth wrote:how far should it travel?l Is 10mm enough? The barrel is 20mm.


For a co-axial, piston travel more than 1/4th of the barrel diameter - 5mm in your case - is unnecessary and wasteful.

JSR you should write a how-to on how to minimize pilot volume to your standards


Tired as I am of answering the above question, I just might :p :D
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Sponsored

Sponsor
 


Unread postAuthor: rixth » Sat Oct 27, 2007 12:28 am

Time for one of those 'how long is a piece of string' questions.

How tight SHOULD a piston fit?
  • 0


rixth
Specialist
Specialist
 
Posts: 47
Joined: Thu Nov 02, 2006 1:35 pm
Reputation: 0

Unread postAuthor: Novacastrian » Sat Oct 27, 2007 12:28 am

rixth wrote:Ok, so piston size:
- as long as the chamber is wide
- how far should it travel?l Is 10mm enough? The barrel is 20mm.

Am I going to weaken the pipe by grinding out the seam? (see picture)


To answer to the best of my knowledge,
Yes that size piston should work fine
You could probably half the piston travel (D4) to 5mm
You may weaken the pipe, but it's plenty strong- don't worry about that.

Good Luck :)
  • 0

America, the greatest gangster of all time. With 200 million odd foot soldiers at it's whim and call.
When you fill your car with refined oil remember that it has been paid for with blood and guts, some from your own countrymen, most not.

Novacastrian
Major General
Major General
 
Posts: 1604
Joined: Sat Aug 11, 2007 6:59 pm
Reputation: 0

Unread postAuthor: rixth » Sat Oct 27, 2007 12:32 am

Thanks for all your help guys!

Now just gotta wait until Monday for the plumbing supply stores to reopen so I can get my barrel!

Will report back.

Tom.
  • 0


rixth
Specialist
Specialist
 
Posts: 47
Joined: Thu Nov 02, 2006 1:35 pm
Reputation: 0

Unread postAuthor: MrCrowley » Sat Oct 27, 2007 12:32 am

rixth wrote:Ok, so piston size:
- as long as the chamber is wide
- how far should it travel?l Is 10mm enough? The barrel is 20mm.

Am I going to weaken the pipe by grinding out the seam? (see picture)


Don't grind the seam, adjust the piston to the pipes standards not the other way round:
With the seam issue, what I did was...

Jam the piston in a vice, then with one hand hold a set square (to make sure the ruler is straight in comparison with the piston) and then using a dremel with a small cylinder tool bit, I dremeled a small groove into the piston.

It fits perfectly in the pipe's seam.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: rixth » Sat Oct 27, 2007 12:45 am

I don't have a dremel though, and I'd rather not buy one, as I can't see myself using it often... a drill is pretty much all I have sadly.
Hmmm found this http://www.dse.co.nz/cgi-bin/dse.storef ... duct/T4823 might consider getting one if I can justify it.

I'm curious as to why you say modify the piston and not the pipe, is that because of weakening it?

What was the piston in your steel cannon made of? Any chance of a picture?
  • 0


rixth
Specialist
Specialist
 
Posts: 47
Joined: Thu Nov 02, 2006 1:35 pm
Reputation: 0

Unread postAuthor: MrCrowley » Sat Oct 27, 2007 1:52 am

It was made of a PVC fitting, the job can be done with a file in no time as well.

I was going to get one of those dremel but got a Riobi one instead, they are handy in this hobby.

It may weaken the pipe a bit as well, but it would also be difficult to file the seam down evenly and completely even if it only 5cm of it. Without a dremel it may also take awhile. It would be a lot easier just modifying the piston.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: jackssmirkingrevenge » Sat Oct 27, 2007 2:30 am

rixth wrote:Time for one of those 'how long is a piece of string' questions.


42 :)

The piston should be as tight as possible but you should still be able to push it along the chamber with 1 finger and without straining yourself. As with many other piston-in-chamber situations, the use of lube is highly recommended ;)
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: rixth » Sat Oct 27, 2007 5:01 am

I may have found my piston, in a material that I could file a groove into.

Was looking through Marley (NZ pipe/fittings manufacturer) documents, and found the information below.

The ID of my pipe is just over 53mm. I figure I buy one, and cut if off at the red line on the diagram. Fill it with glue, then screw a seal on the end. It might be a bit short though.... about 35mm by my calculations.

Sound OK?
  • 0

Attachments
Untitled-1.jpg

rixth
Specialist
Specialist
 
Posts: 47
Joined: Thu Nov 02, 2006 1:35 pm
Reputation: 0

PreviousNext

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'