Build a Pneumatic Cylinder

I needed an electronically controlled pneumatic cylinder for an upcoming project that I'm currently designing. I looked into purchasing one, but it turns out that they're way beyond my budget. Looking through the garage got me thinking that I might be able to build one out of some plumbing bits and bobs, and hook it up to my compressor.

After hours of explaining exactly why this was so important, my wife agreed that I should do it. Well, actually, that didn't happen. I explained it to her, and she looked at me like I have two heads, and quietly accepted that I was going to do it anyway.

This is a preliminary build of the cylinder, just as a proof-of-concept. I built it to be able to be disassembled (nothing is permanently glued). I had thought that this might make the final product weaker, but it turned out to be stronger than I had anticipated. I may end up using this method to build the final one that matches the size requirements, so that I can re-use as many of the parts as possible if the need arises.

For this build, there are a few parts that are must-haves, but everything else was cobbled together from what I had kicking around in the garage. Feel free to modify, substitute, and improvise if you're going to build one yourself.

Step 1: Materials

There are some parts I ended up purchasing at the local hardware store, and a few that I had on-hand that are absolutely necessary for this build. I took a lot of parts from a small compressor that had died after many years of faithful service. It will live on in my heart, and in this cylinder.

Here's a short list. There are probably some things I neglected to write down, but they're the sort of things that you've likely got already.

Plumbing Parts:
- A length of 2" ABS pipe (I used 2 feet)
- A similar length of 1 1/2" ABS pipe (it's not pictured, but I cut a 2' piece off some leftover pipe I had in the garage)
- A 2" inspection end cap and plug (it's a threaded end cap that can be opened if necessary)
- A 1 1/2" end cap (not threaded)
- A 2" to 1 1/2" reducer
- A large O-ring (mine came from a pool hose fitting)
- Teflon tape
- A solenoid valve. I scavenged mine from a defunct dishwasher, but I suspect a sprinkler valve would work in a pinch). Make sure you keep the wiring harness connector for the valve. It will make your life easier.
- Various fittings to make things fit together
- Some hose clamps for good luck
- Compressor quick-connect fitting

Other parts:
- nylon zip ties
- grease
- electrical tape
- "Peel'n'Seal" type removable caulking (mine was Draft Attack)
- Small screw or bolt
- scrap power cord cut from an old appliance
- probably some other stuff that I just picked up off the workbench (like a short length of hose, a net to fit the small screw, and so on)

Tools:
- saw to cut pipe
- drill
- air compressor (the bigger the better, but a small one should be able to operate this too)
- sand paper
- solder
- heat shrink tubing (optional)
- pliers, vice-grips, and/or a bench vise
- file
- power bar with switch

Because I had most of the stuff I needed already, this project cost me in the neighbourhood of $15. If you're starting from scratch, I would guess that it would run around $50 with the valve and stuff, and much more if you need a compressor. If you don't have a compressor, you might want to get one. They're loads of fun!

Comments

[heathbar64]

Also Loved your tapered bolt to regulate air flow. that's a simple but effective trick I will use someday.

[jptrsn]

Can't take credit for the idea, but I can't cite my source, either. I saw it somewhere a long time ago and thought "Hey, that's really neat! I'm going to use that somewhere some day."

Thanks go out to the brilliant, anonymous person who showed the technique wherever it was that I saw it, and to the person that originally thought up the idea!

[heathbar64]

If i'm understanding correctly, the inner pipe is open to the air pressure. this is why you need the seal around it. typically, an air cylinder is sealed at the piston and no seal at all is needed at the outboard end. How about using a leather or rubber cup type piston like was used in the old bicycle pumps.
I one time made a low pressure cylinder from an all plastic caulk tube. I just pushed the piston out and sanded it down to fit a little freer. then used a long bolt for the piston rod.

[jptrsn]

I decided to use the entire unit as an air chamber to add a bit of cushion to the action of the piston. I had thought about using an inner seal that traveled up and down the cylinder body, but I was inspired by the reducer part.

I have an old bicycle pump with a rubber disc sandwiched between two pieces of steel. The whole assembly is on a threaded rod, and the fit between disc and cylinder is fine tuned by squishing the disc by tightening down the nuts to compress the rubber. This seems to work well, and in my next build, I might try to do something similar.

Thanks for the comment!