[MadMark285]

My apologies if this design has been posted many times, I sure someone else has thought of it before. And I agree with the experts here, use a real cylinder if building an elaborate and expensive prop. My props are for a hayride, I can manually operate and reset the props.

This is a single action cylinder ie: you have to push it back down. It is made with 1/2" PVC pipe and 3/8" threaded rod.



For the piston, I use 3/8" threaded rod with a 3/8" ID 5/8" OD grommet (Hillman, purchased at Lowes). The nuts had to be rounded down on a grinder to fit inside the pipe. I used a lock nut on one end, the other nut will need threadlock or hot glue to hold in place. You can squeeze the grommet by tightening the nuts, this will make a tighter seal.

Note: since the grommet has a 1/16" groove, I also added a 014 Buna-N O-Ring inside the groove.



I beveled the inside of the pipe using a router bit attached to my drill.



For my next prototype, I want to make a dual action cylinder which will require that I seal the top using a 3/8" ID ~3/4" OD grommet. I will use a PVC slip joint instead of a cap.

This get more complicated as I cannot use thread rod. This will require a rod with threaded ends. I may just buy a die and thread regular rod myself.



For next year's hay ride, I want 8 hands rise out of the ground one by one. Below is a mock-up on how I plan to do this, the second cylinder is connected to the top of the first cylinder. I hope you get the idea here... The cylinder on the right ws my first attempt, it has way too many parts.

 

[Screaming Demons]

I buy brand new double action cylinders for $12. Not worth the trouble to make one for what will probably end up being about the same price.

 

[Screaming Demons]

This one is only seven inches long but it's less than five bucks.

http://www.mpja.com/Double-Action-9_16in-Bore-Air-Cylinder/productinfo/19184+HD/

 

[MadMark285]

Agreed, that is dirt cheap for a small cylinder. Even with $7 shipping, $12 is still cheap. Not sure what 10-32UNF is for the ports, how do you connect to it?

What do you use if you need a stroke longer than 7"?

 

[J-Man]

Agreed, that is dirt cheap for a small cylinder. Even with $7 shipping, $12 is still cheap. Not sure what 10-32UNF is for the ports, how do you connect to it?

What do you use if you need a stroke longer than 7"?

10-32 is a standard machine screw thread, you can get 10-32 pneumatic fittings.

 

[Screaming Demons]

Agreed, that is dirt cheap for a small cylinder. Even with $7 shipping, $12 is still cheap. Not sure what 10-32UNF is for the ports, how do you connect to it?

What do you use if you need a stroke longer than 7"?

I have a whole box of 13-inch cylinders I bought from MPJA for the $12. Looks like they're out of stock right now.

Then I bought a pair of new four-footers on ebay a few months back for $68 with shipping included.

 

[MadMark285]

I did find fittings on Amazon, they seem to be used with smaller tubing size (5/32" or 6 mm).

I am new here and have no desire to start a DIY vs manufactured debate. I agree with your comment on the "New to custom prop" thread, using a $5 DIY cylinder in a $200 prop doesn't make sense. But it is nice to have options from DIY, new to salvage parts.

I did find a source for cheap grommets (Imperial supplies, ~$.25/each inc shipping), not sure if they sell retail. This make my cost of a 12" stroke single action cylinder with 2 1/4 Tube OD x 1/4 NPT fitting at ~$6/each. For my "8 hands poping out of the ground" prop, 8 cylinders will cost $50. I hope my idea of connecting them in series works. Seeing my hapless victim (an 11 year old kid) being surrounded by hand poping up should be very cool.

 

[MadMark285]

Thanks for the info, I will use anything i can get my hand on cheap. MPJA is an interesting site.

But right now, I am having fun making my own cylinder.

 

[Raydium]

This one is only seven inches long but it's less than five bucks.

http://www.mpja.com/Double-Action-9_16in-Bore-Air-Cylinder/productinfo/19184+HD/

Their prices are crazy cheap! WOW! I've known about MPJA for a while for electronic stuff, never really ordered much from them... but didn't know they sold pneumatic cylinders -- Thanks for the tip!

 

[Raydium]

Thanks for the info, I will use anything i can get my hand on cheap. MPJA is an interesting site.

But right now, I am having fun making my own cylinder.

On the comment about resetting the props, you said that they would need to be manually reset.. What would happen if you ran the air through the series of cylinders in the opposite direction, i.e. have a valve turn on air at the last cylinder in the sequence and a separate valve opened the air input at the start, wouldn't this work to automatically reset the props?

 

[MadMark285]

No.

The seal on the piston is above the top air inlet when fully extended. Running the air in reverse, the air would enter the top of the cylinder but below the piston seal. The air would just exit out the bottom inlet.

Note: my requirement are far different from you guys, My props are for a haunted hayride manned by neighbors. After the trailer pulls away, the person running this prop would just push the hands back into the ground and cover them with leaves. The prop would only run ~10 times then is pack away until next year.

I hope this works, I have another prop called "****ing Birds" which will use a similiar concept. The cylinder will rotate the birds (ravens or harry Potter owls) 180 degree, their asses will face the trailer. The top air exit will connect to tubing running thru the birds and out their asses. I will manually fill the tubes up with some sort of liquid and the air pressure will spray my guest sitting in the trailer. Not scary but I hope it is humorous.

 

[bfjou812]

Your idea for the prop is great. Your ideas for building your own cylinders are at best very poor choices. There is a reason the manufacturers of PVC state that it is not to be used for compressed gasses. I had a PVC pipe that I was unaware of blow up and almost lost the little finger in my right hand. I wouldn't get within 100 feet of those cylinders . If you're doing the prop for next year that gives you plenty of time to get proper parts as well as exploring different ways to achieve the same effect. Depending on your needs you could use a scissors type mechanism, or a cam type setup to move the hands and only use one cylinder of the proper size.
I really am not a huge prick like it sounds, I just really have a strong stance on this subject. I speak from 25 years in the Industrial Maintenance field where I deal with pneumatic s ,electricity ,and hydraulics on a daily basis. So I do have an idea of what I'm talking about. I wish you all the luck on your prop and if you would like some help/advice PM me and I'll be glad to help.

 

[Raydium]

No.

The seal on the piston is above the top air inlet when fully extended. Running the air in reverse, the air would enter the top of the cylinder but below the piston seal. The air would just exit out the bottom inlet.

Yes, I see, that would be the case in this design. Well, I guess I'm thinking of way that double-acting cylinders might work. However, your idea may have other applications to operate several double-acting pneumatic cylinders in series using one valve or two valves, that seems something fun to experiment... (I'd have to give it a try in my copious spare time LOL)... And I realize that your haunt requirements are very different from ours, we require quick automatic resets, rugged design, repeatability, and reliability because we may operate a prop 200+ times in one evening... But I'll give you credit for the ingenious design of your application, and given the low-usage and low-budget requirements; it is probably the best solution for you.

 

[MadMark285]

I truly understand your concerns, long ago I had a air cannon ie: spud gun blow up on me. I would never again use high pressure in a PVC device.

But these fears should not over rule some common sense engineering, My hand prop should only require 20 psi, the cylinders will be wrapped in duct tape and buried below ground. For some of my other props, my diy cylinders will be enclosed inside the prop, 1/2" plywood will contain any shrapnel if the cylinder fails.

Back to the spud gun disaster, the gun was being used to shoot confetti. The gun was loaded up and pressurized for extended time ie: 10 minutes or so. That was the major frack up on my part, never use PVC to hold pressure. My DIY cylnder leak rather badly, they can't hold pressure nor will I keep the pressure on.

I am more concerned with electric in what may be an wet environment. Ground faults are great but the hay ride may be shut down while searching for that single fault which is popping the breaker.

But thanks for your concerns, I do want to keep it safe.

 

[MadMark285]

But I'll give you credit for the ingenious design of your application, and given the low-usage and low-budget requirements; it is probably the best solution for you.

Thank you.

For my rebooted haunted ride, I have so much to build for next year. I am bring back the electric chair, a guillotine, 2 digital projector effects and the big one, a cementery. For my tombstones, I want to make reconfigureable molds (plywood/mdf panels coated with high gloss polyurethane), buy 10 gallons (80 LB) of 3-4 # density urethane foam and make ~10 large tomb stone. I want my fog chiller inside a large tombstone. When I have the detail figure out, I write it up and post it here.

For me, using solenoid and controllers is not viable at this point, everything will be hand operated.