What kind of lathe process would you recommend to make low pressure pneumatic cylinders?

[PaulMakesThings]

I have a Grizzly G9972Z 11" x 26" Bench Lathe. I've mainly used it to bore pulleys and gears to fit, and for some threading.

I was thinking I'd try making some small pneumatic cylinders. These will be for low pressure. Think on the scale and pressure of Lego pneumatics. I'd like any tips on how to make it work better.

I'm pretty sure for the piston the best approach is to machine a plug with 2 (?) O rings, and thread it for a small rod. Those parts will be metal. I'm thinking for the cylinder I might use PVC, I could even just use a 3 inch or so cut of 1/2 PVC pipe and machine it to have the right surface finish and precision to make a good sliding seal. Would another material work way better, and how should I finish the inside for the best results (hone, reamer, boring bar, etc.)

What would be the best way to get the caps to seal? With a cylinder this small I can lock it on by just having threaded rod or long screws go from cap to cap. But I'm not sure how to seal around the sliding shaft. Maybe some small O-rings set into a machined opening with grease?

Or for the piston and rod seal would a slippery plastic work better than grippy rubber O-rings, such as Delrin? Really I could make the cylinder body out of Delrin too, I'm just not sure it would work enough better to be worth the cost.

I found a few tutorials, but many are emphasizing extreme realism, for now I just want to make it work, I'm not quite at the level yet to be making them look exactly like real tiny hydraulic rams.

 

[ShopShoe]

I guess I would consider brass. I know there is thin-wall brass tube available.

On another hand, I think I saw someone's project where plastic hypodermic syringes were used as air cylinders.

--ShopShoe

 

[Gordon]

Ideally DOM tube but for low pressure probably any good smooth ID tube would work. Screw on caps with O rings to seal the ends. One end could be soldered on. Piston with O rings. Look at how Bimba cylinders are made.

 

[Ken I]

Do not use two "O" rings on a piston - it's fatal to the "O" rings - if you want to use two for stability (for instance) then the gap between them must be vented to one side or the other or one ring deliberately cut.
Pressure is pumped up between the rings until they extrude.

O-ring for piston ring

See post #38 at the above link - images from the "Parker-Hannifin "bible".

A good bore or reamed finish is generally good enough - but hone the bore (use one of those cheapies for brake cylinders etc.) to give a fine cross hatch pattern which helps to hold lubricant. A highly polished finish is a bad idea and tends to burn "O" rings - obviously, the higher the velocity the worse the problem.

Regards, Ken

 

[Steamingandy]

I have made some 1/4” dia ones from KS brass tube, the brass end caps were made interference fit and pressed in with a bit of loctite just in case, fitted with a spring for return, single O ring on a brass piston, shaft from stainless welding rod, hose connector machined in the end cap, lubricated with silicone grease, works a treat

 

[Bentwings]

I have a Grizzly G9972Z 11" x 26" Bench Lathe. I've mainly used it to bore pulleys and gears to fit, and for some threading.

I was thinking I'd try making some small pneumatic cylinders. These will be for low pressure. Think on the scale and pressure of Lego pneumatics. I'd like any tips on how to make it work better.

I'm pretty sure for the piston the best approach is to machine a plug with 2 (?) O rings, and thread it for a small rod. Those parts will be metal. I'm thinking for the cylinder I might use PVC, I could even just use a 3 inch or so cut of 1/2 PVC pipe and machine it to have the right surface finish and precision to make a good sliding seal. Would another material work way better, and how should I finish the inside for the best results (hone, reamer, boring bar, etc.)

What would be the best way to get the caps to seal? With a cylinder this small I can lock it on by just having threaded rod or long screws go from cap to cap. But I'm not sure how to seal around the sliding shaft. Maybe some small O-rings set into a machined opening with grease?

Or for the piston and rod seal would a slippery plastic work better than grippy rubber O-rings, such as Delrin? Really I could make the cylinder body out of Delrin too, I'm just not sure it would work enough better to be worth the cost.

I found a few tutorials, but many are emphasizing extreme realism, for now I just want to make it work, I'm not quite at the level yet to be making them look exactly like real tiny hydraulic rams.

Frankly I purchase cylinders befor making them . It’s tough getting precision finishing you could pitch tie rod cylinders and cut them off however you need. Bombs masks many air cylinders , als look into Rc airplane landing gear suppliers Robart makes nice stuff as does Ceres products I’ve never had cylinder issues with either company and support is very good to at won’t make custom cylinders but Cerra may there is also a company that makes small brass air cylinders the name escapes me. I’ll look for it and post if I can find it also Dubrovnik products makes all kinds of linkage solutions at the hobby shops the Rc cars have tons of neat stuff about every ball link and Cleve you can think of.
another though is to just purchase seamless tubing aluminum steel stainless copper and brass are readily available you can make your own pistons and rods McMaster car has a huge on line catalog of about anything you need I buy a lot from them some times there are other places with better prices but not as good service . I done work for them or get deals from them I just spend money with them .LOL

 

[SmithDoor]

You can buy chrome plated tubing inside and or outside.
Before the 1940's they also used nickel plating for air and Hydraulic,
, which is easy to do at home.

Dave

I have a Grizzly G9972Z 11" x 26" Bench Lathe. I've mainly used it to bore pulleys and gears to fit, and for some threading.

I was thinking I'd try making some small pneumatic cylinders. These will be for low pressure. Think on the scale and pressure of Lego pneumatics. I'd like any tips on how to make it work better.

I'm pretty sure for the piston the best approach is to machine a plug with 2 (?) O rings, and thread it for a small rod. Those parts will be metal. I'm thinking for the cylinder I might use PVC, I could even just use a 3 inch or so cut of 1/2 PVC pipe and machine it to have the right surface finish and precision to make a good sliding seal. Would another material work way better, and how should I finish the inside for the best results (hone, reamer, boring bar, etc.)

What would be the best way to get the caps to seal? With a cylinder this small I can lock it on by just having threaded rod or long screws go from cap to cap. But I'm not sure how to seal around the sliding shaft. Maybe some small O-rings set into a machined opening with grease?

Or for the piston and rod seal would a slippery plastic work better than grippy rubber O-rings, such as Delrin? Really I could make the cylinder body out of Delrin too, I'm just not sure it would work enough better to be worth the cost.

I found a few tutorials, but many are emphasizing extreme realism, for now I just want to make it work, I'm not quite at the level yet to be making them look exactly like real tiny hydraulic rams.

 

[Bentwings]

You can buy chrome plated tubing inside and or outside.
Before the 1940's they also used nickel plating for air and Hydraulic,
, which is easy to do at home.

Dave

If you search Amazon for small model airplane air cylinders you can probable find what you need I still can’t find the ones I used. I’ll ask my son as he just got some

byron

 

[SmithDoor]

The last time I got a piece was 2009
I look for chrome shaft

Dave

If you search Amazon for small model airplane air cylinders you can probable find what you need I still can’t find the ones I used. I’ll ask my son as he just got some

byron

 

[Cessnadriver]

I own Century Jet Models and make all of my own Air Cylinders. I can make custom sizes as well. Hit me up at [email protected] if you need some cylinders. Process to make them are done mostly on the lathe which I do manually and on the CNC.

 

[kf2qd]

Do not use two "O" rings on a piston - it's fatal to the "O" rings - if you want to use two for stability (for instance) then the gap between them must be vented to one side or the other or one ring deliberately cut.
Pressure is pumped up between the rings until they extrude.

O-ring for piston ring

See post #38 at the above link - images from the "Parker-Hannifin "bible".

A good bore or reamed finish is generally good enough - but hone the bore (use one of those cheapies for brake cylinders etc.) to give a fine cross hatch pattern which helps to hold lubricant. A highly polished finish is a bad idea and tends to burn "O" rings - obviously, the higher the velocity the worse the problem.

Regards, Ken

For LOW PRESSURE and O-Ring will work just fine.

 

[SmithDoor]

I have a Grizzly G9972Z 11" x 26" Bench Lathe. I've mainly used it to bore pulleys and gears to fit, and for some threading.

I was thinking I'd try making some small pneumatic cylinders. These will be for low pressure. Think on the scale and pressure of Lego pneumatics. I'd like any tips on how to make it work better.

I'm pretty sure for the piston the best approach is to machine a plug with 2 (?) O rings, and thread it for a small rod. Those parts will be metal. I'm thinking for the cylinder I might use PVC, I could even just use a 3 inch or so cut of 1/2 PVC pipe and machine it to have the right surface finish and precision to make a good sliding seal. Would another material work way better, and how should I finish the inside for the best results (hone, reamer, boring bar, etc.)

What would be the best way to get the caps to seal? With a cylinder this small I can lock it on by just having threaded rod or long screws go from cap to cap. But I'm not sure how to seal around the sliding shaft. Maybe some small O-rings set into a machined opening with grease?

Or for the piston and rod seal would a slippery plastic work better than grippy rubber O-rings, such as Delrin? Really I could make the cylinder body out of Delrin too, I'm just not sure it would work enough better to be worth the cost.

I found a few tutorials, but many are emphasizing extreme realism, for now I just want to make it work, I'm not quite at the level yet to be making them look exactly like real tiny hydraulic rams.

I use a cut off cutter under size so cut to size. Remember between the Grove you want .001 to .003 gap foe a good seal and the ring not to break.
Some old auto and machinest books have this information on making ring groves

Dave

 

[Wheat47]

I have a Grizzly G9972Z 11" x 26" Bench Lathe. I've mainly used it to bore pulleys and gears to fit, and for some threading.

I was thinking I'd try making some small pneumatic cylinders. These will be for low pressure. Think on the scale and pressure of Lego pneumatics. I'd like any tips on how to make it work better.

I'm pretty sure for the piston the best approach is to machine a plug with 2 (?) O rings, and thread it for a small rod. Those parts will be metal. I'm thinking for the cylinder I might use PVC, I could even just use a 3 inch or so cut of 1/2 PVC pipe and machine it to have the right surface finish and precision to make a good sliding seal. Would another material work way better, and how should I finish the inside for the best results (hone, reamer, boring bar, etc.)

What would be the best way to get the caps to seal? With a cylinder this small I can lock it on by just having threaded rod or long screws go from cap to cap. But I'm not sure how to seal around the sliding shaft. Maybe some small O-rings set into a machined opening with grease?

Or for the piston and rod seal would a slippery plastic work better than grippy rubber O-rings, such as Delrin? Really I could make the cylinder body out of Delrin too, I'm just not sure it would work enough better to be worth the cost.

I found a few tutorials, but many are emphasizing extreme realism, for now I just want to make it work, I'm not quite at the level yet to be making them look exactly like real tiny hydraulic rams.

What are you making? Where are you headed?
I would think PVC pipe would work good without any need to finish the inside. I'd have to put a little thought
into how make up a rod seal end.

 

[larryg]

What action do you want this cylinder to have? Extend only, extend with spring return, double acting, single or double rod? What pressure are you considering and what force do you need? Any idea of bore and stroke?

lg
no neat sig line

 

[Bentwings]

You can buy brass and aluminum seamless tubing even telescoping stuff . It’s generally got a pretty good I’d finish mc master carr has all kinds of o rings in many different materials .

 

[Scott_M]

This post is several years old. Not sure why Dave dug it up, he replied 2 years ago also ?

 

[Bentwings]

My little steamer has a simple male thread fitting with brass cap and tapered in side seat forvthe shaft running through it I just twist Teflon tape into a small thread then wind it around he shaft outboard ofvthe make threads I just hand turn the brass cup untill the Teflon starts to squish hen just a little more I use air tool oil so it’s pretty slippery ther is little stage and no air leak at about 30 psi. Works great my giant scale air craft retract landing ger shas the cylinder end cap grooved for o Rolf. I don’t think those hav ever been replaced . No leaks at 120 ps I don’t think I’d try honing or burnishingvthe cylinders unless you have good knowledge of this I’ve done it in industry but tooling cost was no object. I YHINK a lot of steam engine use the packing gland I described. Blonde hacks made one for her steam enginge that worked well for her .