Annular Cylinder - Barrel and Piston Clearance

Have you tried finding a "off the shelf" cylinder from a manufacturer?

I have a list of Cylinder Manufacturers that if a "off the shelf" option is not available they can manufacturer one for you custom, which when all is said and done will probably provide a better product, at a comparable price than machining one yourself, after you figure in your tooling and time. They know exactly what they are doing in the cylinder realm, and will guarantee a professional, long lasting product.

The cylinder market is very competitive, and many companies are hurting for work, so prices are very low right now.

Just a thought.

Looking for OTS was actually the first thing I tried. When that failed I began laying out what I would need. A local vendor bid it fairly low and so that was the direction the company took.

If you would forward me the list of custom cylinder manufacturers, perhaps I can convince my management to change their minds.

"A local vendor bid it fairly low and so that was the direction the company took."

You already have a local vendor planning to build it? You should not need to provide any technical information such as clearances, rings, or internal specifics. All you need to specify to any competent vendor, would be the bore, stroke, rod, end connections, porting, PSI rating and materials. The vendor (If they have any competency in building cylinders) should have already figured out the answer to your question. If your vendor does not know about the cylinder clearances, I would NOT have them build me a cylinder, I would find a Vendor who can competently build me a quality product, with the assurance that everything is built by professionals in their area of competence.

The vendor that we used was a small local machine shop, with less experience with cylinders than I have (which you should know by now is practically no experience). However, this shop has a history with my company and when his bid comes in lowest, I have to have a pretty good reason not to use him. Now that I have parts that are out of tolerance and binding, I feel I have a good reason to have someone else do this for me, if I can provide my buyers with someone to go to. So if you have a list of custom cylinder manufacturers, I'd appreciate the help.

(Disclaimer: I work for a (mostly)distributor, and work closely with certain brands, so I will only plug them, however many others are out there)

Without knowing more about your application, I can only make generalizations.

My #1 favorite custom cylinder manufacturer is Purakal, they are a local group here in the pacific northwest, which makes a bulletproof product every time, top of the line, great to work with... but the price reflects it.

We also Carry:

Cunningham: decent prices for Custom cylinders, many off the shelf components

Bosch/Rexroth: The Big Dogs... will do custom but you either need a bunch of $$, or order a bunch of cylinders. However they have a quite extensive product line, so you might find something standard for WAY cheaper than you can have it built custom.

Hy-spec: Canadian outfit, mostly inexpensive agricultural stuff... will do custom builds.

(we carry others but, these are where I'd start.)

If you would like me to pull some quotes for you send me a PM, and we can open a line of communications.

I think you will find the proper clearance will be determined by the materials that both the cylinder and the piston are made from, their respective operating temperatures, and the details of lubrication (type of hydraulic fluid).

Do you have to stick with the 1"wall thickness?? Why is this part of your specs?

What force is required of the cylinder?

What mount styles?

Rod dia?

Does it need any cushioning?

Any special environmental considerations?? (IE corrosion/heat/dust etc)?

What frequency does the cylinder need to operate?

What is the Operating pressure of your system?

One way, Two way? Spring return? etc?

Porting?

Dimensional tolerances for install? (IE barrel length??)

Chances are, you can most likely get away with an off the shelf component if you know where to look, and you know what the important questions are. Things like your wall thickness should not be a spec you define, rather it should be a spec the vendor chooses, based on your other specs.

This is a model of what I am working with. As you can see it is an annular cylinder. The two diameters I mentioned in the first post are inner and outer diameters of the annular bore area, and not an ID and OD of cylindrical bore.

I looked for sometime, trying to find a company that makes something similar, but this is a pretty specific application.

Thank you for the list, at the very least it gives me a place to start looking.

Ahh yes.. clarified.. I was off in the wrong direction.

This must be for Optics of some kind?

I doubt you'll find any standard cylinder manufacturer will have any idea where to start..(but you already knew that) I see why you wound up here... good place to be.

What materials are you using?

Whats the temp range?

Pneumatics, are much more forgiving than Hydraulics...

The materials of contruction are stainless steel, however, after my first iteration (failed due to binding) I think I may look for something considerably lighter. The complete assembly is a two person lift & carry with present materials.

The operating temperature is around 72° F, however, much higher temperatures can be seen, perhaps above 500° F, but only if there is a failure.

This assembly is intended for use with approximately 70-90 psi lubricated shop air.

As for its use, this will be used on a specialized machine for manufacturing.

If you are interested, here is our company website link: http://www.armtecdefense.com/

I still suggest you look at a rolling diphragm like Bellofram. Binding is likely related to the small length/diameter ratio of the piston. Different industries have different rules of thumb. However, for an unguided piston a ratio of 1.5 is common. With your very short piston, only a small amount of cocking will cause it to bind.

While you are most likely correct that my length to diameter ratio is what is complicating my binding issue (I was already concerned with it myself), my piston is not totally unguided. Look closely at the rods, and read the other posts, and you will see that I am using sleeve bearings as rod guides. For my particular application, I may be able to lengthen my piston, maybe as much as two times its current length, but this will increase the weight of the assembly, which is already heavier than it really should be. I know there are methods and alternate materials I could use to reduce weight, but first I need it to work. Having said that, I will look up the Bellofram rolling diaphragm, and weigh its use in my application.

For this type of annular arrangement, I suggest you check into a Bellofram rolling diaphragm design. I think it will simplify your design and reduce leakage to zero.

If you are having trouble with binding, is it due to angular issues, or is it strictly tolerance issues?

The reason I ask, Is many times just because something is built one way, doesn't mean the exact same function can be obtained in a completely different manner. (sometimes much easier)

Is this a set in stone design?

What are the major constraints?

Is this controlled with a single inlet port? multiple ports? I assume you are using decent valving? flow dividers? etc?

I am interested in the application. My world is Pneumatics/Hydraulics/motion control and Automation, so you can see its right up my alley. When It comes to the design/R&D end of things I tend to get Excited... I can't help it.

I'm thinking the binding is coming from the tolerances. I believe if I can get a better set of tolerances, the sleeve bearings will guide the piston correctly. I know that the piston length vs. the diameter could also be an issue. As far as porting, I have a single 3/8 port on each side, however the ports on not shown in the section view. I will be using a multi-valve manifold to control my machine, one valve will be dedicated to this cylinder. The design is somewhat flexible, but my time is limited. I don't have the pneumatics experience to do this quickly, which is the reason I was looking for help. I thought if I could get this into the hands of an engineer that does this for a living (i.e., custom cylinder manufacturing company) I could help with the application. At first I thought some advice from an expert would help, but the more I think about it, the more I am convinced that I need to hand it off.