Machining a Hydraulic Piston

What are the materials of construction?

What is min/max operating temperature?

Etc. Etc.

Have you looked at any of the hundreds of catalogs on sites to determine what the industry is doing?

Is this homework?

Bore +.003″ -.003″

That's the piston tolerance, what do I know?

That sounds like some interference-fit cylinders I've run across....

Lots of hydraulic cylinders for special purposes have no seals at all. Here oil type and viscosity are determinant. No info supplied, however.

1. Are you going to hard chrome the piston after it is machined? This would be normal for an oil hydraulic piston. If so you need to take into account the plating thickness which will vary depending on the plating specification.

2. Are you asking us to assume that the bore is exactly round with zero eccentricity and perfectly smooth interior surfaces. An interesting assumption since you need to apply tolerances to the piston. Just make a perfect piston with the same technology and the same diameter as you made the perfect bore and you do not need any tolerances, or piston seals.

3. How long is the cylinder and how long is the piston?

4. What material are your piston seals made from and how are they constructed. A spring reinforced seal will need more clearance than nit-rile seal, which is different to a Teflon seal or a bronze seal.

4. How much side load is applied?

5. Tolerances for oil, phosphate ester and water hydraulics vary greatly. What hydraulic medium are you using?

If this is a homework question. Allow for all these variables and you should get high marks. Happy New Year.

Much more info is needed sir. Load and operating temperature ranges, oil you plan to use, and your ability to maintain precision in cylindrical roundness, straightness and ability to hold the specified sizes. Meehanite ( a hard alloy of cast iron)is a superb material for your cylinder since it is both stable and hard. If you can also make your piston from this same material you can hold very close fit dimensions. But if you are dealing with aluminum as so many do, then the fit will need to be much more loose to allow for large size changes during operational temperature shifts. The design and shape of the piston will also effect it's ability to hold shape during operation. Since you are using hydraulics instead of pneumatics I will assume you need some strength as well. I have been intentionally vague and have included no actual numbers because much more info is needed before a decent set of figures can be determined. And modern seal kits using teflon and quad x seals ( am I showing my age?) can allow wide tolerancing while still maintaining adequate sealing. Good Luck.