Proper RC tolerance choice for concentric sliding pipe mechanism
Proper RC tolerance choice for concentric sliding pipe mechanism
(OP)
Hello all. I was hoping for some input on an appropriate choice for a clearance fit. The application is a electromagnetic jacking system consisting of 3 layers of concentric pipes. The different layers must be able to slide freely inside one another, so I obviously need a clearance fit. The material is probably a harder plastic like PVC, with a small portion of iron for the magnetic part. I'm not planning on a robust lubrication system, since the mechanism is low duty (its more a proof-of-concept). I was leaning towards something like RC7 or 8, but I'm worried this may be too much clearance, thus allowing the components to wobble within one another.
Your comments are much appreciated.
Your comments are much appreciated.





RE: Proper RC tolerance choice for concentric sliding pipe mechanism
RE: Proper RC tolerance choice for concentric sliding pipe mechanism
PVC can easily be damaged by debris so seals/boots/hoods are necessary and it is difficult to maintain a surface finish.
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RE: Proper RC tolerance choice for concentric sliding pipe mechanism
RE: Proper RC tolerance choice for concentric sliding pipe mechanism
You need to plan on using a machined inside and outside member - which could start out as a "pipe" but standard pipe lengths will not be tight enough nor smooth enough for your application.
RE: Proper RC tolerance choice for concentric sliding pipe mechanism
I know this doesn't answer your question about clearances but I just thought I'd add my two cents.
DOL
RE: Proper RC tolerance choice for concentric sliding pipe mechanism
RE: Proper RC tolerance choice for concentric sliding pipe mechanism
RE: Proper RC tolerance choice for concentric sliding pipe mechanism
I like to use the ANSI fits. I would think that they were worked out for metal to metal contacts. Plastics are relatively compressible, and have low friction coefficients. I am not sure the behaviour would be consistent.
I would also assume that the ANSI fits apply when you do not put massive external loads on them.
If your external loads are substantial, then I do not think the ANSI fits are a good model. You know the loads, you can work out the forces, and the friction and wear. Read up on plain bearings.
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JHG