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concentricity/position tolerance info needed Question
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Posted by: markd

01/16/2004, 10:25:09

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I have a fixture that i am making that is basically a 4" aluminium shaft x 6" long. I am locating rings over the shaft which i will be gluing together. It is important that the rings are as concentric as possible, what concentricity tolerance should i apply to the outside of the shaft or will a position tolerance on the shaft do instead ?



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Re: concentricity of rings
Re: concentricity/position tolerance info needed -- markd Post Reply Top of thread Forum
Posted by: RandyKimball
01/17/2004, 14:24:47

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"As concentric as possible? That is very open-ended ... at what dollar? Please provide a little more data, unless the following answer will suffice.

First, you control the diameter run-out with concentricty call outs as you have mentioned. Do this with a TIR (total indicator reading) from the ring OD (outside diameter) to the center line (axis) of the aluninum shaft. Generally when you call out TIR it is assumed to the center axis, but you may call out to one diameter in respect to another. A TIR of .004 is considered reasonably close at that diameter (this means .002" off center wobble, about 1/2 the thickness of a human hair), but I have no idea of your function. ... .004 TIR may not be close enough.

Second, in your case you may want to call out the perpendicularity of the faces of the rings to the axis of the shaft. In this case again call out the TIR of run-out allowed in the faces of the rings, it will be assumed as to the axis.

To get the "glued rings" truely concentric it would be best to glue them on first allowing extra stock, then have them turned round and square to the face on a lathe.

I hope this helps or chime back in,

The worst idea of you lifetime may be the catalyst to the grandest idea of the century, never let suggestings go unsaid or fall on "death ears".

Modified by RandyKimball at Sat, Jan 17, 2004, 14:29:49

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