"mike" wrote in message
...
On 1/15/2014 9:21 AM, Bob La Londe wrote:
I've got a little project I am working on. Steel shaft in steel hole.
At first I was just going to bore close, and skim cut the bore until the
shaft just barely fit then secure it with a set screw. Some strength
against twisting is important. Then I was wondering if I might get a
better concentricity by heating the part, and letting it cool around the
shaft. Still with a flat on the shaft and a set screw just to be safe.

The part with the hole has an outside diameter where the hole is of
about 1.00". The hole is 0.500" apx. Final cut dimension of the hole
will be determined by trying to figure out how much to heat the part and
how much expansion I can get. The shaft is hardened tool steel with a
diameter of 0.4995" apx. The part is 1018. My thought was to bore to
.49 then ream to .499 with an under reamer. Heat the part, insert the
shaft, snug up set screw momentarily to align the flat, and allow part
to cool. Then tighten set screw. This is to be a modestly accurate
permanent installation.

How much heat do I need on the part? I think I'll need a little more
growth than necessary to fit due to rapid cooling while assembling, and
the slow clumsiness of working with heat heat resistant gloves on and/or
using tongs. Ambient in my shop is around 70F in the afternoon lately.

Please lets not go off on tangents. Thanks for any help or suggestions.






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TANGENT ALERT:

If your intent is perfect concentricity, isn't a flat the last thing you
want to do?

Response to tangent:
A small flat, not the full wall length of the engagement. The flat is to
provide purchase for a set screw to prevent any "reasonable" chance of
twisting like the tiny set screw size flat on the side of an end mill.
There would be full circular engagement above and below the tiny little
flat.



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