On Wed, 15 Jan 2014 10:21:42 -0700, "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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Freeze the shaft and heat the part.
The coefficient of thermal expansion for steel is 0.00000645in/in/deg
F.
You have 1/2 inch to work with, so .000003225" per F degree temp
difference..
If you measure at 70F, and freeze the shaft to 0f and heat the part to
350F you have 420 degrees and .00135 inches of differential expansion.