On Wednesday, January 15, 2014 12:21:42 PM UTC-5, 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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IIRC, shrink fits are generally .003" for the first inch of diameter, .001" per inch larger.

So, you might bore your 1-inch part's hole .4965" for your .4995" shafting.

Slowly and evenly heat the part with the hole to a dullish red. Don't let it develop any scale.

Insert the cool shaft in one swift motion, you won't have time to mess with your set screw alignment.
The shaft instantly starts to expand with the heat, further motion will not likely be an option.

Then cool it all off with water.

Your set screw will probably be redundant.

Good luck.

--
PaulS