Need to shrink steel shaft

[mirage100]

What is this some sort of speed governing system?

How did you know that .It is a governor off a Disston 2 man chainsaw. It has a 2 cylinder Mercury engine on it. REAL big Chainsaw

 

[chips&more]

Cooling the shaft in dry ice will shrink the diameter to .4685". Heating the gear to 200ºC will increase the diameter to .466" so you still have an interference. Shrink fitting parts require the parts are a slip fit at assembly. Otherwise heat transfer will normalize the parts and the attempt will fail.

So in a word, the answer is no.

The easiest solution would be to modify the gear as machining the shaft will require recutting the Woodruff keyway. For .004", you may have that much clearance in the key seat though. I see that the shaft has been brazed. More than likely, it wasn't heat treated afterwards. You might be able to reduce the shaft diameter enough for a fit. As Cadillac said, it shouldn't be a press fit. A heavy slip fit at most.

392F-68F=324F so…324 X 0.0000072=0.00233” so…gear heated up will be .465+.0023=.”4673” or thereabouts.

 

[RJSakowski]

392F-68F=324F so…324 X 0.0000072=0.00233” so…gear heated up will be .465+.0023=.”4673” or thereabouts.

That's .00233"/". The gear has a bore of .465" so the change is .00233*.465 =.00108". The bore would increase to .4661"

 

[whitmore]

WellI I got out the micrometers and bore gauges and checked it out . it was worse than .004. I will be more than happy to send it to you and you can Measure it and then install it. This thing is CRAZY I know

A crazy solution, then: I'd pull out a rat-tail file and try to take .002 off the interior radius of that gear. It's not precision you
need, just clearance, and my experience with taking very-light cuts with the accurate machine tools is ... spotty.

It might be useful, too, to make a plug gage for the 'go'/'no-go' indication, and feel around for the spots
that need the next lick of the file.

 

[Asm109]

Riiiight. Concentricity between shaft and gear teeth is un important. Crazy is correct adjective, disagree with your choice of noun.

 

[mirage100]

I forgot some info . This gear is held on by the shaft. The gear spinning is stoped by the key.

 

[Cadillac]

How did you know that .It is a governor off a Disston 2 man chainsaw. It has a 2 cylinder Mercury engine on it. REAL big Chainsaw

Been a mechanic for almost 30yrs

 

[RobertB]

WellI I got out the micrometers and bore gauges and checked it out . it was worse than .004.

Did you measure the old gear to see if the new one was the same id? Wouldn't be the first time a replacement part was wrong.

 

[whitmore]

Riiiight. Concentricity between shaft and gear teeth is un important.

Concentricity is a number. Careful draw-filing to .002 depth will have a couple of hundred microinches of
uncertainty, and the mechanism can tolerate that much, or normal wear would ruin it quickly.

 

[nnam]

How about rolling sand paper face out, stick finger in and give it x turns. Measure and do again, adjust x turns accordingly. Make sure give room for last turn with very fine sand paper.