Thermal Insulators on Micrometers...

My luck usually is. It mic's .001" over, put some emery to the surface, get it looking pretty. Measure again and it's .0005" under! Hello Loctite. And I keep three different flavors of it, too!


I make inboard boat shafts from marine grade SS. straight motor coupling need to fit so you can drive them on with a block of wood and a hammer. the shafts can be on size to .001 over. the couplings are 1.5 to 2 thou under. We have to polish it with 80 grit emery to size. I have to ice it down before micing. after till it gets there. need about .0005 for a good fit. I have miced a shaft when hot and it was .0005 bigger than when I started then ice it and it is .0005 under.
 
Yes, they are vital, also never touch a part bare handed as the natural oils in your skin will change the dimensions, for best results NEVER take the tools out of the packaging that they came in and use them, this will cause distortion every time.
 
Yeah, don't touch the part after making several heavy cuts. :cussing:
 
Fits matter, dimensions for the most part do not. Using a file and abrasive cloth to achieve close fits will usually result in out of round parts (if they were ever truly round to start with). Mechanical perfection is perhaps a state of mind.
 
In my shop, mechanical perfection is more like a pipe dream....

-frank
 
I make inboard boat shafts from marine grade SS. straight motor coupling need to fit so you can drive them on with a block of wood and a hammer. the shafts can be on size to .001 over. the couplings are 1.5 to 2 thou under. We have to polish it with 80 grit emery to size. I have to ice it down before micing. after till it gets there. need about .0005 for a good fit. I have miced a shaft when hot and it was .0005 bigger than when I started then ice it and it is .0005 under.

This is disconcerting. Are you saying that you allow a press fit for a shaft used in marine propulsion? So if I am of in the gulf and it slips and falls apart before I can get back home before being destroyed in a fast approaching storm it's because of a poorly engineered design? Does anyone wonder why manufacturing in the USA is replaced so easily by foreign companies?

A solution might be to use inductive heating to heat the coupling. The shaft can then be pushed in with either pneumatic or hydraulic force. Let the parts cool and it will be like it was welded in place. Look up induction heating in the internet, it is an interesting system. It can be used for small items soldered, or huge parts being joined. That would make your measurements and machining much easier and the part would be significantly improved.
 
As a generalized statement I deserve a bit of correction. I do speak from experience in part as I have seen many jobs go overseas because of greed and ignorance.
 
How did we get from thermal effects on micrometers to inboard motorboat drive shafts to global manufacturing? Did I take a wrong turn in St. Louis? :confused 3:

Tom
 
Back
Top