| Re: [GMCnet] Lathe Project [message #110352] |
Fri, 31 December 2010 09:26 |
Gary Casey
Messages: 448
Registered: September 2009
Karma: 0
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Senior Member |
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The thermal expansion coefficient of aluminum is about 13 ppm/F, so let's say
you put one part in the freezer at 10F. Then the other part is heated to 350F.
The difference is 340F, so the difference will be 340*13*4*10^-6, or .017. You
could tolerate a pretty tight fit and still get it together. I would suggest a
.010 interference and that will leave you about .007 clearance when assembling.
Then if I were nervous (once you get it part way together and it gets tight you
won't be able to move it, ever) I would heat the hot part - the base - to at
least 400 in the oven. Have the plate sitting on a flat surface so you can just
drop the tube into place, flush with the bottom. Once it cools it will be as
well fastened as if it were welded. And I'd put a bit of a chamfer on the hole
and on the tube so it won't be as likely to catch on the edge when inserting.
Put it in as straight as you can and then turn it a little to make sure it is
in and square. Fun project.
Gary Casey
Working on a project for the MH and have a Q. I have a 4" OD AL cylinder with
1/2" thick walls. Was going to attach to a 1/2" thick AL plate. My welder only
goes up to 255amps and I don't have my TIG torch cooler made(and my welding
skills aren't so hot,,,pun intended!!). So I thought I would bore a precise hole
in the 1/2" plate. Throw the plate in the stove and the cyl. in the freezer.
Now,,,,how much diffrence in size??? .001 or maybe 2 thousands. Or real tight at
.0025??? Whats real tight?? Will be mounted on the engine so it will have some
vibration but no real load. Thanks in advance,,,,,PL
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