Turning a out of round aluminum tube true

V

vajra78 17 years ago

I'm working with some 4.500" x .500 wall 6061 tubing that can be out of round as much as .100 caused by both varying wall thickness, up to .

040, and varying concentricity, up to .080. My big problem comes in final turning stages. After obtaining an OD that is round to .010 +.
010 -.005, I then turn the ID in a pot chuck holding with the minimal pressure allowed to turn the part. One might think that given sufficient stock on the ID one should be able to obtain ID roundness within .005, but it seems that the cutting-tool follows the starting roundness only improving ID roundness .005 to .010 after machining creating more lost time to rounding in order to obtain .005 roundness.

Ideally I would like to through a part with an OD that is within .030 and turn an ID that is within .005, facing one side, then put the part on a expanding collate and turn the OD, and face other side then be done with the turning. Does anyone have any ideas as to what's going on that a true ID will not turn given sufficient material removal?

Vote

C

Charlie Gary 17 years ago

Yeah. It sounds like you've got s*it material that moves when you cut it. What alloy is it?

Later,

Charlie

Vote

B

Bipolar Bear 17 years ago

Suggest use the largest dia neutral rake boring bar you have that is a practical fit and for a 3-1/2 in dia offhand I would say set it to be .01 maybe .02 in above centerline--take several light passes till you get a full cleanup

Vote

B

BottleBob 17 years ago

V:

6061, and many cold rolled materials, seem to have a "skin" that is stressed, and when removed the stresses are released. Face .030 off one side of thin flat plate and it bows, face the same amount off the other side and it can bow back. But virtually never the right amount to make it flat. There's an old machining mnemonic that goes; Rough EVERYTHING, before finishing ANYTHING. And in your case that may be valid.

Vote

B

Bipolar Bear 17 years ago

Solution treated artificially age then stretched.

IIRC you can stress relieve the s*it by taking it up to 700 deg or maybe a bit less using a slightly modified kitchen oven but then you absolutely need to re-age at 350 or so for a several hours--Ill try and look in the alcoa book down in the shop but havent been there in a couple weeks so no guarantee what with the holiday and all.

But probly not really needed in his case

Vote

B

Bipolar Bear 17 years ago

formatting link

Heat Treatment The AL 6061 alloy does respond to heat treatment which is accomplished by annealing and relatively low temperature aging. See "Annealing" and "Aging".

--------------------------------------------------------------------------

Forging No data, although the alloy is considered forgeable.

--------------------------------------------------------------------------

Hot Working No data. Hot working generally is not required because the alloy has very good cold working characteristics.

--------------------------------------------------------------------------

Cold Working Easily cold worked, or cold formed in either the annealed or aged conditions.

--------------------------------------------------------------------------

Annealing Annealing is done at 775 F for 3 hours at temperature, followed by controlled cooling at a rate of 50 F per hour down to 500 F, then air cool. A stress relief anneal (after cold working) may be done at

650 F with air cooling.

--------------------------------------------------------------------------

Aging Aging is done at different temperatures and times, depending upon the finished temper desired as follows : T6 350 F for 20 hours and air cool. T61 440 F for 6 hours and air cool. T63 380 F for 19 hours and air cool.

--------------------------------------------------------------------------

Tempering Not applicable.

--------------------------------------------------------------------------

Hardening Hardens due to cold working or aging heat treatment -- see "Aging".

begin 666 transpix.gif J1TE&.#EA`0`!`(#_`,# P ```"'Y! $`````+ `````!``$```$!,@`[ ` end

Vote

M

Matt Stawicki 17 years ago

I ocasionally run some 3" x 1/4" wall 6061 tube (1.75" long sleeves). To obtain any sort of accuracy, you *must* have it anealed.

Matt

Vote

Turning a out of round aluminum tube true

Join the Discussion

Didn't find your answer?