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Posted by on November 26, 2008, 7:58 pm
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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?
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Posted by Charlie Gary on November 27, 2008, 1:26 am
Please log in for more thread options On Nov 26, 4:58 pm, vajr...@gmail.com wrote:
> 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?
Yeah. It sounds like you've got shit material that moves when you cut
it. What alloy is it?
Later,
Charlie
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Posted by Bipolar Bear on November 27, 2008, 2:26 am
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> 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?
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
--
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Posted by BottleBob on November 27, 2008, 2:57 am
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vajra78@gmail.com wrote:
> 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?
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. <g>
There's an old machining mnemonic that goes; Rough EVERYTHING, before
finishing ANYTHING. And in your case that may be valid.
--
BottleBob
http://home.earthlink.net/~bottlbob
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Posted by Bipolar Bear on November 27, 2008, 3:21 am
Please log in for more thread options
>
>
> vajra78@gmail.com wrote:
> > 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?
>
> 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. <g>
> There's an old machining mnemonic that goes; Rough EVERYTHING, before
> finishing ANYTHING. And in your case that may be valid.
>
>
Solution treated artificially age then stretched.
IIRC you can stress relieve the shit 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
--
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> 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?