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Posted by HeffaLump on May 13, 2008, 7:35 am
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I've developed a problem when facing on my lathe, I do a lot of small
dia disks (20-40mm) in 6082 Aluminium and when it comes time to polish
the face I'm noticing concentric circles appearing on the finished surface.
They're not to pronounced, I'm able to polish them out easily enough,
but I'm worried it might be indicating a developeing problem.
I've tried cutting at 0.5mm down to 0.1mm with little differance both
manually & on powerfeed, I've adjusted to gibs to the cross slide (tried
it loose, spot on & too tight), varied the RPM's, differant cutting
tools/holders and I can see that the saddle isn't moving from the DRO.
I've put a dial guage against the surface with no discernable movement
when rotating !
The circles are easy to see but impossibly difficult to photo, you have
to catch the light just right but they appear to be 2-3mm apart. I
cannot tell if they are truly concentric or spiralling.
I'm thinking 2 things . . . either play in the head bearings or the
crossfeed leadscrew. Please don't let it be the head bearings but I
can't see how the leadscrew can affect the finish if the gibs are
correctly set????
Any ideas?
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Posted by Bushy Pete on May 13, 2008, 8:05 am
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I work on spectrometers, which are used to analyse various metals. The one I
work on that does aluminium samples at one customer's remelt and extrusion
plant does a sample every 45 minutes 24 hours per day, 6 days per week.
Their samples are about 55mm diameter and are cut on a lathe on just one
face.
We found after a bit of experimentation, that using of the shelf triangular
bits with methylated spirits in a hand operated squirt bottle (like from
your local kitchen supplies shop) as a coolant gave the best surface finish.
Prior to that they were grinding their own tips and the variation between
operators gave quite a variation in the surface finish. This affected the
operation of the spectrometer, causing variation in results.
The metho prevents the cutting tip from getting hot and trying to spot-weld
the surface of the sample. It also dries quickly without leaving residue
that affects the spectrometer. It is a simple operation once mastered to
squeeze the trigger with one hand and direct the straight line spray (not a
wide spread spray) at the cutting tip and to operate the hand crank with the
other, and to lean against the toolpost with one hip or knee to take up the
free play in the sloppy old lathe. They have installed a no smoking sign
above the lathe.....
Their sample mold has a 3mm deep depression in the centre to save worrying
about centering the tool, and a 1mm deep swarf breaking depression that runs
from the depressed centre almost all the way to the edge. This reduces the
length of the swarf to one rotation of cut for most of the time.
They normally cut about 3 by 0.5mm to 0.75mm cuts and then a finer 0.1mm to
0.2mm cut to finish the sample. This is fed by hand winding the many years
old lathe toolpost. The finish cut is normally done with a slower winding of
the cutting tool. The lathe has a lot of slop, but you know what companies
are like when it comes to replacing equipment that still does the basic job.
As it is only one face that is prepared, and they do not need to line up the
sample in the chuck for a second time, they are not worried that a fresh cut
uses a bit more sample that it would need to.
They melt a range of 6000 series alloys, and a range of high silicon casting
alloys and these all produce excellent results this way. 6082 is one of the
alloys they produce.
Hope this helps,
Peter
"HeffaLump" <"Percussion Engineering"> wrote in message
> I've developed a problem when facing on my lathe, I do a lot of small dia
> disks (20-40mm) in 6082 Aluminium and when it comes time to polish the
> face I'm noticing concentric circles appearing on the finished surface.
>
> They're not to pronounced, I'm able to polish them out easily enough, but
> I'm worried it might be indicating a developeing problem.
>
> I've tried cutting at 0.5mm down to 0.1mm with little differance both
> manually & on powerfeed, I've adjusted to gibs to the cross slide (tried
> it loose, spot on & too tight), varied the RPM's, differant cutting
> tools/holders and I can see that the saddle isn't moving from the DRO.
>
> I've put a dial guage against the surface with no discernable movement
> when rotating !
>
> The circles are easy to see but impossibly difficult to photo, you have to
> catch the light just right but they appear to be 2-3mm apart. I cannot
> tell if they are truly concentric or spiralling.
>
> I'm thinking 2 things . . . either play in the head bearings or the
> crossfeed leadscrew. Please don't let it be the head bearings but I can't
> see how the leadscrew can affect the finish if the gibs are correctly
> set????
>
> Any ideas?
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Posted by Richard J Kinch on May 13, 2008, 2:17 pm
Please log in for more thread options Bushy Pete writes:
> ... methylated spirits ...
I.e., what we Americans call denatured alcohol, mostly ethanol plus a
denaturant such as a very small proportion of methanol.
It still baffles me how anyone expects us to make billions of gallons of
ethanol for fuel and not have a bootlegging problem. Surely the guys in
the distillery will have every incentive to draw off a personal supply
before the stuff is denatured with gasoline. Or are we going to hire
100,000 IRS agents to watch them? This corn ethanol biz is literally just
making 200 proof vodka on an unimaginably huge scale. And this is the
country that once had Prohibition!
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Posted by Tim Wescott on May 13, 2008, 4:15 pm
Please log in for more thread options Richard J Kinch wrote:
> Bushy Pete writes:
>
>> ... methylated spirits ...
>
> I.e., what we Americans call denatured alcohol, mostly ethanol plus a
> denaturant such as a very small proportion of methanol.
>
> It still baffles me how anyone expects us to make billions of gallons of
> ethanol for fuel and not have a bootlegging problem. Surely the guys in
> the distillery will have every incentive to draw off a personal supply
> before the stuff is denatured with gasoline. Or are we going to hire
> 100,000 IRS agents to watch them? This corn ethanol biz is literally just
> making 200 proof vodka on an unimaginably huge scale. And this is the
> country that once had Prohibition!
You mean ATF.
And we may have had Prohibition, but before that we had areas of the
country where they used whiskey for money, and had insurrections over
the federal government insisting that folks pay taxes with cash instead
of in kind.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
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Posted by ED on May 13, 2008, 5:55 pm
Please log in for more thread options On Tue, 13 May 2008 13:17:29 -0500, Richard J Kinch
>Bushy Pete writes:
>
>> ... methylated spirits ...
>
>I.e., what we Americans call denatured alcohol, mostly ethanol plus a
>denaturant such as a very small proportion of methanol.
>
>It still baffles me how anyone expects us to make billions of gallons of
>ethanol for fuel and not have a bootlegging problem. Surely the guys in
>the distillery will have every incentive to draw off a personal supply
>before the stuff is denatured with gasoline. Or are we going to hire
>100,000 IRS agents to watch them? This corn ethanol biz is literally just
>making 200 proof vodka on an unimaginably huge scale. And this is the
>country that once had Prohibition!
Bootlegers are old school, the new generation grows rope...easier,
more profitable.
It will never matter how cheap ethanol gets IMO , when
it comes down to sippin stock, it's about quality, not price. :-) ED
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> disks (20-40mm) in 6082 Aluminium and when it comes time to polish the
> face I'm noticing concentric circles appearing on the finished surface.
>
> They're not to pronounced, I'm able to polish them out easily enough, but
> I'm worried it might be indicating a developeing problem.
>
> I've tried cutting at 0.5mm down to 0.1mm with little differance both
> manually & on powerfeed, I've adjusted to gibs to the cross slide (tried
> it loose, spot on & too tight), varied the RPM's, differant cutting
> tools/holders and I can see that the saddle isn't moving from the DRO.
>
> I've put a dial guage against the surface with no discernable movement
> when rotating !
>
> The circles are easy to see but impossibly difficult to photo, you have to
> catch the light just right but they appear to be 2-3mm apart. I cannot
> tell if they are truly concentric or spiralling.
>
> I'm thinking 2 things . . . either play in the head bearings or the
> crossfeed leadscrew. Please don't let it be the head bearings but I can't
> see how the leadscrew can affect the finish if the gibs are correctly
> set????
>
> Any ideas?