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Posted by mark on May 13, 2008, 10:08 am
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Try facing from inside to outside if that's possible ...this will drag
your tool ... and not push it .
you may have to set it at a different angle or grind it differently or
use a completly different tool to achieve this
and use wd 40 as lube.
All the best..markj
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Posted by the wizard on May 13, 2008, 1:08 pm
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On May 13, 12:33=A0pm, HeffaLump <"Percussion Engineering"> wrote:
> 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?
Your rings could be caused by an imperfection in the lead screw
bearings or drive, which causes a momentary change of feed speed. The
outcome of which is a slight polishing at the point of the stiffness.
To cure it you could try taking, having already locked the saddle
firmly, a second or third cut at the same setting. Doing this will
tend to polish the whole surface. You could then "texturize" the
surface with one of the "Scotchbrite" type abrasives.
Another thought occurs, you are not using a carbide tool, are you?
Aluminium responds well to a VERY sharp HSS or even silver steel tool
with WD40 or parafin as a lube.
T.W.
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Posted by Peter Fairbrother on May 19, 2008, 5:24 pm
Please log in for more thread options HeffaLump wrote:
> 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 don't know how to adjust gibs perfectly - and I don't know anyone who
does. They can be adjusted as best as they can be, but the cross slide
will still wobble a bit if it experiences a twisting force. Always. That
may well include the change in sideways force when/if you are turning
the knob by hand.
The best solution is to not let the cross slide gibs experience any
twisting forces - ie, if you can, mount things so the cutting point of
the tool is vertically somewhere between the two horizontal cross-slide
bearing surfaces.
Milling machines mostly work like that.
This may be impractical when eg boring - best advice I know of then is
to mount the boring bar a bit high, so it cuts shallower if it sticks,
and do an extra thin cut at the same slide position after the major cut
if you are going to take a measurement afterwards - the relative
measurement of the second cut will be more reliable in a twin-cut
scenario than the measurement of the first cut. Tiresome, but it may be
necessary.
And always lock any slides you aren't going to deliberately move.
-- Peter Fairbrother
(doing horrid things to/and with a tiny C3 lathe)
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Posted by Austin Shackles on May 20, 2008, 3:04 pm
Please log in for more thread options On or around Mon, 19 May 2008 22:24:19 +0100, Peter Fairbrother
>I don't know how to adjust gibs perfectly - and I don't know anyone who
>does. They can be adjusted as best as they can be, but the cross slide
>will still wobble a bit if it experiences a twisting force. Always. That
>may well include the change in sideways force when/if you are turning
>the knob by hand.
and on most machines, it'll be impossible to adjust them perfectly anyway
due to uneven wear. new stuff excepted, natch.
>The best solution is to not let the cross slide gibs experience any
>twisting forces - ie, if you can, mount things so the cutting point of
>the tool is vertically somewhere between the two horizontal cross-slide
>bearing surfaces.
that's a good point. when parting, especially, I try to have compound slide
wound in near the middle.
>
>This may be impractical when eg boring - best advice I know of then is
>to mount the boring bar a bit high, so it cuts shallower if it sticks,
>and do an extra thin cut at the same slide position after the major cut
>if you are going to take a measurement afterwards - the relative
>measurement of the second cut will be more reliable in a twin-cut
>scenario than the measurement of the first cut. Tiresome, but it may be
>necessary.
IME, boring bars are by nature flexible and it takes several cuts to
actually get the dimension you set it for.
>
>And always lock any slides you aren't going to deliberately move.
now that's the one I can never be bothered with. Should lock the compound,
really, for some things especially.
--
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
------------------------------------------------
>> http://www.schlockmercenary.com/ << ...and Kill them.
a webcartoon by Howard Tayler; I like it, maybe you will too!
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Posted by David Littlewood on May 25, 2008, 1:58 pm
Please log in for more thread options >On or around Sun, 25 May 2008 12:20:36 +0100, David Littlewood
>
>>
>>This, BTW, is almost always; I hate trying to do parallel turning with
>>the topslide. Why do nearly all lathes not have a leadscrew handwheel?
>>The time it takes to set the topslide to turn parallel must add up to
>>quite a large part of your workshop time, if that's all you have.
>
>You can hand-feed the student, but it takes a careful touch on the wheel.
>For anything over a few mm I tend to engage the power-feed. For little
>fiddly jobs I use the top/compound slide.
>
>'course it helps having a decent power feed, which not all lathes have.
This is OK(ish) if you don't need a very precise length. If you do, and
don't have DRO fitted, the markings on the carriage handwheel are
nowhere near precise enough though. With a leadscrew handwheel I can get
a length to within a fraction of a thou.
If I get around to buying a larger lathe, as I plan to do, then fitting
a leadscrew handwheel will be one of the first things I do, while
cursing the makers for not bothering.
David
--
David Littlewood
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> 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=