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Posted by HeffaLump on May 13, 2008, 7:33 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 NoSpam on May 13, 2008, 7:46 am
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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'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?
I had a similar problem on a Boxford, it eventually went away when I
replaced the motor so it may be worth looking at the motor, motor
bearings, V belt (if appropriate), etc
Dave
Dave
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Posted by Boo on May 13, 2008, 8:05 am
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'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????
I have a similar problem on my Boxford when turning diameters in aluminium to a
good finish. The problem is a visual "banding" like you describe at around the
same 3mm scale. There is no measurable difference in diameters at the bands and
there is no feeling of roughness to the turned surface. I once saw a reference
somewhere (most likely ME or else one of the GH Thomas books) to something
called "leadscrew shadow" where the author ascribed the problem to minute
irregularities in the relevant feedscrew.
It would be interesting to measure the repetition "pitch" of the pattern and see
if it relates to the pitch of the leadscrew you are using (maybe modified by the
gearing in use) ?
Unfortunately, I don't remember the upshot but it does seem to suggest that
changing the feed rate may help, or alternately using a metric/imperial cross
changewheel in the rive to the leadscrew so as to avoid having the spindle
rotate in a fixed simple ratio with the leadscrew (as far as possible I mean).
Hth,
--
Boo
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Posted by Austin Shackles on May 13, 2008, 8:28 am
Please log in for more thread options On or around Tue, 13 May 2008 12:33:44 +0100, HeffaLump <"Percussion
Engineering"> enlightened us thusly:
>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????
if the feed is non-linear it could do. I'd pull the saddle and examine the
feed, clean it all and adjust if it has any, and put it all back together,
see if it affects anything.
what machine is it?
I've noticed when hand-feeding you tend to leave marks on things if you
momentarily stop the feed.
--
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 jasonballamy on May 13, 2008, 8:32 am
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If they are equally spaced then play in the cross slide could be the
problem, as the handwheel is turned you slightly lift then press but if
you are getting it under power then not so likely.
Is the saddle locked? could be play there
Are you using any cutting fluid, could be metal build up on the tool
tip that builds upto a certain level then comes off before starting
again.
JAson
--
jasonballamy
------------------------------------------------------------------------
jasonballamy's Profile: http://www.rcgroups.com/forums/member.php?u=203943
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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.
>
> 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?