Lathe Facing Problems

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?
Reply to
HeffaLump
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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
Reply to
Bushy Pete
HeffaLump fired this volley in news: snipped-for-privacy@posted.plusnet:
I'm thinking chip relief/breaking. If any part of the chip contacts the work, it will burnish a circle there.
Have you changed your tool or the grinding of it, or is it building a false edge?
LLoyd
Reply to
Lloyd E. Sponenburgh
Use a tenths indicator and check for play in your spindle bearings, both laterally and longitudinally.
Btw..that is one of the signs of increasing backlash in ballscrews/leadscrews in CNC machines.
About .0004-.0006 will start showing the rings
A herringbone pattern on a side turn will often indicate excessive bearing clearance
Plain or ball/roller bearings?
Gunner
Gunner
Reply to
Gunner
One assumes he didnt have the problem before, and now does, and hasnt changed brands/type of inserts?
Gunner
Reply to
Gunner
I second the suspicion about the cutting tool and/or coolant, rather than the rigidity. Sounds more like a finish problem than a positioning problem.
Reply to
Richard J Kinch
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!
Reply to
Richard J Kinch
Could be half a dozen things. It can be built-up edge of workpiece material on the cutting edge, variations in feedrate from your hands (try using the power feed at a very low advance rate). Oh, OK, I see you've already tried that! It could be looseness in the gibs allowing the cross slide to weave back and forth slightly as you turn the crank.
If the spacing of the rings match the thread pitch of your crossfeed screw, then the connection is nearly certain. remeber that no machine is totally rigid, everything is slightly flexible. And, even with the gibs "too tight", there is still an ability of the upper slide part to rock just a little. It is possible there is a misalignment between the screw and the nut that is applying sideways forces on the nut, thus rocking the slide as the screw turns.
Jon
Reply to
Jon Elson
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.
Reply to
Tim Wescott
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
Reply to
ED
It seems possible that the leadscrew may be slightly bent. This can easily rock the saddle enough to form noticeable rings.
Don Young
Reply to
Don Young
For drivin or for sippin, it all starts out as the same vodka out of the still. One goes to the gasoline blender, the other into an oak barrel.
Reply to
Richard J Kinch
I have experienced this problem before and it turned out to be crossfeed leadscrew alignment. Make certain that the follower nut is loaded evenly from one end to the other end of crossfeed travel and that the resistance to turning the dial handle doesn't increase when the crossfeed clamping screw is tightened to the follower nut. Any aberation in the crossfeed travel will show on the facing finish. If the problem only shows when power feeding and not in manual feed, then look at the apron to crosslide fit for drive gear misalignment/binding. Steve
Reply to
Steve Lusardi
There's a micro distillery start up in this local, word is that it's heavly regulated.
Their process is vastly different than a fuel plant. An internal combustion engine doesn't mind nastys like aldehydes and the higher alcohols, but I sure do. Oh I suppose one could consider the fuel grade as a stripper batch and rerun it. and I'm sure someone will do just that. ED
Reply to
ED
What's different about a fuel vs beverage distillery? I would expect they would both be the same. Got any links explaining it? It seems to be an issue not readily Googled.
Clearly some blindfold taste-testing is in order.
Reply to
Richard J Kinch
Start here-very good subject material
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" I heard about this guy" who actually built one of those, reflux devices for,,well you know distilling essential oils, or something like that. (really nice metal working project) Seen pictures...copper is so pretty.when polished....
. The devil's in the details..yeast, wash recipe. ect.
After a number of attempts he's said really have it down to a science. A good percent of what comes out is best used for ligher fluid,(foreshots and tails) but the middle of the run or the heads as its called is said to be pretty darn good.., esp. after a carbon polish.
For fuel a vacuum system would be a good choice. where as on a reflux type thing letting it relux for a long while and getting it stabilized before opening the drip makes for a nicer product, or so it's been said.
On a fuel system just strip it all out quickly...acetones, cogeners, the whole thing...
.ED who collects pint canning jars
Reply to
ED

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