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Polishing metal on a lathe

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The_Apprentice

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#1
Well I don't know... I have always been told (and read) to NEVER let your hands/fingers come in contact with material on a lathe in operation. But I'm seeing this all over youtube, particularly with those who use mini-lathes for making jewelry, or other small items.

I just don't know. Am I a little too cautious at times? For example, this procedure I just saw was making me just cringe--


Thanks in advance. I'm still going to assume it's quite possible to lose fingers on a Mini, even with ones that have plastic gears & belts if the chuck is rotating fast enough...
 

T Bredehoft

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#2
I polish Aluminum on my lathe, finish with Simichrome polish. I apply it and polish it with a cloth, not my fingers, haven't lost a cloth yet. Yes, I am careful.
 

Ed ke6bnl

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#3
2 centers with no dog??
 

Silverbullet

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#4
There are those on YouTube who professes to be machinist . The real ones you can tell , they try to never get there hands or fingers near revolving work . There are some ways to polish without getting close to the point of getting hurt. Watch doubleboost , he gets close but tries not too. He gets cut often but always tries to show the right way. As long as you don't have jewelry or loose clothing and long hair it's very hard to get caught , you must be mindful of what your doing , don't blame anybody else if you go beyond the comfort range you must set.
I see these guys feel the finish on a mill with the endmill still running NOT GOOD , One guy scares the crap out of me at times Keith Fenner , his tied up goat tee is a disaster just waiting to happen. Others no SAFTEY glasses , long sleeves loosely hanging , life's to long to be crippled for the length of it. I've mentioned politely to many of the SAFTEY issues. Some are congenial others ignore. But it's ok my shop teachers taught us to practise SAFTEY for everyone.
 

Bob Korves

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#5
Plenty of people put stock into and finished work out of collets on the lathe with the machine running at speed. You have to touch it more than gingerly to do that. Others test the surface finish with their bare fingers, and seem to know what they are doing. I certainly would not try those operations with my skill level, but people with lots of experience certainly do so, and hopefully understand the risks. The most dangerous things are the ones you do not know are waiting to bite you. Especially in a hobby shop, there is no good reason for not being as careful as possible, which also includes learning, studying, and filing information away in our brains to keep us from getting hurt. Being safe is by no means being a sissy...

I used to have the chuck key to my drill press attached to a strong chain attached to the head. One day it occurred to me what would happen if I ever started the spindle with the chuck key in the chuck. I immediately removed the chain and found a new place for the chuck key, with no tether. I was ignorant, not my fault, but it could still have hurt me badly. I will give myself credit for thinking about the possible danger and immediately mitigating it. There are always more gotchas out there waiting to bite you.

Y'all be careful out there...
 

Rockytime

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#6
There is a guy on u tube that works on the lathe and mill with gloves. Not latex but real gloves. Seem to finish his project with fingers intact. Amazing.
 

chips&more

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#7
Just because it’s on YouTube, does not mean it’s good or correct. Just because it’s on the internet does not mean it’s good or correct.
 
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#8
You mean everything I see on the net, isn't 100% the truth, first it was no dragons, then no unicorns, now its questionable information on the net, my faith in the world has been completely shattered.............<sigh>
 

Cadillac STS

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#9
I just use a buffing wheel with compound to do that.

The youtube guy was taking a chance on severe injury.

It would be possible to make a simple wooden jig with a handle to hold the green and white abrasive pads in a sling and hold that with your hand away for safety. Put same pressure on the fabric in a sling. With a soft cloth instead of paper for the final buffing.
 

benmychree

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#11
I have been wrapping abrasive cloth around things in the lathe for polishing since I was in high school back in '62 and in apprenticeship and as a machinist since then; occasionally, the abrasive strip might catch and pull the fingers in and give them a painful event, but never anything serious, no breakage of anything but the abrasive strip; it seems that the new abrasive strip is weaker in the fabric than years ago, now it seems to break way easier, making it less likely to damage the fingers if things catch and wind up the strip and fingers with it; newer strip breaks before it even catches.
 

dlane

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#12
They used this lathe for polishing SS by hand , they polished the chuck also , amazingly the bed ways are good,
DSCN4382.JPG
 

benmychree

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#13
Another thing about wrapping the abrasive cloth around the part when polishing in the lathe is that it seems that even in USA made abrasive cloth, the strength of the fabric seems to be considerably weaker than the "good old days", Back then if the cloth hung up on the part, and tried to wreck your fingers, it did not break; nowadays, I see the band break just under th force of the spinning part, much weaker than back then; the effect is to make it harder to injure one's self by wrapping up your fingers in the abrasive cloth around the part being polished.
 
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#15
I prefer to use 5C scroll chuck when using emery cloth or polishing, never folding back on itself, using two hands. Jawed chucks have a way of winning when contacted.
 

kd4gij

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#16
I polish on the lathe all the time. But never wrap around the part. I hold the emery or scotch barite between the thumb and for finger. That way when it grabs, it just pulls it out of my hand. No harm no foul.
 

pdentrem

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#17
Never wrap your hand around the spinning part. Simply hold the two ends and pull towards you as mentioned by kd4gij. I polish rolling mill work rolls with a old set of crucible tongs. I have a leather strap that is held by the tongs and use a narrow piece of Emery cloth or paper. The leather forms around about half of the part and supplies the pressure that my hand causes by closing the tongs. Work great and I can stall the lathe with too much pressure, only 1 1/2 hp motor. There is a picture somewhere on this site showing the tongs.
Pierre
 

The_Apprentice

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#18
they polished the chuck also ,
LOL!

Thanks for the replies guys. I'm still overly cautious, after seeing too many incidences, and hearing of much worse from others in my father's machineshop.

At least it's better than learning the HARD WAYS (pun intended).
 

kd4gij

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#19
Best not doing something your not comfortable by all means.
 

BROCKWOOD

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#20
Lotsa good reading here! I saw a You Tuber with loose sleeves & a wrist watch the other day.
I cringed. Fenner's chin hair or even my long hair are much less a danger if we're cognizant
of how aware we must be in each decision & position assumed during a given operation. I'll
use a file to work a piece in a running lathe - but I realize which way to position it should the
unthinkable launch happen. The trajectory would be away from me & out of my hands. I use
strips of sandpaper. My hands are near a foot away from the moving part. Again, if it grabs,
my fingers cannot be pulled into moving parts.
After the high school girl with long hair somehow got tangled up in a lathe (during horse play),
I discovered that OSHA requires a cover on the lead screw in shops with more than 1 worker.
I decided to add this cover, not because of the girl's accident or even because I have long hair.
I added it to keep the screw clean.
There is a point of No Return during every operation. I got confused on which way to start my
cross slide when at full stop & wrecked it. That was a point of No Return. Parts only took six
months to arrive. Take your time. Identify "traps". Check your direction. Do dry runs to prove
your direction is correct. Slow down. Measure twice - with different instruments to prove the
answer is correct & repeatable. Enjoy the outcome!

Pic below is added lead screw cover, rebuilt apron & ready to assemble the cross slide with new
parts.

20160725 031.jpg
 

joezmam367

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#21
I hope this is still active, I'm in a rut here in a new shop and need advice. Been polishing but we only have 400 & done oil that smells like mint? Think it's a rust preventive, either way, after literally hours of rubbing from hard to softer, with fresh oil and a wipe down often, i can't seem to get these "flecks" out.
Spinning around 150-200 rpms, the parts close to 300lbs.
Any ideas here? Any help is appreciated!

Also, i always use thumb and forefinger to hold my paper, but it still scares the bejezzus outta me on some sharp edgrd finish parts
 

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SamI

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#22
What's the material? In some cast materials you can get porosity or other imperfections that could show up like that. Hot rolled plate can also have imperfections near the surface.
 

Bob Korves

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#23
My guess from the photos is that the "flecks" are residual tear outs from the earlier machining. I have not been professionally taught on achieving great surface finishes, but what I think I have learned over time is that you must get ALL the imperfections out with the coarse media before changing to a finer media, and not by working on individual spots, take the whole surface down evenly until it is as good as it can be with the coarser abrasive. Then go on to a finer abrasive, and not in too big of a step. Repeat, getting it as good as possible with each step. So, something like starting at 60 grit, changing to 100, then 220, 400, 1000, then changing to successively finer polishes. Otherwise, you can end up with a beautiful high polished surface that still has imperfections that were not cleaned up in the earlier steps. Amazingly it takes less time overall if corners are not cut, and the final piece turns out better. Sadly, what you are seeing usually means going back and starting at the beginning, or near to it. If you start trying to get a few individual defects out while preserving the polish you have already achieved, it just does not turn out nice.

Of course, having a better surface finish and less defects from the machining is the major cure, well worth working at to save lots of time and effort in the finishing work.
 

mmcmdl

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#24
If you're looking for an 8 or 4 or mirror finish , it's a grinding or lapping job . You could polish on a lathe till the cows came home , and you wouldn't get it . Machining tears or shears metal and leaves imperfections .
 

joezmam367

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#25
The material is "4140" is what I'm told
@Bob Korves i think that's what will end up happening, going back to start and getting everything out completely. Thanks for the input!
 
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