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Old 11-26-2019, 04:42 PM
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Have a 15” diameter round sander at work that we put on 50 grit sanding disc, self stick. It is powered by a 2hp 1750 rpm motor, the plate mounted directly onto the motor shaft. Shop made I believe 25 years ago.

I thought that I could true up the plate that warped or pulled when originally welded. There is .050” runout at 15”. And the stand likes to dance around a bit.

I turned a mandrel in lathe to mount the steel plate too, but am getting a lot of chatter in trying to clean up the 7/16” thick plate.

Suggestions in getting rid of the chatter marks, before I flip it around and try to finish the sandpaper side? I’m already getting flack from other guys in shop for trying to make it better.

Probably the best way would be to set up a grinding when to true up the wheel while it is spinning in the lathe, but I don’t have that setup yet.

High speed sharpened tool bits, or carbide inserts?

Rpms?

I have been trying different combinations, and have not found right one yet. And I don’t want it to take two days to fix it either.

Did I tackle something too hard to do?
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Old 11-26-2019, 04:57 PM
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Is it now flat, but just with chatter marks? If so, I'd try a random orbit sander and see if it smooths it up.
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Old 11-26-2019, 06:10 PM
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Did you slow it down on the way out
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Old 11-26-2019, 06:21 PM
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Quote:
Originally Posted by milomilo View Post
Is it now flat, but just with chatter marks? If so, I'd try a random orbit sander and see if it smooths it up.


It is pretty close, I think within .005 with an indicator. I the back side I am not so worried about, except for looks, but function will be main priority.

The front side I want to make sure gets smooth so the sandpaper adheres well.


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Old 11-26-2019, 06:30 PM
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Quote:
Originally Posted by digr View Post
Did you slow it down on the way out


I did not necessarily change the speed and continue the same cut.

Originally I was using a new carbide insert, but am wondering it that is the best thing.? My reasoning behind this is that carbide inserts shear the metal off, and need more support to take heavy cuts. They do not like light cuts. But with the plate so big, and thin, it flexes easy.

Would I be better off using high speed steel bit sharpen to “cut” the plate? Just need to keep the surface speed in reason? Probably around 70-90 SFPM?

Honestly, sometimes I lose patience if I can’t make fast progress, so I am getting frustrated with not finding the right combination so far.



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Old 11-26-2019, 08:19 PM
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On a big diameter like that I always feed by hand so I can start slow and increase as I get closer to the center. I think inserts would work fine.
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Old 11-26-2019, 08:39 PM
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2 ways spring to mind: A flywheel grinder. Some can still be found in old NAPA stores.

Have it Blanchard ground or turned on a disc brake rotor machine

Sorry, all I got today.

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Old 11-26-2019, 08:47 PM
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I wonder if you faced off a piece of six inch pipe and tacked to the plate and then chuck the pipe in the four jaw? "light tacks" And use high speed steel cutter
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Old 11-26-2019, 09:13 PM
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I have turned some large diameter stuff, and the first thing I want to know is where is low gear.

At 12 inches I find even 50 rpm will still chatter, and that's as low as my rig will go, but was able to damp it by tying a piece of rubber hose around the tool post. Anything that sucks up a resonant frequency or lowers the frequency is good.
It is best to act as if chatter is occurring before it does, because without grinding it is hard to machine out once it's started happening.
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Old 11-26-2019, 09:16 PM
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I’d have mounted a grinder to the sanders rest plate.
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