View Full Version : Precision Sandpaper grinding

02-10-2008, 03:35 PM

This is my second post. Been lurking but not posting.

I've been repairing a Clausing 6903 on and off as I can find time and get access to a lathe.

The other night, I was turning a mandrel between centers when I could not get the tail stock adjusted to turn true. Finally I just got her close and then cranked up the chuck speed and used abrasive paper and periodic measuring to get the 0.001" interference fit I needed.

I have a feeling this isn't that uncommon a practice for HSM type work.



02-10-2008, 03:42 PM
Its a very common practice as long as you are carefull and dont get wound up in the part. people do it at job shops too, its not just a home shop trick.

Its the only way to get good seal surfaces. Cut them about .003" oversize and polish them up real nice.

02-10-2008, 04:40 PM
Leave as little as possible to polish off. The more you leave, the more chance there is of ending up with a wavy surface and inconsistent diameter. If you're careful, you can do a pretty good job.

If you want an accurate and parallel o.d. though, the way to do it is with a lap. A lap will give you a consistent diameter. Again, though, finish as close to size as you can before lapping. 0.001" ought to be plenty.

02-10-2008, 05:22 PM
... the way to do it is with a lap.

Could you elaborate on that?

02-10-2008, 05:49 PM
hasn't anyone out there done slow finishing? Diamond honed H.H.S tool with lots of top rake slow rpm medium feed and lots of coolant = mirror finish

02-10-2008, 06:01 PM
Here are three links from the archives that discuss lapping:

02-10-2008, 07:34 PM
I'm still in the dark about your recomendation of lapping. The thread is about reducing a shaft OD to a precise size. All of the three links that you posted are about lapping an ID or a flat surface. What am I missing here?

02-10-2008, 08:24 PM
There should be discussion in there about a "ring lap" which is the exterior version of an internal lap.

Basically, a split brass or aluminum ring that has a hole in it to accept the shaft you want to lap, and a way of closing it down to (lightly) contact the shaft. Introduce a small amount of lapping compound, and work the lap back and forth on the shaft.

02-10-2008, 08:55 PM
I know exactly what clutch is talking about. On my old Atlas lathe, I often turned to Old Mr. Nicholson to take off that last .001", if the part needed to be Right On.

Clutch, Mr. Nicholson doesn't leave nasty grinding dust on your precious lathe ways like abrasive paper does. Plus, he works faster.

Dunno about clutch, but little of my work needs to be lapped to be "good enough", that's overkill, in most cases.

02-10-2008, 09:12 PM
used abrasive paper and periodic measuring to get the 0.001" interference fit I needed.

I have a feeling this isn't that uncommon a practice for HSM type work.

Yer right, not uncommon at all to get a nice finish to the last thou.. Not just HSM work either. I see it used in many job shops too.

I got a score on some 3M Trizact abrasive rolls. I love it for this purpose for a couple of reasons. First its backing is thick so its tough, flexible and stays "flat". Second, the abrasive is very uniform. Not bumpy like grains of abrasive but structured. Think of a file and thats what the pattern, yes, it has a pattern, is like.. Oh, and it doesnt load up at all. Its a very fine abrasive. Ebay should show some up for pennies on the dollar. JRouche


02-10-2008, 10:12 PM
I've used both methods, paper and files, to get the final finish. I like to reverse the rotation of the part at least once to allow the paper or file to bring up some of the embedded burrs and knock them off.

Sometimes I wet sand using light oil or even water, then for the final polish I'll use something like Mothers aluminum polish, or Never-dull. I've about half learned not to use steel wool on aluminum- and I've about three-quarters learned to remove drill bits from the tailstock before doing the sanding routine. :)

02-10-2008, 10:23 PM
Further to my slow finishing post. If you turn a shaft either between centers or between chuck and tailstock center and you get a perfectly parallel cut go out and buy a lottery ticket. This is one of the most difficult feats if you want to have less than .0001" taper. First few cuts even if the centers are right on you will get a taper as the tool heats up and expands during the cut. hss not too bad but carbide more so. Now is NOT the time to adjust the tailstock. Take two slow finishing cuts with coolant and then check for taper. Now adjust the tailstock using a 1/1000 (tenth) indicator. Take another finishing cut and check. It will probably still have some taper so adjust again. Time consuming I know but if you want to get away from sandpaper this will work. Patience is the key and its all about perfecting your skill. Of course you will move the tailstock half the difference in diameter. Hope this helps those who want to say look what I did. Of course those who have never tried machining will not appreciate what have accomplished. Peter