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How bad is this SB 10L bed?

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
That error depends on the ratio of the width of the ways to the tool height above the ways.

Narrow ways and a tall height (as with many "unmentionable" lathes, makes it much worse. SB as a rule is not too bad.

Scraping the back way to match is not a bad idea. But going to that much work, you may as well make them both good......
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
In addition to the trick that John K mentioned of setting the tool slightly above center for OD or ID turning, if you use an indicator or a DRO on the machine, you can gently "bump" the tool in and out as it travels down the bed. I've done this countless times on heavily worn machines, and can generally hold less than .001" difference down the length of a part pretty easily. A good DRO or indicator will enable . 0001" bumps, which are basically imperceptible. A quick run across the surface with some abrasive paper afterward will make it just about as good as it gets. The trick to this is NOT to attempt use of the handwheel for the bumps. Use a small soft copper or brass block to tap in an appropriate place.

Of course, rebuilding the machine sure makes things less stressful and easier, but sometimes that's just not an option. If it is, I certainly prefer it though, heh. I ran an American lathe for quite a few years that cut in an 'S' curve pattern. I had to bump in AND out, then back in again. That was a bit of a pain, especially as the taper was bad enough that the tool pressure would change in different places on the part down its length, so THAT had to be compensated for also. Good times. However, they actually finally ponied up to regrind the ways and turcite the saddle. Boy was that a pleasure to run afterward after having had to deal with the 'S' curve for so many years.
 

Gard

Aluminum
Joined
Mar 18, 2016
That's interesting, I would not of thought of trying to move it by bumping it, sounds like a good idea. I will give it a try. I have tried a couple of times with the handwheel and had limited success. The special lathe file does work pretty good.
 








 
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