How much runout is O K?

[Tim Pippin]

I have a jet 1442 lathe and have trouble using a faceplate. The stock Jet 6" faceplate works fine but an aftermarket smaller 4" faceplate allows the blank to scrub the motor housing. I bought a 3" extension from packard and have about 18 thousands of runout using it. The item desription says that you may experience some run out but I was expecting 3 or 4 thousands at most. My lathe arbor has about 1 thousands of runout. Any ideas?
Tim

[Bob Hampton]

tim
sounds like same problem I had with my HF lathe ...the shaft on the the aftermarket is to short to clear the motor housing .
Something to try that worked for me...try using a piece of pvc pipe that is the same diameter as the spindel shaft..your doing the same thing as your extension only shorter...cut the pvc just long enough so it allows the faceplate to clear the motor ...this may work better then your spindel extension and decrease or eliminate the run out ....worth a try ..I have ben told by several turners that the longer the extension the more run out you get ..thats why i went with the pvc pipe and it seems to work fine for mine.

Bob

[Bill Boehme]

I have a jet 1442 lathe and have trouble using a faceplate. The stock Jet 6" faceplate works fine but an aftermarket smaller 4" faceplate allows the blank to scrub the motor housing. I bought a 3" extension from packard and have about 18 thousands of runout using it. The item desription says that you may experience some run out but I was expecting 3 or 4 thousands at most. My lathe arbor has about 1 thousands of runout. Any ideas?
Tim

Basically, the problem is that you can't and shouldn't depend on screw threads for places that need precision alignment. Screws are meant as fasteners and for alignment you need a precision reference surface ... that would be something like using a Morse taper OR having a precision register surface on each part that mates together. When you stack parts, the misalignment problem can get out of hand very quickly as you have discovered. However, it depends on what you are doing. If you are turning a bowl, the rotation axis will be the centerline of the lathes spindle rotation axis regardless of what the extended faceplate is doing. As long as you don't remove it and then remount it during the turning session, I can't think of any obvious problem. Now, if you had the tailstock butted up against the other side, THAT would pose a problem because it would be putting the live center into a bind and inducing some shake into the lathe because of the coning motion. If you are starting out with a very large and heavy piece of wood then that could add to your problems, but for a small blank, you probably don't need to use the tailstock anyway.

Bill

[Jim Stoppleworth]

For the same problem I used 2 large washers on the spindle to get the aftermarket faceplate clear of the motor housing. Worked great for me.

Jim

[Paul Engle]

Bill pretty much got it. as a machinist myself I made my own ( 3 inch)extension and It is very hard to tap one hole , flip it and thread the other end and still have the two thrds match. If one could leave it in the chuck the whole time with out moving it you could get runout down to under .0010 inch. when I put mine on I use it for the whole time right up to and including the finish work and the wobble wont show on the finished product.I used some stress proof the second time , the first time i used some 4140 I think and boy golly never again cause if you are off , ur done I used a tap for female side and die for the male ( no gear for the 1-8 thd on the lathe). the stress proof was a little more forgiving just in case you of a mind to make one ur self. DO not use aluminum as is just to soft for turning w/chuck on board.

[Tim Pippin]

Jim I think you have the right solution. I wanted the extension to let me use a couple of aftermarket faceplates but also to distance me from the speed control. I guess I will have to deal with the speed control.
Tim

[Bill Boehme]

Jim I think you have the right solution. I wanted the extension to let me use a couple of aftermarket faceplates but also to distance me from the speed control. I guess I will have to deal with the speed control.
Tim

I think that you might be able to change the indexing on the speed control to get the handle in a different position if it is anything like the Delta 46-715 speed control lever.

[david blowers]

Had the same problem with an older powermatic... everything else on it is pretty much high-precision except where the threads end.

I added a two-part collar to the shaft and it was as true as can be. You can find most any size on EBAY for under $4-

Best Regards

-David