Tailstock Alignment

[CarlosA]

I know this is a common/difficult subject on these mini lathes. I got mine all dialed in where I was happy, left it over night, came back and took another cut on a new centered test bar just to see if it was still good and it was out .003" over 3 inches.

So I dialed it back in, cut 3 test bars in succession and each one is anywhere from .0005" to .003" out. Why is it that this is not repeatable?

I have done all the mods to get it really dialed in with extra set screws and moving the bolt to the top side. In ALL of the above cuts I did not move the tailstock at all, just the ram - being careful to tighten the center against the test bar the same amount each time. There is no runout on the ram, on the inside of the bore, etc - all is right on. The headstock end also does not runout. Lathe is new, bearings are good, etc.

I did get really good at aligning it with a dial indicator anyway .. carefully moving it over .001" at a time after test cuts, and watching the dial indicator for movement when tightening everything back down. I have tested all of this using centers .. both live and dead in the tailstock and dead in the spindle.

Any other ideas or things to look for? I have never had any problem on a real lathe, just this crappy casting used for the mini lathe tailstock.

 

[Bob Korves]

It sounds like something is moving. Use your dial indicator to check the headstock, spindle, carriage, cross slide, compound, and tail stock quill for play and lost motion, while locking down all including the one you are testing. Check all your mods for rigidity and play as well. Are you doing your tests with everything you can locked down? That should be EVERYTHING except for the carriage and the spindle.

 

[Chipper5783]

What is your lathe sitting on? Are you sure you don't have a soft foot condition?

 

[jayman]

Welcome to the club! I found curved surfaces on mine that were supposed to be flat locations for adjustment screws. I finally rebuilt mine so as to be non adjustable, but it is now very solid and stays aligned. I first separated the base and trued the surfaces that contact the lathe bedways with my mill. Then I inverted the base on the lathe bed and the distances between the "flats" that mount the tailstock upper and the bedway flats. That relationship was set up on the mill and the "flats" were milled flat and parallel. Next the tailstock was reassembled on the lathe bed with shims between the flats on the base and the "flats" on the upper. The shims were adjusted until the the tailstock center coincided with the headstock center. The shim pack thicknesses were recorded. Then I drilled and tapped the flats in the base for three 4-40 set screws. I used an AGD indicator to adjust the height of each set screw to match the thickness of the shim pack at its location. I reassembled the tailstock and tested its center position relative to the headstock center. Some minor adjustments were required. When the centers were coaxial, I locked the set screws in place with wicking grade Loctite. I separated and thoroughly degreased both tailstock outdoors parts using baths of odorless mineral spirits and acetone, rinsed both in a stream of acetone, and let them air dry. I mixed a batch of steel-filled epoxy putty (used for bedding rifle barrels and purchased from Brownells) and assembled the tailstock with epoxy filling the gaps. After that cured, I drilled and reamed for three 1/8" dowel pins and Loctited them in place. That was four years ago, and I haven't ever had a problem with alignment since.

 

[CarlosA]

That seems like a great solution. I'd be scared of messing it up during the process and ending up with an annoying paperweight. I'm also trying to avoid working ON my lathe and actually finish some projects for a change.

So far it seems to be holding up with the extra set screws - but I don't trust it so I check it everytime I work.