Wayward tailstock spindle needs new direction in life.

[Shotgun]

I'm slowly getting my Sebastian lathe up to working condition. It wasn't built with levelling feet. Just holes in the middle of the head and foot legs for it to be bolted down. Leveling was to be done with shims. I wanted it slightly higher anyway, So I made pads for it to sit on the four corners, with the front two adjustable using some scrap 3/4" thick 3" rounds, a couple Mazda rotary engine case bolts that I had laying around.

I'm waiting on a level, but last night I dialed it in with RDM, and about 1.5 turns of the headstock side's bolt brought it right into compliance. There's some debate out there whether RDM is a good way to align the headstock with the ways. But, it is what I had on hand and it would get me close(er). Meh! I'll get the level soon enough and check the results. One deficiency I do see in the method as described is that while the bar doesn't need to be perfectly straight, the sections used for the measurement need to be clean and perfectly round. I used a 3ft length of 2"x.065" 4130 tube, and turned a 1/4" section on each end to be clean.

Then I turned my attention to align the tailstock. I was going to use the technique demonstrated by Abom76, whereby a short section of stock is turned the exact diameter of the tailstock quill, the quill is bumped up against the stock, and then a indicator is run the length from one to the other. The first thing to do was the run the indicator the length of the quill to insure it was straight.

It wasn't straight. I got .0035 difference over the 5" length. I hadn't cleaned it yet, so the day got sidetracked into disassembling, scouring, picking gunk out of holes, and finally painting. There was a lot of gunk and debris in places it shouldn't have been. Eventually, with everything back together, I run the test again. No improvement.

The tailstock sits on two flamed-hardened, rounded top V-ways (page 15 here. . . page 14, top left corner here). The quill doesn't have a key, apparently relying upon a flat that the lock bears down on to stop it from spinning. Sebastian patented this "feature", according to the first link. The quill is pointing to the front of the lathe, so my working theory is that over the past 80 years the quill has been pushed hard up against the front side of the tailstock body by the wedging action of the lock. Outside of repeating the jig and hand reaming demonstrated in the first link above, is there any way to bring a wayward tailstock spindle around and point it in the right direction?

 

[Cadillac]

The tailstock should be high a touch and pointing toward the operator a touch. This is to compensate weight of part and deflection from tool pressure
To have to quill in tailstock droop and toward backside of lathe would be worn.
You want to check the droop by retracting the quill all the way get a measurement, then extent quill and see what the difference is. Both measurements done with tailstock locked and quill locked.

 

[Shotgun]

That sounds right for a boring bar. . . but won't it cause a drill bit to go in sideways?

 

[Shotgun]

Well, measuring that way looks better. 1.5thou over the 5" of the quill.

 

[tq60]

Loosen the adjustment screws that shift tailstock forwards for taper cutting.

Extend quill fully.

Tap it from front or back with a 2x4 towards the direction it needs to go to be straight and remeasure.

Could be some slop between top and bottom.

To check for wear just extend quill and place DI against it.

Push it and see if it moves.

Sent from my SM-G781V using Tapatalk

 

[Shotgun]

In this case, there is NO slop between the two halves. It is a squeeze fit to get the halves together. A fairly difficult squeeze. As in my entire 260lbs rocking on it to get the slot in the top half to go down on the tab in the bottom half. I linked to this above, but page 15 of this Sebastian advertisement brags about how they ground the two halves to fit together. If the tailstock offset has ever been used, you can't tell it today from the tightness of that fit-up.

On the other hand, with the quill extended, I can push on it and move it back in line. But, that's without it being locked down. I think I'm just going to have to accept the 1.5 thou that I get with the measurement technique that @Cadillac recommends.