TailStock SetOver Adjusting Modification

Set-over adjustment of the stock 7x1X lathe tailstock is nonexistent to say the least, unless you call finger pressure an adjustment.  J.W. Early came up with an excellent solution by inserting a bit of bar stock and two sets of opposing set screws to allow set-over adjustment and axis alignment.  Working from JWE's concept and having done some pre-machining to correct tailstock alignment problems, I opted to try a single sided set-over alignment solution, at least before going to the two sided route.  My solution also draws upon Don D'Egidio's idea of converting the lock-down screw from underneath to above-board.  Prior to starting this modification, I had re-milled the base castings to align the tailstock ram with the lathe spindle.  The stock machined castings were mis-aligned in all three planes.

Somewhere along the way, I got the idea of using what I call a button in place of the bar stock to serve as the fixed point, off of which the opposing set screws would work, to affect the set-over adjustment.  This accomplishes the same task, requires less machining and utilizes some existing features of the tailstock base.  The button, really just a small threaded stud (6mm) is located on the front side of the tailstock base, in the pre-existing slot of the underside locking screw.  In my case, I made a stud with a threaded hole (5mm) on top so the locking screw could be inserted from above (modified from stock version) to achieve the same function.  A screw-driver slot was added to allow tightening of the stud on the base.

The slot in the base lower half was too wide to hold a 6mm nut, so I enlarged it to 1/2" and made a brass nut to fit.  The stud, screwed in from above can be locking in position using the screw-driver slot.  (That other threaded hole in this and the above photos is not used.  It was D&T'd because I was there and it was easy, in case I wanted to go to the two-sided adjusting route.).

Two, opposing set-over adjusting screws were placed to work off of the stud.  The tailstock upper casting was milled out to make room for the stud.  A hole was drilled through to the top and then milled into a slot to allow use of a position locking screw to be used, accessible from above.

In assembly it looks like this.  The set-over set-screw is visible on the front side; position locking socket head cap screw on top, next to the cam lock.  The companion set-over set-screw on the back looks much the same.  I was able to adjust set-over (horizontal) alignment to within 0.001" using a test indicator in the lathe chuck.  It took some doing as the screw adjustments were not intuitive, being reversed from what my brain expected.  Still, it was relatively easy to do, far easier and more reliable than the stock "no adjustment" method.  Until demonstrated otherwise, this is as much set-over adjustment as I think I need, agreeing with JWE's contention that real set-over for taper turning should be done with a boring head, not the tailstock on the 7x machines.

One reason the single-sided adjustment works in this situation is that I'd already machined the raised boss on the lower casting square with the spindle axis, as well as having machined the horizontal and vertical surfaces of both the lower and upper castings.  You may notice brass shims in some of the photos.  In the horizontal planes, these compensate for material removed during these corrective machining operations.  In the vertical plane, on the raised boss, the brass shim serves more as a gib, in conjunction with the rear located, stock, locking set-screw.  I replaced the stock slotted-screw with a socket head set screw, same as the set-over screws (5mm).

In practice, all three screws are adjusted to be snug enough to hold while still allowing movement, rear set-screw, top locking-screw and cam lock.  Adjustment is made with the opposing set-over set-screws, and when done, the rear and top screws are tightened fully, locking the position.  Its a good idea to check alignment AFTER locking the cam lock.  I found this changed the indicated alignment, and had to make set-screw adjustments to compensate, so when the cam lock was locked, everything was good.

This completes modifications/adjustments to the tailstock, as far as I see it.  Your comments are welcome, krugerr@easystreet.com

Rick Kruger
Portland, OR

BACK to Cam Lock Page                Base Milling Page            Indicating Base Page