12” x 37” Lathe Tailstock Clamp Improvement

[Paul Jones]

I have problems with my lathe tailstock slipping from its clamped position when drilling with larger diameter drills. I have a 1987 Taiwanese built geared-head gap bed lathe with a 12” swing and 37” between centers and looks very similar to the Grizzly model 4003 12” X 36” lathe. The lathe is well made with many hand scraped surfaces but the design of the tailstock clamp plate can be significantly improved. I think this improvement can be used for other lathes of similar design.

The tailstock is clamped in place using a lever arm attached to a cam that is used to raise and lower a locking bolt. The tailstock clamps in place when a rectangular cast iron plate is pulled up tightly against the underside of the lathe bed rails. The cast iron on cast iron contact can be too slippery when there is oil on the contact surfaces. I remember watching a YouTube video by James Greene (EAGLE DUSTOFF 37) where he mentioned a similar problem with his lathe and his solution was to mill a new cold rolled steel replacement clamp from a bar of CRS. I decided to try this approach and to make a 1018 CRS clamp much larger than the original cast iron part so it also had more surface area for improved clamping.

I don’t have access to a milling machine that can do this work so I used two rectangular 3/8” thick by 5” wide CRS 1018 plates as a substitute for milling two side steps into a solid CRS bar stock. The upper plate is 2.97” x 5” and the lower place is 3.83” x 5”. These dimensions allow sufficient sliding clearance between the lathe bed ways and the clamp plate. The plates are held together with six (6) 1/4-20 cap head socket screws spaced 0.6” from the outer edges of the upper plate and screw into threaded holes in the smaller upper plate. Initially, one 1/4-20 screw was used to temporarily hold the two plates together while drilling the remaining holes through both plates with a #7 drill. Witness marks on both plates ensure proper alignment before separating the parts and then drilling clearance holes in the large lower plate with a Letter F drill.

After taping the five remaining holes in the upper plate, the two CRS plate parts were assembled with all six screws. The location of a 9/16” through hole for the locking bolt was carefully measured from the tailstock because this hole is slightly offset from the center. After drilling and chamfering the 9/16” hole, the new locking plate was assembled on the tailstock and the sliding/locking gap adjusted with a single ½”-13 nut (later replaced with a 1/2"-13 Nyloc nut based on a viewer suggestion) and the assembled tailstock placed on the lathe.

The positive tailstock locking is now ensured with the CRS clamp plate and the fact that the actual locking surface areas are almost two and one half greater than the original makes a significant improvement. Now, there is no tailstock slippage when drilling with the improved tailstock and depth of drilled holes can be accurately measured using the combined linear and dial ring measurements.