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.

[knoba]

Nice mod, Paul! Looks way better than the original, like it's actually been engineered to perform a task and executed with care and attention to detail...

[C-Bag]

Very nice and great info. I've got a similar plate on my 9x20 tail stock and have struggled with it slipping too. It never occurred to me it was the cast iron on cast iron that was part of the problem. I'd gone to a lot of trouble to get rid of the locking bolt and adapting cam lock kit that Little Machine Shop sells for the smaller 7x lathes onto my 9x20. With proper adjustment it works good but I can see now the next step is to get rid of that bottom plate. Pardon the noob question but why do you think the clamping bolt is offset?

[Ed ke6bnl]

I did watch the video but do not have that kind of machine. was wondering if you were to take the bottom piece off and sand blast it if it would then have some grip. I did that to a drive wheel on my old cheap mig welder and it worked fine after that. I don't believe that would do any damage to the lathe surface. on my Rockwell lathe the bottom pieces is not a smooth machined piece.

[Paul Jones]

C-Bag, thank you for the feedback. I have been thinking about doing this improvement every since the used lathe arrived last January but I was thinking in terms of milling the part. Then I remembered how I built a small metal lathe when I was a teenager using various rectangular shapes of stacked steel bars joined together with machine screws and no milling required.

I too thought the clamping bolt was centered in the tailstock and had already marked the center of the plate for drilling during layout. I decided to double-check the tailstock locking bolt position before drilling. I found the tailstock has a machined ring opening at the top of the locking bolt that slides on an eccentric cam. The ring is used for up-down unlocking-locking but the ring doesn't slide all the way over to the exact side-to-side center due to the way the cam is machined. The locking bolt is slightly closer to one side of the tailstock and the 9/16" hole was positioned to accommodate the offset.

Thanks for asking

[Paul Jones]

Ed,
Yes, I would have tried the sand blasting approach first if I had access to a sand blaster. However, it could have the opposite effect over time by creating even more pockets for accumulating oil and improve the cast iron on cast iron slipperiness as the sand blasted surface wears down. In a couple of my photos you can see the bottom of my tailstock has a hand scraped finish that creates a very slippery surface using the oil accumulation between the sliding surfaces. That is why hand scraped surfaces glide so smoothly. Probably periodic sand blasting may solve the points of oil accumulation issue on the locking plate but may also provide pockets for additional oil accumulation at a microscopic level and could be worst. We wouldn't know until we try the technique.

Thanks for asking, Paul

[PJs]

Thanks Paul, great write up and nice mod. Nice pic down the ways to see the clearances! Seems to me as with my mini, with the pinch bolt being off center, the pull is not even on the ways and part of the problem previous problem. I have similar problems on my mini tail stock as it just has a stamped plate and the bottom of the ways have been cut with a rock and chisel. Any thing above .375 it slides on me, but have resorted to using my new carriage stop behind it to lock it down...till I can mod it. It's something I have been pondering with the new 14" bed I've been working on for ages now (squaring, flattening and scraping)...how to clean up the bottom of the ways! Think I might try your idea...resized for a peanut! Thanks for sharing!

[Paul Jones]

Thanks PJs. I too own a 7" swing mini lathe I purchased in 1993 and have published a few of its improvements at HomemadeTools. Years ago, I realigned the headstock with the lathe ways using a method that shims the headstock (see the method at MiniLathe Alignment). The new alignment is excellent but the spindle center line became too high for the original tailstock that had no vertical or side-to-side adjustments. I bought a replacement tailstock (see Homemade Tailstock Fine Screw Adjustment) but it moves when drilling with 1/2" or larger drills. When I get time, I will replace the mini lathe tailstock locking plate (this can be seen in one of the photos in my link) with something similar to what I built for the 12" swing lathe. For now I just use a 1" Kant-Twist clamp behind the tailstock to block the movement.

[PJs]

Thanks Paul! Mine has a horizontal adjustment but see your shim/adjuster height mod as a good possibility. I have followed "Gadgetbuilder" John Moran stuff since I got mine (33684) about 2yrs ago now. He has some really great info, insights, and mods on his site. Once I get the bed, extended cross slide, and compounds done to my satisfaction I'll be ready to tackle the headstock and tail stock. Also have to make some better Gibs!!! Found some Timken tapered rollers a while back that are an exact match for the spindle so, no mods to the pickle fork shims. Have to see when I get into it how far I'll take that...its already a $5k, $5oo lathe. But the carriage & cross slide already slides just by looking at it. ~¿@

[kbalch]

Thanks Paul! I've added your Tailstock Clamp Improvement to our Lathes and Clamps categories, as well as to your builder page: Paul Jones' Homemade Tools. Your receipt:

Tailstock Clamp Improvement by Paul Jones

tags: lathe, clamp, plate, tailstock