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Making an Elliptical New Compound Thrust Plate/Large Dial Upgrade

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I'm installing larger dials both the cross slide and compound on a Craftsman 6" MK2 lathe and had the need to make a new thrust plate for the compound because the original is cast and the boss were the dial base needs to mount is tapered due the the draft. The thrust plate is elliptical and I wasn't sure how I was going to do until popped up.? I grasped the concept quickly and did not actually watch the video through the machining process.? Had I done so, I might have been dissuaded as it looked too complicated.?

Joe’s method shifts a vise with the workpiece around on the rotary table by predetermined increments.? Not being aware of this, I went a much different way, but I like how I did it.? I plotted out pin positions ?for milling the two radii using on a backing plate mounted on the rotary table. Means breaking the setup down and repostioning the part for each radius.? I also first used the mounting plate to turn the boss on the lathe.

Start of the project, with the rotary table mount plate and the thrust plate stock pinned to it for turning the boss. Originals are on the left, new dial on the right.

?Turned boss.

Second major radius milled takes rotating the part on the locating pins.

Milling the end radius meant shifting the workpiece on the mounting plate to the second set of pins.? For my part, rotary table rotation was 48? on each side.? Any further would have dug into the primary radii.?


Finishing the thrust plate took drilling and counterboring holes for the mounting screws and filing out the machining marks.? Due to the large dial backing ring, the mounting screws had to be flush or nearly flush with the surface.? This required turning reducing the size of the SHCSs, but I like the look.?

Finished part, original and dial parts ready to install.


New thrust plate installed.


New dial installed. Original thrust plate in the background.

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There is a problem here, however.? It doesn’t work smoothly and will require some remedial work.? The new dial cants when the set screw is locked.? I think because the set screw is off-center and it clamps on the transition between solid shaft and the start of threads on the end for the handle/nuts.?

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More on this to come.

Operation has been fixed, by installing a thrust bearing and a ball bearing, inboard and outboard of the thrust plate and a sleeve for the graduated dial to ride on.? The sleeve corrects the tendancy of the dial to cant and bind the rotation and provides something for the hex nut to clamp against as preload.? Compound is snug and smooth, the only thing to deal with now is the backlash, some other time.?

Thank you.? Changes the entire feel of the compound slide.? Making the elliptical thrust plate was the key to being able to incorporated the bearings, etc.? I did a similar large dial upgrade for a friend's SB 9 a few years ago, so I looked back at my drawings and photos.?

This is actually just temporary though, as I plan on installing direct read dials on both slides in the future.? and a came from .? The direct read dial has 200 graduations.? The cross slide dial currently on the the cross slide has 100, so once the direct read is installed, I'll take that 100 graduated dial and adapt it to the compound.? I will require making another thrust plate, as the boss is larger, so I'm keeping the mounting plate from this one.? I think I'll make the cross slide extended by lengthening the boss, which will proved room to include a thrust bearing on both directions.? The size of the boss on this compound precluded using two thrust bearings, so I'm using the ball bearing as both.?

Once all that is completed, I think I'll make this compound adaptation available.? Should be a direct replacement fit on another MK2 lathe at least, maybe the 618 as well.?

Rick

Bravo!? You will never regret those proper upgrades.? Bearings for tight and smooth operation and just as importantly the sleeve to get the dial out of the load path.? I did my 10" a couple of years ago. Been fantastic.