Sunday, May 15, 2016

Truing up Back Plate and Cup Chuck on a Mini Wood Lathe

Installing an aluminum cup chuck on a mini lathe

Difficulty Level (Easy, Medium, Hard, Insane):

A little while ago I made a Cup Chuck for a local bag pipe business owner. However, because of a fairly significant wobble in his lathe spindle, the chuck (mounted to his back plate) was wobbling quite a bit so he brought the lathe, the back plate and the cup chuck for me to see if I could fix the wobble.

Once I got the mini lathe, I indicated the spindle and it didn't seem too bad (out 0.002") but the real issue was the back plate. There was a good 0.020" wobble in it so I took it off, cleaned the thread really well, put some blue loctite on the thread and twisted the back plate onto the spindle thread.

The owner told me that he was not planning on ever taking the cup chuck off that lathe so I figured using loctite would be a good way to keep the face plate from miss-aligning itself again in the future.

Once the back plate was (semi-) permanently fastened to the spindle, I started the process of truing up the back plate. However, because the lathe was actually a wood lathe, it did not have any mechanism to accurately turn the metal back plate so I removed the cross slide with the mounted compound slide from my metal lathe, clamped it down to the wood lathe with 3 c-clamps, aligned the angle with the compound slide and then turned the face plate right on the spindle.

I turned a recess into the back plate, then indicated the cup chuck on my regular lathe and turned the matching recess into the cup chuck. All that was left to do after was mount the cup chuck back on the (now trued up) back plate with some loctite and the job was done.

The Cross slide clamped to the bed of the wood lathe
Another view
View from the head stock side
Close-up of the profile I cut into the back plate
Another view
Chamfering the edges
The mounted cup chuck with a piece of black acetal
Another view
Metal lathe & accessories
Cordless drill
Scrap metal for shimming

Blue loctite

3 hrs

There's still a little wobble for smaller diameter acetal but only around 0.001" for medium and bigger sized stock.


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