Rebuilding the Carriage Motor and Worm Gear

I tore apart the carriage controller and found the old selenium rectifiers burned out. I called the local Hardinge service rep, Jim Granquist, and he made a house call for free. I think he may have felt sorry for me after inspecting the lathe. I bought two modern bridge rectifiers from him and a set of carriage motor brushes. (He tried to give them to me.)

Anxious to see what would happen, I patched in the field and armature rectifiers with alligator clips. The carriage worked! The motor made a lot of noise, but it went back and forth and the power cross feed worked as well. Emboldened, I flipped the speed switch to "high". Smoke poured out of the motor. I pulled out the armature and found it utterly destroyed. I sent the armature to a motor shop.

The main drive still rattled. The spindle motor platform bounced up and down. I replaced both belts, the motor platform pivot bushings, counter shaft ball bearings and the main motor bearings. At last the drive ran smoothly!

I cranked the speed up and down marveling at the smooth quiet operation. My wife came out to see what I was doing: "Try it out", I said, inviting her to crank the speed up and down. She did. There was a loud thump followed by grinding noises! "Arrg! Stop Stop!", I cried. She fled the garage in dismay.

The countershaft is kept centered in a pivoting bracket by two teflon bushings. These had worn short, allowing the shaft to work out of the ball bearing on one end.  I just happened to have some teflon pipe that fit the shaft. I made new bushings and reassembled the counter shaft. This time all was well.

The armature came back from the motor shop and I installed new ball bearings. The armature worm drives a worm wheel and shaft which also needed new bearings and seals.  Trying it out on the bench, I found it ran smoothly but with a clicking sound in one direction of rotation. I discovered a divot on the drive worm. After much effort trying to polish out the defect, I gave up and called Hardinge. The worm was no longer available for my machine. After some calculating and reading in Machinery's Handbook, I set up my old Dalton lathe to cut a new worm. This is non-trivial because the worm needs to have transcendental tpi to drive the 30 dp worm wheel. I finally found a compound gearing that made a satisfactory approximation.

 

Turning the worm blank on a taper mandrel

Grinding the worm form tool

Form tool close-up

Finished armature with new windings, worm and bearings