Introduction: Repairing a Broken Thumler's Tumbler (Vibrating Polisher)

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TechShop San Jose's Thumler's Tumbler had a couple of issues: The center shaft that held the cover on had come loose, and it made a odd noise when running.  Time for some exploratory surgery!


Step 1:

Take the bowl off the top. Flip the unit over, remove the four screws that hold the base on. 

Turn it over again and peel the neoprene sheet off. 

There it is! The shaft broke out of the base, and the motor cracked the mounting plate.

There wasn't enough clearance to weld a plate on top of or below the existing plate, so I opted to cut out the broken part and weld in a fresh piece of metal.


Step 2: Cut Out the Bad Parts

(Not shown - using VCarve Pro to create a template of the five holes in the middle, and an arbitrary 6" diameter circle to cut out the bad metal).

Using TechShop's Flow Waterjet cutter, I first sliced a piece of 1/8" scrap steel using the template I created. Next I positioned the damaged base plate in the exact same position as the cutout piece, using the 4 holes where the motor mounts as references.  I cut the bad metal out, and got a perfect fit.

Not shown - marking the rotational orientation of the center part -- the motor must be positioned such that the anchors still fit in the holes near the edge of the rim. 

Step 3: Weld in the Good, and Clean It Up

I MIG welded the fresh steel into the base, and ground down the top side to ensure a good fit. The bottom was left un-ground, as it didn't need to be finished. 

After welding i sandblasted the piece.  Since it was previously powder coated, the red finish was stubborn.  I decided to leave it rough and try a non-standard powder coating technique.

Step 4: Powder Coat It

I cleaned the 'blasted part with simple green and water, dried it off and then put it in the baking oven for about 30 minutes or so.  Once I had the powder loaded and ready to go, I pulled the hot piece from the oven and immediately coated it. The powder sticks to the hot finish, even though there is no conductive (bare) metal showing.  The finish isn't as glass-smooth as if done "properly", but is good enough for this workhouse piece of equipment. 

Step 5: Reassemble the Machine

I bought some stainless steel threaded rod and washers and nuts and wingnuts to complete the task. 

First, attach the threaded shaft to the center of the plate. I used Loctite Red and also double-nutted the top of the plate. 

4 bolts hold the motor to the center of the plate, and two more outboard supports complete the motor install. This part attaches to the base using 4 springy bolts - make them tight, but not so tight you over-compress the rubber spacers. 

The bowl slides over the shaft, and I chose to hold it down with a fender washer and another nut.  The cover is held on with another fender washer and a wing nut.

As good as new!