Intel's Ronler Acres Plant

Silicon Forest

Thursday, August 6, 2015

Table Saw


Building the slinky machine

My friend Jack needed a table saw for a woodworking project. He had an old one he had inherited from his father. He tried to get it going but it had variety of small problems. He had worked through most of them but then came a cropper. In order to access the center of the machine, it was necessary to remove the table. The table was held to the base by four big bolts.
    When you go to reattach the table you need to ensure that it is properly aligned with the blade so that the groove for the mitre gauge is aligned with the blade. If it isn't properly aligned, the blade while not be cutting straight, which is the whole point of having a table saw in the first place.
    The problem here is that there was no built in alignment. The table sat on the top of a flat pedestal, and the only thing holding it in position were those four bolts. Loosen the bolts and table can be shifted several degrees to the left or right. You align it as best you can and hope that it doesn't shift when you tighten those four bolts. Bad design.
    So he looks around the used market for another table saw, one that is not quite so fatally flawed and finds one on Craig's List. This one has a bad motor, but otherwise seems okay. The motor is a Repulsion-Induction type. He takes it to an old guy in town who knows how to repair them. The repair costs more than a new motor of equivalent power, but he learns something.

Tiny Repulsion-Induction Necklace
    These motors contain a necklace of contacts that cause the motor to start in Repulsion mode but when it gets up to speed the centrifugal force causes them to separate and the motor changes to Induction mode. This kind of motor is good for devices that require a high starting torque, like compressors. A table saw doesn't really fit in this category, but that's the kind of motor it came with, so that's what we're using.

Broken Necklace for a Repulsion-Induction Type Electric Motor

Repaired Necklace for a Repulsion-Induction Type Electric Motor

    Back when I lived on the farm we had cold storage rooms for apples and big compressors for the refrigeration units. The compressors used Repulsion-Induction motors and my dad told me they had contacts inside that allowed them to change mode after they got started. We never opened them up because they never gave us any trouble, but I imagined that there were a couple of contacts mounted on levers that were controlled by some kind of governor mechanism. I certainly didn't expect a necklace of contacts.
    Shortly after Jack got his new saw running we were out to lunch when he spied another used table saw for sale sitting by the side of the road. We stopped and checked it out. It had a tilting arbor instead of a tilting table, like Jack's, but his was working. It was time to press on with the project and stop fooling around with table saws.

Necklace pictures from story about repairing a Repulsion-Induction motor.

Slinky video via Dustbury.

No comments: