Repairing a Faulty Drill Press On/Off Switch

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As carpenters, we rely on electricity to relieve some of the heavy lifting loads of milling, sawing and drilling. Many of us use both of these machines quite often and I believe many would benefit from being able to maintain them and fix some basic malfunctions.

A few weeks ago I turned on my Delta pillar drill to drill a few dozen holes in a row. After finishing with the last hole, I turned down the on / off switch but to my surprise the engine kept running and I had to unplug the car to stop it. I tried to raise and lower the switch actuator a few more times, but could not feel the recognized engagement resistance when the switch was flipped to hold off.

At first, I thought about ordering a new switch and replacing it whole, but since I needed to use the pillar drill to complete a project, I decided to try to fix the faulty switch myself.

Repairing a switch isn’t that difficult, doesn’t take a lot of time, and doesn’t require specialized tools.

Why do the switches fail?

Switches fail due to mechanical problems such as material degradation, breakage, or the gradual dissipation of internal lubricant. But switches can fail when their conductors lose conductivity, which is when copper (or copper-plated) electrical contact points become covered with contaminants that prevent them from allowing electricity to flow. This is known as arc suppression.

Since the internals of my breaker refused to disengage, I assumed that the problem was primarily mechanical in nature and not an arc suppression problem.

Repair the switch

  1. Disconnect the machine from the power supply.
  2. Open the switch cover, etc., and carefully label each wire connected to it. Then disconnect the wires from the contact tabs.
  3. Pull the switch out of its plate or base. In this case I had to press the two hooked tablets inwards and unhook the switch from its plate.
  4. Gently pry up the plastic tabs to open the switch shell.

    The two plastic spring tabs clip onto the shell. I had to push the hooks out and then open the shell.

    Some switches may have a rubber coating to protect the contactor from dust. You’ll have to lift it up and remove it too.

  5. Pull out the internal “swing” contactor tab and all other moving or soft parts and examine them. Clean any buildup or black coal-like dust with alcohol.
  6. Check the contactor contact points – these are raised points, small discs or domes and clean them too. They could be pitted from the arc, so use an abrasive of some kind to smooth them out. I tweaked the points using a rotary tool (very gently) but a better tool would be a Sandits ™ “Q-tip” abrasive wand. Remember to clean and abrade (if necessary) the fixed contact point at the bottom of the shell as well.
  7. Put a small amount of grease on the pivot point of the swing to help it move smoothly and close the shell.
  8. Reassemble everything in reverse order.

It took me 10 minutes to do this and in the end the switch was almost as good as new. I have saved time, money, and saved a piece of useful electronics from going to landfill, and by the way, I have learned a new skill that I am sure will be useful in the future. It is entirely possible that the entire switch will need to be replaced in the future, but until then I am quite proud of my little solution.

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