Electric Drill Switch and Speed Controller Triac

My 30 year old 1/2" Craftsman electric drill failed last week as I was just getting to the end of all the steel work for the car. The speed limiter dial on the trigger switch snapped off (OK, I used pliers and probably went the wrong way). So I took the drill apart and jammed the speed limiter down, I figured I could live without it since the trigger controls the speed anyway. Then I made the fatal mistake and tested it before I put the case back together.



What I missed, being an idiot, is that the brushes were only held in place by the other half of the plastic drill casing. So as soon as the motor started to spin, the brush that was being pushed up instead of down sprung out of its holder and sparked on the speed control circuit board. I yanked the plug out in a second, but the speed control board showed the damage:



If you notice the holes in the solder joints to the left of the picture, that's where the triac device was soldered in before I removed it. It's the only active component in this very simple speed control circuit, which works just like a dimmer switch. The triac was shorted right through, it is now a piece of wire, so I'm waiting for a new one to get here. The symptom that the triac had shorted out was that the drill would come on as soon as you plugged it in and wouldn't turn off.



It turns out that these triac based speed controllers work very differently from conventional switches, or rather, the entire switching function is on the control board and not in the trigger. All the trigger does is change the value of a variable resistor in the circuit, which sets a bias value for the triac, in terms of how much of the AC cycle it allows through. So you end up with an infinite speed control (within the switching parameters of the triac) for a very inductive load. I'm just hoping I didn't burn up the variable resistor in the trigger as well, smelled a little dicey.

Electric Tape Hacks For Working On Cars

There's a big difference between knowing what needs to be repaired and figuring out how to repair it with what you have on hand, ie, hacking it. For example, I needed to clamp up an angle brace inside a subframe member so I could drill holes, but the "C" clamps I got from Harbor Freight weren't very "C" like. In fact, with the top of the clamp throat being basically in line with the top of the clamp, it appeared to be useless for clamping anything but two flat surfaces together. I needed to get the top of the clamp down inside the subframe, so I used some electric tape and a socket to hack a clamp extender.



Electric tape is ideal for such hacks because it's strong and hold tight if you stretch it, but also comes off very easily unless you bake it on or age it in the sun. Another electrical tape hack is winding it onto your finger in reverse to hold a nut. In this case, I was reuse the same tape from the clamp, making it a frugal hack. The shaky finger is just how us old guys get when we've been exerting ourselves for a while:-)



Some of my proudest moments as a teenager working on cars were getting at nuts and bolts friends couldn't deal with, one of the few advantages of having small hands. But sometimes, you can't get your hand into in to the end of a bolt to hold a nut, not even two fingers. So the best you can hope for before reverting to taping the nut to a stick or into a wrench is sticking it to a reverse tape job on your middle finger. The great advantage of using a finger is feel, since you can rarely see into locations that you can't reach.

Drilling Steel For Sheet Metal Screws

When using regular sheet metal screws, as opposed to the self tapping kind, you have to pre-drill the correct size hole. For the #14 sheet metal screws I'm using to hold the new subframe elements in place on the unibody until I bolt or weld, that turned out to be a 3/16" bit. The hole needs to be just big enough to fit the shaft of the screw, or else you'll break the head off when it gets to the point where the hole is too small. That's what happened here:



When you're sliding a new piece of metal up inside an existing subframe rail, and you don't have any way to clamp it or force it against the surface it will be contacting, you need to pre-drill the hole before you put the piece in the unibody. Otherwise, the drill would just push it back from the hole:

Run Time = 23 seconds



I found this nice little chart for the smaller sheet metal screw size pilot holes after the fact. This other site heavily quotes the I.F.I Fastener Book. While there, I learned that there's a "right" side to a stamped flat washer, something I never knew. The side with the chamfered edges (smooth rounding) faces out to the bolt head or nut. Interesting.