screwgun triggers

I haven't taken one apart for a while but the last time I did it was a little PWM circuit.

Tom

I've always wondered. I bought my Black & Decker drill in 1975 and it has variable speed (but doesnt' reverse). It's trigger is a very small package, and I don't see anything elsewhere, but it can't be a rheostat, too small for that too.

Michael

PWM. A Rheostat would give poor torque, and dump a lot of energy as waste heat under your finger.

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.

SCR speed control, all in the trigger housing. I've had to replace several in the last few decades, but I still have plenty of new spares. I stocked up when the BD surplus store had them for 25 cents each. I bought all 62 they had in stock. The first two I used to convert single speed drills to variable paid for all of them. :)

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.

I think that occurred to me at one point. I think I paid $25 Canadian for this drill in 1975, and the only thing I've had to do to it was replace the brushes about 20 years ago.

About five years back, I found another Black & Decker drill about the same vintage (still a metal case) for $3 at a garage sale, bought it as backup. And then found another one of the same vintage in the garbage when the students moved out. One of the others at least has the reversing switch. But now, I have one to leav in my drill press adapter.

Michael

Those adapters are OK for some work, but they won't do what a full drill press, or a Cameron precision drill will. :(

The floor mounted full height drill press will let me lower the table at least 24" and can have alignment fixtures and/or toggle clamps bolted to the table's slots to get more accurate holes. It also has 12 speeds, selected by moving a pair of belts.

The precision drill only takes bits /8" or smaller. It is intended for a model shop, or watch making/repair. If you ever get the chance to own either, you'll be pleased with the additional capabilities in your workshop. :)

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.

This is cordless (DC) equipment I'm inquiring about. I can see putting an SCR in a drill that runs on AC. What circuit do _cordless_ drills or impact drivers use?

The two I have taken apart used PWM. But not infinitely variable. There were steps to the speeds. They were Harbor Freight tools that I bought specifically to take apart because I needed the variable speed motor and driver for something else. And on one of my cordless tools you can hear some sort of oscillator changing pitch as the trigger is pulled. Eric

I did something similar with Milwaukee battery sockets (on the bottom of the

18V drills). I've epoxied these adapters in Bosch and other 18V drills & saws that someone is throwing away. Now all take the M 18V battery pack.

PWM, as Tom stated in the first reply.

Mike Terrell was replying to Mike Black about his 1975 B&D drill, which is was not cordless. In Mike Terrell's reply to you, his answer was PWM.

Ed

A more recent B&D I took apart (a replacement battery cost more than a new drill) had nothing more than a MOSFET and a slider pot linked to the trigger, the heatsink was custom made (cast aluminium) to fit as much fins as possible in the space behind the brushes.

In theory - the motor causes back-emf, that could possibly commutate an SCR - but a loaded motor produces less back emf so operation could be unpredictable!

That might be, though back in 1975, I don't recall power mosfets.

And while the variable speed isn't perfect, I think it's too smooth to be a rheosstat (or a mosfet or transistor acting as a variable resistor).

Michael

In field controlled dynamos; the field current is much less than the rotor winding - perhaps the same can be true of the field current in a motor.

The rheostat wouldn't have to be so big - but you'd probably burn out the armature with prolonged low speed!