It’s time to follow up on a project I started a while back that started out with making a bushing with a fixed internal key. That thread is here:
Keyed Bushing Thread
The bushing was the starting point for re-powering the drill press my father made from scratch, including castings, about 70 years ago. The project is adapting a treadmill motor/controller with the objective of increasing the speed range and getting rid of a two stage belt drive I had added some years ago.
I wanted to use the multi-vee drive belt system the treadmills have so I needed to make a new driven pulley, the challenges there were cutting the grooves and fitting a brass plain bushing/bearing in the pulley. As it turned out, once I ground a tool for the groove profile, machining it was easy, about the same as cutting a thread without the helix.
Fitting the bushing was a bit of an exercise in math and careful machining. I was aiming to hit the same ID size of the existing bushing and cut the OD so it was a press fit in the pulley housing. If I recall, I aimed for about .0025 for the press fit. I actually fit the bushing in the aluminum pulley using differential expansion (heat) rather than pressing it in.
After doing the math, I put the bushing in the fridge and the pulley in the oven and the bushing just dropped in loosely until the pulley cooled down. I think I used 400F/204C. That was my first try at doing something like that so I was quite pleased at how it worked out.
The rest of the story is the treadmill motor and drive electronics. I grafted the treadmill adjustable motor mount onto a plate that bolts nicely to the drill press bracket and adapted the electronics.
The treadmill uses a PWM controller that gets its speed setting inputs from a set of analog membrane switch buttons so after a bit of tracing the circuits of each button press I was able to mimic them with a single button and a rotary switch. I also incorporated a dedicated switch to replace the STOP button of the treadmill.
What this gave me was the option of up to 9 speeds ranging from very slow to fast plus fine adjust and all I had left to do was measure the speeds and mark my switch settings.
There are several reasons I went this way vs. an SCR controller and a potentiometer etc. First I wanted to use as much of the free material I salvaged from the treadmill as possible rather than inventing things. I also didn’t want to break new ground for me like understanding SCR controllers.
Using the control electronics from the treadmill takes advantage of its built in safety controls. I had read the article by Days (Dazecars.com/YouTube) where he blew up the same power board because his band saw grabbed and stalled. He didn’t use the treadmill control board.
The complete treadmill power & control system gives me the overload safety function that's built into the control board. If the motor is overloaded the controller senses this and “folds back” the drive power until the overload is removed or the machine is shut down.
I mounted the power & control boards in a 8 x 10 x 4 metal enclosure made by Bud Industries that I bought on Amazon, amazingly cheap at ~$20, delivered.
The “finished” product looks like this (Awaiting painting and a belt guard….):
D
