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| Fitting a Variable Speed Motor to a Dore Westbury Milling Machine |
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| andyf:
The original induction motor on my 40 year old Dore Westbury milling machine motor often needs a yank on the pulley belt to get it going, and some of the internal insulation looks a bit dodgy. The machine is the Mark 1 shown in the third and subsequent pictures at http://www.lathes.co.uk/dore%20westbury/index.html . Stepped pulleys give three speeds and an 8.8 to 1 epicyclic gearbox can be engaged/disengaged to give six speeds from 35 to 1360 rpm. I thought I might try a variable speed motor for greater flexibility. According to our US brethren, DC treadmill/running machine motors are ideal for this sort of project. Old ones seem common as dirt in the US, but are rarer in the UK. However, Ebay revealed "Running Machine. Faulty - runs for 10 seconds, then stops”. Only 3 miles away, and £15 secured it. Back home, it took five minutes to find the little magnet for its speed sensor stuck to the steel frame and return it to the pulley where it belonged. After that, it worked perfectly. I feel a bit sorry for the seller, who had ordered a new one for about £400. I climbed on and achieved a dignified canter, but the novelty only lasted five minutes, so I started dismantling it. Here it is cluttering up a corner of the kitchen, before I took it to bits: And here’s the rating “plate” from Leeson in Wisconsin, USA. 220V x 6.5A = 1430W, so 2HP is slightly overstating it. I hadn't realised there was another Wisconsin in China..... Speed was varied by pressing the buttons shown in the first pic. Fine for a treadmill, but hardly ideal for milling. Also, the control board was an inconvenient 12” x 9’’, and the separate “power” board about 6” x 7”. I experimented a bit with streams of control pulses from optical choppers out of an old computer mouse, but results were unreliable. Departing from my usual miserly approach, I forked out £70 for a brand new KBIC 240 controller from a nearby stockist. Input is 230V AC (the UK domestic supply) and PWM output is 180V DC. OK for 2HP motors, when used with a heatsink. 2HP is overkill for this size of machine, so I don’t think the “undervoltage” will make any practical difference. The stockist didn’t have the “official” £20 heatsink to bolt under the aluminium frame on which the board is mounted, and in any case underneath didn’t seem the best place for it. I bolted a couple of salvaged heatsinks to the upstand at the end of the frame, directly behind those semiconductors which were likely to get hot. There was no sign of heatsink compound anywhere, so some was added. The scrapbox also yielded a diecast aluminium box of the right size to accommodate the board. I cut a rectangular hole into one end of it so the heatsink could stick out and get some air. There was room left in the box to fit a potentiometer speed control and a home-made “no-volt” switch comprising a 13A mains relay with a push to make switch to actuate the relay coil, wired so that the coil would hold itself on until the circuit was broken by a push-to break switch, or by a mains power failure. The switch buttons are the usual green for go, red for stop colours. On the bench, I temporarily hooked up the new control box to the motor and gingerly plugged this ensemble into the mains. Success :thumbup: :thumbup: Zero to warp speed and back again at the twist of a knob. And with the low-speed pulleys and 8.8 to 1 epicyclic gearbox brought into play, torque should be high enough to bend the mill column :lol:. So all (!) I now have to do is: 1. Remove the 12lb/5Kg cast-iron flywheel from one end of the new motor’s shaft, and replace the pulley on the other end with the 3-step pulley from the old motor. The bore in this would need enlarging by about 5 thou from 0.625” to 16mm. 2. Fix the new motor in place of the old one. 3. Attach the control box in a convenient position - probably on the spindle head. 4. Wire up properly, with regard to safety. 5. Arrange some way of calibrating the control knob to give the particular spindle speed required for the job in hand. Andy Edited to fix a missing pic |
| John Stevenson:
The cast iron flywheel is threaded on with a LH thread. John S. |
| andyf:
Thanks for the tip, John. This one isn't threaded, though - there's a key and two grubscrews, one bearing on the key and the other at 90 degrees round the shaft. It's off now, and will come in useful for something or other, sometime. The Poly-V pulley on the other end of the motor is going to need a bit of persuasion. Andy |
| Bernd:
Andy, Here's a pic of using a tread mill motor to power an old Buffalo Forge drill press. Used to have a 1HP 3Phase motor on it. Now it has a 1HP DC tread mill motor powwering it. I used the orginal electronics since they were a lot less complicated than the more modern one. I've got 3 more motor assemblies for some of my other machines I plan on putting DC motors on. Anyway here's a close up pic of the drill press mounted motor. I did a thread on moving this drill press from the garage to the basement here: http://madmodder.net/index.php?topic=362.0 Bernd |
| andyf:
Nice one, Bernd. It looks a bit :zap: though I'm sure you've made it safer since your pic. I've put my circuitry in a box so the electricity can't fall out. Andy |
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