View Full Version : Making Jet 1236 Reversible...?
10-19-2010, 9:35 PM
I have a Jet 1236 that I am happy with. I dont turn much, and really dont want to upgrade anytime soon. I think it would be nice if the 1236 was reversible. I was wondering, is its possible to make a Reeves drive type lathe reversible and if so, does the 1236 have a motor that can be wired for reverse?
10-19-2010, 10:33 PM
Normal single phase induction motors don’t generally run in reverse. But…
Some will - sort of. I had a Jet 1442, which I modified to run in reverse. The motor has two capacitors, a start and a run. The purpose of the run capacitor is to introduce a small phase shift that improves motor efficiency at low load. The start capacitor is switched in at low rpm to provide an additional phase shift to get the motor up to speed quickly. I simply removed both capacitors from the motor and mounted them in a separate box with a switch to (dis)connect them to the motor windings. With the caps disconnected the motor will not start without a manual spin, but once given a push will run in either direction. Normally, I’d keep the caps in circuit and only disconnect them for sanding. I’m not familiar with the 1236’s motor, it may have none, one, or both of these caps. The reeves drive on the 1442 didn’t seem to care which way it ran.
This mod is not for the faint of heart and you need to feel comfortable with the electrical work. No load current on the motor will go up with the run cap out of the circuit. On my 1442 the increase was about 1A, just about doubling the no load current. This doubles the heat generation. But at no load, it’s not a problem as the motor’s rated current is something like 6-7A at full load.
The real issue with this mod is the start cap. Removing it (and the run cap if present) from the motor will prevent the motor from starting normally. If you turn it on it will simply sit there and hum. All the time drawing excessive current, well beyond its ratings. Left this way for more than a few minutes and you could easily have a fried motor. You MUST give the lathe a spin by hand in the direction you want it to go and then turn it on. The motor will draw excessive current as it comes up to speed, but not for too much longer than normal. I ran my 1442 this way for 3 years with no ill effects. YMMV.
Also, don’t try turning in reverse unless you can lock your chuck on the spindle.
Disclaimer: I’m not recommending that you perform this non-standard and potentially dangerous modification. I’m only describing what I did to my lathe.
Edit: BTW. Before implementing this mod I did considerable research and experimentation. At one point, I was using a variable inductor in place of one or the other of the caps and in various tests was able to have the motor start and run in reverse as if it were meant to do it. Start up times and current nearly identical to forward running. I dropped the idea of using large inductors (transformers) as too bulky and difficult to source the correct parts.
10-19-2010, 10:55 PM
Some motors have the start winding connected inside the motor, it is difficult to reverse these. On others this wire has a spade terminal and usually a diagram showing where to move the wire to change direction. With a little wiring, you can connect this to a 4-way switch so that a flip of the switch is all that is needed. Do NOT try to change direction while the motor is still spinning!
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