I was thinking about wiring a carriage stop up to the speed switch (not E-Stop) but I'm looking for info on the control circuit. This is likely one of the points of divergence for the various C2/C3 clones but mine is a Cummins 5278 (SCR control). The only non-sketchy looking source I've found so far is our download section, and I'd pony up, except I have no clue if the schematic is actually inside.
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C2/3 7x control schematic
- Thread starter Nates
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I can take a look at it to see if it is or not. What's the file name?
Cummins #5278 Mini-Lathe Manual.pdf
Imported files from vBulletin files system.
www.hobby-machinist.com
thanks
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Unfortunately, the manual you referenced doesn't include a schematic. Owner manuals for this class of lathe don't seem to include them, probably because the motor controllers usually are made by somebody else. They also may use a variety of controllers, depending on whose is the cheapest at the time. That way they don't have to edit the owner's manual (and the info may be considered proprietary by the OEM).
I'd suggest gaining access to the motor controller to see if you can determine who made it: and, better yet, what model it is. KB Electronics was/is a commonly-used supplier for mini lathes. If that's what you have there are a number of schematics that can be found on the web.
Older minilathes used brushed DC motors and SCR style PWM controllers. Newer ones use BLDC motors and ESC style controllers. It's easy to tell the difference, the BLDC models typically have higher-power motors and no high/low transmission gearbox.
There's nothing wrong with the older motors, the controllers use feedback to maintain RPMs under load. You just have to check the brushes on occasion to make sure they're not going to damage the motor commutator any time soon.
I'd suggest gaining access to the motor controller to see if you can determine who made it: and, better yet, what model it is. KB Electronics was/is a commonly-used supplier for mini lathes. If that's what you have there are a number of schematics that can be found on the web.
Older minilathes used brushed DC motors and SCR style PWM controllers. Newer ones use BLDC motors and ESC style controllers. It's easy to tell the difference, the BLDC models typically have higher-power motors and no high/low transmission gearbox.
There's nothing wrong with the older motors, the controllers use feedback to maintain RPMs under load. You just have to check the brushes on occasion to make sure they're not going to damage the motor commutator any time soon.
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A dead simple approach would be to pick off the wiper and ground sides of the speed pot and short them out when you want the motor to spin down. However, note the "spin down" part. The controller can't apply reverse voltage to address that. To implement a faster stop you will need to short the motor terminals -- while avoiding damage to the controller. One approach would be to insert a relay (or two) in the motor side of the controller. Open the connection from the controller to the motor and (only) then short the motor terminals to ground. Timing is important. Relays don't act instantaneously and they also exhibit bounce, but in the case of opening the connection between the motor and controller I think that is a non-issue. On the other hand, the relay that shorts the motor terminals is a different story. It will bounce so the actual "stop" time will vary some. How much is too much? That's your call, depending on what you want to do.
One approach I've read about is an automated scheme that disengages the half nuts. Gadgetbuilder made one and it's complicated. It's an all-mechanical approach. Being an electrical engineer in a previous worker-bee life I'd look at a solenoid operated design but that's just me.
There are other approaches that could only be implemented by using a bipolar linear controller but that would require yanking the existing controller out, and replacing with either a much more expensive off-the-shelf unit: or designing your own. I don't think that's something I would want to take on but I'm not you....