I think I'd go with a fixed speed motor for the blade and a servomotor for the feed.
Maybe a standard saw with a LEM current transducer, plus a positioner (motor, lead screw etc. all in one), assuming your object is to get the job done, not to do it for minimum materials cost.
Best regards, Spehro Pefhany
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Hello
I wish to use a small saw blade to cut parts out of wood in a straight line unattended. Measure the load change on the motor powering the blade to signal the stepper motor to advance the material forward towards the cutting blade. I was going to use a normally open switch once closed to cut power to both motors.
THANKS Douglas
The blade motor should be a fixed speed motor like and induction motor. It would be very tricky and likely unreliable to try determine the wood position or whether it is in or out of the blade by load change on this motor. I wouldn't even attempt to do it that way.
Infrared photo transistor, LED combos or mechanical limit switches are the best way to determine wood position. It should be positive, sure and 100% reliable.
A stepper is fine for the material feed motor, geared, worm drive or however you like.
I don't know of any such kits but there is tons of stuff on stepper drives. Do a search. To me, it sounds like a perfect job for a microprocessor, where inputs are from photo transistor position sensors and control switches and outputs drive the stepper motor plus control a power relay turning on and off the blade motor.
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However, if you want to cut wood of uncertain density at the best speed, servoing the feed speed on the motor current draw may be a good idea.
OP: Why servo the feed speed on the motor current draw? For all of the most insanely cost-conscious applications you'd be better feeding at a constant speed that's guaranteed to be slow enough for a good cut (it'll still be pretty quick).
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The blade drive should be a fixed speed induction or universal motor. The cost/complexity of a stepper motor and drive is unwarranted for this function.
Stepper or other servo system might be OK here. That might be a bit of an overkill if your cuts are similar. It may be sufficient (and cheaper) to program the material feed speed to a fixed value.
If the material is not uniform, there might be some benefit to measuring the blade motor load (by measuring its input power) and using that to modulate the feed motor speed to keep the power near a preset value. The thicker the board being shoved through, the slower the feed.
There are quite a few ready-made stepper controllers available. Google is your friend.
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All that gets dirty rather quickly in this kind of environment.
This company is quite well-known for smaller scale feed and positioning tables:
Unfortunately it seems they only have a German web site. I have used some of their stuff.
And never, never forget to consider the situation of a jammed-up blade. Same for broken parts or imbalance. Otherwise all hell can break loose in a unattended situation.
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Cuts are similar but the material thickness is constant per cut but density will vary.
Thanks for the info, your knowledge and time. Will google the rest of the material.
Douglas
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