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New group: Vicmarc

Doug Rasmussen said:
Probably from the motor manufacturers. And it will. So the lathe makers are protecting themselves with this warning.

High end VFD rated motors have a constant speed fan mounted on the back end of the motors. That keeps the motor cooled no matter what speed it's run at. These type motors are a bit expensive to be putting on hobby lathes.
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Doug, as I said, when I am sanding on my Robust, the motor temperature, tested by putting my hand on it, is much cooler than when I am turning. Not sure what the motor is on the Vicmark, but it runs very slow as well. Not sure if it is 3 phase or not. With my 3520A, my motor never over heated or tripped the circuit breaker or the phase converter. I would think that with the thousands of bowls I have turned that if there was going to be an issue, I would have had it by now.

robo hippy
 
robo hippy said:
Doug, as I said, when I am sanding on my Robust, the motor temperature, tested by putting my hand on it, is much cooler than when I am turning. Not sure what the motor is on the Vicmark, but it runs very slow as well. Not sure if it is 3 phase or not. With my 3520A, my motor never over heated or tripped the circuit breaker or the phase converter. I would think that with the thousands of bowls I have turned that if there was going to be an issue, I would have had it by now.
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Aside from your situation it is a fact that running 3 phase motors slow on VFD's without extra cooling can cause overheating problems with the motor. No lathe maker in their right mind is going to say run as slow as you want. Then somebody is going to come along and put a heavy load on the motor at low rpm and expect it to be still covered under warranty.

If anyone has a concern about motor overheating putting an extra fan on is easy. My special 3 phase motor with the fan is setup with a 120V single phase fan from the factory Other than that motor specifically made for variable speed use via a VFD all my other 3 phase motors on VFD's are older and not VFD rated.

I have a machine with a normal 1800 base rpm motor that in operation usually runs below 60 hz from its VFD. That motor seemed to get a little warm and lacked power at low rpms. I switched it out to a 1200 base rpm motor for more low rpm power and no heating problems.

Talking about lathe warranties I ran into a local individual with a Grizzly lathe who had minor problems (dust on the rpm sensor). Apparently Grizzly does not try to diagnose problems they just sent a complete drive system, VFD and all to him. The guy gave me his old Delta VFD which works fine. I suppose you could conclude Grizzly is making so much money it's cheaper to replace than have a staff to attempt repair.
 
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Doug, I am guessing this is another case of the engineer's conundrum, "You can never idiot proof anything. As soon as you do, some one invents a better idiot." Only uses I know of for slow speeds is sanding and applying finish. My old PM 3520A was one of the first models and would go down to almost zero before turning off. It actually had a small fan under the heat baffle on the back of the lathe. I had to put some screening over the top of the baffle to keep the chips from going down and keeping the fan from running. PM did stop doing that before they made the B model.

robo hippy
 
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