Last weekend I bought an old lathe with 20" swing. It came with a massive 3kW (4hp) 3-phase motor. This draws too much current and thus I will replace it with a smaller 3-phase motor and variable frequency drive. I was thinking about to get a 1.1kw (1.5hp) motor. Would that be powerfull enough for turning larger bowls at lower speeds?
Frank
I think that 1.5hp is fine but 2.0 is better if you can find one at the right price. Under most circumstances any more than 2 hp won't buy you much since you will start to get into belt slipping problems.
Bill
leave the 4 HP motor in place. Program your VFD to treat it as a 2 HP. That way, if you want a larger motor, you just reprogram the VFD. If it came with a 4 HP motor, I'd assume the belts, etc, can carry the HP and not slip.
right price. Under
start to get into
It came with a strange pulley system. One small pulley on the spindle and three larger ones on the motor side and no belt. Minimum RPM is probably somwhere around 2000. So I have to change the pulley system in any case.
I've thought about getting a Yaskawa VS Mini J7 inverter. That is a scalar drive (vector drives a probably too expensive). Would I have enough of torque at all RPMs if I had a 2-pulley system with ratios of 1:3 (or 1:2?) and 1:1? It seems that the J7 cannot handle the 4 hp motor.
Frank
no opinion about the belts - sounds like the motor and lathe are not related. But, look around at VFDs - I bought a refurbished Delta (not the tool company, rahter delta electronics) for $200 from a distributor - and I have a used Minarik vector drive that I could sell for $150 - and of course I'm making money on it - similarly, 3 phase motors are pretty cheap - a 2 hp motor shouldn't cost you over $35 or so in great condition.
"Frank" skrev i melding news:cpsrn6$mrr$ snipped-for-privacy@oravannahka.helsinki.fi...
IMHO, motorsize is almost irrelevant, as long as it is 1/2 hp or more.
I have turned a lot of bowls of 10" - 12" on a Record lathe with 1/3hp. On this one I also turned several wheels for spinningwheels of 23" diameter on a hommade faceplate weighing in at 10 pounds +.
Your hand is holding the skew, why should anyone want 3 or 4 hp behind a good catch? I am sure that too much power is far more of a hazard than a help.
My present lathe came with 2 hp, and I am still getting used to that.
A woodturner I know turns 8' x 20" gateposts with 1,5 hp.
Bjarte
There is a certain logic to what Bjarte says. It's not like this is a metal lathe where the tools, tool feed and chips get larger as the lathe gets larger, resulting in a larger requirement for Hp. As wood lathes get larger the gouges, feed and chips don't increase all that much. The power required to remove chips using a 1.5" gouge on a 8" bowl is about the same as the same gouge removing chips on a 24" bowl. What needs to change is the pulley ratio so the tangential speed stays about the same. Since the pounds of wood removed per hour stay about the same, then the Hp stays about the same, too. Dan
I sort of agree. The problem, though, is that as we get better at turning we want to remove more material faster. And with bigger diameter pieces there is a lot more material to be removed. Underpowered lathes become more frustrating as time goes on. So do we want to buy one motor or several motors? If you only do spindle turning -- even big spindles -- you don't need all that much power. Bowls are a different matter, though, I think.
Bill
no, not correct - with a larger lathe you turn larger diameter, and take larger cuts - If I put a 35 inch blank on my lathe and lean into a 5/8 glaser gouge, I can pull 1/4 inch thick shavings - that takes a fair amount of power, and near the rim I can easily stall a 2 hp motor. Torque X RPM gives you power, and the shaving thickness gives you pounds, so shaving thickness/width times radius gives you torque.
That would have been exactly what I was looking for, but unforunately wrong continent wrong voltage.
Frank
Yesterday I went to see a guy nearby here who stocks used and new motor and VFDs. I bought an 1.1 kW (1.5 hp)(1420 rpm, 3-phase) motor and the Yaskawa J7 VFD. Both new. Based on the discussion we had and some posts on this newsgroup it seems that that kind of a scalar drive can be used to reduce the rpms roughly by the ratio of 1:5 without loosing much torque. On the other hand the torque will start to decrease after about 100Hz. That would mean that the workable range of motor rpms would be 300-2800. With pulley ratios of 1:2.5 and 1:1 I would have two rpm ranges: 120-1100 and 300-2800. The guy also had a used 1.5 kW (2hp, 700 rpm) motor. I thought that I would sacrifice high rpm torque with that motor. Am I correct? The guy said that I can still change the motors. Should I do that or keep the one I have?
I will go to a shop that sells pulleys tomorrow. If I cannot find the wright ones from there I thought about turning temporary pulleys out of birch plywood (and hardening the surfaces by epoxy). I will have access to metal lathe later on so I could replace them by aluminium ones.
Frank
personally, I'd go with the higher horsepower. And, I'd see what extra you have to pay for a vector drive (used, or refurb) - you should be able to get the drive for under $200, and the motor for closer to $50 (used)
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