2-Speed Motor Speeds

[Beckerkumm]

The spindle pulley should be larger than the motor pulley to gear 1700rpm down to 1200 ( example 4" motor to 6" spindle ). The motor pulley would have been swapped with the motor so is likely not original. You can go online and calculate the various mating diameters. Ebay is a great resource for NOS Browning, Martin, Matco, etc pulleys. The motor diameter will be easy to source, the spindle pulley might not be so if you can reuse that one and match the size, you will be golden. I'd not sweat getting a three belt one unless the price is good. BX belts ( or whatever the proper size is ) have better grip than old Vee belts did so two will be plenty for that machine. What is the spindle pulley diameter as that is probably original?

Dave

 

[walterwoj]

@mksj : Though I didn't say as much, I did use a tach to confirm the motor speed. I was hoping someone who owns a similar lathe might be able to measure theirs. Eyeballing part sizes in diagrams is seldom a reliable method in my experience.

@Beckerkumm : The spindle diameter is 6.25", I did use an online calculator to figure the ratios and the motor pulley came out to 6.5" by my calculations. Those pulleys are pricey so I don't want to guess (even educated) unless I have to. Also the drive-to-headstock has a ratio of ~1.5:1 from my figuring.

 

[mksj]

That measurement appears close to what the manual showed where they were both about the same size (the belts to the motor were parallel. Alternative if you were to replace the motor with a 5Hp and run it off a VFD you can then over speed the motor to get the desired spindle RPM. Most 1750 RPM motors will easily run to 2X their base speed (larger motors less so). A 3-5Hp inverter/vector type can be used to 5-6K, although I usually keep them to 2X their base speed for lathes. This assumes that the input pulley shaft are not significantly over speeded, You would use a smaller motor pulley in that scenario.

 

[Beckerkumm]

Mark, the picture may be the Colchester with the single speed motor. The single speed option topped out at 800 rpm so similar sized pulleys would make sense assuming a 900 rpm motor. The picture could also be a Euro spec machine. With eight speeds available, you could size the motor pulley so the existing motor could run from 30-80 hz or so and maintain the ranges without going to a vector duty motor. You would want to limit the amp draw as 10 hp at full is more than the machine is engineered for. I'd look for a decent price on a 5 hp inverter duty ( I bought two Baldor ECP NOS for 200 each so it can be done ). If the op was in Wis I'd make him a deal but 5 hp three phase motors are pretty common. A $300 motor will likely make up for the difference in price for the vfd and wiring needed to run the 10 hp motor. Dave

 

[twhite]

I have the 13” model. I will look this weekend and give you the pulley sizes on mine. Mine is a 2 speed motor also.


Cutting oil is my blood.

 

[walterwoj]

I plan on swapping the static phase converter to a VFD soon, but I don't see a point in changing out the motor to get it DOWN to 5 HP. At lead with my smaller lathe (10x36 Sheldon 3/4HP) I have always wanted MORE power, never less.

I plan to wire the VFD and motor for stock full speed and then rpm DOWN to the lower speed. Hopefully less wear on the motor and more TORQUE at all speeds. I think the last guy put the 10HP on there to compensate for the SPC so he would still have 5-ish HP. Why he didn't put the right pulley on the new motor is beyond me!

 

[mksj]

There are a couple of reasons to go with a 5 Hp motor and over speed as opposed to under speed. The lathe was never designed for a 10 Hp motor so more likely to cause damage, although torque usually is constant down to around 15-20 Hz on these types of motors you loose the mechanical advantage of torque below the base speed and Hp declines in a linear fashion. Less of an issue with such a large motor. The cost of a VFD will be substantially more in particular if your supply is single phase. Everything would need to handle the increased VFD size, typical norm is to double the size of a VFD if running off of single phase for a 3 phase input VFD. A 5 Hp motor are quite plentiful and a single phase input 5Hp VFD would be about 1/2 the cost of a 20Hp 3 phase input VFD that would be used with a 10 Hp motor. A 5Hp motor TENV/TEFC NOS can probably be picked up for $250-300. At the end of the day a much better combination and better overall performance. Wear on the motor is a non-issue, these motors are made for industrial usage 24/7, they use the same bearings in the 4P as 2P, inverter/vector types are designed to run continuously under load at 2-3X their base speed. They also have very wide continuous torque ranges, but as mentioned you loose the mechanical advantage below the base speed. Bottom line you will never have a power issue with the gearbox you have, most factory VFD lathes in this size use a 2 speed headstock with a 5 Hp motor.
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[walterwoj]

@mksj You prolly won't like this but I have this VFD in my amazon shopping cart >> China VFD I do no have the budget for a $600 VFD and a $400 motor. Especially when I already have a motor and the Chinese VFD is only $250. I know its not as good quality as that ?Japanese? one but I have use this brad on 2 other machines in my shop (1.5 Mill and 3 HP Surface grinder) and have had great results. If I had that kind of budget I would have bought a better lathe!

 

[mksj]

No reason to not continue using the static converter with that size motor. You can get a 2 or 3 groove pulley for the current motor. I still feel that a 5 Hp motor is more appropriate, you can check the local Craigslist/FB and see if a 5 Hp motor pops up, you should be able to sell the 10 Hp for a bit more. Also makes sizing the VFD a bit easier and less expensive.

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[walterwoj]

@twhite : Any word on that pulley size?