Found a lathe with a bum motor - motor replacement viability?

It seems that this may be the best forum to ask such a question as many are familiar with drive solutions. I found what appears to be a Colchester round head 14x40 or 15x50 which has a dead motor. Apparently one of the shop guys plugged it in wrong and fried the motor. The lathe is in good shape, but needs a power plant. What options are available in this situation? Are aftermarket DC motors available to circumvent purchasing a 3 phase and then VFD? I'd love to hear some insight on this.

Without first hand experience with that machine, we need to see the motor. Many lathes have plain motor with belts, some lathes have motors integrally mounted and need exact replacement, or modification to work. I see no great benefit going to DC, could actually be more expensive than going 3ph/vfd/rpc route.

dalmatiangirl61 said:

Without first hand experience with that machine, we need to see the motor. Many lathes have plain motor with belts, some lathes have motors integrally mounted and need exact replacement, or modification to work. I see no great benefit going to DC, could actually be more expensive than going 3ph/vfd/rpc route.

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Thanks for the heads up. That's what I needed to know. I'm currently waiting to see if the seller has the burnt motor. I believe it was a 7.5hp 3-phase motor. I believe Colchester lathes use a dual belt to the geared headstock.

I'm not electrical guru, but assuming this thing was plugged into a single phase supply, what kind of damage should one expect in the motor? What are the possibilities it may be able to be repaired? I'm dumb enough to try anything.

In this size machine I see no benefit to a DC motor other than being much more expensive and complicated at this Hp level. Your best bet would be to pull the motor and take it to a local motor shop to be evaluated, they are often standard sized frame motors that are readily available for a few hundred dollars. Nothing special in most circumstances. Ask the seller what is wrong with the motor, if it is "burn't" then chances are there is a short in the insulation and it is not worth rebuilding.

Going the VFD route will be much more expensive at this Hp level, you would need a 15Hp 3 phase VFD and run it in a derated mode if feeding it with single phase. Setting up the VFD, is a much more complicated install to do it correctly on a lathe, you just do not connect the power to the VFD and have the machine run. Look at an RPC for 3 phase, at least to get started.

What does it take to fix the motor? If you want everything original.

I know about VFD's and RPC's. In my opinion a over-built RPC is going to be more dependable than a VFD.

the price difference between a 10hp RFC and a 15hp RFC is pretty shocking. Looks like I'll be buying used, in that case.

If the PO plugged it into single phase, depending on how long he left it plugged in, it may or may not be dead, it just did not work for him so it was declared dead. If you get the "dead" motor, start by ohming the leads to each other (should show connectivity and should read the same), and ohming individual leads to motor case, should read as open(ie, no connection).

You can have the motor re-wound if it has been fried. If it was connected to single phase long enough that may be a possibility.

unfortunately it appears the owner threw the motor our due to frustration. My concern now is the pulley I've clearly lost. Not sure what the motor speed was or the pulley size. I'm sure I can probably get some info, but it will look like I'll need a new motor. It appears the motor in the lathe was either a 3 or 5hp. I plan to stop by and take a look, if it's in good shape I'm probably going to offer him $1k or so on the lathe, they typically sell for around 3-5k. Said he has a ton of tooling.

Could be the motor "was removed" for any reason, and without being able to run it,
you would not find the spindle bearings noisy/shot or any other number of problems.

Pyrex said:

It seems that this may be the best forum to ask such a question as many are familiar with drive solutions. I found what appears to be a Colchester round head 14x40 or 15x50 which has a dead motor. Apparently one of the shop guys plugged it in wrong and fried the motor. The lathe is in good shape, but needs a power plant. What options are available in this situation? Are aftermarket DC motors available to circumvent purchasing a 3 phase and then VFD? I'd love to hear some insight on this.

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The ONLY way you could afford DC re-motoring is to find a rebuilt or rebuildable motor of the right "type" for machine-tool use. New ones have been around US$ 12,000 each @ 5 HP, more-yet for larger, for many years. They are physically larger and seriously heavier than 3-Phase AC as well.

Even if a sub - $1,000 used DC motor was found - not easy with guys like me hoarding about a dozen already - that would make it only about three times as expensive as a 3-Phase motor plus RPC. And then? You have to find a place to PUT it if the machine-tool wasn't designed for it.

Example: .

My HBX-360-DC is around a 14" X 30", similar size to your Colchester.

- The OEM 7 HP 3-P motor weighs as little as 30 lbs Avoir. were I to strip the dual juice pumps off its arse.

The same shaft-size 180 VDC Reliance RPM III Type TR 5 HP I have handy weighs just under 400 lbs Avoir, had a MSRP of over $11,000 USD - over 30 years ago!

So long as the Colchester still has all its gears & mechanical ratios in working order, it doesn't NEED a VFD.

New or used-but-good 3-P motor + purchased or DIY'ed RPC is your least hassle and least-cost solution for this lathe.

Not my area of expertise, but I'd guess it had 2 if not 3 "options" for motor.

Plenty of other PM members will know what those were, what you need, and what it takes to get it installed and running.

Pyrex said:

unfortunately it appears the owner threw the motor our due to frustration. My concern now is the pulley I've clearly lost. Not sure what the motor speed was or the pulley size. I'm sure I can probably get some info, but it will look like I'll need a new motor. It appears the motor in the lathe was either a 3 or 5hp. I plan to stop by and take a look, if it's in good shape I'm probably going to offer him $1k or so on the lathe, they typically sell for around 3-5k. Said he has a ton of tooling.

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The pulley is fairly easy. Just set up for some known nameplate speed of the spindle, then turn the input pulley by hand and count turns per turn. Divide spindle speed by that ratio. Now, you know what the pulley speed will have to be for the correct spindle speed.

Your new motor rpm will then let you figure the motor pulley size to get the right spindle speed.

I've got the roundhead "student" 6 x40 and had the same issue.
On mine the motor is rated at 3HP with a motor rpm of 1425 ( I'm in uk so yours will be higher for 60hz not 50 hz)
Any standard foot mounted motor should be fine to fit as the mounting is just a large hinged plate which the motor is bolted to.
Mine had twin vee belts rather than a flat belt so I used a taperlock pulley to mount to the motor.
I did a vfd conversion on mie as the original switchgear was junk, a new front panel holds the vfd and coolant switches along with a tacho.
The vfd is wired into the original switches

Oilyneil said:

I've got the roundhead "student" 6 x40 and had the same issue.
On mine the motor is rated at 3HP with a motor rpm of 1425 ( I'm in uk so yours will be higher for 60hz not 50 hz)
Any standard foot mounted motor should be fine to fit as the mounting is just a large hinged plate which the motor is bolted to.
Mine had twin vee belts rather than a flat belt so I used a taperlock pulley to mount to the motor.
I did a vfd conversion on mie as the original switchgear was junk, a new front panel holds the vfd and coolant switches along with a tacho.
The vfd is wired into the original switches

View attachment 268910

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Ah, that is a very nice lathe! I hope mine will look that nice one day.

So, an update -

I did end up purchasing the lathe for a great price. As best as I can tell, the lathe is a 1967 Clausing Colchester 13x36" Master MK 1.5. The owner destroyed the original motor and tossed it. With that being the case, it would seem the most economical and easiest solution would be to install a 3HP single phase motor at 1800rpm. My machine was a two-speed variant, with 1800hp being the higher of the two RPM inputs, so that would give me the greatest rpm spectrum.

I'd like to get some input on the viability of doing a single phase motor in this lathe. What concerns should I have switching to single phase? Will I be able to use the factory switches/levers? I would assume they would work seeing as they (presumably) would just be simple relays. What effect will an clutch headstock having on a single phase motor - presumably starting it without any load - from my understanding this can damage the windings on single phase motors.

Pyrex said:

What effect will an clutch headstock having on a single phase motor - presumably starting it without any load - from my understanding this can damage the windings on single phase motors.

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I've never heard anything like that. If you go single phase, for 3 to 5hp you will be needing 240V single phase, you can get 3 to 5hp motors with 1750 rpm, they cost more than 3450 rpm motors. You can try to source one on surplus market, but they are not exactly common. You could use a 3450 rpm motor if you use a pulley on motor half size of what was on original motor. Only problem I had on my 1 ph lathe was if I was running high speed on spindle (not much reduction in gear train) and put a heavy load on it, the motor could slow enough for centrifugal start switch to re-engage. If you want to be able to reverse spindle, wiring a 1 ph motor to a reversing drum switch is more complicated (mentally) than 3 phase.

Pyrex said:

Ah, that is a very nice lathe! I hope mine will look that nice one day.

So, an update -

I did end up purchasing the lathe for a great price. As best as I can tell, the lathe is a 1967 Clausing Colchester 13x36" Master MK 1.5. The owner destroyed the original motor and tossed it. With that being the case, it would seem the most economical and easiest solution would be to install a 3HP single phase motor at 1800rpm. My machine was a two-speed variant, with 1800hp being the higher of the two RPM inputs, so that would give me the greatest rpm spectrum.

I'd like to get some input on the viability of doing a single phase motor in this lathe. What concerns should I have switching to single phase? Will I be able to use the factory switches/levers? I would assume they would work seeing as they (presumably) would just be simple relays. What effect will an clutch headstock having on a single phase motor - presumably starting it without any load - from my understanding this can damage the windings on single phase motors.

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It's an "honest enough" lathe, but old and to an older-yet basic design concept. It will be a better partner if you don't let it eat so much of your budget there's nought left for tooling or consumables.

Personally, I'd use 3-Phase motor and do an RPC, even if I didn't already HAVE such.

Single-phase will make chips. Just buy a NEW "farm duty", preferably one set-up to be switch reversible as-shipped, and so-nameplated or documented. Then sort the wiring to the "drum" switch per advice of others who have already done that, and more than once.

Used 3-Phase motors are low-risk. Used 1-Phase potential PITA, rather, so new is better.

Even so, TWO used 3-P, one for prime-mover, other for RPC idler, might actually be no more out-of-pocket spend - perhaps much LESS. Mostly, that's about shipping costs, so "local" or same-day out-and-back go-fetch - economy motorcar, not tractor-trailer - makes a huge difference.

Even then.. "specialists" who know their s**t on shipping, can flat-rate those costs to beat the price of fuel.

Search ebay for Aurora stainless steel motor this very month, for an example of one of several among "the usual suspects" - check the freight cost. There is always competition - plenty of it.

You cannot stick in a single phase motor on a 3 phase machine and expect it to work the same. You would need to rewire the contactors/switch gear, and this all depends on the single phase motor leads for reversing. On a lathe in particular you get a better surface finish with a 3 phase motor. A clutch doesn't care if it is single phase or 3 phase motor. If you want simplicity then go with a 3 phase motor and a RPC. Alternate is a VFD, which requires a rewire of the machine to some degree. An external braking resistor is also recommended to assist with braking, so the VFD needs to be able to support this.

mksj said:

You cannot stick in a single phase motor on a 3 phase machine and expect it to work the same. You would need to rewire the contactors/switch gear, and this all depends on the single phase motor leads for reversing. On a lathe in particular you get a better surface finish with a 3 phase motor. A clutch doesn't care if it is single phase or 3 phase motor. If you want simplicity then go with a 3 phase motor and a RPC. Alternate is a VFD, which requires a rewire of the machine to some degree. An external braking resistor is also recommended to assist with braking, so the VFD needs to be able to support this.

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I had a good idea of what was in store for me should I choose to do a single phase motor. All of that makes sense to me, and I was aware there would definitely be some sacrifices. Initially, I was under the presumption finding a replacement three phase two speed motor was unlikely, but it appears I may have gotten lucky. If that's the case I will probably end up doing a RFC over a VFD because, honestly, it's easier and I don't really see a ton of benefit on this particular machine, seeing as the gearbox affords me a wide spectrum of speeds. Granted, I'm still wet behind the ears, but the VFD's I've had the past were worth the trouble because of the spindle speed control on my drill press and mill, but on this lathe it seems like the factory gearbox should be more than adequate. I also really like the fact I'll have 1800rpm available for carbide.

I'm starting to come around to the idea of just doing another VFD for the lathe, but I've never done a VFD on this high HP of a motor. I've also never done a VFD on a lathe, so I'd have plenty of questions - especially how a two speed motor would best be configured, and if it's possible to wire the VFD to use the controls on the machine itself. First and foremost, does anyone have any recommendations on which VFD I should choose? Don't want to break the bank, but I would like (and would assume it would be of use) a braking resistor.

I had been looking at the Fuji FRN0020C2S-2U, but I'm not seeing mention of a braking resistor. I've been searching the previous posts but keep running into 10 year old threads.

So a few suggestions should you decide to go the VFD route. First, you would only go with a single speed motor, there is nothing to be gained with a 2 speed motor in this case. In fact, even if you didn't go with a VFD, I would probably go with a single speed motor. My brief review of this model was the 2 speed motor gave you very low speeds, you could get by with a single speed. I have also had a disproportionate amount of problems with 2 speed motors when using a VFD (with the exception of constant Hp motors).

If you are installing a VFD on a lathe, it is a bit more complex as there are a lot of safety issues that need to be incorporated into the design. Also this particular lathe is a bit different as to the operation with the clutch, that might work in your favor as to disengage the drive but leaves the motor running. I would need to see the schematic/manual to give any specific suggestions. It is all doable, but not easy like on a mill. You pretty much have to do all the electrics. If the forward/reverse contactors were replaced I have stripped out the high voltage connections to the contactors and used one set of poles on each contactor to trigger the FOR/REV inputs on the VFD.

The Fuji drive you mentioned is a 3 phase input 5 Hp, could be used in a derated mode but would need a DC choke. I would stick with a single phase input 3 Hp 230VAC VFD (FRN0012C2S-7U). For Fuji I would check Wolf Automation, seems to be a line that they are using. They do support an external braking resistor and are pretty full featured.
FRN0012C2S-7U | Fuji Electric | AC Drives
FRN0020C2S-2U | Fuji Electric | AC Drives

I often used the Hitachi WJ-200-022SF (3Hp single phase input),
Teco Westinghouse E510-203-H-U, Yaskawa V1000, etc. All good VFDs, if you have experience with Fuji then go with that if you choose to do a VFD.