Motor size

[Stephen FollowsParticipant @stephenfollows82099]

I'm shortly going to upgrade the motor on my Myford ML7 lathe, probably NewtonTesla.

Question is: half horse power or one horse power? Anyone gone for half and wished they'd gone for more or gone for one and found it too big?

[Stephen FollowsParticipant @stephenfollows82099]

[old martParticipant @oldmart]

Go for the larger, assuming it will fit in the space ok. Then you can run it at lower rpm and still have twice the power that a 1/2 hp motor would have. If you are concerned with the motor being too powerful for the lathe design, just slacken off the belts a bit so they will slip. The museums Smart & Brown model A has 1.5hp, but in deference to its age, I allow the final drive belt to slip if the torque gets very high, particularly when drilling holes about 1" diameter in steel.

[Mark RandParticipant @markrand96270]

When I put a VFD on mine, I used a 3/4hp motor, so that splits the difference. If the lathe's got the upgraded hardened mandrel with bronze bearings (mine has), it'll easily handle 1hp and 1500rpm.

[bernard towersParticipant @bernardtowers37738]

NT 3/4 hp on mine for the last 7 years and I haven't stalled it yet (and I do try). I machine a lot of stainless and it takes it in its stride.

[Phil WhitleyParticipant @philwhitley94135]

Go for 1 or 1.5hp. If you don,t need the power you will not pay for it in current consumption, but if you do it can be available, you may also save on motor cost because 1 and 1.5 are manufactured in larger quantities than fractionals.

Phil

[John HaineParticipant @johnhaine32865]

NT have a 3/4 hp package which isn't shown on their website, give them a call. Cheaper than the 1hp and recommended. Recently fitted one to my S7 which is transformed. Highly recommended.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Phil Whitley on 28/04/2022 09:01:31:

Go for 1 or 1.5hp. If you don,t need the power you will not pay for it in current consumption, but if you do it can be available, you may also save on motor cost because 1 and 1.5 are manufactured in larger quantities than fractionals.

Phil

All true, plus a 50% duty 1.5HP motor will deliver ¾HP continously if the lathe is worked hard. (Few hobby lathes work hard continously.)

But I'm wary of over-motoring tools because the extra power is also available to damage the machine or operator in the event of an accident. A 0.5HP motor might just stall during a head-crash, whilst 1.5HP is likely to tear gear teeth off, bend shafts and wrench bearings.

Using extra power greatly increase wear and tear too. The damage is silent and non-obvious – for example, bearings that would have lasted 20 years fail after 5. I'd think twice before buying a lathe that came with a giant motor fitted by a previous owner.

Dave

[A SmithParticipant @asmith78105]

My ML7 tri-Leva has a 3/4hp 3ph motor, fed by a VFD. No shortage of power, excellent speed control. Two things though. I wish I'd bought a TEFC (Totally Enclosed Fan Cooled) motor, I had to make a guard to stop swarf getting in. Also, the 3/4 motor is right on the physical size limit of what can be fitted on the original mounting plate. I'd suggest that you ask the supplier if they have any knowledge/photos of their motor fitted to a ML7, if you go to something in excess of 3/4hp.

Andy

[A SmithParticipant @asmith78105]

[Alan Johnson 7Participant @alanjohnson7]

I had thought that Myford recommended nothing more than 0.75HP (0.56kW).

[Phil WhitleyParticipant @philwhitley94135]

Posted by SillyOldDuffer on 28/04/2022 10:39:40:

Posted by Phil Whitley on 28/04/2022 09:01:31:

Go for 1 or 1.5hp. If you don,t need the power you will not pay for it in current consumption, but if you do it can be available, you may also save on motor cost because 1 and 1.5 are manufactured in larger quantities than fractionals.

Phil

All true, plus a 50% duty 1.5HP motor will deliver ¾HP continously if the lathe is worked hard. (Few hobby lathes work hard continously.)

But I'm wary of over-motoring tools because the extra power is also available to damage the machine or operator in the event of an accident. A 0.5HP motor might just stall during a head-crash, whilst 1.5HP is likely to tear gear teeth off, bend shafts and wrench bearings.

Using extra power greatly increase wear and tear too. The damage is silent and non-obvious – for example, bearings that would have lasted 20 years fail after 5. I'd think twice before buying a lathe that came with a giant motor fitted by a previous owner.

Dave

Leave the belts a bit loose!

Phil

[SteviegtrParticipant @steviegtr]

I fitted the 1.5HP motor a few years ago. Never regretted it. The only thing was the shaft diameter is larger so i had to fit a different pulley. The motor mounted to the Myford swing frame with no problems at all. Mine is a Super 7B , but it should be the same. I did a Youtube video of the Myford with the VFD & showed the speeds it will do.

Steve.

[not done it yetParticipant @notdoneityet]

I’ve seen this talk of leaving belts loose umpteen times on the forum.

A potential waste of good belts if slippage is needed, gives no gain if fitting an over-powered motor (if the belts slip before that extra power can be used, anyway), extra heat generated if belts are slipping on every motor start (mainly single phase motors for hobbyists).

You will not find any belt manufacturer/supplier suggesting their belts should not be tensioned correctly.

That adds up to I don’t recommend that practice and it is a waste of time and expense. Fit the correct motor such that it will not damage or cause early wear to the machine – and it is much safer for the sensible users, who do fit the proper power supply to their machines.

25% would be about the maximum increase over the OEM supplied power unit I would consider. I want to look after my machinery. Doubling the power likely means it needs twice the belt rating – may need twin-sheave pulleys, for instance.  Geared machines will likely require stronger gear trains (larger teeth and/or wider gears.

I doubt that many, who just over-power their machines, think of all the considerations sensibly before making the change.

 

Edited By not done it yet on 28/04/2022 21:51:40

[SteviegtrParticipant @steviegtr]

NDIY is probably correct in the assumption. Personally i only went to 1.5hp because i had bought a used Omron inverter & it was 1.1kw.

1hp is probably the best size to go for & with it's smaller frame may be easier to fit . The origonal one i took of was .75hp. single phase. Certainly do not leave belts slack. I have tripped mine twice & no damage done with 1.5hp.

Steve.

[Phil WhitleyParticipant @philwhitley94135]

Good Grief! Belt manufacturers settings are the MAXIMUM tension, I am not suggesting leaving them loose, just below the maximum! In normal use they will never slip, remember it is a WEDGE belt, and even a properly adjusted belt will slip if the machine (any machine) is locked up. If however the machine is lightly built it is more likely break the machine rather than slip the belts. Think of it like an overload clutch, belts are much cheaper than machine parts! It was common practice in schools and colleges to run machines with the belts looser than recomended tension to allow for learners cock ups, and we were actually told at college that industrially set up machines were not so forgiving because of this!

Phil

[not done it yetParticipant @notdoneityet]

Stevie,

Only ‘probably’’? Please point out my possibly wrong ‘assumptions’.🙂

[noel shelleyParticipant @noelshelley55608]

WHY NOT take the advice of the makers, or the next size up as used on the Super 7 ? 3/4 Hp or approx 550W. ! Noel

[SillyOldDufferModerator @sillyoldduffer]

Posted by noel shelley on 29/04/2022 09:43:18:

WHY NOT take the advice of the makers, or the next size up as used on the Super 7 ? 3/4 Hp or approx 550W. ! Noel

Very sensible, but it would spoil the dream. More power is always better. It's a man thing: I secretly lust after fitting a NOX boosted Merlin to my sensible Corsa… Despite knowing it's insane!

Dave

PS Who with a headache doesn't triple the dose of painkiller?

[not done it yetParticipant @notdoneityet]

Posted by SillyOldDuffer on 29/04/2022 09:58:24:

Posted by noel shelley on 29/04/2022 09:43:18:

WHY NOT take the advice of the makers, or the next size up as used on the Super 7 ? 3/4 Hp or approx 550W. ! Noel

Very sensible, but it would spoil the dream. More power is always better. It's a man thing: I secretly lust after fitting a NOX boosted Merlin to my sensible Corsa… Despite knowing it's insane!

Dave

PS Who with a headache doesn't triple the dose of painkiller?

Dave,

I like your analogies. I expect there are a few more that would fit the bill.🙂

[SteviegtrParticipant @steviegtr]

Posted by not done it yet on 29/04/2022 09:33:16:

Stevie,

Only ‘probably’’? Please point out my possibly wrong ‘assumptions’.🙂

Assumptions are probably guesses.

What seems to be missed is that once a 3phase motor is fitted , then the speed can be run at pretty much anything required by the task. As shown in my Myford video's. The single phase being only 1 speed is reliant on belt pulleys. So any advise is not from a metalurgist calculation, but an assumption based on that persons grey matter.

Electrical insulation is tested at + 100%. So is weights tested by Lloyds. Most things are tested that way.

So i am not sure about being 25%. Just saying.

A lot of Myford owners go for the 1hp package which comes complete. Don't know who worked it out But not heard of any breaking from it.

Anyway i was pretty much agreeing with you for once.

Steve.

[Howard LewisParticipant @howardlewis46836]

At one time it used to be said 3/4 hp single phase or 1/2 hp three phase, for a ML7.

But with a VFD, would still be inclined to opt for 3/4 hp motor. It will run more smoothly than a single phase motor.

HTH

Howard

[Robert Atkinson 2Participant @robertatkinson2]

Old post but OP has raised subject in a new post.

Having got a ML7 since thsi was posted I've done some research.
THe motor originally supplied with the ML7 was a 1/3 (one third) HP 1420 RPM 2 phase motor. It is generally accepted that a 3 phase motor of the same rating as a existing 2 phase motor will give improved performance on a lathe. Thus not much need to increase the rating. When fitting a VFD there are further improvements. One that is often missed is that you can run the motor faster than nominal as well as slower. this opens the possibility of using a 6 pole motor rather than the more common 4 pole. 6 poles give about 930 RPM at 50 Hz (depends on slip) and to get the power the torque is also about 50% higher at rated speed. Running at 60Hz gives 1100 RPM . 75Hz gives the full original speed.
So fitting a a 0.5HP (375W) 3ph 4 pole motor is more than adequate and if you use a 6 pole it is real upgrade in terms of low speed torque and smooth operation.
I chose a modern 0.5 HP TEFC 6 pole motor that was £35 (new old stock) and fits the ML7 with no modifications other than new pulley and belt.

Robert G8RPI.

[ZanParticipant @zan]

As you are going for vdf speed control, go for 1 hp. Mine (S7b) is 3/4 and at times the vdf safety features trigger , although most of the time it is perfectly satisfactory. I run in smallest spindle pulley, but change to biggest when low speed or more torque is needed

[Robert Atkinson 2Participant @robertatkinson2]

Zan,

That sounds more like incorrect VFD settngs than too small a motor. Or you are overloading the lathe. Myford recommended 1/2 HP (4 pole) for a 3 phase motor so you are already at 50% oversize.
Running on the smallest pully is not ideal unless you are doing high speed work You should pick the belt position that keeps the motor near rated speed for the work you are doing. Running the motor well below rated speed is not the best set-up.

Robert.

[Author]

Posts