ML7 motor size

Do you see any problem fitting a 3/4hp motor to an ML7? I understand from literature that 1/2hp is the maximum recommended. However, a 3/4hp resilient mounted motor is readily available locally, just can't seem to find a 1/2hp.

A motor only produces its rated power when you load it sufficiently. If you don't overload the machine there is no problem.

Russell

If you don't overload the machine there is no problem.

The machine may well only be overloaded when done accidentally and the result may be far more damage than if the maximum power motor is affixed. Thinking here, that of stripping gears rather than stalling the drive. Torque is the real enemy, I would suggest, particularly if not a soft start motor.

As 1/2HP is quoted as a "maximum", clearly some lower powered motors are far more acceptable than exceeding the maximum advised, which you do at your risk. I suggest you try to understand/find out why that maximum power was advised

NDIY, you have asked the question I was going to ask. What is the weak point that limits the machine to 1/2 hp. Surely even with a 1/2hp motor gearing it down or using pulleys to increase torque will give similar effects as putting on a larger motor. I would think that for most people not working at maximum metal removal rates the only noticeable difference between a 1/2hp motor and a 3/4hp motor would be less slowing of the motor under some loading conditions using the larger motor.

I do not have a Myford lathe, this is just a question born out of curiosity.

Martin

As I know from engaging the clutch with the spindle lock engaged, the belt just slips!

John answered your question, over load the lathe and the belt slips, the belt head lathe has this advantage for the beginner(or clumbsy), with only an A section belt driving it the 3/4hp motor will be ok, and will not use any more power than the smaller one, it will just be doing less work compared to it's maximum ability.

Ian S C

Most people fit a more powerful motor if they fit an inverter to maintain power when they reduce speed. Doesn't seem to cause them a problem - hasn't for me either but getting the bigger motor to fit was a bit of a problem on both mounting holes and getting the connection box in the right place by repositioning the motor feet. I had measured up carefully but accounting for the connection box in that respect is difficult.

From lathes I have seen at work that have had a problem the lead screw will snap, twist or strip before the gears break even with their standard power motor fitted so I wouldn't be too bothered about that aspect and as pointed out the belts will probably slip. I was offered a job early on turning up new lead screws for machine for the rest of my life - no thanks even given a free choice on what lathe to buy.

John

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I'm not sure how credible this [hopefully, some of our experts can comment], but it's quoted verbatim from http://www.lathes.co.uk/myford/ **LINK**

MichaelG.

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Electric Motors:
For quiet and smooth running the makers recommend a resilient-mounted motor (with rubber rings isolating the main housing from the foot) and, so equipped, an ML7 will turn almost silently. While all Super 7s had a clutch fitted as standard, on the ML7 this was an optional extra - but one well worth having. The ML7 unit economised by utilising the brake shoes from the front wheel of a Nottingham-made Raleigh moped, the "Gadabout".
Unfortunately one-phase motors are not the most reliable of devices. They are best run near their rated capacity all the time (i.e. worked nearly flat out); if such a motor is switched on and off frequently against "no load" the windings will be damaged and, if run through a cycle where it is started, worked briefly, stopped and started again, the capacitor will fail prematurely.
It is very important not to "over-motor" a Myford (or indeed any other lathe); any accident or dig in will have far more serious consequences - and if the machine is worked beyond its capacity, excessive wear will occur. Early ML7s were fitted with 1/3 hp motors, later ones with 1/2 hp - the latter a figure that should not be exceeded. Apart from the very first examples, the Super 7 has always been equipped with a 0.75 hp motor (necessary to pull the top speed of over 2000 rpm) and this too should be respected as an absolute maximum. The original Brook-Crompton motors are very expensive; however, direct replacements, of exactly the same specification but more economically priced, are now available.

The limiting factor is looking after the bronze bush bearings. If you want to run tehm faster or at a heavier load, extreme care with lubrication is needed.

Neil

Personally I think that there is more need to worry about higher speeds. Ideally that needs to relate to bearing diameter 'cause bigger ones have to run at a higher surface speed than smaller ones.

Comparing ML7's with super 7's as lathes co has doesn't make much sense in that respect. i'd expect the ML7 to be more capable at running at higher speeds with better bearing life. Originally they used white metal too - think about car big end bearings but those have the advantage of forced lubrication. Lathes co are selling something, Always a point to bear in mind who ever they are. I vaguely recollect that Myford deliberately set the belt tension lower on the highest speed. People complained about them slipping. That was probably to avoid overloading the motor not the lathe. I've heard of Schaublin 70's being fitted with 1hp motors for a lot of high speed work to keep the torque up. Not exactly a big rigid lathe and not exactly a tiny spindle either.

The best example I have seen of high speed being a bad idea was a chipmaster. Not very old and 20 apprentices a year made the round bits for depth a micrometers on it. Most of the year it sat idle. Every week on Fridays it was oiled up etc. When it was used it was always at 3,000 rpm - as close as we could get it to try and make the chuck look stationary under fluorescent lighting or better still make it look like it was spinning slowly. Not possible. It just looked a bit weird for odd split seconds. Not much chance of thinking it was still. All of the lathe was in perfect condition apart from headstock bearings. The net effect was that rings appear along the work periodically. The finish can be so good that even ones a few microns deep stick out like a sore thumb. Next stage would be a poorer finish especially with lighter cuts unless the chuck was heavy enough to keep the bearings home. Next stage a rough finish and maybe chips flying around.My ML7 was like that - belts as they should be. There were plenty of other lathes about that had similar and even bigger sized spindles that didn't have this problem at all and did far more work. Usual top speed was under 1,000rpm maybe a bit more in a few cases. The only one I can recollect was a Holbrook that had push button electric gear changes.

Personally I don't run my lathe any faster than I need to. That might mean sizing small screws etc in one go where the stock is sufficiently stiff enough to take the load. Otherwise it's tiny cuts still at a low speed that take some time to run. Mostly this is what high speeds are for - to speed up the time it takes to do the job.

All makes me wonder about the quick fix dual speed and 2,800rpm motors that came about along with more use of carbide - mainly to speed the job up.

John

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Thanks for the comments guys.

I notice Myford supposedly has a 1/2hp:

**LINK**

Although it's listed as a 1/2 550W in the description - not sure how that works?!!! Then you click through the photo and the nameplate has 3/4hp listed on it... To be honest not the first time I've noticed this kind of thing on their site (or in fact received the wrong thing in the mail)... It looks similar to the Crompton Greaves motor from India.

I was also looking at going the whole hog and purchasing a VFD and motor. Could anyone confirm if the resilient (cradle) mount is less crucial with a 3 phase? i.e. are they naturally smoother?

.

^^^ Confirmed

MichaelG.

Well a three phase motor with resilient mounting would be best if possible, but you might be able to make your own resilient mount. as I have done. Unable to find a 3 phase resilient mounted motor locally I obtained a non resilient mount motor and using some rubbery type nearly circular things from the motor factors.. My motor has almost two circular end pieces upon these rubber things fit, just like the proper resilient mounts have. I copied the resilient mount cradle using some scrap, about 3mm sheet steel, a bit of welding and it works. Once it was fitted the original mount was cut off with the angle grinder. The motor is at the back out of the way, so with a coat of paint you soon forget about it. If you do make your own mount as I have done, don't forget the earthling links as the rubber mounts electrically isolate the motor form other metal work. John

Thanks MichaelG.

And thanks for the DIY tip John, will keep that in mind when I continue my search!

The Newrton Tesla VFD and motor packages that they supply for Myfords came with resiliant mounted motors (even though the photos in the link show solid mounts, BUT call them to check to make certain, if you are interested) :-

**LINK**

They can also supply a 1/2 HP Single phase resiliant mounted motor:-

**LINK**

I can confirm that the package fitted to my Super7 is extreemly smooth and quiet.

Nick. (Just a happy customer. No connection with Newton Tesla etc.).

Edited By Nick Hughes on 06/12/2016 10:45:50

Thanks, just so happens I emailed to ask that very question today

Mine didn't. I really don't think you need a resilient mount motor if it's 3 phase. They are inherently smoother. The 3ph solid mount on my S7 is smoother than the original 1ph resilient mount motor.

Cheers,

Rod

Mine did.

Nick.

Not that I have received it yet, but another happy customer Nick based on service and advice alone! Should have investigated this one sooner, superb service (I'm finding this such a rarity these days!).

Can't wait to get it, and mine is indeed coming with the resilient motor mount.

To be honest (going the single phase route) by the time you add up a decent quality DOL starter, reversing switch, and a motor + cabling etc. it's not a heck of a lot more to get a package such as this.