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

Russell

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

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

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.

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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^^^ Confirmed

MichaelG.

Mine did.

Nick.