Alexander Master Toolmaker

[Andy Pomfret 1Participant @andypomfret1]

Thanks Brian, not too late!

The existing motor has a 1⅛" shaft with (I'm pretty certain, measured it twice because it seemed so improbable) an 8mm key. The replacement I'm looking at has a 28mm shaft and an 8mm key. 1⅛" is 28.575mm, so the new shaft is undersized, but not by a lot – a shade over 10thou on the radius. How practical is it just to add some shim stock? Or should I be looking at boring the pulley and using a taper fit coupling or a keyed sleeve?

Andy

[Brian WoodParticipant @brianwood45127]

Hello Andy,

I don't think sleeving with shim stock would be satisfactory at all, far better to grip the new size of motor shaft with a taper fit coupling.

You should be able to find one with the keyway cut to suit the new 8 mm wide key. They are not a silly price either.

I have refurbished an old Churchill lathe that had a huge 55 kg 1 HP 3 phase 2 speed motor with a shaft of 1.125 inch diameter and 1/4 inch wide key—the replacement from Newton Tesla is 2 HP with a shaft diameter of 26 mm, 6 mm key and weighs 17.5 kg. The march of progress in motor design and technology!

Regards

Brian

[Andy Pomfret 1Participant @andypomfret1]

I do like those taperlock couplings – and as you say, very reasonably priced.

I can bore the taper easily enough, but I'm not quite sure how I'd drill and tap the holes for the grub screws, if they're not parallel to the pulley axis, given that I don't have a working mill until the pulley is complete! Ideas welcome…

Andy

[Brian WoodParticipant @brianwood45127]

Hello Andy,

They are parallel to the pulley axis but displaced downwards around the circumference by 5 degrees either side of the equator.

I found the most satisfactory way of tapping them [3/8 inch whit in my insert] was to drill and tap the holes first before boring the 8 degree taper so that you finish up bisecting them on the face of the bush.

If you are in anyway unhappy about all that, do a Google search and find someone who has a believable drawing showing the correct geometry, there are lots of entries under taper lock bushes

Regards

Brian

[Andy Pomfret 1Participant @andypomfret1]

Ah I see, thanks – so spaced 170 degrees apart, essentially? That sounds doable with just the 4-jaw, though it might need a counterweight! Indeed, drilling and tapping first sounds like the only reasonable order of operations. I can't imagine that tapping a partial hole would end well at all!

Andy

[Andy Pomfret 1Participant @andypomfret1]

Thank you Brian for setting me on a very helpful track. When shopping around for taperlock bushings, I found a supplier that would also sell me a pulley with a taperlock fitting that's a perfect match for the original (double V-belts, B profile, 112mm outside diameter) for a shade over £10 plus VAT. For that price there's simply no point in firing up the lathe, and it means I can retain the original pulley intact if ever I want to restore the machine to its original condition. Pulley problem solved!

Re. the size and weight of motors, I've had a similar experience – I'm replacing a dual-speed 1.5hp motor (of unknown mass!) with a 3kW (4hp) motor that's physically significantly smaller in all directions, and almost certainly lighter too. An interesting observation is that the physical size of a motor appears to be related to its torque rating rather than its power rating. A 1.5kW 750rpm motor is roughly the same size as a 3kW 1500rpm motor (and as a 2.2kW 1100rpm 6-pole motor, indeed) and they deliver the same torque. As an electronic engineer this should not have surprised me, but I hadn't thought about it and power electronics is not my area.

The reason I'm going for a 4hp motor, which definitely seems like overkill on the face of it, is that I can run it off a VFD and get almost 2hp out of it at half speed, hence replacing and slightly upgrading the 1.5hp dual-speed motor.

[Brian WoodParticipant @brianwood45127]

Hello Andy,

In the words of a well known but deceased TV presenter " Didn't he do well ! "

I agree whole-heartedly with your course of action and the logic of going for a motor with good low revs torque, I imagine with a machine tool of that calibre, shifting metal as a grunt operation will be the more frequent use rather than doing things at high speed.

I'm glad to have been instrumental in pointing a way ahead, I hope the rest of the restoration goes well for you..

Regards

Brian

[Andy Pomfret 1Participant @andypomfret1]

Thanks Brian! Hopefully there's not much to restore, the machine was in regular use when I bought it and seems to be in excellent condition. It just needs power.

I anticipate tackling a wide variety of jobs. With the mill set up in horizontal configuration in particular I'm sure the power will be useful. For high speed work I have the separate high-speed vertical head that goes up to 6000RPM, which should be great for small cutters in soft materials. That needs rewiring for 230V and a VFD adding but it's a dual-voltage motor so it'll be no big deal.

Andy

[Bob SillitoeParticipant @bobsillitoe83708]

Hi Andy,

I too now have one of these machines and have the same issue about what to do about the motor. Just wondering what you did in the end.

Bob

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