Electric motors

[MikeParticipant @mike89748]

My workshop is 60 yards away from my house, and I can’t get a mains electricity supply to it without spending a fortune. As a consequence, electric power is supplied by a 3.2KVa petrol-powered generator. This provides power for lighting and a small lathe and drilling machine, and powered hand tools. Now for the problem: I have constructed a light milling machine based on an old Amolco milling attachment acquired in the days when I had a Myford lathe. I now need a motor of around 1/4 to 1/3 HP to power it. I have tried a couple which should be well within the capacity of the generator, but they cause the generator to all but stall when the capacitor starts engage. Is there a type of motor available which will not do this? I don’t mind waiting while the revs build up. I am a reasonably experienced amateir mechanical engineer, but a real dimbo when it comes to electrics!

[MikeParticipant @mike89748]

[Ian S CParticipant @iansc]

The starting current for your motor will be about 4 or 5 times the running current,so while your generator seems ok,it will be on overload when you start up.I’m not sure if a universal(brush type)motorwould be ok they usually rev too high,I think your portable electric drill will work.I’v heard of people using DC motors,don’t know where you’d get one.Tread-mills have one of about 1hp,I think 200 or so volt,and it works of a reasonably small generator.An old car generator(not alternator)may be run as a motor,there is an artical in ME starting 17 march 1989 about this,it states that it will run ok on voltages up to 24v.Hope this is some help Ian.s.c

[MikeParticipant @mike89748]

Cheers, Ian – this is pretty much what I expected. I’ll look at the brush-type motors first: high revs don’t matter, as I can use suitable pulleys to reduce to about 300 or so, which would be fine. I had also thought of a 12v or 24v electric motor, so will give that a try if all else fails.

Thanks again for your helpful reply.

 

[Ian AbbottParticipant @ianabbott31222]

I had a bench grinder on which the capacitor failed.  Being cheap, I didn’t buy a new one, but spun the wheel up with a (gloved) hand before starting it.  Worked well like this for years.  Perhaps disconnecting your capacitor and doing a hand start, may help until you find a permanent solution.

Could be like starting an old Seagull outboard.

Ian 

[MikeParticipant @mike89748]

Thanks Ian Abbott. I’d thought of this, but on investigation the innards of the old 1/3hp motor proved to be corroded beyond sensible safety limits – the result of 15 years storage in a damp garage on the sea shore! One thought is an old washing machine motor – any ideas from you guys?

[AndyPParticipant @andyp13730]

The cheapest motors I have come across are bench grinders – less than £20 at the DIY sheds when on offer. OK they run at 3000rpm so you are going to have gearing and mounting issues but they can probably be resolved. I use several for home made kit.

The modern washing machine motors I have seen are huge affairs that go like the clappers, twin tub motors used to be the thing but I suspect they are a little thin on the ground now.

[MikeParticipant @mike89748]

That’s great, Andy P. I have such a bench grinder that doesn’t cause the generator to hiccup, so I’ll get another. Problem solved! Aren’t these forums great!

[Ian S CParticipant @iansc]

A universal motor is governed by its load,so its basicly made for driving a constant load ie vacuum cleaners cake mixers,and portable hand tools.I tried using a vacuum cleaner motor with an electronic speed reducer on a flexable drive,it played merry hell with all the nearby radios,and to get any power it was still too fast.

[Ian AbbottParticipant @ianabbott31222]

I ran my bandsaw and Randa lathe on 110v 1435 rpm washing machine motors for thirty years in Canada.  Should have brought a few back with me.  Didn’t cost me a penny, as they all came from discarded machines.

I did bring most of my power tools (but not the bench grinder) along with a generator and a few inverters.

There is however, a washing machine in the barn with the lathe’s name on it…… 

Ian 

[MikeParticipant @mike89748]

After no response to my original posting for weeks, you guys have suddenly given me some very useful ideas. Thanks a million from the far North of Scotland!

[MikeParticipant @mike89748]

Hi everybody:

I have now finished the construction of my light milling machine based on an old Amolco attachment left over from the days when I owned a Myford. I still don’t have a motor, but at least I now know what I want.

 

Thought you guys might like to see it. The base was built up out of a slab of very hard 3/4″ plywood bolted to the bench top. On top of this is an 8mm layer of a very hard industrial plastic and, finally, two 3/8″ x 3″ x 12″ strips of bright mild steel stiffened with a couple of lengths of 1″ steel angle. The X-Y table was bought from a ME advertiser.

Will this Heath Robinson arrangement be stiff enough? Well, a 30lb lateral force applied to the tool tip produces a movement of 0.0003″ measured with an accurate dial gauge, so I have high hopes.

One snag: the X-Y table is graduated in mm, while vertical movement is in inches. I shall have to sharpen up my maths!

 

[John HaineParticipant @johnhaine32865]

Mike, I used to have an Amolco imperial head that I paired up with a metric Amolco XY table.  I replaced the vertical feedscrew with a new one made from M12 stainless studding, with a new nut turned up from brass bar.  Also added ball thrust races to the bearing which made it a lot freer.  It worked well, though I never got round to re-doing the graduations which were still “imperial” based and didn’t work so well with a 1.5 mm pitch screw.  Anyway, the maths was easier than using the imperial screw!

 

John.

[Ian S CParticipant @iansc]

Just rig up a scale using a digital caliperand don’t worry about what thread the feedscrew is,IAN S C

[MikeParticipant @mike89748]

Hi Ian:

I have just acquired a digital caliper for this very purpose. Although cheap, I am amazed at its accuracy, having checked it against a couple of good micrometers and a vernier gauge. This isn’t exactly engineering standards room stuff, but quite good enough for my purpose.

Thanks to all who contributed to this thread. Sorry my picture didn’t upload properly – there must be a trick to it that I haven’t yet mastered. – Mike

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