CovMac Lathes

[Phil WhitleyParticipant @philwhitley94135]

Wow, beat me to it! excellent knowledge, glad to see there are others out there, I will add that generally, Z1 and Z2 are the start windings, which you swap over to reverse the motor and may have capacitors in series with it., A1 and A2 will be the run winding, and A3 and A4 will be the auxillary run windings. For 240 volts these will be in parralell, for 460/480, they will be in series.

Phil

[9fingersParticipant @9fingers]

Not quite right Phil I'm afraid.

The motor/starter combination is single voltage. The windings are paralleled up by the control box during starting only and when you release the start button, they are connected in series for the run mode and the start winding is switched out.

Please see my write up for the detailed operation.

Bob

[Les Jones 1Participant @lesjones1]

Hi Bob,
I would have thought that the windings would be in series for starting and parallel for run mode.

Les.

[MuzzerParticipant @muzzer]

There is a slightly more conventional summary of EN 60529 (IP ratings) in Wikipedia. The table in the paper is perhaps a little dated and incomplete today. No criticism intended!

[9fingersParticipant @9fingers]

You need the higher current to get the motor moving.

I think it harks back to days when capacitors were expensive and short lived and copper was relatively cheap. It predates the reversible electrolytic capacitors that were then used as start capacitors of relatively high value but limited to a few starts per hour.

Bob

[Phil WhitleyParticipant @philwhitley94135]

Hi 9fingers, the motor is marked as dual voltage, not series/ parralel starting, it may start that way, it may not. If you try to run that motor with the windings in series you will be feeding a 460/480 volt (2 phase) winding on 240v, which won't work.

[9fingersParticipant @9fingers]

Hi Phil, yes I noticed that when I looked at your photos last night. Bit of a mystery. I wonder if your starter is subtle different from the one I looked at for Chris?

There is not really any such thing as two phase as it it just double the voltage. I did read about a system that was used somewhere for a while which was two phases at 120 degrees explicitly for running motors without the need for a starting capacitor but of course the phase to phase voltage would not be doubled in that case.

Chris's stayrite starter had a circuit diagram pasted inside, a bit tatty but that is what I based my write up on. Maybe yours has too and you can see if it is essentially the same or different. Chris's motor was not labelled as Stayrite so I think it might not have been paired with the Stayrite starter originally. The wiring was bodged with six red wires threaded up some garden hosepipe (Not by Chris I hasten to add!) but (bless him!) had just cut through the lot so it was a detective job to work out what was what in the first place. Hence connecting lightbulbs to the starter first to watch what happened.

Apologies if I have introduced noise into the discussion……. It was not intentional

Bob

[Phil WhitleyParticipant @philwhitley94135]

Hi Bob, no problem, when I was serving my apprenticeship (late sixties in East Yorkshire) as an electrical engineer, there were a couple of remote farms that used, and for all I know still use , a 2 phase system. I remember lots of big capacitors, some for starting, and some for PFC,I also remember we had to search the country for motors and starters to install a fairly simple mill and mixer set up to produce animal feed from the farmers own crops. I believe it was derived from a line transformer situated on an 11kv line, but cannot remember the exact details, although I do remember the voltage rating of the motors was higher than the normal 415 volts from "normal" three phase. I think it was 460/480, but it was a long time ago!!

Phil.

[Phil WhitleyParticipant @philwhitley94135]

PS, I liked the light bulbs idea,, very old school, safe, and it works! We used to carry test lamps for that very purpose, used to put one on each phase line connected between phase and earth, then start all the motors, and see if we could detect any flickering under load, which was usually an indication of bad line tap connections on overheads or elsewhere. We used this met5hod of fault detection with installations that were constantly blowing the same phase fuse, but had no apparent motor or control gear faults.

[Phil WhitleyParticipant @philwhitley94135]

Incidentally, I wasn't the OP .My Covmac uses a variable speed single phase induction repulsion (commutator) motor, which must be 1930,s vintage, and weighs in at about 3 cwt!

[Phil WhitleyParticipant @philwhitley94135]

[Phil WhitleyParticipant @philwhitley94135]

http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=38062 This is a fairly good explanation of 2 phase (they call it split phase, and they are the IET, so they should know (LOL) Derived from a transformer on a single phase MV line.

[Ralph HParticipant @ralphh]

I saw this on ebay today for those interested, it is another of their seemingly rare lathes.

**LINK**

[duncan webster 1Participant @duncanwebster1]

It claims to be still in use. Up in the frozen north we tend to keep our machine tools indoors when in use, but I suppose effete southerners (is Leicester in the south) can work 'au dehors'

[Brian WoodParticipant @brianwood45127]

Hello Duncan,

​Leicester is in the Midlands and any drive down South on the MI passes nearby in the area after Derby/ Nottingham. Distance from London is about 100 miles.

There is a service area called Leicester Forest East. It is certainly not in an area of the country where global warning is encouraging the spread of vineyards!

Regards
Brian

[Phil WhitleyParticipant @philwhitley94135]

Yes, that is the big one I think the 17" geared head model, looks in good nick, and it seems to have the war finish plaque on it, which will reveal who actually made it, but can't read it from the pictures, more at http://www.lathes.co.uk/covmac.

Phil

[john fletcher 1Participant @johnfletcher1]

Hello Phil and many others. This has been a very interesting read regarding both lathe and the motor. You are correct Phil re the 440/480 volt motors, there were quite a few in the Scarborough area. I think the pole mounted transformer were know as the Scott connected type. 11KV input and 440/480 two or single phase or call what you will out. If you have access to JOHNSON & PHILLIPS transformer book there is an explanation on the transformer side of things.John

[Phil WhitleyParticipant @philwhitley94135]

Interesting John Fletcher, now you mention it, I remember a, installation on a farm at Broxa, out on the moors near Scarborough, which I think was split phase, and to tie right back to Covmac, my Covmac came from Andrews motorcycles in Scarborough!

Phil

[john fletcher 1Participant @johnfletcher1]

Hello Phil, there was a lot of split phase around Cloughton and Ravenscar. and on the farms up in the Whitby direction The Duchy of Lancaster saw mill was split phase. You could see the small unusual pole mounted transformer, with 11KV input, that was in the days of YEB and NEEB of course. OK about Andrew's, motor bike shop, we have bought several Honda 90 from them when Nick was the owner. Changed hands about 5 years ago when you bought your lathe from, can't remember his name, Dave Whittaker! . The lathe saga has been very interesting. Its good when people help each other out and share experiences.John

[Phil WhitleyParticipant @philwhitley94135]

I bought the lathe from Nick Andrews who was in the process of transferring the business to some other guys, Nick had a lot of other engineering gear of his dads(?) which he was goning to get back to me about, but I lost touch with him and it never happened, Also bought a B&D valve refacing machine from him, it was in poor condition, with some bits missing, but I am still thinking about converting it to grind lathe tools, if it works! It is a winter project which may get done this winter as my massive workshop rebuild is almost finished!

Phil

[CHRISTOPHER MILLS 1Participant @christophermills1]

Phil,

I have just noticed, or recalled, that the top speed of our CovMac 13" lathes is just a chugging 335 rpm?

What are the limitations of such a modest top speed?

It compares badly to my Lang Junior, a similar sized machine, which will go nearly 1000 rpm.

What work can we do with these go-slow CovMacs, when we have them running?

Chris

[Brian WoodParticipant @brianwood45127]

Hello Chris,

​If you still have the Holbrook gearbox, I'm pretty sure that could be built into the drive chain somewhere between the motor and lathe to double the speed as required for those occasions when it is needed.

A little ingenuity is about all it takes. I can't believe the lathe itself couldn't handle that

Brian

[Phil WhitleyParticipant @philwhitley94135]

Hi Chris and Woody,

The limitations are not that important really, as we are not manufacturing hundreds of identical parts at piece rate! the only real problem and it can be got round, is turning to a fine finish. The usual way to get this is high speed, fine traverse feed and a light cut. All you need to do is work within the limitations of the machine, and you will get approximately the same finish, but it will take marginally longer! When running a machine faster than its design speed, you have to consider that these lathes have plain bearings, which would need greatly increased lubrication, maybe in the form of a drip oiler, and also the condition and weight of the chucks and faceplates. My faceplate has so many blowholes in the casting that I don't even think I would risk it at 335rpm! The forces on a lump of poorly balanced cast iron at 335 rpm are considerable. Therew are stories of overspeeded chucks bursting with centrifugal force, whilst I have no experience of this, I would not wish to be in the same building when it happened! These lathes were used during wartime, and I am sure they managed to produce components adequate for the very demanding tasks required. Don't worry about it untill it becomes a problem, and if it does, you can always step across the workshop to a different lathe Part of the fun of engineering is thinking of inventive ways round the problems we are faced with!

[Ian S CParticipant @iansc]

HSS tools, a good size chunk of steel, and a good depth of cut and 335 rpm, it will remove quite a good amount of metal with a good finish, it's not made for watch making, it would be happier with a 6" bar of steel in the chuck.

Ian S C

[Phil WhitleyParticipant @philwhitley94135]

+1 wot Ian SC said!!

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