CovMac Lathes

[Ian S CParticipant @iansc]

Neil, that's a nice little lathe. I see it does not have the on/off, and reversing switches, have you got the motor, and foot control?

Ian S C

[Gordon WParticipant @gordonw]

It'll be perfect with CNC fitted, and DRO's on all axis.

[CHRISTOPHER MILLS 1Participant @christophermills1]

Now the CovMac is safely under the Christmas tree, might I wish all you engineers a very Merry Christmas, and a Happy New Year!

Many thanks for all your help in 2014. It was a very great deal appreciated.

[9fingersParticipant @9fingers]

I've not posted in this thread to date but have been involved with Chris's COVMAC lathe assessment and move since being introduced via a mutual friend.

I've been working with single and three phase induction motors for very many years but finding this one with 5 power connections and a separate controller was a new one on me and also a couple of friends older than I.

I now have the motor and controller on the bench and had some time to investigate it thoroughly.

There are a total of 6 terminals each going to the ends of 3 three separate windings. One of these is the Start winding marked Z1 and Z2 and the other two winding are both used for Run A1-A2 and A3-A4. It has no internal capacitor or centrifugal switch.

If you come across one of these motors then it is vital that a standard direct on line (DOL) starter is NOT used.

The regime for starting these motors is to connect the run windings in series and momentarily connect the start winding with a series capacitor in parallel with the run windings. Once the motor is up to speed, the controller disconnects the start winding AND switches the run windings from series to parallel.

As far as I can tell, this series parallel switching is there to keep the starting current reasonable. Even so the peak start current on this motor (3HP) is 34 amps before settling down to just over 10 amps once running.

Full load current is specified as just over 13 amps.

 

I will be supplying Chris with full documentation of the motor and controller. If there is interest here, I can publish it here too if I can workout how to insert files.

Cheers

Bob

 

Edited By 9fingers on 27/12/2014 17:06:39

[Phil WhitleyParticipant @philwhitley94135]

Hi 9fingers, I would be interested to see the motor/ starter sort out! This is why I emphasised to Chris how important it was to get the original starter with the motor. It is an AEI Stayrite, and looks like it is the right one for the series parralell capacitor start. I have been in electrical engineering since 1967, and although these were not common, we did used to meet them on things like original Heidelberg printing presses which had been fitted where 3 phase was not available. There is nothing similar in my "Brooks" motor book, but I gather Chris marked the terminals when he disconnected the motor from the starter, so it should be a matter of servicing the starter and reconnecting as was. Capacitors in these installations are sometimes fitted in the starter itself, and switched in when needed. In the meantime I will have a rkae around my old paperwork and see if I can come up with any diagrams.

Phil

[CHRISTOPHER MILLS 1Participant @christophermills1]

Bob and Phil – Many thanks – and Happy Christmas to you both.

So, I can see now that the previous owner of my CovMac was just about managing to run it on a 13 amp plug, on its 10 to 13 amps normal running range, but how can his house electricity, on a 13 amp plug, have coped with 34 amps starting power?

When his son tried to start it, for me to see, on my first viewing, it blew the fuses, and he tried again, to no avail. It blew twice.

[Phil WhitleyParticipant @philwhitley94135]

Hi Chris, when you say it blew a fuse, do you mean a fuse in the 13A plug?, not surprising really, you will need a seperate circuit wired back to your consumer unit and rated at 35 or 40 amps. Not a problem, as some modern electric showers draw this region of current and because of the clutch on the input shaft of the covmac, you will be starting the motor off load. There is a long way to go before you need to press the start button!

I am having a day off eating tomorrow!!

Happy Christmas!

Phil.

[CHRISTOPHER MILLS 1Participant @christophermills1]

Phil,

Have you put on weight, this Christmas, ol' son?

Best. Chris.

[9fingersParticipant @9fingers]

Posted by Phil Whitley on 27/12/2014 20:05:39:

Hi 9fingers, I would be interested to see the motor/ starter sort out! This is why I emphasised to Chris how important it was to get the original starter with the motor. It is an AEI Stayrite, and looks like it is the right one for the series parralell capacitor start. I have been in electrical engineering since 1967, and although these were not common, we did used to meet them on things like original Heidelberg printing presses which had been fitted where 3 phase was not available. There is nothing similar in my "Brooks" motor book, but I gather Chris marked the terminals when he disconnected the motor from the starter, so it should be a matter of servicing the starter and reconnecting as was. Capacitors in these installations are sometimes fitted in the starter itself, and switched in when needed. In the meantime I will have a rkae around my old paperwork and see if I can come up with any diagrams.

Phil

I've all the diagrams in visio and instruction .doc files – all I need is a way to upload the files to this forum. Any ideas?

I'll possibly use .pdf for maximum readability for here though.

Eventually I'll write a new section to this as my collected work on induction motors

http://homepage.ntlworld.com/bob.minchin/Induction%20motors%20-%20Issue2.pdf

Bob

[CHRISTOPHER MILLS 1Participant @christophermills1]

Hi Bob,

I think this website will only accept Jpegs as visual inputs.

Best.

Chris.

[9fingersParticipant @9fingers]

Posted by Phil Whitley on 27/12/2014 20:29:56:

Hi Chris, when you say it blew a fuse, do you mean a fuse in the 13A plug?, not surprising really, you will need a seperate circuit wired back to your consumer unit and rated at 35 or 40 amps. Not a problem, as some modern electric showers draw this region of current and because of the clutch on the input shaft of the covmac, you will be starting the motor off load. There is a long way to go before you need to press the start button!

I am having a day off eating tomorrow!!

Happy Christmas!

Phil.

I've only been starting off load – not even a belt so a 13amp fuse will supply the 34 amps for a short while.

Ultimately I will recommend a 32amp commando plug with a type c 20 or c 32 amp MCB for the installation.

Bob

[9fingersParticipant @9fingers]

Posted by CHRISTOPHER MILLS 1 on 27/12/2014 20:50:22:

Hi Bob,

I think this website will only accept Jpegs as visual inputs.

Best.

Chris.

OK when I have the write up complete, I'll add it as a new appendix to my motor paper and link it here.

I'll also send you you own copies of the individual documents. I now have all the instructions in word format after doing OCR on photos of the insides of the controller.

Bob

[CHRISTOPHER MILLS 1Participant @christophermills1]

Sorry Phil, about the fuse blowing – When I first saw the lathe, it was run straight into the Stayrite starting box from a three pin plug on the house supply – but I do not know what rating fuse it had in there.

[Roger Williams 2Participant @rogerwilliams2]

Hello all, Chris, you will have probably had this suggested before, but have you considered changing to 3 phase with an inverter. My DSG had a new motor fitted ( badly !) just before I bought it, so the original 5hp motor (might have been 7.5hp) was scrapped. The new 5hp motor ran off a RPC ( which was not up to the job ) so I took a chance, reduced the size of the motor to 3 hp, bought a VFD, which gives plenty of power, all off a standard 3 pin plug.Save a lot of trouble !.

Regards, Roger.

[CHRISTOPHER MILLS 1Participant @christophermills1]

Hi Roger,

Many thanks – all points taken into consideration – but now that I know from Bob Minchin that the motor looks to be in reasonable shape, I will almost certainly stick with it, being the lathe's original.

It is a very handsome piece of work, by English Electric, complementing the lathe as a museum project, and I would not like to see this aspect abandoned.

Having said this, I certainly do not intrinsically like the Stayrite Box, and might have to disguise or hide that.

The Box is hard to date – nobody yet can put an accurate date to it, but I feel it looks of a 1960s/'70s ilk to me, likely not with the lathe when it was made in the 1940s.

Having said that, perhaps the Stayrite Box might have emanated from the lathe's reconditioning, of 1955? In which case it becomes a bit more tied into CovMac history.

Would you please show us a few more details of your rather handy chuck crane you use on the DSG? I will need to make one, for handling both the big faceplate, and for mounting and dismounting the motor.

When can I come and "have a go" with your DSG!!??

[9fingersParticipant @9fingers]

I have to agree with Roger, that a VFD and three phase motor is by far the best solution for a working lathe. I can't imagine anyone wanting to revert to fixed speed powered lathe (or mill) having used infinitely variable speed drives.

However i can see Chris's point regarding historical accuracy. If the AEI Stayrite is not original then the EE motor would have needed something similar although I'm not totally convinced that a single phase motor would have been fitted to such an industrial lathe originally.

My hunch is that it could have been converted to single phase operation when it was refurbished in 1955 and the AEI Stayrite fitted then. I've not found anything internally to date the box. Usually capacitors are dated if nothing else but curiously not in this instance. They are made by DALY – a name from the right era – and don't look like they have been changed from original manufacture of the control box.

Chris's point about hiding the control box away is viable as provision is made in its construction to have remote start and stop buttons wired in. A DOL starter of "correct age" could be re connected internally to provide this function and look the part.

Bob

[Roger Williams 2Participant @rogerwilliams2]

Chris, Ive only got one other picture of the crane, so hope this is of use. I pinched the idea off the American Skyhook version, which bolts to the crosslide, but somewhat "iffy" because of the weights involved in my view. I welded a couple of lengths of 1 3/8inch pipe to an upright, with an adjustable bar and a pulley at the business end.A bracket is bolted permenantly to the lathe with an inch diameter bolt sticking up, so the whole lot just slips onto it when needed. A trailer winch completed the crane, with a "c" hook for the chuck, Skyhook fashion. You can play with the DSG anytime.( will PM address !.) Roger.

[9fingersParticipant @9fingers]

I've now completed my investigation and documentation of Chris's COVMAC motor and associated AEI Stayrite series parallel starter.

The details have been incorporated into the latest version of my motor paper at Annex G

The current version can be downloaded from here:

http://homepage.ntlworld.com/bob.minchin/Induction_motors_Issue3.pdf

I hope that it will be of interest.

Cheers

Bob

[Brian WoodParticipant @brianwood45127]

I for one am very grateful that Bob 9fingers has taken the time and trouble to unravel the mysteries of the motor/controller combination used on this lathe, then documented it for us all so thoroughly and explained in some detail his simple and very positive methods of working to sort it out.

It may not be of direct use to me as I am unlikely to need to power up a motor of this type, but the knowledge is now there for us all to use if the need arises.

This old Covmac lathe has produced some rather interesting side stories which might not have surfaced otherwise.

Brian

[9fingersParticipant @9fingers]

Thanks for your kind comments Brian.

I enjoy solving puzzles and jobs like this motor help keep the little grey cells working.

Bob

[Phil WhitleyParticipant @philwhitley94135]

cracking good work Bob!

[BikepeteParticipant @bikepete]

Looks like the ebay 17" Covmac ended unsold… last chance perhaps for someone to contact the seller and save it from the scrappie…

[Neil WyattModerator @neilwyatt]

It would fit in my workshop, but then nothing else would.

Perhaps a museum or two should be contacted?

Neil

[CHRISTOPHER MILLS 1Participant @christophermills1]

My feeling is that at £750, this chap is not yet near scrapping it, and it might reappear at a lower price. Scrap value must be about £200.

It is a rarity, but it is such a big lump to move and store.

I have considered it, but 80% of it is identical to my 13" model, and it is missing its gap piece, rather a major loss, if contemplating a sympathetic restoration.

It is hard to know if the headstock has been butchered, too, with those front mounted electrics.

I wanted pictures of the remaining coolant system, but the chap did not even bother to get back to me.

Let us hope it does not get scrapped, that would be a real shame on a machine so rare.

[Ady1Participant @ady1]

I have considered it, but 80% of it is identical to my 13" model, and it is missing its gap piece, rather a major loss, if contemplating a sympathetic restoration.

Someone with a big shaper would probbly help you once they see the size of the project you are willing to take on, especially if you could supply the lump of cast iron

 

Edited By Ady1 on 11/01/2015 13:11:14

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