CovMac Lathes

Michael,

Thank you. I have experience cleaning old rifles with WD40 & wire wool, but the chucks are more than I have ever dealt with, rust-wise.

The were stacked (four of them) toward the outside wall of the shed, and as you get towards the wall, the chucks show more and more rust, until the last one, a pretty, deep red, with a fur coat, same colour. It is solid, but has no visible deep pitting. I hope I can save it.

You Tube shows de-rusting with electrolysis - using a car battery charger, a tank of water & washing soda, and four old steel rods as electrolytes. This looks a pretty effective method. Worth considering?

I will certainly try the plus-gas, first.

The CovMac story will run - these Coventry made lathes are rare survivors: I have evidence for only six, so far.

I will complete the move in a few weeks time - the seller has to clear access for me - at present the way is blocked by a couple of tons of scrap iron.

Incidentally, is the wooden clutch handle, running the length of the lathe on a CovMac, unique to the make? I have never seen it on any other lathe. It is an oddity, in my limited experience.

I will do a comprehensive renovation, cosmetically. I believe the working bits are probably mostly okay. One of the levers on the feed gearbox is solid.

Chris.

Here is a more detailed photograph of my CovMac's headstock. The right hand lever on the feed gearbox is solid. The left hand one works fine, and the gearbox turns okay, when you rotate the chuck. The lever is either a speed changer, or a reverse?

The patch of darker colour on the headstock, under the big speed lever on the top, is, I believe, the lathe's original colour, darker than its battleship grey repaint. I wish to restore it to that original colour. 

Chris.

Edited By CHRISTOPHER MILLS 1 on 19/09/2014 09:34:12

Hello Chris,

I have successfully cleaned up chucks and other pieces with wire wool and light oils, Scotchbrite pads are also helpful with a gentle abrasive action to polish up otherwise cleaned surfaces.

Michael G's tip about wicking in penetrating oil is the way to go, with or without heat to help it. You can also use a paint stripping heat gun to advantage, although flame is quicker.

If you can lock the spindle against rotation to remove the chuck, I would stongly recommend unscrewing it using a bar across the bolting on the back plate as a lever and shock it free with a clout on the end. Don't use the chuck key, it might work but if not you are likely to break off the square or worse, split the square socket in the chuck body.

I can't advise on the freeing off on the top lever that is solid other than trying gentle persuasion with a rubber faced dead blow hammer in both directions on the end to promote some easement. Without knowing what it moves internally I wouldn't go beyond that without opening up the head after you get it home.

I think there are quite a few.of us watching this thread with real interest now, it will become a saga. I tried to view the Covmac page on Tony Griffith's excellent lathes website today just from interest, it refused to load up----adjacent entries loaded without any hesitation, so maybe he is working on that with some updates.

Once again, thank you for an interesting and developing story, I feel sure it will all have been very worthwhile in the end.

Last thought---do you have 3 phase available to run it? Not only is the motor huge, it will be big capacity with an appetite to match.

Best wishes Brian

Hi Brian,

Tony's website has a permanent probelm on the CovMac page, but you can access it another way. Try Googling "CovMac lathes" - you should see Tony's "Covmac Title Page" - I always get in that way. Let me know, if you cannot, I will give the precise HTML address.

The motor on my Covmac is actually single phase. I am sure it will use a lot of electrcity, though; it is a massive motor.

The chuck on the machine it fine, it is the loose spare chucks I am wanting to re-rust.

Many thanks for your further tips. The advantage of beginning something in middle age, is that you have the widsom to understand how little you know, and not being shy to ask the way.

Best.

Chris.

Brian - There is the motor. A very big one, but single phase, so far as I know: It is certainly on a conventional three-pronged plug.

A family of spiders surely lives in the motor. I am going to turf them put in a couple of weeks.

Best,

Chris.

You may well find the stuck lever will move when the other lever is in one position only or once the lathe has run. Harrison's can be a bit like that. Force last resort.

SteveW

Useful information Chris, it took me straight there.

I have read it through. The wooden bar that puzzled you operates a clutch on the outside of the headstock, running it overhead allows the operator to use it anywhere along the lathe. So, an original feature for you to preserve.

There is a very helpful picture of the open headstock with the lid off; the left hand lever selects the speeds, three of them I think, the right hand lever [the seized one on your machine] is a reversing lever, in use it operates a sliding dog clutch on the main spindle just behind the chuck end of the headstock. That will have enjoyed oil splash in running, so I imagine the handle pivot through the lid of the headstock is where the tightness lies. It should be easy enough to free off with the cover removed and access for penetrating oil from both sides.

You surprised me with the motor, I hadn't expected single phase. I hope when you are ready to run it you will at least be using a suitably rated no-volt release starter, I could see the 3 pin plug in your picture Yuk big time. Others on the forum will no doubt recommend a modern 3 phase inverter drive instead,. It gives a much better level of control along with variable speed, much depends on how close to original supply you want to be. In any case I would get the motor properly checked out if you will be using it, wiring 70 years old is likely to have deteriorated badly and could well be 'leaky' now. It will certainly make itself felt with the starting current it will need. lights will dim briefly.

When you are ready at the appropriate stage I'll do what I can to suggest ways of using the screwcutting gearbox for threads like metric and perhaps others; a lot will depend on what you find in the way of change wheels. I will need some simple information on the gearbox itself, internally that is, to work from.

Enough for now I think

Brian

Edited By Brian Wood on 19/09/2014 14:26:08

Many thanks, SteveW -

Brian - the seized lever is actually on the feed gearbox, not the main spindle gearbox. It is the lever on the right in the very bottom of the headstock picture.

It seems seized, as all the others have a spring action, before you move them, and in this one there is nil spring, it seems completely solid.

I will get the wiring on the motor sorted by a competent electrician. I thought an inverter was strictly to convert a three phase machine to run on single.

I will investigate no-volt release starters.

Somebody told me the older motors are better than new, if you have them rewound and brought up to modern safety standards. I am aware a metal lathe is a large item, and metal conducts electricity. I do not wish to fry myself.

This lathe, originally, was not a high speed machine, I think Tony's website says it has an upper limit of 450 rpm.

I will not be using it a huge amount; this is more of a museum project. I want to restore it, and understand how it works, etc, and do some small amount of work on it.

Saving it, as a piece of industrial artwork, was my priority - also for its wartime history. ( I am a military historian). This was a War Department lathe, and still has its original War Department serial number, on a brass plaque on the tailstock bed.

As far as I have been told, by the son of the man who owned it, it was regularly used, for Ministry of Defence work, making Chinook helicopter components, into the 20th Century. I think the old chap stopped using it regularly as late as 2004. So, it must still be in pretty reasonable shape, if it was fit for such precision work in the 21st Century.

I am very proud of it, already!!!

Best.

Chris.

Hello Chris,

My mistake, sorry.

Usually screwcutting gearboxes have a cone of gears inside which govern the 'basic core' of gearing, yours will have 7 gears if the website picture and Tony's description are true of this model. Those are accessed by the ramp shaped slider control on the left. Pull out the [probably knurled] knob, slide to the TPI group required and release to hold it in the dimple under the ramp slot to lock in place.

The second lever is likely to be a quadrant action perhaps labelled A,B and C to select the multiples of the selected core TPI; these are always X2 or divided by 2. It operates in the same way, pull out the knob, move to letter choice, release knob. Try soaking it with pentrating oil, even to the point of immersing the knob overnight. Twisting the knob while pulling may free if off. It works internally by moving a dog clutch between the gearing multiliers. If all else fails you can take the cover off to work on it. There might be a spring loaded detent ball built into the operating arm inside, bear that in mind.

Tony's website states that there were 28 ratios available, thus far we have identified 21. The final 7 will come from a gear change in the drive to the gearbox, again a multiple of 2 to give the final set of ratios. Depending on what is still fitted, you should be able to sort out what you have from the plate on the gearbox.

It is true, older motors are almost indestructible, but get it checked out anyway. Yours, the lower power version ran at 750 rpm, which suggests it is a multipole unit to get down to that speed. That might explain it's size as well. Take it to a decent rewind firm for their opinion. It may well be absolutely fine, but earth leakage checks with a Megger tester will pick out any weakness. Having been in use until relatively recently it is most unlikely to have any open circuit conditions, my concern was leaving it in close proximity to the outer asbestos sheet wall of the shed where there would be the risks of condensation inside it from humidity changes. A sheet wall like that isn't noted for keeping things dry nearby, look at you cxhucks for example

The inverter drive option runs a 3 phase 240 volt motor from single phase, the motor is not the industrial 415 volt 3 phase version.

End of sermon for today!

Brian

Brian - I may be quiet for a day or two.

My beginner's brain has exploded.

Have a good weekend.

Chris.

Have I overdone it Chris!!!

LOL

Brian

Brian,

You need to know that I failed my maths O Level! Had to re-sit it.

Subsequently dropped all maths, and maths-related, at 17.

Best.

Chris.

Perhaps a clue is there for the stuck CovMac lever: The plate behind the right hand lever, (the culprit), with two holes, was actually painted over in the lathe's battleship grey repaint, unlike the plate behind the left hand gear change lever, which was left bare metal. Could it be that this right hand lever was never much used, and was regarded as redundant by the time the lathe was repainted? The left hand lever, when you pull on it, and has a nice spring in it, then moves - right hand lever has no spring, and simply seems totally solid.

Chris.

Edited By CHRISTOPHER MILLS 1 on 20/09/2014 10:49:42

Edited By CHRISTOPHER MILLS 1 on 20/09/2014 10:50:39

Hi Chris, Is the knurled knob on the right hand scewcutting lever able to rotate? If it isn't and the knob won't pull out against the spring, the pin will not release from the hole, and it will not move, I am going to my workshop later, I will check on mine.

Phil

Hello Chris,

First of all, my apologies, I can get rather carried away with enthusiasm and the minutae of technicalities which can become a bit full on to those battered by it. I will try and limit the responses in future!.

Your picture rather knocks my earlier thinking, I can see a hole recess peeping out on the extreme right, that will be the alternative position from the one it has frozen into. It might then be to couple/decouple the drive to the carriage feed rod, that is also driven from the gearbox.

In which case how are the gearbox selectors arranged I wonder? I don't see any other likely levers. The brass gear box plate will give clues to that puzzle.

Phil will no doubt be the man to resolve it.

Brian

Hi Chris, Is the knurled knob on the right hand scewcutting lever able to rotate? If it isn't and the knob won't pull out against the spring, the pin will not release from the hole, and it will not move, I am going to my workshop later, I will check on mine.

Phil

OK, I Bin an gon an Dun it!

here are a couple of pics, you can see the amount it needs to pull out to disengage the pin from the casing, mine moves freely between the three positions without having to turn the gearbox over, but yours has been stood a long time and may need a turn to free the gears, The knurled knob should rotate freely, and pull out approximately 3/4"

Phil

Phil,

Many thanks for going to this trouble - I had not realised until I saw these pictures that there are three positions, A, B and, presumably, a neutral in between.

I will get the Plus Gas onto my lever!

Best.

Chris.

Hello Chris,

Blowing up Phil's picture which also shows the brass plate on the gearbox, the A and B selector positions are clearly visible and relate to thread counts on that plate.

I can't figure out yet what the central position between A and B was for, a neutral possibly as you think. It is odd.

That is normally achieved from a mid point in the reversing cluster down from the gear on the end of the headstock spindle; you will see that bit inside the door covering the change wheel enclosure.

Good luck in getting that bit freed off again, it will behave eventually but might need some heat and a good soak in Plusgas to show it who is boss.

Brian

Edited By Brian Wood on 20/09/2014 16:46:20

No trouble Chris, I was going anyway, we had a torrential downpour last night and I wanted to pick up all the "rainfall" apples and take them to the cider man! Also showing the latest progress to the wife!

Phil.