Myford S7 jamming when using live centre

[Thomas GudeParticipant @thomasgude37285]

[Thomas GudeParticipant @thomasgude37285]

Hello,

This is not the first and certainly won't be the last post I will make about my mkI Super 7. I really appreciate everyone's patience and input. Goodness knows how slowly I would be progressing if it weren't for the internet.

Aaaanyway, when engaging the live centre when the part is revolving everything goes well. However if I engage the live centre when the part is still or dis-engage the clutch to make an adjustement and re-engage to carry on cutting the motor driven V-Belt spins, continuously slipping on a stationary countershaft Twin V-Pully (v. horrible!!) as it is unable to overcome the moment of inertia.

Power off – I try to spin the chuck by hand – no luck. Try to spin the chuck with a chuck key – sometimes get it loose. More often than not I have to dis-engage the live centre and get it moving. It seems the force of the centre pushing the chuck and headstock jams up the headstock completely, at first I thought I had accidentally left a gear engaged somewhere!!

I don't think I am over tightening the centre into the part, as it were, as I have done the same on the ML7 at work and it is fine.

Any advice is, of course, much appreciated.

[Jeff DaymanParticipant @jeffdayman43397]

Not sure what the thrust bearing arrangement is like on your lathe, but it sounds like it is not doing its' job of supporting end loads. I would look for it and clean it out then re-lubricate it. Many lathes I have used have this bearing just inboard of the left headstock bearing.

I recently replaced the ball thrust bearing on my 65 year old and well used South Bend lathe as I was getting clicking noises when drilling from the tailstock. The replacement bearing was a radial needle type with hard ground washers each side. It works very well and was not expensive. I bought the bearing and washers from McMaster Carr in the USA. Link to catalogue page is below. No more noises. These bearings will carry thousands of pounds of end force so for manual lathe applications will more than do the job for a very long time. JD

http://www.mcmaster.com/#5909k39/=qg38dp

[Martin KyteParticipant @martinkyte99762]

Sounds like out of adjustment bearings. The pressure from the live centre is reducing the front bearing clearance to zero. Carry out the following as per Myford (Nottingham) practice.

1. Power Down

2. Remove all belt tension.

3. Remove Chuck

4. Rotate RH collar one complete turn. (top towards you).

5. Rotate LH collar one complete turn. (top towards you).

Spindle should be completely free of front bush.

6.Loosen allen screw on collar at end of spindle.

7. Using the Allen key tighten collar as tight at it will go by hand.

Inner tapered roller races are now locked together with correct pre-load.

8. Back off LH collar one complete turn + a bit (top away from you)

9. Rocking the spindle by holding the spindle nose tighten the RH collar by hand (top away from you).

10. When you feel resistance to movement stop.

11. Collar should be just tight enough that spindle can just be moved by hand holding the nose.

12. Do up the LH collar by hand (top towards you).

You should still feel resistance when turning the spindle by the nose.

13. With the crescent wrench on the LH collar tap the end smartly with a 12oz hammer.

The spindle should move forwards by a couple of tenths and be completely free running.

14. With the lathe running slowly (lowest direct speed) put the oil gun in the front oil cup and pump until oil issues from the front bearing. (It comes out of the back and is sprayed around by the bull wheel at least it did on mine)

15. All should be sweetness and light with great rejoicing in heaven and on the earth.

regards Martin

[DMRParticipant @dmr]

Thomas,

It certainly sounds like your twin angular contact rear bearings are not set correctly. All assuming there is oil getting to the front taper journal? Was the mandrel getting warm/hot at the front end?

You have the later manual but the setting up of the mandrel is the same for the early drip feed oiler. you need to study the section HEADSTOCK SPINDLE BEARINGS (about page 23 in the manual) and go through that set up. You need one and preferably two C spanners. It is hard going trying to use a screwdriver in the castelated nuts! Not difficult to make one but it is a sawing/filing job.

No offence to Martin but I have never used a hammer (item 13) and there is no "oil cup" (item 14) as he describes. Just follow the manual.

Dennis

[Martin KyteParticipant @martinkyte99762]

The instructions I gave were from Malcolm (original Myford Ltd) and that was how they set the lathes up at the works. They don't originate from me but from the manufacturers and if they don't know how to do things no-one does. Super7 Bs are fitted with an oil cup to feed the headstock bearing via a felt wick which is why item 14 was included as these were the instructions I was given when I replaced my thrust bearings. I have a Super7B. Please feel free to use the instructions I gave or the ones from the Manual. They both originate from Myford. The gentle tap with the hammer just gives you the tiniest bit of extra movement to push the front bearing clear so it runs freely.

regards Martin

[IanTParticipant @iant]

Hi Thomas,

I have a Mk1 Super 7 and agree with others here that it sounds like the spindle bearings are a little out of adjustment. You will need a thin 'C' spanner to get at the appropriate adjustment (locking ring) and I assume these spanners are still available from (new) Myford.

The adjustment is pretty straightforward but I found it useful to have the drawings of the headstock (helped me to understand what's going on) and to follow the step by step guidance in the Myford maintenance notes. I have these for the Mk1 S7 and if you want the two pages scanned and sent as a PDF to you – please PM me.

Regards,

IanT

[NobbyParticipant @nobby]

Hi Thomas & Guys
Adjustment is required as Martin & others have said . Ian's right you need one of these
Nobby

[Rick Kirkland 1Participant @rickkirkland1]

I was confused when reading this thread until I realised the writer was talking about a RUNNING CENTRE as opposed to a LIVE CENTRE. If at first it confused me please consider others reading this forum who may end up with the wrong idea as to what a live centre is. The live is the one which is not hardened and sits in the headstock spindle, for the benefit of the uninitiated.

Rick

[Thomas GudeParticipant @thomasgude37285]

DOH!! The annoying thing is I questioned myself when writing the post so I did a quick Google image search of "live centre" and it came up with a whole load of images of running centres. Shows you can't rely on anything.

I wonder if I can edit the topic…

Thanks everyone for the advice, pretty comprehensive I will give it a go once I have received the plans and spanner. I will reply to the PMs also.

FYI my S7 is SK5874

[NobbyParticipant @nobby]

Hi Guys
As Rick says Here is a live centre . When in chuck as it is soft can be turned true using top slide set at 30 degrees
Nobby

[blowlampParticipant @blowlamp]

As far as I'm aware, a live centre is one that doesn't use the workpiece as the bearing for its rotation.

Martin.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by blowlamp on 29/01/2014 15:40:09:

As far as I'm aware, a live centre is one that doesn't use the workpiece as the bearing for its rotation.

Martin.

.

That's a nice logical definition, Martin.

MichaelG.

[Thomas GudeParticipant @thomasgude37285]

Hello,

So I have bought said C spanner – **LINK** and toay set about to do the task in hand and I have fallen over at the first hurdle!

I cannot, for the life of me, get the C spanner to turn the collar. The collars are stuck fast and the spanner keeps on slipping out and sometimes damaging the spanner and probably the collar as well (I cannot see the position it locks into so have no way of telling). As I understand it, the spanner can only be used one way so for Nobby's picture it will be used anti-clockwise as looking at the photo. That is fine and to undo them as instructed it is positioned the opposite way round. But the fact that I am getting no where fast is not fine .

I'm not sure how much advice anyone can give me from here. But any pointers are very welcome.

Thanks

[NobbyParticipant @nobby]

Hi
My picture shows I am about to release / undo the nut. Thomas at this stage just give the spanner a sharp tap with a hammer not a soft one .
Nobby

[Thomas GudeParticipant @thomasgude37285]

Hi Nobby,

Does that mean it will turn clockwise as looking at the photo? I originally tried it like this and it messed up the spanner. If you say this is the case though I will try again.

[Thomas GudeParticipant @thomasgude37285]

Sorry Nobby I mustn't be on the same wavelength. I tried using it the other way round and I cannot see how the spanner could work if the "tab" & "shoulder" parts weren't both engaged. Either way the tab keeps popping out and it doesn't grip so I think the nut may be too worn. I think I'll try and source a strap wrench of the right size and see where I get with that.

(I wouldn't be offended if the mods wanted to move this to the beginners section lol)

[Michael GilliganParticipant @michaelgilligan61133]

Thomas,

Forgive me if I am stating the obvious ...

Nobby's photo shows the C-Spanner "not yet engaged"

When correctly engaged, the spanner wraps around the nut [with Nobby's spanner, nearly half way round; with yours, rather less] and, if correctly sized, will lock itself in place whilst in use.

MichaelG.

[Terence Yates 1Participant @terenceyates1]

Thomas, give it a heavy smack anti clockwise with a hamer and piece of brass rod in one of the cut out sections. Did this on mine after faffing around for hours. IT WORKED

Terry

[Thomas GudeParticipant @thomasgude37285]

Posted by Michael Gilligan on 09/02/2014 20:59:31:

Thomas,

Forgive me if I am stating the obvious ...

Not at all! That's how I've been using it but it still slips and doesn't manage to grip the nut. I got confused because Nobby said that photo the nut was being loosened but the instructions are the other way round…

Right on Terry I may just give that a go

[Terence Yates 1Participant @terenceyates1]

Thomas, on Nobby's picture, in front of the c spanner is a screwed round collar with a screw in it. Loosen the screw and unsrew it anti clock wise first before you hit it with hammer. That locks it all up.

Terry.

[Michael GilliganParticipant @michaelgilligan61133]

Probably superfluous, but

I've just found a PDF of the Super 7 manual, here.

MichaelG.

[Les Jones 1Participant @lesjones1]

Hi Thomas,
As the locking ring seems to be so tight it may be worth making sort of a box spanner with 4 pegs to mate up with the notches in the locking ring. If I was making it I would machine it from about a 1" length of solid bar and weld it to a length of tube. You could then drill a hole in the other end of the tube for a long tommy bar. It may also help to heat the casing around the bearings with a hot air paint stripper in case the previous owner had put loctite on the thread. (I used this method last week on my Chester DB10G lathe to remove the idler shaft for the first gear in the screwcutting chain. See my post "what did you do today" 05/02/14) The heating of the casting would also have two other effects. 1 It would slightly increase the diameter of the outer thread that the collar is screwed into. 2 It would slightly increase the distance between the two collars. This effect may not work very well as heat would be transferred to the bearing outers and spacer. I have not checked the difference in coefficients of linear expansion between cast iron and steel to see if a difference would help or not. Thanks MichaelG for the link to the drawings of the bearing arrangement which gave me a better understanding of the problem.

Les.

[Sub MandrelParticipant @submandrel]

> As far as I'm aware, a live centre is one that doesn't use the workpiece as the bearing for its rotation.

My understanding is that the definition goes back to the days before chucks.

A 'dead centre lathe' is one that has two non-rotating centres, on at each end, like a watchmaker's turns or a bodger's pole lathe. Don't dismiss these as primitive as inherently they produce truly circular work.

The 'live centre lathe' is therefore one with a spindle in the headstock and therefore the point fitted in the spindle is the 'live centre'.

Live and dead in this context mean rotating or fixed, just as fast and loose do with pulleys.

Personally, I like the way specialist uses keep old meanings of words alive.

Neil

[IanTParticipant @iant]

Thanks for the PDF Michael, I already had a hard copy but it's useful to be able to print out some pages.

Readers should note that this manual is for the later (Mk2?) S7 and whilst a good bit of it is still pertinent & useful, the clutch adjustment and headstock oiling arrangements are different – as well as some bits of the illustrated parts list of course.

IanT

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