Myford Super 7 chuck alignment issues.

Hello all, I decided to change the belts on my Super 7, a nightmare of a job! Finally got the machine back together today, all seemed good, until I attached the chuck. For some reason I can not get it on straight.

Using a clock I checked the spindle, and all seemed fine. I used set squares to ensure the chuck went on as square as possible. The threads on both the spindle and chuck are in good order. As soon as I turned it on, it was very apparent the chuck wasn't square.

Prior to the belt change, all was good.

If I tighten up the adjusting collar anymore, the head stock cone bearing sticks, so it can't be play in the spindle.

To remove the spindle, for the belt change, I used a mallet to free it from the bearings, so I can't see that damaging it in anyway.

Any ideas? I have removed and replaced the spindle four times now, and the chuck always acts the same.

I am loathed to buy a new spindle, so i am hoping it is something to do with the bearings.....

Many thanks in advance, Nick, going slightly mad!

If the threads on the spindle and in the back of the chuck are obviously not buggered and there is no crud stuck in the threads, particularly the chuck thread, it should screw on. Lightly oil it and keep trying. try locking the spindle from turning first using the spindle lock. Changing the belt or even poor bearing adjustment won't cause your problem.

If you have a morse taper test bar it would be informative to fit it and take some readings to prove the spindle has not been moved during the belt fitting process. If you have a faceplate does this clock as being true? I feel that is is important to prove the spindle is still true before suspecting a problem with the chuck. The spindle register is very small and it would be very difficult to prove the truth of the spindle by clocking it. The headstock is located against the rear shear by two screws located in the front shear, if you have a gearbox these will be obscured. If any of the headstock mounting bolts or thrust screws were loose, tapping the spindle to remove it may have moved the headstock.

Mike

Try fitting a different chuck (eg four jaw) and/or the faceplate or even catch plate and see how they run. If they all wobble, then the problem is most likely something on the spindle. If only the one chuck wobbles, then the problem is with that chuck.

Also, check the register collar, the larger diameter smooth section to the left of the thread, on the spindle for burrs and bumps. The chuck actually seats on this register collar, not the thread, so any burrs or dirt there will set the chuck off centre. Likewise, check the register recess in the back of the chuck for burrs and dirt.

Many thanks for all the replies and useful info. I have tried two different chucks, but both were difficult to screw on..so neither got anywhere near the collar. I wasn't sure if they needed to go all the way back, I assumed so, as the collar would automatically ensure they are square, but was wary of too much force. Are the threads tapered to form an interference fit? The chuck was stiff to remove in the first place. I shall definitely try using some oil, and see if that helps.

I agree the spindle length is only about 1 1/2" so any out of balance would be difficult to notice. I hadn't heard of a test bar before. How would it work?

I'll also check the alignment is still ok, as it is a secondhand lathe, I don't know the history of it, But as the movement is circular, it indicates a vertical component to the problem. I also have a gearbox, and the thought of taking that off to access some screws.....

I am hoping it is just a mater of oil, and me being cautious about damaging threads, but when the knuckles go white, one gets concerned!

Many thanks again, as always it is a true education.

Naive Nick.

Nicholas,

I have sent you a PM please check the inbox near the top left.

Eric

I'm with Hopper - check the spindle thread and register for burrs or dings.

Nick,

Logic dictates that if the chuck did go on before the belt change but doesn't now something must have changed? It sounds like something has been damaged but you are saying not, does the chuck screw on but is tight?

Tony

Check the spindle nose register and threads and those register and thread on the chuck are absolutely spotless.

The chuck should screw all the way on but not be forced.

1. That is your problem right there. The chuck should screw on freely with no forcing until it seats firmly on the register collar. You need to clean up the threads in the chuck and the spindle until they screw together freely.

2. No the threads are not tapered. In fact they are often made a bit undersize so they are a loose fit. The thread does not locate the chuck or hold it in alignment at all. All location and alignment , both axial and radial, is done by the register collar fitting size-for-size into the recess in the chuck. Again, threads need to be cleaned up until the chuck freely screws all the way on until the end of the register collar on the spindle meets its mating face in the chuck.

One thing to check, as you have removed the spindle, is the fitting of the distance sleeve (H31) on the outboard end of the spindle. If it is at all tight on the spindle it may not seat back against the shoulder and it is impossible to set the bearings up correctly. The way to do it is to adjust the locking rings so that the front bearing is well clear and then tighten the adjusting collar as tight as you can get it. This will ensure that the distance sleeve is hard up against the shoulder on the spindle. Slacken off the collar and set up preload and front clearance as normal.

When I got my refirbished Super 7 the sleeve was a tight fit on the spindle and had originally been set so that there was a slight gap between the sleeve and the shoulder. The first time I did and drilling the spindle moved inwards and all the clearances went to pot.

If you didn't remove the angular contact bearings they cannot be back to front which is the other stupid mistake that could be made.

The only other thing I can think of with regard to the spindle is that the felt wick is seated right and hasn't got trapped in the front bearing.

regards Martin

Hello again, and thanks for the replies. Bearing in mind the information about where the chuck should sit, and the force required, I have come to the conclusion the spindle is the problem.

I tried today with two different chucks and two different face-plates, and got the same results. After about half a turn, it sezies up completely, still a good 1/4" away from the collar.

The threads look ok, on both the spindle and the chuck / plate threads, so I am at a loss...I want to get the chuck / plate on first, before I think about the bearings, I am still hoping I am doing something stupid, but screwing something on seems so straight forward I don't quite know what.

To my eyes the threads look ok, but here is a picture of them:

This is as far as I can get anything on:

Nick...

Look at that thread with a magnifying glass, I can see bits of swarf in the photo.

Neil

Following on, what is the thread of the spindle? I thought it was a Whitworth, but for a 1 1/8 Whitworth, it should only be 7 or 9 TPI, but the Myford is 12 TPI...which relates to the 1 1/8 UNF..I am thinking of getting a die to go over the threads...

You will have to check the spindle thread very thoroughly, small chips can embed themself in the thread and swiping it with a cloth or brush will not remove them. You will have to remove them with a small tool. The same is true for the thread of the chuck you try to fit. Niko.

I use an old toothbrush to clean swarf out of my Boxford spindle -nose and the chuck backplate threads.

Dont really know the Myford, but I certainly wouldn't put a UNF die on the spindle theads. I'd expect it to be Whitworth form.

The thread on my S7 is 1.25 whit x 12 TPI Chronos do a die link

H

Just a thought anyone wanting to change their belts in the future should consider using Fenner belts.

**LINK**

The Myford spindle nose is 12tpi 55deg Whitworth, I doubt you will find a die as it is non standard. Taps are available. the nose is hardened and would not be kind to to a die. The nose thread should be perfectly clean before fitting a chuck and also the thread in the chuck backplate. As you have tried a couple of things on the nose it may well have a piece of swarf pressed into the thread. A brass wire brush is useful to clean the thread and a pick or scriber to remove anything that will not brush clear. The chuck thread is a little more difficult to clean but people often bend a piece of thick wire so it has two points to engage in the thread and screw it down the thread to clean it. The chuck thread will need to cleaned every time before mounting it. I would strongly resist the temptation to do anything drastic to the nose as it is a precision piece of machining. Get it spotless and inspect very closely for any damage and do no more than is absolutely necessary to correct the damage. The register which is the diameter and face beyond the thread is made to a very tight tolerance and unless it has sustained any identifiable damage should not be touched. Any polishing will affect its dimensions even with very fine abrasive.

Mike

Well while I was typing Harry has found a die but I would seriously resist the temptation to use one on the nose.

Edited By Mike Poole on 03/07/2017 21:54:13

Edited By Mike Poole on 03/07/2017 21:55:07

Yes...I did consider the link belts, but read a review that they were much noisier than the normal ones....I think I will suffer with the noise in future!

I shall try the suggestions regarding cleaning the thread, I didn't realise how sensitive things were.

Thanks for the recommendation on the Chronos Die. If I can't sort things by cleaning, I shall be getting one.

On the good side, no one has spotted any obvious damage to the spindle, so hopefully a good clean may sort things out.

My slight worry is that it was such an effort to remove the chuck, that it may have been forced on by the previous owner, who didn't have access to this very informative forum. Any swarf may be firmly embedded.