Myford Super 7 chuck alignment issues.

[Martin KyteParticipant @martinkyte99762]

I was going to suggest the above but be aware the unused portion of the thread is very likely to have loads of swarf in it.

Tony

Absolutely so get things as clean as you can.

Martin

[Neil LickfoldParticipant @neillickfold44316]

Posted by Nicholas Hill on 02/07/2017 21:07:17:

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!

At some point you have either damaged the spindle on the threads or the register diameter, or you have damaged the back plate some where. The damage will be very small, so look for a small ding or dent or some bruising on the back plate register face. Look very care fully, it will be there and just scrape that damaged area to make it fit again.

Neil

[Clive HartlandParticipant @clivehartland94829]

The real answer is to put a 55 deg. threading tool in the tool post and offer it up to the mandrel after engaging 12 Tpi. thread setting. Then turning mandrel by hand follow the thread and slowly try to engage thread but not cutting. this will find any high spots along the thread. (No metal removal) Agree with full cleaning before hand. Do not waste your money on a Die you will never use again. Initially grind off the point of the 55 Deg. tool as Whit. thread form has a rounded crest. Maybe find a 12 Tpi. thread chaser?

Clive

[KWILParticipant @kwil]

Reverse your catchplate and screw on, you will then be just using the threaded part, my guess is a bruise on the leading edge of the Register not the thread at all. Easily done if the spindle was a little mishandled whilst off.

[Dick Ganderton 1Participant @dickganderton1]

It's a bit too late now, but you don't need to remove the spindle to change the belts on a Myford S7. The best way is to just cut off the old belt and fit a Nu T Link belt. My S7B is fitted with this and find that it runs quieter than than the conventional belt. You can buy it from your local Fenner drive stockist. The motor to countershaft belt is a 'Z' and the countershaft to headstock is 'A'. I did have problems with changing the belt due to lack of clearance between the headstock casting and the pulley, but a few minutes with the Dremel soon cured this.

I can also recommend the taper roller bearing mod to the back end of the spindle.

DickG

[Nicholas HillParticipant @nicholashill23289]

Many thanks for all the suggestions. I finally sorted it this evening. After cleaning the threads, using a wire brush, a tooth brush, and still no joy, it looked spotless, but nothing would go on further than half a turn. So rummaging around in the tools that came with the lathe, I found a 12 TPI Thread restoring file. After about 5 iterations of file and try, I finally managed to get it screwing on smoothly. Whatever was causing the issue, was beyond my eyes.

But, it is still about +/- 5 thou out, so i am onto the bearings now.

Thanks again for all the info….I'll probably be back tomorrow with more obvious questions.

[Howard LewisParticipant @howardlewis46836]

Where are you checking the chuck for concentricity?

The O D does not matter, but how it holds a piece of KNOWN round bar does. Suggest holding a piece of inch diameter Silver Steel in the chuck (Make sure that the jaws are clean, where they grip the work).

It might be worth removing the jaws, and cleaning the chuck jaws where they engage the scroll. To try to avoid stripping the chuck, try holding an old, clean, toothbrush in one of the slots for a jaw, and rotating the scroll,with the chuck key, to brush any swarf out of the scroll, before refitting the cleaned jaws.

Then grip the Silver steel in the chuck, and clock it for concentricity, close to the jaws. A good 3 jaw would probably be within 5 thou T I R, but a worn / badly butchered one could be wildly out (Once saw one 0.036 inch T I R !)

The run out may well be different if you recheck with a different size bar in the chuck.

Howard

[NJHParticipant @njh]

I don't know if this is relevant to your problem but it may be of use to others having difficulty in fitting chucks.

I have a very low mileage S/H S7 and decided that I would buy a collet chuck for it. Try as I might I couldn't get the thing to screw onto the mandrel nose – it was all too tight. I went through various ruses but finally hit on the answer – the problem was one of alignment. The solution was to chuck an appropriate sized piece of silver steel in the tailstock drill chuck then fit the appropriate collet into the chuck and close to a sliding fit on the bar. Slide the chuck and collet down the bar towards the mandrel nose and, hey presto, perfect alignment every time and the chuck screwed on easily!

Norman

[duncan webster 1Participant @duncanwebster1]

Posted by Howard Lewis on 04/07/2017 23:01:24:

Where are you checking the chuck for concentricity?

The O D does not matter, but how it holds a piece of KNOWN round bar does. Suggest holding a piece of inch diameter Silver Steel in the chuck (Make sure that the jaws are clean, where they grip the work).

The run out may well be different if you recheck with a different size bar in the chuck.

Howard

It might be better depending on which drive dog you use, try all 3 and the mark which one is best. There's no point chasing the last few thou, that's not what 3 jaws are for. Even the much vaunted Griptru is only bang on at the diameter it was set

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