Myford Super 7 chuck alignment issues.

Try fitting a catch- or faceplate first before you try a chuck, because you can acces the thread of a those plates from both sides they are easier to clean, if they fit you know the spindle thread is fine. Niko.

It appears in the picture that the catchplate screws on until it comes to the register collar. Check that the register collar has no burrs or bumps on it and that the recess in the chatchplate is free of burrs and rust.

How is the thread as it screws on up to this point? Does it go on easily, indicating the thread is ok? Or is it tight to screw on up to this point, indicating the thread needs cleaning up on both spindle and catchplate?

Hopper is heading in the right direction I feel.

If that catch plate has a thread that goes right through, screw it on back to front. That should show you if the threadsare tight. Don't force it right down and bruise the parallel register. If the thread enguagement is OK blue up the parallel register using micrometer blue and screw the catch plate on as far as it will go. You should then be able to see where the tight spot's' is/are. It may just be a bruise on the edge of the register. If so you should be able to stone that off gently without doing any damage.

I really would not start winding dies onto the nose.

regards Martin

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

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

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

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.

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

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.

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

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

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