Myford super 7 taper turnin

Allan,

It is more likely that your 3 jaw chuck is a bit inaccurate than the headstock being out of line. 3 jaw cucks, even new ones, are not to be relied upon to hold work accurately. This is why many experienced operators use 4 jaw chucks or collets for accurate working.

You need to turn a piece of bar exactly as shown on pages 13 & 14 "Checking The Levelling" of the handbook.

Do this very carefully taking very light cuts "levelling" the lathe accordingly..

It is best not to disturb the headstock casting. .

How tight is the saddle on the bed? With other slides locked of course, is the measurement point close to the middle of the saddle?. If you have a DTI hanging off a holder on the front of the toolpost any rotation of the saddle about a vertical axis due to the thou of clearance on the gib will be exaggerated.

You do not need to take cuts at least initially. If the 'test' bar is of consistent diameter you can set one end dead true in the 4 jaw or in the 3 jaw with shims of beer can then set the outer end true regardless of cross slide setting. Then you know it is in line with the spindle and can measure your offset taking into account backlash in the saddle twist. With the DTI set on the outer end and the bar rotated to max or min offset point you can observe the effect of shimming.

+1 for the saddle maybe being a little sloppy.

That was a problem with my S7

IIRC the rear bed face had a little wear and also mine did not have all the shims between the saddle and rear saddle strip! They just left the bolts loose... so it could float around as it wanted.

Allan B You cannot check for round with a micrometer the bar could be lobed like a twenty pence piece ( uk )

Allan B

Where are you located? Is you test bar just cylindrical or is it on MT2 taper?

The turning test is the best and easiest way of setting your lathe up. What you see is what you get. That's why the Myfrod manual recommends it as the final test, and as a complete substitute for leveling if no engineer's level is available. Holding a ground test bar in a chuck introduces all kinds of errors. Save the test bar for setting between centres to adjust the tailstock, after the bed has been set up.

You have to remember too that on an old or worn lathe, there will be wear on the bed shears that will throw out the readings on an accurate level. Hence the handiness of the turning test on old machines.

That said, yes there is adjustmemt on the head stock. Two jacking screws at the front of the headstock and four hold down bolts inside the headstock box casting. But you want to have eliminated all other possibilities before messing with them.

What sort of condition are your headstock bearings in? More than the regulation half a thou or so of up and down movement of the spindle measured at teh collar behind the chuck, while you yank up and down on a piece of 12" long bar held in the chuck will affect alignment too. (Another reason the turning test is best: it takes into account any slack in the bearings that allows spindle to move under cutting load conditions.)

Edited By Hopper on 07/02/2017 23:46:51

Edited By Hopper on 07/02/2017 23:48:21

As far as I am aware, those two `jacking screws` are thrust screws that push the headstock to the rear shear face. Not for adjustment.

I would guess scraping would be required to change that setting?

As ASF says, the headstock screws mentioned are not adjusting screws! I get the impression that you are short of a a S7 manual? I am only about 15-20 miles from you and have sent you a PM.

Allan,

Many of us have been here before on this forum, firstly the run out or otherwise of your chuck will have absolutely no effect on how the lathe does or does not turn parallel.

Please get a copy of the S7 manual before doing anything else & to be honest jacking the headstock should not be necessary at all

Tony

Absolutely, but it will hold his ground test bar cockeyed and give a false reading as he runs his dial indicator up and down the length of it, as he has been doing. Hence, another reason the turning test is the ultimate test; chuck runout does not affect it.

Edited By Hopper on 08/02/2017 23:50:25

Yes, their operation depends on scraping the headstock mating surface, or in a pinch adding thin shims to one end of the contact area. Then the screws jack, or thrust, the two surfaces togehter firmly to set alignment. As has been said, it is unlikely this will need adjusting and all other possibilities need to be elimiinated and double eliminated first.

It would pay, too, to measure the bed wear on the front shear, both in the vertical and horizontal planes. More than .005" is cause for serious concern and will affect parallel turning etc. It is easily measured with a 0-1" mike for the vertical and a 1-2" mike for the width measurement. The bottom outer surface of the shear is relatively unworn as it takes little or no cutting forces so can be used as a reference surface. Ditto the front surface of the front shear. It is the top of the shear and the inner vertical surface of the front shear that take most of the operational load.

I really suggest you don't start messing with the headstock until you have absolutely determined you have a problem.

Level the lathe with a turning test as specified in the manual, making the necessary adjustments using the jacking screws at the tailstock end. Unless you have a precision machine level you will not be able to set the lathe to turn parallel by that method. Building levels are just not sensitive enough to do the job. Even using a precision level a turning test and a mic is advisable as a final check.

I recently took delivery of a refurbished Super 7 and did set it up with a precision level (0.0002"/10" and did a turning test as a final check. I could detect no difference in diameter over the 4" test piece using my best digital mic.

Building levels are good to get in the right ball park, precision levels are a very good short cut and the turning test is the final arbitor.