Myford S7 cutting double!?!

[Thomas GudeParticipant @thomasgude37285]

A bit of a weird one. I just jumped onto the imperial Super 7 at work to do a small fiddly job as I usually use the metric Colchester.

I'm fine with imperial and I also own a Super 7 so no problems there. Except when I started using it I thought I was going potty. After a bit of investigation I found that machine is cutting twice the amount shown on the dials.

Now, I understand that on a Myford the cross slide dial measures the radius. Don't worry, I haven't fallen into that trap.

If the cross slide dial is rotated 20 thou, the machine will remove 80 thou off the diameter of the work and if the top slide dial is rotated 20 thou, it travels 40 thou!

Has anyone come across this before? The mental gymnastics are starting to hurt.

[Thomas GudeParticipant @thomasgude37285]

Both cross slide and tool post slide indicators cut double of shown

[noel shelleyParticipant @noelshelley55608]

Has someone changed the feed screws ? Seems the only answer to me ! Noel.

[blowlampParticipant @blowlamp]

How far does one turn of the feedscrew move the cross slide?

Martin.

[Mike PooleParticipant @mikepoole82104]

I would check the feedscrew pitch and the number or graduations on the setting dial. The imperial screw should be 1/10” or 2.54mm per rev. and the metric option is 2mm per rev. You may have non standard screws or dials or a mixture of metric and imperial causing confusion.

Mike

[Neil LickfoldParticipant @neillickfold44316]

Does it have the new Metric dials , that are in 0.05mm radial increments. So 20 units is 1mm radial , which is 2mm or 80 thou, but really should be 0.0787inches. I got a new dial and screw and nut assembly for my S7 , and the dial is marked effectively in Radial increments, not the Diameter increments that I have been used to since 1987.

The Top slide dial is in 0.05mm increments as well, so no change was there for me on that one. But it does not indicate if the dials are Metric or inches.

The old imperial one was obvious as it was 100 graduations on the cross slide, with a 0.100 inch lead thread. I use the imperial 100 count dial with my 0.5mm pitch lead screw for 0.01mm diameter graduations.

Neil

[bernard towersParticipant @bernardtowers37738]

Thomas surely your maths is wrong if you dial in 20 the dia changes by 40 not 80

[Thomas GudeParticipant @thomasgude37285]

Posted by Neil Lickfold on 27/06/2022 11:23:30:

Does it have the new Metric dials , that are in 0.05mm radial increments. So 20 units is 1mm radial , which is 2mm or 80 thou,

I think this is it, thank you Neil. Both cross slide and top slide dials have 40 "units" and move 2mm per rotation (40x 0.05mm), and they are both also 2mm pitch lead screws as you'd expect from the movement.

I admit, its been so long since I used my myford at home I forgot that the dials go from 0-100 on the imperial versions. I think what threw me is I would have expected to see something like this *metric dial* rather than a dial of 40x 0.05mm "units".

Thanks all.

Edited By Thomas Gude on 27/06/2022 13:35:40

[Howard LewisParticipant @howardlewis46836]

We assume (Dangerous ) that the Super 7 has Imperial leadscrews fitted Normally they are 10 tpi, so that a dial with 100 graduations would move the Cross mor Top Slides by 0.100" per turn.

Some lathes do have Cross Slide Handwheels that are graduated in Diameter, but they will actually put on a cut of 0.005" to reduce diameter by the 0.010" indicated Which is the reverse of what seems to ,be your problem.

It could be that someone has modified the machine and fitted leadscrews of double the pitch (5 tpi instead of the 10 tpi that is normally standard. )

Rereading more carefully, an Imperial dial on a 10 tpi leadscrew would have 100 graduations.

If the dials have 40 graduations, I suspect that they might be Metric but on an Imperial 10 tpi Leadscrew.

Safest way is to check the travel "Applied" against an Imperial DTI. And then recheck using a Metric DTI

Howard

Edited By Howard Lewis on 27/06/2022 21:01:58

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