Screw Cutting

[Alan]

Good afternoon Gentleman,

I am about to venture into the field of screwcutting on my S7. Firstly my thanks to "Redmog" for steering me towards the instruction booklet for the S7 gearbox.
My problem is this: To engage the thread dial indicator does one simply push the indicator in, to engage into the leadscrew?, If so the indicator revolves only when the saddle is stationary and the lead screw turning, if I engage the saddle the indicator stops revolving because it's going along with the lead screw. Does this make sense ?

Alan

[brozier]

Hi Alan,

This is correct operation. The indicator is used as a guide to when to engage the saddle.

If I remember correctly you wait until a whole number lines up with the index line and engage the saddle. When you get to the end of the thread, disengage the saddle wind the cross slide or top slide out to clear the thread and return the saddle to the start position.

Then you add feed on the topslide/cross slide, watch the indicator and wait until the same number lines up with the index line and re-engage the saddle.

There are some rules on which numbers you can use depending on TPI.

The Myford has an 8TPI leadscrew so when cutting any multiple of 8TPI (e.g. 16, 24, 32,40)you can engage the saddle where ever you like.

When cutting even tpi threads you can use any 4 marks at 90 degrees to each other. E.g first cut on number 1 second on number 4.
When cutting odd tpi threads you can use any 2 marks at 180 degrees to each other. E.g. first cut on number 2 second cut on number 4.
When cutting half threads (11.5 TPI) use any 1 mark. e.g always on number 3

When cutting Metric I think you have to keep the saddle engaged and reverse the motor to wind back.

I can recomend the Ian Bradley Myford series 7 manual, buy it from Myfords rather than the ripoff merchants on ebay!


Cheers
Bryan

[Alan]

Thanks for that Brian

I understand, all it now needs is for me to practice !!


Regards

Alan

[Tel]

Always picking up the same number, regardless of the thread being cut, is a good habit to fall into - kind of like always locking my truck door with the key - so I never lock 'em (the keys) in the vehicle.