Cutting worms with less tpi than lead screw

Hi Gents

Recently aimed to make a replacement 5 tpi worm shaft for a mini cultivator on myford ML7/ ML10 without gearbox as the lead screw is 8 tpi has anyone achieved less than 8tpi lefthand worm shaft on these or could anyone offer suggestions

Rufus

No practical experience; but I believe the preferred method is 'thread milling'

A milling spindle replaces the normal lathe tool, and away you go.

MichaelG.

Common solution is to set up as normal but use the leadscrew handle to provide the power. I believe the ML10 has a handle....

Hi Rufus
Seen here in photo cutting a 5 start worm ,i think it
is .8 mod as it was done about 6 years ago , if
so the pitch is just under 1/2 inch ie 2 tpi.
See article in MEW 241.
Photo in album rotary table.

John

Bazyle,

Do you mean a mandrel handle?

Otherwise how do you guarantee 5TPI?

[Edit: Oh, I think I see now - Doohh. Is the idea to drive the spindle from the leadscrew? - thanks]

Jon

Edited By Jon Gibbs on 13/04/2016 10:03:24

5 tpi from an 8 tpi leadscrew should be ok it's not pushing things all that far. Just run the lathe at min speed and check how fast the carriage moves to be sure you are comfortable with it or turn said leadscrew or the lathe spindle with a handle.

If you were making lots and lots of them things will wear out more quickly than more normal pitches but you aren't. For one offs the main problem with this sort of thing can be the speed the carriage moves at. I recollect Rod cutting helical gears like this with a much coarser pitch so had to use a handle.

John

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I've cut 1" pitch oil grooves by use of a leadscrew handle driving the spindle through the change wheels. More than one way to skin a cat!

Russell.

Indeed. That was using a milling spindle powered gear cutter - analogous to thread milling. Driving a single point threading tool from the leadscrew handwheel is probably going to be difficult since the mechanical advantage is all the wrong way. Personally, I'd do as John suggests and set it up in the conventional way to cut 5tpi - just be aware of the issues, take it slowly and carefully and see if it works. A hand crank on the lathe mandrel is always a useful thing to have and I often use it for thread cutting, it will give you some feedback as to how the job is going before anything breaks!

HTH,

Rod

Edited By Roderick Jenkins on 13/04/2016 13:19:28

I suppose I should have added set the compound slide at the correct angle so that this can be used to set the depth of cut and take cuts that are well within the capability of the machine especially as the "thread" get deeper - just as anyone would when cutting coarse threads. Or may quickly realise that they should have done it this way handle or not.

John

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