Threading Gear ratios and other what nots..

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NeoTech:
yeah.. its me again.. and im stupid. *so thats done*

As you are all aware now by now is that im learning threading.. and now have gone through the usual metric and imperial i can do on my lathe with a norton gear box.
So i figured out its a metric pitch of 3mm on my leadscrew, when cutting a 1.5mm thread i do 60/120/60 gearing and some tinkering with the gearbox and voila.. threads. cool.

So i in my eternal wisdom went and looking for Aciera F3 mill.. and found out that Schaublin/Aciera is.. well evil, and made the 19.7 x 1.667 buttress thread on all the collets.
also known as W20.. so i thought well i just buy new collets.. but nooo i has to make em or i will go broke just buying one of those collets..

Heres the problem i guess.. i can make a collets in my lathe.. but how the hell do i cut the 19.7 x 1.667 buttress thread.. ive figured out a 45 x 5 form tool is needed, and it wasnt
that hard to grind one from a hss blank and thread a 1.5mm thread with it.. But now i need to figure out how i regear my lathe. I have bunch of gears with the late thats good.
But how do i do the calculation? i have googled skimmed through a bunch of books but i cant really find a practical example. And im a really practical person... Math theory isnt
on my highest list over stuff im great at.

Pete.:
You don't strictly NEED a form tool for cutting those threads, you can set one edge of the tool to the angle of one flank and in-feed the tool at the other flank angle via the compound.

What lathe do you have?

mhh:
If you can make the collets in the lathe...... Why not make a new drawbar aswell?

But if you do, remember to take pictures! Always nice to see what other people make!

:D

DMIOM:
Neo,

You could have a look at the Electronic Lead Screw which apparently allows free choice of thread (no connection, and I haven't needed to build one yet either!)

Dave

BillTodd:
Your lead screw is 3mm you need a 1.66666666666666666666666 mm pitch thread, so that's a ratio of 1.8:1 - i.e. 1.8 turns of spindle to one turn of the lead screw. To avoid any maths just swap the ratios into teeth e.g. a 10Tgear on the lead screw would require an 18T on the lead screw. 10T & 18T are too small, so multiply both by say 3 and you get 30T and 54T

i.e by pass the box, if you can, and use 30T driving a 54T (or any similar combination) . If you can't bypass the box, set it to 1.5mm and use 30T driving 28T ( or 60:54 etc.)

Check pitch before cutting ;)

Bill

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