Re: [CAD_CAM_EDM_DRO] Helix Angle

Okay, now you've changed your parameters... The original post didn't say
anything about 3-starts. So, with the new data; 18mm times 'pi' equals
2.2263255 inches. Then, 3 starts at 1/8" each equals 0.375", so the angle
with a tangent of .375 / 2.2263255 equals 9.5611 degrees. Do you bore a
'rough' hole thru the center of the couplings first? How many 'turns' on
the coupler? Your AutoCAD drawing should be a true 'sine-curve', not a
straight line. Also, the cut you make will not be a true, straight-walled
slot, but will be tapered wider, toward the outer surface, due to the fact
that you're beginning cutting somewhere 'off' that sine-curve. G' Luck!

RayHex
----------

> From: Terry Owens <terry@...>
>
> Hi,
>
> Thank you for the replies but they don't help as everyone came up with a
> different answer.
>
> What I'm trying to do is cut a 3 start helical slot around an aluminium

bar

> to make couplings for stepper motors. The way I would machine them is to
> hold them in the lathe chuck and use a slitting saw in a milling spindle

set

> at the helix angle of the slot, which happens to be 8 TPI. This is easy

to

> do, once I have the helix angle, but not very productive. As I wanted to
> manufacture a lot of these couplings, of different sizes, I have designed

a

> jig which consists of a screwed threaded bar which the part to be

machined

> is locked to. The threaded bar is used to advance the part to a slitting

saw

> held in a horizontal miller but the jig must be set at the helix angle.
>
> All the machining is easy once I have the helix angle but drawing the

slot

> in ACAD is a different matter. I tried to do it all day yesterday with
> results that didn't please me. I draw it the same way I machine it, not
> forgetting I got a different angle to all of the posts :-)
>
> As to the question why 18mm with an 8 TPI thread. I'm English and come

from

> that generation that had to learn measurements ambidextrously and as such

I

> think in imperial and draw in metric. I machine in either depending on

the

> machines scales. Metal here can come as imperial or metric and one is

often

> sold for the other. If I order 3/4" I'll sometimes get 19mm or visa

versa.

> The 18mm measurement was after machining a 19mm or 3/4" bar to 18mm.
>
> Anyway my question is still the same, which of us is right. The thread

I'll

> be using will be square or acme form.
>
> Regards,
>
> Terry