Re: [CAD_CAM_EDM_DRO] Helix Angle

What you're describing is; 3-start, 1/24" pitch thread, since the
definition of pitch is the distance from the center of one thread to the
center of the adjacent thread (this allows for multi-start threads). So,
the helix angle should be the 3.2136° as a number of us originally
responded.

RayHex

----------

> From: Terry Owens <terry@...>
>
> Hi,
>
> Isn't it difficult making one understood when it has to be written down.
>
> Yes the helix is 3 start but each of the starts is 8 tpi indexed 120

degrees

> to each other. This should give about 0.040" between each slot. I am

doing 1

> and a half turns on the short couplings, two turns where the length

permits

> and a double set of helix's on the very long wider couplings for type 34

and

> 42 steppers.
>
> They are machined up on the lathe first to finished sizes with holes down
> the centres, relief bored and the ends sized to fit the shafts before the
> helix is machined on the horizontal miller. The smallest slitting saw I

can

> getis 2" in dia and the slots will be 0.025".
>
> I have just finished the design of the jig and last night wrote the

program

> to machine on the lathe. Unfortunately the miller is not CNC yet.
>
> Regards,
>
> Terry
>
>
> > 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!