hobbing helical gear

Hello LCNC Community

@Henk
Does your pfauter p500 could cut helical gear ?

@Andypugh
For maths of Differential Indexing of helical gear it could help 


I also want to convert mine manual Hobing machine with Linuxcnc 

I’ve been planning to take some time to dive into helical hobbing for a long time. I struggle to make sense with the geometry in my head. I can’t seem to visualize what makes straight teeth hobbing different from helical ones.

Then I found this video. This guy simple uses the very same electronic gearing for both, straight and helical teeth! He just places the work piece in proper angle (taking the hobb angle into account) and that’s it! He did the electronic gearing is an ultra-simple fashion.

By 11:05 he explains how he implemented the gearing.

By 18:05 he cuts the first helical gear.

Is it that simple? No additional crazy math required for helicals? Just this simple gearing and tilting spindle to the correct angle?

I can't decide.
I think that if you hob one side then the other then you get a pair that mesh correctly. But i don't think you get the angle you expected.

One interesting thing he did was splitting the final angle into two components: The cutter angle (accounted by tilting the spindle) and the gear teeth angle (accounted by tilting the work piece). In this way it is much easier to visualize what is going on during cutting.

I don’t think I currently have the math background to prove it, but at least visually I believe that the final teeth angle will be just the work piece angle.

If so, Andy’s component will do the job for both, helical and spur gears.

Andy, have you ever tried your component in such way?

Hi. I agree with Andy, don't think this method will produce an accurate helical gear.

Think of it this way....

If you cut a radial groove on a round disc using a normal 4th axis but you keep the 4th axis stationary, using the x and y axis to produce the angle, the groove will not have a constant depth measured from the OD. Neither will it be truly radial across the width of the disc.

Alternatively, if you produce the slot using the X axis and the 4th axis in a synchronised move, you will end up with a helical slot. This slot will be truly radial and have the same depth at any section of the disc across its width.

The method above will not work IMHO. The error may be negligible at small helix angles, but a pinion with a small amount of theeth and a large helix angle of say 30 deg will show it clearly.

Henk

Or maybe not....I'm not so sure anymore...have to think about this a bit more
Henk