Gear Hobber

It takes a relieving attachment for the lathe to make a hob that cuts freely, and also gearing for either DP leads or module, not a simple matter, nor are commercially made suchlike articles plentiful, in fact quite rare; I started out to build an Ivan Laws relieving attachment, but abandoned it due to design problems.
 
MattM said:
Very interesting. I have no need for that level of precision.
Click to expand...

There are 360º around the sky.
There are 60 minutes per degree.
There are 60 seconds per minute.
So, there are 1,296,000 seconds around the sky.

A 12" gear has 37.699" circumference.
So, the tooth-to-tooth error needs to be 1:34,377.46 to achieve 1 arc second tracking.

Most of the mounts of this quality go the other way and use <high resolution> Renishaw encoders and put a servo motor in the loop.
These encoders have to be concentric with the declination axis to fractions of a thousandth of an inch to let the servo motor achieve its stated accuracies.
 
I suggest you bootstrap the machine with 3d printed gears to allow you to cut the metal ones the machine needs.
Another idea would be to use toothed belts and pulleys. Those print very well! You would want to add an idler to deal with belt length.

Sent from my SM-G892A using Tapatalk
 
I had the impression that the hob both cuts and turns the gear blank which is free spinning, no gearing required. Is this wrong?
 
No, that's "free hobbing" which is popular poor man's way of doing it. To work well, you need to "gash" the teeth in roughly to begin with. Genuine hobbing rotates the hobb and blank in sync. Commercial models often have dual gear trains that get integrated by a differential gear, as it's sometimes not possible to create the required ratio with a simple gearset.
 
The machine in discussion rotates the hobb and the blank in sync.
 
You must log in or register to reply here.
Back
Top