Electronic gearing

Is it possible to gear spindles together electronically using Linux??

I want to cut some gears on my mill when my conversion is done using a hob. The hob will rotate at a fixed speed, and the speed of the 4th axis will vary depending on the diameter of the gear. The 4th axis is worm driven by the servo. Obviously the greater the accuracy the better so a few questions.

Is it possible to easily gear the two shafts together. Bear in mind it is angular position that I want to gear together, not just revolve them both at different speeds, i.e. for 1 turn of the hob the blanks needs to move 3 deg for example. And is it possible to program Linuxcnc like that?

Would I be better driving the hob with a servo and full encoder, or could I just use a normal motor and fit an encoder to the shaft the hob is on, the electronic gearing taking into account any slight speed variations?

Would it be possible to fit the encoder to the 4th axis spindle rather than the motor, my thoughts were to fit a friction device (or brake) to the spindle so that there is a bit of resistance. My thoughts behind this were if I have say a 6 inch 4th axis and want to cut a 12" gear, any backlash or pitch error will be magnified, therefore using the encoder directly on the axis would mean the motor could move whatever it needs to to keep angular position, the gear blank will always be rotating and in the same direction so this would mean slight speed variations in the motor rather than it having to oscillate to keep position

Many thanks

He has other videos..

there is also information in the Wiki on Hobbing , and how to set up etc ,
as well as a few posts around the forum , look around 18 month - 2 year back .

you can use a normal motor , but you'll find a servo is far more forgiving , and use a good encoder , with a,b & index
if you can directly drive the 4th spindle , you'll find better than say using a rotary table , as per the videos
and make sure your mill spindle also has a good encoder , ideally try and find an encoder that will divide into 360 degrees fully rather than giving you some werid remanders . and use toothed belts rather than v belts .
and you should find the process a lot easier , hope this helps .

Thanks for the info, I think I was searching for the wrong topics, should have just looked up hobbing!!

Have been doing a few sums on the index division vs encoder count. At the extremes, a 15" dia gearwheel using a 7200 count encoder gives a tolerance of approx 0.16mm on the pitch.

If I direct drive the 4th axis spindle with a 7200 line encoder would a setup using MESA boards, etc still work ok or would I have to start to consider latency problems etc. I think 7200 would be the minimum I'd want to use

Many thanks