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# Machining a helical gear

#### Mike Gre

##### Plastic
I have a 3k K&T universal mill. I have a dividing head that I have rigged a stepper motor to that with the help of an Arduino cuts spur gears with a hob based on an encoder on the spindle. I have used this for years and created many good spur gears. If I rotate the table to the lead angle of a helical gear and then run the hob the same way I do for a spur gear, will I get a helical gear? Most people I have seen cutting a helical gear on a regular mill are running the dividing head off the x axis leads screw but with a standard gear cutter and not a hob?

#### Dr. Rob

##### Hot Rolled
”…If I rotate the table to the lead angle…”

Taking a chance by posting before having morning coffee here, but I would say no.
But, if you swivel the dividing head to the lead angle of your desired helical gear, then yes.
So, table angle = direction of travel = lead angle of hob. Always.

Beyond that, some additional math to figure out the size of the gear blank (diameter increases with increased helix angle) and you’ll be on the right track. It sounds like you know what you are doing; you’ll figure it out. Good luck.

.

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#### Mike Gre

##### Plastic
Thanks,
I will have to give that a try and see what I come up with. I have lots of books on gears but very few of them have anything to say about hobbing on a conventional knee mill.

#### snapatap

##### Aluminum
To use a hob to cut a gear you need to synchronize the rotaion of the hob and the work piece cant see how you can do that on a mill.

#### Mike Gre

##### Plastic
To use a hob to cut a gear you need to synchronize the rotaion of the hob and the work piece cant see how you can do that on a mill.
Through an Arduino, stepper motor, driven dividing head, and a optical encoder on the spindle. If you are seriously interested let me know and I would be happy to share the code and some pictures of my setup.

#### Garwood

##### Diamond
Through an Arduino, stepper motor, driven dividing head, and a optical encoder on the spindle. If you are seriously interested let me know and I would be happy to share the code and some pictures of my setup.

Would you mind sharing what you've done in this hobbing thread? https://www.practicalmachinist.com/forum/threads/electronic-gearing-for-gear-hobber.407814/

I don't know if you can tip the gear blank and get a correct toothform? On a hobber, you turn the hob spindle to the angle of hob's pitch then you comp the helix angle of the gear in the blank to hob ratio.

#### Mike Gre

##### Plastic
Would you mind sharing what you've done in this hobbing thread? https://www.practicalmachinist.com/forum/threads/electronic-gearing-for-gear-hobber.407814/

I don't know if you can tip the gear blank and get a correct toothform? On a hobber, you turn the hob spindle to the angle of hob's pitch then you comp the helix angle of the gear in the blank to hob ratio.
I posted the code and a brief description in the other thread. Having some trouble with the pictures though.

Based on what you said above I should be able to obtain both those angles with the universal table and by rotating the dividing head if necessary?

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