Mill/Drill Gear Hobber

[cfellows]

A slight diversion from my engine projects...

I need a 20 tooth, 48DP gear for my Lister D build and I don't have any 48DP cutters. I do, however, have several 48DP gear hobs which can only be used on a hobber. I've always had a hankering to own a gear hobber, but the castings are expensive, it would just take up more room in my already crowded shop, and frankly, I just don't know how much use it would get.

So today I got to thinking, I have virtually everything I need to hob gears on my Enco Mill/Drill. I have an electronic dividing head which includes a spindle to hold the gear blank and a stepper motor to turn it. It fits in my milling vice so I can easily adjust the angle of the gear blank to suit different gear hobs. And of course, I have the milling spindle to hold and turn the gear hobb. All I need is a way to synchronize the stepper motor with the milling spindle.

Here's a video of a similar setup that another fellow did:
[ame]http://www.youtube.com/watch?v=ZhICrb0Tbn4[/ame]
So, today I made a 90-slot encoder ring, 9 inches OD, which will be affixed to the bottom of the large v-belt pully on the milling spindle. I also have a quadrature encoder module with an LED and sensors which will be mounted over and sense the slots in the ring. The wiring will lead to my Arduino micro controller which is also used for the dividing head... hence, the cabling and connectors for the stepper motor are all in place.

I think with some additional wiring and a piece of software that I should be able to put together, I will have a full blown gear hobber!

Chuck

 

[gus]

Hi Chuck,
You are my hero.

Other than cutting spur gears tooth by tooth,we were not taught gear hobbing in trade school.
Singapore Polytechnic had all the machines tools except for the Gear Hobbing Mill in the 60s.
Today we have 6 Polys with latest CNCs. In 1983 Gus went for the CNC course with some hands on .CNC lathe and Centres were equipped with Fanus.

Plan to cut some gears the old fashion tooth by tooth way.

 

[kuhncw]

Hi Chuck,

This looks like another interesting project you've come up with. Please keep us tuned in.

Regards,

Chuck Kuhn

 

[MuellerNick]

As shown in the video, it is not a huge hurdle with LinuxCNC.
Sooner or later, I will build a spindle encoder for my mill … for rigid tapping and maybe hobbing.


Nick

 

[cfellows]

Thanks everyone for the continued interest. By the way, Gus, I've cut quite few gears using the one tooth at a time method. Unfortunately, involute gear cutters are quite expensive and I've not tried to make my own.

Got the slotted encoder wheel cleaned up, dressed up, and mounted on the pulley.

Here's the pulley mounted on the Mill/Drill.

Here's a picture with a quadrature encoder which would let the software detect which direction the spindle is turning.

This encode only detects steps, it won't detect direction of spin...

I'd like to use the quadrature encode if I can. It has a much narrower gap, but should still be useable.

Chuck

 

[MuellerNick]

I'd like to use the quadrature encode if I can.

You can! You just need an other detector that is phase shifted by 90°. Means if one detector is in the middle of a gap, the other one is in the middle of an island.
You also need an index signal, so you can start at the same position of the hob in case you switched off the power or your electronics lost position.
Both work and spindle should start in a precisely known position.

Nick

 

[rodw]

Chuck,

Did you make any further progress with this?

I am starting to get interested in this stuff. My Arduino is on order and the plan is to add a stepper to my Vertex Rotary table initially and maybe make something like yours later on as the gearing in the Vertex might be a limiting factor when it comes to spinning the table at a decent speed.

 

[cfellows]

After some additional research, I decided that the aluminum encoder disk would not give me enough resolution for what I wanted to do, so I tabled the project.

I did buy a higher resolution encoder so I'll probably get back to this project at some point.

Chuck

 

[aonemarine]

I suppose that doing a cnc lathe conversion would be about the same? Something I have planed for a future project...

 

[cfellows]

I suppose that doing a cnc lathe conversion would be about the same? Something I have planed for a future project...

What are you planning to do? Are you wanting to attach an encoder to the spindle then have steppers move the carriage in sync with spindle rotation?

Chuck

 

[aonemarine]

What are you planning to do? Are you wanting to attach an encoder to the spindle then have steppers move the carriage in sync with spindle rotation?

Chuck

Im electronics illiterate, but yes. I want to be able to thread with it, so I guess thats what needs too be done...

 

[rodw]

After some additional research, I decided that the aluminum encoder disk would not give me enough resolution for what I wanted to do, so I tabled the project.

I did buy a higher resolution encoder so I'll probably get back to this project at some point.

Chuck

Chuck, SparkFun sell 1024 step and 200 step encoders that may do the job.

https://www.sparkfun.com/products/11102


You will need to study the example code which uses interrupts to service the encoder for a 50 fold performance increase on the Arduino

http://www.hessmer.org/blog/2011/01/30/quadrature-encoder-too-fast-for-arduino/

I thought you could drill and tap a hole in the end of the drawbar to take a shaft extension that this could be attached to.