Author Topic: Gear Hobber  (Read 9420 times)

Offline cfellows

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Gear Hobber
« on: December 21, 2012, 05:15:42 AM »
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:

http://www.youtube.com/watch?v=ZhICrb0Tbn4

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
« Last Edit: December 21, 2012, 05:20:00 AM by cfellows »
So many projects, so little time...

Offline Captain Jerry

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Re: Gear Hobber
« Reply #1 on: December 21, 2012, 05:29:01 AM »
Go, Chuck! :whoohoo:
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline Don1966

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Re: Gear Hobber
« Reply #2 on: December 21, 2012, 05:31:07 AM »
That's is awesome Chuck, you have my attention. I am pulling up a chair and watching.

Don

Offline swilliams

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Re: Gear Hobber
« Reply #3 on: December 21, 2012, 09:55:48 AM »
Very cool Chuck

I'm watching
Steve

Online sco

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Re: Gear Hobber
« Reply #4 on: December 21, 2012, 10:10:06 AM »
I love this kind of project -will be watching with interest.

Simon.
Ars longa, vita brevis.

Offline gbritnell

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Re: Gear Hobber
« Reply #5 on: December 21, 2012, 12:50:04 PM »
Hi Chuck,
It looks like another great project. I do have one question though. If the encoder ring is attached to the spindle pulley will the clearance in the pulley to spindle spline cause a problem with the accuracy of the cut?
gbritnell
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Offline steamer

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Re: Gear Hobber
« Reply #6 on: December 21, 2012, 02:27:45 PM »
OH Im watching this!

 :DrinkPint:

Dave
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Damned ijjit!

Offline cfellows

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Re: Gear Hobber
« Reply #7 on: December 21, 2012, 05:33:10 PM »
Hi Chuck,
It looks like another great project. I do have one question though. If the encoder ring is attached to the spindle pulley will the clearance in the pulley to spindle spline cause a problem with the accuracy of the cut?
gbritnell

Thanks, all, for the enthusiasm.  George, I don't believe the small amount of rotational clearance between the pulley and the spindle will make any difference.  Each full turn of the milling spindle will result in 1 tooth's rotation of the gear blank, plus the spindle will be under a constant load in one direction so I don't think it will matter.

The slot in the encoder sensor is only .070" wide and the encoder wheel is made from .040" thick aluminum.  Clearly I can't tolerate much wobble or the wheel will hit the sides of the sensor slot.  I checked the bottom of the pulley this morning and there is less than .002" measurable wobble in the rim so I think if I fasten the encoder with enough screws wobble won't be a problem.

Chuck
So many projects, so little time...

Offline cfellows

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Re: Gear Hobber
« Reply #8 on: December 21, 2012, 10:06:04 PM »
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
So many projects, so little time...

Offline John S

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Re: Gear Hobber
« Reply #9 on: December 21, 2012, 10:22:18 PM »
Also interested.

I have an electronic gear hobber, probably one of the first to do it but it uses a simple but dedicated controller, very interested in how the Arduino handles it.

Chuck one thing I can tell you is the magic number for the encoder is 4,000
Found this out by trial and error, above 4,000 and the driver can't keep up with the pulses, much below this and the steps are too course.
i use a 1024 encoder geared up to do 4,000 per rev.

Some info here.

http://bbs.homeshopmachinist.net/threads/11224
John Stevenson, Nottingham , England

Offline cfellows

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Re: Gear Hobber
« Reply #10 on: December 22, 2012, 09:11:49 PM »
So, John, I've spent the past day or so thinking about your post and looking at your links.  I assume you used a commercial encoder?  I don't have any easy way to couple a commercial encoder to my spindle.  I may have to remake my encoder wheel with more divisions, but there is no way I can even approach 4000.  I think 240 is about the best I can do. 

I think I will also have to start using half stepping on my stepper since I only have 1000 steps per work spindle revolution.  If I use half stepping I can get it to 2000.

Chuck
So many projects, so little time...

Offline John S

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Re: Gear Hobber
« Reply #11 on: December 22, 2012, 10:18:16 PM »
Chuck,
Also used half stepping and yes it is a commercial encoder.

Still interested in what the Arduino can do. Mine is just a simple divide chip that counts the input pulses and divides to output steps, probably very dated  and modern processors can handle the signals better than a simple chip.

One problem mine has is that you have to do everything in one pass, when you stop to take a measurement as it stops you can see it loose steps. Same when it starts up it takes a small while to catch up.

Not saying that yours will in fact I'd be very pleased if it didn't as I could copy it  :ThumbsUp:

It can be done the EMC setup shows that.
John Stevenson, Nottingham , England

Offline cfellows

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Re: Gear Hobber
« Reply #12 on: December 28, 2012, 05:35:24 AM »
So, I've scored a nice, 1000 PPR quadature encoder on ebay.  It has ball bearings and if I count the pulse rise and fall on both channels, I can get 4000 counts per revolution.  I also have an idea of how I can run it with a .200 pitch timing gear and belt from the spindle and detach it when not in use.  Using the timing belt, I could gear it up to turn 2 or 4 times for each spindle revolution, and may consider doing that.
Chuck
So many projects, so little time...

 

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