Author Topic: Has anyone ever used these?  (Read 7236 times)

bogstandard

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Has anyone ever used these?
« on: December 14, 2008, 06:17:14 PM »
I am refering to gear hobs.

http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Gear-Hobs

I have used normal gear cutters, in sets, and home made flycutting gear cutters, where each tooth is cut individually, but have never really delved into this area.

As much as I know is that one hob does the job of a whole set of normal cutters, but how are they used?

I know I could do a 'google' on the subject, but you usually get the full technical jargon, what I need to know is what the hands on experiences are, easy or hard, good or bad.

It looks like it could be a much cheaper (at least 50% saving) and faster way of being able to cut gears than the full sets syndrome, and if it looks a feasible proposition, I will invest in the full setup.

Bogs


Offline Bernd

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Re: Has anyone ever used these?
« Reply #1 on: December 14, 2008, 06:39:26 PM »
Ok Bogs I'm going to let the cat out of the bag so to speak. I'll try to make this short. I worked for a company here in the US that made gear cutting machines, they have a subsidiary in the UK. Google Gleason Works. In 1980 they starting building hobbing machines for the front wheel drive craze that took over the auto market. Let me just say I started out as an apprentice operating machines in the machine shop, worked on the assembly floor were they were built and run for the first time. So I know a bit about hobbing gears.

Ok now on to see if I can answer your question. The machines that use these cutters are complicated because both the part and cutter have to run in relationship with each other. Think of the hob as one tooth on the mating gear that has been turned into a cutter. I know it's hard to wrap your mind around that concept. The first machines that we built were mechanical, meaning gearing was used to set the ratio between cutter and part. There were several pages of settings that were need to get all the angles right.

Now having said all that It can be done in a horizontal mill with the proper setup but would be quite time consuming for a home style cutting operation.

I now wish I had keep some of my manuals and notes on this. Reason being several people have mentioned they like to hob gears. Well there's a bit more to it than just mounting a cutter in a machine. You actually need a hobbing machine to do it. The last I knew these machines were selling for several 100,000 dollars. But do google Gleason Works if you have time.

Bernd
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Offline John Stevenson

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Re: Has anyone ever used these?
« Reply #2 on: December 14, 2008, 06:43:51 PM »
Bogs,
The hob needs to be geared to the blank by some means.
They are not meant to replace the single Brown and Sharp type gear cutters.
The tooth space on a hob is a spiral with the pitch equal to the circular pitch.
If you try to use these as a cutter feeding into a stationary blank they will just cut a wide swathe thru the blank.

Image a jubilee clip whist the worth [ hob ] is revolving it drives the blank [ band ] stop the band and it strips it.

Can be done mechanically.



Setup on a Parkinson mill, the table is slewed equal to the hob helix angle and there is a right angle drive under the alloy cover on the spindle that takes the drive to the dividing head.
In this case is all the gearing was equal at 1:1 it would cut a 40 tooth wheel as that is the internal gearing in the dividing head.
reduce it 2:1 and it cuts 80 teeth.
it's just like screwcutting.

Can be done on a turret mill, you need to slew the head to the helix angle and cut on the side of the blank but you still need gearing.

You can cheat and use electronic gearing driving a stepper driven dividing head.
Read  http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/Gearhobbing.txt

and follow the pics at

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/hob%20indexer1.jpg

Thru to

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/hob%20indexer26.jpg

Nice thing about hobbing is only one cutter needed, fast and you can do specials that the B&S type can't do.



These three gears are all cut on the same blank, only the 21 tooth is geometrically correct, the 20 has been corrected to get stronger teeth and the 22 is running with lighter teeth but all will run together because they have been generated from the same hob instead of being cut.

And this is Bling  :headbang:



.

John Stevenson

bogstandard

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Re: Has anyone ever used these?
« Reply #3 on: December 14, 2008, 07:32:09 PM »
Bernd and John,

Looks like you have saved me a lot of heartache, and cost me even more money.

Methinks I will stick to my old methods, and bite the bullet when it comes to paying for cutters.

Thanks gents, you have answered my question perfectly.

John

Offline Darren

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Re: Has anyone ever used these?
« Reply #4 on: December 14, 2008, 07:32:17 PM »
Feel free to shoot me down in flames here, cos I could well be wrong,

But I think I once saw a Utube demonstrating how these hobs are used, I believe the hob was mechanically spun and the gear blank was free rotating, only driven by the hob itself? Or did I just misunderstand?

« Last Edit: December 14, 2008, 07:37:39 PM by Darren »
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Offline Bernd

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Re: Has anyone ever used these?
« Reply #5 on: December 14, 2008, 08:56:14 PM »
Feel free to shoot me down in flames here, cos I could well be wrong,

But I think I once saw a Utube demonstrating how these hobs are used, I believe the hob was mechanically spun and the gear blank was free rotating, only driven by the hob itself? Or did I just misunderstand?



No Darren you saw right. It'll work. It's just like a worm gear driving a worm wheel, except that it's cutting. But remember that the gear your cutting is free wheeling so one wrong move and you could end up with a broken cutter or even worse a broken machine. It'll work with a tap also as a cutter. The other thing is the cut gear would not be of proper form. Hope this has answered your question.

Bernd
You can't fix "STUPID".

Offline Darren

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Re: Has anyone ever used these?
« Reply #6 on: December 15, 2008, 03:01:53 AM »
Thanks Bernd,

I had another search for that demo but all I could find was both parts driven in sync.

I was beginning to question how old I was...!!  :D
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Offline Bernd

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Re: Has anyone ever used these?
« Reply #7 on: December 15, 2008, 01:30:15 PM »
Can you supply me with a link? I'd like to have a look at that.

Bernd
You can't fix "STUPID".

Offline Darren

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Re: Has anyone ever used these?
« Reply #8 on: December 15, 2008, 01:46:14 PM »
Hi Bernd, just search Utube under "gear hobbing" loads of vids to watch if that's what tickles you  :)

http://uk.youtube.com/watch?v=jsDdELruCe4
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Offline Bernd

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Re: Has anyone ever used these?
« Reply #9 on: December 15, 2008, 02:16:49 PM »
The pic was of a very old manual hobber and as you said driven in sync. If you go to the bottom of that pic you'll find a video of a Gleason hobber. I worked on the first generation of these when the company came out with them. All driven with servo motors. Very little to no gearing in the machine it self. Kind of ironic that a company producing gear machines gets rid of the gears in thier own machines. But the quest for speed is what drove that.

Bernd
You can't fix "STUPID".