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Where to learn Gear Hobbing?

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Russ B02/11/2018 13:12:41
547 forum posts
21 photos

Can anyone recommend any literature on gear hobbing. Its something that's always fascinated me, I'd love to get a little hobbing machine and have a go but I'm afraid it would just be overly complicated to setup and wrap my head around.

I'd love to be able to cut the gears to make a small differential gear one day.

Regards,

Russ

Michael Gilligan02/11/2018 13:38:43
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14024 forum posts
609 photos

Russ,

This is an excellent little book from 1914: **LINK**

https://archive.org/details/hobsgearhobbing00edgarich

... A very good place to start.

MichaelG.

Andy Pugh02/11/2018 16:08:14
47 forum posts

Whilst the Ivan Law book doesn't describe hobbing in any detail it is probably a good starting point.

https://www.amazon.co.uk/Gears-Gear-Cutting-Home-Machinists/dp/1565239172/

Hobbing is, in essence, very simple. The gear blank needs to go round at 1/n the speed of the hob, and the hob has to cut the teeth to the correct depth.

The speed division is pretty trivial nowadays, with cheap steppers and encoders readily available.

You can even do it on a milling machine if you have an encoder on the spindle.

The only other wrinkle is that the angle of the hob to the blank is not 90 degrees. The required angle is marked on the hob, but not all machines make it easy to set.

The video above uses a tilting head. My current setup uses a Harrison Milling machine where the table swings.

Hopper03/11/2018 01:52:42
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3715 forum posts
73 photos

Did you have a look at this thread here: **LINK**

for quite a bit of discussion on the topic and a simple way to start - using taps as hobs.

BW03/11/2018 02:18:49
245 forum posts
40 photos

This page is also pretty good

http://www.helicron.net/workshop/gearcutting/

Brian G03/11/2018 07:32:32
589 forum posts
25 photos
Posted by Russ B on 02/11/2018 13:12:41:

...

I'd love to be able to cut the gears to make a small differential gear one day.

...

My son and I keep going back to this video. There we were, happily converting 1:87 trucks to Faller car system when we realised just how much further some people go.

Brian

Mike E.03/11/2018 08:57:17
192 forum posts
1 photos

Currently there is an old Koepfer gear hobber on the G and M tools site.

Phil P03/11/2018 09:07:55
510 forum posts
137 photos

Actually, learning how to use a hobbing machine is very straight forward. More often than not is a case of applying the settings from a chart and the information marked on the hob, and switching the machine on. Workholding can sometimes present its own challenges, but no more than making a special mandrel or spacer.

Buying or making a gear hobbing machine is the easy bit, but bear in mind you will have many years of locating and buying the hobs to tool it up. Involute, Cycloidal, 14¼° Pressure Angle, 20° Pressure Angle, Ratchet Teeth, Splines.........The list goes on depending on what you want to do.

I have had a Mikron hobbing machine for over 35 years, and I have about a hundred or so hobs for it but still dont have what I would call a complete set of hobs and probably never will. Also even if you can find them, the cost of hobs has rocketed over the years, so that needs to be thought about.

If you only need a few gears for one specific job, I would say its not worth it, either buy them ready made or buy a set of single point cutters for the size you need.

Just my 2p worth

Phil

Edited By Phil P on 03/11/2018 09:12:00

Edited By Phil P on 03/11/2018 09:15:00

Neil Wyatt03/11/2018 09:35:11
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16585 forum posts
687 photos
75 articles

I'd contradict Phil, (sorry!)

If you are more concerned about making gears for your own projects than matching existing gears, then a couple of hobs for appropriate sized gears are all you need.

A 1 mod hob will cover most of 'our' general purpose power transmission needs and 0.5 mod will cover many needs for small gears for mechanisms.

Obviously as soon as you start replacing gears from existing machinery the number you need will start rising rapidly!

Neil

Russ B03/11/2018 10:05:27
547 forum posts
21 photos

Thanks for these suggestions, they're going on my list of things to do!

Brian G's video hits the nail on the head, I want to make a small differential, for an RC truck although not that small!! I'm looking around 1/10th scale - however....... I'd love to make a torson differential on day. I'm sure by the time I actually get to the stage where I've enough knowledge and the skills equipment required to give it a shot, I'll have other interests, but for now, this is good.

I'm holding off on buying anything, this is purely academic for now, I have an 19 week old baby so I'm out of the workshop and into books now, although I do still get 2 or more hours to myself most nights during the week as both mum and baby go to bed early!!

I do not know how small a gear/worm I could make on something as big as that Koepfer (althoguh it looks very compact) I would guess, I might want to make my own miniature hobber, I've a slight inclination towards horology too, some of the things I've seen online are incredible pieces of engineering, and then when you realize the scale, it's just mind blowing!

again, thanks for these suggestions, things are becoming clearer, it's a very in depth niche though!

Andy Pugh03/11/2018 12:11:25
47 forum posts

You can make a differential with only spur gears, the Dennis Patent Overhead Worm Drive differential is such a device:

The first picture here shows one.

https://en.wikipedia.org/wiki/Differential_(mechanical_device)

The spur gear design makes it possible to put a pair of diffs inside another diff, for four co-axial outputs:

https://photos.app.goo.gl/BKPQMLMt94ACWR4e9

Edited By Andy Pugh on 03/11/2018 12:12:00

Phil P03/11/2018 23:10:26
510 forum posts
137 photos

My Austin 7 had a spur gear diff like that one, another interesting diff is the one fitted inside the crankshaft of a Sentinel steam waggon.

http://archive.commercialmotor.com/article/22nd-february-1921/30/sentinel-wagon-design

https://www.google.co.uk/search?q=sentinel+waggon+differential&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi62pDQq7neAhWJ26QKHVfQBFUQ_AUIDygC&biw=1920&bih=938#imgrc=X_XVy2OE-wATuM:

Phil

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