Calling all gear hobbers

[Brett W]

Since I build race cars and parts, I have an interest in the gear machining process as well as splined shafts. What type of hobbs are used for normal automotive sized parts?

 

[EmGo]

What type of hobbs are used for normal automotive sized parts?

Depends on the part. Long skinny things like axles is one thing, basic helicals another, blind back-tapered teeth like a synchro are another. Helicals, spurs, splines, sprockets will all use different methods depending on the part.

"Normal" is a pretty vague description

 

[Brett W]

Input shafts for transmissions, gears with syncros, straight cut gears with syncros, not necessarily axle parts, but broaching splines in hubs would be a useful capability.

Guess I would need the ability to do both, so cutting helical gears is useful, but without the ability to cut the internal splines, its kinda of useless.

Probably something dumb to think about bringing in house, but still would like to learn about it.

 

[EmGo]

... gears with syncros, straight cut gears with syncros ... but broaching splines in hubs would be a useful capability.

Guess I would need the ability to do both, so cutting helical gears is useful, but without the ability to cut the internal splines, its kinda of useless.

The minute you start talking synchros, you get into complexity ...

The synchro teeth themselves are cut with a back-angle usually on a shaper with a tilted table. There's one machine for ya. Then another to point the teeth.

Synchro tilting isn't like tramming a Bridgeport, usually they tilt the whole top half of the machine, so you pretty much set up one machine for just that process.

The teeth, not on all but on just enough to be annoying, can't be hobbed because the synchro teeth get in the way. Need a shaper, with cutters for that specific lead AND a helical guide (used to be $3,000 plus, I don't dare think what they run now) to give the cutter the twist it needs traversing the face.

There have been some experimental and weirdo cnc attempts to do the twisting electronically, either big money or big trouble, take your choice.

Spur teeth are usually straightforward, either hob or shape depending on the geometry of the blank. In practice you need both You'd like to hob as much as you can but sometimes there is stuff in the way. Shaper time.

As far as the internal splines, you used the right word, broach. For which you need a broaching machine and a broach, to match every spline you want to cut.

Involute splines you can do on a shaper with an internal cutter, but an awful lot of automotive shafts are straight-sided. Can't very well do straight sides with an internal cutter because of the way the parts revolve with the cutter during the generating process. It can be done with a single tooth cutter in an nc shaper tho. CNC gear shapers are also pretty expensive, even twenty year old ones.

Obviously can be done because there are people doing it but it's not something you want to get into casually. Doing a couple of parts is reasonable but the wide variety you described, that's a lot of tools and equipment to buy.

 

[Turbowerks]

Like all machining , the machine is the least of the cost, tooling? Not so much. If you want to be able to do some internal splines and couplers you should look for a fellows gear shaper. The right one can do od spur, helical with the right guides and internal. A hob is external only. then you need a broach machine,but the tooling is very costly especially for low volume. And in transmissions very few internal splines are a standard. I found this out the hard way.


When I find it I don’t need it
When I need it I can’t find it!

 

[Peter from Holland]

On automotive gears it is not unusual to have specific pressure anglesIts not like you buy a 20dgr hob and machine away If you do not have the specifics of the gear you always have to make at least a set of gears and do your own calculations It is very hard to measure a gear and then copy one
Peter

 

[EmGo]

It is very hard to measure a gear and then copy one

Used to be. Now you can just throw money at it. Big money. Zeiss, Hoefler, Gleason ... they all have computerized measuring machines that will give you back the data you want.

You could probably do it using a cmm as well, but that would involve thinking.

 

[Peter from Holland]

Indeed And then a 5axes machine The software from klingelnberg and go at it
peter

 

[EmGo]

Indeed And then a 5axes machine The software from klingelnberg and go at it

Too slow, except for big one-off spiral beevils. If'n I was crazy and wanted to do short-run automotive, I'd get :

14-15 or D type Barber-Colman for shafts - hole through headstock is okay, can't put a watermelon through it but still good enough, and they all have a diff, so useful for other stuff.

Fellows 7 or 8 or 4 for synchros, whichever is cheapest, butcher it for the tilt.

Latest nicest 45 or 75 Maag you can find for teeth. Cheapest fastest tooling, any helix you want, blind corners not a problem, could even do the occasional internal spline.

If you want to get carried away, a little Reishauer or Gleason gear grinder might be nice. Nice to have a Red Ring lapper or hone, those do reduce noise, auto people like quiet. Or both.

If you're doing very many but don't need ground accuracy, you could get a shaver. GCU or GCY maybe, def get one with crowning, and some cutters. About $1500 each for cutters in the US but I know a guy in China ...

Don't forget you need a heat treat shop that's good with carburizing close by, and reasonable, or that will be a problem.

Then a hob sharpener and a shaper cutter sharpener and at least involute and lead testers, rolling tester with master gears can be useful, red liner maybe and a surface grinder for the Maag cutters and maybe a wire edm so you could make your own and a cylindrical grinder for the shafts and an i.d. grinder for the bores and either a tooth pointer or a small vmc with a fourth axis for pointing the synchro teeth and of course you need a lathe, maybe get an nc one as well in case you want more volume, and probably a Bridgeport or Gorton for quick and dirty stuff and a compressor and a hardness tester would be helpful, optical comparator wouldn't hurt, twenty or thirty thousand dollars in small tools and cutters, a place to put it all that isn't going to rob you as soon as they figure out it'll cost you a fortune to move, heck, let's get started ! In two or three generations we'll be rich ! Filthy rich, I tell you !

How much did you say to buy a hot dog cart ?

 

[Turbowerks]

After doing this in my younger years Eg, should have read your post 30 years ago lol i can really relate! All except the filthy rich part. I guess Ash got that part of it. Should have listened better theres no money in that Motorsports stuff. At least long term.


When I find it I don’t need it
When I need it I can’t find it!

 

[Brett W]

The minute you start talking synchros, you get into complexity ...

The synchro teeth themselves are cut with a back-angle usually on a shaper with a tilted table. There's one machine for ya. Then another to point the teeth.

Synchro tilting isn't like tramming a Bridgeport, usually they tilt the whole top half of the machine, so you pretty much set up one machine for just that process.

The teeth, not on all but on just enough to be annoying, can't be hobbed because the synchro teeth get in the way. Need a shaper, with cutters for that specific lead AND a helical guide (used to be $3,000 plus, I don't dare think what they run now) to give the cutter the twist it needs traversing the face.

There have been some experimental and weirdo cnc attempts to do the twisting electronically, either big money or big trouble, take your choice.

Spur teeth are usually straightforward, either hob or shape depending on the geometry of the blank. In practice you need both You'd like to hob as much as you can but sometimes there is stuff in the way. Shaper time.

As far as the internal splines, you used the right word, broach. For which you need a broaching machine and a broach, to match every spline you want to cut.

Involute splines you can do on a shaper with an internal cutter, but an awful lot of automotive shafts are straight-sided. Can't very well do straight sides with an internal cutter because of the way the parts revolve with the cutter during the generating process. It can be done with a single tooth cutter in an nc shaper tho. CNC gear shapers are also pretty expensive, even twenty year old ones.

Obviously can be done because there are people doing it but it's not something you want to get into casually. Doing a couple of parts is reasonable but the wide variety you described, that's a lot of tools and equipment to buy.

Yeah staring at the design of the syncro teeth left me with several questions. Now I have even more HAHA. Thanks for the education.

 

[Mannyadarve]

Hello.i have a gear hobbing machine a had a problem my gear hobbing machine has no differential its non differential the only way i do helical gears is non differential method.can i ask a help the formula of nondifferetial gear hobbing machine or can you do a sample computation.thanks for helping

 

[IceCzar]

Hobbers aren't rated just by size, they are rated by the pitch they will cut. That Mikron would struggle with 16 DP. It's probably happy with 24 DP and finer. (....)

I had a question, within a specific context. If the goal is prototyping one off gears rather than production, can a multipass or some other strategy push that rating?

Not an idle question as I've acquired a Mikron 79

 

[Peter.]

The Mikron 79 only cuts spur gears AFAIK so yet you can take as many passes as you like.

It uses 8mm bore hobs does it not?

 

[IceCzar]

I believe so, it's still on it's pallet at the back of the firm I work for. Been crazy busy building two servo hydraulic systems for Universities.

 

[IceCzar]

So far all that has occurred is looking for a manual and parts list that isn't overpriced, cleaning cutting fluid varnish off the plating, picking up an incomplete TU-79 work holding set and research.

 

[ratbldr427]

The splines on auto gears can be made on a "shobber",a combination machine that hobs the gear and splines at the same time. The ones I saw didn't appear to have any change gears so they were for a spacific gear. Pfauter-Magg(sp?)made the ones I saw . A really stripped down machine.
The machines I saw were mounted on a carousel , six or more, and the whole machine indexed to load and unload the gears. No cnc involved,60's era.
Due the volumes that auto mfg's have they have all kinds of processes that are just not practical for "one offs". Also their ratios and pressure angles can be odd ball to what standard industrial gear boxes use.All are hunting tooth design.
I have never noticed any back cut on the splines of any of the trans I have worked on but never tried to find any.