Gear Hobbing on a Lathe

[19brendan81]

I read a few posts on practical machinist that indicated you could use a gear hob (as attached) to cut gears on a lathe, with the hob mounted on an arbor between centers and the gear blank mounted on an axle on the cross slide that can be fed into the hob. I think the gear blank needs to be tilted off the vertical axis at a precise angle for this to work properly.

Apparantly the hob itself will index the work, so you dont need an indexer or dividing head, and that you only need 1 hob per module/pitch that you are working with. These are two big advantages in my opinion.

Has anyone heard of this being done before? Does anyone have any further info such as how you actually do this?

Brendan

[pipeclay]

Cant give you any help in a setup like this on a lathe,but can give advice if you do it be very carefull.

[.RC.]

AFAIK the hob will not index the work properly and will cut more from one side them the other.

[Jekyll and Hyde]

I read a few posts on practical machinist that indicated you could use a gear hob (as attached) to cut gears on a lathe, with the hob mounted on an arbor between centers and the gear blank mounted on an axle on the cross slide that can be fed into the hob. I think the gear blank needs to be tilted off the vertical axis at a precise angle for this to work properly.

Apparantly the hob itself will index the work, so you dont need an indexer or dividing head, and that you only need 1 hob per module/pitch that you are working with. These are two big advantages in my opinion.

Has anyone heard of this being done before? Does anyone have any further info such as how you actually do this?

Brendan

Not quite the same, but I've cut a worm wheel on the mill using basically the same method (saw a few guys doing it on a lathe, and saw no reason why I couldn't do the same with my mill). Mounted a tap in the spindle, and mounted the blank in a little stand on the table. The blank should be free to rotate, but without having any side to side play.

There is talk of needing to also gash the blank to allow the proper indexing, although I didn't do this. I was also only using aluminium, and did it as much as proof of concept as anything. Started off with a few to many teeth (was shooting for 90), but I just fed it in a little more until I got down to the correct number of teeth. Not a textbook way of doing it, there are calculations which give you the desired blank diameter, and gashing would also help. At the time I had no lathe, so worked with what I had, and the end result is functional (depending on what it was used for).

Should be no reason why a hob wouldn't work in the same way? A search on homemade worm wheels should turn up more discussion of the concept, and a few youtube videos.

[pipeclay]

What you have to consider is the size of the hob.
How ridgid a setup you will have.
What method of rotateing your blank you will use?
Unless the Hob is spirally cut you wont get any rotational drive from it,unless you have at least 2 if not more teeth of the Hob engaged with your blank.

[nadroj]

I know next to nothing of gear hobbing, except for reading about some do-it-yourself arrangements to synchronise the work and tool.
There's a video of someone who used stepper motors instead of gears.

There is some info here:
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/hob%20indexer1.jpg

...and indexer2.jpg etc

Jordan

[hobbytrees]

:no:hi brendan. i done lots of ghear cutting and spline on a hobb machine ,and know
wat the requirments are to cut ghears, i also have a ward no7 lathe that i use as a hobby now , and i can assure you that ghear cutting cannot be done on a lathe ,
how ever nothing is impossibile with a special attachment ,
even then there is no guarante of precision that the hobb machine can give you .
cheers,

[pipeclay]

Have a search for gearcutting on a lathe and you will find numerrous items.
Not the ideal way but it is done,usually with single point tooling.

[19brendan81]

I cant find the post I referenced but there is some debate about the concept here...
Gear Hob questions - Practical Machinist - Largest Manufacturing Technology Forum on the Web (http://www.practicalmachinist.com/vb/general/gear-hob-questions-209473/)

Its called free hobbing apparantly and the hob itself spins the blank. the original thread I was looking for had a link to a youtube video that showed a bloke doing it on his lathe. I couldnt see the vid at work and now I cant find the thread.

I think i'll just write off this concept and order a set of involute cutters.

[pipeclay]

That would probably be your better choice.