gear hob info

[cessna]

Hi, I need to cut some gears in mod 0.7 size. I have in the past made a hobb for imperial gears with some success. Is there a post on info needed, such as depth of cut, spacing between teeth etc. I need one 12t, one 24t and one30t? Any help or direction would be appreciated.
Thanks
Terry

 

[Hopefuldave]

A good place to start is the metric gear spec. - Mod 0.7 is 0.7mm diameter per.tooth at the pitch line, so the tooth pitch will be Pi x 0.7mm, tooth thickness half that.
The pressure angle is 20 degrees so as a hob is effectively a rack cutting the teeth you can make the hob flanks straight with 20 degree angle (40 included angle).
Depth of cut will be (if I remember right) twice the tooth thickness plus a few thou bottom clearance, you'll need to do a little trig to work out the width of the flat on the tip of the cutter to make the hob!
The larger the hob diameter the better, particularly if it's a helical hob - if it is, for *strict* accuracy you have to compensate for the helix angle (that you angle the blank axis at) - increase the hob pitch by a factor of 1/cos(helix angle)

 

[cessna]

Thank you for your reply and info. I will try and get my fuzzy head around it.
Terry

 

[Cogsy]

I have had success with the info othis site http://www.helicron.net/workshop/gearcutting/gear_cutter/

There's more info / calculations on the other pages, just check the site map on the right hand side of the page. I've made 2 hobs and several gear sets so far and all have worked perfectly.

 

[cessna]

Thank you for your reply cogsy, that is a good site, I think I have finally got it thru my head the info needed.
Terry

 

[trizman]

Terry,
I have just cut a 50 tooth helical 0.7 mod gear. I used the approach and information from here:-
http://homepage.ntlworld.com/peter_harrison/workshop/gearcutting/

Peter

 

[Fluffy]

Terry,
Below is a link to a very informative site.
The section on hob like cutters is dated 31.07.2008.
I used google translator to print an approx. English version & then made a number of cutters for differing module gears. All worked very well & the gears run well.

http://www.metallmodellbau.de/

Don.

 

[cessna]

Thanks for the link Don, I think I have a handle on it now. A few years ago I made a hob and it worked fine, but the years pass and the brain gets foggy.
Terry