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Paul Alciatore
01-10-2013, 11:36 PM
I was inspired to do some reading by the other thread on bevel gears and I came across the word "octoid" in the description of the profile of bevel gears in this article. (Page 1, Column 4, Line 2)

http://www.cad.sun.ac.za/catalogs/MachineComponents/bevellgear.pdf

He states that it is the bevel gear analogy of an involute. Other sources state that it is similar to an involute. Several different sources said that in exactly the same words suggesting they all copied one original source. A fairly extensive search of the web did not yield any further information.

Can anybody shed any further light on this? I would like to know exactly how does it differ from an involute?

oldtiffie
01-11-2013, 12:36 AM
http://www.google.com.au/#hl=en&sugexp=les%3B&gs_rn=1&gs_ri=hp&cp=11&gs_id=18&xhr=t&q=octoid+gear&pf=p&tbo=d&rlz=1R2IRFC_enAU360&sclient=psy-ab&oq=octoid+gear&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&bvm=bv.1357700187,d.dGI&fp=62de6c98bf44ccb6&biw=1920&bih=818

Paul Alciatore
01-11-2013, 01:22 AM
http://www.google.com.au/#hl=en&sugexp=les%3B&gs_rn=1&gs_ri=hp&cp=11&gs_id=18&xhr=t&q=octoid+gear&pf=p&tbo=d&rlz=1R2IRFC_enAU360&sclient=psy-ab&oq=octoid+gear&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&bvm=bv.1357700187,d.dGI&fp=62de6c98bf44ccb6&biw=1920&bih=818

Thanks, that is precisely what I searched for. So which search result goes further than just "...similar to an involute"?

ikdor
01-11-2013, 02:36 AM
This one:
http://pdf.directindustry.com/pdf/quality-transmission-components/bevel-gearing/11708-82731.html

Igor

Rich Carlstedt
01-11-2013, 12:14 PM
What you want is in the American Machinist of September 7, 1899 as it gives the history
See this

http://books.google.com.au/books?id=fMtMAQAAIAAJ&pg=RA1-PA70&lpg=RA1-PA70&dq=octoid+gear&source=bl&ots=4Akz_vzyIC&sig=0YzXoa7SHCZbrw5-J_eWZ_MiUrQ&hl=en&sa=X&ei=kUfwUIfpB6jo0gHjwIAY&ved=0CE4Q6AEwBjgK#v=onepage&q=octoid%20gear&f=false

Rich

Paul Alciatore
01-11-2013, 02:18 PM
This one:
http://pdf.directindustry.com/pdf/quality-transmission-components/bevel-gearing/11708-82731.html

Igor

OK, that one changes the wording to "slightly simplified form". That does not answer my question. Just a different way of say it is different.

Paul Alciatore
01-11-2013, 02:46 PM
What you want is in the American Machinist of September 7, 1899 as it gives the history
See this

http://books.google.com.au/books?id=fMtMAQAAIAAJ&pg=RA1-PA70&lpg=RA1-PA70&dq=octoid+gear&source=bl&ots=4Akz_vzyIC&sig=0YzXoa7SHCZbrw5-J_eWZ_MiUrQ&hl=en&sa=X&ei=kUfwUIfpB6jo0gHjwIAY&ved=0CE4Q6AEwBjgK#v=onepage&q=octoid%20gear&f=false

Rich


Rich, Thanks.

I had to read this one twice and some sections several more times. It does not actually say what the shape of the teeth is or exactly how it differs from an involute, but it does hint at the reason why that shape is used. Apparently, due to the spherical nature of bevel gears, a crown gear (which is considered the generating form, like a rack in spur gears) with straight flanks does not generate bevel gears with involute shaped teeth. Instead another, slightly different shape is generated and it is called "octoid". This shape is close to the involute form, but not the same.

But consider, even spur gears can have a modified involute curve.

Not a complete answer, but a start. I am still very curious.

demerrill
01-11-2013, 04:57 PM
I've become enamoured with Google Images search to aid in identifying objects. Tried this on 'octoid bevel gear' and got:

http://www.google.com/search?num=10&hl=en&site=imghp&tbm=isch&source=hp&biw=1215&bih=1042&q=octoid+bevel+gear&oq=octoid+bevel+gear&gs_l=img.3...1358.8088.0.9281.17.6.0.11.11.0.66.29 5.6.6.0...0.0...1ac.1.gr8KpE6l0yk

among which this one (and probably others) reference the 'octoid' tooth profile:

http://www.qtcgears.com/Q410/QTC/Q410P356.htm

Ctrl F to find octoid on the page

David Merrill