Re: Kapp Hob Grinder


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Posted by RonV on December 23, 2005 at 10:12:52:

In Reply to: Kapp Hob Grinder posted by Ben on December 21, 2005 at 17:00:05:

I donít know of any articles that could give you this information but there is a chap who gets around on the forums who has a web site where you can purchase his gear design software and also runs a forum where perhaps you could contact him, http://www.gearcam.co.uk/4598.html. He works for Acedes in the UK. Perhaps he could help. Another option is to go here, http://www.eng-tips.com/threadminder.cfm?pid=406&page=1. This is another great forum with a lot of smart people contributing to it. Perhaps posting a question will give you some good leads.

Iím still learning about all this stuff so forgive me if I sound a bit ignorant. The form a grinding wheel produces as it rolls through a helix is called an involute helicoid. Itís the same form thatís generated when grinding thread worms. Buckingham talks a lot about it in his book ďAnalytical Mechanics of GearsĒ, excellent book. I donít see how adjusting the rake offset or any other angles can change or compensate for the way the form is generated on a hob sharpener. As far as I know, the only way the profile can be corrected is by dressing the wheel convex to compensate for the convex shape generated on the hob.

There was a lot of argument in the early days of hobbing machines as to the accuracy of involutes generated by a straight sided cutting tool. Because the teeth on a hob are travelling through a helix the same problem occurs as on the hob sharpener. Any hob, because they are all straight sided will not produce a true involute because of this. But getting back to reality, the amount of error is infinitesimal.

Iíd be interested to know how much error you found in the base pitch of the gears cut by one of the hobs with the crowned profile.



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