Machining Bevels.

For discussions of the various methods of Bevel Machining.
Damo
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Re: Machining Bevels.

Post by Damo »

Actually, I like this book, goes into the cutting tool manufacture in detail.

http://books.google.com.au/books?id=wZp ... te&f=false
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ArtF
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Re: Machining Bevels.

Post by ArtF »

Damo:

  Heres a photo of an octoidal generation. If the rack in this picture were not bent into a circle, the output
woudl be an involute tooth. BUT, as I suspected if you simply bend the rack into a circle, the result is an
octoidal tooth. Thats why no math formulas seem to exist. Its a physical manifistation of the bending of the rack to a circular form.
  Now..the golden question. I generate my bevel "Involutes" by formulas derived from standard involute teeth ( so a linear rack ), BUT then I bend those teeth into a spherical form in order that they taper
correctly in a bevel. If a octoidal is generated by a straight rack bend round, then is a tooth generated from a linear rack but then folded spherically now a proper octoid? I highly suspect the answer to this is yes. If we consider just the infinitely thin outside tooth of a spur for example, mentally its easy to see that if you take this tooth and fold it upwards in bevel form so it fits a spere, you have folded a modification into that tooth. I would submit its the same process as folding the rack and then generatign the tooth prefolded. I would have to do a great deal of math to prove that though, its simply my intuition that tells me this is so..
  I will give this more consideration, but I highly suspect an octoidal tooth is what we have. It cannot, after, all be called an involute tooth as the process of folding it into a bevel has changed its shape, so if it isnt an involute..what is it?... I suspect perhaps its an octoid. Since the term "Octoid" refers only to its contact pattern and not its shape, I can only surmise this as yet..

  SO perhaps just putting out this tooth shape for grinding will work..
Art


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octoidalgenerator.jpg
Damo
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Re: Machining Bevels.

Post by Damo »

Hi Alf, yes i think you're right. If you get a straight rack and project onto a sphere you will get 2 crown gears. But what happens to the tooth form when you get closer to the centre? This is where the octoid comes in. If you take one tooth flank of that crown gear, and another flank on the opposite side and imagine a surface that runs through those 2 flanks. As if you were holding a circular disc of paper and on one side twist it to that flank angle, then on the other side twist it to the other tooth flank angle. If you look at this shape side on, it looks like a figure "8". So microscopically where the tooth flank is, so so minisculely, it's slightly "s" shaped. Would be nice to prove it mathematically. And remember this is just the crown gear, not yet bent around a smaller gear. What'd you think?
Damo
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Re: Machining Bevels.

Post by Damo »

I think all the calculations for a stanard involute are correct, just have to do one more function to them. Imagine a spur gear and the flat plane on the side of the spur gear, now all of a sudden that flat plane is spherical? Image the teeth. They are still an involute, just the world they live in is now a sphere. Now imagine 2 spur gears working together on parallel shafts, no imagine the flat plane on the side has become a sphere and the 2 shafts are now at right angles. Gives more meaning to me now of the work spherical involute. :-)
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ArtF
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Re: Machining Bevels.

Post by ArtF »

Damo:

  To the first question:  I cant imagine that piece of paper, though Im sure you can. Its the problem with such dicusions, their very hard
to describe in words. To the second comment.. exactly, I think when you take that spur tooth and fold it into a sphere you create a spherical
involute whos pattern of contact is then an octiod if its done correctly. Are mine? Christ only knows. I know they mesh very well, but if they pattern
on a figure 8... beats me.
  When I do finish the non-circ's in GT, I will visit the Gcode generator to add bevels. Since we're speaking only of using a ground cutter for these
the GCode will work fine no matter if we're rigth or wrong..the entire issue will be the cutter shape.. so we'll see.. :)

  Ill have the Gcode put out so that the blank will have to be tilted to root angle..

Art
Damo
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Re: Machining Bevels.

Post by Damo »

Hi Art, I tried to draw what I meant. Sort of looks like a potato chip. The line passes through 2 sets of axes at the same angle. From the side it looks like a figure 8. Imagine the rack going around the circumference and 2 opposite tooth flanks are on the surface.
Cheers Damo

Not sure if this will work, am attaching 2 images
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octoid-2.jpg
octoid-1.jpg
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ArtF
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Re: Machining Bevels.

Post by ArtF »

I see what you mean, it is a figure 8 on profile..  Im just not sure how that helps me in terms of getting the rigth profile..

Its interesting to note that the specification for the calculation of the bevel toothform produces a very bad looking curve in the
axial plane..its only once you fold that to spherical that the curve looks correct as a semi-evolute..

Art
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ArtF
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Re: Machining Bevels.

Post by ArtF »

Damo:

Just found this out there..

>>While gear manufacturing is well developed, with precision gears cut under
tight tolerances and producing smooth motions, the geometry of gear meshing
is not yet fully exploited in the industry. For example, bevel gears are
still designed using Tredgold?s approximation, under which the tooth profile
is designed so as to yield a projection onto the tangent plane of the back cone
that matches the profile of an equivalent involute spur gear.


  This IS what Im doing. The tooth form IS created to be correct as a typical spur when viewed from the
tangent plane on the back face..

  This link explains how to make the correct  (if thats the correct word) method..
http://www.geometrie.tuwien.ac.at/stach ... g_Proc.pdf


  As you can see, its not something Ill jump into lightly. :)

Art
Damo
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Re: Machining Bevels.

Post by Damo »

Out of those 5 theorems, they lost me at the first.  :D
Cheers Damo

Damo
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Re: Machining Bevels.

Post by Damo »

Actually, i'm just happy i understand the word "octoid" now.
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ArtF
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Re: Machining Bevels.

Post by ArtF »

Words just dont work..do they. :)

Art
John S
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Re: Machining Bevels.

Post by John S »

Yes but will it cook the turkey on Gas MK 5 ?
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CMcDaniel
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Re: Machining Bevels.

Post by CMcDaniel »

Hey Art, Anything new with the bevels or are You busy working on other things?
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ArtF
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Re: Machining Bevels.

Post by ArtF »

Hi:

  Bevels will be dealt with in a waterline engraving module, but probably not till next fall.

Art
Chuck
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Re: Machining Bevels.

Post by Chuck »

Art,

Here is another paper on spiral bevel gear generation and inspection.

http://gear-net.com/report/rep-03.html

Also Klingelnberg method is in a spread sheet with macros that create tooth form for Solid Works IGES inport.

https://www.youtube.com/watch?v=k-WdPTxinZk

Chuck in Wyoming

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