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Author Topic: Bevel Gear sample pictures.  (Read 9540 times)
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ArtF
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« on: January 14, 2011, 03:28:55 PM »

Hi Guys:

  As bevel gears are tested, Id appreciat e if anyone who can take photo's do so and place them here so I can analyse what I see in case of problems. Im hopefully getting close to at least getting to test. Ill post the first pictures of the early tests on this topic..

Art
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ArtF
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« Reply #1 on: January 14, 2011, 03:33:54 PM »

Hi Guys:

  Some problems still remain for me to fix up before release, but here's the first photos of Gerotic Bevels.
Wont really know if its all possible till the final testing on various angles.

This gear was cut for 35 degree shaft and was tilted by 22 degrees for the cut. It has bad trochoids though, where it shoudl have none, so Im adding code to make sure the bottom of the mill cant create a troichoid by lifting it to the involute level being shaved..




* bevel1.jpg (295.04 KB, 800x600 - viewed 789 times.)

* bevel2.jpg (291.93 KB, 800x600 - viewed 716 times.)
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ArtF
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« Reply #2 on: January 14, 2011, 03:35:31 PM »

By the way, cuz someone WILL ask.. Smiley

  The material is styrofoam insulatio n , it NEVER breaks a bit, and cuts like a dream.... plus Im cheap as well as nervous.. It was cut with a 3.2mm end mill.. took about 45 minutes for the cut..

Art


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geneb
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« Reply #3 on: January 14, 2011, 04:58:31 PM »

Art, if you would like to send me an STL of that gear, I can see how well the model is processed by Cut3D.

I like the foam idea - when I get a chance, I'll try it with some 3" long 1/8" tapered ball end mills I have.

g.
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ArtF
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« Reply #4 on: January 14, 2011, 05:22:33 PM »

Hi G:

  Latest version of the program will save the stl of bevels.. it does take a long time as the stl is generated triangle by triangle and only when commanded to do output. So since the solid never actually exists until
output time, a delay of 30-60 seconds per bevel can be necessary .

  This is just a 35 degree 25 tooth vs 15 tooth pinion Master.


  Styro cuts real well, seems to hold detial well too, and like I said, never breaks a bit. Smiley

Art
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John S
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« Reply #5 on: January 14, 2011, 08:02:19 PM »

Art,
What is the relations hip between the 35 degree bevel and the 22 degrees angle ?.

I'm getting 'geared up' by making a mould in alloy that I can cast some engineeri ng plastic into for blanks.
I made a big batch a while ago from some big surplus candles and some LDPE [ or something] Look on Cnczone for engineeri ng wax.

John S.
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John S.
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dansfoundry
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« Reply #6 on: January 14, 2011, 09:01:36 PM »

Hi Art, I think I'll output a bevel gear to an STL import into Aspire and scale it to a size larger to compensat e for shrinkage . the foam gear I will use as a pattern for lost foam casting. I can than use the resulting casting for a blank to finish. sorry I think about every thing in terms of foundry. Dan
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ArtF
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« Reply #7 on: January 14, 2011, 10:59:53 PM »

Hi John:

   The tilt angle ( pitchcone angle)  of a gear is based on the tooth count ratio between them , and the shaft angle.

For example a 90 degree shaft angle, with a 30 and a 15 tooth master/pinion, would have a pitch-cone
angle of 60 degrees on the pinion and 30 degrees on the master. ( or 2:1 ) The face angle is the addendum angle added to the pitchcone angle. Ive designed the cutting to be done with the gear tilted to pitchcone angle, so the actual top of the face tilts slightly down to cone center. ( by the addend angle).

   This means we can always zero at the back of the tooth at TDC, hanging towards chuck by 1/2 tool diameter. Ive modified the code to correct for a couple small errors in judgement and hope tomorrows test works better. If so Ill get a video done showing a run..Turn s out I was completel y wrong about the math,
once analysed the simple answer bit me in the arse. Still more testing to do, but it looks good for pretty much all bevels, at any angle 0 - 89 degrees of pitchcone or so.

  On the other hand if tomorrows test fails, you might want to hold off on the alloy work. Smiley

Art

 

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John S
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« Reply #8 on: January 15, 2011, 06:06:32 AM »

Hi John:

   

  On the other hand if tomorrows test fails, you might want to hold off on the alloy work. Smiley

Art

 

In the famous words of Donald Sutherlan d [ Kelly's Hero's 1970 ]

Oddball: Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?
Moriarty: Crap!

John S.
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John S.
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ArtF
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« Reply #9 on: January 15, 2011, 04:36:04 PM »

Hi Guys:

  Well, here's todays test. ( or the final one anyway..).

  Ive had a lot of trouble due to my setup not allowing tilt very well. Turns out the 4th was getting retilted by hitting the rear gantry bearing. Im very limited in how much I can tilt my table, so my tests are taking longer than Id think.. Im not convinced all is well, BUT this last one looks pretty much like I expected, I havent managed to cut its mate yet..

 Ill release a version probably tomorrow with the code generator that produced this one in hopes that if someone else cuts one we can see a pattern of what I may need to change.

  Theres a few things to consider. Firstly, when you design a bevel the handbook and other books have you design the gear with a virtual tooth count, changes in profile shift..a lot of things get modified mostly due to the way their about to be machined. Ive gone with the theory that a tooth considere d as to the plane of the rear cone at 90 degrees to the pitch angle should as a start simply be a normal spur gear tooth in its profile
to roll properly. Ive assumed this beacuse if you look at any two bevels, and take a thin slice at any point on the face, you basically have the rolling action of two spur gears. Going by this assumptio n  there are no modificat ions to gearotic bevels as Im not sure what the handbook is modifying to match a process, and what is mechanica lly necessary .

 Another thing Im unlclear about is the helical radius of the cutter. The books seem to indicate its chosen by the user of the machine? At the moment I have it set to the cone distance as the actual helical radius. I then tilt it to 35 degrees as thats the most common helical angle on a bevel. But the actual radius of the helical that should be used is a mystery to me. Users manuals seem to indicate ( simpson machine for example) that various radius of helical cutters may be used, but they rarely state when exactly youd switch to a differing radius.

  That last part isnt yet important as only straight bevels will output code at the moment, but if testing shows they work, Ill turn on helical and zerol..so it'd be nice to know exactly what helical radius we should use as a standard, or if its something a user should set.


  Anyway, here's the photos of the last test, they show involutes on the teeth, and they look to me as Id expect in terms of shape and appearanc e.. ( They look like a spur gear from the side of the right size.. getting smaller as a function of their conicalli ty..( that cant be a real word! :-)  )



* bevel2 001.jpg (509.41 KB, 1024x768 - viewed 622 times.)

* bevel2 002.jpg (490.59 KB, 1024x768 - viewed 584 times.)

* Bevel2-003.jpg (513.9 KB, 1024x768 - viewed 641 times.)
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ArtF
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« Reply #10 on: January 15, 2011, 04:41:36 PM »

Incidentl y, when I cut my blanks I dont cut the rear bevel and front tooth bevel , I just make a blank from 1" styo, then shave the face to the face angle. I zero to a spot where the gear is the correct outside dia. on its cone . After its cut I drop the tool in back of the tooth and rotate once, and repeat on the front.

Art
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Chuck
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« Reply #11 on: January 15, 2011, 06:26:03 PM »

Art,

They are looking good.   The correct tooth form depends on it's applicati on and a wide range of teeth are used.  Many are designed based on tooth load and the tooth form results.

The most important thing is: do the mating gears MATE?

You need to run both gears in the set and see how they work against each other!

By the way I have been using pink or blue foam for years.... .I have broken tools but never when just hitting the foam with a bad move!

Chuck
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ArtF
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« Reply #12 on: January 15, 2011, 09:52:37 PM »

Chcuk:

 Hopefully Ill be able to tell you tomorrow if they mate. I just ran out of time today to do the second one after fixing my table up a bit. Going by measureme nt, ( the mate is an identical tooth count ) , they should mesh fine.. should..

Art
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