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Author Topic: Bevel gear dimensions  (Read 4399 times)
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ftkalcevic
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« on: January 24, 2014, 08:00:11 PM »

How are the dimension s defined for a bevel gear pair?  I have a pair of Mod 1, 20 deg, 28 tooth gears at 90 degrees. 

GM says the gear center is 28.0.  When I put the models of the gears into my CAD program and try to align them by eye, the back of the gear is about 15.0 away from where the axis meet.  What is the position on the shaft, and from where to where do I measure it?

When I create the gear, I ask for a face width of 5.  The Gear Thickness on the project display shows 4.2426.  Is face width supposed to be the thickness of the gear?

Thanks,
Frank

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ArtF
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« Reply #1 on: January 24, 2014, 10:40:22 PM »

Hi Frank:

 The center of a bevel is in the center of its face width. The thickness is the horizonta l distance of the facewidth which is measured on its angle.
If you drop a single one on and look what the mouse coordinat e is as you point to sections of it, youll find the 0,0,0 point is dead center
of the face width.

Art
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ftkalcevic
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« Reply #2 on: January 25, 2014, 12:34:49 AM »

Thanks for the reply, but that didn't help.

I did what you suggested, and this is what I got, see attachmen t.

The red cross is approxima tely 0,0,0

It doesn't help me position the gear on the axle at the correct position to mesh with the other gear. 

I'm trying to position 3 gears on a tee shaped bar as shown in the picture.  I need to know the positioni ng of the gear on each shaft just as I would use the center distance of the spur gears to place them


* bevel.png (49.75 KB, 671x780 - viewed 503 times.)

* joint.jpg (31.23 KB, 640x480 - viewed 506 times.)
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ArtF
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« Reply #3 on: January 25, 2014, 08:41:25 AM »

Hi:

   I see what you mean. Even my memory was faulty on it. The 0,0 point is the pitchline start of the gear. It is the point of the gears profile that stayed in position as the rest of the profile bevels in or out. ( Above or below the pitchline .).

  SO I guess what you need is to have the pitchcone distance. This woudl be the distance from the theoretic al center of cone to that 0,0 point.
It would give you a distance from the intersect ion point of the two shaft planes to the 0,0 point of each gear in relation to the other. Do you agree
that would work for what you need? I can add that to the text output for bevels. I have trouble thinking of any other number that would be easy
to use in designing set centers.. .  I will add that to the program and probably have a new version otu tomorrow with that data and we'll see if that
helps. Let me know any thoughts on other numbers that may help and I ll see what I can do.

Art
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ArtF
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« Reply #4 on: January 25, 2014, 09:53:39 AM »

Hi:

  If you redownloa d now, youll find the text for a gear now includes the CenterDis tance on the bevels. However, its a matter of finding reference .
The number indicated is the distance from the pitchdiam eter on the outside of the bevel to the center of the shaft of its mate on its
normal angle. So for 90 degrees as in your example, its the distance from center of mates shaft to the pitchdiam eter point on the outside of that
bevel gear. I will eventuall y give you trhe distance to the rear of the gear, but the collars they use now will be going away in future for a new
collaring facility for any gear, so it may not occur till then.

Thx
Art
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ftkalcevic
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« Reply #5 on: January 25, 2014, 04:40:31 PM »

Thanks for making a new release for me, unfortuna tely I struggled to find the reference point to use.

What I ended up doing was calculati ng the distance using the Outside Diameter, Face Cone Angle and Cone Distance.  See picture below.  I'm not sure if Cone Distance is the correct value to use, but by eye the results look ok.

Using the outside corner made it easy to define a reference plane using my CAD software.

I look forward to the future release where we can just use the distance from the axis intersect ion to one of the gear's front or back faces.

Thanks,
Frank


* distance.png (20.1 KB, 977x382 - viewed 534 times.)
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ftkalcevic
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« Reply #6 on: January 25, 2014, 05:14:53 PM »

What I ended up doing was calculati ng the distance using the Outside Diameter, Face Cone Angle and Cone Distance.  See picture below.  I'm not sure if Cone Distance is the correct value to use, but by eye the results look ok.

A bit of a brain fade there.  Cone Distance isn't used.  It's just...

L = OD/2 * tan( Face Cone Angle )
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ArtF
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« Reply #7 on: January 25, 2014, 09:27:57 PM »

Frank:

  Good to hear youve got it. I've made a note to make this one easier by referanci ng to the outside of the collar..

Thx
Art
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