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Author Topic: Newbie question on shaft angle variations  (Read 530 times)
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magic36
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« on: February 22, 2020, 05:17:19 AM »

Hi, My name is Doug, and I am building a 3" scale Traction engine and need to make various gears (some of which are bevels not at 90 degrees).

I have been experimen ting with the different ial bevels as these should* be fairly straight forward I thought.  When I enter the data on the input page, I can select 36 T crown wheel, 12 T pinion, 6DP, 0.75" face width. but strangely the shaft angle even though I edit the setting to make them add up to 90 degrees, comes back with just under 90 degrees.  When I export the project, and view the project details, the angle is even less than 90 degrees - I am confused as to why this might be.

I know what the gears "should" be for the different ial as I made a set for a previous model using a published design, and thought I would check them with Gearotic, but I get slightly different numbers, and am not sure it his is because the dimension s are only shown to 2 decimal places, or if it is even possible to change the precision to include more decimal places.

Thanks in anticipat ion, and apologies if this is a very basic question. ..

Regards,

Doug
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ArtF
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« Reply #1 on: February 22, 2020, 10:13:08 PM »

Hi Doug:

  For archival purposes Ill answer this here, though I also answered in email to you.

In looking into this I can see the two displays for individua l angles are not used as entries, only
the shaft angle should be used. The program then finds the matching conical angles for that pair.
Only two gears with the same number of teeth can have 45 degree angles for example, and they
subdivide by a formulaic calculati on of the required cones for the requested shaft angle.

   Its been awhile since I coded it but the formulas demand this to be calculate d values for the
bevel angles for any shaft angle. As a result you cannot for example pick 80 and 10 degrees
for a 90 degree bevel pair.

   Im not sure why this is so, intuitive ly Id think any pair of angles would do so long as they total
90, but the formulas are pretty specific so I suspect I had good reason to implement it that way
though it may simply be a demand of the specifica tion I used for its inception .

Thx
Art


Art
 
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ArtF
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« Reply #2 on: February 24, 2020, 12:56:55 PM »

Hi Doug:

  I looked into this to refresh myself as to why you can not simply pick two arbitrary angles
that add up to the required shaft angle. Intuitive ly you should be able to, BUT, the reason is
that each bevel is based on a cone and the meshing rules are that both cones must meet
at one rotationa l origin. So as tooth count changes, each cone changes to meet that objective,
  The formulas I send offlist detail how its calculate d, but its basically a formula for the intersect ion
point of two cones of differing radii.

Art
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