Mating functional gears to circular gears

[Edward French]

Are there any guidelines for creating functional or non-circular gears and having them mate with circular gears?

[ArtF]

Hi:

I'm unaware of any published guidelines. This likely due to the unlimited
number of possible combinations.

My thoughts are:

In general, the maximum radius of concavity
of the functional gear must not be less than the outside radius of any mating
circular gear and the shaft must allow motion equal to the maximum convexity
and maximum concavity as a range.

  Other than that your usually good to go ,BUT, functional gears vary their
pressure angle on every tooth, so as you distort more from circular, you do
get increased wear I think..like everything else, moderation is probably advisable.

  If you do make such  a set, do me a favor and post a picture.. Id love to see such
a thing run..

Art

[Nate]

...
  Other than that your usually good to go ,BUT, functional gears vary their
pressure angle on every tooth, so as you distort more from circular, you do
get increased wear I think..like everything else, moderation is probably advisable.
...

In order to mesh non-circular gears with circular gears, the distance between the instantaneous axis of rotation has to change over time.  Depending on the application, that degree of freedom may allow for constant pressure angle non-circular gears.

[Edward French]

Here's a video of a triangular gear running: http://smg.photobucket.com/user/etfrenc ... 1.mp4.html

Photobucket still seems to be down for me , but you may be able to get on.  If not I can send the video.

Is there a way to calculate the pressure angle between circular and non-circular gears?

[Nate]

Here's a video of a triangular gear running: http://smg.photobucket.com/user/etfrenc ... 1.mp4.html

...

Is there a way to calculate the pressure angle between circular and non-circular gears?

The video didn't work for me, but based on 'rose engine' it seems like you're looking for some kind of 'spirograph lathe' thing.   Maybe something like the one at the start of this video:

https://www.youtube.com/watch?v=4XDIonkwTRo&t=30s

...

It seems like you're not that familiar with gear terminology or theory.  The pressure angle is something that has to do with the shape and meshing properties of individual teeth, and is not necessarily determined by the shape of the gear.  It can be a little tricky to measure.  Depending on your situation and application it may be easier to make a complete set of gears than to measure the pressure angle of one.  Alternatively, might also get satisfactory results simply by getting close.

[Edward French]

I've tried multiple times to attach the video as a txt file, but it's failing to post.

Another way to ask about the pressure angle is how do I ensure the pressure angle will be less than 50 when mating circular and non-circular gears?

[Nate]

...
Another way to ask about the pressure angle is how do I ensure the pressure angle will be less than 50 when mating circular and non-circular gears?

Can you make a drawing of what you mean  by pressure angle?  The notion is a little ambiguous when dealing with non-circular gears.

As far as I'm concerned, all the `rolling gears` in the attached pdf have the same pressure angle.

[ArtF]

>>In order to mesh non-circular gears with circular gears, the distance between the instantaneous axis of rotation has to change over time.  Depending on the application, that degree of freedom may allow for constant pressure angle non-circular gears.

  This sounds correct. Since the functionals are created with a 20 degree hob, there is no pressure angle variation when considered from the point of view of the hob, so there shouldn't be from the point of view
of the circular gear on that functional. Sorry if I misled, but considering the hob, I cant see where the
pressure angle would be an issue.. It IS an issue as to the circular gear being able to fit within the concavities
of the functional of course, but other than that your likely fine..

Art

[Edward French]

Thanks for the reassurance.  It looks like photobucket is back online, so the video should be viewable.

[ArtF]

cool machine...

Art

[Nate]

...
Is there a way to calculate the pressure angle between circular and non-circular gears?

Let's assume that the teeth are very small, so that we can ignore the effect of the path of contact.

Let's also assume that the tooth meshing is as with involute gears with pressure angle phi.

Let r(theta) be a polar formula for the non-circular gear's pitch profile, centred on the axle for that gear.

Then the pressure angle (as Art would think of it) is going to be equal to:

arctan( dr/dtheta / r ) +/- phi

Where dr/dtheta is the derivative with respect to angle.

[ArtF]

  So long as your using the functional gears and your circular gear is small enough to stay tangent to the
drivers curve.. then the pressure angle will be equal to the hob's, 20 degrees. And Id think youll always
want to maintain tangency when using a circular on a functional gear.

Art

[Edward French]

I think all of the gears that will work on a Rose Engine would need to stay tangent.  I've just started modeling functional gears.  It will be interesting to see what kind of patterns will be generated.

Here's a sample (We've already tried the 120T and 108T circular gears with elliptical and triangular gears).


Thanks for all of your help.

[ArtF]

Excellent work..


    Yes, I think youll be fine, in your type of operation the round gear shoudl always be in tangency so I think your fine..

Art