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double-circular-arc gear generator softwareHelpful Member!(4) 

factsb4pride (Automotive) (OP)
13 Jan 11 18:35
Does anyone know of a gear generator for CAD systems that will produce double circular-arc gears? Both internal and exxternal? I am working with solidworks. Please post your suggestions. thanks.
Helpful Member!  factsb4pride (Automotive) (OP)
18 Jan 11 10:37
So no one here knows of a gear generator that will create double circular arc gears?

Barring that, please feel free to post any thoughts on this gear tooth design, positive and negative, when compared to involute gear tooth profiles.
Occupant (Mechanical)
18 Jan 11 11:58
Do you know the profile for the rack? If yes, I'll look at it.
factsb4pride (Automotive) (OP)
18 Jan 11 12:44
I don't have the design I am working on down to that level of specificity yet. My goal is to develop my own skill set in this regard, but thanks anyway. Just want to acquire some software and learn to do the modeling and then subsequent simulation/analysis.

Would still appreciate any comments regarding experience with double circular-arc gear tooth profiles...
gearcutter (Industrial)
18 Jan 11 16:42
By "double circular arc gears" I guess you are referring to a Cycloidal tooth profile.
You can purchase a GCode Generator from here: http://www.delphusa.com/index.htm

Cycloidal gears tend to mesh with pure rolling action and are therefore more efficient than an involute profile.
A quick search on Google will reveal a wealth of information on the subject of the pros & cons of using either of these profiles.

As to why anyone would consider using the Cycloidal profile in a general industrial spur gear application is beyond me.
Some cons:

1. Tooling to generate the profile is near impossible to find off the shelf and would therefore be extremely expensive to produce.
2. There are no load rating standards available to validate a design.
3. Generally only used in very low load applications such as time keeping devices.
 

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
 

gearcutter (Industrial)
18 Jan 11 23:10
Please disregard my last post.
I've only just realised that the DCA gear profile is not a Cycloidal profile.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
 

factsb4pride (Automotive) (OP)
19 Jan 11 10:20
Thanks anyway gearcutter! Appreciate you taking the trouble to post.

I have several papers on double circular arc gears, I was just looking for additional input and experience, and also the software, I will check out what you recommended.

China is head over heels in love with double circualr arc gearing, and most of the papers on the subject are in Chinese as a result. The West seems to have chosen to ignore the benefits of DCA gears over involute for some reason. Can anyone offer as suggestion as to why that may be?
Helpful Member!  gearguru (Automotive)
19 Jan 11 20:10
If what are you looking for is the Wildhaber/Novikov gear, try to google for it.
One interesting link is here:

http://www.zakgear.com/WN.html
factsb4pride (Automotive) (OP)
20 Jan 11 8:16
All of the easy searching on google has been done. DCA gears are modified forms of Wildhaber/Novikov gears, as those are single circular arc gears (if I recall corectly).
Thanks for your link.
factsb4pride (Automotive) (OP)
20 Jan 11 15:29
My previous post contained an error regarding this sugject.In fact WN gears can be of single, double, or triple circular arc configuration. I am focusing on the double and triple variety.

One paper I recommend is:

FUNDAMENTAL DEVELOPMENT OF HYPOCYCLOIDAL GEAR TRANSMISSIONS

by Park

http://www.lib.utexas.edu/etd/d/2005/parks77965/parks77965.pdf

In chapter 4 these kinds of gears and their history/development is covered in detail. Though this paper deals with a slightly different application than mine, it still has many informative sources.

My application is a ring gear/pinion with a 2:1 ratio. Double or triple CA gears seem to offer greater strength in this application than involute gear tooth profiles could provide. If anyone has a gear tooth design to suggest that exceeds DCA or TCA gears, please post some info.
Helpful Member!(2)  Clyde38 (Electrical)
21 Jan 11 6:46
factsb4pride (Automotive) (OP)
21 Jan 11 9:24
I already have that one, but thanks anyway Clyde.
 
Occupant (Mechanical)
21 Jan 11 10:04

Quote:

The West seems to have chosen to ignore the benefits of DCA gears over involute for some reason. Can anyone offer as suggestion as to why that may be?

Some of the things seem obvious even for a "not a gear" expert like me: You would have to use helical gearing to improve contact ratio, the tooling would be expensive - different cutters for gear and pinion - and these gears are very sensitive to axial misalignment.
factsb4pride (Automotive) (OP)
21 Jan 11 10:31
@ocupant: What I am reading tells me different. Many gear designs that are involute use helical designs, so no manufacturing cost difference there for circular arc gears being helical. My sources say that producing circular arc gears is cheaper than producing involute gears. But that may be hard to nail down since so few circular arc gears are produced outside of Russia and China.

And I have also found that modified forms of circular arc gear tooth profiles are not as sensitive to axial misalignment as was initially thought. As well, many gearing applications have very accurate machining and tolerances, and misalignments are few, or very small.
factsb4pride (Automotive) (OP)
21 Jan 11 15:09
I also want to add that I am focused on the Russian version of the double circular arc tooth profile, not the Chinese version, which has a step. The Russian standard design has a smooth transition from one circular arc to the next, with no step.

You can find diagrams of this in the paper I last referenced.
factsb4pride (Automotive) (OP)
28 Jan 11 9:58
I have been away for a few days, and I'm frankly surprised that more gear engineers haven't posted about circular arc gearing. Are these gears really that rare in the west? And if so, why is that?
dinjin (Mechanical)
28 Jan 11 14:23
Until this post I was unaware of these.
They do sound promising.  Thanks for
calling these to our attention.
gearguru (Automotive)
28 Jan 11 19:09
I have books where they were described 40+ years ago. It was also part of our engineering education at that time. Never saw any in real life. In the school (and in that books) we were told that the manufacturing costs are high, that the gears are very sensitive to center distance variations. These are probably the main reasons why they are not used more often.
By the way - the link posted by Clyde38 is probably the best what one can find about the topic and it should be sufficient to calculate the geometry. Litvin is good...
factsb4pride (Automotive) (OP)
30 Jan 11 9:35
With regard to the sensitivity of CA gears, does that sensitivity exceed the likely level of tolerances that exist in most bearing systems and/or our current level of machining capabilities?

Lets say a double circular arc gear is mounted via hydrodynamic bearings. Do the subsequent variations in center distances that come with using that type of bearing preclude the use of DCA gears in that application?
factsb4pride (Automotive) (OP)
30 Jan 11 10:16
Here is an interesting site where the author claims to have generated more accurate 3-d models of these types of gears:

http://www.zakgear.com/Gallery.html

This URL also has some relevant animations that show the contact point of DCA gears is not an ellipse as so many have claimed in the past, which results in a much higher contact area under loads.
mfgenggear (Aerospace)
31 Jan 11 13:26
Factsb4pride

what is the accuracy req'd. equivalent to the AGMA std.

One question was asked, what type of machines & tools are req'd to manufacture. shaping & hobbing may or may not be an issue.
is Grinding or honing with the current machines possible.

Is China & Russia tooled for such designed.
I never seen no less Mfg such gears in the USA

Mfgenggear
factsb4pride (Automotive) (OP)
4 Feb 11 14:34
I am still looking for some software that will produce various forms of circular arc gears, that I can subsequently import into solidworks.

@mfgenggear: no offense, but I am having trouble discerning your comments. The accuracy requirement on my end is whatever will work in the chosen application. I am planning on using hydrodynamic bearings, and want to insure that any subsequent center-to-center deltas or errors are tolerable by the chosen circular arc gear.

I am aware that these types of gears are mostly made in Russia and China, and not in the U.S. That is one of the reasons I am here seeking information from people in the industry. Often a design may be rejected due to politics or the "not invented here" syndrome, and I do not want to overlook what may be a practical, superior alternative to standard involute tooth profile gears for those reasons.

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