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Challenge: Where are the good gears (with good teeth)?

Question asked by Roland Schwarz on Nov 20, 2014
Latest reply on Aug 23, 2016 by Robert Conklin

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Here's a challenge for all the regular visitors here: Where are there good gears to download? Good gears, with good teeth!

It's a subject I see here all too often: users working with downloaded gears with absolute dreck for gear teeth. I have yet to find one decent configurable gear in Toolbox or 3DContentCentral that has gear teeth with a proper involute tooth shape.

Unsuspecting designers without enough knowledge are putting these gears into products with dreadful results. I personally know of multiple products that have had problems due to this.

I don't want to launch into another lecture about how and why this is vital. I just want to know, are there any good gears out there?

No one else has this question

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Christopher Estelow Nov 20, 2014 3:48 PM
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Try downloading one from Rush Gears to see if it works for you.

Chris
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Kelvin Lamport Nov 20, 2014 3:55 PM
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I've not found any yet. Certainly none of the free download sites offer true involute tooth forms. They all just use a "close enough for graphical representation" radius.

Does GearTrax use involutes?
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Jamil Snead Nov 20, 2014 4:36 PM
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We bought GearTrax because we needed to machine gears with the proper profile. You need to select the tolerance you want and it creates a table of points for the involute and will join them with a spline or arcs (you choose). However the solid model that it spits out is not configurable. We have an assembly with dozens of configurations, and each config uses a different size gear, and so we had to generate a separate gear part for each size and use suppression to control which size is in each config.

I doubt that there are any configurable downloads with the proper profile.
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Roland Schwarz @ Christopher Estelow on Nov 21, 2014 9:51 AM
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Swing and a miss on Rush Gears. I was ever-so-hopeful, but their gear teeth are simple arcs. I'm sure their production gears are good, but...
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Roland Schwarz @ Jamil Snead on Nov 21, 2014 9:57 AM
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I like Geartrax. I've worked with the resulting product. Good product.

I wrote a blog post once about Geartrax gear geometry. It's a bit dated, so there likely were updates. It was only meant to be an analysis of the geometry, not a criticism of the product.
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Mike Pogue Nov 21, 2014 10:00 AM
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I don't have the model at this company, but I have made a model of a gear with selectable parameters. I just followed these steps:
Tutorial: How to model involute gears in SolidWorks and show design intent. - GrabCAD
Then I parameterized it and was able to make any gear I wanted within the accuracy of SW spline interpolation.

It took a few hours, but it was fun.
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Christopher Estelow @ Mike Pogue on Nov 21, 2014 10:47 AM
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Mike,
Would you be able to share the file with us?

Chris
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Mike Pogue @ Mike Pogue on Nov 21, 2014 11:36 AM
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I'd love to. But it was at my last company.
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Roland Schwarz @ Mike Pogue on Nov 21, 2014 11:53 AM
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I'll be posting something. I've actually shared it here before. I have a gear model that uses equation-driven curves to generate the involute.

I used to have a gear model that used a series of sketches to "unwrap" defining points of the involute. Introduction of equation-driven curves made that obsolete.
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Mike Pogue @ Roland Schwarz on Nov 21, 2014 11:56 AM
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That's how I did it. With arc-length dimensions and tangent lines to unwrap the involute on one side of the tooth, then mirror, then fillet, then circle pattern.
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Jamil Snead @ Roland Schwarz on Nov 21, 2014 12:34 PM
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Roland when you say "equation-driven curves", are you talking about some curves that have parameters driven by equations, or are you actually talking about the SW command "Equation Driven Curve"? I didn't think an involute could be represented by an equation in SW Equation Driven Curve.
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Roland Schwarz @ Jamil Snead on Nov 21, 2014 12:45 PM
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Can and does! Got the equations from WIkipedia. In the equation-driven curve formulae, use t for theta, with a range from zero to whatever makes the curve long enough.

$\, x = r \left( \cos \theta + \theta\sin \theta \right)$
$\, y = r \left( \sin \theta - \theta\cos \theta \right)$

Involute - Wikipedia, the free encyclopedia

Involute gear - Wikipedia, the free encyclopedia
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Robert Conklin Oct 21, 2015 10:48 AM
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Attached is a method of modeling a TRUE Involute Spur Gear in Solidworks
file: "Spur Gear with True INVOLUTE Tooth Form.SLDPRT"
This is with the Gullet of the first tooth cut on the "Y" axis
USING:
"Diametrical Pitch" , "Number of Teeth" & "Pressure Angle"    as User Input
Note: the template is set for the User input of the
following Global Variables in Solidworks:
"DiametralPitch"=    ____    Diametral Pitch
"NumTeeth"=      ____ Number of Teeth
"PressureAngle"=    _____ deg Pressure Angle

See also
Another method of modeling a TRUE Involute Spur Gear in Solidworks - SOLIDWORKS - 3D CAD model - GrabCAD
Attachments
- Spur Gear with True INVOLUTE Tooth Form.SLDPRT.zip1.1 MB
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Brian McEwen @ Robert Conklin on Oct 21, 2015 11:58 AM
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Cool, thanks Robert. It is usually possible to break something like this, and looks like I did it.
I set DiametralPitch 25.4 (for a module 1mm gear), NumTeeth 75, and PressureAngle 20deg. I overlaid it on another gear - the blue is my gear (not modelled by me, correct per a gear manufacturer).

The obvious problem with the Conklin gear is the base circle is ending up inside the dedendum circle. I have not analyzed the equations I just looked at sketch3. The rest of the tooth form matches up perfectly (I had to crank the image quality to max to before that was obvious).

Thanks for sharing the .sldprt!
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Jim Sculley @ Brian McEwen on Oct 21, 2015 1:51 PM
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Brian:

Can you upload your blue gear? I'd like to compare it to my own true involute model.

Jim S.
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Roland Schwarz @ Brian McEwen on Oct 21, 2015 2:56 PM
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Great stuff, guys. Hopefully with more good gears out there, fewer designers will unwittingly use bad ones.
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Robert Conklin @ Brian McEwen on Oct 21, 2015 4:38 PM
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Here is an earlier version of the model where I attempted to address the issue above.
BUT I changed the model to center the first tooth on the "Y" axis.
and did not go back to look at the problem above.
how does this model compare to "Blue" gear?

Also this model mirrors the surface created by the involute over a mirror plane on the center of the gullet of first tooth....etc..
I did not like this methodology (I went down the wrong track)
The previous model "Spur Gear with True INVOLUTE Tooth Form.SLDPRT" is a better attempt, I think,
it just needs a little refining.
Is there a way to incorporate one of those programing IF THEN statements in the equations to modify how it
creates geometry based on a the No of teeth input and Pressure Angle etc....???
This perhaps would be more of a programing thing????
Attachments
- Equ Drvn DP & T Gear LARGE.SLDPRT.zip2.2 MB
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Casey Bergman Oct 21, 2015 6:04 PM
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Have you looked on Grabcad? I found this one there and it looks pretty good, haven't broken it down fully though.

Equation Driven Involute Curve Spur Gear Tooth Form in Solidworks - SOLIDWORKS - 3D CAD model - GrabCAD
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Brian McEwen @ Casey Bergman on Oct 21, 2015 8:14 PM
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Lol. Did you look at the name on Grabcad? ...That is Conklin too.
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Brian McEwen @ Jim Sculley on Oct 21, 2015 9:03 PM
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Here is the "blue gear" as a parasolid, and saved in SolidWorks 2014 (just a solid). The CAD file was created for us on request during a project with a gear supplier. I'm pretty confident it is an accurate tooth profile for a 75 tooth, module 1mm spur gear (with 20deg pressure angle).

Hope it helps.
Attachments
- Spur Gear, 75T, module1, true.SLDPRT.zip423.3 KB
- Spur Gear, 75T, module1, true.x_t.zip347.2 KB
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Brian McEwen @ Robert Conklin on Oct 21, 2015 9:12 PM
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I have not looked at this gear model.

It is possible to put in some conditional statements in equations. I have not tried it much myself.
2014 SOLIDWORKS Help - Visual Basic If Function

CATI Tech Notes: SolidWorks IIF equal’s to “the syntax is wrong” error workaround
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Robert Conklin @ Brian McEwen on Oct 21, 2015 9:23 PM
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Mind you My gears work GREAT (for a given range of values)
They are just not universal, they will not work for the whole range of gears.
Ya got to tweak them. I am putting forth here gears that will WORK, they have a TRUE involute tooth form.
I made the "Equation Driven Involute Curve Spur Gear Tooth Form in Solidworks - SOLIDWORKS - 3D CAD model - GrabCAD"
for a sets of gears I required running 1:1 that required a particular Pitch diameter and tooth count.
There is a whole family of these gears I use, they vary only slightly in Pitch diameter and tooth count (they all have the same Pressure Angle)
They work great! I EDM them out so I did not need to adhere to a set/standard Pressure Angle, I just needed a good "involute form"

I would like to know if there is anyone that can take and improve on what I have done.
To make a template that would work for lots of gears.

The main thing is that these gears utilize the parametric “equation driven curve” for the involute form.
Giving a TRUE involute. This is necessary for any gear set that going to be used in the real world.
The TRUE involute is sorely lacking in all/most of the gears posted that I have looked at.
And
I have tried to utilize Global Variables to drive the gears. (and they do work for a given range of values)
I just have not determined what that range is and at what point the template breaks and how to make it so it does not.
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Robert Conklin @ Robert Conklin on Oct 21, 2015 10:25 PM
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also look at this :

three lobe root blower design

Where I have taken the template to an extreme to try to model a pump (3 Lobe / teeth) Just to see if I could.
I was able to tweak it, the template, to do what I think the patent called for in the last post by me.
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Robert Conklin @ Robert Conklin on Oct 22, 2015 3:15 PM
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I would say that it is a 95% sure bet that there is a commercial ADD IN product out there or in development that utilizes the behind the scenes features in Solidworks ie... the IIF THEN statements the VBA code the SQL links the API programming.... to be a great commercial gear design product.

I know of one that will imbed its self into Solidworks and when you request a feature it will "call home" do the math and display configure what you desire right in your local session of Solidworks. No doubt that it works as intended. But it has a, If I remember, a fee per use structure. Which I thought was a bit steep.

The commercial programs will/do command a hefty price and do a lot lot lot more than simple spur gears. And their output is/may only be an x_t, or dumb solid, something that cannot be modified without the original program.

It is my intent to try to open up the discussion to those individuals with the "Share Ware" - "Open Source" community mind set to contribute, post, improve upon, a simple gear generation tool utilizing a true involute tooth form.

I, for one, only know so much about how to do it.

Therefore I would solicit any contributions that would further that end.
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Casey Bergman @ Brian McEwen on Oct 22, 2015 9:11 AM
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I didn't even notice that!
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Challenge: Where are the good gears (with good teeth)?

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