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Involute spline generator?

metty

Plastic
Joined
Dec 21, 2010
Location
Pittsboro, NC USA
So, our Baja SAE team is running a spool that accepts polaris rear CV shafts. in the past we have just turned down a set of hubs that are already splined then pressed them into the spool housing and tigged them in. this year we are trying a new approach; machining a spool out of 4340 and then having the splines cut with an EDM. this allegedly will save us a lot of weight because the hubs are pretty heavy to start with and we have to leave a fair amount of material around the splines so they dont shatter after they are pressed into the spool.

all that being said, we are having trouble drawing the splines so we can give a .dxf to our EDM guy. we have all the dimensions as required by the machinist handbook for creating splines, but it does not translate to our solidworks knowledge. the only way we have figured to draw it in SW is to draw concentric circles for the minor and major diameter of the splines, do a circular pattern for each peak and valley, then connect them with an arc to create the curved face of each spline. the problem is that the dimensions in the machinist handbook dont give the radius of the spline face arc, so its a guessing game drawing it that way. also, we have not figured out any method of measuring said curvature.

soooo, the real question here is how do you create this drawing? what program would you use? is there a solidworks add in that we are not aware of? sorry if this is a really obvious answer to you guys but in the past we have just cut external splines using a TNG or SPG insert in a specially made cutter to get a 30* or 45* spline pitch which has been "close enough", but because we are using the EDM method this year for internal splines we would like to actually cut the right profile.

your help is greatly appreciated! :)
 
I'm not 100% sure of this method but here it is: if you have software that will draw involute gears at any specified pressure angle, you might be able to modify the resulting geometry to suit.

The trick is to understand what the spline specification stands for: example a 1.375" OD, 21 tooth 16/32 DP 30° PA means that the spline has the height charactersistics of a 32 DP gear but the circular pitch characteristics of a 16 DP gear.

So the involute is not a different shape simply because the tooth height is truncated (but that is only a supposition on my part).

However, you need to know the pitch diameter of the spline, and this can be deduced from the spline OD and the addendum height of a 32 DP gear in this example. The addendum height is 1/DP or 1/32" in this example. So given a 1.375" spline OD, then the pitch diameter is 1.3125" (twice the addendum height was used across a diameter).

Going to your gear software, generate a 30° pressure angle gear with 21 teeth on a 1.3125" pitch diameter. I use OneCNC and it has this flexibility to draw any pressure angle on any pitch diameter (within reason, I guess).

Now sketch in the OD of the spline with a 1.375" diameter circle based on the gear center.

Sketch in another circle representing the root depth of the spline, it will be somewhat smaller than the addendum height because root clearance is usually given. That would be somewhat less than a 1.250" diameter circle.

Then trim one of the generated gear teeth to these two new circles and delete the remainder of the generated gear geometry. Copy and rotate 20 copies of the trimmed geometry to get the whole spline.

Then of course, you need to figure in some sort of 'fit tolerance' when profiling the geometry so the spline will actually fit a gauge. Probably that fit tolerance is greater than any slight errors of drawing the spline with this method. If I had an EDM, I'd have already tried it to tell you if it works or not :D
 
+1 for Gearotic.

You don't have to work anything out as most of the regular splines are in the library.

gearotic_spline.jpg


Top left is the library button and you then get a drop down.

Ignore the mating gear, it has to put one in and because the PA is 30 it looks a bit weird.

If you need to fine tune it you can do with the boxes at the top.

John S.
 
I'm not 100% sure of this method but here it is: if you have software that will draw involute gears at any specified pressure angle, you might be able to modify the resulting geometry to suit.

The trick is to understand what the spline specification stands for: example a 1.375" OD, 21 tooth 16/32 DP 30° PA means that the spline has the height charactersistics of a 32 DP gear but the circular pitch characteristics of a 16 DP gear.

So the involute is not a different shape simply because the tooth height is truncated (but that is only a supposition on my part).

However, you need to know the pitch diameter of the spline, and this can be deduced from the spline OD and the addendum height of a 32 DP gear in this example. The addendum height is 1/DP or 1/32" in this example. So given a 1.375" spline OD, then the pitch diameter is 1.3125" (twice the addendum height was used across a diameter).

Going to your gear software, generate a 30° pressure angle gear with 21 teeth on a 1.3125" pitch diameter. I use OneCNC and it has this flexibility to draw any pressure angle on any pitch diameter (within reason, I guess).

Now sketch in the OD of the spline with a 1.375" diameter circle based on the gear center.

Sketch in another circle representing the root depth of the spline, it will be somewhat smaller than the addendum height because root clearance is usually given. That would be somewhat less than a 1.250" diameter circle.

Then trim one of the generated gear teeth to these two new circles and delete the remainder of the generated gear geometry. Copy and rotate 20 copies of the trimmed geometry to get the whole spline.

Then of course, you need to figure in some sort of 'fit tolerance' when profiling the geometry so the spline will actually fit a gauge. Probably that fit tolerance is greater than any slight errors of drawing the spline with this method. If I had an EDM, I'd have already tried it to tell you if it works or not :D

so i think what you are describing is what John S. said Gearotic does automatically. i tried making the spline in Gearotic, and it is indeed in the library of standard splines. however, when i try to save it as a dxf the program keeps crashing and or freezing up. do you have to buy the full version to save files? im hesitant to do that because we dont know if it will work and i dont know if we will be using it again or not. if anyone wants to take a crack at it to help out the Baja team, here is the info that i have.

No. of Teeth
20

Pitch
24/48

Pressure Angle (deg)
30

Base Diameter
0.7217"

Pitch Diameter
0.8333"

Major Diameter
0.921"

Form Diameter
0.879"

Minor Diameter
.792"/.797"

Circular Tooth Thickness

Max Actual
0.0680"

Min. Effective
0.0654"

thanks all,
metty
 
I use Inventor Pro and if you are looking for a ANSI B92.1, 30deg, fillet root, side fit this should be it. I have a wire EDM and I have used it to cut splines from Inventor before with excellet results.
 

Attachments

  • ASSEMBLY2.zip
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Forgive me if I'm butting in where I don't belong, but maybe I can help...
I cut splines on the EDM "a lot".

I use Inventor Pro and if you are looking for a ANSI B92.1, 30deg, fillet root, side fit this should be it. I have a wire EDM and I have used it to cut splines from Inventor before with excellet results.

That's a flat root spline. Also, the "space width" looks off (is .07816 ??). Again, I don't mean to butt in, and maybe I'm missing something.

If you like I can generate your spline for you. I would need to know what kind of fit you want (nominal / tight / big) and I'd run the space width accordingly. I would think that you'd want to start with something in between .0680 and .0654 ??

The "circular tooth thickness" you specify should be noted as "circular space width", when generating splines with CAD programs it does matter. But that's not a big deal, it looks pretty clear what you need.
 
If you don't want to hassle the EDM route-
Mark Williams Enterprises has a good selection of common automotive axle spline broaches and is quite reasonable broaching a few parts. Call them and ask what pilot diameter the parts need to have after you confirm if they have the broach you need. I think they charged me about $75 to broach several spools a few years ago. Unless your EDM guy is doing you a favor, I doubt you can wire these for that much.
Dan
 
Here's my go at it. Ya'all aint gonna get better than this...

Ran the major diameter towards the high to be sure to meet the form diameter requirement with a .014 fillet radius. Minor diameter nominal. CSW nominal @ .0667.


EDIT: I use Esprit with the gear module.
 

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  • 20t bk spline 2.zip
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I have used both Geartrax solidworks plugin and the Esprit gear generator.

The esprit generator generates a cleaner export file than the 'hundred points profile' solidwoks DXF export does.
 
FreeCAD has a built-in involute gear generator that will work for ISO involute splines as well by modifying the addendum, dedendum and root coefficients.

AIL4fc9zp85dzzjz2rKvSqznC6ujexU83NxvrgauvRhbXjQbboVFrIVoQE_4j6xW-7d7R5x0sZ6XZb7d9WdDsaIcnf9XO_s4JGOYOVoDH7Yr8SWqT3CZDGGnuOX2EfGHcBqV_oRdbcIb477rm63cCQJ-KAn39w=w1598-h1130-s-no


AIL4fc-dQMKTa1gXx-m1TSeJG15Z9LNP2Xw0_x8Nhx1BFBD12IjO-tWZPwM3kkC29RoINk3-NOc7vv8nT2IsvQQIUPuTB03oTj_XxOLfsfCTLMpdKoJWCeLuKc8cNa_fTERsuej8NUm4SrUbuWZbT2KyijuP8Q=w1598-h1130-s-no
 
FreeCAD worked well for me. But i need to do an ANSI B 92.1 1996 spline. Is there something out there for that?
I only have one spline to make (internal with mating external) and rather not buy software for it.
 
shanej45,

You're cutting the internal, and you have access to the/an existing external? If so, how will you cut it? Shaper cutter, broach, wire-edm?

PM
 
A true involute is easily generated with Creo, just a half dozen lines of code. I don't know anything about Solidworks but would expect the same can be done.
 








 
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