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cuslog
12-10-2010, 05:30 PM
Can anyone tell me what tooth form these are ?
I've become interested in gear / spline cutting and since I have a 9" Ford diff. under the ol' hotrod, I thought it might lead to a project ??
Thanks in advance :D

Willy
12-10-2010, 06:52 PM
You may find this article by Mark Williams Ent. an interesting read.
Some very good info here as well as some interesting points raised as well.

http://www.markwilliams.com/schmaxles.aspx

becksmachine
12-10-2010, 11:36 PM
You may find this article by Mark Williams Ent. an interesting read.
Some very good info here as well as some interesting points raised as well.

http://www.markwilliams.com/schmaxles.aspx

Much information in that link, not all of it correct in my opinion.


"Another key aspect of the spline is its shape. All OE axles, differentials, and so on, have involute splines, which means that the faces of the splines are slightly curved to provide optimum contact and even pressure distribution during engagement. The only way to achieve this shape is through hobbing (or rolling) the spline. Axles that have been resplined or manufactured using a flycutting procedure, however, have straight-cut splines. Matching a flat axle spline with an involute spline differential concentrates pressure on both the internal and external item, creating excessive levels of stress. In terms of reliability, an involute spline beats a straight-cut version hands-down."

No argument with the involute profile being stronger in this application, but it seems to me somewhat naive to assume that all flycut splines would have a "flat" or straight sided (?) profile.

Or am I reading this wrong?

Dave

ADGO_Racing
12-11-2010, 12:16 AM
It is incorrect. I have cutters for the horizontal mill that have the involute shape. All you need is an indexing head, a tail stock, and a horizontal mill. Could probably be done on a vertical mill, but would require lighter cuts.

Mcruff
12-11-2010, 09:33 AM
"Another key aspect of the spline is its shape. All OE axles, differentials, and so on, have involute splines,

That depends soley on when the vehicle/axle was built, my old jeep has straight cut splines on all the axles, not a curve to them. Even the transmission and transfercase shafts are straight cut splines. Real coarse spline to, 10 spline and 19 spline if I remember right.

vpt
12-11-2010, 09:47 AM
Yeah, I don't remember seeing any curved splines in any vehicle lately besides gears.

cuslog
12-11-2010, 10:11 AM
Just going from memory here, but I was thinking that my 9" Ford axles were a straight cut spline but I thought I would ask because I'm no expert and its been awhile since I've had any out.
I have no intention of making my own axles but I do need to replace a sway bar and some aftermarket (race) sellers make a sway bar with splined ends and if I was going to buy a cutter I might buy the cutter for axle splines and make the sway bar spline the same as my axle splines.
Can anyone tell me the tooth form DP etc. ? for Ford 9".

cuslog
12-11-2010, 11:15 AM
OK, finally read ALL of the Mark Williams article :p (didn't have time yesterday).
Thanks Willy !
Looks like they're 35tooth, 24 pitch, 45 deg. pressure angle.

LES A W HARRIS
12-11-2010, 04:39 PM
I think much of the confusion on the straight sided teeth, was that in the beginning, the internal member only could have a straight sided option.

Then later when a new external was being retro fitted, the unknowing seeing the straight internal, believed that the external was also straight & so went ahead and made it so.

And of course for highly stressed applications, both should be involute form, and properly heat treated.

The article referring to 24 pitch, I think the author was trying to keep it simple, because it is of course 24/48 Diametral Pitch, with either a 30 or 45 Pressure Angles.

Cheers,

lazlo
12-11-2010, 05:49 PM
The author is correct, IMHO.


It is incorrect. I have cutters for the horizontal mill that have the involute shape. All you need is an indexing head, a tail stock, and a horizontal mill.

Involute spline cutters are exceedingly rare: 30 pressure angle, with a stub tooth form.

http://bbs.homeshopmachinist.net/showpost.php?p=459220&postcount=74
http://www.ashgear.com/pdfs/ff30.pdf

Involute splines are short and squat, with a very pronounced curve. This is one Sir John drew up in CAD for me:

http://i164.photobucket.com/albums/u15/rtgeorge_album/JacobsSpline.gif

It's very popular on the hobby forums these days to cut straight splines with a TPG flycutter, but a straight-sided spline has far less power transmission capacity than a involute spline -- about 3 times less, which is why the auto makers use involute splines for power transmission.

This is a chart showing the torque load of a straight-sided SAE spline against an involute spline. Note the torque capacity axis is logarithmic.

For 1.25" OD, a 16 tooth straight-sided spline has a torque capacity of around 1,000 in/lbs per inch of spline. A 1.25" involute spline has a torque capacity of 3,000 in/lbs per inch of spline:

http://i164.photobucket.com/albums/u15/rtgeorge_album/involutespline.jpg

The wrench
12-12-2010, 03:30 AM
For what it's worth, my brother just got done narrowing a Ford 9" . We explored the option of cutting and re-splining vs buying custom-made. All the machine shops said the same thing: after buying the proper cutter,shop time,etc. ,you are better off to buy new custom made axles. I talked to 2 machine shops that used to re-spline and they quit due to axle failure and not wanting to be responsible for an accident.

cuslog
12-12-2010, 12:23 PM
Not trying to start an argument here, trying to learn something.
I have to wonder: in an application such as an automotive axle spline where the gears are not repeatedly meshing and un-meshing, is an involute really necessary ?
I think I understand the priciple and I don't dispute the math that the involute is the better choice when both gears are rotating and transfering power, one to the other but in an axle spline application, the splines just lock the two pieces together, there is no rotation relative to the other, no meshing and un-meshing, so why wouldn't a straight cut spline be just as good or maybe even better (full contact on the side of the tooth vs a smaller contact patch on the involute) ?

becksmachine
12-12-2010, 03:52 PM
There are others here that know much more about splines than me, but just from a logic standpoint, think about this.

Your analogy of an involute profile having less contact area is just backwards. For a given depth of tooth, the involute profile is going to have a greater area of contact than a straight sided profile.

Which then allows a larger minor diameter, translating into making the splined area stronger, everything else being equal.

Dave