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post #1 of (permalink) Old 08-26-2000, 06:30 PM
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axle splines-why is more better?

Just wondering why an axle with 31 splines is stronger than one that has 28 or whatever. Is it the actual number of splines that make the difference, or just that axleshafts with more splines are stronger elsewhere and are just identified by the spline count? I know it's probably a pretty simple question, but if somebody asked me why more is better, I'd have no proof to back it up. Thanks!

Keith
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post #2 of (permalink) Old 08-26-2000, 06:57 PM
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Re: axle splines-why is more better?

The fine splines are stronger for a number of reasons:
fine splines allow for a larger root diameter, the same reason that fine thread bolts are stronger than the same size coarse thread bolt when placed in tension. cutting a fine pitch leaves more of the axle (or bolt) undisturbed.
fine splines and high strength threads are usually rolled in, this is a cold forging operation that compresses the metal making the surface dense and wear resistant. cut splines break up the grain patterns in the metal weakening the area rather than strengthing it.
fine splines reduce stress risers, because the height of the spline is shorter and the included angle at the base of the spline is 60 degrees rather than 90 degrees the stresses applied to the spline are more in compression than shear.

good luck, jjc

P.S. In the case of the 31 vs 28 spline axles they are both involute design splines, the 31 spline has a larger diameter giving it slightly more strength. The really big difference in strength is seen when you start looking at the old 6 and 10 spline axles
post #3 of (permalink) Old 08-26-2000, 09:49 PM
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Re: axle splines-why is more better?

[img]/wwwthreads_images/icons/shocked.gif[/img] Wow! After reading that response I felt like I wuz back in engineer skool. GREAT post jjc! VERY well explained! [img]/wwwthreads_images/icons/smile.gif[/img]

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post #4 of (permalink) Old 08-27-2000, 01:07 AM
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Re: axle splines-why is more better?

yes... i keep trying to explain to people about the rolled threadsvs cut threads...
heres another reason the fine splines are stronger...they have more contact area. the finer the splines, the more contact you will have(assuming the cut is the same depth. the old axles used to have a bunch of dead space between the splines, and the splines were cut deep...bad bad bad..now all we have to do is figure why i saw that 10 spline 44 in front of a 35 spline 60 in the rear of the same vehicle.... maybe i should stop drinking now.....rambling.....you people might just want to ignor my late saturdqay night posts...........

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post #5 of (permalink) Old 08-27-2000, 01:04 PM
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Re: axle splines-why is more better?

Isn't it also that true that the higher spline count is associated with an axle of a greater overall diameter, or does it happen to work out that way? D60 35 spline is 1.5" in diamerer and the 30 spline is somewhat less 1.25"(?) or so in diameter, for example.

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post #6 of (permalink) Old 08-27-2000, 02:00 PM
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Re: axle splines-why is more better?

doug, yes you are correct, their are a specific set of formula for determing the spline count for any given shaft diameter. this is similar in some respects to the way standard gearing is described (tooth count divided by diameter) or the way screw pitch varies with diameter.
Just sitting here thinking about this, I discovered something interesting: 90% of 35 is 31.5, 90% of 31 is 28.35. I will put my money on the engineer at dana was your typical engineer (lazy, no disrespect intended) and he just figured out one set of splines and then increased it by 10% for each axle he had to design!

jjc

post #7 of (permalink) Old 08-27-2000, 04:38 PM
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Re: axle splines-why is more better?

OK so if axle shafts with more splines have a larger diameter, then wouldn't the actual spline size/depth be the same as one with less splines? making it the actual difference in the diameter that equals more strength, not the difference in the splines? Say this.../\... is one axle spline, wouldn't a 1.5 diameter axle just have 35 of these little guys (.../\...) and a 1.25 diamter one only have 31 of the same splines (.../\..)?

Keith
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post #8 of (permalink) Old 08-27-2000, 05:09 PM
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Re: axle splines-why is more better?

Actually, back around the 70s, SAE came up with a 'standard' size spline used for any splined shaft. All the splines on any axle using this 'standard' are the same, to increase shaft diameter you increase the number of splines. There are a few exceptions to this rule, the most common being the GW 14 bolt, which has 1 9/16 diameter shafts, but is only 30 spline. Also, shaft diameter is measured as the 'major' diameter, which is the length across the outside of the spline, as opposed to the 'minor' diameter which is the diameter on the inside of the spline.
JEEPRZ

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