Reverse Engineering a Spline

[cobra46]

Hi All,

I'm attempting to reverse engineer a motorcycle transmission shaft that has recently gone obsolete. The shaft has two sets of splines neither of which I can readily identify. The one on the end where the sprocket mounts has an involute profile while the other two where the transmission gears slide are parallel straight splines.

I have already measured the internal as well as case hardness and can make a reasonable guess of the material. I would like to perform an actual material analysis but that's secondary to my current spline ID issues.

The bike is made in Austria so I'm guessing the splines conform to a DIN standard. Beyond that, I have no clue. Machinery's Handbook and the Web have been of little help so far.

At work, I have access to the most common metrology equipment including a couple CMM's. Using calipers I have measured the following:

Parallel Splines
Major OD - 25.00 mm
Minor OD - 22.25 mm
Spline width - 6.00 mm
Spline Qty - 6

Involute Spline
Major OD - 25.00 mm
Minor OD - 21.44 mm
15 Teeth

Can anyone help in identifying what splines I'm working with?

Thank you for your time.

 

[gearguru]

If those splines are per DIN, than the major dia should be smaller.
For the involute spline per DIN 5480:
major dia = 24.7
minor dia = 21.7
pressure angle = 30 degrees
module = 1.5 etc...
How did you measure those diameters for 15 teeth splines by the calipers ?

 

[cobra46]

This is strange. I've checked back here nearly every day hoping for a reply and just saw yours today.

Thanks for the reply. I was hoping you would reply as you seem pretty knowledgeable around here.

I measured the 25.00 major diameter right next to the splines using my Mitutoyo calipers. With an odd number of splines this was the most accurate with an odd number of splines. I will measure the actual spline OD tomorrow at work on the stone using vee blocks and height gauge.

 

[gearguru]

The area behind the spline probably locates a ball bearing. The bearing's ID has the H5 size limit (ISO tolerances), which means that the MMC (min. size of the bearings "hole") is exactly 25.000 mm (in your case) That's why the DIN splines are standardized with the major dia slightly smaller than the ID of the bearing. It is a very useful feature, makes designing the shafts much easier.
Can you also get the over the pins size (it is used to calculate the tooth thickness/space)?.
I recommend that you purchase that DIN spline standard. There is a lot of useful info in it.

 

[spigor]

On many occasions I've seen spline specs in automotive being just a bit off the standard, sometimes with an apparent reason, sometimes without. But if we assume your spline is DIN5480 1.5MOD 30PA 15T flat root then the standard shows us (in mm):

OD: 24.7 -.13
Minor dia.: 21.7 -.65
Form dia.: 21.94
Nominal arc tooth
thickness on ref.d: 2.847
Pin size: 3.25
Over pins: 28.446
OP change factor: 1.35
No of teeth spanned: 3
Span measurement: 11.675
SM change factor: .866

The change factors show you how much the measurement will change when the arc tooth thickness is changed by a certain amount. Unfortunately, the span measurement is marked as unreliable, but should it be close enough and if all the parameters above match, then you could consider having this verified by a Gear Measuring Center. The determination of the fit is a whole new story.