Metric Spline Callout 1

[tristar804]

I'm new to posting here but I've read through a couple of threads in the process of trying to figure this out and figured I'd be best off just posting a question, so here goes.

I'm in the process of trying to reverse engineer a spline. The issue is it was built to some kind of metric standard, and I'm not sure which. What I'm missing in the callout is the refernce diameter and the fit class. I have a module of 1.5, pressure angle 25, and 12 teeth. Any advice where to go next?

 

[gearcutter]

I know of no metric standard where 25 deg PA is used. The only standard I know of which uses anything less than 30 deg PA is a Japanese Automotive spline which uses 20 deg PA.

There are three common metric standards; DIN 5480, DIN 5482 and ANSI B92.2M-1980.

The first place to start is by measuring the base pitch of the sample. This is done with a good set of verniers and measured tangentially in the normal plane over a certain number of teeth. The number of teeth over which to measure is worked out by laying the jaws of the verniers over the "best fitting" number of teeth. By this I mean the number of teeth that allow the jaws to contact the tooth profile somewhere around the pitch line (about half way down the profile from the tip of the tooth) and not allow the tips of the jaws to make contact in the root area nor have them make contact right up on the tips of the teeth. Then take the next best fitting measurement either side of that; so in your case the first measurement might be across 3 teeth, then take a measurement over 2 or 4 teeth, which ever fits best. Subtract the smaller measurement from the larger and what you have is the base pitch.

Then all the usual measurements are required such as major diam., minor diam. and any details on the mating part you might have.

Let me know what you measure and I’ll let you know what to do next.

 

[dimjim]

How did you get 25 degrees.
30 degrees in normal for most splines.
What else do you know? Bore, etc.?

 

[tristar804]

With the measurements I took I ended up with a minor dia. of .641" a major of .782", which comes out to a pitch of .711". I thought the 25 degree PA was a little off myself, maybe I just ran through the calculations wrong. I used the formulas listed in the 1994 Machinery Handbook. Specifically D=mZ where D is the pitch, m is the module and Z is the number of teeth. In conjunction with DB=mZcos(alpha), where DB is the base diameter, and alpha is the pressure angle. Unless I'm doing something wrong here, two equations, two unknowns gave me a module of 1.5 and a PA of 25.
I took the measurements for the base pitch like you said gearcutter and came out with .280" across two teeth, and .445" across three. Which leaves me with .165" for the base pitch.
Thanks for the speedy response!

 

[dimjim]

The metric splines often use enlarged pitch diameters
and you have to have the standards to know how they
are enlarged. Because these profile shifts are standard,
using general equations or formulas will give you wrong results unless you know the amount of profile shift that
pertain to that particular spline. You might search on
metric spline standards and see if you can find the
standard.

 

[dimjim]

ansi b92.2M-1980 is probably the standard that you need.

http://quickgear.bizland.com/id9.html

offers a spline calculator and is free
for 7 days. Do not know if this will help.

 

[gearcutter]

It looks like DIN 5480 is it, although there are slight differences with diams. The base pitch for 1.5 mod 30 deg PA is 0.161 and you measured 0.165, I'd say the error is due to the span measurments not making the correct contact. This is sometimes the case with certain numbers of teeth, PA or pitch. As you can see, the BTL is on the money although the best way to check tooth thickness is over pins. If you don't have the specified pins let me know the closest you have and I'll re-enter the data.

 

[dimjim]

Gearcutter,
Great program. I assume you wrote it.
I could not remember the DIN 5480.

 

[gearcutter]

dimjim,
I agree, it is a great program. It opens up with EXCEL.
No, I didn't write it. Below is link to the web site where you can purchase it.

http://www.emip.de/home_e.htm

 

[tristar804]

Hey, thanks a bunch guys. We're going to prototype a few splines here and see how they hold up. I think we'll start with the 5480 ;-) Let you know what we decide to run with. Thanks again!