Automotive Spline Question / Conundrum 2

[robertspark]

Hello, this being my first post here, can i say that over the past few years I've been browsing here on the various topics the info & responses has always been great to read up on.

I have very little (read: no) knowledge of splines, but I have an automotive task that requires a gear to be internally resplined to match an existing male (external) spline.

I was kindly given the male spline specifications from the manufacturer of the said spline which is a transmission / gearbox mainshaft output shaft.

My intention is to be able to draw in CAD the female (internal) spline so that I can give it along with the gear to be resplined to an engineering company for them to EDM wire cut the spline for me.

The problem I'm having is that the spline dimensions I've been given do not appear to follow with the ANSI or metric spline calculations as given within the Machinery's Handbook (26th Ed).

Below is the specification for the male (external) spline I was given (as given):
Number of Teeth - 31
Diametral Module - 1.09247
Pressure Angle - 30º
Pitch Diameter - 33.86667
Base Circle Diameter - 29.32932
Major Diameter - 34.72 - 34.34
Minor Diameter - 31.37 - 31.12
T.I.F. Diameter (maximum) - 31.953
minimum fillet radius - 0.29
circular tooth thickness max. effective - 1.422
circular tooth thickness min. actual - 1.321
measure over pins minimum actual - 37.424
pin diameter - 2.438

Given this is an automotive transmission, and the Diamtral Module appears to be be a bit of an oddball number, and given that I have a 31 spline slip yoke reportedly for a ford mustang which fits without issue, all the guidance / other direction I can find on the internet seems to point to the fact that it should be an imperial (non-metric) spline, which almost aligns with a 24DP spline (25.4/1.09247 = 23.25DP), which seems to the common automotive DP of choice for vehicles of US origin Link

I've basically put a spreadsheet together to calculate all the other values out using those within the Machinery's Handbook, however try as I may I just cannot get the numbers to tally up unless I change some of the other factors within the standard formula's to achieve almost the same numbers as listed above.

I've run both the ANSI and Metric calculations via spreadsheet, and although the metric calc came close to getting the same numbers as those above, when I got to calculating DFE (Form Diameter External), in order to calculate the DIImin & DIImax, I seemed to really fail as the DIImin & DIImax was less than the DIEmin & DIEmin

I've drawn the external spline in CAD using the above numbers already, and what I'm trying to do is draw the internal spline to overlay over the top and ensure that it looks right (appears to interface correctly) before sending the internal spline off to EDM wire machining.

Any guidance would be greatly appreciated.

I've also noted that the Machinery's Handbook also provides a spline interchangeability table (pg 2138), and as this is an automotive spline I'm guessing it's a profile from old, hence that's where my problem is... I also have not got access to the "old SAE handbook" which would probably provide the answer I'm looking for.

It does not have to be "perfect" as it's going to be EDM wire cut and not broached, but within reasonable tolerance would be useful so that the two mate together with minimal backlash.

I'd also like to get the new internal splines case hardened given I'm told that the gear I'm having resplined is case hardened, and any guidance or direction anyone can given as to an amount of undercut / clearance fit to allow would be great.

Thanks for your time in advance,

Rob

 

[gearcutter]

None of those numbers conform to any of the standards that I know of; SAE, ANSI, DIN, JIS, or BS.
It's not at all uncommon for OEMs to come up with their own completely non-standard profile.
I've run those numbers through some calcs and none of it seems to add up.
Can you get hold of a shaft so that you can measure the spline yourself?
If so, the base pitch is the most important measurement to get.

 

[robertspark]

Gearcutter

Thanks for having a look into this for me

Yes I have the mainshaft and a slip yoke too

I've taken some dims with a vernier as accurate as I could

Root dimension from root of tooth 1 to 15 or 16 is 31.28mm
Major dimension from tip of tooth 1 to 15 + 16 is 34.51mm
(As the tooth count is odd (31) I can't get a straight dimension from roots to tips)

I took a few more dims to check to

From the outer tips of ten teeth is 32.8mm
The tooth tip thickness is approx 1.2mm
From the outer tips of two adjacent teeth the dim is 4.71mm
The root to root of 4 teeth is approx 12mm
From the top of tooth no 1 to the root of tooth 15/16 (ie direct opposite dim) is 33.0mm

Thanks for any guidance or pointers you can give

Rob

 

[gearcutter]

Download this guide and let me know what you measure the base pitch to be.

http://www.artec-machine.com/_images/documents/Base_Pitch_Tables.pdf

 

[robertspark]

Gearcutter, thanks for the guide

I've taken some rough measurements with a vernier, but will use a micrometer later this evening using better light + a bench setup.

2T span - 5.05 - 5.10mm

diff - 3.4 to 3.3mm​

3T span - 8.45m - 8.40mm

diff - 3.1 to 3.2mm​

4T span - 11.55 - 11.60mm

diff - 3mm​

5T span - 14.55 - 14.60mm

diff - 2.90 to 2.90mm​

6T span - 17.50 mm

not sure why the readings are decreasing hence best for the retest this evening. difficult to get an exact tangent on such small teeth from the base circle.

 

[tbuelna]

You also need to know the type of fit the spline uses and the tolerance class required. Based on the tolerance given for the external spline OD, it does not appear to be a major diameter fit spline. So it is likely a fillet root, side fit spline. The typical fit with these splines is usually cl.5. Re-run your spline spreadsheet for a fillet root, side fit, 30degPA, cl.5 spline and see if the numbers make sense. The actual DP value used does not matter as long as it is consistent for both parts.

When you have narrow top land widths on the external spline tooth tips and the spline teeth will be case hardened, it is common to cut them back to reduce the likelihood of through-hardening of the tooth tips.

 

[gearcutter]

I've been able to get the numbers to work and they look pretty good.
I've assumed we're dealing with a full fillet profile, as is usually the case in these applications. All other dimensions are as per your original data.

For the internal profile:

Pitch = 1.0924 module
Pressure Angle = 30deg
Profile shift coefficient = +0.3116
Dedendum coefficient = 0.9310
Addendum coefficient = 0.6500
Root radius coefficient = 0.30


1.0924 Hub by ronvol, on Flickr


Clip_4 by ronvol, on Flickr

 

[gearcutter]

Here's what the profiles look like when meshed together.
Blue is the external, green is the internal.
The two green circles represent the form diameters, as you can see, there's plenty of clearance.


1.0924 Meshing by ronvol, on Flickr

 

[gearcutter]

That last image isn't displaying too well.
Here's the link to the actual image -

https://www.flickr.com/photos/94603494@N06/15853985728/sizes/o/

 

[robertspark]

Wow, thanks very much for taking the time with that Gearcutter, very much appreciated.

I'll have a look at the numbers this evening + the spreadsheet and see if I can draw it up.

(out of curiosity what did you use to draw that profile up in?)

tbuelna, thanks for the input.

 

[gearcutter]

I've made a bit of mistake.
The radius coefficient for a full fillet profile should be closer to 0.40.
In this case, you'll also have to alter the internal addendum coefficient to 0.60.

 

[Occupant]

I did a similar thing, however, when I was drawing the profile I found out that I could either match the circular tooth thickness that you have given above or the measurement over pins, but not both???

 

[gearcutter]

This is what I get for the shaft, looks pretty good to me however the recommended pin size of 2.438mm is too large.
Data is per DIN5480 (non-standard0.

Transverse module [mt] 1.092
Pressure angle at PCD [alft] 30.000

Profile, shaft:

Dedendum coefficient [hfP*] 0.931
Root radius factor [rhofP*] 0.400
Addendum coefficient [haP*] 0.703
Profile shift coefficient [x] -0.3116
Profile shift [x*m] -0.3404
Reference diameter [d] 33.864
Base diameter [db] 29.327
Tip diameter [da] 34.720
Root diameter [df] 31.149
Root form diameter [dFf.e/i] 31.828
Tooth height [H] 1.785
Effective tip clearance [c.e/i] 0.303
Pitch on reference circle [pt] 3.432
Base pitch [pbt] 2.972

The following are Actual Dimensions:

Tooth thickness [Smax/Smin] 1.3203
Base tangent length [Wk.Smax/Smin] 14.6082
Number of teeth spanned [k] 5
Diameter of contact point [dMWk.m] 32.7675

Measurement over pins [MRe/Mri-pin] 37.42
Eff. Diameter of pins [DMeff] 2.4380

 

[gearcutter]

Here's what I get for the final model.



Mesh Model by ronvol, on Flickr

 

[robertspark]

I have downloaded the 30 day trial of Kisssoft.... given it spits out DXF's that seems to be the easiest solution for me to pass the external profile off to be EDM wire cut

put in the numbers and got something similar (never used this before, first evening of playing), so I'm probably going to now have some daft questions....

On the manufacturers shaft data above, it lists the pin diameter as 2.438, and the measure over pins as 37.424, do I take this as 3 pins, given 31 tooth is an odd profile and 2 pins would not really work?

thanks again for your time and effort on this one

 

[gearcutter]

KISSsoft is what I use. All the info above has been generated with the package.
I'm never going to able to afford it but fortunately I know a young engineer that works for a company that has the full package. I send him what I want entered into the data fields and he sends me the results.

In this case; the measurements are taken over 2 pins.

 

[robertspark]

Yes, I know what you mean, I kind of fell over when I saw the cost, then I saw the option for a 30 day trial and as this is a one off (save all data in case I have to do it again to replace the gear in the future), I thought it would be beneficial than trying to hack it via excel + drawing tangents and splines in CAD.

Question... I'm now getting a message that tooth tip of shaft will probably collide with root area of shaft

Any suggestions on adjustments?

 

[gearcutter]

Sorry, haven't got time to give you a crash-course on how to run KISSsoft other than to say that you'll need to manually enter the Reference Profile data and use the info that I've already given.
Good luck

 

[robertspark]

Thats great gearcutter, I've just figured it out and found the error of my ways, thanks for your time

Kind regards Rob

 

[tbuelna]

Rob-

If you only need a software tool that can generate high-fidelity spline/gear CAD models based on standard or modified geometry, there are applications like GearTeq that work very well and are relatively inexpensive. Spending $1600 or so to buy software that will make your spline design task much easier and greatly reduce the possibility of making an error seems like a wise investment. I can understand if you want the learning experience of creating your own design and modeling tools. But since you will be spending a fair amount of money to have parts made based on the results of your work you'll want to be sure it is 100% correct. Consider that the cost of scrapping one modified gear (including the cost of the gear, EDM, HT, finish grind/hone, etc) will probably be more than the cost of purchasing a GearTeq license.

gearcutter did a very nice job modeling your spline joint using KISSoft. KISSoft works very well, but is indeed quite expensive and requires some training to become proficient.

It is not unusual with a full radius root fillet spline profile to have a small amount of interference between the external tooth tips and the internal root fillets. You can break the tip corners of the external tooth tips, cut back the OD of the external teeth, or modify the root profile of the internal spline (using something like a conic profile rather than a radius) so that there is no interference.