Automotive Spline Question / Conundrum
Automotive Spline Question / Conundrum
(OP)
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
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





RE: Automotive Spline Question / Conundrum
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.
RE: Automotive Spline Question / Conundrum
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
RE: Automotive Spline Question / Conundrum
http://www.artec-machine.com/_images/documents/Bas...
RE: Automotive Spline Question / Conundrum
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
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.
RE: Automotive Spline Question / Conundrum
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.
RE: Automotive Spline Question / Conundrum
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
[url=https://flic.kr/p/puwSCq]
[url=https://flic.kr/p/qrwdoF]
RE: Automotive Spline Question / Conundrum
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.
[url=https://flic.kr/p/q9XPBw]
RE: Automotive Spline Question / Conundrum
Here's the link to the actual image - https://www.flickr.com/photos/94603494@N06/1585398...
RE: Automotive Spline Question / Conundrum
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.
RE: Automotive Spline Question / Conundrum
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.
RE: Automotive Spline Question / Conundrum
RE: Automotive Spline Question / Conundrum
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
RE: Automotive Spline Question / Conundrum
[url=https://flic.kr/p/qpBAjY]
RE: Automotive Spline Question / Conundrum
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
RE: Automotive Spline Question / Conundrum
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.
RE: Automotive Spline Question / Conundrum
Question... I'm now getting a message that tooth tip of shaft will probably collide with root area of shaft
Any suggestions on adjustments?
RE: Automotive Spline Question / Conundrum
Good luck
RE: Automotive Spline Question / Conundrum
Kind regards Rob
RE: Automotive Spline Question / Conundrum
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.