PDA

View Full Version : dividing rant



loose nut
09-20-2006, 10:13 AM
I recently finished making a splined shaft for a friend who is building a 1940 Wileys gasser street rod, I don't like doing jobs like this because I'm only an amature machinist but he has done work for me on my truck and debts must be paid. Now for the rant. The shaft mates to a steering knuckle of a Honda of some kind and has 29 splines on it, what idiot would design that, 30 splines sure, that divides easy into 360 degrees but 29 is 12.4138 degrees per division. I'm sure the original part was broached but some poor shmuck had to machine the cutter to do that. Don't designers think about the people that have to make there creations How much of a difference would it have made to use 30 splines. Does anyone have some enlightenment on this.:confused:

Evan
09-20-2006, 10:49 AM
The use of odd numbers of splines helps to reduce repeating patterns of wear in the bearing supporting the coupling. Since the splines will never be exactly perfect it helps to prevent a recurring pattern of vibration that lines up repeatedly with the bearing rollers or balls, especially since 29 is a prime number. This is very commonly used in gears so that the gear teeth don't repeatedly mesh in the same sequence with the same teeth every revolution or multiple thereof.

agrip
09-20-2006, 10:52 AM
LN

Your post seems that you really are upset.
Sorry bout that.
I guess this is your lucky day.
There is an old time attachment to milling machines, called a dividing head.
29 is a common number on these devices.

Used to be kinda pricey but in the days of CNC, and Chinese industrial revolution, they are available at more reasonable prices.

For a one-off, I suggest you borrow or purchase a 29 tooth gear, or sproket to use as an index locator and go from there.

Hth Ag

J. R. Williams
09-20-2006, 10:56 AM
The odd number of teeth is to prevent others substituting other connectors to the product. Some will skip a tooth and leave a blank space so the unit will assemble only one way. Now that you have made a coupling did you consider the material used for the application and the liability of of building a critial part ?

JRW

BadDog
09-20-2006, 11:24 AM
This doesn't come from any personal ME knowledge, but rather is something I recall discussed in an automotive context regarding axle splines.

The engineer will design the shaft for the use to suit the required parameters. This determines the diameter and material. Continuing to apply the target parameters, the diameter then tells you the preferred(?) number of splines based on physical properties such as material characteristics, involute profile, pressure angle, etc.

There is certainly no law against some arbitrary selection of the number of splines as evidenced by abominations like the 10 spline coupling in certain old manual trans to transfer case shafts. But whatever the mechanical benefits of engineers following those standards, it does mean that similarly sized/purposed shafts will surprisingly often interchange (among domestic vehicles) allowing for some really cool and creative combinations of parts without always needing an adapter.

Again, this comes from what I recall (my memory is certainly not perfect) of discussions that have come up on other boards where MEs and industry professionals explained why some shafts that share a common interchangeable spline while other similar shafts do not.

Evan
09-20-2006, 11:28 AM
it does mean that similarly sized/purposed shafts will surprisingly often interchange (among domestic vehicles) allowing for some really cool and creative combinations of parts without always needing an adapter.

Yep, a 9" Chevy clutch plate is a perfect fit in my Land Rover.

Magic9r
09-20-2006, 05:59 PM
When dividing the angle is rarely calculated if you know the number of divisions required.
If you have a plate that supports the number of divisions you want forget the angle.
It's when you don't have a plate which supports the number of divisions you want that you should consider crying - been there:rolleyes:
Nick

CCWKen
09-20-2006, 07:37 PM
Yep, a 9" Chevy clutch plate is a perfect fit in my Land Rover.

Or, with only slight modifications, GM TH400 clutch disks in a 1925 Model T. :D

loose nut
09-20-2006, 09:36 PM
The guy who is building the car also had another splined shaft off the same linkage ( almost the same dia.) that has 22 splines, an even number, so I don't get it, what ever. I don't have a dividing head, beyond my pockets so I used a rotary table with a chuck on it, the dividing technique just has to be more creative. I guess if I wanted an easy hobby I would have taken up something simple like computer programing. thanks for the help.

p.s. I wasn't upset about it, I just had an spontanious over powering urge to bitch about something, sorry it won't happen again. Well it probably will!

Carld
09-21-2006, 12:25 AM
Hey Loose, you did good. Sometimes you payback more than you recieved.