Cut or Rolled Splines?

[75Bronc]

Are stock axle shaft splines cut or rolled? Tom's advertises rolled splines being stronger than cut splines. I figured stock was rolled?

 

[broncodriver99]

Rolled. They are stronger.

 

[Apogee]

Most stock axles I've seen look like they were hobbed, which would classify as cut. With that said, rolled splines, just like threads, are always stronger because they don't interrupt the grain structure like cutting does.

More generically speaking, external splines can be broached, milled, ground, extruded, rolled, hobbed or shaped depending on the finished part and material used.

 

[metal1]

back in the day I used to narrow a lot of ford 9" rear housings and shorten the axle shafts ,ford used some really good steel for them, I had another shop cut the splines and on high powered street cars never had an axle break

 

[Rustytruck]

Rolled splines are supposed to be stronger but in mass production rolled splines are very quick to make. Of course it takes expensive dies and really expensive machinery to do it.

https://www.youtube.com/watch?v=Si_2ImWeEuo

 

[sanndmann3]

Neat clip! makes it look so easy...

 

[Apogee]

Don't they...GROB uses a special spline forming technique with rotary dies that works pretty slick as well. My brother used to design custom co-rating twin-screw extruders, and the splined shafts that they stacked all of the elements on were upwards of 20 feet on some of the bigger machines.

https://www.youtube.com/watch?v=Xa4-oBz6Cso

 

[Yeller]

Rolled is stronger but I've found axle profile and metallurgy to matter more. If the smallest diameter of the axle is the root of the spline that is where it breaks every time. And off road is way harder on axles than drag racing ever dreamed of. Drag racers always apply max torque in one direction. We apply mad torque forward, get bound up, put it in reverse and do it again. That back and forth is murder on shafts.

 

[Digger556]

Material alloy and carbon content, heat treat and geometry matter the most.


That said, the best axles will have rolled splines with an involute profile at the proper pressure angle, usually 30 degrees for OE axles. You can still have strong axles with cut or hobbed splines so long as they maintain the involute profile.

Inexperienced shops will straight cut splines with a 60 or 90 degree cutter. This is bad practice and despite what anyone tells you, the splines will fail sooner.

Some axles are cut at a 45 degree pressure angle, but the differential needs side gears with better hoop strength, so these are usually only used in performance applications. Toyota's are the only OE I'm aware of with 45 degree pressure angles.

Having a properly necked down minor diameter will help the axle shaft absorb shock and reduce stress risers. There are some engineering reasons for this and they are a bit counter-intuitive, but the math doesn't lie.

I'm not sure when Ford changed or added heat treat to their axle shafts, but my friend had an older 28 spine 9-inch and the splines twisted while wheeling. It was clear the shaft was not case-hardened and experienced a ductile failure. Contrast that against the 28-spline axles from my Ranger pickup that exploded in spectacular fashion with little twisting before failure. You could clearly see a .120" case depth of about 50 HRC (very hard).

If your aftermarket shafts are properly case-hardened, they will likely be much stronger than your older stock axle shafts.

 

[75Bronc]

I know that rolled is stronger. But are stock axles rolled, cut or hobbed? Does everyone agree that they are hobbed?

 

[Evolkid]

Stock axles from OEMs are rolled for the simple reason of cost. Usually made from 51XX series steel IIRC.
If they're case hardened, also cheaper to do than full hardened. Can be done on an induction heat treated or "scanner"

Most aftermarket axles made in small numbers (<100) and made from 4340 or 300M are usually hobbed. These are usually through hardened the get the full benefit of the material.

For flanged axles, most of these aftermarket guy are sourcing directly or indirectly from someone who also makes them for the OEMs. They're usually already set up to make them so it's usually the cheapest option as long as they can get to the min quantities.

When I worked for Sway-a-way, if we made torsion bars/axles in house we'd find that the OEM factory was less than a 1/4 the price.