Material for driveshaft 4

[Rowyco]

I made a center driveshaft for an off road race car from 1" 1018 steel. The shaft failed by twisting through about 30 degrees and bending slightly. I am trying to figure out what material to upgrade to. I have room to go as large as a 1 3/8 inch dia. shaft and can find 1215 grd. splined shafting and hubs (5 spline or 22 slpine) locally. I am not familiar with the metalurgy ... would the 1 3/8 inch dia. 1215 shaft provide signnificantly more strength that the 1 inch dia. 1018? Any other suggestions for matl and where I might get splined shafting?

 

[diamondjim]

What kind of heat treat are these materials?
Are you buying hardened and ground stock?
I would think you would want a 1040, 4140,
4130, ie a higher carbon content in the material
selection for a shaft.

 

[TVP]

Rowyco,

Neither 1018 nor 1215 have the high strength necessary for a demanding application such as a driveshaft. Heat treatable, meaning quenched and tempered, grades like 4130 and 4140 are suitable, and frequently used for smaller quantities like yours. Without knowing the forces/stresses involved, I would estimate that heat treating to a hardness of 35-38 HRC would be a good place to start.

 

[NickE]

1018 and 1215 are both low carbon. The 1018 will have a yeild strength btw 45ksi and 50ksi. The 1215 will not be any stronger, and likely will have less fatigue life.

As diamondjim says I would reccommend going with an alloy steel like 41xx or 43xx.

I dont have hardenability data on these steels handy, but for normalized bar you will see strengths of over 90ksi. The 43xx will have higer hardness through the thickness, whereas at ~1" the 41xx alloys will have a tough ductile core with a hard case.

You might also want to try thick walled alloy tubing, if you can get the diameter larger you will have more stiffness and wont suffer a huge weight penalty.

As far as getting splined shaft I have no idea. You could likely find a machine shop in your area that will be able to machine raw bar.



Nick
I love materials science!

 

[M1Can]

My son races karts (go karts) and we run an 1 1/4" axle, ours is a North American kart , most are from Europe and metric. The axles come with several key ways cut (for brake, hubs, drive, and are about 50" long.I'm not sure what they are made of but if you do a google search on kart supplies or kart clubs and look for links you should be able to track it down.

Mark

 

[Rowyco]

Thnaks for the info. everyone. I appreciate the help. In answer to some questions raised the material that I can get locally (the 1018 keyed stock and the 1215 splined shafting) are both ground, not heat treated. I called my supplier and I can get nromalized, rough turned 4130 but they do not have it splined. I was hoping that by going from 1 inch to 1 3/8 inch diameter and from keyed to splined shaft that I would get more surface area from the size and better load distribution from the splines versus the 1/4 inch keyway and maybe be OK. I have tired searching for 4130 alloy splined shafting for about an hour this morning and so far I can not find anyone who sells it. If anyone else knows of a source for splined 4130 shafting I would appreciate a reply. Thanks! Tim

 

[unclesyd]

Give the following a call , Stressproof would be good choice

http://www.seshafting.com/index.html

You might want to check with these people also.

http://www.gorbinc.com

 

[DesignerMike]

the keyslot decreases the strength quite a bit (but probably a neccessary evil)

I have used Hex shaped shafts before with good success.
As Rowyco states, the 1/4" key give less surface area for toque transfer.

The splined shaft will center itself in the joint, while the keyed shaft may do some other things.

Some more information might help: are there u-joints at each end, is there a lot of movement (shaft sliding in one yoke), how long is the shaft?

 

[Rowyco]

Designer Mike ... in answer to your question the shaft is 12 inches long and it is supported by two bearings, each 1 inch from the ends of the shaft. A drive hub with sprocket is mounted in the center, and 2 drive hubs for the CV's which drive the axles are mounted on each end. The drive bubs do not move on the shaft as the sprocket drive hub position is fixed the ouboard axle shafts are driven by CV joints which are specially designed with enough plunge to allow for the supension movement.

 

[GregLocock]

1 go to a Fenner taperlock hub (or equivalent) to eliminate the keyslot (I assume that is the drive for the sprocket)

2 use axle steel to make axles

Increasing the OD will help, obviously, but axle steel is good stuff.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[diamondjim]

Turned, Ground & Polished 1045 Steel
should be a great improvement that
unclesyd's site referenced.
This seems like a cheap alternative.
Larger diameter is always better as
the area increases by the square of
the diameter. The 1 3/8 diameter would
give you 89 percent stronger shaft.
A 1 1/4 diameter would be 56 percent
increase is in area. A 1 1/8 diameter
would give you a 26 percent increase.
You mentioned a 30 degree bend. Is the
load overhanging or offset?

 

[Philrock]

Rowyco,

Sounds like you're trying to keep cost to a minimum. I agree with the others that a heat treated alloy steel is the preferred solution. It is certainly possible to buy heat treated 4140 round bar stock and have a gear shop machine splines into it, though this would certainly be more costly than off-the-shelf splined shafting.

That being said, going from 1" 1018 to 1-3/8" 1215 is a very large improvement.

1215 is designed for easy machining - not for fatigue strength. Though it's yield strength is similar to that of 1018, it's fatigue performance will not be as good because of the sulfur and phosphorous which are added to make machining easier.

Other things being equal, strength increases as the cube of the diameter - you would be multiplying your strength by about 2.6. Even though you'll suffer a slight loss due to lower fatigue performance, you'll be way ahead with the size increase.

 

[Rowyco]

Thanks again for all the help everyone. Diamond Jim in answer to your question what I meant to say but probably wasn't clear was that the old shaft twisted an it's axis through about 30 degrees but did not bend. For a short term fix I guess I'll buy the off the shelf splined shaft, meanwhile based on all the good input that I got here I talked to a machinist at a local refinery and he said if I get a foot long piece of 1 3/8 inch 4130 round stock he would would see if he can spline it for me in his off hours as a more permanent race fix. Then I just have to figure out how to heat treat it. Do a 30 minute high temp soak, then rapid quench, then temper for a couple of hours around 500 F right? Thanks again, Tim

 

[DesignerMike]

I would definately agree with Greg and suggest the taperlock or ring-fedder type attachment to the shaft. Any machining of the shaft will result in decreased strenght. The stress concentration factor for a Key is 1.6-2 (meaning that a smooth shaft is approximately twice as strong in torsion as a key shaft).
A spline is even more detrimental to the strength since you are removing more material. If you need to spline or key the shaft, do so at the ends ONLY....this will also save you a lot of machining.