Driveshafts........hollow or solid?

[Pauly]

We are considering using hollow steel tubing with the driveshafts but are uncertain of the wall thicknes. The OD is 1" and we are thinking of something around a 7.5mm wall thickness.

What is everyone else using?

If the shaft is hollow are the splines also hollow or are solid steel spline sections welded to the hollow tube?

Also we are not sure as to the magnitude of the torque shock loads on the driveshafts? ie tyres spinning then suddenly getting grip.

[mtg]

Get a machine design book, read about shaft design and fatigue strength factors.

Then determine what load you want them to withstand (you'll have to make some assumptions, but it is engineering, right?)

Crunch numbers; said numbers will answer your question.

[Pauly]

mtg,

our driveshaft guy has dome all that as far as i am aware and he believes empirical testing as the only way fwd as he could not find anything on said shock loads.

just wanted to know what other people were runnng.

[CrazyDave]

I would assume you are running a shaft supported at both ends, so therefore only torsion loading. Would the tyre really be able to resist "shock" or impact type loadings? I am curious to know for those of you out there who actually did design driveshafts if these factors were taken into account (or believed to be significant)

I would wager that there would not be any impact type loadings and that it would be a simple static type equivalent load easily analyzed.

Is this logic reasonable?

[Denny Trimble]

I don't think we've ever had a welded shaft last, but since we've gone to gun-bored solid 4340, heat treated, machined with large radii, polished, protected, min. OD ~10% smaller than spline minor diameter, we haven't had a failure.

We'd go with a larger OD but we're constrained on our CV splines, and making the shaft bigger than the splines is "dumb" to quote one famous racecar engineer.

[Storbeck]

"dumb"

Is it bad that I know exactly what you're talking about, what book and where in the book.

That picure labeled dumb, it's just so well put. You can't use any more clear plain english than "dumb"

I believe he also calls it a "crime against nature"

[John Burford]

The stiffness of the halfshaft has a significant effect on the peak load seen by the halfshaft. So for those of you who are thinking about large diameter thin wall shafts, I'd recommend against it.

John Burford
UTA, Alumni

[Agent4573]

just use carbon fiber.....

[osubeaver]

Originally posted by CrazyDave:
I would assume you are running a shaft supported at both ends, so therefore only torsion loading. Would the tyre really be able to resist "shock" or impact type loadings? I am curious to know for those of you out there who actually did design driveshafts if these factors were taken into account (or believed to be significant)

I would wager that there would not be any impact type loadings and that it would be a simple static type equivalent load easily analyzed.

Is this logic reasonable?

I don't know to what degree, but it seems like dropping the clutch could induce quite an impact load on the drive shafts. Of course, it really does go back to the tires like you said. If they are going to just break free than the impact load wont be that huge.

[Frank]

If I had the ability to make small splines well, time, and money... I'd probably use EN 26 steel (basically 4340, with slightly less impurities), and...

Option 1

I'd use a shaft with 23mm OD 10mm ID, 35 Rc, (soft I know, but you should be able to cut splines at this hardness easy enough), and probably not bother with further heat treatment because of distortion issues.

(Order of operations, anneal, rough turn, gun drill, harden to 35 Rc, final turning, cut splines, polish shaft, shot peen spline start point, black oxide coating)

Option 1 is what I do to splined stubshafts.. but the splines are large (16/32DP 16 splines), unlike what you want for driveshafts


Option 2

If you could overcome the distortion issues during heat treatment.. then 21mm OD 10mm ID, with 43Rc

(Order of operations, anneal, rough turn, gun drill, final turning, cut splines, heat treat to 43 Rc, polish shaft, shot peen spline start point, black oxide coating)


Option 3

I'd use a shaft with 21mm OD 10mm ID, 43 Rc, (If you can cut splines in fairly hard material).

(Order of operations, anneal, rough turn, gun drill, harden to 43 Rc, final turning, cut splines, polish shaft, shot peen spline start point, black oxide coating)


Option 4

I must admit to not understanding grinding processes, but I'm guessing you'd...

Roll splines, heat treat, and then perform spline grinding.. Then 20mm OD 12mm ID, with 43 Rc

(Order of operations, anneal, rough turn, gun drill, final turning, roll splines, heat treat to 43 Rc, grind splines, polish shaft, shot peen spline start point, black oxide coating)


Option 5 (what we actually do)

buy GKN shafts and CV's (pray for quality, but you won't get it)

If: shaft soft enough to gundrill
Then: Gundrill
Else: Don't Gundrill

Then: polish shaft, shot peen spline start point, then black oxide coating



BTW, for any caustic cleaning, cathodic electrolytic cleaning, or black oxide cioating applied to steel above 39Rc.... I conduct hydrogen embrittlement relief (bake immediately @200 deg C for 1 hour)

regards

Frank

[murpia]

Originally posted by Denny Trimble:
We'd go with a larger OD but we're constrained on our CV splines, and making the shaft bigger than the splines is "dumb" to quote one famous racecar engineer.

Hmmm, for sure a larger OD could mean the shaft ultimately _fails_ at the CV spline, but what if torsional stiffness is the design criteria for the shaft itself?

Ian

[Frank]

if torsional stiffness is the design criteria the shaft will be big, heavy, and made of mild steel.

[Frank]

could someone who has made driveshafts outline their proceedures?

can any professional manufactures surfing this site add anything?

i'm especially interested in more info on spline rolling... I'm led to believe 26-28Rc is the maximum hardness that you can roll splines?

or can you roll splines with harder material, but it is just not ecinomical for batch production?

has anyone found a company that will roll a "short order" of shafts?

[Broderick]

The way I do it, is start with 4340 steel, machine down the diameter, gun drill, heat treat to Rc 34-38, do finish diameters, have Moser Engineering spline it. They never asked/complained about the hardness of the metal to me.

Ryan B.
Rutgers