Heat treat a shaft for strength

Joe T. · Oct 2, 2014

I have a chassis dyno for snowmobiles. There is a splined shaft about 10" long connecting the rollers to the dyno. This shaft is twisting under heavy loads. The shaft was made from a generic splined shaft.
My guess is the shaft is 1015 steel. It cuts and taps very easy. What can I do to strengthen this shaft?

atomarc · Oct 2, 2014

If the material doesn't have enough carbon or other alloying elements I don't think you can modify it through heat treatment. My guess would be to make a new shaft, oversize if feasible or make a replacement out of a material like stress-proof or a 4140 materiel, maybe in some form of pre-hard.

These are just guesses on my part. I'll bet the splined shaft was made from something softer to facilitate the machining of the spline..again, just a guess.

Stuart

Winterfalke · Oct 2, 2014

Simple answer, increase the diameter.

Dan from Oakland · Oct 3, 2014

Is the splined portion twisting or is the whole length of the shaft splined? If the spline is twisting, a larger shaft won't help and the only solution is a larger spline or use a material with a higher shear strength. What is the spline spec-? not that difficult to custom make a spline shaft out of heat treatable material or 4140 HT. Pretty easy to calculate the stress due to the torque, as you know the HP and rpm the shaft sees.

redlee · Oct 3, 2014

All of our Splined Shafts are 17-4 SST H900

Fulmen · Oct 3, 2014

I was about to suggest case hardening as the only option, but after a bit of reading it appears that even 1015 can be hardened (somewhat) with an sufficiently aggressive quench (http://www.material.chula.ac.th/Journal/v21-1/67-74%20KORAD.pdf). I would expect shallow depth and significant distortion, so case hardening or a different material would probably be a better choice nevertheless.

Joe T. · Oct 6, 2014

The shaft connects two splined couplers that have about a 2" gap. One is the chain drive off the dyno and the other is the dyno itself. The shaft is twisting in the center where it is not engaged in the splines.

magneticanomaly · Oct 6, 2014

Have you talked to the dyno mfr? Exceeding its rated capacity? Make a new shaft out of better material. You're on your own.

Gary E · Oct 6, 2014

Joe T. said:
The shaft connects two splined couplers that have about a 2" gap. One is the chain drive off the dyno and the other is the dyno itself. The shaft is twisting in the center where it is not engaged in the splines.

Measure the Spline Dia on each side and measure the twisted dia...
Is the area where it is twisting a smaller diameter than the splines?

CalG · Oct 6, 2014

Winterfalke said:
Simple answer, increase the diameter.

A "tricky way" Would be to get two more spline coupler halves, Machine them to fit (weld) to a piece of tubing that slides easily over the present splined shaft.

Assemble the three new parts (couplings and tube) on the spline shaft and tack weld to get things clocked correctly. Remove and weld complete.
Reassemble

This way, your reinforcement is removable,

IF you need to control end to end position, use shaft collars. A pinch up with o-rings between should serve to quiet any clanking due to loose spline fits.

Just an idea! ;-)

Orange Vise · Oct 6, 2014

What kind of twisting? Temporary (elastic) or permanent (plastic)?

If it's the former, there is no real solution to the problem short of redesigning the device for a larger shaft. All steels have roughly the same Young's modulus of elasticity regardless of alloy and heat treatment condition. In other words, as long as the twist is springing back, even a hardened 4340 shaft with triple or quadruple the strength will bend just the same.

Dan from Oakland · Oct 6, 2014

That's true, but a heat treated shaft with a higher yield strength will not permanently deform at the same stress level as a shaft made from lower tensile strength material and that's the real issue here I believe.

TDegenhart · Oct 6, 2014

If you have access to heat treating facilities, I would case harden to a depth of about .03 and draw to Rc 48.

Tom

Fulmen · Oct 6, 2014

Orange Vise: I think it's safe to assume he wants to increase yield strength, the flex in a short coupler on a dyno would be tiny and not affect the measurements to any degree. But if flex is important you are right, increasing the diameter is the only option.

amdinc · Oct 6, 2014

If it is a standard spline order a new one out of 4140 from Grob.

John

AlfaGTA · Oct 7, 2014

My vote is new shaft made from 300M and heat treated as required. Neck down to below the minor dia of the spline in the center with generous radius.
Should solve the spline twisting and move the failure somewhere else in the system...
Cheers Ross

michiganbuck · Oct 7, 2014

Just a stab in the dark but are the ends rigid enough and out of alignment to stress the shaft as if it were bent when under load.

Joe T. · Oct 11, 2014

I have actually not seen the Dyno. I cut the supplied shaft to size and modified some couplers to adapt things.

The problem is the shaft is twisting permanently not just flexing. The other problem is the new snowmobiles are turbo charged and making a lot more power.

Gary E · Oct 11, 2014

Joe T. said:
I have actually not seen the Dyno. I cut the supplied shaft to size and modified some couplers to adapt things.

The problem is the shaft is twisting permanently not just flexing. The other problem is the new snowmobiles are turbo charged and making a lot more power.

When it's discovered how to put10 lbs in a 5 lb bag, maybe the solution to your problem of putting 100 HP through a 50 HP shaft will be next.

From the movie JAWS........ you gona need a bigger boat.

Heat treat a shaft for strength

Cast Iron

Diamond

Stainless

Titanium

Titanium

Cast Iron

Cast Iron

Titanium

Diamond

Diamond

Titanium

Titanium

Diamond

Cast Iron

Hot Rolled

Diamond

Diamond

Cast Iron

Diamond

Similar threads