Lengthening Hardened Shafts

That has got to be the best thread title ever!

Just a suggestion, but I would have thought a stub shaft at the coupling end, designed to be the weakest link for easy replacement on failure?

Regards JD.

JD the shaft has factory made very hard splines on both ends, and I wanted to keep the shaft as a 1 piece unit. These splines allow free movement through the constant velocity ball races, and are important to the free action of the vehicles suspension. It has to articulate through 35 degrees in the vertical plane, with a veriation off line of 28mm in the forward to aft as it travels through the vehicles suspension range.

I have tried an interfferance press fit extension to achieve the desired dimension, and have also tried to thread the ends (left and right hand of course) and then apply a socket to achieve the length. This worked the longest about 2 hours and then failed again.

So I'm looking for a variation of what I've tried that will allow me to get the right dimension without sacrificing the strength and hardness of the shafts especially at the splines.

Regards,

PBB

Why 'left and right hand' threads?

For a particular direction of rotation one thread, left or right hand thread, only will be suitable.

If rotations are required on either directions, threaded connection is not suitable suggestion.

Have you tried sleeve with keys?

No I haven't tried a keyed joint yet.

This Saturday I'm going to attempt a 0.2mm interference fit on the stepped shaft ends as one of the posts indicated. I believe some success will be had using the press fit by shrinking of the shafts with liquid Nitrogen and a fairly warmed up sleeve section, combined with some plug welds. The process is a varience of what we have already tried but maybe that's the problem with the welding method used before.

To all who have offered advise and ideas - thanks for your time and efforts, I'll let you all know how it goes next week when we try this method out.

Do as you say, but test shaft first without the plug welding part,

welding hardened/spring steel drive shafts without proper pre/post heat treatment...mmmmmmmmm

PS dont forget to machine a radius/slight taper a few mm deep in the bore of the sleeves to take away the sharp edge contact area with the 2 shafts

regards, cryogen

0.2mm interference fit on the stepped shaft ends as one of the posts indicated

The step could be a serious problem being a stress riser, and a substantial weakener of the shaft, because the area goes down with the square of diameter, at the same time that the torsional load goes up with the change in diameter. If the only problem with an oversized sleeve is fitting the boot, you could 1. probably stretch the boot without damage, 2. punch a hole at the end of a slit in the boot, and then slit the boot, using a hose clamp afterward, 3. etc.

Any reduction in shaft size at any point is likely to lead to failure, even if the reduced size is brought back up to original by welding.

Sure I've thought about it. Most logical solution, however where I work and live you can not get induction hardening done, so the shaft would need to be made from 43/40. Difficult product to work with and it still will not be hard enough to manage the job at the end of the process.

Thanks anyway

PBB

Thanks for your comments, I have already tried to join the shafts using a drilled out sleeve with a machined spiggot on the half shafts with a 0.1mm interferance fit. Then the 3 parts were pressed together and welded around the joins. the whole shaft was machined back flat to allow the instalation of the rubber bellows and installed to the ATV.

Yes it is the length I'm trying to achieve, the spline length is fine, due to the original design there is enough movement in the cup and hub I just have to make the shaft the correct length to go between the two.

All failures have been torsional and have originated from the weld area.

Thanks for your comments, any other ideas.

I've been down this road myself with pretty much the same result.

In the end my solution was to extend the differential end mounts out the extra amounts and use the shafts 'as is' . I used an extra bearing just behind the shaft seal to take the shaft end load and braced the lot together in a 1/4" welded steel plate cage. I made the actual stubs by machining the teeth off some long axle gears I had and joining them to the real axle gears with a short length of drive shaft spline.

I found it worked fine though it did bugger up the steering a bit on really rough ground; a result of the shaft lengths not matching the steering arms correctly. You could fix that by shortening the steering rods to match if it bothered you.

By your reply, I see that you have a restriction in the shaft diameter that prevents you to use a larger sleeve to increase the shaft lenght. Instead of it, you were forced to machine the joint back to the original diameter. As your part is working with high load, it failed because you had a weld compromissing the surface heat treatment, and the interference fit adding in causing a tri-axial load state.

I'd try to use a sleeve with inner diameter press fit against original shaft outter diameter, installing it in a way the shaft could still be installed.

By the way, you mentioned that you do not have access to good heat treating. Maybe your original solution of interference plus weld works fine for the old good 4340 steel (which has good weldability), but keep in mind you're gonna be forced to do a good heat treatment after weld, at least tempering. Without it you are most likely to have retained austenite and untempered martensite, even in your original part. Both structures very prone to failure.

This is a good method, (big sleeve, light press, braze) which I have used, and it works well. I have even welded (instead of brazing, which does less damage) a larger diameter machined tube, with a light press fit onto the shaft stubs at each end (replacing the solid shaft for most of the length) and the welds did not fail, if the penetration was sized fort the load. Without heat treating facilities and really sophisticated welding equipment, I can't imagine that an end-to-end weld (especially with subsequent machining of the weld area) could work. If the shaft is already highly stressed, getting the metallurgical structure right would be very difficult.

Given some precision machining, the spline ends and a little stub of each could be simply heavy pressed together into the heavy wall extension tube (internally machined), with a check of the pressing force to ensure that the torque shear load at the two surfaces was well under the slipping point. (Without doing the math, I'd guess that 20 ton press force would be adequate.)

If the only reason that the shaft needs to be small diameter is for boot installation, then that is a comparatively simple problem to solve (relative to the metallurgical problems).

Hello Ken,

Anything over ten tons should be augmented by some heat and or cooling then ten tons is all that is required; it's far safer

True. However, press fits with heating and/or cooling always make me nervous. I've been pretty lucky, but fear the parts getting halfway together and the temperatures equalizing from their intimate contact. Pure shrink fits, though, are kind of fun, with many dropping together without any force, and then locking together magically.

The thought of something as long as a half shaft in a 20 ton press is a little intimidating isn't it? The headlines: "Local Man gets the Shaft A local man was impaled by an axle shaft while attempting...

Good morning all, to everyone who offered advise and had the time to proffer ideas or information on this problem.

On Sunday morning I had a grin from ear to ear, it worked so well I'm going to make another set to keep for "just in case".

We machined a sleeve with a 10mm wall thickness (50mm dia) and had to use the liquid nitrogen on the shaft stubs - taking the advise of radiusing every shoulder were a stress riser could occur - and slipped them bits together by hand. It didn't take long and you couldn't twist the stubs anymore and the shaft just locked up into the sleeve, we did the next shaft stub and then we had a complete half shaft ready to try. No welding or any heat what-so-ever.

Tried real hard to snap them on Sunday, I guess I'll have to try again next Sunday as well.. What a lot of fun it is, making things that work and then give us hours of fun....

Good advise from all - Thanks to CR4 for and all you wise men who have offered your time and thoughts to make this work.

Thanks IndoPaulB2

Excellent! Glad to hear it worked.

I'm really glad to hear that. Sounds like our thoughts were not so wrong so far...

Regards.

Got'er done, cool!

whoop-de-do

Visit your local junk yard and salvage a couple of shafts that can be used for rod stock. Almost any car shaft has to deal with much more power and abuse for an extended time than an ATV. How many half-shafts have you heard of that have actually BROKEN. Chances are it will be larger diameter and probably of a material that can be welded.

In one of the cars we built, we had to shorten a half-shaft from an XJ6 to fit a D-Type replica. we tapered both ends to get a complete weld from the center out and then welded a sleeve to cover the butt weld, not plug welded, complete circumferential. In the 12 cars built, many of them raced, not one failure.

Hello Jaguar

Is that a D type, as in D type Jaguar, the prettiest sports car on 4 wheels?

I have never seen a real one here or anywhere else for that matter.

Do you have any idea how many are still in existence?

BAB

Try this.

http://www.coventryracers.com/

Go back to the Hi-Tensile (4140 ...4150 machined Hollow bar) larger dia sleeve in the middle idea,

DO NOT weld it but but heat shrink it with a reasonable overlap length, say..60 to 80 mm.on each join point.

I have done this to a large pump and also a John Deere Header (widened the wheel track by a couple of feet each side) they still work.

Hope this helps

It sounds like the 30.5mm may not be strong enough for the torque and bending. Can you make the sleeve longer, maybe to the point of keeping the splines and no more of the smaller diameter shaft?

Gas preheating of the weld area will help reduce the distortion

And post heating is highly regarded.

Good Morning IndoPaulB2 ,

I'm not sure that you'll be successful trying to lengthen these shafts. With 40 points of carbon the welds will require a post weld heat treat, as one of the other posts mentioned.

Have you considered making the shaft from an elevated temperature drawn steel such as LaSalle "Fatigue Proof". This steel (as produced) has a hardness of Rc 30 and would not require heat treatment after fabrication. I've machined this in production applications and it machines pretty well.

Good Luck

I would think you could do a interference fit by freezing the male part with liquid nitrogen instead of heating any of the parts. I have a buddy that does this routinely on very large cantilevered journals on large paper machine rolls with great success. Usually the hardened steel contains to much carbon and welding or heating it will only make it brittle in the HAZ in the end. If you do not have a way to anneal some of this hardness out of the shaft after heating it is always going to break IMO. By not heating the parts and instead use freezing to shrink one of the parts to provide the interference fit of the parts you may not effect the original heat treating. Just an idea.

Hi,

search CR4 and maybe Google for "Hirth gear"

this is machined onto the axial parts of the shafts and clamping is provided by a central screw.

RHABE

The best answer is out sourcing...a new extended shaft.

Dear Friend,

As the shaft is hardened,

It is better to make new hardened shaft, instead of joining to extend.

Warm regards,

D.N.Shenoy