Thread: machining an axle

Originally Posted by LowRanger

I also spoke to Keith on numerous occasions as well as emails pics of the type of areas that I use to wheel in,and Keith mentioned that,while where I wheel was a lot more sandy and loose than where he normally drives and tests,he had actually used his vehicle fitted with 35's and bounce tested the axles,deliberately trying to break them,and was unable to.So he was happy to guarantee that they won't break on 35's.But would recommend different axles if going any larger in wheel size..
There wouldn't be many road registered Defenders that have their driveline pushed much harder than my poor old truck,and the axles have taken all the punishment that I dished out to them.So I have no problems.And in that time,I will say that I did twist a set of Maxi rear axles.But I now have a set of Hi Tough rears and they seem to be ok at the moment.....but time will tell !!!!

Wayne, do you run 30 spline fronts?

Originally Posted by uninformed

Wayne, do you run 30 spline fronts?

Serg

No I run 24 spline front and rear.

In discussions I had with Keith,I intimated that I was only running a 200Tdi with the boost turned up a bit,and had no intention of running anything more powerful,even though I do have a lot of torque with the very low gearing.He indicated that his testing was done with a V8 and that the 24 splines would handle anything the 200Tdi could put out to the 35's,even with the underdrive and 4.1's.
If I was ever going to any larger tyres or something with a lot more power,I would uprate axles front and rear,but I am more than happy with what I run now,even though I do have a noisy CV.But I can put up with that

I was just reading some of Billavista's tech articale:

the question was posed, does the proper profile design gain benefits over gaining extra dia by not wasting or neckdown......

Carrol Smith is quoted, saying that Hy-tuff is not as good as 4340 300m or even 4340.

I think that in the usa, becasue alot of the axles have 1 piece shaft and flange, that they make them from "forged blanks". Can anyone add some light to this? would a forged blank have different qualities to solid bar that would be used by say Hi-Tough? (taking same materials, ie 4340 forged and 4340 not forged)

Originally Posted by uninformed

I was just reading some of Billavista's tech articale:

the question was posed, does the proper profile design gain benefits over gaining extra dia by not wasting or neckdown......

Carrol Smith is quoted, saying that Hy-tuff is not as good as 4340 300m or even 4340.

I think that in the usa, becasue alot of the axles have 1 piece shaft and flange, that they make them from "forged blanks". Can anyone add some light to this? would a forged blank have different qualities to solid bar that would be used by say Hi-Tough? (taking same materials, ie 4340 forged and 4340 not forged)

Serg - in theory, MDE/HTE axles are a much better design as they are waisted across their length. (I believe Ashcroft axles are as well?).

In practice though, failures of all of the above can and have happened, though they seem equally rare.

material properties aside, a LOT comes down to the hardening/heat treating process.

Early MDE axles made from EN25/EN26 gained a reputation for failure. I have seen one break that was only used on a 109 with 7.50s. That was when Mal switched to AMS6418. McNamara on the other hand still uses EN25 and claims that Mal's heat treater wasn't treating it peoperly.

So in terms of failure rates, I believe apples and being compared with apples.


These are the forged 1541H axle blanks I mentioned earlier which are supplied already hardened then splined and drilled to suit the application.

http://karnagemotorsports.com/images/BlankBoltIn.jpg

I am not sure if the axles being discussed here from Keith are also supplied hardened and machined, or if Keith didn't waist them to cut down on machining time.

Originally Posted by isuzurover

[snip]

material properties aside, a LOT comes down to the hardening/heat treating process.


[snip]

Sort of quoting Carroll Smith (I don't have Engineer to Win anymore, I lost a lot of reference/engineering books about fifteen years ago) so I'm going off memory here, in the section on materials he wrote of an off road race team he consulted to that was bending a lot of machined stub axles/uprights and in the short time before a major race they didn't have time to re-engineer and fabricate a new upright. (IIRC it was all 4130, including the stub)

A very switched on metallurgist mate of Mr Smith's called out a radical heat treatment for the compromised hub assembly, on the understanding it would be replaced soon after with a redesigned part made of a more appropriate material.
It lasted the race without any deformation or breakage.

Of course the part wasn't redesigned as it worked so well, until the upright failed completely at a major race meeting X amount of months down the track.

Anyway, the story was one to show that the bits need to be designed properly and the right material used in the first place, but it also shows what can be achieved with the approopriate heat treatment.

this is quoting Carroll Smith from "engineering to win"

SAE 4130
Best known of the family of CHROME-MOLY steels, 4130 is often considered, in racing circles, to be the ideal steel for all high-strength/high-stress applications. IT IS NOT! In thin sections (that is, in tube or sheet form) its unique combination of excellent tensile strength, toughness and response to mild heat treatment combined with its good formability in the annealed condition and its outstanding welding characteristics make it virtually unbeatable for fabrications subject to high stress levels. It is critical that all welds be stress relieved. I prefer the use of OXWELD 32 CMS welding rod with 4130 for the simple reason that it both normalizes and heat treats well in conjunction with 4130. Many welders prefer to use a stainless rod, but the high nickel content of stainless welding rods means that the weldment will not respond well to heat treatment. Since I believe that not heat treating 4130 fabrications is DUMB (if you don't heat treat you end up with an expensive part with the same strength as 1020—and brittle weld areas). Smith's law says to use the heat-treatable rod for EVERYTHING. I heat treat 4130 fabrications to Rock-well C Scale 26 to 30 and no higher. This results in an ultimate tensile strength of about 130,000 psi with sufficient ductility that I do not have to worry about brittle parts. The other side of the 4130 coin, often unknown to (or at least unappreciated by) the racer, is that it possesses poor deep-heat-treating characteristics and has an inborn dislike of varying cross-sections. These characteristics make 4130 a poor choice for machined or forged parts—it doesn't forge very well anyway. It also doesn't machine very well, at least in the normalized condition—too gummy. Those people who make hubs, steering knuckles and the like from 4130 are kidding themselves—and their customers. It doesn't make very good shafts, either, as in drive shaft, or axle, or torsion bar.

SAE 4140
This is a deep hardening chrome-moly steel with excellent impact resistance, fatigue strength and general all-around toughness. It is commonly used for small-aircraft forgings. I use it in bar form for all of the little gub-bins and small parts that we are always machining. It doesn't weld as well as 4130 but it does weld satisfactorily. Welded to 4130 tube or sheet, with Oxweld 32 rod, a 4140 machined component can be heat treated to the same spec as 4130.

SAE 4340
This is the nickel-chrome-moly deep-hardening steel that we SHOULD use, in its vacuum-melted configuration, for our hub forgings, drive shafts, axles and the like. Its tensile strength, toughness, fatigue resistance, excellent deep-heat-treating characteristics and very high tolerance of stress reversals (which is just another way of saying that it has excellent fatigue resistance) make it just about unbeatable. It is also weldable (with care and a lot of pre-and post-heat) and eminently forgeable. In use it should be heat treated to the 180,000—200,000 psi range, maximum—although it can be taken to 220,000 psi without significant loss of toughness. The hardness range between Rockwell C Scale 46 and 48 should be avoided with this steel as it becomes brittle in this range.

SAE 4340 MODIFIED (300M)
This is, as you would expect, very similar to 4340... The addition of a trace of vanadium and an increase in the silicon level (while they have no notable effect on the hardness, strengths, or ductility of the resultant alloy) work miracles in the toughness and resistance to fatigue, producing a steel which, in the 270,000 to 300,000 psi range, is the toughest, most impact resistant and most fatigue resistant of the usually available steels. Unfortunately, even in the normalized condition, it is a bear to machine. Reducing the hardness by reducing the level of heat treatment or by tempering has the curious effect of reducing the tensile strength WITHOUT increasing the ductility or toughness. The most common use of this outstanding steel, also known as 300M, is for military and commercial aircraft landing gear. We use it for hubs, for drive shafts, axles and torsion bars—when we can afford it (or when we cannot afford NOT to use it). At its normal, heat-treated hardness level of Rockwell C 52/56 it is hard enough that we can and do run roller bearings directly on its surface. While the material is great, the heat treating is tricky. There is a very real danger of surface decarburization which can only be avoided by copper plating prior to heat treat. The ONLY heat treat specification for 300M is MIL H 6875, but there are tricks to every trade. MIL H 6875 calls out a two-hour quench at 575 degrees F. Doubling the quench time to four hours will notably increase the ductility and fatigue resistance of the finished product. Another trick is to absolutely forbid the heat treat shop to perform Rockwell or Brinell hardness tests on the actual part, supply a "test coupon" of the same material and cross-section wired to each part and insist that the coupon be heat treated along with the part and that all hardness tests be done on the test coupon. This is a good idea with ALL parts heat treated much above Rockwell C 40.

THE HIGH SILICON, NICKEL CHROME STEELS
These are usually known by trade names such as Hi-Tuff and Stress Proof. They contain up to about 3 % silicon and are, as the names suggest, tough as hell. They are popular for stock car and off-road racing axles—and the alloys are very suitable for these applications. They are not as good as 4340 M or even 4340, but they are also a damned sight cheaper and, especially where the minimum weights imposed are high, the fact that a part with the same strength and fatigue resistance can be made lighter by using a better steel may be a lot less significant than the cost difference. However, these steels are tough only because of the high silicon content, which is mainly in the form of longitudinal fibers or strings of silicon. This limits the efficient (and safe) use of the alloys to parts with minimal section changes and virtually no transverse machining (we don't want to cut the longitudinal strings that make the stuff tough to start with, do we?). They also don't like being bent very much because that may rupture the silicon strings. Mind you, I have made a lot of street car antiroll bars from Stress Proof with excellent results and pretty severe bends—but in this case the bends are almost, by definition, in lightly stressed areas.[7]

Originally Posted by isuzurover

Serg - in theory, MDE/HTE axles are a much better design as they are waisted across their length. (I believe Ashcroft axles are as well?).

In practice though, failures of all of the above can and have happened, though they seem equally rare.

material properties aside, a LOT comes down to the hardening/heat treating process.

Early MDE axles made from EN25/EN26 gained a reputation for failure. I have seen one break that was only used on a 109 with 7.50s. That was when Mal switched to AMS6418. McNamara on the other hand still uses EN25 and claims that Mal's heat treater wasn't treating it peoperly.

So in terms of failure rates, I believe apples and being compared with apples.


These are the forged 1541H axle blanks I mentioned earlier which are supplied already hardened then splined and drilled to suit the application.

http://karnagemotorsports.com/images/BlankBoltIn.jpg

I am not sure if the axles being discussed here from Keith are also supplied hardened and machined, or if Keith didn't waist them to cut down on machining time.

thanks Ben, I agree with your apples to apples comments now.
I have no idea on the manufacture process of material that keith has used, and without seeing a pic, I can only imagine the blanks are supplied +/- dia...to me the end is just machined to a dia and splined....hence why the spline will pass and shaft go in about 6 inches...the shaft dia is larger than major dia of spline...

Originally Posted by Vern

Agree 100%, you can feel where it tapers up, about 6" up the axle, short axle is perfect. Could probably linish it.

That's not from deflection during machining is it?