Topic: Anything Special About Front Axle Material?

[lostinthe202]

I'm making an axle for a front end conversion I'm doing that will use the stock spoked wheel.  Actually, I've already made it out of a piece of 304 SS.  I chose that because it was close to size already and I happen to have it handy. 

I don't have a stock axle or I'd check the hardness on it, but I was thinking that it wasn't made out of anything special.  Anyone have any more info?

Thanks!

[jamesb]

I just had one turned down to the size I needed. I talked to a guy about making a axle he said you wouldn't want to use harden steel he thought that if a person was to hit a pot hole or something of that nature there could be the possibility or it snapping in stead of bending. So I went to a bike shop/garage found a used one that was bigger than I needed and had a machine shop turn it down. For 40.00 dollars I thought it was worth the peace of mind of being safe. You might want to try that route

[lostinthe202]

OK, that jives with my reasoning.  304 is pretty ductile so it won't snap like a piece of hardened steel would, but I was thinking it might be too ductile and would bend prematurely

I like  your idea of turning down a larger shaft.  Perhaps if I get more negative feedback on the SS axle, I'll go that route.

[trueblue]

SS work hardens like a b!tch, and would be more prone to snapping down the track after it has been in use for a while.  I would be more inclined to use an old axel or a piece of 4140.

[donpark1086]

Rather than making the axle of rod (from a rod mill) or wire (thick wire from a drawing mill), make your axle from a large structural bolt.  It will be good tough steel. Not soft, Not brittle. Strong and stable.  Unlikely to find stainless though.

[wildcatmahone]

If you're gonna make a vehicle axle from scratch I would strongly suggest you do your homework first. The stock Honda axle may or may not be a high tensile steel but "probably will work fine" isn't good enough when your ass is on the line. The only way to go about this properly is to ask a mechanical engineer or take the original axle to a lab to get it positively identified. Then you can review the specs and choose your axle material accordingly...

[lostinthe202]

SS work hardens like a b!tch, and would be more prone to snapping down the track after it has been in use for a while.  I would be more inclined to use an old axel or a piece of 4140.

Dang, hadn't thought of that.  So 4140 or 4130 but at a pretty soft temper?  Aren't both of those prone to brittleness in a shock-prone environment?

Rather than making the axle of rod (from a rod mill) or wire (thick wire from a drawing mill), make your axle from a large structural bolt.  It will be good tough steel. Not soft, Not brittle. Strong and stable.  Unlikely to find stainless though.

Doesn't need to be stainless, like I said, it was just a piece I had handy.  doubt I could find the creature you describe easily, but it's a good idea. 

If you're gonna make a vehicle axle from scratch I would strongly suggest you do your homework first.

I'd love to, do you have some suggestions of where to find my assignments?

The stock Honda axle may or may not be a high tensile steel but "probably will work fine" isn't good enough when your ass is on the line. The only way to go about this properly is to ask a mechanical engineer or take the original axle to a lab to get it positively identified. Then you can review the specs and choose your axle material accordingly...

I appreciate your insightful post that was no doubt intended to be not only an immense help, but the very timely and prescient answer to my inquiry.  Also the reminder that caution must always be used when making one's own parts is appreciated as I have a tendency to ask questions first and try it out later, a very bad habit I know. 

I really appreciate your offer of assistance and I look forward to considering your referrals of mechanical engineers with the appropriate background.

Please be sure any attachments are in a format acceptable with monkeys as they are the only work-base readily available to me accustomed to handling feces.

[dave500]

the axles will be a high quality almost spring steel,not hardened,,you can dent them,you cant dent a drill bit easy.

[trueblue]

SS work hardens like a b!tch, and would be more prone to snapping down the track after it has been in use for a while.  I would be more inclined to use an old axel or a piece of 4140.

Dang, hadn't thought of that.  So 4140 or 4130 but at a pretty soft temper?  Aren't both of those prone to brittleness in a shock-prone environment?

Here is some info on 4140 from here. 

http://www.interlloy.com.au/data_sheets/high_tensile_steels/high_pdf/Interlloy_4140_High_Tensile_Steel.pdf 

I have never seen any problems from 4140 with brittleness, unless it isn't tempered correctly.

4140 is a 1% chromium - molybdenum medium hardenability general purpose high tensile steel - generally supplied
hardened and tempered in the tensile range of 850 - 1000 Mpa (condition T).
4140 is now available with improved machinability, which greatly increases feeds and/or speeds, while also extending tool
life without adversley affecting mechanical properties.
Pre hardened and tempered 4140 can be further surface hardened by flame or induction hardening and by nitriding.
4140 is used extensively in most industry sectors for a wide range of applications such as:
Adapters, Arbors, Axle Shafts, Bolts, Crankshafts, Connection Rods, Chuck Bodies, Collets, Conveyor Pins & Rolls, Ejector
Pins, Forks, Gears, Guide Rods, Hydraulic Shafts & Parts,Lathe Spindles, Logging Parts, Milling Spindles, Motor Shafts,
Nuts, Pinch Bars, Pins Various, Pinions, Pump Shafts, Rams, Sockets, Spindles, Sprockets, Studs, Tool Holders, Torsion
Bars, Worms etc..

[Rigid]

No one has mentioned the delicate machine work required.  Turning down and potentially threading the axle can introduce irregularities and stress points that lead to cracking.  An axle has many hidden chamfers and steps that cannot be readily inspected.  At the very least, I would remove a homemade axle every few miles for a thorough liquid penetrant inspection.  Magnetic particle would be best if available.  Personally, the thought of axle failure, forks hitting the pavement at 60 mph, and the resultant end over end carnage would prevent me from doing it.  I build many custom parts, axles just aren't one of them.

[trueblue]

I forgot to mention that it should be ground to size rather than being turned, to prevent stress points.

[solo 2]

I'm not an expert on steel and don't claim to be but I am a machinist who works with many exotic metals and loads of stainless. I have considered making my own stainless axles, this would take very little time, but safety wise the choice of material is critical, I prefer to err on the side of overkill. Most stainless steels that I would consider using for an axle are very expensive, heat treated 400 series or 17-4PH. I have access to 316 coming out my ears, but the tensile strength worries me, it's less than low carbon steel. 316 is essentially the same as 304 just better corrosion/chemical resistance.
17-4PH would be my first choice as it has a strength comparable to 4140, but my cost on that is not worth it to me.

Stainless does work harden but in this usage would not be an issue I don't think as there's anything really running against it.

4140 or 4340 would be fine choices as they both have excellent mechanical properties, but you have to deal with rust unless you have them treated. These are not the type of steels that you would use for through hardening typically so don't worry about heat treatment, the bars are usually HTSR from the supplier.

I suspect that the originals are some sort of plain carbon steel that has been case hardened, it's highly unlikely that a factory part is made of high carbon steel. In an axle application I would suspect that shear strength would be the ultimate design property. I may take one to work now and see exactly what it's made of as we have the machine to check this, I will not try to name it as I don't know.

And finally any machinist worth his salt does not leave stress risers in a shaft of any kind, grinding should not be neccessary, a slower feed rate with a radiused tool will do fine.

[lostinthe202]

An axle has many hidden chamfers and steps that cannot be readily inspected.

The axle I'm making is just a straight shaft.

I'm not an expert on steel and don't claim to be but I am a machinist who works with many exotic metals and loads of stainless. I have considered making my own stainless axles, this would take very little time, but safety wise the choice of material is critical, I prefer to err on the side of overkill. Most stainless steels that I would consider using for an axle are very expensive, heat treated 400 series or 17-4PH. I have access to 316 coming out my ears, but the tensile strength worries me, it's less than low carbon steel. 316 is essentially the same as 304 just better corrosion/chemical resistance.
17-4PH would be my first choice as it has a strength comparable to 4140, but my cost on that is not worth it to me.

Stainless does work harden but in this usage would not be an issue I don't think as there's anything really running against it.

4140 or 4340 would be fine choices as they both have excellent mechanical properties, but you have to deal with rust unless you have them treated. These are not the type of steels that you would use for through hardening typically so don't worry about heat treatment, the bars are usually HTSR from the supplier.

I suspect that the originals are some sort of plain carbon steel that has been case hardened, it's highly unlikely that a factory part is made of high carbon steel. In an axle application I would suspect that shear strength would be the ultimate design property. I may take one to work now and see exactly what it's made of as we have the machine to check this, I will not try to name it as I don't know.

And finally any machinist worth his salt does not leave stress risers in a shaft of any kind, grinding should not be neccessary, a slower feed rate with a radiused tool will do fine.

Good info.  I'm a machinist too and I agree with your last statement 100%.  I might get my hands on a stock axle and see if I can't mod it to work.  We've got one of those nifty ray-guns at work that tells you the composition of a piece of material, but I don't actually have an axle to bring in.  Please let me know if you end up doing this.

Thanks!

[Rigid]

The axle I'm making is just a straight shaft......... So no turning down, no threads, and no recessed areas for bearings and such? Interesting axle.

[lostinthe202]

I've made two sleeves for each fork tube that will pinch the axle in place so the axle only needs to be a straight shaft of the appropriate size for the wheel bearings to ride on.  Spacers will keep the wheel in position just like it is originally setup.  This isn't a press fit, it's a slip fit the same as the original axle.  So no, no recesses, no shoulders or other places for cracks to propagate. As I didn't have an axle to measure, I measured the bearing and went about five tenths or so under that. I made the axle on a Hardinge using a KC730 coated insert with a 2/64th radius running at about 200 sfm to rough, and 300 or so to finish keeping it wet the whole time.  I didn't measure the finish, but I'd say it's a 16 or better.

I won't be threading the outside of the axle, but I will probably drill and tap the ends so I can thread on a couple of, well large washers basically to keep the shaft from migrating out either end.

[solo 2]

Our ray gun at work is dead, no replacement till Jan. . The axle is pretty soft, 177 brinell and after some research I'd guess it's more than likely 1045. Before using your stainless I think I'd look at the ultimate yield strength first, much lower than even the low carbon steels.

I know people who have made axles for bikes out of 316, but as I said before I think I would err on the side of caution or at least have a chat with one of your engineers at work if you have one.

[lostinthe202]

Right on Solo, thanks for the info.  I've since got my hands on a 750 front shaft, so I'll bring that in and see what I see.  I'll ask around and see if I can find an engineer's ear I can bend.

Cheers,

[camelman]

Why not source an original axle for your forks and get bearings to adapt it to your stock wheel?  That's what I did. Worked perfectly.

[lostinthe202]

It's funny you said that,

As usual, I was going about this the hard way.  Digging into bearing sizes, turns out the bearings from the wheel of the front end I'm using (cbr f3) are the same OD as the CB500 wheel I'm using.  They're 12mm thick instead of 13mm for the CB, but I'm making spacers anyway, so I don't care much there.

Thanks for the input everyone, I'll still zap that axle when I get a chance since now I'm curious.