Jim

The bible for this sort of thing is Volume 2 of the three book series "The Racing Motorcycle, a constructors guide" by John Bradley.

He recommends 605M36 in T condition for wheel spindles. That should be what you get if you ask for EN16T from a reputable supplier but I can't see the sense in asking for something that should be to a long obsolete standard and ought to be equivalent. Ask for the right stuff and be done with it.

Although you could use 080M40 which is what ought to be supplied if you ask for EN8 it's a bit lacking. Only goes to tensile range R at 19 mm diameter so limited to very small spindles. John says you need to make sure that it actually is heat treated to a sensible range and not just plain bright drawn or, worse hot rolled bar. Even in 2003 when that volume was published hot rolled EN "equivalents" could be pretty noisome stuff. Its only got worse in the intervening period. When was the last time you actally say EN8R advertised? Like John I reckon there is too much carbon in it for comfort.

If you only want a foot for a spindle might as well get summat a bit decent.

When it comes to safety related things like spindles the job must be done properly.

No excuses.

Ever.

You may know its for parade only at low speed with a careful pilot but no one else will care. Two part construction just won't do. Not forgetting the effect that silver soldering may have on the tensile range.

If I'm making a spindle I want the right material with certificates.

Clive

Edited By Clive Foster on 29/08/2021 22:34:36

I asked the question of Norman White (Norton restorer of note) "What material are Norton Commando wheel spindles?", his response was "EN16"

cheers

Bill

Edited By Bill Pudney on 29/08/2021 23:02:17

I don't consider EN8 to be strong enough for this application. I would NOT risk my neck on this material. Colin

Mike

Fundamentally the issue with wheel spindles is crack resistance rather than strength per se. Especially with threaded end ones that screw into one fork leg where the thread end creates a stress riser.

Even then odds are is more a case of what happens if things aren't correctly installed with the spindle properly fitted into the master leg and the other settled into its natural position by bouncing the forks.

Agreed that spindles are rarely destroyed in a crash. Seen plenty of bent ones tho'. Something I always check when involved with a bike whose history I'm unsure of. Mild bends are more common than I'd like. Regrettably seen some "professionally" fixed (not) bikes with handling or fork issues where the bend should have been obvious on installation.

When you don't have factory or real engineering company resources / expertise to sort out and get ideal fit material for the job it becomes a question of what can reliably be got off the shelf that is known to be suitable for the job.

605M36 in T condition with a certificate is. Anything else folk like us can't really be sure about. 080M40 in R condition with a certificate should certainly be up to the job on anything small enough to have a spindle under 19 mm diameter. I don't do ordering under an EN number, unless "a bit of steel sort of like this" is up to the job and the price is very right, because I can't get real certificates specifying the properties of what I've just paid for.

Of course, like any sane Home Workshop guy I tend to duck jobs where "a bit of steel sort of like this" isn't an adequate specification!

Stainless steels are a minefield. Pretty but you do need to know your engineering if applying serious loads. Crack behaviour and effects of certain chemicals can be a little surprising.

Clive

I like your reasoning Clive, choosing a suitable material could still be undermined by not taking care with suitable radii in the right places. Making a wheel spindle seems a straightforward job until someone who knows what they are doing explains the things that can go wrong. We had some conveyors at work that would break quite large shafts simply because of poor alignment, the actual loads from the parts on the conveyor were minimal but the alignment being slightly out would in time snap a 40mm shaft, I suspect the design was not too brilliant either.

Mike

Bottom line is any commonly available steel heat treated to T condition will be amply strong enough for spindle duties. When you look a tabulated properties there is no discernible difference so far as the likes of us are concerned.

But I'd still rate 603M36 T (En16 T) over 709M40 T (En 19 T) and 817M40 (En 24 T) for this sort of thing because its a manganese-molybdenum alloy and so much less susceptible to temper brittleness than chromium alloys. Its also a somewhat tougher and more shock resistant at normal temperatures.

709M40 (En19) is a chrome-moly steel and 817M40 (En24) is a nickel-chrome-moly steel so both can have temper brittleness issues at higher temper ranges if heat treatment is not done well. Pretty much unheard of in practice for 709M40 on suitable duties, especially since Euro Norms rationalisation has reduced the chrome content a little, even at the highest tensile range. T is pretty much bullet proof. 817M40 (En24) has an unfortunate history of occasional, inexplicable, brittle fracture even in T condition. That alloy is, and always has been, known to be sensitive to less than precise control of heat treatment conditions so best reserved for applications that need it. Not purchased on the "Its more expensive so it must be better." basis.

What you are really buying with these three different steels is the maximum diameter at which a given tensile strength range can be reached. 605M36 (En16) manages 63 mm diameter at T, maximum practical is V at 19 mm diameter. 709M40 (En19) goes out to 100 mm diameter at T and can make W at 19 mm. 817M40 (En24) hits 250 mm diameter at T and 29 mm at W.

Can't see any point in paying extra for properties at a size much larger than I plan to use.

Its worth remembering that the Griffith crack length at which catastrophic failure occurs gets shorter as the tensile range gets higher. There is a double whammy in that steels capable of higher tensile ranges in larger sections tend to have shorter crack lengths too. Generally no great worry up to T condition but beyond that its important to pay proper attention to such things.

As Mike says sharp edges and other stress raisers can cause things to break even when the official loads are well within limits. Motorcycle forks are surprisingly flexi. Even the hefty racer breed.

Always a good idea to avoid seriously low temperatures too. Below -50°C or so unfortunate things start happening. I may be a 603M36 T fan boy but no way am I taking it to deepest Antartica winter as it seriously doesn't like getting really cold.

Clive

Edited By Clive Foster on 30/08/2021 22:40:47

Back in 2004 I made front/back and swingarm spindles from grade 5 Titanium , also known as 318 and Ti6AL4v , at 20mm dia its more than up to the job, if I was going to go for a steel to use I would go for EN57T stainless , a tough steel and pretty easy to machine as well.