Inconsequential ramblings of an Old Git

[Tricky]

Not sure if it helps much ( if at all) , as mine's the Factory but couple of pics below of my standard Gen1 Tuono top yoke.
On mine the "leveling up" is part of the top surface casting

[weeksy]

Now that makes more sense... a flat surface to mount something to

[Screwdriver]

Not sure if it helps much ( if at all) , as mine's the Factory but couple of pics below of my standard Gen1 Tuono top yoke.
On mine the "leveling up" is part of the top surface casting

To my untrained eye, that looks a lot more like it's been machined from billet.

I could be mistaken but it has all the hallmarks. A wider shot would help.

[Mr. Dazzle]

Think it might be a finished machined casting, looking at the underside?

[weeksy]

To my untrained eye, that looks a lot more like it's been machined from billet.

Would that make it stronger/better ?

[Mr. Dazzle]

To my untrained eye, that looks a lot more like it's been machined from billet.

Would that make it stronger/better ?

Received wisdom of the internet is that billet is stronger.

Reality is far more complicated! It's undeniably true that you see a lot of "billet" (no-one calls it that) in motorsport and the like, but that's mostly for lead time and low volume production reasons.

Looking at the pics again, I think Screwd is probably right, I think the underside is just dirty. Doubly so when you look at the risers themselves, clearly machined from plate. I suspect the driving reason was cost more than anything, Aprilia probably don't/didn't make enough to bother setting up castings.

That yoke is what....40-50mm deep overall? 50mm Ally plate is basically an off the shelf product, cheap as chips.

[Tricky]

To my untrained eye, that looks a lot more like it's been machined from billet.

Would that make it stronger/better ?

Received wisdom of the internet is that billet is stronger.

Reality is far more complicated! It's undeniably true that you see a lot of "billet" (no-one calls it that) in motorsport and the like, but that's mostly for lead time and low volume production reasons.

Looking at the pics again, I think Screwd is probably right, I think the underside is just dirty. Doubly so when you look at the risers themselves, clearly machined from plate. I suspect the driving reason was cost more than anything, Aprilia probably don't/didn't make enough to bother setting up castings.

That yoke is what....40-50mm deep overall? 50mm Ally plate is basically an off the shelf product, cheap as chips.

It's a machined casting.

They are Ohlins forks in my model- I don't know whether Aprilia buy the whole assembly including the top yoke from Ohlins or just the fork legs, but whatever, the top yoke is quite different (and a lot more substantial) looking than the one on the non-Ohlins variant of the Tuono.

[weeksy]

So now he needs yokes, forks, calipers and a wheel?

[Skub]

Mrs.Mango will have his balls.

[Screwdriver]

We're in a bit of a grey area with "machined casting" vs "billet". Both terms are quite vague.

I use billet in the vernacular where an item is machined from a shapeless lump of metal, a billet. At some stage that billet would of course have been molten in order to be formed. But there is a difference between a "cast" lump of material and a "casting" Typically a casting would be alloyed (or doped) with other material to help it flow, reduce casting defects like cold shuts, cavities etc.c due to the difficulties in having the metal form inside a complex shape. For thinner sections like engine casings, that's going to be excess silicon which I mention only because that can be a bastard to weld or not weldable at all!

A machined casting is in my mind, something which has been cast into the gross shape of the desired object and then the precision surfaces are machined into it, like a typical engine block. But they will have both machined and cast surfaces on display because if you were going to machine the entire surface, you'd be better off with a billet or regular metal stock which can be produced more easily without doping or compromising the alloy structure merely to flow into a mould.

There are differences in the strength of cast vs. machined due to the properties of the material. A billet is an homogenous lump of material which might also be further modified by rolling or even forging into a regular shape, rod, sheet, billet etc. A casting will have a "skin", which forms differently from say the inside since it cools more quickly (among other issues) and will have different material properties from an homogenous lump of nominally the same material.

And here's the rub; if you machine away the surface of a casting, you are removing a hardened, stressed skin which leaves behind only the compromised, doped inner. The part is weakened by doing so and that needs to be taken into account during the design. If you were intending to machine the entire part therefore, you wouldn't start off with it being cast into shape but use a much more reliable and predictable billet.

I am more than happy to be put right on this waffle, it's just an opinion I have formed over the years I have been playing in my little machine shop.

[Mr. Dazzle]

Reality is far more complicated!

Told ya

[Screwdriver]

Reality is far more complicated!

Told ya

Indeed. So is my laymans understanding way off or about right?

[Mr. Dazzle]

Generally. I don't think it is as simple as you make out with the skin thing though.

I wouldn't mind betting Aprilia (and others) also have a common parent yoke casting whcih gets machined into different models.

That Touno one does look to be machined all over though, it's all chamfers and corners, no rads or swoops...which is why l reckon/reckoned its machined from solid. The risers are blatantly plate.

[Count Steer]

Reality is far more complicated!

Told ya

(As you suggested earlier) The whole 'billet' thing probably adds more confusion than light. Probably because of steel billet which is hot forged/rolled and has particular properties as a result. Aluminum/alloy 'billet' is usually just a cast lump.

I'm pretty rusty on all this stuff now (the last time I was involved was making Hepolite pistons - cast, machined).

[Mr. Dazzle]

Unless it's Ally plate, which is rolled to thickness....

Honestly...of all the bits of metal I've seen stacked up in the machine shop, it's almost universally rolled/drawn plate and bar.

Pistons on the other hand are often pressure die cast, rather that just straight up cast. Exactly what it sounds like. They're pretty much universally post cast heat treated too, which completely changes the effects Screwd mentions. Indeed, that's the point of doing it!

[Count Steer]

Unless it's Ally plate, which is rolled to thickness....

Honestly...of all the bits of metal I've seen stacked up in the machine shop, it's almost universally rolled/drawn plate and bar.

Pistons on the other hand are often pressure die cast, rather that just straight up cast. Exactly what it sounds like. They're pretty much universally post cast heat treated too, which completely changes the effects Screwd mentions. Indeed, that's the point of doing it!

Some alloys work harden on rolling too. I don't suppose they anneal it after - unless it's part of the continuous rolling operation. As you say, the heat treatment of pistons was a big part of the operation (along with some pretty thorough NDT).

Complicated business.

[Mr. Dazzle]

Plate is often heat treated after rolling too though!

So for example 6082 T6 is a pretty go to material, the "T6" refers to the heat treatment it's had. A 250mm square of 40mm thick material would only cost you £95 as a member of the public, so you can probably guess how little it costs in industry. 6082T6 would make you some nice yokes, certainly compared to stock casting (I'd bet).

https://www.aluminiumwarehouse.co.uk/al ... fEQAvD_BwE

EDIT: BTW, if one thing should be clear from this conversation, it's that putting two yokes next to each other and declaring they perform the same because they look the same is a very bad idea

[Screwdriver]

It is a minefield and you dare not make assumptions.

My takeaway from all this is that if you are going to modify a part then you really need to consider the material properties, especially if you are drilling holes into critical parts.

In this case, the part is clearly a cast item and an example was shown of a "similar" item which was fully machined (either from billet or a shaped cast solid). Clearly the different manufacturing process suggests the parts are not as similar as they appear and that therefore extra care needs to be taken when poking holes in it.

[mangocrazy]

They are Ohlins forks in my model- I don't know whether Aprilia buy the whole assembly including the top yoke from Ohlins or just the fork legs, but whatever, the top yoke is quite different (and a lot more substantial) looking than the one on the non-Ohlins variant of the Tuono.

Tricky has the super-posh and rather rare Factory version with Ohlins everything. Council spec Tuonos made do with Showa forks and Sachs shock.

To attempt to get another opinion on this I rang Griff Woolley of AP Workshops fame and all round good geezer and asked him a number of questions. He confirmed that the 'Showa' Tuono top yoke is cast, as are the Mille/Falco yokes, but the T yoke has revised webbing for additional strength in key areas. But they do also poke a 10mm hole in it to fix the risers to, and the top deck of the T yoke does look identical to the M/F yoke.

I then told him what I'd done to beef up my Mille yoke and asked him his opinion. Without hesitation he said, 'yeah, that should be alright. If you'd just drilled a hole in it I'd tell you to stop, but what you've done should be fine'.

So there we are - completely unscientific, but a view from a man who gets his hands dirty working on bikes 5 days a week and is very highly regarded in the Aprilia community. That's good enough for me.

Flame away...

[Screwdriver]

Hang on, is he saying the Gen1 Tuono yoke, like the one @Tricky posted earlier is cast?