Race chassis

[husaberg]

Various frame spars, mostly ali extrusions, but the small CBR600 one is steel and there are some fabricated ones, too.

The GSXR750 Srad had geometry entirely based on Kevins RGV500 of the time. likely a bit wider at the top.

[IMG][/IMG]
One of the most hideous tails ever made though.

If a production frame: cost. If a one off, easier construction if the extrusions are readily available to you.

Yip, hence Honda's love for them.

[Ocean1]

If a production frame: cost. If a one off, easier construction if the extrusions are readily available to you.

Yes, cheap and easy.

But they often then spend a lot bending them and adding detail to accommodate design deficiencies caused by the use of parallel sections.

The GSXR frames pictured above point up how much going to the simpler beam frames saved in fabrication time - and cost.

The half - shell pressings which are then seam welded are probably cheaper initially than an extrusion - but still have to be seam welded.
Given that they can be produced in already curved form - and sized appropriate to the loads at any given point they are probably more cost effective than parallel extrusions which still have to be bent...

But later still are the current frames which are using more cast sections than before. They can be produced quickly and can be sized appropriate to loads as can be seen in the Buell ? frame Ocean put up. Bent sections can be accurately finished as cast. Fewer welds as the main pieces get bigger too. Even automated welds cost money.

Not a lot of this is appropriate to the home builder though...Unless you want to get into limited volume presswork.

Yes Buell XB series. Not a spectacularly light frame, but there isn't much on an XB that isn't either frame or engine, (shades of Collin Chapman). Dry weight around 178kg iirc.

Home build from pressed shells? Why wouldn't you? It's no more technically challenging than bending extrusions and fabricating / machining intersection pieces. Yes you have to make press dies, and there might be an hour's extra welding involved but the big advantage is the welds are all longitudinal and as far from the neutral axis as you can get, not laterally, across the highest load point cross section on the frame.

You don't have to cast the headstock either, probably better not to in fact, starting with a lump of 6" round 6061 would be better than the nearest casting equivalent from both structural and welding perspectives.

Now the swingarm I probably would stick with extrusions....

[WilDun]

.........frame Ocean put up. Bent sections can be accurately finished as cast. Fewer welds as the main pieces get bigger too. Even automated welds cost money.

Call me old fashioned, but cast frames would still worry me (cracking and shattering), however I do realize there have been big advances in casting technology and materials.

What interests me most is the type of casting technique employed, obviously it's not something someone with a home foundry could do (really defeats the purpose for homebuilt machines) - very interesting just the same!
Is it done by 'shell moulding' with resin sand or 'squeeze casting in metal dies' and what type of alloy is used? - probably needs to be ductile and also weldable (as well as castable!) - I guess it's heat treated after welding also ??
It all seems pretty expensive to me and would obviously have to be produced in large quantities with expensive specialized machinery to be viable!

I would be inclined to agree with the pressed shell idea too!

As always, I could be wrong.

[husaberg]

Call me old fashioned, but cast frames would still worry me (cracking and shattering), however I do realize there have been big advances in casting technology and materials.

What interests me most is the type of casting technique employed, obviously it's not something someone with a home foundry could do (really defeats the purpose for homebuilt machines) - very interesting just the same!
Is it done by 'shell moulding' with resin sand or 'squeeze casting in metal dies' and what type of alloy is used? - probably needs to be ductile and also weldable (as well as castable!) - I guess it's heat treated after welding also ??
It all seems pretty expensive to me and would obviously have to be produced in large quantities with expensive specialized machinery to be viable!

I would be inclined to agree with the pressed shell idea too!

As always, I could be wrong.

Greeves I beams downtube Sand cast.

Norton 750 Cosworth Challenge had a rather nice cast alloy swingarm with a real neat Chain and Sprocket set up disc was outside the chain so it was QD wheel and Sprocket

Honda did quite a few Castec frames VTR250 and NSR125
Likely investment casting or die and investment casting

I have a hollow section cast swingarm made by renthal for my Husaberg its about 1 kg lighter than my already light fabricated std swingarm

[F5 Dave]

The Japs banged on at the time (early 2000s) of development of a new high pressure/purity method which made this all more feasible

[Ocean1]

The Japs banged on at the time (early 2000s) of development of a new high pressure/purity method which made this all more feasible

New alloy? Or new moulding process?

There's more or less a continuous range of processes from cast to wrought to forged. But the big improvements in strength occur around the points where the material gets hot enough to form distinct crystals as it cools, (cast), the point where the crystals are stretched and elongated without getting hot enough to actually re-melt them (wrought) and then again when the material is less hot again, and more pressure is used to shape it, (forged). The extra strength comes from aligning the grain structure of those crystals with the shape of the product, and with some tweaks to the forging process even better aligned with the expected loads.

I'm really impressed with the fact that what I already instinctively knew as a kid, that hitting something really really hard makes it better turns out to be correct in the real world. Turns out I wasn't right about much else.

[Grumph]

Back to the half pressings....I have two FZR250 frames here (thanks again Neil) which are superb examples of just what has been said.
Curved pressings - about 3mm thick - seam welded. But not continuously, some areas are just spot welded. Considerable overlap too.
I'm unsure about the steering head, it could even be forged. Other bits are definitely diecast.
No internal ribbing in either frame or swingarm - obviously for a 250/4 they didn't consider it necessary.
Quite light, simple and probably much cheaper to make than the part extrusion, part pressed, part cast frames of the bigger FZR's

[Ocean1]

No internal ribbing in either frame or swingarm -

I've added serious rigidity to hollow sections before now by filling them with epoxy/microspheres.

Might add a couple of Kg to a typical bike frame. Can't supply actual numbers but I reduced the wall thickness of a structure dramatically using that system.

[Grumph]

I've added serious rigidity to hollow sections before now by filling them with epoxy/microspheres.

Might add a couple of Kg to a typical bike frame. Can't supply actual numbers but I reduced the wall thickness of a structure dramatically using that system.

Guy I know who builds drag car frames recommends foam filling frame tubes. He did quote me the figures for improved stiffness but it was a while ago...

I know at least one of his foamed frames has survived a brake failure at the end of the Ruapuna dragstrip. End over end and the pilot walked away.

[guyhockley]

Bimota, supposedly, had a frame that was internally pressurised to support the extremely thin wall tubing. I'm sceptical, I think it had a valve for pressure testing for cracks plus a bit of racers' bullshit.
Weirdly, my phone's spell checker changed Bimota to Nikita!

[guyhockley]

Back to the half pressings....I have two FZR250 frames here (thanks again Neil) which are superb examples of just what has been said.
Curved pressings - about 3mm thick - seam welded. But not continuously, some areas are just spot welded. Considerable overlap too.
I'm unsure about the steering head, it could even be forged. Other bits are definitely diecast.
No internal ribbing in either frame or swingarm - obviously for a 250/4 they didn't consider it necessary.
Quite light, simple and probably much cheaper to make than the part extrusion, part pressed, part cast frames of the bigger FZR's

The FZR250 frames sound similar to the ZX600 section I posted, then. Presumably ali but some early Yam Deltabox frames are aluminium looking but actually painted steel. Latest R1 I've peered at under the fairing looks to have a fully cast frame in 2 half sections bolted together.
Aprilia RS125 road bikes have had a swinging arm like that for years as well as fully cast frames. They also have a plate on them giving their torsional stiffness.

[Ocean1]

Guy I know who builds drag car frames recommends foam filling frame tubes. He did quote me the figures for improved stiffness but it was a while ago...

I know at least one of his foamed frames has survived a brake failure at the end of the Ruapuna dragstrip. End over end and the pilot walked away.

Walking away is always an excellent idea.

One of the products I developed that used epoxy/microspheres was a deep water float. Was good for 4000 meters, 6000psi in the old money, and I had someone trying to sell me some syntactic foam which is apparently the duck's nuts for stuff like that. They use it a lot in advanced naval applications, I don't think anyone else can afford it.

One of the problems with using any of the high compression strength stuff in a bike frame is you wouldn't get any second chances with it, throw it down the road once and you'd have no idea if the core had been compromised.

[guyhockley]

http://m.ebay.co.uk/itm/APRILIA-RS12....c100408.m2460

[Ocean1]

Bimota, supposedly, had a frame that was internally pressurised to support the extremely thin wall tubing. I'm sceptical, I think it had a valve for pressure testing for cracks plus a bit of racers' bullshit.
Weirdly, my phone's spell checker changed Bimota to Nikita!

Not uncommon for big crane booms. There's an old American Crane and Hoist beastie around NZ somewhere that had every tube in it's rig sealed and pressurised with argon, transducers from every one back to a PLC in the cab. Any pressure drop triggered an override which put the load down on a pre-designated clear zone.

Can't recall what the pressure was, pretty sure it wasn't enough to represent much by way of structural improvement.

[guyhockley]

Greeves I beams downtube Sand cast.

Looks like there is a story behind that particular frame.
Greeves are back in production, apparently:
http://www.greevesmotorcyclesltd.com/frame.html