Material Rigid Thickness

[PJ-27]

It's a bit of an odd question, and not one easily answered through web searches so thought I'd simply ask what were other peoples experiences.

I need a material for my BW that is as light as possible for it's size while maintaining rigidity. At the moment it uses 1mm HPDE (Light strong, NOT RIGID) and Grade 4 Ti (Light, incredibly strong, very bendy!).

So I'm looking for alternatives:

Would Polycarb be more ridig at a similar thickness? And what would the weight increase be?
What about Aluminium for the chassis, this would be less bendy than G4 Ti, but what thickness? And what would the weight increase be?

Also if people have Density stats for the materials (and the specific grades) that would be great. I don't know if there is a measurement for rigidity? And I'm assuming this in some way relates to overall size of the sheet.

Thanks,

ps. I don't think I could have gotten the word rigid into this post more times if I wanted to......

[Mouldy]

id suggest 1.5-2mm ali, bend it up at the edges to make a U section down the length... that way you will get the rigidity of thick material while keeping it light.

[maddox10]

Stiffness is more a question of shape than thickness.
For example, a tube is stiffer for the weight compared to a simular diameter rod.

Another example is corrugated sheet metal.

The ultimate weight/stiffness ratio record is held by Aerogel. But I guess this material ain't good for RW.

[PJ-27]

Neat idea, do you think it would work with the Ti?

[maddox10]

Bending Ti into a U , why not, but keep in mind Ti doesn't like sharp corners. (most metals don't)
Bend it over a piece of rod, 2 times the thickness of the sheet in radius.

[PJ-27]

The thickness is 1.9mm so the rod has a diameter of 3.8mm. 3.8 x Pi = 11.9mm of material to make the curve (assuming a full circle is formed). I'll have to check if I have that much available on either side of the chassis.
Any advice/resources on how to machine it?

[maddox10]

Machining Ti?
Anglegrinding gives nice sparks.
TIG welding is possible with an inverter (DC) and loads of argon.
Use enough coolant/cutting oil to keep the drill in reasonable shape. But a normal good quality steel drill will do fine.

[PJ-27]

Sorry, I mean to do the bend? A rod that thin I can see being impossibly difficult.

And yes you get amazing sparks! Dan spent quite some time in the workshop just grinding an offcut for laughs.....

[maddox10]

Any rod of nearby diameter will do. Twice material thickness is a minimal guideline.

Another option is to use a thick walled box section , that has a nice round corner too. Is also easier to put in the vice together with the Ti plate.

[gizz]

I'm not sure on the difference in bending between different grades of TI, but my 1mm grade 2 seems very stiff.
Thought the higher the grade the harder and stiffer it would get?