aluminum baseplate made from recycled aluminum. Usable?

[Nii]

A small local business recycles aluminum cans into aluminum sheets and blocks. I contacted them and the price is pretty good. For smaller projectors, will a molded aluminum 50x40 1cm thick sheet be usable as a baseplate, or does molding produce less dense aluminum pieces unlike the way aluminum sheets are mass-produced and it won't be usable for such application because of less density?

And yes, they surface grind the rough sheets and blocks.

[NobleGas]

Do they just compress the scrap into sheets or do they melt it and cast it?

[Nii]

They melt it. I didn't even know compressing metal pieces was an option to get one solid metal object.

[NobleGas]

Well it's not, but a lot of recyclers bale the material to go to the foundries.
If it's made purely from cans then the grade should be reasonably well controlled; cast aluminium is likely to have some defects / porosity so won't be as homogenous as bar or sheet from the foundry and it will likely need machining to give a flat surface.

[Nii]

I see. Well they use a surface grinder to finish the blocks and sheets. I could get it surface grinded somewhere else but their job looks good to me.



I'm more concerned about something else. Is there a chance that aluminum pieces produced commercially via extrusion or injection molding are denser than cast pieces and therefore the latter is more prone to warping/misalignment caused by heat to be usable as an optical base, or is that not how physics works?

[mixedgas]

Place 25.4 mm by 25.4 mm / one inch solid aluminum bar stringers along two edges with a countersunk retaining screw every 2 inches / 5 cm and it will be nearly as stiff as a stock Newport optical table. Run one reinforcing stringer down the center. You can then use t-Slot tubing to hold the sides and lid.


That is how made mine in the past... For 20 some years..

1 cm is thick enough for most baseplates..

Steve

[NobleGas]

Looking at that piece, I'd be happy to use it!

[planters]

If they bother to surface grind it then it will be flatter than almost all commercial cast or extruded aluminum plate that is not ground. These sources can be pretty bad. The surface grind I am talking about is not a human with a belt sander, but an actual table based, automatic surface grinder. This is the actual name for this type of machine, not a description of what a person does with a hand tool.

Porous or not, I would not be concerned about warp-age other than mechanical stiffness and here thickness is everything. Stiffness is to the third power of thickness. That is why Steve's approach is so good because it increases the effective thickness where the bar is located. If that 25mm bar is attached to a 12mm plate the stiffness will increase 27x where the bar is located.

[Nii]

Great info. Thank you.