Clamping 0.2mm aluminum sheets together with screws - how many and what size screws?

[EIJPN]

I want to stack some parts on top of each other. These are 17 discs, 75mm in diameter, made from 0.2mm thick aluminum sheets.
The problem is that the sheets are not totally flat, and when stacked on top of each other there are small gaps between them that can be seen when looking at the stack of sheets from the side.
I need to make sure there are no gaps between the sheets, and each sheet sits flush against the sheets above and below. To solve this problem, I am thinking of having sheets made with holes in them that I can put screws through, and then tighten bolts on the screws to clamp the sheets together.
I want to minimize the number of screws I need to use, but I want to make sure there are no gaps between the stacked sheets.

I have included an image of the 75mm diameter part with some possible places for the holes and the screws. (Holes are numbered 1-25)
Can anyone suggest where it would be best to locate the screws, and how many might be needed? Should the holes be located somewhere else?
Note, the hole for the screws is 1.2mm diameter, and the head of the screw is 2mm - if this is too small, please comment.

 

[JohnRBaker]

Why use stacked sheets of thin material? Why not just fabricate a single, thick plate?

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[btrueblood]

Why 17 sheets, vs. one monolithic piece of aluminum at 17 x 0.2mm = 3.4mm thickness? Can you use an external fixture to clamp the sheet flat instead of multiple screws?

As far as how many and what pattern - dunno, the requirement of "no visible gap" is a bit too vague. Well made parts, perfectly flat, with polished surfaces, can be "wrung" together like Jo blocks (gage blocks) without any fasteners needed.

 

[SnTMan]

0.2 mm, about like foil. Lotsa luck

Regards

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[BrianE22]

Can you use backing plates? There will be distortion under every bolt head otherwise. Can you glue the pieces together?

 

[dik]

Adhesive would be my first choice as noted above. You can get electrically conductive adhesives, if you need them. First choice would be a thicker plate.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EdStainless]

My first thought also is adhesive. They could be fixtured and clamped while curing.
Second would be backing plates. These need to be stiffer than Al.
Could be steel, could be composite, but they need to be stiff.
And even with plates I would suggest starting with 1-8, 9, 11, 13, 15, 18, 20, 22, 24, 25

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dvd]

Watch out for burrs/flash/dross/slag/spatter/etc. from your cutting/blanking process. You may end up with the need for a secondary operation to cleanup the edges. If you are using a die to cut these, there will be die-roll on one surface and a burr on the opposite, which will result in a gap. Evaluation of edge lifting on circular plates would probably show that the clamping force is going to change the gap just as much as the hole locations, so, without getting caught up in an analysis loop, I would just start with what seems intuitively reasonable and experiment.

 

[GregLocock]

Perhaps if you told us what the purpose is we might make better suggestions.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[rb1957]

don't use the dozen screws you're planning to.

I 2nd Ed's idea of plates.

Seeing how thin these are, I'd probably use a disc of plastic in between the steel sheets (17 steel and 18 plastic).

Do you care how "rough" this looks ? Maybe use C-clamps to hold the stack together ? Something with a spring (like a cloths peg) would be "better", or maybe some other clamp (like with an over center locking lever) ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[zeusfaber]

Put the whole lot in a plastic bag and suck the air out?

Anodise all the sheets and connect alternate sheets to positive and negative poles of a high voltage supply?

Both would eliminate the gaps effectively though, without knowing the ultimate purpose, it's impossible to tell whether either would meet your needs.

A.

 

[dik]

I've used vacuum for clamping and it works great... My brother showed me how you can use White glue for laminating veneer by letting it dry on both surfaces and using a 'clothes' iron and ironing it on. Easier and not as tricky as using contact cement.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SnTMan]

They could be fixtured and clamped while curing.

^This: If you bond the leaves with any kind of liquid or paste adhesive they *will* move around under clamping pressure. They must be positively aligned or made ovesize and trimmed afterwards.

EDIT: aanndd the squeeze-out will need trimmed after curing. Repeating myself, lotsa luck

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[JohnRBaker]

All of these comments about adhesives and clamping and stuff, it's all a waste of time until the OP tells us WHY he can't use a plate fabricated from a single piece of material.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[SnTMan]

Absolutely

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[dik]

Maybe he doesn't have 1/8" material, and he's using tinfoil?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[GregLocock]

Since OP is maintaining radio silence, can anybody guess what this is supposed to do? it sort of could be a battery electrode, but the screws will corrode it, and spacers would be a good idea. Other that some sort of diaphragm or spring, but the mass laoding of the screws will do weird things to the dynamics.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[zeusfaber]

No suggestion of a load-bearing attachment to any other component. Bolting pattern that would make a circumferential seal (clamped between a pair of flanges difficult). Willingness to accept screws sticking out both sides, so unlikely to involve motion parallel to the surface. Screws also suggest there's no electrochemical element.

So my wild guess: A target for trapping small, high-energy particles. Multiple layers for post-trial disassembly to make it easier to gauge depth of penetration, with voids undesirable as they disrupt shock wave propagation.

A.

 

[3DDave]

In the case it's a target vacuum bagging would be ideal. The plastic would alter the energy very little and the uniform pressure and removal of air that might cushion the collision would be a dealt with.

 

[SnTMan]

OP proposed a screw smack in the middle of the "target". So, who knows?

The problem with sloppy work is that the supply FAR EXCEEDS the demand