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Flattening rolled sheet metal?

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pfarber

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Aircraft Spruce can roll .032 Al for shipping. I'll assume that there are no issues once you unroll it? Will it lay truly flat of will there always be a slight bow?

Thanks!
 

ScaleBirdsScott

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It will flatten mostly fine, but it does take a slight roll. It won't be enough to prevent working the material and using it in the structure or as a skin. But if you're trying to just have a dead flat, straight, and true sheet to lay on a table, you won't get that. Also, I've tended to get a bit of kink a few inches from one end which, hasn't affected any parts I've ended up making, but it has affected where I cut those parts from the sheet.

If you are just making ribs or smaller skin pieces I'd have no issue using the rolled sheets. If you're gonna make a big wing skin or something and are using basically the whole length, it's iffy. If you had one bad corner, would it kill your part, or are you cutting a big corner off anyway?

Of course I'd never want to pay the freight charge for just a few sheets so after we ran out of our main order of metal we went to rolled. If you'll use it, definitely try and see about ordering a bunch of sheets at once to spread that freight cost out.
 

pfarber

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It will flatten mostly fine, but it does take a slight roll. It won't be enough to prevent working the material and using it in the structure or as a skin. But if you're trying to just have a dead flat, straight, and true sheet to lay on a table, you won't get that. Also, I've tended to get a bit of kink a few inches from one end which, hasn't affected any parts I've ended up making, but it has affected where I cut those parts from the sheet.

If you are just making ribs or smaller skin pieces I'd have no issue using the rolled sheets. If you're gonna make a big wing skin or something and are using basically the whole length, it's iffy. If you had one bad corner, would it kill your part, or are you cutting a big corner off anyway?

Of course I'd never want to pay the freight charge for just a few sheets so after we ran out of our main order of metal we went to rolled. If you'll use it, definitely try and see about ordering a bunch of sheets at once to spread that freight cost out.
The sheet will have laser cut parts, so if will not lay flat under its own weight then its a no go. I found a local supplier, but they are kinda hard to deal with, so I wanted a backup. I'll ask the shop if they have a way to deal with a little bow.

Aircraft Spruce and Wickes are basically about the same cost, even with shipping (locally I have to pay tax). Evidently there is just not a lot of margin for commodities like aluminum. Every quote I have is within $10 of each other.. the kicker is shipping.
 

ScaleBirdsScott

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I cut the parts on my router table, but I to use screws and glue for hold-down. On a laser, yeah, probably not going to work. Does your source for laser cutting not have a way to get in the right material?
 

wktaylor

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IF the sheet metal has a bow here are a few tips for using it... especially 0.032 aluminum.

When working with bowed sheet metal always turn the natural-bow 'UP'... NOT DOWN. In this-way simple pressure in the middle of the sheet will tend to flatten it 'gently/mostly'. If the bow-is 'down' then edges always rise up and are a pain to deal with. Sometimes steel or lead weights, discretely placed in open spaces will provide a nice flattening effect. OH YEAH... round off all sheet corners to avoid 'sharp-corner effects' that unpredictably mess with everything.

The laser cut vendor should use a vacuum table and/or picture-frame around the [bow-up] raw material to secure it flat. IF NOT, then You need to consider a making a heavy picture frame.

During the laser-cut operation, leave a few short un-cut 'bridges' [0.25-0.38] along the part-outline [skip-cuts]... spanning between the part edge and the 'cut-off' [scrap edges]. This is poor-mans' fixturing. IF PRACTICAL, consider drilling holes intermittently around the outline for hold-down fasteners [screws/washers, clecos/washers, lock-pins/washers, etc]. Then, have the vendor make small cut-off-tabs around these fasteners . Likewise if the part has a wide-open area in the middle, or large lightening holes. When the part is finished, then simply finish-cut thru the 'bridges' and cut-off the tooling tabs.

NOTE. IF you intend to cut multiple tightly nested parts by laser then the previous suggestion, [skip-cuts and tabbing] will likely be a necessity.
 

PMD

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Vacuum table is ideal, but if your laser contractor doesn't have one...see above answers. The other is, of course, to simply run the sheet through a plate roll - but unless the rollers are in extremely good condition - or unless you have a protective "sacrificial" cover on both sides...either adhesive plastic from original supply or two sheets of utility aluminum - you risk putting scratches and dents into the new 2024 or 6061 sheet
 

dog

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Re rolling in the oposite direction,around a form
with a heavy canvas wrap and straps.
The size of the form would be dependent on how tight the metal was rolled.
I would ask the suppliers if they know any tricks.
 

ScaleBirdsScott

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Aircraft Spruce rolls their sheet for postage shipping a fair bit tighter than the sort of coils these sheets come off of. I think we're looking at a 8-10" diameter roll and stuffed in a regular old cardboard box? The roll left in the material isn't that serious by any rate, barely anything to be sure. But the creases I've seen from what I presume is the way they clamp it for the final roll into the box does affect things. I would be hesitant to trust AS supplied rolled sheets to a third party unless everyone was on the same page and knew how to deal with it. If cutting it yourself you can take note of any wrinkles or creases and try to arrange your sheet layout to avoid those areas.

Maybe a good laser operator would pay that attention and solve the problem, but maybe your design doesn't leave a lot of room for error, or its hard to judge over the phone when they explain the issue, or someone gets the cut paths and the sheet origin indexed backwards? That's the sort of stuff that bothers me. I don't want the vendor to think I'm a pain in the butt and slowing down their production, because I want them to keep cutting my crazy projects.

Not saying it would help here in the OP's case, I assume they've already been down this road or maybe it's the road they're on; but generally I've considered it easier to just work with the vendor to try and get proper material through their normal supply channels and see that it comes in on a truck like everything else. Then that specialty sheet is just a tiny percentage of their regular delivery costs and so shipping may not even be added. Maybe the per-sheet cost is higher than AS, but probably cheaper than a few sheets and a freight charge.

I've also had vendors get in a piece of material from their normal supply chain and had the protective films removed (if it ever had them) leaving an unholy mess of a surface finish when done. And the holes were in the wrong spots compared to the profile cuts. So there's that end of the spectrum as well. :grave:
 

pfarber

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Evidently the cost of AL is pretty much commodity priced as every quote has been within $10-20 of each other. The killer is shipping.

I found a supplier in Maryland that is close but they cut off the roll to length, so I assume even that will have a bit of bow, but nothing like rolled for UPS shipping. Sucks I can't find anyone closer, few places seem to stock the thin stuff. I can get .060 and better all day long.

I'll email the shop and ask if they have vacuum or clamps or how they will deal with a slight bow. My project will allow for spacing, but I need to maximize the cuts per sheet to keep the cost sane.
 

Geraldc

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The laser shops sometimes hold a slightly bowed sheet with scrap offcuts. Also good lasers have automatic height control.
 

PMD

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way back in my airboat building days, I got custom lengths of 0.080 and 0.040 5052 from rolls. The metal center would straighten them with a dedicated set of rolls on line between the uncoiler and the shear. I would simply take a flat deck trailer a few hundred miles over and pick them up myself, stacked. Makes for perfectly flat, undamaged material every time, but not practical for everyone.
 

proppastie

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pfarber

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Spruce now has an outlet in Harrisburg....they do not handle aluminum but maybe you could talk to them as to if you could pick it up there as a special?
Jim Irwin, president of Aero Performance and Aircraft Spruce presented Bill with an award celebrating his 50 years of outstanding service to thousands of pilots, aircraft owners, and aviation companies nationwide.
Oct 24th, 2019
Let us know how you make out I would like to be able to pick up stuff there.
If they don't handle Al then I won't bother. Aluminum is basically a commodity. No one is varying significantly on price. I have 10 quotes and all are right at $160 +/- $10 for 48x96. The kicker is how close they are/shipping.
 
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