RC: create a 3d stl file for a rounded corner tray. 75mm wide x 180mm long x 15mm high. corners are 25mm radius. side walls to be 2.5mm thick.  tray walls top edge rounded on both inner & outer edges. bottom is 2mm thick.

Gem:

Did you have to install openSCAD and paste the Gemeni code into it?

Yeah, that was all.  Exported the stl and it loaded in Tinkercad without any flags or problems.

Thanks. I created a model today with Gem and ported to openSCAD. Sent it out to a bunch of laser cutters for quotes. The instant quotes were mind-blowingly high. 39" by 23.5" aluminum sheet to be laser cut with a .375" hexagon pattern... $1,500 is the best so far. Yikes.

application?
thickness?

I'm thinking CAD-driven cnc shops ought to be available around your locale.  A water-jet would likely work, though I don't know if they're even more expensive.

Well that's awesome. I usually spend most of my time making small enclosures when designing.

I want to cut some aluminum sheet to add a walkable roof deck to my SUV's aftermarket roof rack.

The panel is 39 inches by 23.5 inches, material is .25 inch 6061 aluminum. Need four copies of this panel.

I fed Gemeni the use case, roof rack support specs. I asked it for a slotted holes design, then a round holes design, then a hexagon holes design to minimize weight while maximizing strength.

It said hexagons are the most efficient. I asked it to optimize the hexagon size and spacing for the use case.

Unfortunately, the first optimized design was a small, dense hexagon pattern with 2,800 holes. The fabricators said the laser will warp the panel with the tight spacing. Also the initial burn through for a new hole takes extra time, raising cost. I did get one quote back for $36,000, heh.

The below photo is an updated version with larger hexagons. Trying again today with the simplified design.

Update: Moving in the right direction, but sheesh. I need to find the Chinese equivalent of SendCutSend to make this viable.

FRP might work.  It's used for pier decking now.  A similar aluminum grid panel is used in farm equipment a lot --these may be cheaper since they're sorta commodity items.

1 1/2" Deep x 3/4" Mini Mesh Molded FRP Grating
https://www.americangrating.com/Products/1-Deep-x-34-Mini-Mesh-Molded-Grating__GPM-10.aspx

1 inch tall grid like that on the roof is going to create a ton of drag. I asked Gem about any kind of plastic/polymer sheet material it could think of. It said for the application, aluminum is the absolute best.

>drag

Could you fill the gaps with some lightweight foam? That should actually add some rigidity (like a SIP or a filled bollard), though not much

>hexagons are the most efficient

Endorsed by honey bees the world over. And then copied by engineers for application in military aircraft, skis and lunar landing modules.
https://en.wikipedia.org/wiki/Hexcel

there are 9 bars going left to right across the top of the truck. Gemeni says solid sheet of anything will create a sail effect with a lot of drag. It's odd to me that the quotes are so expensive. The manufacturer of the rack offers roof deck panels for different models.. similar laser cut panels they make in house, then powder coat, and sell the whole floor for $600. Not sure why my current quote for bare aluminum is $2400 for the same area. Gem seems to think my quote should be $800 for the 4 units. I'm going to try local laser shops.

Gem estimates:

"Your single honeycomb panel will take roughly 22 to 25 minutes of active machine time to complete on a modern fiber laser.

If a commercial job shop is billing their 6kW or 10kW laser out at $240 an hour ($4 per minute), the sheer machine time alone costs around $100, plus the $70 to $90 cost of the raw aluminum blank, plus setup time and overhead. This is why you should expect realistic, competitive commercial quotes for a single panel to land in the $200 to $250 range."

Send Cut Send is quoting $600.

Maybe. We have tested with and without a large Thule box and it didn't make that much difference.

I wanted to remove it but my wife wanted it to stay. So we drive a couple hundred miles with and without and couldn't see any difference. Contrast that with the small trailer which looks 25-30% off the mileage. As a cheap test, could you put a piece of 1/2" plywood on it and see if it significantly affects performance?

Also, Thule makes some deflectors. There must be a way to handle the drag. 

I wonder if Gem thinks you want to mount it broad side into the wind.

CR says 13% drop in fuel economy with fully loaded roof rack on a RAV4. Much bigger impact on sedan. Probably lower impact on a large SUV or van. Probably much higher on a Ferrari or Corvette.

https://www.consumerreports.org/fuel-economy-efficiency/how-rooftop-carriers-affect-fuel-economy/