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DangerousThing
04-10-2014, 02:26 PM
Hi,

I'm building a large robot on a wheelchair base. This robot has a torso that is approximately a 24" cube of aluminum extrusions and will need panels on the outside that can be painted for a steampunk theme.

It needs to be something I can easily drill holes into and cut into for access panels and such. I will be using nylon and PLA for 3d printed decorations.

Foam board (Sintra) is a bit too weak. I'd hate to accidentally lean against Steam Automaton Grouch and accidentally poke a hole in his side.

I'm thinking that aluminum panels might be OK as they are barely within my abilities. ABS panels might be better.

Any help will be appreciated.

jwatte
04-10-2014, 03:05 PM
I would use 1/8" or 5mm plywood, or perhaps MDF.

DangerousThing
04-10-2014, 03:58 PM
I would use 1/8" or 5mm plywood, or perhaps MDF.

It has to be painted to look like metal. Can this be done with MDF?

BTW: Why doesn't anybody use HDF?

Thanks much!

ps. I think if you answer any more of my questions i have to put you in the forward to the book. :)

tician
04-10-2014, 04:47 PM
The density names are not terribly accurate in their descriptions of fiberboard. Hardboard and pegboard are both forms of HDF. I've got a few 2'x4' panels of 3/16"~1/4" hardboard still waiting to be turned into something. It was intended to be the structure of a 3D printer, but that was abandoned a couple years ago before any cutting started. Not sure how well it takes paint, but the surface finish is really nice and would easily resemble actual metal if using a suitable metallic paint.

jwatte
04-10-2014, 07:14 PM
MDF boards (of various density -- there's also "lightweight MDF" !) are made to be painted and finished in various kinds of finishes. Theatres and film use it extensively for props. I know there is gold, silver, and copper spray paint that can be used; if you want rusty steel, that should also be possible.
You can also use think sheet metal to avoid too much weight -- 28 gauge stainless steel, or 20 gauge aluminum, for example -- but those are not particularly easy to use for mounting things on, as they will bow/flex.

DangerousThing
04-11-2014, 02:48 AM
Thank you for the answers.

I have one more question for now: why not ABS sheets?

jwatte
04-11-2014, 10:50 AM
ABS is easy to drill, and it is at least as heavy as MDF, it flexes more in my experience, and it's frickin' expensive compared to MDF. It's also a lot harder to paint! I know of no water-based paints that stick to it long-term.
Another option is polycarbonate sheet, probably in 1/8" thickness. It will likely be stronger/tougher than ABS. It will be shiny. It will flex a fair bit. I use it for see-through side panels for my bot's control box, so I can peek at all the LEDs of the boards mounted in there...

baronaaron
04-11-2014, 11:05 AM
Might want to try corrugated plastic thinwall/panels. It's cheap, lightweight and durable. This stuff is used for interior walls, so it will hold up to punishment.

Not sure about painting, but it's just polypropylene so any paint made for plastics should work.

http://www.homedepot.com/p/Unbranded-18-in-x-24-in-4-mm-Thick-Plastic-White-Corrugated-Twinwall-Sheets-15-Pack-COR-2418-15/202038093

DangerousThing
04-16-2014, 11:36 AM
If it's made for interior walls it should be paintable. And it has the advantage of not needing to be sanded for hours. I'm still trying to figure out what exact look I'm going for: probably shining and polished for the most part.

tician
04-16-2014, 05:33 PM
Don't think I've ever seen polypropylene twinwall used for walls except maybe inside pet cages, sheds, and greenhouses. It has been used for pretty much every professionally-made yard sign in at least the last decade, so lots of paint/ink should be available for it.

Twinwall can bend a bit between the corrugations if it is not well secured along the edges perpendicular to the corrugations. It can be bent in a nice curve for a while, but there will be permanent deformation if the face (on the inside of the bend) between the corrugations buckles. Have 10 12"x12"x1/8" panels that were supposed to be cut, folded, and bonded (same process to make a USPS letter crate) to build a lightweight, inexpensive, and relatively stong biped chassis/exo-skeleton. Still have not gotten around to that yet...

baronaaron
04-17-2014, 07:02 AM
Don't think I've ever seen polypropylene twinwall used for walls except maybe inside pet cages, sheds, and greenhouses.

I worked in a office where all the interior walls and workspace divisions were aluminum studs covered with this stuff. Held up well to people leaning against and using it as pin board for notes. Looked pretty cool too.

DangerousThing
04-17-2014, 10:34 PM
Do you think that taking two squares and bonding them together with the corrugations at a right angle would work to make them stronger?

tician
04-18-2014, 12:44 AM
Do you think that taking two squares and bonding them together with the corrugations at a right angle would work to make them stronger?

Almost certainly. The difficulty is in successfully bonding polypropylene to itself. Polypropylene and Polyethylene are best bonded using heat and do not work really well with many adhesives. Even gorilla glue has warnings about its ineffectiveness with PP and PE.

jwatte
04-18-2014, 11:34 AM
Scotch-Weld DP-8010 can do it, but application is not kitchen table friendly...

tician
04-18-2014, 01:15 PM
3M also makes double-sided, and adhesive transfer, tapes with an acrylic adhesive (300LSE) that works well for bonding 'Low Surface Energy' materials like PP and PE plastics and powder-coat paint. Not sure you get the same coverage per cost as the epoxy and the bond is not as strong (cannot hang 240kg from it), but it often has a 2+ year shelf-life and is a bit easier and safer to use on multiple projects. 9274 appears to be among the best bonding with a ~115 Oz./In. peel adhesion at application and increasing a bit with time.