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"Experimenting with Styrene and MDF" Topic

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CorSecEng20 Jan 2013 7:57 p.m. PST

MDF buildings are cool but they are always so boxy. I want something sexy :)

I've been experimenting with curved walls using styrene and MDF.

This is crude but if I add a top railing or roof then it will be easier to make the walls straight.



Also if anyone has an resources on the maths involved with creating complex shapes from flat objects then let me know. First try at this wall was a disaster. I had the walls tapered in a few degrees and it wouldn't go around the corners without bunching up. I need to work out how to adjust the shape to go around that corner.

Jonathan Bowen
CorSec Engineering

Static Tyrant21 Jan 2013 2:19 a.m. PST

Looks like you might have more luck duplicating the interior uprights on the outside… So the pairs of uprights 'sandwich' the plasticard and really force it to conform to the shape you want it to take. An etched groove ("trench") on the base board (and on the underside of any "roof" piece) would also help.

I don't know that there is any maths which would really help… at the end of the day, you're stretching the outer edge of the styrene curve, so we're talking about things like the elasticity of the material. If you notice the plastic changing colour at points of high stress (typically, high tension) then you're dealing with a non-homogenous material that doesn't have uniform properties throughout. The maths gets so stupidly hard at that point, that days of trial and error will still probably be easier!

I assume you have a handle on basic geometry so you can figure out how much material is needed to go around particular curve radii, etc.

floating white bear21 Jan 2013 4:13 a.m. PST

Would you not be better off with two wooden formers, the exact curved corner shape, top and bottom, supported by the uprights and then wrap the plastic around it? The plastic needs to be thin enough to take the bend, but it will generally need to be supported to retain the shape. Also depending on the thiokness of the sheet (no matter what the sheet is made of) you will have to determine the spacing of the stiffeners and decide how large an area can be left un supported. Give it some time as well, since what looks supported today can get droopy later. Regards Rob.

Darby E21 Jan 2013 5:57 a.m. PST

Or, you can heat the plas with a heatgun or hair dryer and use a pipe with the diameter you want as the form. Wooden jig as FwB said is probably your best bet.

CraigH21 Jan 2013 6:58 a.m. PST

Measure the inner radius and draw that on paper (to start) and then measure the outer radius and "centre" that with reference to the inner radius the height of the building away. Now extend that out the length of the building (on one side) and width on the other then repeat with the radii again. Keep going until you get all four sides and corners. It's not going to be a straight line but going off at an angle after each curve – more of a shallow V shape.

The thing is, you're going to need a large sheet of styrene as you're going to end up with something angled like a pentagon (but obviously only four sides) so you might be better off making the corners separate and then attaching the sides, filling the gap with putty or covering it with a column.

I think this would work – feel free to PM me if you want to try but I'm not clear.

CorSecEng21 Jan 2013 6:59 a.m. PST

I tossed the upright supports and went a different route. I do have some uprights but they support an upper rail. So the styrene will wrap around the top and bottom rail. This should hold the shape very well and prevent warping. I also cut the center out of the top rail. Adding another roof piece completes the building and makes it removable.

I finished the design last night but the building didn't fit in one mdf sheet so I'm going to rework it before I cut the prototype.

As for the maths, I somehow ended up spending 5 years in college and getting an electrical engineering degree without taking geometry… Not even in high school. Of course I can google the basics but sketchup lets me read the total element length and that gives me the outside area needed. I've experimented with adding some arcs to sheet. Those seem to help a bit but I hate shooting in the dark like that. It wastes a lot of time/material.

BTW before I get ripped into for my lack of math training :) I did take all the advanced courses like calculus and differential equations. Just not geometry :)

Personal logo MrHarold Sponsoring Member of TMP21 Jan 2013 7:44 a.m. PST

Have you tried a grove in the base that will hold the styrene in?

John Treadaway21 Jan 2013 7:47 a.m. PST

What Mr Harold said. How about a top and a bottom (a base and a cap) in MDF with a groove in it that sandwiches the textured styrene between them?

John T

CorSecEng21 Jan 2013 8:10 a.m. PST

I did some experimenting with that. The issue is the styrene is thicker then even 2 passes with the laser. So I'd have to do several passes at a higher power to make a groove deep enough for the styrene to sit in. This of course weakens the overall structure. I only have 3mm to play with. If I cut 1mm deep then it might snap off at some point. Drop it and the enter thing falls apart.

The railing idea takes more material but it also secures the styrene and makes assembly a lot easier. I have to make a frame anyway. The styrene can't hold the building weight. So I have to build in internal frame work to support it.

@craigH Your kinda onto something but I need to look into some stuff. I found a document describing the math involved with cones. I need to expand the two cones (upper and lower radius) and combine them to create the piece that wraps around. I did a test and it seems to work. However I need to figure out how to make sketchup draw the arc correctly. I'll probably have to do some external calculations. I have to determine the distance between the points and draw the arc between them.

It looks like the height of the buildings will be determined by the radius of the sloped corners. I'll have to derive a formula that will let me pick one or the other.

CorSecEng21 Jan 2013 9:20 a.m. PST

Well I got a working building. It needs a lot of adjusting and I cut it stupid. (forgot to focus the laser for the mdf) It is WAY to tall. 50mm looks huge in 15mm. I think I'll shrink it to 30mm or so.

Assembly was a pain and I need to put some more braces in. Every joint will need a brace. I'm also way off in the back. I'll need to add some extra for those longer runs or stick with shorter ones.

The walls are straight and its fairly sturdy. I've also got to extend the styrene a bit to create a lip for the top to fit into.

Some pics





artbraune21 Jan 2013 11:06 a.m. PST

You are playing with LASERS man. That more than makes up for any lack of math training or geometry…

CorSecEng21 Jan 2013 11:26 a.m. PST

haha yes but I have to justify those 5 years spend getting an engineering degree somehow :)

TheBeast Supporting Member of TMP21 Jan 2013 12:03 p.m. PST

I may have missed that part of the discussion, but why don't you router the curve into the MDF? Finiky, I know, but I'm pretty sure some have done it.

Also, a series of shallow cuts upright on the inside of the material should allow it to bend to your will.

Note, my typing is very slow because all opposable digits, so no actual craft experience should be assumed.


CorSecEng21 Jan 2013 12:15 p.m. PST

@Doug that was mentioned earlier. The issue is the laser would have to make 3 or 4 passes to make a groove wide enough. This method is really easy to glue together. Just ignore the gallon of super glue covering my fingers :)

Curving the styrene isn't the big issue. These are just flat panels that I glued on starting in a corner and worked my way around. The bigger issue is a slanted and curved wall. The straight walls are easy but I'm trying to stretch the idea as far as I can. I want to see how many complex shapes I can make and keep designing buildings along the way. I also need to skin as much of the building as possible. This will allow for more (and better) details to be etched into the design.

I'm going to work on interior stuff as well. I'm going to cram as much design time into the next week or so as I can. Orders are piling up but I had a delay some stock for the omni-stand bases so I can't fill them. I need a production assistant…

Samulus22 Jan 2013 2:01 p.m. PST

This looks really good – looking forward to seeing the finished saleable product. i agree with you that most scif-fi offerings are too boxy, to me, the future is curvy!

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