Complex styrene sheet shapes.

[Chas B returns]

So it's quite easy to create something like a cube in styrene sheet. But, things get trickier if you were to make ( for example) a six sided shape because the edges of the styrene need to be angled in order to work and look neat. Is there an easy way to achieve the bevelled edges?

[Zubie]

This comment applies to "prisms", that is 3d shapes resulting from projecting a 2d shape along one axis such as cylinders or boxes.

Speaking from a paper modeler's POV, you would need to cut with an extremely sharp blade with a metal straight edge along the edge at a 60 deg angle, i.e. half the angular width of the internal angle. Admittedly that would be difficult, but not impossible.

Personally, (again from a paper modeler's POV), if I need to make something like that, I prefer to make the thing out of one solid piece of material and score (not cut) the edge and fold the material along the score which allows for a smooth matching edge. I would suspect that for styrene this would work if it's not too thick and if you warmed up the area to be folded first. This just leaves the last edge which you could bevel, or just tab glue and then do a fill and sand.*

Here are a couple of images I drew up for the paper modeler's forum (I think it was over at zealot) that explains typical paper modeling joins. I think these could apply to sheet styrene as well, acknowledging that these media are not identical

On the left you have matching continuous surfaces such as on a cylinder. You could overlap the edge (a). This will leave a visible edge which you could fill and sand to shape using plastic sheet. How noticeable this is will vary depending on the size of the shape and gauge of the sheet. A better method is using an internal tab (b,c), but note that the edges need to match perfectly to avoid gaps (c) which would be visible. In plastic sheet this is still fixable with some fill and sanding.

Corners (figures on right) present a slightly different problem. Depending on the gauge of the sheet, a hard right angle fold may not work, so an internal tab (d) might need to be made from thinner sheets or made up of layered or thicker pieces that allow for a bonding edge without a fold**. There would still be a problem with an exposed edge, and possibly a visible gap where the inner edge folds in and under the other one. An internal tab (e,f) can get rid of the gap, but you will still have 1 exposed edge: either a slight overlap (e) or 2 if there's no overlap (f). A worse case would be if you leave a gap because the edges are too far apart or overlap too far so you get an overhang (g). In any case, even internal tabs would need filling and sanding, just more so in case g. Hiding the edges would need a bevel cut - see below.

Because paper cardstock is fairly thin, this image details a variant on internal tabs and that involves some layering of the edge to be cut. This allows for a wider bonding edge. Given that cutting plastic stock is a harder than cardstock, I would probably approach this by marking the edge I want and then sanding the piece down using some kind of a pre-set template block to hold the edge at an appropriate angle.

Personally I think that outside of things that are furniture size, beveling is overkill but admittedly for some people looking for that perfect fit definitely an option. Plastic is so amenable for fill & sand, particularly if you are going to paint over the part anyway, going further than simply an internal tab seems unnecessary. Also, while a hexagon has a fairly easy angle to work out (60°) other shapes such as octagons or pentagons are not as neat (67.5 and 54 respectively). I think more importantly you would need a pre-made bulkhead or internal brace to maintain the angles on the part as it sets. Having the end pieces might not be enough as my own experience has been that the ends go in after you have made the main shape.

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*Because corner edges can be harder to hide, when I design a paper part that wraps around like a prism, I often purposely put the edge on a flat or continuous side that preferably is away from the point of view. This makes butt end joins as shown on the right of the first image possible. The best bet is put the edge where it won't be seen in the first place

** I recall that it isn't unusual for me to use the "number" tabs from trees to improve bonding edges

[Wug]

Chas B returns

You can make a tool to bevel edges of styrene sheet. In Gundam Scratchbuild Manual, the author epoxied a blade to the arm of a protractor. Just set the desired angle and scrape the edge.

Mike

[Zubie]

Chas B returns

You can make a tool to bevel edges of styrene sheet. In Gundam Scratchbuild Manual, the author epoxied a blade to the arm of a protractor. Just set the desired angle and scrape the edge.

Mike

I found this to be an intriguing idea. I presume you mean a compass? A protractor only gives you an angle, but doesn't actually set one. If you attach a blade to the arm of a compass you could presumably set it to a particular angle and then run it at a set angle down a straightedge over the material. I think you would need to use one of those higher quality ones that screw into the angle as opposed to the stamped school ones which would not hold their angle. It needs a bit of math to work out the angle setting you want, as the bevel angle should be 180 minus the open angle of the compass (θ) divided by 2. A protractor would help with that ...Interesting.

These are some caveats I can think of

• The math works out IFF the distance between the rotation joint of the compass arms and the ends of the blade and compass point are the same. the device still works if this isn't quite true, but you would need to adjust for the diff if you want to be absolutely accurate on this

• For the angle to remain true to the desired bevel angle, the compass needs to be kept perpendicular to the surface during the cut. Tilting the assembly will cause some deviation, albeit somewhat minor for small deviations.

• Setting the angle would require a protractor or some math. Might not be a bad idea if you do make one of these to do the work beforehand and have a set of preset markings on a ruler for the settings for various angles (square, triangle, hex, octagon, etc).

• There will be a limit to that maximum bevel angle, but I don't think that might be so bad as it only really applies very sharp corners. So for instance if you need that bevel for a sharp angle of 20deg, that would need a 10deg bevel. A 10deg bevel would need the compass opened to 160deg and that might be more than a typical drafting compass might handle

• There might be a slight angular deviation on the blade introduced by how it's attached to the blade. This is more easily visualized on those compasses that have an angled pencil attachment. These are often angled in somewhat which is fine for drawing, but if your blade is angled inward or outward, you would need to compensate for that.

The caveats are perhaps not major, but again, it seems easier just to get 90% there and fill in & sand the difference . It's definitely something that seems like an option though.

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*The first time I worked out the bevel angle for this thing I got it totally wrong. I'm surprised how much math I learned in middle school and high school I got to double check on the Internet So, yeah...check my math!

[Wug]

No I mean a protractor. Wikipedia calls it a half-circle bevel protractor. I called them carpenter's protractors.

https://upload.wikimedia.org/wikipedia/ ... C4%9Br.jpg

https://archive.org/details/Gundam_Scra ... 5/mode/2up

The Gundam Scratch Build Manual is an excellent resource for everyone.

Mike

[Zubie]

No I mean a protractor. Wikipedia calls it a half-circle bevel protractor. I called them carpenter's protractors.

https://upload.wikimedia.org/wikipedia/ ... C4%9Br.jpg

https://archive.org/details/Gundam_Scra ... 5/mode/2up

The Gundam Scratch Build Manual is an excellent resource for everyone.

Mike

I didn't even know such a thing existed (they also seem to go by the name "machinist protractor"). I can't find an available one that also cuts so it does seem quite practical to make one for one's self. You could correct me if I'm wrong, but it seems to basically work by scraping down to the bevel angle after a straight cut.

The only ready made thing I have seen are matte and foam bevel cutters (pull bevel cutters). These do not appear to be adjustable much beyond straight or 45deg. Cos-tools used to make a foam cutter that was adjustable to some pre-set angles (20,30,45,60,90) but I can'f find any reference to them on their web site anymore and pretty much everywhere is sold out. Of course, foam is not sheet styrene, so how well they would work there may be an open question.

[Wug]

Yep, you set the angle and scrape along the edge.

I think you can buy machinist protractors or carpenter protractors at hardware stores and maybe the hardware section of department stores.

The Gundam Scratch Build Manual author made his own edge scrapers. One of them looks like a regular protractor with a home made arm.

[Chas B returns]

Thanks to you all for your input and apologies from me for not getting back sooner.