Ideas/source for rectangular tubing with rounded corner

apsilon · Post by **apsilon** » Wed Sep 28, 2011 10:42 pm

I have an idea that to execute properly (in my eyes) requires rectangular tubing with rounded corners. I'm after a few sizes but the most important needs to be about 0.6" on the long side.

Any ideas for how to make or a source to buy from? I'd prefer styrene but can work with pretty much anything.

kenlilly106 · Post by **kenlilly106** » Thu Sep 29, 2011 10:16 am

I know that Plastruct makes a lot of rectangular tubing but with sharp corners, I've also seen thin wall rectangular brass tubing but it has sharp corners as well.

I take it you're looking for something that looks like structural steel tubing?

Best idea I have is to sand off the corners of the Plastruct tubing, it has a fairly thick wall so you'll be able to get a rounded corner without sanding through the wall.

Ken

M3 · Post by M3 » Thu Sep 29, 2011 10:35 am

My local Dollar Store sells glow-stick type necklaces that have rounded-corner plastic rectangular tubing as a protective insert.

Kylwell · Post by **Kylwell** » Thu Sep 29, 2011 11:47 am

What radius are you looking @ for the rounded edge? Evergreen plastic's normal styrene box tubing is round edged. Only issue is most hobby tubing doesn't come in such sizes. USPlastic, as usual, has acrylic rod & tubing about that size, the extruded stuff has a small radius. After that I'd start looking @ places like SmallParts.com and OnlineMetals.com for extruded aluminum box tubing.

apsilon · Post by **apsilon** » Thu Sep 29, 2011 4:45 pm

Thanks all.

kenlilly106, yes something like structural steel tube.

Re radius I'm not sure but something that is obviously rounded for the size. I have a heap of Evergreen tubing around the size I want but it's all sharp edged. I did originally think of sanding it but I'm going to have a few pieces all next to each other with the ends visible so any inconsistency is going to annoy me.

M3, thanks. I know the sort of thing you're talking about so will check out a few brands.

smallparts.com does have what I'm after, just not small enough.

srspicer · Post by **srspicer** » Fri Sep 30, 2011 8:45 am

Hey apsilon,

I have been told, but never investigated for myself, that you can have extruded aluminum created to your specs. Its worht a shop.

Good luck.

Scott

kenlilly106 · Post by **kenlilly106** » Fri Sep 30, 2011 2:59 pm

srspicer wrote:Hey apsilon,
I have been told, but never investigated for myself, that you can have extruded aluminum created to your specs. Its worht a shop.

Minimum order quantities and tooling charges will kill you unless you order thousands of feet.

I checked around to see what it would cost and one place offers no minimum order (though 20ft is the shortest they'll make), tooling charges are $500-1500 though. There are places that offer tubing with rounded corners but it doesn't appear to be a stock item.

apsilon:

Got another idea if you don't need the tube shapes to be hollow. How about making your own out of MDF cut to size? You could take a small router bit and radius the edges so you'd get consistently smooth corners. A couple of coats of shellac and a couple of coats of lacquer primer and a quick sand and you won't be able to tell they're not plastic.

Ken

apsilon · Post by **apsilon** » Fri Sep 30, 2011 4:14 pm

Thanks Ken but they do need to be hollow.

I think I'm going to see if I can come up with a jig to hold the evergreen stuff so I can sand them down consistently. I also know someone who own a business that makes plastic packaging so I'm going to speak to him and see if he has any ideas as well.

Kylwell · Post by **Kylwell** » Fri Sep 30, 2011 4:32 pm

Make a radiusing tool. Some hard steel, filed to the curve you want with enough length on the arms to give you a consistent fit and just scrape the styrene down to fit.

Ziz · Post by **Ziz** » Fri Sep 30, 2011 6:55 pm

How big do these need to be? You could literally construct them from Evergreen strip and quarter round.

http://www.evergreenscalemodels.com/Str ... l%20Strips

http://www.evergreenscalemodels.com/Sha ... er%20Round

Lt. Z0mBe · Post by **Lt. Z0mBe** » Fri Sep 30, 2011 9:38 pm

Kylwell wrote:Make a radiusing tool. Some hard steel, filed to the curve you want with enough length on the arms to give you a consistent fit and just scrape the styrene down to fit.

+1

Kenny

apsilon · Post by **apsilon** » Sat Oct 01, 2011 12:15 am

Ziz, I can make the largest rectangular tubing from Evergreen work so about that size.

I was hoping for an easy solution but it looks like I'm making it. Thank you all for the suggestions.

Andrew Gorman · Post by **Andrew Gorman** » Sat Oct 01, 2011 11:41 am

I'd start with standard evergreen tubing and round off the corners with a tool like this one:
http://www.leevalley.com/en/wood/page.a ... 1182,41200

Take a close look- it's really pretty easy to make one out of an old hacksaw blade or some signode strapping. You'd probably have to build up the inside corner of the plastic with some smaller square stock.

Scotaidh · Post by **Scotaidh** » Sat Oct 01, 2011 5:49 pm

Have you tried US Plastic?

http://www.usplastic.com/catalog/item.a ... &catid=817

apsilon · Post by **apsilon** » Sat Oct 01, 2011 6:29 pm

Scotaidh, no I hadn't but they don't seem to have anything. The square tubing you linked is too big at 1.5" as I need around half that.

Andrew, I hadn't seen those before. Gives me another idea - create a wood form then heat and wrap sheet styrene around it. Hmmm.....

apsilon · Post by **apsilon** » Sat Oct 15, 2011 4:13 am

Andrew Gorman wrote:I'd start with standard evergreen tubing and round off the corners with a tool like this one:
http://www.leevalley.com/en/wood/page.a ... 1182,41200

For anyone interested, these tools do work well but I'm not able to get the radius that I'm after due to the thin walls of the Evergreen tubing (and placing pieces internally to thicken it will be seen as these will be seen end on).

When I get more time I'll use them to make a wood form and wrap it with heated styrene sheet. I'm fairly confident this will allow me to produce what I'm after.

Thanks again for all the suggestions.

seam-filler · Post by **seam-filler** » Sat Nov 12, 2011 2:00 pm

apsilon wrote:For anyone interested, these tools do work well but I'm not able to get the radius that I'm after due to the thin walls of the Evergreen tubing (and placing pieces internally to thicken it will be seen as these will be seen end on).

If you want thin sections at the ends, does it really matter what's between?

What I mean is, you could make thin-walled pieces for the ends, but the main length could more or less be solid - allowing you to use all sorts of tools to produce your radius corners.

apsilon · Post by **apsilon** » Sun Nov 13, 2011 9:12 pm

If I ever get a chance to build it, they're going to be lit from behind so need to be hollow all the way through.

ajmadison · Post by **ajmadison** » Mon Nov 14, 2011 11:13 am

Lt. Z0mBe wrote:
Kylwell wrote:Make a radiusing tool. Some hard steel, filed to the curve you want with enough length on the arms to give you a consistent fit and just scrape the styrene down to fit.
+1

Kenny

Actually, w/o trying to be a nay-sayer. I've gotten very good results with a similar device made out of regular sheet styrene or a 1/4 section of round tubing. With the sheet styrene version, yes, cut out a rectangle except with the desired round-over in the corner, which becomes a filet on your tool. You'll want to be slightly oversized, because I insert a segment of 320 grit sandpaper between the tool and the section you want to round over.

Another alternative is to cut some evergreen tubing with an inside diameter that matches your desired round over. Cut the tubing lengthwise to get a 1/4 of the round. Make it long enough so you can grab it with a thumb & two fingers, but not so long that it becomes unwieldly. I've found that I cannot cut tubing at the precise amount of "arc" or section I want. So I generally cut it oversize, then sand lengthwise to get a consistent section. But since you're making a tool rather than a model detail part, this is not that critical, but I mention it so you don't ruin more than one piece of tubing trying to make your round-over sander. Again, insert a piece of 320 grit between the section of tubing and the region you want to round over, and sand away.

ajmadison · Post by **ajmadison** » Mon Nov 14, 2011 11:19 am

seam-filler wrote:
apsilon wrote:For anyone interested, these tools do work well but I'm not able to get the radius that I'm after due to the thin walls of the Evergreen tubing (and placing pieces internally to thicken it will be seen as these will be seen end on).
If you want thin sections at the ends, does it really matter what's between?

What I mean is, you could make thin-walled pieces for the ends, but the main length could more or less be solid - allowing you to use all sorts of tools to produce your radius corners.

I have done exactly this kind of construction. Used 80 thou sheet for the main body of the spar, then built tiny four sided boxes to suggest the spar is hollow. Or in another case, I just made a flat piece stuck on the end, with the center cut out. I only make precise cuts on the center hole/rectangle. I let the edges of the end cap reach outside of the spar, and sand the excess down to the exterior edges of the spar, getting a nice precise shape that matches the beam profile. This works especially well when the spar/beam/rod cross section is a convoluted shape, and not some simple right rectangular quadrilateral.