Tube Coping Calculator

- Universal Version

I've recently combined all of the versions of this script into this one, which has all the previous options rolled into it. Please update your bookmarks and links to:
http://www.metalgeek.com/static/cope.pcgi


**Standalone program update, see below.


Diameter 1
(cut tube)
Wall Thickness
(cut tube)
Diameter 2
Angle
Offset

Download pattern:

PDF
PNG
Postscript
HPGL
G Code
      pattern height: 3.14"

coping pattern

common sizes

Tube Gauge Decimal | Pipe-nom. Decimal Wall (sch 40)
10 .134 | 1/2 .840 .109
11 .120 | 3/4 1.050 .113
12 .109 | 1 1.315 .133
13 .095 | 1-1/4 1.660 .140
14 .083 | 1-1/2 1.900 .145
16 .065 | 2 2.375 .154
18 .049 | 2-1/2 2.85 .203
20 .035 | 3 3.500 .216

Recent Updates

This script now makes use of cookies (if you have them enabled) to store your most recent entries. This should save you some annoyance if you're using metric or if you happen close the window and then realize you just want to change the angle a couple of degrees. Let me know if this causes any trouble.

Description

This is a reconstruction and expansion of Eric Fahlgren's clever "miter" program written in 1994 to help in building bicycle frames.

The PDF version seems to scale better without regard for browser or OS weirdness. If you're cutting big pipes, you could still need to use one of the other images because the PDF might clip the path.

The PDF is converted from a simple postscript file with ImageMagick. The scale seems to be pretty good either printed or imported into something like Adobe Illustrator.

If you have kudos, complaints, or pictures of things you've made with this that you'd like to share, just let me know. If I get enough interesting pictures, I'll put up gallery (with credits, if you'd like).

Some Explanation

In case it's not entirely obvious, the point of this thing is to create a cutting pattern for a tube or a pipe to accurately fit it at an angle to another tube or pipe so that you can weld or braze it. This is a whole lot easier than eyeballing the cut and scribing it by hand, and if you do it right, both the grinding and welding are pretty easy. This process is also frequently called "tube notching" or "pipe notching". Apparently, this script/form/PHP widget has become popular with a number of hot-rod, off-road, and vehicle modding freaks engineers.

"Offset" is the distance between the two axes of the tubes. In other words, it moves one tube sideways in relation to the other tube. If you try to join two 1" diameter tubes and specify an offset of 1", then the coping pattern will be completely flat, because the tubes won't intersect. Not useful.

Specifying the tube's wall thickness makes the cut fit to the inside diameter of the tube, which makes it easier to fit, and makes a nice notch for welding. If you're trying to get a really snug fit, like for brazing a bicycle frame, you might want to try selecting a rather small number for the tube thickness. But if you get carried away with making it perfect, you'll spend a lot more time grinding it down.

Sometimes, I find I need to specify a wall thickness that's actually a tad smaller than it is in reality. I don't know if this is because of my sloppy grinder work, or my sloppy math. Some experimentation may be necessary to get it just right, depending on you own techniques.

For really big pipe, you might want to use a cutting torch, but most of the time I just use a chop saw to get it close and then an angle grinder to finish it up. And while I'm mentioning grinders, The Really Big Hardware Store That's Taking Over The World sells Rigid brand 4-1/2" angle grinders that are actually made by Metabo, but for a lot less than the Metabos usually go for. They last much longer than any other angle grinder I've tried. I've got three of them. And no, I'm not making anything from this tip. I've burned up at least a dozen (even a couple Metabos) over the years, and I thought it was worth mentioning.

Can you give me a standalone version of this so I can run it on my laptop out in the shed where there aren't any internets?

No. I'm not really a programmer and writing this whole thing from the ground up is just too much for this busy old geezer to take on right now. Web scripting simple. Actual programming hard. Just thinking about it makes me want to take a nap. And another nap.

If you're a real geek, you could always just set up a web server with PHP and ImageMagick on your own computer and just run it yourself. But if you were a real geek, you'd already have wi-fi in your shed, so you wouldn't care.

Update on the stand-alone program thing:

Dan Hopper has written a little DOS program that's slightly similar to the coping calculator. You can check it out here.



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