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I'm trying to create a segmented/lobster back bend out of some straight sections of 200mm diameter acrylic pipe, like so:

Segmented Bend

As you can see the bend is made from two types of parts: Part 1, which is a section of straight pipe with one end cut at an angle, and Part 2, where both ends are cut at an angle. Some drawings of the two parts are shown below:

Part 1 drawing:

Part 1 drawing

Part 2 drawing:

Part 2 drawing

I'm trying to figure out how I can go about making these pipe sections. The problem boils down to two questions:

  1. What's the best tool to cut reasonably precise angles (say, nearest 0.5-1 degree) for such a large pipe diameter (200mm)?
  2. Cutting Part 2 might be more tricky because I need to make sure that the pipe doesn't rotate around its longitudinal axis when I come to cut the second angle. Otherwise, when I put the bend sections together, the pipe will start to form a sort of spiral. How can I go about cutting those sections?
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    I'm curious what you're making :) – Matthew Mar 27 '15 at 0:11
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    RE part 2: I tape a piece of scrap lumber to the pipe before making the first cut, then lay the pipe down so the wood stablizes it on the cutting surface. Tightly taped, the pipe can't rotate with respect to the wood; so second cut will always be in same plane as the first. – Wayfaring Stranger Mar 27 '15 at 2:41
  • @Matthew I'm building a test rig for this guy: Gough-Stewart Based Internal Pipe Inspection and …: youtu.be/CcVgF740vGk – Amr Bekhit Mar 27 '15 at 17:46
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I think the answer in both cases is a handsaw in a mitrebox. For 200mm pipe, that's probably going to be a home-made mitrebox with 250mm tall sides and 200-202 mm between the sides.

enter image description here

The simplest solution to the second problem for relatively short segments is to make the box long enough to cut both angles without moving the pipe, and clamp it in place - perhaps with wedges, or perhaps a strap clamp or hose clamp attached to the bottom of the box.

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Mitre-box is definitely the way to go - but I'll offer another alternative that I use with a power mitre saw when I need to match angles on irregular stock. Set a stop block with the other angle, and then just rotate the pipe until the cut angle is flush with the stop:

enter image description here

  • Yup, that would work too. – Ecnerwal Mar 27 '15 at 1:23

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