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I need to join different sized pipes together at a 45 degree angle, but am struggling when it comes to what methods are available.

The main pipe is 75mm radius, the smaller is ~40mm. I've opted to 3D print the smaller pipe, so I don't need to worry about messing with that at all.

Exploded view (side profile) Required hole (front profile)

As you can see it's an awkward shape due to the curvature of the main pipe, plus I'm worried about warping the cut by putting excess weight on it. The only method I've come up with so far is using a pair of hand nibblers, but I'm not sure how well they'd work on a curved surface.

Any ideas / suggestions? (I need to do a few of these joins, and the cost of pvc saddles a bit silly).

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  • 2
    If it's plumbing, spend the money for fittings, this won't pass code/inspection.
    – Ecnerwal
    May 24 at 13:27
  • For any liquids, sewerage etc., you're better off using the proper fittings. Leakproofing can be a nightmare.
    – Tim
    May 24 at 13:57
  • It's a small aeroponic system, I'll save the real plumbing for professionals!
    – Caia
    May 24 at 13:59

2 Answers 2

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The appropriate way would be to:

  • Make a jig out of wood that will hold the pipe to be drilled
    • The jig could be flat or have the desired 45° angle built into it.
    • Building it flat allows it to be used for drilling holes into pipe at any desired angle in the future, making it more useful
  • Clamp the jig to the table of a drill press.
    • Either have the drill press table level (for a jig with the angle built in) or tilt it to 45° (for a "flat" jig).
  • Drill the hole with an appropriately sized bit.
    • I would use a hole saw from a set with a replaceable pilot bit.
    • Replace the supplied bit with a long one that will reach the pipe before the edge of the cutter will reach it.
    • Use the long pilot bit to ensure that the center of the hole is where you want it to be.

A hole-saw set like this:

hole saw set in plastic case
image courtesy of lowes.com. No endorsement intended or implied

Has a pilot bit that can be replaced. Simply purchase a longer bit that will fit so that the pilot bit hits the pipe before the larger cutter hits, like this crude drawing:

crude drawing of hole saw hitting pipe
image courtesy of lowes.com. No endorsement intended or implied. Edited by me.

Where the red line indicates the pipe and the blue line indicates the longer drill bit.

This is the kind of drill press (or "pillar/post drill" as it's called in some countries) I'm referring to. This model has a 10" (254mm) capacity between the the chuck and the lowest position of the table:

Drill press on floor
Image courtesy of HarborFreight.com customer review. Note that this shows it sitting on the floor, not yet installed on a bench top. Click to embiggen.

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  • Thanks for the visualization, now I know what I should be aiming for. (Not asking for Specific products) Do you have a recommendation for the drill press? I can see plenty of "manual" ones that I could stick my handheld drill in, but none of them look large enough for the 150mm diameter pipe. Am I missing something obvious or am I looking at the wrong thing?
    – Caia
    May 24 at 14:00
  • I have a bench-top drill press in my garage/shop - it is a stationary tool (I believe the British and others around the world call it a "post drill" or "pillar drill"). There are jigs that are designed to hold a hand-held drill to allow you to drill more precisely, though I would agree with you that finding one with a large enough capacity to hold your pipe may be difficult. (con't...)
    – FreeMan
    May 24 at 14:13
  • ... If this is something that you're going to be doing a lot of, an investment in the proper tooling may be worthwhile. If not, talk with friends/neighbors to see if someone has one, or look for a local Maker Space/shared workshop to see if you can rent time/space for an afternoon for your one-time project.
    – FreeMan
    May 24 at 14:13
  • @Caia something that just occurred to me: You might want to pre-drill a small dimple into the pipe at a 90° angle, or possibly use a file to make a little scratch in the pipe before drilling. This will give the pilot bit something to bite into instead of allowing it to slide slightly "downhill" (to the right in my mock-up, above) as it attempts to bite into the plastic. It depends on how precise you need the location of the hole to be.
    – FreeMan
    May 25 at 13:50
  • This will work, but needs a steady, strong hand as one side of the holesaw will start before the other, causing it to jump - a lot. Very, very slowly is the way to go.
    – Tim
    May 25 at 13:58
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A jig to hold a holesaw and the pipe to be drilled is one method.

Start with a block of wood (or whatever material, it doesn't matter much if it's solid-enough.)

You drill a hole for the pipe, you drill the hole for the hole-saw to run in at the correct angle to the hole for the pipe, you fasten the pipe in place so it cannot slide or rotate, and run the hole-saw into the hole-saw hole to cut the hole in the pipe.

The smaller pipe can be easily done (a lot faster than 3D printing one) by making a similar jig, but with a sanding drum the same size as the larger pipe, that you feed the smaller pipe against until it's fully "fish-mouthed" to shape. That can also be done freehand with some practice, or with a less robust jig/guide, if you use care.

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  • I spent more time finding pictures. :)
    – FreeMan
    May 24 at 13:39

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