PARALLELS FOR MARKING UP OFFSETS & PASSOVERS

This has proved to be one of the most useful gadgets I've made so far.  I use it regularly when I'm out on plumbing jobs and want neat-looking offsets that will be seen by the customer.  When you're bending an offset or a passover in copper pipe, you need a pair of parallel lines a given distance apart to act as a marking guide.  Instead of having to mark lines on the benchtop, floor, or wall, just open up the parallels to the required distance and use them as the guide!

Parallels for marking up offsets in copper pipe, showing marking guide
The parallelogram action guarantees parallel lines, and the neat marking guide (also based on a parallelogram) grips the pipe and guides your felt-tip marker pen over the awkward curved surface making it easy to mark the oblique bending line just where you want it.
See the closeup below.
Copper pipe held in marking guide. Helps steady pipe and guide marker pen over curved surface

Of course, pro plumbers do all of this by eye, so they mightn't be interested in this device.  But it's great for beginners, and when you really do need an accurate offset in a tight spot.  It's also neat for people who — well — like gadgets!
Here's one way to bend an accurate offset
These instructions do NOT assume you are in possession of a set of parallels! (But the whole thing is quicker & easier with the gadget.)

1  Measure the size of the required offset — let's assume it's 100mm (4").

2  Draw a pair of parallel lines 100mm apart on a sheet of paper or handy bit of wood, or undecorated wall or floor (!).  One way to do this — if you don't have a set of navigating parallels or my gadget — is to mark 100mm on a sheet of paper, then fold it over to give you a parallel edge and crease.  (Alternatively, simply open up the gadget by this amount.)
Creating parallels by folding a sheet of paper

3  Pull the first bend in the pipe using a pipe bender (e.g. a Hilmor).  The bend angle is up to you and will depend on the offset size and how much room there is for the pipework.  About 45 degrees is usually OK.  It helps to open up a folding rule to the angle you want.  NOTE  If you must position this first bend at a definite location on the pipe, mark this spot on the pipe (use a pencil or black felt-tip), then position the mark in the bender as shown in the photo:
How to bend at a particular point on the pipe

4  Now determine which side of the bent pipe will be facing towards you when it is positioned in the pipe bender for the second bend.  This is the side you will mark in step 5, ready for the second bend, and of course the mark must be visible!.
Determining which side of the pipe you must mark for the second bend

5  Lay the bent pipe on the parallels you have drawn, with the correct side facing upwards (which you determined in step 4).  IMPORTANT  Position the inner edge of the pipe on the parallel, NOT the centre-line of the pipe!  This is to ensure that the second bend will end up in the correct position.
Laying the pipe on the parallels

6  Holding the pipe firmly in position, mark an oblique line where the pipe crosses the parallel, as accurately as you can.  Try to keep the mark as wobble-free as possible, fully across the pipe and in line with the parallel — a little dot will not do!  A felt-tip pen and a steady hand definitely help here.  (This is where the gadget's pen-guide makes life easier.)
Marking the pipe with an oblique line, aligned to the parallel

7  Fit the pipe into the bender, adjusting its position to get your mark at a tangent to the edge of the guide, that is 'kissing' the edge (see first photo below).  If your mark cannot actually touch the guide at a tangent, you must extend it in your mind's eye and shift the pipe so that the extension still 'kisses' the guide edge.  In any case the line must not 'cut into' the guide edge!  (See second photo below)
The oblique mark must be at a tangent to the curved edge of the guide

For marks that cannot 'kiss' the guide edge, an imaginary extension of the mark must be at a tangent to the guide edge. The oblique mark must NOT cut into the guide edge!

8  Next, sight along the pipe with one eye to check that the first bend is in the same plane as the second bend will be.  Rotate the pipe in the bender if necessary, to bring the whole length of pipe parallel with the bender's guides (unless of course you WANT a skew bend!)  Re-check that the mark is still at a tangent to the guide!
Rotate the pipe to get both bends in the same plane

9  When you're sure that the pipe is correctly positioned in the bender — do not rush this! — pull the second bend to the same angle as the first.  You can judge this by eye, or use a straight-edge or the folding rule (still at the correct angle) to help (see next photo).  Either way, remember that a bent pipe springs back slightly when you release the tension, so you may have to overbend a little to get the correct angle.  NOTE  If you find that you have overdone the second bend, you can reduce the angle a little as shown in the second photo following — but don't overdo this or the pipe will suddenly buckle!:
Pulling the second bend, using a folding rule to check the angle

Reducing an overdone bend!

Bending partial and full passovers
1  To make a partial passover, start as if you were doing an offset, but when you come to the second bend, pull it to twice the angle of the first bend.  So, if your first bend was 30 degrees, pull the second bend to 60 degrees.  You can use a protractor or judge it by eye.  Finally, cut off the tube after the second bend to the required length, to fit into the tee joint (etc.)

2  To make a full passover, start by making a partial passover as above.  Then lay the bent-up tube back onto the parallels with the inside of the second bend over the line (not the centreline) as usual.  Mark the position of the third bend with an oblique line as usual.  Finally pull the third bend to make the pipe line up with the first leg of the passover.  (You have to work fairly carefully to get the passover in the right position.)
... Hope this helps!
Back to 'Click a Gadget/Idea'