Pipe Bender for Long, Smooth Curves

For a particular project, I needed to bend copper pipe into a smooth curve that was about ¾ of a complete circle. The best way to do that is probably with a 3-roller bender, but I don’t have one and getting a local fabricator to do the bend was going to cost way more than the job was worth to me. I tried filling the pipe with water, freezing it solid and then wrapping it around a cylinder of suitable size, and while that was just about possible with microbore (8mm / 5/16"), I’m not strong enough to bend ice-filled 15mm pipe – and in any case, I couldn’t fit the straight length I needed into my freezer.

My attempts at making a 3-roller bender from a vice were unsuccessful as I only have basic metalworking equipment and no welding kit - the Dexion I used bent under the load. (Dexion is slotted steel angle iron that is usually used to build racking, etc. It has bolt holes/slots spaced at regular intervals, which makes it good for this sort of job because it keeps the metalworking needed to an absolute minimum.) Instead, I came up with a single-roller solution where it didn’t matter if the Dexion flexed a bit. No metalworking is required (other than maybe drilling a few holes), but you will need access to a 3D printer to make the roller and a router table to make the former. This works for copper pipe but is unlikely to be strong enough to bend steel pipe unless it is very thin walled.

• A sheet of MDF big enough to cut a disc of the desired bend radius, and thicker than the pipe OD
• A router table and flush-cut bit
• A round nose router bit to match the pipe OD, or a 90° V-groove bit
• A bandsaw or hand saw
• Scrap wood
• A CAD system, eg Fusion 360
• Access to a 3D printer (or use a printing service)
• 3D printer filament - PLA will do, PETG might be better
• 2 lengths of Dexion type 140 slotted steel angle iron, or plain steel angle iron
• Dexion slotted angle corner plates, or similar steel corner plates
• Nuts, bolts and washers to suit the Dexion holes
• A drill with bits to suit the bolts and the pipe OD
• A vice or clamps
• Fine sand
• A small funnel (or make one from paper)
• 2 rubber bungs to suit the pipe ID, or wine corks
• Other basic workshop items: pencil, hammer, nail, string, duct tape

NB: OD = outside diameter, ID = inside diameter

Copper plumbing pipe in the UK has a wall thickness of about 0.6 – 0.9mm (depending on the diameter) and it will kink very readily if you try to bend it unsupported. Plumbers tend to make swept bends either by feeding a spring down the pipe to support the walls internally and then bending it by hand, or by using a manual pipe bender incorporating a former that supports the walls externally. Neither method is suitable for long, near circular curves – you’d never get a spring out, and the physical constraints of the design of former-type pipe benders mean they don’t go beyond a 180° bend.

I decided that the way to go was to make a (nearly) 360° former to support the pipe externally around the inside of the curve, with a profiled roller that could run around the outside and support the outer half of the pipe as it was bent. With the pipe fitting snugly between the former and the roller, rotating the roller around the former’s centre point forces the pipe into the groove around the edge, resulting in a smooth, circular bend. The image above, from my Fusion 360 design, shows the circular former, the roller (blue) held between twin rotating Dexion arms, and a block (secured to the former with a corner plate on each side) to hold the start of the pipe in place. To keep things simple I didn't bother modelling the bolts needed to hold everything together. In the image, the roller would have started in about the 2 o’clock position before rotating clockwise to the 12 o-clock position.

Inevitably, there was some springback when I tried out my new bending tool – the radius of the resulting curve was larger than the former. This is just as well, because otherwise it could be tricky getting it off the former. To get the precise radius of curve I wanted I had to repeat the bending process, making the former successively a little smaller each time, but that wasn’t a problem because once the router table was set up it was a quick job to reduce the diameter of the former and deepen the groove. It was also necessary to shorten the rotation arm to keep the roller (and pipe) pressed fairly tight against its edge, which was just a matter of moving the bolts along it.

Also, to be on the safe side, I filled the pipe first with sand packed in as tightly as possible and bunged the ends to stop it escaping. I don’t know if this was strictly necessary, but I didn’t think it would do any harm to support the pipe walls internally as well as externally.

The former needs to be cut from sheet material that’s thicker than the outside diameter (OD) of the pipe you want to bend. I used two layers of 12mm MDF for a 15mm OD pipe. MDF is probably a better choice than a less homogeneous material such as plywood or chipboard.

The first task is to cut a disc – or however much of a disc you need for your bend – of the radius you want to achieve. Aim for the radius of the mid-line of the pipe circle to start with. Draw the circumference using a pencil and a piece of string with loops at each end, one for the pencil and the other to go over a nail knocked into the centre point. Then cut the circle out close to the outside of the line with a bandsaw or a hand saw. If you have a circle-cutting attachment for your bandsaw, you should be able to get a perfect circle without needing to use the router, in which case go right down to the line. But if not, knock the central nail into something that you can clamp onto your router table and then rotate the edge of the MDF former past a flush-cut bit to bring it down to a smooth curve of the right diameter. (See the final photo in Step 7 for a photo of the set-up.)

Ideally, you will have a round nose (aka core box) router bit of the same diameter as the pipe’s OD. Such a bit will cut a slot with a hemispherical profile into which the pipe will fit perfectly. I don’t have a round nose bit and wasn’t prepared to buy one just for this job. Instead I used a V-groove bit with a 90° angle. This meant that the half of the pipe on the inside of the curve was only supported at two points on its circumference rather than a full semicircle, but it worked. I wouldn’t recommend dispensing with the sand filling though if you too use a V-groove bit.

Drill out the central hole in the former to a size that will take the bolts that suit your Dexion. (If you aren't going to use steel strips with pre-drilled holes then I suggest that around M8 / 8mm (5/16") is suitable, which is the size of the Dexion type 140.) Rig up an attachment for your router table fence to hold the MDF circle vertically - see 3rd photo. I didn't have a suitable bolt to hand at the time so I used the shaft end of a drill bit as the central pivot point. This allowed me to rotate the former's edge past the V-groove bit, taking successively deeper cuts until I could fit my copper pipe into the groove to very slightly less than half the pipe's depth.

To bend a pipe around the former we need to sweep a profiled roller around the circumference, with the pipe trapped between the former and the roller so that it has nowhere else to go. I've called this profiled roller a jockey roller, because it rides around the edge of the former. It will be held in place against the edge by a Dexion arm on either side that pivot about the centre of the fomer.

I had my doubts that a 3D printed roller would be strong enough for pipe bending, but then I came across MattTheMaker's 'Ible Using Fusion 360 to Make Custom Parametric 3D Printed Dies for Harbor Freight Tubing Roller to Bend Metal Tubes for a TallBike. He shows that it's possible to bend even steel tube with PLA dies, albeit his are sandwiched between steel plates. I thought bending copper tube using PLA rollers without the steel plates was worth a try, and it worked.

For 15mm (0.6") OD pipe I designed my roller with a 61 mm (2.4") diameter and 25 mm (1") thick, using Fusion 360 which is free for students, educators and non-commercial users. The diameter needs to be large enough to accommodate both the central hole and the edge profile that takes half the depth of the pipe, with enough material between the two to provide strength. And the roller needs to be about the same thickness as the MDF former - say 10mm (½") thicker than the pipe's OD or the edges will be too weak. (Any minor discrepancy in the thicknesses of the former and roller can be taken care of later by adding washers.) My central hole was 8.1mm (5/16") diameter so that I could use an M8 bolt as an axle.

I made the semicircular profile around the edge 16mm diameter, a little larger than the pipe OD, to ensure the roller wouldn't bind onto the pipe as it forced it into a curve. I also offset the centre of the profile about 1mm (1/32") - actually I used 1.05mm for some unknown reason - outside the circumference of the roller so that the pipe will fit into the profile to slightly less than half its depth, again to prevent it sticking. A dimensioned drawing is shown above.

Before designing your jockey roller ready to print, measure the pipe's OD in several places. Whatever size it is sold as will only be a nominal size. If in doubt, make the edge profile on the large side, because if it fits onto the pipe too tightly then rotating it around the edge of the former will be very hard work.

Given the sizing information above, designing the roller should be straightforward - you just need to:

1. create a cylinder by extruding a circle of the roller's diameter
2. draw a second, smaller circle for the profile in a plane orthogonal to the first circle, with its centre in the appropriate place as shown on the drawing
3. sweep the small circle around the axis of the cyclinder to cut the profile
4. add an axle hole down the middle (of whatever diameter the holes in your Dexion are)
5. apply small fillets to round all the edges and make them less likely to break
6. save the resulting body as an STL file or whatever your slicer needs.

But if you need more detailed advice, especially if you're a Fusion 360 user, you should find it in MattTheMaker's 'Ible linked above.

The most obvious way to print an object like this roller is lying flat, ie with the cylinder's axis vertical, so that it doesn't need any support. The force on the roller when it's in use will be radial and quite severe, so we need to think about the infill and be sure to use one that's strong in the X and Y directions.

Gyroid or honeycomb patterned infill is often recommended for prints that need to be strong in the X-Y plane, but in the end I saved an hour on the gyroid print time at a 40% infill level by using rectilinear infill at 40% instead. My jockey roller in PLA held together for the single pipe bend I used it for, plus a short trial bend. There's no significant damage but it does look a little the worse for wear - see photo. For a more durable roller I would up the infill percentage, maybe even to 100%, choose gyroid pattern and probably switch to a tougher filament such as PETG.

Slice your model in whatever slicer you use - I wouldn't try to get away with anything less than 40% infill - and print.

The next job is to create an arm - or rather a pair of arms - that will rotate about the centre of the former to sweep the jockey roller around its edge.

If you have a couple of Dexion strips that are the right sort of length - something like 1½ to 2 times the diameter of the former - all is well and good. If not, you'll need to find some angle iron that you can use and drill the necessary holes in it. Flat steel strip would do as long as it's thick enough to have the required strength, but it's easier to push against a flat surface when you come to do the pipe bending. (But as you can see from the photo, I had my Dexion the wrong way around.) Also, you'll be glad of a long lever arm, so don't cut the arms too short.

With an arm on each side of the former, bolt through the centre point, with washers against the MDF and under the nuts. The arms need to pivot quite close to their free ends, or else the part beyond the pivot point will get in the way when you come to hold the former in a vice or clamp it to a bench.

Now put a length of pipe in the former's groove and use it as a spacer to get the right position to bolt the jockey roller between the steel arms, again with washers. It's best to use a part-threaded bolt as the roller's axle, so that it can spin easily. With the pipe removed, check that the roller will both spin freely on its axle and rotate smoothly around the edge of the former - ideally there will be just a tiny gap between the two.

The pipe bending device needs some means of holding the end of the pipe stationary and tangentially against the edge of the former while the jockey wheel sweeps around its circumference. Otherwise the whole pipe will have a tendency to slide around the former and it won't bend.

As you can see from the photos above, I used a block that's bolted to the sides of the former with a wedge under it to anchor the pipe end. Both wedge and block are made from wood and have half-pipe profiles to grip the pipe tightly and hold it tangentially against the edge of the former.

To make these wooden pieces, drill a hole of the pipe's OD down through a piece of scrap wood that's about 75-100mm (3-4") thick. Then cut its width down to the same thickness as the MDF former. That done, saw through the wood along the centre line of the hole, so that you have two pieces of wood each with a semicircular groove down it.

Fit a length of pipe into one of these pieces - the block - and hold it against the edge of the former with the pipe fitting snugly into the former's groove. Rotate the jockey wheel up into position against it, as shown in the first photo of this step. This is best done with the lower ⅓ or so of the former held in a vice, or clamped upright, and the rotating arm sticking up vertically, as in the photo. The free end of the pipe will be sticking out horizontally. You need to fix the block to the former in this position, tight up against the roller. I used the triangular steel corner plates that are intended for use with the Dexion slotted angle product. Similar pre-drilled corner plates are quite easy to find in hardware stores.

Cut the second piece of wood at an angle to make a wedge that you can knock into position with a hammer to hold the end of the pipe firmly - see 2nd and 3rd photos.

Now we're ready for action. Dry the sand you intend to use, then seal one end of the pipe by driving a rubber bung in firmly if you happen to have one of the right size, or else cutting down a wine cork or even whittling a wooden bung. Wrap plenty of duct tape around it to make sure it stays put. Then pour in sand using a funnel. Keep tapping the pipe to make it settle until you can't get any more in. Bung the second end and add more duct tape.

Clamp the bottom of the former in a vice. Secure the end of the pipe against the edge of the former at about the 3 o'clock or 9 o'clock position (depending on which way you are going to rotate the jockey roller) by knocking in the wedge. If the pipe is long and unwieldy, get someone else to support the free end of it, but make sure they allow it to move as the bend progresses around the former. Then rotate the arm slowly to guide the roller around the former. It won't be a problem to stop part way around and reposition the former in the vice if necessary, but do keep the rotating arm in the same position (relative to the former) while you do that.

When you've gone as far as you can, or as far as you need to, stop and release the pipe by removing the wedge. It should spring back enough to lift off easily, even if it's more than half a circle. Measure its diameter and make adjustments to the former if needed, to reduce its size, and then re-cut the groove. You will also need to shorten the arms to keep the jockey roller fairly tight against the former.

Repeat until you have a curve of the diameter you need, then unbung the ends and shake all the sand out.