Thump the welded end of the tube onto the floor as you pour to help settle and compact the sand.The ram rod can also be used to help compact the sand.Start pouring the dried sand into the tube through the large nut.Carefully weld the other end of the tube to the open end of the squash pipe.Flatten one end of the tube with a hammer or in the vice, and weld the flattened end to seal it.To form your first bend, cut a length of exhaust tube slightly longer than the proposed finished tube.If all is well, finish welding the nut to the pipe. Screw the bolt into the nut and check that it can enter the pipe without fouling it. Make a few tack welds to hold the nut onto the pipe.Place the nut face down on a flat surface and carefully centre the piece of pipe on top of it.Using a set square, make sure the ends of the length of DN32 squash pipe are perfectly square.The only other itemsrequired are a 1¼” UNC nut and bolt, and a length of 32mm (1¼”) wooden dowel or curtain pole to use as a ram rod. You’ll need a piece approximately 250mm (10″) long. 125″ NB pipe) which is the standardblack pipe available at every steel yard. Most motorbike headers you’ll come across will be 38.1mm (1½”) OD so the best size of pipe to use for the squash pipe is DN 32 x 3.2mm wall CHS (1¼” x. Tightening the bolt further compacts the sand inside the tube to be bent. It sounds highly technical and complicated, but consists of nothing more than a large nut welded over the open end of the pipe into which a bolt is inserted. The squash pipe incorporates a mechanical tamping device for ensuring the sand is soundlypacked into the tube to be bent. Being thick-walled, the squash pipe can be held tightly in a vice while you work on the attached thin-wall exhaust tube. The squash pipe is a very simple tubular device, which is stouter than the thin-wall exhaust tube you’ll be using, and must be securely welded to the tube you wish to bend.
The best sand to use is a coarse sand such as washed builder’s sand, but it must be thoroughly dried overnight on a shallow tray placed in a low oven.īefore any bending begins, you’ll need to make a “squash pipe”. Therefore, t he sand used for stuffing into the tube must be bone dry to avoid the production of steam and consequently, internal pressure. Any latent pressure within the sealed tube could rupture the tube wall, particularly if it were red hot, and shower hot or molten metal about the place. There are a number of safety issues concerned with applying pressure to (hot) plasticised metal that must be observed. The sand prevents the tube from collapsing, and in most instances, retains the concentricity of the tube throughout the bend. The process basically involves stuffing sand tightly into a tube, sealing both ends, and then applying heat to the tube until it becomes pliable. We have covered the making of sectional exhaust systems in Make Your Own Exhaust System , but this article offers an alternative method of forming tubes for the more adventurous, or for those who prefer the looks of single-piece “pipes”. It is invaluablewhere the exhaust tube must twist and turn in configurations not possible with moderately priced tube benders. However,exhaust tube is often very thin walled – 1.2mm-1.6mm (.0469″-.062″), and virtually impossible to bend cleanly without the use of very expensive mandrel bending equipment, and sand-bending is a perfectly suited technique for forming un-stressed exhaust systems. Sand bending is not a practicable method of bending chassis tubes, as the constant heating and re-heating of the tube during the process would almost certainly lead to failure of the tube if used in a stressed situation such as a chassis.
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