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Motorsport Fabrication Fundamentals: Bending

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00:00 - An essential aspect of fabricating with tube is our ability to accurately bend the raw material.
00:05 This is obviously critical if you want to fabricate roll cages, however even on simpler tubular structures, the ability to bend tube will significantly expand the design options available to you.
00:17 There are a variety of tools available for bending tube but the most common is the manually operated horizontal tube bender like the Pro Tools 105 bender that we're going to be using.
00:28 If you're planning to bend a lot of tube, you may want to consider spending a little more money for a hydraulic version, however the actual process of bending the tube is very similar between the two models.
00:39 Before we get into bending tube, it's important with the manual bender to ensure that it's securely attached to the floor of your workshop.
00:47 You're going to be applying a lot of force while bending your tube and the mounting will need to withstand the forces involved.
00:53 Generally, dyna bolting the bend amount into a concrete floor in four locations with half inch dyna bolts is sufficient and this still allows the bender to be removed when not being used to free up space in the workshop.
01:06 When selecting a suitable location for the bender, it's also important to have sufficient clear space around it, particularly when we consider a long piece of tube like the front lateral legs of a roll cage, we're going to need enough space on both sides of the bender to clear the length of tube before and after it's bent.
01:24 If you're using a hydraulic bender, then we have a little bit more flexibility in the way it's mounted since we aren't manually applying force to the bender in order to bend the tube.
01:34 Instead, this is achieved with a hydraulic ram.
01:38 The mounting of a hydraulic bender still needs to be stable enough so that the bender isn't likely to fall over when a long length of tube is loaded into it.
01:46 However it's common to mount this type of bender on caster wheels so that it can easily be moved around the workshop or stored out of the way when it isn't needed.
01:56 For our demonstration here, we'll be making a 45° bend on a piece of 1.5 inch mild steel roll cage tube.
02:04 We want to start by marking the centreline of the tube so that we can be sure that the alignment of our bend is exactly right.
02:11 This isn't too relevant when we're adding a single bend to a straight length of tube, however as soon as we have other features such as a notch or another bend, the alignment between these features becomes critical and the centreline gives us an easy reference.
02:26 To mark the centreline, we've simply clamp the tube to our workbench and used an adjustable square and a sharpie marker to draw the centreline.
02:34 By running the adjustable square along the underside of our steel benchtop it provides an easy way of drawing a straight reference line that's guaranteed to be parallel to the centre of the tube.
02:45 Next we want to mark where we want the bend to start.
02:47 This isn't too important for our test bend but of course for more complex tubes with multiple bends, this becomes critical if you want the completed bend to fit correctly.
02:57 For these more complex bends, it's a good idea to add some marks or notes onto your tube with your sharpie so that you can be sure which side of your mark you want the bend to be on.
03:08 Before we load the tube into our bender, you may want to apply a lubricant to the follower die.
03:14 This isn't strictly essential however a light coat of grease on the die can help reduce the chance of scratching or galling on your tube and improve the surface finish.
03:24 The quality of the finished bend will depend on the specific bender that you're using and the quality of the dies so it's worth performing a few test bends with and without a lubricant to see what works best for you.
03:37 You'll also see that the follower die is marked with top on one side and it's important to make sure that this faces up before it's installed into the bender.
03:47 With our tube marked, we can load it into the bender by feeding it through the U strap that attaches to the die.
03:53 The U strap supports the straight section of tube before the been and the actual bend will start at the point where the tube contacts the die so we want to carefully align the mark on our tube with the start of the die.
04:06 Before we tighten the clamp, we can align our centre mark for correct orientation.
04:11 In our example, we've made a horizontal reference mark on the follower die and we can align the centreline with this.
04:18 You can see that there are multiple holes in the bender frame for the pin that locates the follower die and these allow for various bend radius dies.
04:26 In the correct location, the follower die will almost contact the former die, snugly supporting our tube.
04:32 You won't be able to form a bend with the follower in the wrong location so this is essentially impossible to get wrong.
04:38 Once we're happy with the alignment, we can tighten the bolt to clamp the tube into the bender which will support the tube and prevent it moving or backing out as our bend progresses.
04:49 This needs to be done firmly, however we don't want to over tighten it or we may mark or begin crushing our tube.
04:55 This needs to be done up firmly, however we don't want to overtighten it or we can mark the tube.
05:00 Now we want to engage the ratchet with the drive link on the bender and apply just enough force to take the slack out of the bender so that we can adjust our reference pointer and set this to zero degrees for the start of our bend.
05:14 We can now begin our bend which is an iterative process of applying force to the handle to turn the ratchet until we reach full extension.
05:21 From here we can return the handle to the starting point, locate the drive pin in the next tooth of the ratchet and repeat the process until we reach our desired bend angle.
05:30 If we worked our way out to the last tooth on the ratchet and we still haven't reached our desired bend angle, then we can remove the pin from the die and align it with the next hole and carry on.
05:41 We do need to understand that the tube will be under tension during the bending process and therefore will have a certain amount of spring back when that tension is released and this will affect the bend angle.
05:52 The amount of spring back will depend on the material type, diameter and wall thickness, as well as the bend radius.
05:59 With some benders, it's enough to remove the tension on the handle and watch to see how far the pointer moves in order to measure the spring back.
06:07 However in some benders, the tube tends to stick in the die slightly and this can affect the accuracy of the spring back measurement using this technique.
06:15 A more foolproof method of measuring spring back is to perform a test bend on some scrap tube and then compare the bend angle displayed by the pointer to the actual angle using a digital angle gauge.
06:27 In our case, we found the spring back to be 1.3° which means that to achieve our desired bend of 45°, we actually need to slightly over bend the tube to a displayed angle of 46.3°.
06:41 Remember here that we're bending mild steel tube and stronger material like chromoly will produce more spring back.
06:48 Once the bend is complete, we can rotate the bender back to our starting position, loosen the locking bolt and remove the U strap before extracting the tube from the bender.
06:58 As mentioned, the tube can tend to stick a little in the dies in some benders and this may require a little force to be applied to free it.
07:05 If you can't free it by hand then a light tap with a plastic mallet should be sufficient.
07:09 We can visually see that the dies have retained the cross sectional area of the tube through the centre of the bend with very little distortion.
07:19 This is important for safety structures like roll cages as your motorsport governing body will stipulate the maximum amount of crush that is permissible through a bend, and this can be confirmed with vernier callipers.

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