Tube Bending — What You Need to Know

Transcript

- Hi and welcome to today's webinar where we focus on the process of bending tube. Tube is an integral material in motorsport fabrication and we see it used extensively in all aspects of two and four wheel motorsports. They all make use of its great strength to weight benefits. Tube in its raw form is sold in straight lengths and to bend it there are a number of things that we need to consider. During this webinar we will cover tube materials, tube measurements, bending tools such as the benders and their associated dies, die CLR and its effect on your project along with many tips and tricks including producing a bend template that will allow you to fast and accurately measure some of the more difficult operations in motorsport fabrication.

In my experience, having a tube bender is one of the biggest assets of my fabrication workshop and with a few well chosen die sets, this tool will greatly expand the range of fabrication jobs that you're able to complete but before we do that, let's look at the tube materials that we'll be most commonly bending. So the tube that we most commonly bend is obviously those that are used in motorsport. Now I have a range of bits and pieces here, it's a little known fact that most tube benders actually allow the use of square tube bending so you can get dies for square tube but most of the time we're working with round tube because of its uniformity and its ease of bending. So let's start with probably the most basic material and this is mild steel. This itself is actually ERW mild steel so this has a seam and it starts as a flat rolled material that's then rolled, electric resistance welded which is where the ERW comes in and it's good for many operations, it's not ideal for roll cages because it's usually a bit of a second rate material that doesn't have the necessary strengths that we need in roll cage scenarios.

A material that does is CDS or CDW. Now CDS is a mild steel and that stands for cold drawn seamless. So because it doesn't have a seam it actually starts life as a solid billet bar and then it's drawn through a mandrill to then create a perfect inside and outside diameter and a really controlled grain structure that actually fits most of the rules that we have in motorsports for the use of tube bending and roll cages. CDW is cold drawn welded so it actually does have a seam and then that's actually drawn over a mandrill as well which actually smooths out this seam and creates the strength properties that we need for our roll cage setups. Here I've got some chromoly, now this needs no introduction into motorsports, chromoly is a really strong material.

It will give you bender a workout because of its strength. It's sometimes twice as difficult to bend and it'll go through about 30% more cutting tools just because of the strength of the material. These benders are designed to use chromoly and it is a great material to work with. Just be mindful that obviously it's a lot stronger and you're going to need to do a little bit of analysis if you're looking to do some roll cage stuff and this does differ between different countries so make sure that you read your guidelines before jumping in and using chromoly for your roll cage because the extra expense may actually not be worth it in the end if you can't get it approved. So different sizes and materials, this is actually one inch chromoly and we also have Docol which is a really common material.

Not here in Australia but especially in America. It also has the strength of chromoly but it does not have some of the weaker properties that, or the problems that it has once it's heated that chromoly does so that's a new material. And then, basically that's the range of diameters and tubes that we're working with. Now that we understand the types of tube that we may use for our project, we need to look at how to measure them and ensure that they are fit for the bending process. The first thing that we need to understand is that tube is unlike pipe.

Pipe is manufactured for the process of moving liquids or gasses and therefore it's measured on its inside diameter. Pipe measurements can get really confusing. For example NB pipe refers to the nominal bore or nominal dimension of the internal diameter and so when the wall thickness or schedule as it can be called, changes, the outside diameter also changes. So tube is much easier to understand as we have our outside diameter, commonly called OD and the inside diameter known as ID. Minus the ID from the OD and divide that number in two to form our wall thickness.

So let's go ahead and measure this to see what tube and wall thickness we are working with here. So let's start with this CDS mild steel. So to measure this outside diameter and inside diameter, I like to use a vernier caliper. This is a 200 mm version and it's digital so we can turn it on and it'll give us a read out to 0.01 of a millimetre. So like I said before, to measure the actual wall thickness we need to measure the outside diameter which in this case is 38 mm or 1.5 inch and then the inside diameter which in this case is 32.9 and then minus those two dimensions and divide that by 2 and you should come up with 2.6 mm.

Obviously an easier way is just to jam the vernier caliper right on the wall thickness there and it will measure it and tell you what it is but it's always a good idea and especially when you're purchasing tube, just to double check all of these dimensions because your tube may actually not fit within the ruling so actually in Australia, this is the perfect tube that we need to use for motorsport roll cages as 2.5 mm is the minimum wall thickness that we're allowed. So that's how to measure tube and wall thickness will have a bit of a factor on how you can bend your tube. So tube benders, so with our tube measured we can now look at the bending process. Manual tube benders are available in two different configurations, the vertical type which will support 120° die and the horizontal type that will support a 240° die. Both designs work extremely well and the correct choice will depend on what you're wanting to do and how much space you have in your workshop.

I built my tube bender over 10 years ago and I've really put it to use over the years with great results. So this here is my vertical bender and I use this vertical bender and find that it is much easier and better suited to small garages or workshops. This is because the vertical bender's force acts within the frame by using a die set that utilises an offset hole position that only requires an inexpensive bottle jack to be placed inside the frame. The vertical bender uses 120° dies, this means that one piece 180° bends can't be made from your vertical bender. It will top out at just over 90° which in most motorsport applications will be ample.

I'll send out the plans and DXF files to create your own upright bender in a follow up email. Moving onto the second style of manual tube bender is the horizontal bender. The manual horizontal bender needs to be mounted securely to the floor but it does have a few redeeming features over the vertical bender's design. As I mentioned, the horizontal bender allows the use of 240° dies and this means that one piece 180° bends can be made from your horizontal bender. Here at etsfab we have designed our own horizontal bender and we will add these plans and DXF files into that follow up email to make sure that you have the ability to make either bender.

The great thing about this is that we have slotted the pin position for the drive arm and I'll show you this in a video soon, this means all dies should fit in this style of bender, allowing you to save some money along the way. Now the downside to the horizontal bender when used manually is the force it needs to bend the tube. This comes about because of the pulling action on the die and this either comes from sheer force from us pulling this around on a ratchet style arm or the pressure applied via a hydraulic ram. All of this force gets put through the base plate and requires a fixing arm to the floor or a bench that you're working on. As you can see here, I've set up our horizontal bender to use a hydraulic ram and I'll just grab this little video for you.

This is one that I've put together this morning and I will grab a little video. Firstly let's just have a look at the horizontal, sorry the vertical bender. So I've just put together a few clips here that you might be interested in. So this was over 10 years ago when I first built my horizontal bender. This actually started tube bending for me obviously.

This is an upright tube bender and as I said, all of the force is located inside the frame. So this allowed me to bend my main hoop for the Hilux project and also the front legs. Along with a whole bunch of other bits and pieces as you'll see. So it was, I'll just try and move this out of the way shall we. As you can see on this project, there's a whole bunch of tube in this and a whole bunch of bends and this upright bender that you see beside me was the process of doing all of this.

We'll just pause it here and we'll speak a little bit about smaller tube. If I rewind you'll see this, this is a plumber's bender and that tube is actually, I think that's 0.5 inch diameter so 12.5 mm and a plumber's bender makes short work of any small diameter tube. So when we usually talk about tube bending we think about the thicker stuff but there's also a lot of smaller diameter tube that we work with in motorsport and it can be really handy to have one of these benders. They're nothing special, they're not expensive and you can find these at your local hardware store or search under plumber's bender, just make sure that you match the outside diameter that you're using with that style of bender. And it should work a treat.

Obviously we're not stretching the material as much as we would with the larger diameters so it's not really necessary to have big expensive benders for smaller style of tube. And when you're working with smaller styles of tube like this, half in and 5/8th, you can really get creative and do a lot of bits and pieces that require multiple fixing points, this is the front end off the Hilux and as you can see, there's multiple bends on this, all done with that plumber's bender using that tube that I spoke about. This is all ERW. So then back to the chassis, there's bends all over this. It was a big project but one that the bender really had no problem doing.

Like I said before, those smaller components, when you're using bent tube, can actually turn out really really nice and it's not difficult to do and if you have one of those plumber's benders, then you're able to do that. This was a few bends that I used for the lower cradle setup that holds all the suspension arms on the Hilux. As you can see, it has a number of bends in its construction as well and this is all mild steel, CDS tube. So when it comes to motorcycles, a tube bender is also necessary. Obviously when you're working on chassis and subframe loops and stuff like that, they come in really really handy and as you can see here I used it extensively on the BMW project.

It's always a good idea to make sure your tube's nice and clean before you whack it in the bender, just so that you're not introducing contaminants into the followers. Here we go, this is what I was working on this morning, so these are just some recent photos and videos. This is our horizontal bender that we've just set up. I'll turn the sound off on that. So as I said before, the upright bender allows us to bend 90° bends with our 120° dies and this bender will allow me to do 180° bends with our 240° die.

So we've developed this with a pin position here that you can, let's just try and get this out of the way. So this pin position that you can see here is actually adjustable. So this is different to a lot of benders that you'll see on the market that use their own proprietary dies. This will actually allow you to use many different dies from many different markets and many different places around the world. I've actually set this up with a hydraulic ram and it's an air over hydraulic setup that was quite inexpensive and quite easy to hook up.

So all of this was laser cut, we'll supply you with all of those DXF files and this is for the purpose of the roll cage for the S15 project. But it took some setting up and I'll run you through the process of how this actually works. So obviously depressing the pedal on the hydraulic, the air over hydraulic setup, you can see that's starting to take up, this is sped up two times so it's quite a slow process but it gets there in the end. So as you can see, the stroke on the ram obviously is quite a lot so you'll have to really look into what stroke you need. I think this one was 20 inches or thereabouts but this is why our dies have a number of holes on them as you can see in this video.

Once the ram is out of stroke, you can then back it off, it will react and come back to the next hole position. Just puling the pin out will allow that to happen and then by putting the pin back in and allowing the ram to come back in, you´ll be able to then go another probably 45° or maybe even, that´s probably a little less, around 30°, whack the pin back in. Depress the pedal again and off you go. So I reckon the upright bender is a little bit of a faster process but obviously if you´re looking to bend 180° bends then the horizontal bender will probably be the one that you´ll need. So this tube here was just a bit of a test and it´s only 1.6 mm thick so this hydraulic setup was not even stressed out.

It can bend probably up to 4 mm wall thickness or even over depending on the diameter. But I think you kind of get the idea behind this. So if I fastforward it a little more you´ll see as we go further around, we index that into the next hole and obviously then bend that amount of distance and you should achieve the bend that you´re looking for. So that´s a bit of an overview on the upright and the hydraulic actuation of bends. The hydraulic actuation can add a fair amount of cost into the bender setup but it does make sense if you´re looking to have a portable setup that´s ready to go and wheel into action to get to work.

I´m using a single acting self returning ram with 10,000 psi hydraulic foot operated unit. And to give you an idea, 44.45 mm or 1.75 inch diameter tube with a 3 mm wall thickness will take about 3000 psi of pressure to bend with this setup. This ram was $700 AUD and the hydraulic unit that drivers it was just over $150 so it is a big investment but one that I feel will be worth it due to the amount of bends I see in my future. Alright let´s now focus on the dies and followers that mount inside our benders. A die is made up of 2 halves, a die and a die follower.

Both of these will have a half circle machined into their face and when they come together, will support the diameter of the tube and maintain this diameter throughout the bending process. This should not be confused with mandrill bending which refers to an internal mandrill maintaining the inside diameter of the tube. Conventional dies still do a great job of maintaining uniformity of the tube´s diameter throughout the bend. For each different outside diameter of tube we need to bend, we need that specific die set. Each die set will come with a main die, a follower a bar pin and clamp.

So I´ve lined up a few on the bench here just to give you a bit of an overview on the different benders and followers. As you can see here, this is a smaller 3/4 setup. So this is a follower that is actually produced by Speedwerx here in Australia and this is for use in an upright bender. So the mating die that fits with this is here, this is made out of steel and the follower´s made out of aluminium and the reason that they do this is to cradle the steel or whatever material you´re bending without scratching it and then obviously all of the force is pushed through the die which as you can see here, does all of the work. So this is actually machined in a way that it tightly pinches the actual outside of the tube and then gives the tube some freedom to grow on the inside.

This maintains a nice uniformity to the roundness of the tube and all of these dies are actually specially produced to be able to do this. So these are motorsport specific dies that should be available from your local motorsport fabrication outlet. So that was a 3/4 die, moving on up to a one inch. Obviously the follower´s a lot larger and then the die that corresponds with that, again is larger and you might be able to see that machined finish on the inside there as well. So again this is a 90° or 120° die that is suited to an upright bender which will give us a 90° bend.

Made out of hardened steel for a long life. Now then when we talk about our, so actually the acting force that you can see here, the centre hole here is obviously offset from the centre and this is to act on the bender as it´s getting pushed up by the bottle jack. The over centre force actually sweeps the tube around and I´ll show you that in a minute with our setup here. And that´s how the upright bender works. This is different to, these are heavy, this is different to our 240° dies that fit in our horizontal bender.

Again it´s machined with that perfect profile as you can see there and the pin holes for each different index for the over centre travel of the hydraulic ram. So you´ll see the pivoting is from the middle here and that´s because we´re basically sweeping the tube around with force rather than relying on the acting force of the over centre. So the followers look very different on a horizontal bender than they do an upright bender. So this is a follower for a horizontal bender. Basically it has two half round machined contours here and these do actually create quite a lot of scratching on the material.

I´ll show you how to get rid of that in a second. But this fits into the die, into the bender frame and then is adjusted by this little bolt here to bring up any slack between the actual die and the follower. So to get rid of any scratching they actually produce some plastic or I think it´s a special material, I can´t remember what it is now but it´s actually a special plastic that won´t deform the tube and won´t scratch it on its way through. So these are available if you´re bending aluminium or smaller wall thicknesses. I don´t know how they would handle the thicker ones but it´s probably worth a shot if you´re looking to do really clean work so those are the dies and followers that we most commonly use with our upright and vertical benders.

Now understanding CLR, once you have selected the tube that you need to bend, you´ll have figured out the diameter of the die set that you need to purchase but there is another dimension that we must consider before purchasing our die set and it´s known as CLR. CLR stands for centreline radius and this affects how tight the resulting bend will be. Most die manufacturers will offer a range of different centreline radius dies for the given diameter of the tube. A lot of people who purchase tube benders will be planning on building a roll cage and this will define the centreline radius that you need to satisfy your sanctioning body´s rules regarding roll cage structure regulations. We´ll get into this in more detail in our upcoming specific roll cage construction course.

But the best way of understanding a CLR is picturing a complete circle. By multiplying the CLR by 2, we find the circle diameter and for example a 12 inch circle will have a CLR of 6 inches, a 14 inch circle will have a CLR of 7 inches. This radius runs through the centreline of the tube so a larger CLR will suit a larger project such as a roll cage and a tighter CLR will suit tighter bends such as those found on motorcycle frames. So we have a few different CLRs here for our little 3/4 die and it´s always stamped onto the die. We have a 3.5 inch centreline radius so if we were to bend a loop for a motorcycle frame, then it would be 7 inches wide in total and that´s from the centreline of the tube.

This is different to if we were producing a roll cage using a large 1.75 die like this one. Now this has a 7 inch centreline radius so that actually will give us a 14 inch circle from the centreline of the tube. So usually when we´re purchasing these dies, they will give you a recommendation on the different wall thicknesses that can be complimented by a particular centreline radius. If you take a really small wall thickness such as 1.6 mm and you try and bend it on a tight centreline radius then it may crinkle and be a bit of a drama. Here you´d usually take these to a mandrill bender and get them done or if you´re using thicker tube then you can get away with a tighter CLR, being centreline radius.

So this kind of brings me to the bend template. So this CLR can be better understood when we look at the bend and more specifically a bend template. So here we´ve got a bend template and what this is, is that when you´re bending tube, I always recommend that you produce a bend template. So here we´ve got what I´ve done for our roll cage course which is a bend template and how you do this is by taking a piece of tube roughly around 600 mm in length of your chosen diameter and of your chosen material that you´re going to use for your roll cage and to produce a template you want to use the bender that you´re going to use for the project. So what I like to do is measure around 120 mm in from the end and then put a nice groove in the tube, as you can see here.

So we want this to be ever lasting on this piece of tube so the groove needs to be quite deep and recognisable. If you do it with a pen then it may wear off over time and we want to keep this bend template around for as long as we can. So then we want to create a 90° bend. So we put this in our bender and then set it up so that our bend starts at the start of our line and then we start pumping or pushing our bender to create a 90° bend. Or our bend template.

What this will tell us is the actual centreline radius that our die will create and it´ll also tell us the spring back. So spring back is something important that we work with in bending. Obviously the stronger the tube the more spring back you´re going to get. So spring back is the tension that the tube has and as we put it through the bend forces, it´s always resisting and when we let off the bending force, either through the bottle jack or the pressure on the horizontal bender then our tube´s going to spring back a slight amount and we always need to equate for this amount. So what I like to do with the bend radius is use this, with the bend template, is to use this as a measurement for that spring back.

Then we can equate that into all of the bends that we need to make from that point on. So here I´ve actually stamped into this the centreline radius which is 6 inches. And then the spring back which is 3°. So this is measured on this piece of tube which then is my bend template. So this will tell me where my bend can start and finish and this is really handy when we´re working with something like a main hoop in a roll cage.

It´ll give us an opportunity to sit this up against say the roof and the B pillar and understand the distance between the middle of the roof to the start of the first bend. We can then take that tube that we´ve done one bend on, swing this around and then measure from the outside of this bend to the outside of the bend we´ve just completed and this template will tell us, and take into account any of the miscalculations that we´ve actually completed in our bending. Because all tube is different and all dies are different and all setups are different, it´s important to complete one of these bend templates and obviously that´s 1.75 diameter and I´ve also done one in 1.5 inch diameter for roll cage purposes. And this tells me everything I need to know. So with 3° springback, I know that if I´ve got to bend a piece of tube with a 56° bend, then I´ve got to go 3° over so I take it to 59° and then back it back and it should spring back to the 56° that I measured and that is how a bend template can help you out in that process.

Before we go too far, I want to whack some tube into this bender and we´ll run it through its path and I´ll show you how it all works. So I think before we go too far, we need to talk about measuring these bends. So this is a tool that I like to use quite regularly. This is a digital angle finder and obviously you open it up to the angle that you require, I think you saw in the video before working on the BMW chassis. You open it up and find the angle that you need to ascertain for your project and then record that onto the tube.

By using our bend template, we can understand where this needs to start and then we need to mark that on our tube so that when we put it into the bender, we can actually know the exact point where this tube needs to start and it´s also important that you should mark on the tube that there´s a section that goes into the die and there´s a section that hangs out of the die. Sometimes it´s hard once you get out of the car and into the bender, which section this will go and if you get it wrong then obviously you can pretty much say goodbye to that bit of tube because it´s going to be bend in the wrong position. So I´ve got my piece of tube in here so how we do this is the saddle clamp uses this little saddle and a pin and that drops into the die. This is 1.5 inch with a pretty small wall thickness of only 1.6 mm. So we have a retaining screw here, I´ll just run this through a little bit deeper so that I can put my, there we go.

So we put the saddle on, run the pin through, secure the tube. We can tighten this up then. You don´t want to tighten this so far that it crushes the tube, you just want to stop the tube being able to slip back into the bender because if it does that, it will start to crush and elongate the inside. So always make sure that your tube´s centred. Now this is a really handy little tool, this is a bevel box and this is something that I really like to understand my measurements and be able to measure the amount of bend as I´m doing it.

So we can turn this on, it´s a little digital bender that you can sit on the tube. I always like to take up the slack that is in the system. So bring up the hydraulic pressure on our bottle jack and this is a 10 tonne bottle jack that is available at many automotive stores. So you want to bring up the pressure so that the back of the follower is just resting or is just hovering above the follower cradle. So once we bring this up I can zero out my little bevel box.

So then that´s set at zero an then we can start the bending process. Always make sure that your pins are in position and then we can start the bend. So this is only 1.6 mm wall thickness like I said so it´s quite easy to bend. If you were doing anything larger then you would probably want a larger handle on just so that you´re not having to work so hard on this bender. And see all of this force is acting through the body of it which means that it´s portable, you can just store it under the bench and bring it out when you need to bend.

The one problem with it is if you´re doing a main hoop then obviously the top of the main hoop can be way up there so you sometimes need two people to get one of those done by the time you get it into the bender and then get the bends completed and getting them out again can be a little bit of a trick. So I´ve currently got 43° on this bend and we´ll keep going until we get to around 60 and I´ll just show you the resulting finish. So we´re currently at 55. And I´ll take this 1° past. What do we have, 58.

61 so then once you´ve got, once you knock over everything on the bench, we can back off the bender, bring the tube back down. Obviously the springs on the side of this will pull the hydraulic ram back into home position. And as you do that, you want to keep that bevel box well away from it so that you don´t drop it and damage it. Take the saddle clamp off and then your tube will just require a little wiggle to release from the bender. And here we have the resulting bend.

So this is again 1.6 mm wall and ERW mild steel tube. As we were talking about before, the amount of crush on the tube is very important. Usually in our motorsport governing body´s rule book they will allow for this measurement here to be 10% smaller than the outside dimension on the tube so that means that we, on this we have a diameter of 38 mm so we are allowed to have 3.8 mm of crush. So we have 36.5 mm there so we´re well within that tolerance and again by the time you´ve done your template you can measure the amount of crush on that and just make sure that you´re doing it properly and that you´re not getting results that won´t be allowed by your sanctioning body once you rock up at the racetrack. So that´s a bend and we usually would measure that and make sure that we´re in the ballpark there.

Again, as we go on things can change, our benders can get a little flogged out and the spring back can change with certain materials so always make sure that you measure your bends once they´re completed. It´s very hard to take the bend out of a piece of tube, you can add a little bit more but again it´s very difficult, you want to get it right the first time and just by checking things and doing your bending templates then this will allow you to have a little bit more precision in that process. So that´s measuring the crush and when producing a template or any bend for motorsport use, we should always measure that crush just to make sure we´re in the ballpark. This will be noted in the roll cage rules usually and it´s usually like I said around 10% so if this was 1.75 inch tube, then it would be around 4 mm allowable crush. So that´s basically it for tube bending.

I´m going to ask for a few questions but while I do that I just want to show you a few of the arms that we´ve laser cut. So as you saw before, this is the slot that will allow you to fit different dies in, we´ve actually done some FEA analysis on this and it will allow you to bend some pretty thick stuff without even getting close to deforming. So usually there´ll be a series of holes here that suit a range of dies, usually from that manufacturer. So here we´ve put the slot in and we´ll supply you with those DXFs. So that is for our horizontal bender.

And then for our upright bender, this is one of the laser cut plates that we use for that. So this is the upper body that sits up and will allow you to then produce one of these. And again, which one suits you will depend on what your project is but my personal preference is the upright bender. It´s a lot easier to operate, it´s a lot quicker and it allows some versatility in the workshop and if you´re working out of a small garage then it´s quite easy to take this thing outside and bend some pretty large things. You may just have to get some help to obviously set those and get them into the bender.

So let´s have a look what sort of questions we´ve got coming in. Again thanks everyone for coming along today. It´s always good to talk about bending because it´s one of the big processes in motorsport fabrication that a lot of people get a little bit daunted by. I certainly was when I was starting out and it stopped me from doing a few things early on. One of the first roll cages I did, I actually made a template for my main hoop and I actually went to an exhaust shop, took the tube to them and actually got them to mandrill bend it and it ended up costing me around $300 just to get that tube bent when I probably could have actually put that money into building my own bender which I ended up doing anyway and saving a whole bunch of cash.

So mandrill bending is obviously great for smaller diameters and if we´re, sorry smaller wall thicknesses and if you need tighter radius bends, something like this then it needs to be mandrill bent because the tube can´t physically stretch around that that far, but for everything, obviously chassis wise then I think producing your own bender, either the horizontal version or the upright version is a great way to go and it will allow you to get stuck into your projects and get them finished in a matter of saving a bunch of cash and saving a heap of time while you´re at it. So we don´t have any questions, we´re probably going to call it. If you do have any questions then make sure that you jump into our forum and ask them there, I´ll be happy to answer any questions that you may have or if you need any advice on setting these benders up, again in our roll cage course we will put the worked example of producing our horizontal bender and we´ve got one on the way as well for the upright bender. I think that´s all we have for today, thanks for joining us and hopefully we can see you next time, thank you.