CBH Vertical Tubing Bender - (CBHVTB)

As many readers know I’ve been using and building tubing benders for about 40 years now and I have some opinions about what makes or breaks a bender for doing production bending work and I’ve always preferred to use a ‘horizontal’ style manual bender.

However when I moved into the new Texas shop I realized right away that there was no way that I’d have room for a conventional horizontal bender like the JD2 model 3 or the Pro-Tools model 105 which are two of my favorites.

As a result of this situation I started to take a serious look at buying or building a small vertical type of bender that I could tuck away in a corner of the small shop when it wasn’t being used.

I bought a couple of plans and downloaded free plans from the net for several different vertical benders and then I went around to shops and dealerships to see some of these machines in action and to be honest I wasn’t to impressed with what I saw. The best of what I did see were home made models but even some of these had limitations.

A lot of the vertical benders are marketed using what I’d call ‘fantasy-wear’ where the manufacturer makes some wild-assed claims that simply can’t be substantiated in reality. At one sales demonstration I actually saw a bender frame buckle over sideways just trying to bend some 1.5 x .25 wall DOM tubing and the model they were demonstrating was their supposedly ‘heavy-duty’ model. They blamed the failure on the Pro-Tools die which they said had a poorly cast pivot pin hole which even an idiot could tell wasn’t the case. Most of us at that demo clearly saw that the unrestrained ram shaft was moving towards one side of the drive links causing a twisting and binding situation that the operator should have taken care of. That experience immediately soured me on looking much further at mass-produced benders since the unit I was looking at was supposed to be the ‘ultimate’ bender. Ironically the maker came out with an ‘improved’ model a few weeks later that had much thicker arms.

I was also extremely disappointed to find out that almost all vertical benders that I saw demonstrated needed to have the drive links reset just to do a simple 100-degree bend which is about what you need to do in order to get a good ‘90’ after ‘spring-back’ is taken into consideration. I could not believe that these various bender manufacturers and designers didn’t have a clue about the most basic fundamentals of making good tube bends.  It was pretty obvious that selling a ‘canned’ product was far more important that selling something that was useful and actually worked in the environments of a small fabrication shop.

To me having a bender that needs the drive links reset after turning a 60 to 70-degree bend was just a non-starter with respect to serious fabrication work. Even guys just starting out with a bender realize that the biggest reason for ‘kinking’, wrinkling’ and ‘distortion’ is due to spring-back and every time you have to reset the drive links you are letting the tubing ‘relax’ or ‘spring-back’ and when the drive links are re-engaged there will be a slight indentation in the tubing once pressure is reapplied.

None of the vertical benders I looked had any provision for adding one of the various anti-spring back devices like we typically use on horizontal benders.

This simple design flaw with vertical type benders is one reason that they have not taken a market share over the old traditional horizontal benders in the commercial fabrication industry.

As I mentioned earlier some of the best vertical benders I saw were custom made in small shops and most of these had incorporated workarounds about the bending angle problem.

It was pretty obvious to me that some bender manufacturers where pretty good at having parts water-jetted but not so good at actually bending tubing so I went back to the plans that I’d originally downloaded since most of them were drawn by guys who actually had to bend some tubes in a real-world environment.

My first choice of the home-brewed benders based upon recommendations by dozens of fabricators was the little Pro-Tools model HMP-200 but after I reviewed the plans in detail and built a mock-up it was immediately apparent that this bender had some rather significant limitations so I put that one away on the shelf.

This is a good low-cost bender but I don’t think that it works very well in a production fabrication environment and it’s relatively expensive to build.

The next bender I took a look at was another one recommended by a lot of people and that was the AH – Bender designed by Frank Takacs known to most of us as ‘EuroFrank’ at the boards. The plans for this bender have been around a long time and have gone through several stages of refinement and improvement.

I have yet to talk with anybody who uses one that doesn’t have anything but good stuff to say about them.

Since this bender had such a good reputation I didn’t even bother looking at the plans in detail with respect to operational issues and went ahead and built one. This is an excellent bender but it didn’t end up meeting one of my primary requirements and that was making a 110-degree bend in one clean sweep without having to reposition the drive-links. My other issue was that the unit was simply to low to the ground so that I always had to stoop over to load tubes, set the die and follower and position the digital protractor. I ended up using the bender while it was sitting on top of two plastic milk-crates and then it ‘felt’ great.

The other drawback was that this bender is designed to use the Pro-Tools Model 105 die sets and I much prefer the JD2 dies especially for bending thin-walled materials and stiff material like chromoly.

While researching vertical benders I had a chance to use a machine based upon one of Franks very early models (the HD-Bender) and to be honest I much preferred it to his latest version. I think that the plans for his original benders are still available and if you’re serious about building a bender I’d suggest that you buy both sets of plans if at all possible. Franks site is: http://www.gottrikes.com

Vertical Bender Geometry

Building a vertical bender that uses a hydraulic ram is a whole lot different than building some of the other benders that we’ve posted fabrication plans for. The biggest issue and a significant restraint is the hydraulic ram itself.

Almost all vertical benders including some of those high-end models you see advertised on the Net use cheap imported ‘air over hydraulic’ long throw 8-ton rams. The physical dimensions and characteristics of these hydraulic rams actually set most of the design parameters a person can come up with when trying to build a bender.

Another problem with 'cheap' hydraulic and air over hydraulic rams is that most of them do not function unless they are mounted in such a manner as to have upward slope to the cylinder.

‘Alltrade’ in Southern California distributes the ram I used for my particular project under the brand name of ‘Powerbuilt’. This ram is sold by dozens of retail outlets under some other trade-names but in almost all instances it is just one of a dozen Chinese clones that make their way to America. Some of these branded clones are verging on being pure junk and others are actually quite well made. It pays to shop around and buy your parts ‘in person’ so you can actually ‘see’ what you’re getting.

In general almost all of these cheap rams have a capacity of 8-tons with an air supply of 110-120 psi. The minimum saddle height is 24.5-inches and the maximum saddle height is around 43.5-inches which equates to a stroke length of 19-inches. There is nothing wrong with the capacity of these rams with respect to the force applied to the drive links. In reality an 8-ton (16,000psi) ram is massive overkill since it only takes about 5000psi to bend 2-inch diameter heavy-walled tubing in a typical bender.

Beware that the stroke length is usually less than what is published. My particular ram had a useable stroke length of only 18-inches and I think this is fairly typical for the lot. Most of these rams have what I call a ‘deadzone’ at the beginning of the stroke, which shortens the effective stroke length by as much as an inch. There is a corresponding ‘deadzone’ towards the extremity of the stroke at full extension.

I’ve also the seen the minimum saddle height for these rams range from 23.5 to 25.5-inches depending upon a particular brand. For this reason I strongly suggest that you buy and measure a ram before doing anything else if you’re planning on building one of these benders.

 

 

Figure 1

 

Figure 1 illustrates the primary dimensions used to describe the characteristics of a typical long-stroke air/hydraulic ram. As you can see the ‘minimum saddle height’ is the distance between the centerline of the base mounting bolthole and the center of the pivot pinhole in the ram shaft. When the ram is fully compressed. The ‘maximum saddle height’ is the distance between the mounting bolt center and the pivot pin in the shaft when it is fully extended. The ‘stroke length’ is determined by subtracting one number from the other.

When you set up the control points for a vertical bender you’re basically interested in working with three dimensions that define points on the radius of the moving parts of the assembly.

The first control radius is that established by the minimum saddle height of the ram that you’re using as seen on the left in Figure 2. In this case we’re saying that it is 25-inches.

 

 

Figure 2

 

The next control point is the one that lays on the radius of the fully extended ram shaft as seen on the right in Figure 2. In this case we’re saying that it is 42-inches from the center of the ram base mounting bolt. Keep in mind that the ram pivots as it moves through its range of extension. A lot of first-timers forget to take this into account.

In this particular example our stroke length is 17-inches.

The two fundamental radii will never change no matter what you do to the ram that you buy. You can move the mounting point of the ram up or down or left to right but the radius points will always remain constant relative to the base of the ram unless you change to a ram having different stroke characteristics.

The next radius point we have to consider is that defined by the length of the drive links. This is pretty simple to calculate since we know that the drive link pivot pin or pins have to be coincidental with the arcs formed by the movement of the ram shaft.

You don’t need long drive links in order to create bending torque with a hydraulic unit like you do when building a manually operated bender. The drive links on my little prototype are only 10-inches long and I bend 2” by .188 wall tubing all day long with this configuration.

Figure 3 illustrates the relationship of the drive link radii with the ram shaft radii for two different configurations. The design on the left in the illustration has drive links that are 10-inches long and the design on the right has a set of drive links that are 16-inches long.

 

Figure 3

 

Note that the radius of the ram shaft pivot point in the fully compressed mode coincides with the pivot point of the drive link pivot pin when the bender is at the ‘start of bend’ position. This is pretty elementary stuff but I don’t think anybody has ever covered these basics before so I just want to make sure everybody is fully aware of the fundamental operational characteristics of a typical vertical bender before going any further.

Now the fun begins because we have to come up with a bender design that can bend a specific tubing size to a specific angle at a specific centerline radius with the least amount of hassle possible and this involves some compromises.

A lot of folks go out and build their benders based upon a false assumption that once they have the ram and drive link arm pivot points coinciding then everything else is good to go but that’s simply not the case.

The ram shaft is a physical object and you have to take the location of this shaft into account as the ram moves through the full range of motion. The design length of the drive links and the pivot hole location for the ram shaft in the drive links are determined to a huge extent by the size of materials that you plan on bending.

Figure 4 illustrates a typical vertical bender shown with the drive links rotated a full 110-degrees. In this particular illustration the bender is set up to bend 1-inch diameter tubing along a 3.5-inch radius. The length of the drive-link is 10-inches in this particular example.

 

 

Figure 4

 

This configuration of 10-inch links using a typical ram will work just fine on tubing up to 1.25-inches in diameter bent on a 4.5-inch centerline radius. You can make a nice 110-degree bend in one clean sweep without having to reset the drive links.

So you don’t have to start from scratch I can tell you that based upon actual field experience and mathematical calculations a hydraulic bender using an 8-ton ram with a set of 10-inch drive links can easily bend 2-inch diameter thick wall tubing. So a longer set of drive links are not needed to create additional bending torque.

However longer links are indeed needed to make room for the ram shaft to ‘clear’ the tubing in the die as the bends are being made in larger tubing or tubing bent on a larger radius. The ram shaft will actually bump into the tubing at some point during the die rotation, which will jam up the whole machine. This is the single biggest issue facing the designers of vertical benders. We can blame it all on the relatively short 18-inch stroke of most cheap long-throw hydraulic rams. If we could get a few more inches of stroke length then bender design would be a whole lot easier. Unfortunately going up in cylinder size to get that longer stroke length costs big bucks and for most small fab shops this is the deal-breaker.

Figure 5 shows a typical bender set up with a die set for 2-inch tubing bent along a 6-inch radius but still using the short 10-inch drive links.

 

 

Figure 5

 

As you can see the shaft of the ram will actually bump into the tubing if you try to make a complete bend in one sweep. To use the short links with larger diameter dies it becomes necessary to reset the drive links so you end up making a series of short bends to make a final longer bend. This will work but it’s really inconvenient. Unfortunately this situation is exactly what you end up with when buying some of the mass-produced vertical benders on the market today.

A better way to handle this situation is to just use longer drive links to begin with but then another problem comes up.

As the drive links become longer the effect is to reduce the amount of rotation possible before the ram reaches its maximum extension point.

Figure 6 illustrates this situation using a bender set up with a set of 18-inch links, which are fairly typical on a lot of vertical benders. Using this type of arrangement you can bend up to 3-inch diameter tubing on an 8-inch radius die without much problem.

Note however that you can only make somewhere between a 70 and 80-degree bend with these long links before you need to reset the links on the die.

In effect the ram simply can’t extend far enough to continue making the bend much past the 80-degree point on most benders. In fact many of both the commercial models and the home-built models can’t make a bend beyond the 70-degree point without repositioning the links on the die.

 

Figure 6

 

As I mentioned earlier, from my standpoint the single most important bender design element was the ability to make at least a 105-degree bend in tubing without having to reset the drive links.  If you do any handlebar or exhaust header work the reason for this should be well understood.

To meet this requirement it will become necessary to use links that are somewhere between 10 and16-inches long and it will also become necessary to ‘offset’ the ram shaft bolt location relative to the centerline of the links themselves. If you search the net you’ll see that this what almost all manufacturers do to create a bender that works over a broad range of tubing sizes and die diameters.

The reason for this long discussion on basic geometry is because I know that almost everybody who builds a bender based upon our plans will most probably modify it as much as possible to suit their specific requirements. Armed with this information they can make better design decisions without having to resort to a lot of trial and error experimentation.

 

Ram Pivot Pin

The hydraulic ram I used for this project had a 5/8” diameter bolt hole bored into a 1.5” shaft. This is a fairly typical arrangement but I have seen similar rams using a 1.25” diameter shaft bored for a 3/4” pin as well as cheap rams using a 1” shaft bored for a 1/2” pin. Before you drill anything, double check the actual dimensions of the particular ram you end up using.

It is actually a good thing to bore the drive link hole for the ram pin slightly oversized, as this will allow you to seat the die follower by hand without having to actuate the ram unit. For instance if you have a ram using a 5/8” pin then drill the drive link ram pivot hole to 3/4”. This tip is not shown on the plans.

It is critical that you attach the ram shaft to the drive links so that the shaft is always perfectly centered between the plates of the drive links.  The best and maybe the easiest way to do this is cut and cope some tubing spacers to fit inside the drive links instead of using washers or free-floating spacers. I’m still using washers as shims on my bender and it works but it’s a really poor way of doing things.

 

Summation

I haven’t had time to finish the actual building steps for this new bender but I’ve had so many inquiries about mounting the old model vertically that I thought I’d post this now and finish it later.

I built the original prototype for this bender from scrap materials and it worked so well that I haven’t bothered to build or photo-document a final version yet but here's a photo of the working mockup.

 

You can see here that the bender can easily extend to do a full 110-degree bend in a single stroke without having to reset the drive links and even though the die is not installed in this picture there is plenty of clearance for a 2" die having a 6-inch centerline radius. I'm pretty sure this version of the CBH vertical bender is the only vertical on the market with this capability.

 

 

In this photo you can get a better idea of the overall size of the unit. I didn't bother to put casters on the prototype but it's still easy to drag around the shop. About the only change I want to make on the final version is to add a remote pressure release valve and a 'return' spring for the drive links.

I've been making a lot of handlebars lately and I've found that I can install 2 one-inch dies side by side and get identical bends in two different bars at the just one pass which is kind of handy.

I'm thinking about making the links and frame for this bender from 5/8" plate so it can be mounted vertically or horizontally and operated manually or with air/hydraulic assist.

The plans are, like most of our stuff large format prints so you'll need to take them down to Kinko's to get them plotted. Even though the plans were drawn primarily for my own use in building the prototype I think that most people will be able to figure out things I might have left off the drawings.

I'll keep updating this material and revise the plans as we start to build some final units for some local shops.

The download links for the plans are:  

http://chopperhandbook.com/VTB1-1.pdf

http://chopperhandbook.com/VTB1-2.pdf

http://chopperhandbook.com/VTB1-3.pdf

http://chopperhandbook.com/VTB1-4.pdf

http://chopperhandbook.com/VTB1-5.pdf

http://chopperhandbook.com/VTB1-6.pdf

 

The following links may be of interest to folks building a new bender.

http://www.blindchickenracing.com/tools/tube%20bender/tubingbender.htm

http://www.mechwerks.com/Mechwerks_plans_drawings.htm

http://www.gottrikes.com/Tube_Bender.htm

http://www.probender.com/

http://www.jd2.com/c-12-benders.aspx

http://www.pro-tools.com/tube-and-pipe-benders.aspx

http://www.jmrmfg.com/tag/tube-bender/

http://www.probender.com

 

 

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