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 vertical 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
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.
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.
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.
have yet to talk with anybody who uses one that doesn't have anything but good
stuff to say about them.
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
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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
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.
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.
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.
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.
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.
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.
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
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.
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.
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
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:
The following links may be
of interest to folks building a new bender.
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