How the tube gets bent.

The JMR MB1000 is what is known as a "rotary draw bender". Basically, a rotary draw bender works by drawing the tube through a die-and-follower-block as the die is rotated - hence the name! The die and follower-block are just large, heavy chunks of specially-shaped steel.

Using the picture at left, imagine the die and follower-block were held rigidly in position, but the die was free to rotate. Now imagine that the die were to be rotated in the direction of the red arrows. You should be able to envision that, as the die rotates, the tube (held securely to the die by the U-strap and tensioner bolt) is drawn between the die and follower-block. As the tube rotates with the die, the follower-block prevents the tube from swinging out, and forces the tube to bend as the die rotates.

This is a die and follower-block set. Die's come in different specific sizes for bending a single size of tube (more on this later) and each must have a matching follower-block and U-strap.

The picture at left is of a JMR die for 1" tubing.

These are the main components of the tube bender itself.

The main arms are held fixed, the handle is inserted in the lever, and together they operate the drive rack which opens the pivot arms in relation to the main arms.

It is this action of opening the pivot arms that rotates the die that bends the tube.

Basically, the main arms get fixed to a stand, and the pivot arms are ratcheted away from the main arms by the rack as the user pulls the handle attached to the lever.

As the pivot arms "open up" in relation to the main arms, the die is rotated and the tube is bent.

This is the whole assembly in the "open" position, as it would be if the tube was being bent.

Note that the pivot arms and die both rotate about the pivot pin, and that the drive pin is what locks the pivot arms and die together, so that when the pivot arms are "opened" by means of the rack, the die rotates and the tube is bent around the die, held in place by the follower-block.

Here's a close-up of the bender with a tube in the process of being bent.

Note how the tube is held against the die by the U-strap, is prevented from swinging out by the follower-block, and is therefore forced to rotate with the die and get bent.

Note also that in this pic I have removed the drive pin from the drive pin hole so you can see how, when inserted, the drive pin pins the pivot arms and die together.

In this pic, the drive pin has been temporarily set in an open follower-block pin hole, right next to the follower-block pin (which is holding the follower-block in place).

I ordered the following components:

• JMR MB1000 manual tube bender.
• ASN100 Anti-spring-back kit.
• DGW100 Degree Ring.
• 1.75" round tube, 240°, 6" CLR die set.
• 1" round tube, 240°, 3" CLR die set.

The ASN100 Anti-spring-back kit is an optional accessory that you can install on your bender to prevent tube spring-back as you bend.

All steel tubing has a tendency to want to return to its original size and shape. This means that, as you bend tube, it will "spring back" a little so that the actual bend that you achieve will be a few degrees less than indicated during the bending process.

Without an anti-spring-back kit, this means that every time you pull on the handle and then relax the handle to engage the next tooth on the drive rack, the tube will spring back a small amount. This makes it challenging to achieve quick, smooth, accurate bends to a specified number of degrees.

This is the 1.75" die set. Each die set consists of:

• The HD heat-treated billet die with integrated drive lug and installed tensioner bolt.
• Billet machined, case-hardened, follower-block with installed height positioning pin.
• U-strap
• Heat treated 4140 chrome-moly U-strap pin.

The shear size and weight of these dies is a fairly awesome thing.

This is the 1" tube die set.

We'll cover the details of die specs, like CLR, and how to choose dies, later in the article.

Both of my dies are 240° dies, both for round tubing, and the 1.75" has a 6" CLR, while the 1" has a 3" CLR

This is the "optional" degree ring for the JMR bender. It is part number DGW100, and includes the machined aluminum degree ring, the flexible pointer, and two mounting screws.

I say "optional" in quotes because, although the kit is an optional extra that you need to order, I can't imagine having a bender without one.

The JMR degree ring is rugged, accurate, and very easy to read - even during bending.

And finally, this is the bender itself:

with the included rubber-gripped handle packed separately on top...

The bender ships with all the pins, all of which are precision-machined, heat treated 4140 chrome-moly alloy steel.

There is a pivot pin, follower-block pin, and two drive pins - one for larger dies (like the 1.75" tube die) and one for smaller dies (like the 1.0" tube die).

In this pic, the pivot pin and follower-block pins are both installed, and the two drive pins are each in a different drive hole in the pivot arms.

Install the release lever assembly with sleeve and spring, back between the pivot arms.

With the assembly installed, hook the end of the spring over the lower pivot arm, as shown.

Make sure the assembly and spring are installed in the correct orientation, as shown.

The lower pivot arm is uppermost in this picture.

Another view of properly installed release lever assembly.

In this pic, the top side of the bender is uppermost.

Turn the bender around so that you can work on the main arms.

Remove the nut and washer from the innermost position of the main arms. This is the larger of the two nuts on the main arms.

Install the collar and anti-spring-back rod eye over the removed sleeve.

Do not tighten the set screw in the collar yet.

Re-position the sleeve between the main arms and insert the anti-spring-back rod through the hole in the flag on the release lever assembly.

As shown, when the rod is installed in the proper orientation, the collar will be on the lower side of the sleeve, below the rod eye.

Set the bender down in the normal orientation, as shown, and test the operation of the anti-spring-back lever as follows:

Pull the main arms and pivot arms apart, as shown. They should open smoothly with no binding or resistance.

If there is any binding or resistance felt, it is likely due to slight misalignment between the anti-spring-back rod and the hole in the flag on the release lever assembly.

The anti-spring-back rod MUST be located parallel to the main and pivot arms for proper operation.

Slight adjustments can be made to the position of the anti-spring-back rod eye on the sleeve.

When the action is smooth, tighten the set screw in the collar.

Cycle the pivot arm several times to ensure the anti-spring-back rod is not binding through the release lever assembly. Some fine tuning of the collar position (up or down) may be required for smooth operation.

DO NOT use any grease on the anti-spring-back rod.

...and slip the lower main arm off the bender assembly.

Note the large bronze bushing that connects the main arms and pivot arms at the pivot point.

We'll see this again, as it is a great feature that not only ensures smooth, accurate bending, but also prevents the bender falling apart when you change dies.

...then drilled the holes and bolted the plate to the underside of the lower main arm.

This plate will become the top of my stand.

Note that I replaced the supplied Nylok locking nuts with all-metal deformed-thread locknuts since I will be welding the plate to the top of the stand and didn't want the heat to transfer and melt the nylon in the stock locknuts.

The nuts must be extremely tight to prevent the main arms from "scissoring" against each other. I used 230 ft/lbs for the smaller, outer bolt and about 300 ft/lbs for the larger, outside bolt.

With the top of the stand made, I needed to choose a location for the bender and make the base.

When choosing a location and the orientation of the bender on its stand, consider which way the tube will be fed and how long the pieces of tube you will bend are.

I found the best choice to be at the front of the shop, close to the door, on the right-hand side (right when facing out the door), with the "back side" of the bender closest to the door (so tube will be loaded from outside the door).

I wanted a good sturdy base for the stand, so I laid out a 6" square bolt pattern, again in 1/4" steel plate, for 1/2" mounting bolts.

The stand will be bolted to my concrete garage floor, so I picked up four of these 1/2" concrete anchors.

This style of anchor is designed to be driven into a hole in the concrete until it is flush with the floor (this lets me completely remove the bender if need be).

The action of driving the anchor into the concrete splays the lower end out so that it anchors securely in the concrete.

Anchor driven flush with the floor.

These anchors are sold under numerous brand names, and you should be able to get them at any of the major hardware or building-supply stores.

To finish the stand, I simply welded a 32" long piece of square tube to the base plate, bolted the base plate to the concrete using the anchors, and then welded the top plate to the top of the square tube.

This is a view of the top plate.

Bender mounted on its stand.

This is at the front right of the shop, just in front of the door opening.

Another view of the bender mounted on its stand.

Note the orientation of the bender  - in this installation, long pieces of tube will be fed into the bender from outside the door.

You can also easily customize the stand to your liking by adding hooks or mounting points for tooling, die sets, etc.

This is the degree ring for the JMR bender. It is part number DGW100, and includes the machined aluminum degree ring, the flexible pointer, and two mounting screws.

The JMR degree ring is a very nice piece of machined aluminum - rugged, accurate, and very easy to read - even during bending.

Degree ring installed.

At this point, all that is required is to install the die and follower-block of your choice and start bending.

The JMR has a unique 3-speed drive mechanism.

The lever can be connected to the drive rack using any one of the three pairs of holes. The change is quick and easy to make using the quick-release pin.

The position closest to the main arms (shown) provides the greatest leverage - great for large OD or heavy-wall materials.

The position furthest from the main arms provides the least leverage, but the greatest speed of bending - great for small OD or thin-wall materials.

Essentially this clever design provides an adjustable lever that allows the user to trade leverage for speed - which is the principal operating principle of any lever.

Here's the theory, for those interested:

Work is force times distance (W = F x d). By looking at the equation we can see that if work remains constant, increasing force decreases distance or increasing distance decreases force. A lever is a simple machine that trades force for distance or vice versa. We all use levers every single day. The simplest example is a door. Imagine you open a door by pushing near the hinges. Now imagine you open the same door by pushing near the handle. In either case the same amount of work is done. But, when you push near the hinges you must push harder (force is greater) but over a smaller distance (distance is less). When you push near the handle less force is required, but you must push for a greater distance. The door is a lever that trades distance for force - putting the handle on the opposite side of the door from the hinges makes it easier to open and close. Other examples of levers that cost distance but payback in force are a bottle opener and a crowbar.

The arms of the JMR are massive 9/16" alloy steel that are heat treated, blanchard-ground, and completed with an anodized black finish for superior strength, durability, and corrosion resistance.

JMR dies and follower-blocks are made from heat treated billet steel.

follower-blocks are case hardened to a min depth of .050".

All dies carry a lifetime warranty against breakage.

The main and pivot arms of the JMR are held together by bronze bushings.

Not only does this provide smoother, more precise action with less wear...

This is a 240° 1" tube die set with a 3" CLR.

This diagram illustrates the differences between bends of different radii - that is, bends made with dies having different CLR's.

Note that, generally, the tighter the bend, the greater the possibility for tube distortion or wrinkling in the bend, especially for thin-walled materials.

I haven't tried every material type and thickness with every possible combination of dies (there are hundreds of possible combinations), but if you have questions or concerns about which CLR may be right for your application, the experts at JMR can help guide you.

Because we will reference them a lot in this section, as a quick review, here are the names of the pins again:

• P = pivot pin (there is only one pivot pin).
• F = follower-block pin (there is only one follower-block pin) .
• D = drive pin (for larger dies).
• SD = small drive pin (for smaller dies).
• U 1.75 = U-strap pin for U-strap for 1.75" tubing.

Begin by removing the pivot pin so that you can install the die.

Install the follower-block between the main arms, as close as possible to the die.

Be sure to position the follower-block with the height-pin facing down, so that the pin positions the follower-block close to the correct vertical height.

Secure the follower-block with the follower-block pin inserted through both main arms.

With the height-pin down, the radius in the follower-block should be close to vertically level with the radius in the die, like this.

The pin is not designed to hold the follower block at the precise height required - it actually floats vertically on the follower-block pin and will self-alighn onde the tube is inserted - but the height-pin holds it close to ease insertion of the tube.

Lightly grease the working surface of the follower-block.

Close the pivot arms against the main arms, using the anti-spring-back lever as required to do so.

Insert the drive pin, locking the pivot arms and the die together.

Grab some tube, making sure it is clean, dry, and free from defects.

Move to the rear of the bender...

Position the tube for the start of the bend.

The bend will begin at the leading edge of the die, as shown here.

Depending on the die and tube being used, you may be able to view this start position by looking down through one of the open drive-pin holes, or you may have to look under the top pivot arm from the front as is being done here.

Insert the drive pin (the largest one that will fit through the die), and tug on the pivot arm to take up the initial slack.

Check and re-position the tube as required, then snug up the tensioner bolt.

Engage the drive rack teeth with the drive sleeve on the end of the pivot arms.

Make sure the teeth fully engage the sleeve.

Pull on the handle to advance the drive rack and open the pivot arms.

At the end of the pull, disengage the drive rack from the drive sleeve, return the handle to the starting position, engage the next tooth, and pull again.

Repeat as necessary.

Don't forget to check the degree pointer as you go, and to account for spring back before you finish the bend.

If you are bending to more than about 55°, you will reach the end of the drive rack before you have finished the bend.

The exact number of degrees you get from "one rack" will depend on the lever selection position - max leverage, max speed, or the middle position.

Press the anti-spring-back release handle towards the main arms and, while holding slight pressure on it...

... as indicated on the degree ring.

Don't forget to account for spring back before stopping the bend.

Slide the tube out from between the die and follower-block, towards the front.

And you are done!