Bend-Tech setup for JMR tube benders: die calibration, step by step

Bend-Tech is only as accurate as the die numbers you give it. Skip calibration and your legs come out long, your bends land in the wrong spot, and you burn tube figuring out why. This guide covers the whole setup on a JMR bender: what each number means, how to bend and measure the test piece, the math behind it, and how to fix a part that comes out off.

1. The four numbers Bend-Tech needs

Every die in Bend-Tech's Die Library carries a few values. These are the ones that decide whether your parts come out right:

Because the die itself is held that close to its stated radius, the differences you'll see from one calibration to the next come from the tube — material, wall, and how it springs back — not the die. That's why every material gets its own calibration. For more on what CLR means and how to choose one, see CLR Explained.

2. Before you bend

Calibrate for the tube you'll actually bend. A calibration belongs to one die and one material. 1-3/4" × .120 DOM and 1-3/4" × .120 HREW won't give identical numbers, and neither will a different wall thickness. Use a scrap of the same stuff you're building with, and set up a separate die entry for each combination you use regularly.

Make sure the tube is inside the die's spec. Every JMR die is rated for a range of tube size and wall. The thin end of that wall range is the thinnest wall that will bend cleanly — calibrating on something thinner will give you a wrinkled test piece and bad numbers. Check the capacity charts if you're not sure your tube is in range.

Lube the follower bar, not the die. Lubricant isn't required on a JMR bender, but it does improve bend quality. Put it on the follower bar only — keep it off the center (radius) die so the tube doesn't slip in the clamp. Whatever you do for the test bend, do the same on real parts so the numbers stay consistent.

Line up on the edge of the die. Bend-Tech needs to know where on the bender you line up your bend marks. On a JMR bender, use the edge of the radius die where the tube enters it. The bend doesn't start exactly at that edge — on JMR dies it starts somewhere between 1/8" and 3/8" past it, depending on the die size — and the Bend Location Offset is what accounts for that. The important part is using the die edge every time, for the test bend and for every real part after it.

3. Add your JMR die to the Die Library

1. Open the Die Library. In Bend-Tech, go to Tools → Die Library, or pick Die Library from the Task Menu that comes up when you start the software. (Menu names can shift a little between Bend-Tech versions.)
2. Start a new die and give it a name you'll recognize. Include the die and the material, since this calibration only applies to that pair. Something like JMR 1.75 x 6 CLR – DOM .120 works well.
3. Launch the Calibration Wizard. If this is your first calibration, the wizard walks you through the bend and the measurements one screen at a time. If you've done this before, the Calibration Worksheet is a faster one-page version of the same thing. Either one is fine — the math is the same.
4. Choose your bender. Pick JMR Bender from the bender list — it covers every JMR model. JMR benders are rotary draw benders: the tube is clamped to the die with the U-strap and drawn around it while the follower block supports the outside. (If you're on an older Bend-Tech version that doesn't list it, Any Rotary Draw works the same way.)
5. Print the instructions. The wizard can print its steps with blanks for your measurements, which saves walking back and forth to the computer. You can also use the calibration log at the bottom of this page.

4. Bend the 90° test piece

1. Cut the test piece square and measure it before you bend. Write down the exact cut length. This is the one measurement you can't go back and get later, and an error here throws off the Calibrated CLR.
2. Measure the actual OD. Use calipers if you have them. Tube is often a few thousandths off nominal, and the formulas use the OD directly.
3. Make a mark a known distance from one end. 12" from the end is an easy number to work with. Wrap the mark all the way around the tube so you can see it from any side. Write down the exact distance — this is your Mark Location.
4. Load the tube with the mark lined up on the edge of the die. Put the marked end toward the clamp side so the mark sits right at the edge of the radius die. Set the U-strap and pin, then install the follower block. Double-check the mark didn't shift when you tightened things up.
5. Bend until the tube measures a true 90° after it springs back. Don't trust the degree wheel for this one. Bend a few degrees past 90, back the bender off so the tube relaxes, and check it with a framing square. If it's still open, go a little further and check again. Sneak up on it — you can always add degrees, but you can't take them out.
6. Note how far past 90° you had to go. That's your springback for this die and material. Write it down; you'll use it later.

5. Measure and calculate

Lay the test piece flat. Measure each leg from the cut end of the tube to the outside face of the opposite leg (see the diagram above). Leg 1 is the leg with your mark on it.

Enter the cut length, OD, mark location, and both leg lengths into the wizard or worksheet and Bend-Tech does the math. If you want to understand what it's doing — or check its results — here are the formulas.

Calibrated CLR

Where the 2.33 comes from: in a 90° bend, the two leg measurements together include twice the radius, but the tube itself only used a quarter-circle of material through the bend. The difference is about 0.429 × the radius, and 1 ÷ 0.429 ≈ 2.33. Because real tube stretches through the bend, this number comes out larger than the die size — usually 5–20% larger. If yours lands way outside that range, re-check the cut length first.

Achieved CLR (optional 180° check)

Some versions of the wizard ask for a 180° bend as well. On a 180°, measure across the outside of both legs:

Bend Location Offset

If the bend had started exactly at your mark, Leg 1 would equal the mark location plus the radius plus half the OD. Whatever's left over is how far the true start of bend sits from your reference. A negative BLO means Leg 1 came out longer than that — the bend started further down the tube than your mark. Lining up on the edge of a JMR die, expect a BLO somewhere around −1/8" to −3/8" (−0.125" to −0.375"), depending on die size. If you get something far outside that, re-measure Leg 1 and make sure the mark was right at the die edge when you bent it.

Sign convention: The formula above is for rotary draw benders like JMR's. Bend-Tech notes that rotary compression benders flip the sign, so if you're comparing your numbers to a forum post from someone running a compression-style bender, don't be surprised if theirs has the opposite sign.

Worked example

These are example numbers to show the math — your own test piece is the only thing that will give you real values for your setup.

So for this example setup, the Calibrated CLR is about 6.70" (roughly 12% over the 6" die — right in the expected range), and the true start of bend sits 1/4" past the edge of the die.

Save the results to the die. From here on, every part you design with this die uses these numbers for cut length and bend marks.

6. Square tube and pipe dies

The calibration process is the same for square tube and pipe — one 90° test bend, the same measurements, the same formulas. Each one has a couple of things to watch.

Square tube

JMR makes square tube dies from 1/2" through 2" square, on CLRs from 3" to 8".

• Enter the side width as the "OD." For 1-1/2" square, the OD value in the formulas and in Bend-Tech is 1.500". Measure across the flats, not corner to corner.
• Seat the tube flat in the die. Square tube has to sit flat against the bottom of the die groove for the test bend and every bend after it. A tube that's tipped even slightly will bend out of plane and throw off your measurements.
• Rotation is in 90° steps for most parts. Square tube can only seat in the die four ways, so most multi-bend square parts only rotate 0°, 90°, 180°, or 270° between bends.
• Check your Bend-Tech version. Bend-Tech EZ only works with round tube. For square tube parts, you'll need EZ-3D, Pro, or SE.

Pipe (NPS)

Pipe is not sized by its outside diameter. Nominal pipe size (NPS) is a name, not a measurement — 1" NPS pipe actually measures 1.315" OD. This is the most common setup mistake with pipe: entering "1.000" for 1" pipe in Bend-Tech throws off every number the software gives you. Always enter the actual OD.

• Wall thickness comes from the schedule. Schedule 40, 80 and 160 pipe all share the same OD for a given NPS — only the wall changes. Enter the actual wall for your schedule in Bend-Tech's material library, and calibrate each schedule separately.
• Schedule 160 limits. JMR pipe dies are not rated for schedule 160 on pipe larger than 1" NPS.
• Don't reuse tube numbers. Pipe springs back differently than tube of a similar size, so measure springback on a pipe test piece.

7. Dialing in springback

Springback is the amount the tube opens back up after you release the bend. It's why bending to 90 on the degree wheel doesn't give you a 90° tube. It depends on the material (DOM vs. HREW vs. chromoly vs. aluminum), the wall thickness, the die radius, and to a lesser extent the angle of the bend itself.

• Get a starting number. JMR's tube bending springback chart gives typical values to start from before you've bent anything.
• Then confirm it with your test bend. The number of degrees you had to go past 90 in Step 4 is a solid starting point for that die and material. A few degrees is common for steel tube — the only way to know yours is to measure it.
• Check it at a shallow angle too. Springback isn't always the same at 30° as it is at 90°. If you do a lot of shallow bends (bumpers, hoops), bend a 30–45° test and see how it compares.
• Use your bender's degree wheel to bake it in. On a JMR bender, set the pointer so you're reading the overbend you need, or just keep a note on the bender of how many degrees to add for each die/material you run.
• Higher versions of Bend-Tech can do the math for you. Bend-Tech SE can output springback-compensated bend angles, so the bend sheet tells you the number to bend to, not just the finished angle.

8. Troubleshooting a part that comes out wrong

Once the die is calibrated, bend one real part and check it against the drawing before you commit a whole stack of tube. Here's how to read what's off:

9. Using Bend-Tech's numbers at the bender

With the die calibrated, Bend-Tech gives you a bend sheet for each part: cut length, where to put each bend mark, the bend angle, and the rotation between bends. At the bender, the workflow looks like this:

1. Cut to the length on the sheet. Cut it square — a crooked cut throws off every mark you measure from that end.
2. Draw a reference line the full length of the tube. This is your zero for rotation. Every rotation on the bend sheet is measured from this line.
3. Lay out all your bend marks from the same end. Measure each mark from the starting end, not mark-to-mark, so small errors don't stack up.
4. Line each mark up on the edge of the die. The BLO in your die setup already accounts for where the bend really starts.
5. Bend to the angle plus springback. Check the first bend with an angle finder before moving on.
6. Rotate, line up the next mark, repeat. Set the rotation from your reference line before each bend.

10. Printable calibration log

Print this section and keep it at the bender. One row per die and material combination.

Frequently asked questions

More tube bending tools and resources

Bend-Tech is a trademark of Bend-Tech LLC. JMR Manufacturing sells Bend-Tech software and wrote this guide to help customers set up JMR benders and dies in it. Menu names and wizard screens can vary between Bend-Tech versions.