Bending Tube with a the Rogue Alpha Bender, 101: The basics
The Rogue Fabrication bender has a fixed bend offset for every radius of die. The bend offset is the distance between the start of the bend and where you line up the tube in the machine. See the image below.
If you want to make a bend on a 4.5 radius die, and you want that bend to be 10 inches from the end of a piece of tube, mark a line on the tube 10 inches from the end. Your BEND STARTS HERE. Now draw a line that is 5 3/16" closer to the end of the tube from your first line (5 3/16 is the bend offset from the table below). This line you just drew is where you line up the tube with the clamp block in the machine ("MARK TUBE HERE" in above image). The bend will start at exactly 10 inches from the end of the tube.
What About Springback?
Here is the best way to measure your springback- Put straight material in the machine and hand pump the ram until it is just barely tight but not bending yet. Zero the degree indicator. If you want to bend a 90, bend EXACTLY 90, and then release ram pressure until the material is loose in the machine. Tighten the valve, and hand pump the ram until it is just barely tight on the material. Read your degrees, we'll say for example that you read the degrees at 86.5. Now overbend by the difference. So you bend to 90, snug the machine up, read 86.5, then bend to 93.5 and pull out the tube and you will be at EXACTLY 90 after springback. Now you can overbend every 90 on that material by 3.5 degrees and they will all be spot-on! Springback is different for every material.
Bending Tube with a the Rogue Alpha Bender, 102: making a "U"
Here is a simple layout, 2 bends, 90 degrees each. Image below (left). We are concerned about the distance between the legs here. Start by marking the center of the tube. Next, use the table to figure out how far apart your clamps will go to make the bends have the right spacing. Draw a line on your tube for bend A and for bend B where you will clamp the tube into the machine for each bend, and go bend. This is easy to calculate on your own once you know the bend offset for your die.
Bend Offset: Distance from start of bend to face of clamp block.
Dimension C: Distance from front face of clamp block on bend A to the same for bend B.
Dimension X: Distance between the legs, measured at tube center.
At some point as your legs get closer together, there is a point when the clamps will be in the same place for both bends (but with the material loaded in one direction for bend A, and the opposite for bend B). Once you go closer than this, the dimension C is shown negative, since the clamp block locations are past the center of the tube for each bend (see image, below-right).
Bending 103: A Little More Complex
1. Draw your layout full size with sharp corners and dimension it (you can draw it on concrete, cardboard, paper, etc).
2. Trace the bends accurately into the corners with the correct radius. Mark the beginning and end (optional) of the bends.
3. Put a mark on your layout in the center of the tube. This is where we will start fabricating from.
4. Move from the center of your layout to the right, draw a line 5” from the beginning of every bend (6 5/8” for 6.0” CLR, 6 13/16” for 5.625” CLR, 6 3/16 for 3.5” CLR). Label these lines “clamp block”. Repeat this process to the left.
5. Now cut your tube to length, and put a mark in the very center of your tube.
6. Measure out from center and draw your clamp block lines on the tube (7.75” and 10.75” in the example above).
7. Grab the tube centerline. Load into the bender (from front) until the clamp block line is on the front face of the clamp block.
8. Make your bend per machine instructions.
9. Remove the tube and lay it on top of your layout. You will be able to see any error. Now is the time to account for any stretching that may take place. If your second clamp block location doesn’t seem to be as close to the bend as you drew it, you may draw it closer and maintain as much accuracy as possible.
10. Repeat this process until you are done bending your layout. If you cut your tube to the full “sharp corner” length. You will have to cut the ends after you are done.
Clamp block face highlighted in blue:
Bending 201: Starting From One End of the Tube, Not the Middle
The following paragraph is a VERY DENSE explanation of another way to bend the same shape drawn above in Bending 103.
We’re going to bend from one end to the other, starting with the 90 degree bend. We want a 10 inch leg with a 4.5” bend, so we need 5.5” of straight tube. Our offset is 5” for a 4.5” CLR die, so hang 0.5” of tube out of the end of the clamp block and bend 90 degrees. The takeup for a bend is pi * diameter * bend length/360. So for our 90 that is 3.14*(2*4.5)*(90/360)=7.065 inches. It is another 28.5 inches from the end of the first 90 to the beginning of the next bend (add up the dimensions in the drawing). We can put the clamp block 28.5-5 inches from the end of our first bend, our we could have drawn a line on the tube before we started that was 5.5+7.065+28.5-5 inches from the starting end of the tube and used that as a clamp block location. Clamp on the second line and bend, and you’re done.