This tutorial will help you accurately place 90 degree bends in tubing using the Imperial 180 degree tubing bender. But before that, I'll make two recommendations. Number one, buy some extra tubing in 1/4" and 3/8". Unless you've done this before, you're going to make a few mistakes. Tubing is relatively cheap. It's better to save yourself some frustration and not run out.
The next recommendation is on tubing benders. I first bought a 90 degree bender from Home Depot (top item in picture below) for about $20. There are two problems with this bender. It can't bend a full 180 degrees and doesn't produce tight bends. If you're using the electric boost pump from Vans you'll need to do a few 180 degree bends, and the HD bender won't cut it. I ended up buying the Imperial 370-FH bender from Sears.com for $50 (bottom item in picture).
This shows the bending required for the electric boost pump.
This picture below shows the difference in bend radius on 1/4" tubing for even just a 90 degree bend. The 370-FH produced the top bend.
Now, there is one drawback with the Imperial 370-FH bender. It's a little more complicated to make 90 degree bends, but the instructions with pictures below should have you bending aluminum tubing like a balloon animal artist in no time.
These instructions are particular to the Imperial 370-FH, but should adapt to most other models. The keen eye will notice the measurements in the pictures are off slightly, but that's strictly due to the parallax of my camera shooting position. All of the bends were within 1/16" of the desired location.
I'll start with 1/4" tubing, as it's a little easier. 3/8" is covered after that. 1/2" tubing follows the same directions as 3/8", so I won't cover is separately (plus Vans kits don't use 1/2" tubing that I know of). There are two ways to measure the location of a bend, from the left and from the right. You'll find that you'll need to do each at certain locations.
1/4" Tubing Left Measured Bend Let's start with a bend measured from the left end. Let's say you want the bend to be 4" from the end of the tube as shown in this picture.
First mark the tubing 4" from the end. That's where the middle of the bent tubing will end up. You can make this measurement from any spot on the tube, but I'm using the end of the tube in all of the examples.
Set the holder so that '1/4"' is visible just below it.
Pull the handle around to the top and place the tube in the 1/4" slot in the bender. Line up the mark on the tube with the "L 1/4" label on the handle.
Pull the bender around until "0" on the handle lines up with "90" on the body. You might have to experiment a little with this part. I find on mine that I need to pull just slightly past 90.
1/4" Tubing Right Measured Bend It's equally easy to make a bend measured from the right end of the tube. Mark the tube where you'd like the bend to be. In this picture it will be 4" from the right end of the tube.
Pull the handle to the top of the bender and place the tube in the 1/4" slot with the mark lined up with the "R 1/4" label on the handle.
Pull the handle around to 90 degrees.
The bend is complete.
3/8" Tubing Left Measured Bend Here's where things get a little tricky. There's an extra step to bending 3/8". First, let's start by setting the tube hook to the middle position where '3/8"' appears just below it.
It starts off the same, by measuring the desired location of the bend.
The next step is where things are a little different. You must adjust the mark location. You can either use the table in the instructions, or I find it easier to use the labels on the handle. Line up the mark made above (blue) with the "3/8 Left" label on the handle. Then put a new mark (red) where it says "Hook Alignment Mark".
Next, pull the handle to the top of the bender and place the tube in the middle 3/8" slot. Line up the new mark (red) with the right edge of the hook. This is different than before. Ignore the original mark (blue).
Pull the handle around to 90 degrees.
3/8" Tubing Right Measured Bend It's a similar process to make a bend measured from the right on 3/8" tubing. Mark the desired location of the bend.
Next line up that mark (blue) with the "3/8 Right" label on the handle and make a new mark (red) where it says "Hook Alignment Mark".
Pull the handle to the top of the bender and place the tubing in the middle slot with the new mark (red) lined up with the right edge of the tube hook.
Pull the handle through 90 degrees and check the results.
Hopefully these pictures and descriptions will help you make accurately place 90 degree bends with your Imperial 370-FH tubing bender.