How to Cope or Notch Tubing
Metal fabrication tips and tricks
Joining the end of one piece of tubing to another is known as notching or coping (pronounced like "hope" with a c instead of an h) the tube. It's all based on angles that are determined by where you are placing the tube. Notches range from a true 90-degree cope (forming a T joint) and on down from there, with copes with the small angle less than about 20 degrees becoming slightly awkward (as the two pieces of tubing approach parallel). There are several ways to notch tubing, and if you want to do much fabrication, you'd better get good at doing one if not all of them.
Here are the ways we usually add a cope or notch to steel structural tubing when we build a rollcage, bumpers, shock towers, frame crossmembers, roof racks, tire carriers, and more.
Sadly, coping involves some math or trial and error
The first step in coping tubing is to figure out the angle that you need to cut into the tube that will be joining the side of the other tube. You can do this by eye and trial and error, or get busy with angle finders and plastic see-through protractors. Also, your smartphone almost certainly has an app or is angle finder app-capable, and if you are like us, you'll want to check any math with the phone's calculator. We generally use our "eye"crometer, which has been honed by some experience. The truth is the human eye is pretty good at determining if two lines are parallel or perpendicular. Also remember that the two angles on both sides of a cope with a straight piece of tubing will always sum to 180. So a perfect T-joint would have angles of 90 degrees on either side (90 + 90 = 180) and so on. This means you can focus on one of the angles on the smaller side of the joint (just because math is easier with smaller numbers) basically only worry about numbers less than 90 to about 20.
The easiest way to cope tubing
The easiest way to cope or notch tubing is to use a tubing notcher. These tools use a hole saw with a solidly mounted shaft and an adjustable clamp to hold the tubing in place while you use a drill to turn the hole saw. Most that we've seen have an angle finder on the tool so you can set the smaller angle of your cope, but many only go down to about 55 degrees. (That number is subtracted from 90, which would be a perfect T-joint, to give us our small-angle number of 35 degrees.) Anything below that, and you'll have to modify the cope with a grinder (see below).
We'd also recommend using a heavy-duty drill and plenty of cutting oil, and cut slowly without applying a ton of force. Also be ready to let go of the drill because if it catches an edge, it will suddenly turn you or your wrists into ragdolls. Once your cope is in the tubing, chances are you'll have to clean up the inside edge of the cope because as the hole saw reaches the end of the cut, it almost always pushes out of the tubing slightly. Opening up that inside notch is also the way to get the cope less than the 35 degrees that will be the minimum.
Notching or coping with a saw
If you have to, you can cope tubing with a chop saw or band saw, or even with a sawzall. For perfect T-joint copes, we've found that you'll use about 5/8-inch on 1.75-inch tubing. Mark the top and bottom of the tube. Cut small wedges off each side of the tubing at about 45-50 degrees, leaving a flat center. Once you're done, you'll have to clean up the cuts with a grinder with a flap wheel or rounded-off stone. To change the angle of the cope, you just have to cut one side of the tubing with a larger wedge and the other side with a smaller wedge.
Coping and notching with an angle grinder
A hand-held angle grinder, usually for 4 1/2-inch stones or flap wheels, is a must-have for almost all fab work we've done. Also, as you've seen if you've read this article, a grinder is a must for cleaning up just about any cope or notch, including those made with the tubing notcher. We like using a flap wheel because they, after some use, generally have a nice, rounded profile and are easy for us to control, but your experience may be different.
Coping tubing that's nearly parallel or has an angle less than about 20 degrees
To cope tubing that is less than about 20 degrees, you'll need to add a bend to the tubing to open up the cope a touch. Then add the cope or notch to the portion of the tube after the bend has started.