You have a project that requires you to weld tubing together at a right angle, but you do not have any commercially made equipment for cutting a nice concave in the end of a tube where it joins another tube. This Instructable will show you how to do a good job in your home workshop.
I do not like welding EMT (conduit). I am using it here solely for the sake of illustration. What this Instructable demonstrates would work well with black pipe.
Step 1: My Setup
I am using a metal cut-off wheel mounted on a radial arm saw. The metal tube rests on a small accessory table I made.
Step 2: Make a Table
I made an accessory table from scraps of plywood. It is about 4 inches high. The surface is about 6 x 17 inches. I use it for a variety of things, including holding work while I use a drill chuck on the right end of the arbor for special drilling operations. The table has a flat surface on its bottom so I can clamp it to the saw table.
Any horizontal arbor would work if you do not have a radial arm saw. But, there will be some things about this process that will rely more on your eye and less on the guidance provided by the table.
Step 3: Raise or Lower the Saw Arm
Raise or lower the saw arm so the center of the shaft is at the same level as the center of the tube. When you grind a profile in the top of the tube, the same profile will be produced in the bottom of the tube. That is the key to coping the tube end for the tube to which it will join by welding.
Step 4: Use Masking Tape
I use masking tape to mark something I want to cut or grind. It makes something very easy to see, despite the bright sparks and (normally) dark metal against a dark stone. Wrap a little masking tape around the end of one tube.
Step 5: The End Goal
The end goal will be to cut a profile in the end of one tube so it very closely fits the contour of the other tube's side.
Step 6: Mark the Profile
Use a marker pen to outline the desired profile on the masking tape. Do not worry if you cannot accurately draw the whole profile.
Step 7: Start Grinding
Start grinding. You are guiding the process by your hand and eye while the tube rests on the accessory table. Go slowly. Try not to roll the tube, but to keep pointing up the same part of the tube that was upmost at the start of the grinding process.
Step 8: Check Your Work
Stop frequently to check your work, especially as you are nearer to completion of the task. Here you can see quite a gap. More grinding is needed on the two shoulders. Go slowly and check often.
Step 9: Finished
Here you see the two tubes fitted together ready for welding or brazing. The fit is almost as good as a machine designed for this job might do. Obviously, this is not for the demands of production, but it works well for an occasional project at home. Any small gaps can easily be filled by the welding or brazing process.
With some care, you could use this process to cope tubes that will meet at angles other than 90 degrees. Some extra planning would need to go into your setup.