Welded square tubes can be welded in a conventional manner, 45 degrees requires one lap weld, one fillet weld and two plane welds. 2. No preparation is required prior to the fillet and lap weld positions, only the removal of rust, dirt or debris from the weld area. 3. Before performing two plane welds, the metal needs to be cleaned and bevelled to ensure weld penetration. 4. When cutting square tubing, make sure each piece has a 45-degree angled end, using a band saw set for a degree miter cut. 5. After cutting use a sander to remove burrs and bevel the edges of the cut 45 degree angles. 6. Place the square tube in the work area with the miter cuts facing each other, leaving a 1/16" gap, and use a straightedge to make sure the angle is 90 degrees. 7.Before switching on the welding machine, ensure that all welding equipment is worn. Apply spot welds to the inside corners first, continually checking with a right angle ruler to ensure the angle is correct, then apply spot welds to the faces and 45 degree miter cuts. 8. After completing the spot welds, weld the back corners of the square tube starting at the top and working downwards, then flip the tube over and weld the other side. 9. Apply flat welds to the 45-degree miter cuts, welding from the inside corner to the outside corner. 10.After all the welding is done, grind the corners to get perfect 90 degree square tube corners.