Hello everyone, a lot of the time fabricators are required to assemble frames to any number of sizes and specifications. Sometimes it makes sense to setup the first frame and then use it as a fixture/jig to fit additional frames. A lot of the time these frames might be built on sawhorses, tables or other supporting structures. One of the first considerations for the fitter/fabricator is to properly level the pieces to ensure that the finished frame will be flat and free from twist. Personally, I generally level the two longest pieces of the frame and then fit the rest from there.
     This is where my comments might seem just a bit strange so please bear with me. If you "level" the two long pieces so that they have the same amount of levelness, or out of levelness, you can still build a flat frame. They could be tilted upwards in either direction from level as long as they are both tilted the same direction and amount and not opposite directions from one another. Hope that this statement makes sense and is readily understandable.
     In the photos of the example frame that I have included with this post, I have used plates clamped to the ends of the long members. I have then rested the short cross pieces on the surfaces of these plates and used additional clamps to secure them on the same plane/level as the other long members. You might additionally use bar clamps, comealongs, or other types of clamping systems to bring the corners together to hold everything in it's correct perspective. A squaring process is generally implemented at this point, diagonal measurement from opposite corners of the frame will usually provide the most accurate squaring information. Sometimes a corner to corner measurement is difficult based on how the corners are clamped or otherwise restrained. You will notice in one or more of the pictures that there are +'s that are circled in red just back from the corner on both ends of the two longer pieces. These are reference points that allow squaring to take place based on their location and not the actual ends of the frame. This is a common practice for many applications.
     Once you have gotten your pieces leveled, roughly squared, and otherwise checked for dimensional accuracy you may need to use either 1 or 2 comealongs or other types of pulling/pushing aides to further bring the frame into square. If you are using 1 aide it is generally going to pull the longer diagonal measurement in to allow both diagonal measurements of the frame to be the same and thus the frame is square. If 2 aides are used this serves the same purpose, yet the second aide will keep the frame from moving out of square as welding is introduced to complete the fabrication process of the frame. Snug one, loosen the other, and finally a bit of tension on both of them will keep it from getting out of square. I have not shown this process in the pictures as my example is "scaled down" mock-up.
     Hope this might be of some use to those of you out there that face this sort of challenge and possibly haven't been around a lot of it. For those of you who have, I hope that you might share your thoughts comments, suggestions, and possibly pictures to further expand this topic. Best regards, Allan