Hello everyone, I just thought of this one the other day. It's probably one of the most basic of things that most fabricators learn at the beginning of their careers, so it could also be overlooked fairly easily too. Whenever an item requires a series of parts to be laid out on a specific spacing such as the rails for handrails or rungs on a ladder or other similar such items, it is usually simpler and more accurate to make these layouts using a running dimension and also lining up the parts, edge to line.
An example: a simple ladder made out of 1-1/2" tube steel. Let's say the ladder is 5'-8" tall and the rungs are 1'-6" wide, the first rung will probably be located on a 1'-0" center above the ground line and then each additional rung will be 1'-0" away from the other one until you reach the 5'-0" mark, thus requiring 5 rungs for this ladder. To begin the layout you will generally find the center point 1'-0" away from the end of the ladder side rail, once this point has been located you can either go 3/4" less than this dimension or 3/4" more than this dimension and draw a line across the material, this is the edge that you would line up the edge of the rung with. If I drew my line at 11-1/4" I would put an X on the side of the line that would be greater than this dimension and that is the side that I would locate the rung on. If I put my line at 12-3/4" I would put an X on the side of the line that is less than this dimension and that is the side that I would locate the rung on. After I had located the first mark at either the 11-1/4" or the 12-3/4" point I would use this mark to layout the rest of the lines for the additional rungs. I would put my tape's 1'-0" mark on the first line and then at the 2'-0", 3'-0", 4'-0", and 5'-0" points I would put the other marks on the ladder side rail. Once I had completed this process I would take the other ladder side rail and put it side by side with the rail that I had just marked and transfer the marks across the one rail to the other one. I could then proceed to line up the rungs with the marks on the two side rails, pull them into place with some furniture clamps or similar holding devices and then take a diagonal measurement from corner to corner from both sides of the ladder, shifting it until these dimensions were the same and proceed to tack it together. Once I had tacked it, I would most likely use a piece of scrap material tacked diagonally across the two rails to hold them in position while I welded it out.
When you did the layout for the side rails you would NOT want to make your measurements with a 1'-0" rule measuring from one layout point to the next, as you could accumulate a lot of error this way. Hope this made sense and that someone might be able to use this process to help them out. Regards, aevald