Model t Frame Dimensions
With your frame sketch in hand, you can head out to the shop to begin turning your dream into reality. What this chapter will be showing is the fabrication of a "ladder frame", which takes its name from its straight rails on each side, and a series of steps or crossmembers to keep those side rails stable and square. This frame style is a staple of hot rods going back to the early use of Model T frames for souped-up bombs from the 40's and 50's.
Using the scaled measurements on your plan, you first cut the side rails and the two elements of the rear kick-up, commonly referred to as a "Z". I am using 2" x 3" 1/8" wall rectangular steel tubing for the frame shown here. Tubing size will depend somewhat on your choice of engine, the horsepower you intend to create, and the amount of "X" member or "K" member support you intend to include in the frame design. There are instances of builders using smaller 1 1/2" x 3" tubing for lower horsepower engines and 2"x4" or even larger tubing for higher horsepower applications.A 14" chop saw is used to cut the tubing pieces, which keeps the ends fairly square and true. The basic tubing pieces for the frame rails are shown in Photos 2-1 and 2-2.
Creating a front frame hornAlthough it isn't absolutely necessary, a more traditional look for the frame rails can be achieved by creating what is known as frame horns at the front. This frame shape is found in many stock frames from the 20's and 30's and makes the home-built chassis stand out from typical square-cut tubing corners.
To create the front frame horn, first draw a pattern on heavy paper stock (Photo 2-3). You'll have to experiment a bit to see what looks proportionally correct for the tubing size you use. Then, cut out the pattern and transfer the outline to both sides of your tubing (Photo 2-4).Then, cut the tubing. A 4 1/2" grinder with a thin-blade cutting wheel works well for this task, but other cutting tools, like a metal-bladed saber saw, can also be used. Your frame horn should look like Photo 2-5 after you slice it up. Use clamps and some hammer work to bend the top piece of metal over the curved side sections, and then tack weld it in place. You will also need to cut a small section of sheet metal to piece in at the front tip of the horn, to round it off and fill in the gap shown in Photo 2-6. Photos 2-7 and 2-8 show the frame horn after welding, grinding smooth and applying a quick coat of primer to protect the metal from rusting as fabrication proceeds. Speaking of grinding the welds, you will note throughout the chassis fabrication the welds are ground as we go. That is not mandatory. Some builders, who are excellent welders, do not grind and smooth their welds at all, leaving them as testament to their craft and workmanship. Or, they simply prefer the look of a welded seam versus a smooth seam. This is totally up to the builder's personal tastes. However, if you leave your welds raw, it is highly recommend you wire brush them immediately and then apply a quick primer to prevent oxidation. And if you do intend to smooth all your weld joints, it is best to do your grinding immediately. There is nothing more dreaded than staring at a week's worth of weld grinding. By doing your grinding and smoothing after each small section of welding, you break that loathsome job into lots of little pieces, making the task much less daunting.
Assembling the side rails
You are now ready to weld together the side rails. Be aware, however, that frame rails are subjected to a good deal of stress, both from horsepower loading and from road conditions. You don't want your frame cracking or actually breaking apart due to these stresses. To make your frame more stable, you should go beyond simply butt welding the frame pieces together. This can be done through the use of hidden gussets to reinforce the critical joints of your frame.