Issue: The four wheeled AGV frame consists of machined horizontal and vertical 1″ x 1″ 16 gauge steel tubing pieces welding together. In addition the vehicle platform has four vertical 7/8″ x 7/8″ x 3″ tubing stubs at the platform’s corners that insert tightly into the four 1×1 vertical frame sections of the two side assemblies.
A key manufacturability requirement is that the four vertical 1×1 tubing pieces are welded into the side assemblies as parallel as possible to one another. Otherwise, the platform’s stubs will bind when inserted 3 inches into the tops of the 1×1 verticals. The use of welding magnetics and vice clamps doesn’t guarantee parallelism and slows the welding setup process considerably.
Solution: To address this issue, I fabricated jigs, described below, to help ensure parallelism.
Each of the 2 identical jigs includes two 7/8″ round stock steel bars cut to 3″ lengths with ends milled square. The inside dimensions of the 1×1 tubing is presumably 7/8″ x 7/8″ but the fit with the 7/8″ round bar stock was still too loose to ensure parallelism. Therefore, I knurled 1/4″ of both ends of the round bars providing the tight fit required. Then the ends are drilled, tapped and screwed at the ends of spare 1×1 tubing at the correct distances (20″) required for the vehicle side assemblies.
The two jigs are inserted into opposite ends of the four vertical frame pierces and perpendicularity of the vertical frames to the base spare 1×1 tubing is checked to guarantee parallelism of the verticals.
Finally, the jigs with verticals are laid sideways and clamped on top of the top and bottom horizontal frame pieces between the verticals and the welding table to ensure parallelism in the orthogonal direction as well. Welds are done inside the two ends of the bottom horizontal tubing through 1/4″ wide slots cut in the wall of the bottom tubing in connect with the vertical. As was done for the front end of the top horizontal tubing and top of its vertical.
For the weld of the top horizontal and top of the back vertical the weld had to be do inside the top end of the vertical with the welding slot cut in the vertical instead. This is because the top horizontal tubing extends another 6″ beyond the vertical to provide for the motor mount at the rear of the AGV. Inside welds eliminate the need for grinding and interference of welds with the guards and generally improve the appearance of the AGV.
Leave a Reply