Last week I tried to beat, heat and straighten a piece of hot-rolled steel plate. Unfortunately, when I finished welding and unclamped the piece it was still warped too much to use. All that cave-man engineering for nothing! Oh well, you live and learn. Deciding to cut my losses, I set aside the weldment and went back to the drawing board (actually my computer and CadKey) and redesigned this component. My original idea was to use the plate as the main structural element and attach the other items to it by welding. I had forgotten how much welding can distort things, and how unstable and prone to warpage hot-rolled steel plate can be.

The new design features a welded square steel tubing sub-frame, upon which an aluminum plate will be attached with machine screws. The tubing frame will act as the mount for all the other components. The aluminum top plate, which is made of 6061-T6 tooling grade aluminum alloy, is very flat and of a uniform thickness. I thought that with proper clamping, careful welding of the frame, and a "balanced" series of welds I could minimize heat distortion and warpage and get a strong, flat frame. And I figured that by bolting the aluminum top to the frame I could keep the top surface flat by careful shimming between the top of the frame and the bottom of the aluminum plate.

The first job was to cut the 2" x 2" x 1/8" steel angle and the 2" x 2" x 11 gauge wall thickness steel tubing into the proper lengths, and clamp the pieces to the top of my welding table. I checked the cross-pieces for perpendicularity and proper alignment by using a steel square and made sure the two long pieces were centered by measuring the diagonal length from corner to corner. When I was satisfied with the alignment, I sprayed the area with some anti-spatter compound, to prevent "frogeyes" (little balls of molten welding wire that pop off the weld and stick to adjacent surfaces) and to make cleanup easier.

The cross-pieces were then tack-welded into place. This does not create much heat, and serves to hold the pieces in alignment when the full strength welds are applied.

The angle steel pieces on the ends were welded in place first. Since there was a little more gap between them and the long pieces of square tubing than I liked, I resorted to "backing up" the weld joint with a piece of scrap brass stock. Molten steel will not stick to brass, and the brass back up prevents the weld from burning through the joint.

The rest of the frame members were then welded into place. I turned the piece several times so that the weld was always applied in the "flat" position. This is the easiest type of weld joint to make. Note that when the piece was oriented vertically clamps and braces were used to keep the piece from falling over - a basic safety precaution.

The next task was to lay out the locations for the holes that the screws would go through. After laying out all 51 holes, the hole centers were punched with a center punch and the subframe was moved to the drill press. The drilling would require several operations:
1. With the top of the frame up, drill a hole all the way through with a 9/32" diameter drill.
2. Flip the piece over and drill through the bottom side of the frame with a 3/4" diameter drill. This would allow the 1/4 - 20 socket head cap screws with washers to be inserted through the bottom of the frame, with the threaded part of the fastener able to go through the 9/32" clearance hole in the top of the frame, where it would be threaded into holes which would be drilled and tapped into the aluminum plate.
3. Align the subframe with the aluminum top plate and locate the hole centers in the aluminum plate using an alignment punch.
4. Drill and tap the holes into the aluminum plate.

Drilling the top side:

Drilling the bottom side:

The piece was then moved back to the welding table, where it was deburred all over:

Finally, everything was brushed off carefully and the aluminum plate was placed face down on the table, The subframe was placed face down on top of it and aligned properly. Since I didn't have the right size alignment punch, I added this item to my shopping list and quit for the week. Next week I'll mark and drill the plate, and work on the conveyor belt rollers.