Fabricating Stainless Doorsills - Fresh Entry

I started the project by making a paper pattern (arrow) of each of the original sills. After comparing similarities and differences, and figuring out rough dimensions, I traced the patterns onto a sheet of 0.048-inch 304 stainless steel and cut them out using a vertical bandsaw.

To form the radius along the top of the sills, I removed the rear and front fingers from the sheetmetal brake. After figuring out the amount of offset needed for using the 5/16-inch radius fingers in the brake, I formed the longest bend first, along the narrow length of this sill. I used a “0” torch tip to heat the inside corner to a glowing orange while slowly bending up the sheetmetal, to keep the radius from kinking.

The brake is limited in how far the radius dies can form over center, so I used the 5/16-inch radius T-dolly, clamped inside the radius, and a body hammer to slowly finish forming the edge over center.

I then swapped the rear and front brake fingers from right to left to form the shorter forward portion of the sill, which flares out wider toward the front of the sill. As the angle of the radius changes, the sheetmetal was once again heated while being slowly bent, which allowed the metal to shrink at the inside angle.

To duplicate the step bead from the original sills, I marked a measurement of 3/4 inch from the outside of the radius to the point where the step bead would begin. I also measured and marked how much offset would be needed to clamp to a straightedge while installing the bead detail, which was an additional 1/2 inch.

To straighten the inside corner where the radius bends, I clamped the wide end of the sill to the bench along with a 5/16-inch radius T-dolly inside the newly formed radius (arrow A). I heated it with the torch and slowly pulled down on the longer leg (arrow B) until the piece was straight.

It is important to pre-stretch the sheetmetal before forming the bead in order to keep the sheetmeal from distorting in the Pullmax. I used a linear stretch die flipped parallel with my straightedge; the small contact patch helps pinpoint the area for the bead.

I used a flat-top die with one edge ground flat, which is engineered to match the 1/2-inch offset of the upper step die for the Pullmax. This centers the contact patch of the die exactly at the location of the step bead and increases the accuracy of regular pre-stretching using the straightedge (arrow) as a guide.

After pre-stretching, the part was already naturally starting to take its final form. Here, the sill is flipped over and you can see the slight form beginning.

I made slow, multiple passes on the P9 Pullmax to form the step bead detail. When installing bead details, always set the machine to the shortest stroke to prevent hard-to-remove tool marks on base materials. After every pass, I raised the bottom die approximately 0.050-inch (about one turn of the handle) until the desired depth was formed.

You can see the amount of deep forming that is possible with a Pullmax, which would be nearly impossible to accomplish on stainless with a bead roller.

I noticed some irregularities in the gap along the bottom edge of the original sills, so I made a 1/8-inch plywood pattern to accurately transfer the radius from the top of the rocker to the new stainless steel sills.

When transferring the pattern to the sheetmetal, I added 3/16 inch of material along the bottom of the sill and cut out the sill radius with a band saw. The cut edge was finished with sanders and files to smooth out the cut line and remove burrs. This step is the most important because any irregularities along that edge will affect the consistency of the bend while forming the piece in the steps that follow.

Here is an original sill (left) next to the new sill. Notice the radius along the top edge of the sill and the 3/16-inch 90-degree bend along the bottom. The straightedge next to the new sill highlights the sweeping radius from front to back.

[B] [A] The extra 3/16 inch needed to be formed 90 degrees using this machine. It’s an Erco former and flanger, which works like a leaf brake, with a brake plate tool (A) that oscillates in tracks in the frame, at as much as a 95-degree angle. I had a 3/8-inch 90-degree hold-down tool that I machined down to a 3/16-inch 90-degree hold-down tool (B), and used the 3/8-inch brake plate tool and adjusted the machine to maintain proper alignment to create the angle. After every pass, I slowly raised the brake plate tool two turns (approximately 0.060-inch) until a tight consistent 3/16-inch 90-degree bend was formed along the bottom of the sill, following the radius from front to back.

[B] [A] The extra 3/16 inch needed to be formed 90 degrees using this machine. It’s an Erco former and flanger, which works like a leaf brake, with a brake plate tool (A) that oscillates in tracks in the frame, at as much as a 95-degree angle. I had a 3/8-inch 90-degree hold-down tool that I machined down to a 3/16-inch 90-degree hold-down tool (B), and used the 3/8-inch brake plate tool and adjusted the machine to maintain proper alignment to create the angle. After every pass, I slowly raised the brake plate tool two turns (approximately 0.060-inch) until a tight consistent 3/16-inch 90-degree bend was formed along the bottom of the sill, following the radius from front to back.

Sometimes the most effective tools are the least expensive. I added a slight overall curve to the piece, using a block of wood and a little downward pressure—moving the part left to right to maintain consistency.

The leading and trailing edges of the sill were mocked up and trimmed for a good fit. With the test-fit a success, I taped along the top of the rocker panel and marked the location of the mounting holes on the inner sill structure (see the second photo of this story), then transferred the lines on the tape to the new sill to get the proper locations for the screw holes.

I transferred the holes, using the originals as a guide, and with the marks made from the tape in the previous photo. I drilled 1/8-inch holes and de-burred them with a counter sink bit.

The stainless sills were sanded with a DA sander, starting with 180-grit, followed by 320-grit to remove all sand scratches. I then blocked the sills by hand with 180-grit and finished with a maroon abrasive pad. It is important to sand all surfaces before stamping the screw hole bead detail because it is nearly impossible to finish that area uniformly after forming.

[A] [B] To create the countersunk mounting holes, I used the lathe to machine a male (A) and a female (B) die for the Pullmax, which were aligned with an 1/8-inch pin in the upper (male) die. I made a few test stampings with the dies before welding them to the shafts. I used test pieces of aluminum and stamped it in a vise to check for proper material clearance, and fine-tuned until there were no tool marks and the screw bead detail accurately matched the originals.

Now I was ready for the sills. Working my way from one end of the sill to the other, I inserted each previously drilled 1/8-inch hole into the alignment pin on the upper die and slowly raised the lower die, stamping the screw bead detail into the stainless steel.

Here are the shiny new stainless steel doorsills compared to the originals.

You can see the amount of accuracy that is possible when duplicating a part from scratch.

Notice the stamping detail for the screws and the good-looking matte finish of the 0.048-inch 304 stainless steel. Take another look at the opening photo on page 88 to see the finished passenger side sill on the project Dodge. What an improvement.