Making a Rubber Faced Top Die for the Powell Hammer
It is difficult to make a straight, even highlight line just following a line drawn in the panel when running it through the hammer. So, I worked on a system to keep the line straight and even and allow ease of running it through the hammer. I cut 2 lengths of 18 gage steel and bent them 90 degrees to form angle bars. I then curved the angle bars to fit the test panel. I am simulating putting a highlight line down the middle of a high crown fender. So I formed a sample section of a fender to test the channel fence. I also made a second insert with a 24" radius to match the curve of the fender panel.
I then cut the sides of the die to the 2.250" square dimensions of the Powell Hammer dies. I cut the 70A hard rubber face to fit the recess in the face of the die and fit checked it. I decided to carbonnitrated (case harden) the mild steel die. It isn't necessary but my thinking was that I wanted the wedge that is used to hold the dies in the hammer to be sacrificial and not the die. In other words I wanted to keep the dovetails from wearing over the years as the die is inserted and removed from the hammer. The carbon nitrate process leaves an oxide (rust) on the surface. It is also expensive...more than twice the cost of the vacuum hardening I have done on the S7 tool steel dies at the same facility. I wouldn't recommend case hardening the die now that I have done it.
I turned the blank out of mild 1018 steel round bar, then cut the 10 degree dovetails to hold the die in the hammer slide. The recess in the face of the die is 0.250" deep and I will use a 0.500" thick rubber face which leaves 0.250" of the rubber face proud of the die.
The 2 angles were tacked on to the inner section of the fender to form a channel that the insert in the lower die could ride in and follow. A quick but soft run through the hammer with the rubber top die resulted in a straight, even and crisp highlight line down the center of the simulated finder section. I am happy with the system and the result.
I machined a die holder that accepts an insert that can be used in conjunction with the rubber face upper die to set a highlight line in a panel. The die holder is machined from 1018 mild steel and the insert is 1.5" X 1/4" mild steel bar stock. A smooth radius is used on the insert to form the line. Different inserts with different radii can be used as needed for the shape panel being formed.
A sample highlight line was formed here on 18 gage steel using the rubber faced upper die and and insert shown in the die holder. Just like everything on the power hammer, this will take practice and some trials to get the line straight and even. I plan to play around with several different inserts and will probably look into a fence for the hammer to keep the line straight. We'll see what works best.
This is the high crown shape I raised in the test. It only took a few passes and very little time. I didn't shrink the edges or planish the surface. This is what the test material looked like as it came out of the hammer.
My thoughts on the rubber faced upper die is it's a very useful tool but care must be taken when using it. I believe it should only be used with high crown shapes and only to set the shape...it is a very aggressive tool and with just a little too much force can over stretch the work quickly.
I used a 3M 1838 B/A Green 2-part adhesive to secure the rubber in the die. After a 48 hour cure, I tested the die on 18 gage steel with a 3" radius lower die first and then a 6" radius lower die to smooth the shape. The rubber die with the high crown lower dies are very aggressive and care must be taken not to over stretch the material.
Copyright © Jack Pledger