Last weekend I attended Ron Covell's "Extreme Metalshapinig" class. I thought I'd share some pictures and some pointers I picked up. The class was hosted by Cotati Speed Shop. I've seen their work, and it's always beautiful, their shop was very impressive too. First class operation. The plan for the class was to see a scaled-down 37 Ford-style fender and flush-fit skirt fabricated from scratch. Without giving it all away in the first breath, let's just say that Ron didn't disappoint!
Ron began by explaining the "basics" of metal shaping, having been to other metal shaping workshops before I have to say Ron got the key information across with no muss and no fuss. In a nutshell, there are only 2 things that you can do to shape a piece of metal: shrink it or stretch it. Folding/bending will change the geometry of a part, but it doesn't create "shape" -- compound curves. Ron explained it better than I can, and he had a couple of good visual aids to make the point. With that out of the way, Ron talked about the project for the weekend. For the workshop he used a combination buck/hammerform that he had constructed. He also spent time explaining how you could make a flush-fit skirt without a buck, to fit an existing fender. He talked about the important details of the buck construction, and alternate approaches. One of the keys to developing the bucks he used for the fender and skirt is planning in the correct clearance between the edge of the fender opening and the edge of the skirt.
Why is this both a buck and a hammerform? A buck is just a form that describes the shape of a part so that you can shape metal to fit it. It could be made from sheetmetal sections, wood, steel rod and probably 100 other things. A hammerform is a rugged form that you hammer the metal over (or into) to actually create a shape. The buck Ron made includes steel inserts which are used to directly form the edges of the fender opening and the skirt opening after the metal is shaped to fit the buck. You can see the steel flat bar around the fender opening, and if you look closely you can see some 5/8" round bar that is used to form the bottom edges of the fender.
One really important point Ron talked about (it was important for me, because I forget to think this through sometimes when I make a paper pattern for a shaped part) is to make the pattern accounting for how the part will be shaped. I don't have a good visual, but I'll try to describe it. On this fender, if you make the pattern for part of the fender by pinninig the paper to an edge of the buck (say the fender opening) and then pull it down to the top edge you will have to form the part my shrinking the top edge severely, pulling the metal down in the same way. If you pattern it by laying the paper against the high point of the shape and pulling the edges down to meet the top of the fender and the wheel opening then you can shape the part by shrinking booth edges and stretching the middle. That way the shaping work is spread "evenly" across the panel.
Here Ron is using a Lancaster-style shrinker to, well, shrink the edges. You can see the blue lines on the part, this is the area Ron intends to shrink. Ron also talked about how to divide the part into separate panels for shaping, and the pros/cons of putting the seam(s) in different spots. For this fender he's making it in two parts (not counting the skirt). If you have less experience/confidence you might make it in 3 parts.
After about two passes on the shrinker on each edge Ron test fit the part to the buck. What he's checking is not that it fits the buck at this point, but he's trying to judge whether he's done enough shrinking. Looking at the angle of the edges he deemed it far enough. Also, look at the white board in the background. See the diagram in the bottom left whith the green marker? That is a cross section of the fender (in blue) showing how the metal will be progressively shrunken on the edges and stretched in the middle to shape the part.
After shrinking, Ron used an English Wheel to stretch the middle of the panel. You could also do this part (the stretching) using a ball-faced mallet and sandbag. The advantage of the wheel is that it reduces the amount of metalfinishing/smoothing later and it's not as hard on the joints.
Here is a great e-wheel tip: Cross up your wheeling patterns. Think of it like block sanding. When Ron and I wheeled the top insert for my Stude pickup (on the "Chopping and Sectioning" video he sells) we did that and it really helps maintain a smooth surface and an even shape. The first pass on this part Ron did at about 30 degrees to the long direction. This is the second pass, crossing the first pass at 90 degrees. Also, you want to use the flattest wheel you can that will fit the curve of the panel you're making. More sharply curved wheels shape faster, but they also leave more marks (tracks) in the part.
Here is the third angle of attack on this part, side to side across the short dimension of the panel. If you compare this wheel with the one in the first e-wheel picture you can see he's moved to a flatter wheel (because it fits when wheeling in this direction). He's also blending into the shrunken areas along the edges. The shaping process involves repeated checking of the part on the buck to make sure everything is moving in the right direction. When you find an area of the panel hitting the buck either it needs to be raised (wheel it) or everything around it needs to be shrunk.
If you over-stretch a small area it is possible to "cold shrink" it by working it with a slapper over the buck. You'll probably put in some kinks in the process, but they can be worked out with a little careful hammer/dolly work. Just make sure you don't stretch it again!
Ron fit both panels to the fender buck, and scribed a line where they overlapped. The bottom panel was trimmed on this line, and the two panels were tacked together. Ron went into a lot of detail about the proper fit and welding technique. He TIG welded the joint, then used an air planishing hammer to smooth the weld. There was almost to weld bead (maybe 1/2 the thickness of the base metal?) and the weld hammered out perfectly flat and glass smooth. This planishing hammer is one of Clay Cook's "Proline" tools, it's really a nice piece.
Ron did some wheeling and hammer-and-dolly work to make sure the transition (the takeoff) between the panels was a smooth curve. He also tuned up the edges of the fender. He fit the fender to the buck, and scribed a trim line around the perimeter. The trim line is offset from the edge of the buck to leave the right amount of metal for rolling the edges over.
Here is a close-up of the hammer forming process. Ron was careful to select a hammer with a face that fits into the curve of the opening.
There are two things to take note of in this picture. First Ron is using wood blocks to clamp against the outside of the fender to keep from marring it. More importantly, notice that on this tightly curved flange he started by forming the ends first, then he moved on to the middle. Rolling the ends like this locks the edge in place so the edge of the fender doesn't deform as he forms the roll.
Next Ron moved on to a very detailed explanation/demo of "metal finishing". This is a process where all of the lumps and bumps are smoothed out so that the fender is as smooth and true as possible. A key point is to be able to solidly position the fender so that it doesn't move as you work on it. You can't do good work if you're chasing the part all over. Ron has the two back edges clamped solidly to the bench, and two sandbags holding it down. This process depends on several factors -- being able to "read" the panel and identify what needs to be changed (low spots and high spots). It also depends on proper hammer and dolly technique and know the difference between on-dolly and off-dolly hammering (and when to use which one) (the book by Frank Sargent "a guide to metal bumping" covers this pretty well as I recall. Eastwood used to sell it)
The wood clamp strip made a few indentations in this area of the fender. Ron started by hammering off-dolly (holding the hammer tight against a large low spot and tapping down the surrounding high spots. In some cases where there was a low spot in a neutral area Ron would hammer on-dolly (you can tell because of the distinctive ring of the hammer hitting the the dolly through the sheetmetal)
Once Ron had the lumps that he could feel worked out, he used a body file ("vixen file") on the surface. The point of this is to find any remaining low spots, not to file the metal smooth. He makes just enough passes with the file to show up any problems, then it's back to the hammer and dolly.
Here you can see the first area Ron is working on. The areas the file didn't hit are low, and he will hammer on-dolly in these areas to raise them. Knowing how much to hit each area to raise them enough is an experience thing.
The process is hammer on-dolly to raise the low spots, file again to see if you missed any and hammer again. Ron worked across the face of the fender, and I think there was only one area that wasn't just right on the second filing. You can also use a "bullseye pick" to raise small how spots, but with the fender clamped to the table there isn't enough room.
After the work on the fender, the skirt went REALLY fast. The shape is very low-crown, so no shrinking is required on the edges. Ron use the flattest wheel available and made I think 3 passes, changing his angle of attack each time.
Ron marked the surface of the skirt to show his plan for wheeling the skirt. He had the shape into the part really quickly.
Here is the outside of the finished fender and skirt. Ron only metal finished a 3" strip around the wheel opening, on a customer part of course the entire fender and skirt would be metalfinished.
Here is the back side of the fender and skirt. Ron talked about different ways to mount the skirt, for the purposes of the demo it is just tacked to the fender.
And that's pretty much it. Two intense days of metal education. I got to meet some cool guys in the shop (Kent Fuller was one of the workshop attendees!) For what it's worth, I've been to most of the seminars Ron offers, and I've also taken workshops with Fay Butler and Scott Knight. Even with that as background I picked up several good pointers in the class (not to mention that I'm totally inspired to tackle a couple of shaping projects I've had in mind), it was a great time and I'd highly recommend it. If you can't make a workshop, his DVDs are really helpful too.
The Jalopy Journal
