Shrinking with a Stump - by Richard Crees
Original content provided by Richard Crees - aka - TheRodDoc
~ Working With A Stump ~
This is my main stump. I have three, and with this stump almost any shape can be made without the use of tucking forks or hand tucking, and made quickly at that. Seems to be a lot of confusion when I say I seldom use hand tucking. I put this tutorial together to show that you can shape metal without hand tuck shrinking. It should be plain as day that I do shrink and stretch to make any panel for a car, I just do it different than those of you that think hand tucking has to be the only way to shape sheet metal. It's not, and to me it's the least favorable method at that. In the past four years many have discovered the helve hammers. Well this is a very simular method of doing the same thing, only it's done on the stump. The main difference is that with the stump the amount of stretching can be cut way down to a minimum. If stretching is needed it can also be done quickly on the stump. To start with I will mention that the main hollow in my stump is cone shaped rather then a half hemisphere shape. This gives straight flat sides to hammer the wrinkles or tucks flat against. The sheet metal isn't hammered down to the shape of the hollow. The hollow is used mainly to do the shrinking needed to form the part you are making.
In this picture I have laid the sheet on top of the hollow with one edge of the sheet along one edge of the hollow. I then hit the sheet once with a large heavy wooden mallet. This causes a wrinkle to appear from where I hit to the edge of sheet. While the sheet is there that wrinkle can be hit from the inside point first to flatten it. It won't spread out like a hand formed tuck will. It is trapped by the force of the mallet hitting it and the stump hollow. Just hit it head on straight against the side of the stump hollow two or three times and its done.
As you can see I opted to make another wave or tuck by moving the sheet over some and hitting again next to the last hit rather then hammering the wrinkles down at that time.
Now I have made a third hit with the mallet. Another wrinkle formed. Sometimes I smash them when they first appear and sometimes after several are formed. Depends on what I'm making. This will be learned or figured out as you get some time in on using the stump. So far in real time, what I have done so far has taken only 2 to 3 seconds. (the time it takes to hit 3 times)
I have now placed the sheet in position for flatening the wrinkles out. A little better shot of the three wrinkles in this picture.
Here I have flattened out the wrinkles roughly. It can be done very quickly. About another 5 or 6 seconds to do this.
I have made another one. one more blow of the mallet.
This one I have flattened with the next mallet blows. The sheet is slid around in the hollow to change the curve of the sheet and how much traping is needed. After using a stump to shape with for a while, this process becomes so quick and easy that you will wonder why you would do it any other way.
Here is the part after quickly finish hammering out all the wrinkles with the mallet. This finish hammering is done on a flat place on the stump. The finished part is fairly smooth with no marks in it that won't planish out easily. All done in less then a minute in real time. If more shape is needed then repeat the process. The length of the wrinkles and depth of shrinkage into the sheet is easy to vary by just starting inward on the sheet with the first hits. With some shapes, you might want to start a second row out farther so that you get much more shrink at the outside of part. Pretty much anything is possable with this method. For stretching you will use a smaller diameter hammer head, and rest the sheet over a smaller hollow, hitting only hard enough to stretch but not to form a wrinkle, moving the sheet as you do so. Much like doming dies on a pullmax work. The hammer being one die and the stump hollow the other. A modern chopper type rear fender can be roughed out in less then ten minutes this way, ready for planishing. A rear 30's style fender can be finished in around 8 hours using the stump for the main shaping, and the e-wheel for finishing. All with almost no hand tucking.
This is a picture of another hollow I use some. This one lets me form deeper shapes like a rear inner tub for a car. Could also be done on my main stump but this one helps speed it up even more. This one is made up of end grains of oak two by fours. Each one cut to rough length then glued and bolted together. The finish sanded to shape.
When I said sometimes i cut and weld to make a corner rather then mega srinking this is an example of a place I might do that. After the weld it will be flat in the bend areas and maybe peaked at the point at the end of the cut. The point part is shrunk by hammering from the outside. The metal is now trapped so it shrinks easily. Same for the flat part. It is hammered out from the inside to stretch that area. No difference than stretching or shrinking another way. Just much quicker and with less metal fatique then tons of hand tucks that would have to be piled up on top of each other. And in a part like this it would take a bunch of them. Why some of you think this isn't metal shaping I'm not sure. Guess because you don't understand enough about shaping yet. Or it's from seeing someone do it that had no idea of how to do it right. I noticed the man from Tialand that hand made the floor beads with a chisel also did it this way on the steering cover for the VW. He knew how to do a cut and weld the right way. With many more years of experience you will figure it out, or maybe in your short time at learning shaping you have learned only from a very few and are to stubborn to even try to learn from another long time shaper. This will only lengthen your time it takes to be a quality shaper. Try any and everything, you might just be surprised at the outcome. Some shapers might just make the part in two or three different pieces, then weld them all together to get the same part. Thats great. I too do it this way sometimes. Depends on what I'm making. So what's the difference if I put my weld in the corner instead of doing that. But if you are making it from one piece then the cut in the corner is the best way to go. I guess with all the years I have been shaping I make my parts in as big as piece as I can work with. Making a part as large as I can work with cuts down on a lot of the welding and grinding and reshaping that goes along with that, and really shortens the time to make a part. The fact is, I use many different ways to form different shapes. And I know when it is best to use which one. This is what you gain from doing it for a long time. And this is what shortens the time it takes to form a part. And if in buisness doing that the time saved is very important. Learning some of these methods can save you a bunch by not having to buy expensive power tools but still be able to produce a fairly fast output. If it got so I could not keep up with customers demands with my methods then I would go with power tools but for me it just isn't needed now. The cost of a pullmax that you would only use on a few parts a year would take a long time to have it pay for itself.
Original content provided by Richard Crees - aka - TheRodDoc