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jcarpenter 01-19-2021 10:00 PM

Newbie needs advise
2 Attachment(s)
First off I am an almost complete newbie. I want to fabricate two sided 3D fish in sheet metal. There will be two sides with opposing direction crowns that are placed together and the perimeter where they touch is welded together.

My shop has a Kent White air powered hammer and a home built English wheel. Plus normal metalshaping hand tools. I use the air hammer to stretch the fish shapes.

My problem is that I am having trouble shaping two similar sides of the fish that can be welded together.

As a practice object I have a symmetrical teardrop shape that I am using to simulate a fish body. See first photo. I have successfully shaped two circular bowls of the same size and welded them together. I have not been able to shape two sides of a teardrop shape that have a border capable of being welded. The edges warp to the point that the two sides will not close the gaps necessary for welding. See second photo. I use paper templates in the transverse and longitudinal direction to gauge the amount of crown developed.

So what am I doing wrong? I do not know how to read the warpage in the teardrop shape to know what to avoid or what corrective actions are necessary. I have been semi able to correct the warpage by backing up and using a blocking hammer with a sand filled bag to beat the shape back into submission. And then I planish on the air hammer and then stretch again until the warpage becomes too much. Any suggestions?

Attachment 58647

Attachment 58648

Jaroslav 01-20-2021 01:52 AM

I would shape where the sheet bends the worst place. In that narrow place. When it starts to take shape, do the rest. You can bend it with your hands over the edge of the table or step on the part. This will show you where to shape.
Learn to stick templates. The paper will show you where to shape.
Maybe my thread will help you.
Work so that the plate is still soft. If you make a basic shape on a sandbag and then smooth it out on the EW. Or a rubber tool.

If you don't have machines, you can use a comb hand press with some household tool for basic contours. You will send another photo.
Everything is in your head - hands and machines only after then.:)

Ron Naida 01-20-2021 05:07 PM

I might try shrinking the perimeter edges downward.
This should cause the center to want to crown up a bit.
Once you have the perimeter shrunk it is then easy to
use a mallet to raise your center.

Or switch back and forth.
Do you have a means to stipple shrink or tuck shrink?


mark g 01-21-2021 10:33 AM

Hi John,

If your form is to be symmetrical, you could hammer each half through a "plywood" cut out. (Substitute material of your choice for plywood). You would get a two flanged halves that you could trim and weld.
If your form were to be asymmetrical, your "plywood" would also have to be curved as you wish your form to curve. Weathervanes can be made this way.

When I work free hand without aids like the plywood, I prioritize work this way: Identify the shapes within the form first, remembering that a simple bend should not be mistaken as shape. A straight edge won't lay flat on a crown, so that's useful to know, but it will lay happily on a bend, and could lay transversely on a reverse. I like to put reverses in next, since I find an advantage to starting them in a flat sheet, and they contribute to the work needed to make the crowns. Fill in around the reverses with crowns lastly. There will be some back and forth to adjust and fill out the form, but by working "hammer and dolly" with an "off dolly" approach you can adjust areas that need it readily with a little practice. When a gap appears at the weld-line in a reversed area, try reversing it more in that area; or in a crowned area, by crowning it more, causing the edge to drop closer to the weld line in each case. A lengthier description may be needed here, since various methods will produce similar results in different hands.

I made a bird body once by shaping both halves at once, by pop riveting two metal pieces together and shaping until they would lay flat on the table, then popping one of the two pieces inside out after the two were separated then welding them at center. It worked ok, but I never did it that way again:)

Ballantino 01-21-2021 12:32 PM

As a newbie myself, I highly recommend doing an advanced search, "find threads started by user" and search for Mark G and Jaroslav (to start). They do an excellent job with pictures and descriptions. It has helped me along tremendously.

metalmarks 01-21-2021 01:51 PM

Quoting Mark G, "......remembering that a simple bend should not be mistaken as shape. " Meaning that the entire piece doesn't need the same amount of shaping. As Jaroslav suggested, a paper template will show you what has to happen, and where.

jcarpenter 01-21-2021 02:47 PM

Wow, thanks for all the replies!

Jaroslov: Yes, back to basics I think you are saying. Think I will get the form roughed out in a stump or bag and leave the machine work till the end.

Ron: I have an HF shrinker only. Not concerned about finish as these are learning pieces. I will try the edge shrinking and see how that goes.

mark g: I am going to have to study your response for a while and see if I can get my head around it. BTW your stuff is awesome.

Ballantino: Yes, I have been searching everyone who does fish. Not so many do two sided stuff. My real problem is that I have just not made enough stuff to know what I am doing. But that is half the fun!

metalmarks: Used flexible shape patterns in the past but have just started using paper and those cool magnetic pushpins. I used paper on one of the pieces that went completely bonkers trying to see where the stretch actually was and if stretch areas corresponded to warp.

jcarpenter 01-21-2021 04:59 PM

mark g:

Reread your post and looked at the link. I understand now what you are doing. I have exactly the problem you show in the link where the weld line of the two halves do not meet without gap, And changing the gap also changes the overall shape. Not simple to fix I think

mark g 01-21-2021 07:45 PM

In the picture of the frog sculpture where the halves don't meet, the gap was intentional and planned. That design uses another metal piece to cover over the centerline gap to hide it. If I wanted the gap to close though, I would have had to start with a bigger blank with extra metal at the edge to fill the gap. If I'm unsure of the shape, I start with plenty extra to begin with, and trim it away as soon as I safely can.

Your fish form will have some reverses where the body transitions into the tail section, even if the body is straight head to tail. Much more so if in a swimming pose. I find those shape very manageable and fun when approached as described previously. This sunfish is one-sided, and turned to hide the open back. No significant reverses because of the back flipping tail, but the opposite side would have a big reverse. The fins were fun to make.

mark g 01-21-2021 07:56 PM

Looking at your teardrop again, brings up an interesting point. If your contour lines form concaves as they travel along, they describe reverses and if they are straight they are bends, convex are crowns. I'm guessing that that form doesn't need much shaping at all in the narrow end; it's mostly bending.

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