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  #11  
Old 05-26-2022, 06:36 AM
dwmh dwmh is offline
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Paloma, I have just made an 18" hemisphere from 1.2mm 1050 Aluminum. But I made it in 3 segments (like an orange) as I like gas welding aluminium it is easier for me. I shape the segments by wheeling the centre and shrinking the edge with thumbnail dies (American tooth). If you go silly you will split the edge, but I anneal it if it is getting stiff. The marks left do mostly wheel out.
Doing it in one piece will take an awful lot of shrinking.
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  #12  
Old 05-26-2022, 06:01 PM
crystallographic crystallographic is offline
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Hi Paloma,
Shrinking the circle is harder than straight edges, or curved edges.
I have used "hemisphere shaping" as a challenge in my Metalworking Instruction workshops for a long time.
Not for all beginners - only the precocious.

What happens is this:
The ruffles are evenly spaced all around the circle and made each to the same size.
Then they are all set down, the same way, and to the same amount. Almost exactly.
Like playing scales on a keyboard, all notes must be even in tone and intensity.
Then, Repeat this circle.
And repeat again.
Anneal.
Again with the shrinks.
Etc, until even and circular, and then move the shrinks in further towards the center, going around and around the circumference.

This will teach mastery of this shrinking technique, like few other exercises can.

(As but one example, I know a very good metalman in Sedro Wooley who once made a hand shrinking press all of wood, long ago, which makes the ruffles and then presses them down, consistently and accurately. He understands very well the angles, lifts, and compressive forces for this type of shrinking.)

Some History:

P1110766 c.jpg

The test for a craftsman to work at this very top coachbuilding shop, in Europe, in 1930's .... was to be taken out into the shop and left at a workbench with a complete tool set, with the single goal of making two hemispheres that fit together:

P1110757 copy.jpg

Otherwise you simply practice on getting one-half to manifest:
P1110754 copy.jpg
P1110753 copy.jpg

-end-
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Last edited by crystallographic; 05-26-2022 at 06:19 PM.
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  #13  
Old 05-27-2022, 12:02 PM
BTromblay BTromblay is offline
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Hi,

Dome shaping has challenges but can be done in one piece. I made these two brake drum covers for a 1946 Fairchild 24 aircraft out of 3003-H14 x .040" thick aluminum. I only used plastic tooling and no annealing to make these pieces.
IMG_20220313_104229 (1).jpg
IMG_20220313_104154 (1).jpg
IMG_20220313_104205 (1).jpg

I used my #2 Pettingell power hammer and CP planish hammer to make these parts. But... The principals are the same if using a tucking fork and English wheel. Power tools allow the process to be some times quicker, but not always better.

IMG_20220421_093727 (2).jpg
IMG_20220421_093735 (2).jpg

I recommend you build a buck to shape your part to. On my piece, the part is 11" in diameter and 5" deep. The center area has a 9" radius, that blends into a 6" radius that blends into a 2-1/2" radius at the bottom of the part. The 9" radius at the center of the part I put in by stretching. The balance of the 6" and 2-1/2" radiused areas I shaped by shrinking. I used a dull center punch and lightly marked the panel at every 60degree segment from the center. I used this as a visual reference so that I would put even shrinks into each 60 degree area. With the drilled hole in the center of my part, it would locate on a dowl pin in my wood buck. Consistent part location on the buck and consistent shaping is needed for this kind of domed part. When you place your part on the buck, where the part touches the wood, is the location for the next series of shrinks.

When shrinking with a tuck fork, you need to be sure that each shrink is effective. A practice piece to perfect you tuck process helps a lot.

Hope it makes sense, please don't think that you need fancy equipment to make your part.

Bill
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  #14  
Old 05-27-2022, 08:56 PM
steve.murphy steve.murphy is offline
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Bill,
That came out very nice!
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Last edited by steve.murphy; 05-27-2022 at 10:52 PM. Reason: Spelling
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  #15  
Old 05-28-2022, 01:15 PM
Ducatichica Ducatichica is offline
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I appreciate all the advice this weekend is tucking practice time. I think my challenge at this point is my tucking fork does not reach the center of the 10” diameter. I also brain faded on locking them in. Please let me know if I am correct is assuming smack over at the outer edge then tamp them down in a motion to gather the metal. I have watched a few videos on the utube.
My question do I need to make a stump bowl as I am currently just using a shot bag?

Can a stump me made out of dimensional lumber? Is it adequate or should I shop Craigslist for free stumps
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  #16  
Old 05-28-2022, 03:03 PM
crystallographic crystallographic is offline
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Hi Bill,
Very nice parts.
1 Q ... How thick is finsihed edge?
2 Q ... Any stress corrosion/fatigue towards edge?
3 Q ... (Ranger/Menasco engine in this Fairchild?)

Very good to see this clean accurate work.
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  #17  
Old 05-28-2022, 03:15 PM
crystallographic crystallographic is offline
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Quote:
Originally Posted by Ducatichica View Post
I appreciate all the advice this weekend is tucking practice time. I think my challenge at this point is my tucking fork does not reach the center of the 10” diameter. I also brain faded on locking them in. Please let me know if I am correct is assuming smack over at the outer edge then tamp them down in a motion to gather the metal. I have watched a few videos on the utube.
My question do I need to make a stump bowl as I am currently just using a shot bag?

Can a stump me made out of dimensional lumber? Is it adequate or should I shop Craigslist for free stumps
Hi Paloma,
First, try to set the tuck at the apex, peak of triangle.
Use cross pein hammer - rounded chisel end of body hammer.
Keep strike angles at about 45deg to each other, like roof peak angle of snow country cabin.
Start at apex and criss-cross down to the edge.
Start with a one inch triangle tuck, and work down to edge.
Start by working on hammer hit accuracy, angle left - then angle right .... and so -left-right-left-right-left-right, stepping down to the edge.
Work on this. Watch what is happening as the hammer blows step to the edge.

This is the "wedge/chisel" look of one face of a "raising" hammer:

P1000837.jpg

Use gently as it delivers "stretching" force with little effort.
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  #18  
Old 05-28-2022, 05:51 PM
steve.murphy steve.murphy is offline
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You can make a stump from dimensional lumber if you like. There is a nice YouTube video from japhands customs just for this.
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  #19  
Old 05-29-2022, 01:00 AM
skintkarter skintkarter is offline
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Hi Paloma, whilst you can sort of create a ruffle or pucker with a sand or shot bag, you really need a solid surface to hammer the pucker down onto. This is where a stump is handy for both parts of the operation. I did see a video (which unfortunately I can't find again) where a chap was making I think a top for a chopper style petrol tank. He had a gizmo he had made which clamped in his bench vice which gave him a vertical tucking fork at one end and at the other end was a 6 or 8" circle of 3/8 or 1/2 steel. So it looked a bit like the Starship Enterprise... He was able to manipulate the panel in the tucking fork, moving all around the edge of the panel to create the desired ruffles and then move to the other end of the gizmo and belt them down to create the shrink. The gizmo was welded up on a piece of 2" x 1/2" flat bar or similar probably 12"-15" long.
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  #20  
Old 05-29-2022, 10:37 AM
BTromblay BTromblay is offline
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Quote:
Originally Posted by Ducatichica View Post
I appreciate all the advice this weekend is tucking practice time. I think my challenge at this point is my tucking fork does not reach the center of the 10” diameter. I also brain faded on locking them in. Please let me know if I am correct is assuming smack over at the outer edge then tamp them down in a motion to gather the metal. I have watched a few videos on the utube.
My question do I need to make a stump bowl as I am currently just using a shot bag?

Can a stump me made out of dimensional lumber? Is it adequate or should I shop Craigslist for free stumps

Hi,

Another thing to remember is the ratio of stretch verse shrink on a panel. Material is resistant to shrinking and more so the deeper you go into a panel. Many metal shapers feel that the excepted depth from the edge of a shrink is 4". That number is not engraved in stone and changes depending on the application. In the panel that I made, I stretched 20% of the center of the panel, and shrunk 80% of the panel edge. For your application and tools available, it would be easier if you stretched 60-80% of the center and shrunk the 20-40% of the edge.

IMG_20220529_102746.jpg

This photo is how I lay out a round panel with the percentage.

Bill
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