How would this sheet metal part be formed?

SRT Mike · Jul 23, 2014

I have seen a few parts like this - couldn't find an exact picture online, but this is close - just imagine if it the dome part was all one piece instead of having the perforated inner part... it can't be spun (can it?) from one piece because it would trap the form inside.

Would it be hydroformed using some sort of 3-piece mold that splits top/bottom and one half splits left/right?

Or perhaps a totally different method? I know it could be made in 2 pieces and welded... but I'm thinking something like a lamp shade where you would need absolutely no visible seam... wouldn't a welded seam always be visible if it was made in 2 parts?

bryan_machine · Jul 23, 2014

I may be misremembering, but I'd swear a DVD I have on spinning shows such a part being made - it involved a multi-part form, and maybe some other tricks. I don't think it was one setup.

climb-101 · Jul 24, 2014

metal spinning would be my guess

dian · Jul 24, 2014

the art of metal spinning - YouTube

neilho · Jul 24, 2014

How many pieces needed? Material? Size? Or is this curiosity? Onesies could be done using sheet metal shaping techniques without any welding- start with a round blank, shrink the outside, stretch the inside, planish when final shape is achieved, then machine holes.

Or machine it from solid with radius attachments.

And...some spinning companies stock spheres- for example http://www.churchmetal.com/hemispheres.htm . Buy a sphere, whack part of it off, finish welds, polish, polish, polish.

Neil

norin1373 · Jul 24, 2014

Made in tow pieces - welded - polished - chromium coating or other kinds of coating. And there would be no shade or something.
like kitchen sinks. The two deep tanks will made separately and then spot welded to the main sheet. But they are stainless steel and there is no coating there. You may didn't mentioned that at all as they are very clearly made.
Polishing and coating will hide every dirt!

SRT Mike · Jul 24, 2014

I guess it would be spun as well, but it would have to be in two pieces... the video linked to above wouldn't apply, because that only applies to shapes that allow two parts of a form to meet in the middle... this part wouldn't allow that - unless it was some kind of complicated multi-part form that would form a sphere but could be disassembled and removed through a hole smaller than the diameter of the assembled parts.

You don't see too many shapes like this being used in stuff, so I imagine it's a bitch to make.

Peter from Holland · Jul 25, 2014

If I had to make them first OP would be spinning and then finish it of on a swaging machine with the right rollers
I first have to learn how to spin though

Peter from Holland

sfriedberg · Jul 25, 2014

Stuff like this can be spun in one piece very easily using multi-part forms. The forms are designed so the pieces of the form can be removed from the finished part. Same technique could be applied to press forming, too, although cost of the die set is usually impractical. Much more practical on a press would be a urethane inner punch which forces the part to fill an recess in the die (probably a three-parter with two sliding parts) and then relaxes when the press stroke retracts so it can withdraw from the part.

magicmaker · Jul 25, 2014

I am NOT guessing ... the part is spun in one operation. See attached illustration from my CD. Once the segments with the metal spun over them are pulled from the center post, all easily disassembles from within the spun metal form. Prepolishing can be done before the item is removed from the lathe. Also, some spinning lathes (from Italy) can be ordered with a buffer attachment as part of the lathe. It swings down from above to do the buffing.
Jim

Clive603 · Jul 25, 2014

Jim

Thats really clever. Being totally pants at multipart assembly 3D visualisation myself I'm amazed at how talented folk can see how such things can be arranged to go together as a seamless assembly yet still come apart for extraction.

That CD sounds very interesting. Whats the title and where did you get hold of it. Some time in the future I need to try my hand at simple metal spinning myself to replicate the cases of three light fittings. Shallow dishes with raised rims around a foot diameter, 1/4" (ish) dish and 1" rims. About as simple as could be.

Clive

magicmaker · Jul 25, 2014

Clive,
Here is the preview:
CD Preview
Jim

JRIowa · Jul 25, 2014

Anybody can spin it. I'd figure out a way to use explosives.

JR

gwilson · Jul 25, 2014

Yes,that is a simple job of spinning with a segmented steel chuck. I made quite a few segmented steel spinning chucks when we used to make the PGA trophies behind the scenes in the silversmith manufacturing shop in Wmsbg.

The chucks are segmented like slices of pie,but one slice is sliced backwards so it is larger on the inside than the outside. This is the key slice. The slices are arranged around a steel core. When the core is pulled out,the key slice is next pulled out. Then,there is room to extract the normal looking slices.

Another,solid steel chuck has to be made to spin the first half of the shade here. It stops where the shade reaches max. diameter. Then,the segmented chuck is inserted. The metal,which has been spun into the shape of a round nosed bullet,holds the segmented chuck together. The shade can then be spun to its closed shape,and the segmented chuck removed.

There are other methods,too,used for many years. High pressure water can be used to force metal that cannot be spun,into the shape of a steel cavity. Fluted teapots and the like can be made that way.

kustomizingkid · Jul 25, 2014

You could shrink and planish... But for any semblance of efficiency spinning is the way.

SRT Mike · Jul 25, 2014

magicmaker said:
I am NOT guessing ... the part is spun in one operation. See attached illustration from my CD. Once the segments with the metal spun over them are pulled from the center post, all easily disassembles from within the spun metal form. Prepolishing can be done before the item is removed from the lathe. Also, some spinning lathes (from Italy) can be ordered with a buffer attachment as part of the lathe. It swings down from above to do the buffing.
Jim

Wow, thank you! That helps a lot.

I was in a meeting with a client a couple of weeks back and saw a rendering on their "idea board" for a part that had a similar shape to this.. and it made me curious how such parts would be made. Thanks again!

magicmaker · Jul 26, 2014

George, a second steel spinning chuck is not needed nor ordinarily used for such jobs. Look at my drawing above and notice the locking ring. This secures all segments throughout the entire spinning process. Only one segmented chuck is needed and used. This is the same type of chuck as used when spinning a Jefferson cup.

gwilson · Jul 26, 2014

Magic maker,The locking ring is clever. I never made them that way,but wish I had. With the sheet metal disc pressed up against the ring,it could not have flown apart when the lathe was started. I was not a metal spinner,and just did what the spinner told me to. I made so many spinning chucks,dies for wire drawing and other tooling,I was able to put a good down payment on a house.

I made the core,and then turned the shape,leaving extra. The body was sliced up and everything soft soldered together. Then,the shape was trimmed to fit the core again,and put onto the core. The shape was trimmed down to final shape and polished to a mirror surface. Then,I would put the shape into the furnace and melt it apart. Solder was wiped off everything,and the shape re polished clean. It's been many years since I made a spinning chuck,as someone else came along and under bid Wmsbg. to make the trophies. It was good while it lasted!! If I make another,I'll remember your locking ring.

Doug,you may be right about making something as cheap as a lamp shade. I wonder if urethane could produce a completely wrinkle free shape? Another problem with spinning is the spinning marks have to be polished off. That wouldn't be practical on a cheap lamp shade.

9100 · Jul 26, 2014

The St. Louis Craft Alliance had a silversmith's show where they asked smiths to send their best piece. One was a bowl about 2 1/2 " dia very similar to the part discussed here. The curator asked if the silversmith had it spun. He became very indignant and replied "It's raised, dummy!" I walked round and round it holding my head at different heights while watching reflections in it. I could not detect the slightest waviness or ovality. This smith had started with a slug of silver and hammered it into the bowl. The St. Louis Art Museum has a lot of silverware on display. Most of them could not pass the same scrutiny.

Bill

Clive603 · Jul 26, 2014

magicmaker said:
Clive,
Here is the preview:
CD Preview
Jim

Thanks. Very interesting indeed. Is there any way to get it in the UK.

Clive

How would this sheet metal part be formed?

Stainless

Diamond

Cast Iron

Titanium

Titanium

Plastic

Stainless

Diamond

Diamond

Hot Rolled

Attachments

Titanium

Hot Rolled

Diamond

Diamond

Titanium

Stainless

Hot Rolled

Diamond

Diamond

Titanium

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