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Old 10-16-2018, 12:37 PM
Diydan Diydan is offline
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Default forming a small steel frustum

Hi everyone,

I'm working on a personal project and I ran into a wall trying to fabricate part of it. The project is a branched light fixture using 3/4" and 1/2" tubing, and a small frustum at the end of each tube. I'm trying to make or buy the frustums(about 15-20). I contacted a few metal spinning shops and got no quotes. I have access to a friend's wood lathe so I could attempt spinning it, but I don't have a slip roll, if the best way is to roll and weld.

The small diameter is important to hold in order to weld it to the tube, but I'm slightly flexible on the other dimensions. Also, it does not have to be super precise since it is mainly aesthetic, so if I end up with a small flat portion from rolling and welding that would be ok. The entire weldment will be powder coated when complete.

Any suggestions on the best way to fabricate this are appreciated and welcome.

Here are my drawings and weldment:
http://www.allmetalshaping.com/album.php?albumid=1118

Thanks
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Old 10-16-2018, 06:13 PM
Charlie Myres Charlie Myres is offline
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I would use rolls to make the cone, or if they are too small for that, fold them around a mandrel and then weld, or solder them along the seam,

Cheers Charlie
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Old 10-16-2018, 07:00 PM
fciron fciron is offline
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That is a poor candidate for spinning,

I would either make male and female dies and try to form the taper onto some existing tubing (1/2 or 5/8", stretching is easier than shrinking) or I would work up a pattern and roll up the cones.

They're smaller than any slip roll I'm aware of, but .032" could easily be bent with round nosed pliers or over a 1/2" bar. Then weld the seam grind off the excess and true up over the s same 1/2" bar. You could make a precisely sized mandrel, but it might not save enough time to be worth it.
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Old 10-16-2018, 07:08 PM
fciron fciron is offline
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These are a bigger, but formed from sheet as described. They were trued over a blowhorn stake because I have one. Your cones have less taper, so a round bar is fine.

https://www.instagram.com/p/BK9wydhB...d=jrch7nhuevgo

https://www.instagram.com/p/BLGzya3h...=11isv54nec647
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Old 10-16-2018, 07:20 PM
crystallographic crystallographic is offline
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Default rolling up a small conic by hand

3_cone forming.jpg
4_cone_hand roll.jpg

016_trying for accuracy.jpg
037 soldered_cleaned_waxed_ready for rooftop.jpg


Helps to have a taper mandrel, like an old candlestick mandrel, used here.
Leather-faced whapper helps form w.o. marks.
hope this helps you.
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Old 10-17-2018, 12:27 AM
Marc Bourget Marc Bourget is offline
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Have you considered swedging it on a lathe?


.
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Old 10-17-2018, 05:50 AM
metal manny metal manny is offline
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I stand under correction, but in my experience, hand forming like Kent has shown is your only option without a slip roll.



However, one can "fold a cone" on a bending brake by doing multiple wedge-like bends, but this would leave visible bend lines.



So with this possibility in mind, try manually rolling/ gently bending the flat sheet with your hands over a round iron bar (also in wedge-shaped sections) until you have a rough cone shape similar to one of Kent's first pics. You can use a soft hammer to help near the sharp end, as this will be most difficult to form. Then weld the two ends together and planish smooth with leather-faced slapper and tapered stake as shown, again by Kent. Finally cut/enlarge the hole on the sharp side to fit the stem.
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Old 10-17-2018, 08:26 AM
Gareth Davies Gareth Davies is offline
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I'd just have them CNC turned out of solid with a plain (or stepped bore). Cheap and easy, no messing around making your own tooling.
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Old 10-17-2018, 10:55 AM
billfunk29 billfunk29 is offline
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Default cones

sst at Mcmaster pn 45735K411, $12
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Old 10-17-2018, 03:57 PM
Diydan Diydan is offline
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Default thank you

Thank you ALL for your input and advice! It is greatly appreciated.

Here's my takeaway, let me know if I'm wrong:

It seems like spinning is out of the question, and the 1/2" diameter makes slip rolling difficult because roll diameters aren't typically that small.

I like the idea of forming a tube over a male and female die from the perspective of speed, but I feel like I'd mess that up somehow.

Sounds like cutting out the flat pattern and hand forming it over a round rod is a good solution. If I do this I'll have to make a small whapper!

fciron: beautiful candlestick project! Did you hammer the stems to taper them?

billfunk29: thanks for the link. That isn't the ideal shape I'm looking for but I started searching reducers and found a tube reducer thats almost exactly the size and shape I'm looking for: https://www.austenitex.com/shop_by_b...31&custcol22=1

It's $17 and becomes expensive since I need 15 so I'm searching for alternatives. So far I found a DIN tube reducer that may work.
At a minimum I figure I could use the one from Austenitex as a form to create the rest from flat sheet.
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