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Old 07-26-2020, 12:20 PM   #1
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Cutting notch's sheet metal curve


I want to make a duct for a project and would like to make a curve in sheet metal, notching the top piece to wrap around the curve.


Is there a formula or rule of thumb as to how far apart and wide the notches should be. I find nothing on the net? Where do I find the info??



26 gauge sheet metal.
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Old 07-26-2020, 01:04 PM   #2
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Re: Cutting notch's sheet metal curve


The notches will be determined by the amount the edge is turned to 90 on the bending brake. Scribe your lines on the flat. Cut notches then bend the edges 90 on the brake. You might like some Dykem Blue layout ink.




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Old 07-27-2020, 12:44 PM   #3
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Re: Cutting notch's sheet metal curve


You could start with the radius of the curve you want to match and whatever that is plus the width of the lip that you need to modify. Take each of these numbers, multiply by two, multiply that by 3.14, and divide by 4. That will give you the circumference of the quarter arc for the piece you want to match and the piece that needs to be modified. Subtract the smaller number from the larger one, and that will tell you how much total metal needs to be removed. Divide that by the number of notches you guestimate you'll need and you'll have the width of each notch.
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Old 07-27-2020, 02:38 PM   #4
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Re: Cutting notch's sheet metal curve


Thanks for the responses. I took some thin cardboard and pretended it was metal. I hacked away at it with scissors until it looked like it would work. Then transferred the dimensions to a piece of scrap and cut it with those dimensions.



Likely not up to your standards but does not look like Curly, larry and Moe did it. So I am good to go. Now trying to hack together a brake. Was going to buy a $60 Harvard Freight one, looking at the videos I will be ok with some chopped up bed frame and clamps!



Thanks again. Jim
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Old 07-27-2020, 03:03 PM   #5
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Re: Cutting notch's sheet metal curve


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Thanks for the responses. I took some thin cardboard and pretended it was metal. I hacked away at it with scissors until it looked like it would work. Then transferred the dimensions to a piece of scrap and cut it with those dimensions.



Likely not up to your standards but does not look like Curly, larry and Moe did it. So I am good to go. Now trying to hack together a brake. Was going to buy a $60 Harvard Freight one, looking at the videos I will be ok with some chopped up bed frame and clamps!



Thanks again. Jim
Standards? You said Standards I have a 1947 craftsman table saw mounted on a stand made of bed frame. That was a few years ago , like 40 , when my eyes allowed me to weld.
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Old 07-27-2020, 07:44 PM   #6
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Re: Cutting notch's sheet metal curve


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Standards? You said Standards I have a 1947 craftsman table saw mounted on a stand made of bed frame. That was a few years ago , like 40 , when my eyes allowed me to weld.

Along time ago in a land far away, I first worked as a burner, then went to school and could melt things together. In various fabrication shops between Buffalo NY and Erie Pa.



Now I cannot see the puddle and sometimes miss the joint completely. But can run a bead for an inch or two.


Back in the day American bed frames were made from old rail road track.
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Old 07-28-2020, 06:15 PM   #7
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Re: Cutting notch's sheet metal curve


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Now trying to hack together a brake. Was going to buy a $60 Harvard Freight one, looking at the videos I will be ok with some chopped up bed frame and clamps!

Thanks again. Jim
I made one of those a few years ago when working on my solar collector.
Worked great. Unfortunately the spring steel used in bed frames keeps the working width relatively small. But I suspect you are working on smaller projects and that should be just fine. I was able to clamp mine in a vise to use it rather than bolting it down.
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Old 07-28-2020, 06:47 PM   #8
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Re: Cutting notch's sheet metal curve


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I made one of those a few years ago when working on my solar collector.
Worked great. Unfortunately the spring steel used in bed frames keeps the working width relatively small. But I suspect you are working on smaller projects and that should be just fine. I was able to clamp mine in a vise to use it rather than bolting it down.

Yes I am working on small, 26 gauge sheet metal with longest bend about 20 inch. I found a simple design on You tube that fastens to the edge of the workbench. Needs a couple welds or could be bolted. Probably could do it with wood also.
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Old 07-28-2020, 06:51 PM   #9
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Re: Cutting notch's sheet metal curve


I would think if you welded a few gussets to the inside angle of the frame it would stiffen it up enough to make one with a larger capacity.
Mine was about 2' long and I used regular butt hinges for the folding action.
But I will checkout the Youtube video...I may need to work on a larger model.
Good luck with your project.
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Old 07-28-2020, 07:02 PM   #10
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Re: Cutting notch's sheet metal curve


Yup, butt hinges.I will not be using the wood, although a good idea, I will not

even add the handles, using large wrench's for leverage, I will only be doing at most a dozen bends. Cannot imagine this not working for such thin material. But I have been wrong before, lots of times!



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