Designing for Sheet Metal

What works on paper, doesn't always work in the physical world as planned, for a variety of reasons. What follows here are some of the various lessons I have learned while laying out sheet metal projects. Hopefully you can benefit from this guide and save yourself the time I spent learning things the hard way!

Step 1 Sheet Metal Has Thickness

When you're making something out of paper, the thickness of the sheet is negligible--everything will line up and work out most likely in the end. Sheet metal is a different creature in this respect. Bends have radius, sheet has thickness, and tools need space to access a bend. When laying out a simple box with tabs, the tabs will meet the perpendicular face of the next side when folded up to 90 degrees, so when you are folding your tabs, measure in from the edge of the material the length of the tab, plus the radius of the bend, plus the thickness of the material for a perfect corner.

When folding over a seamed edge, the folded-over portion is going to need to clear the adjacent faces on both sides. Slightly notching these helps resolve these issues. A file is sufficient for fine-tuning these bends.

Think of bending sheet metal as what it really is: stretching one face, while shrinking the opposite face in a controlled way.

Comments

[metalman1138]

Ive been a sheet metal worker for close to 20 years now. Went from old school techniques to modern equipment. This is a GREAT instructable. Very well done.

[trojan52]

While this is a great instructables, there's two small thing I could suggest to help you improve it.

1. The scratch awl is a good idea to precisely trace a flat pattern on sheet metal, BUT I would not recommend using this method for any "structural" component. The reason is simple, you are adding weak spots all over the place,and they will sooner or later result in fractures.

2. You probably did this for the convenience of it when cutting your metal, but the "sharp corners" on your flange near the bending lines are also weak spots waiting to transform in fractures. You can easily drill a small hole in those corners before cutting the metal with your snip to create small radiuses that will help increase toughness.

[VagsmaCutter]

Very nice instructible, brought me back to a better day. As does just thinking about the glorious sheets of 060 stainless steel (with the edges so dul, gloves were merely a fashion statement) and 12 foot skids of clad and unclad aluminum stacked 15 + feet high, with brown paper sandwiched betwixt every sheet. Oh yes, those were the good old days and now that you've mentioned it, there's no reason they can't be relived a bit for old timer's sake. Thank you for this. One question; I've a pair of straight tin snips that need to be sharpened and perhaps tightened up, what type of edge should they have and how tight should they be etc. I think you are the person to ask. (if the good old days were still here I'd have a brand new pair)

[cdousley]

True story, one time i bought some sheet metal and thought it had a little rust on the edge but when i started working with it i realized it was dried blood.

[doomsdayltd]

looks like the engineer's toolbox (i know its not, its an older design of a toolbox)

[iminthebathroom]

Excellent instructable, truly

[Phil B]

Thank you for a very fine, useful Instructable. I am thankful to have a welder, but find there are times when my pop rivet gun is the better choice. As regards "free" metal, we recently replaced a water heater. The old one is full of lime and heavy. I am cutting it up in pieces before trying to haul it up the basement stairs. The outer shell is a nice gauge of sheet steel I want to use for various projects, including some small parts trays. I hope your Instructable is featured and makes the newsletter.

[freewheel]

Thanks! To make that outer shell lay flat, you can "cross break" the sheet using a break press. Make an X across the sheet, then a box around the perimeter and it will lay flat.

[scavanger]

Nice intro into becoming a diy tin knocker, thanks.
I have been thinking about making a small brake and trying my hand at it.

[freewheel]

If you just want to get a feel for sheet metal without a huge investment, there are tool called "bar folders" which are basically a hinge that bolts to a surface with a machined-flat piece of bar stock that you clamp over the material you want to bend. Bend the piece up to the desired angle. Harbor Freight has one for $40: http://www.harborfreight.com/18-inch-bending-brake-39103.html

[zazenergy]

This is a great intro to working with sheet metal! I learned a ton.