Need Some Sheet Metal Bending Tips

[FlyingPilot]

I just built Dave Clay's bending brake in order to tackle the basic shape z channel stock parts. I have questions regarding accuracy of the bends and could use some sheet metal bending 101 without all the formulas and techno mumbo jumbo. I watched some videos on the youtube, but I can't find a bend allowance chart for .032 or .025 to make the formulas work. Dave Clay recommends making the flanges over sized to then be trimmed down to spec. This is fine for an "L" shape bend. I need help understanding how to layout the sheet for a "U" channel bend with the correct setback so I can get for example the 2-29/32" width between the bends that the plans call for. Could someone who has done this give some pointers.

Thanks,
Rob

[Bryan Cotton]

Rob,
I am a technical, formula oriented guy. I never use them on the brake though. It does not share my enthusiasm for math.

First rule of thumb: make your bend radius 4X the sheet thickness. To achieve this I took some .010 flashing, bent it in half (hemmed is the real word) to make it .020 thick, then I bent it around the nosebar of the brake. The inner radius is zero, outer is .020. Do it again and you get .040. Rinse and repeat as necessary.

Now onto bending Z's or channels: take a piece of scrap about an inch wide, mark your guess for the two bends, and bend it. Then measure it. Make adjustments on your next piece of scrap and try again. Rinse and repeat as necessary.

Once you know how to mark and bend scrap to make the right shape, you know how to mark and bend real parts. Go for the gusto!

[FlyingPilot]

Hey Bryan, thanks for the reply. Was just messing with the brake. I didn't use piano hinge. I used (4) steel 3" flush mount hinges that I got from Ace hardware. I can only get the brake to go a little past 90 degrees.

So to clarify your first rule of thumb, you suggest using the .010 flashing on the nose to get the radius (1/8) for instance ? I did not grind down the 3"x3"x 1/4" angle yet (as Dave suggests) to achieve the 1/8 radius, as I have been testing it stock and it seems like I'm getting more then a 1/8 radius. This may be due to the gap from using the different hinge. How can I get a 1/16 radius with this rig? Most of the channel requires 1/16 bends. So tempted to get the 36" HF Brake. I have the 30" HF brake. but the vert and horiz spars are 31" and need 1/16 bends.

Roger you on the trial and error with scrap, lol most my scrap pile is bent up. :D What brake do/did you use and suggest?

Thanks,
Rob

[Bryan Cotton]

Rob,
I am not familiar with David Clay's brake design. I have an 8' Tennsmith, which is...AWESOME! I got a good deal years ago. Just remember you don't need your own brake if you have a friend or EAA chapter with one. Most brakes have a moveable clamping leaf so you can adjust for different thicknesses of metal, or so you can add stuff (like my radius things made of flashing). If you have a fixed brake the flashing trick won't work and you would need that radius or something.

Too large of a radius is ok unless a bolt or rivet head rides up into it. Too small of a radius is bad because the metal can or will crack.

[DCASonex]

Setting back the clamp from the hinge will give what looks like a proper inside radius, but you are still bending around a sharp edge. Use flashing, or just scrap material about the thickness of the inside radius you want to make a nose piece, make it full length and keep it for later use.

For most thin gauge applications, just layout your bend line on what would be the inside corner as if it were to be zero radius. Then check with scrap. With most brakes with thin material, the limitations of eyeballing the line is greater than the refinement gained by calculating where to draw the line.

David A.

[mike.smith]

Don't make the bends too sharp. Other than that, common sense prevails, even for a novice. I didn't find any way to get accurate bends that conformed to any formula and I really don't think it mattered. The bends in a Sonex are not that precise. Dave Clay's brake for the larger pieces, and the small Harbor Freight brake for the smaller pieces all were close enough and did not create any unusually tight bends. I scratch built. Just do a practice bend for each new type of bend. You'll figure it out quickly.

[FlyingPilot]

Went to go buy the flashing and I bought a couple of pieces of "corner bead" for sheet rock corners. They have a perfect outside radius of 1/8. Paid $3.00 for 12 foot and it worked out nicely on some test bends. Thanks for the direction guys.

Rob