make sheet metal weak along a bend line?

[metalmagpie]

I no longer own a box & pan brake. I have friends that own such but none have deep enough fingers to fold up the box-like part I am making. The part is a dust collection chute for my surface grinder.

I recall a technique where a guy wanted to make a sturdy lathe pan. He cut out his profile with his plasma cutter (think it was 1/8" steel plate) and then made slitting cuts along the bend lines leaving only short tabs to actually bend. Then he was able to bend the sides up easily by hand. Welded, the end result was very cosmetically pleasing. I do own a plasma cutter but I quail at the thought of actually making several precision cuts like that. I think my cuts would be wobbly or that I'd go too far and cut my tabs.

If I were one of the new youtubers I'd just whip out my angle grinder with a cutoff wheel and zip out some perfect bend lines. Again, I don't think I have the chops to control the tool enough to make straight partial slit grinds.

I did consider drilling a bunch of 1/16" holes. I have an old Orbit 14" drill press which I've fitted with a DC motor. I can get its spindle going pretty fast. That method might work.

Or, I could get out my blacksmith's slitting chisel and carefully walk it along the bend lines. Might be easier to keep that straight if I clamped on a "fence".

The sheet metal I'm using is 16 gauge steel. If I could grind a single point tool that would actually scribe a deep line, that would work maybe. Not sure what topology that tool would be.

The best solution I have thought of is to have my buddy make the slitting cuts with his little waterjet machine. Only I seem to have worn out my welcome with him, or maybe he's spring skiing in Colorado or something - anyway, he's not answering my emails.

I have a friend who used a smallish vee cutter in a little horizontal mill to make precision folding grooves in brass sheet when he was making up some jewelry boxes. Maybe I could find an engraving bit or something and find a way to mill grooves using my knee mill (a BP clone).

Before I go start wrecking sheet metal pieces, can you think of any other ways to try?

If you're curious, here's my working drawing: http://nwnative.us/Grant/images/temp...tretchout3.pdf

Thanks! - metalmagpie

[nickel-city-fab]

I used to do stuff like that at work to make sheet metal hoppers for product. Depending on thickness I would use either a box knife to score along the bend line, or the edge of a slitting wheel in the angle grinder. On 16 ga that's what I would do. Just go about 1/2 way thru, use a piece of angle or scrap to guide the cut. Clamp it down good on the edge of the table right along the score line and bend it there. If you wanted to try just scribing it, a regular carbide scriber and a zillion passes would do it.

[Mr Fixit]

Metalmagpie,

I have a plasma cutter, and like you I have a hard time keeping a straight line sometimes. The plasma cutter and a steel fence, anything that is 1/4" high or more works perfect for a straight line cut.
I would take a scribe and a straight edge like a level and scribe a line, or even a sharpie marker or a paint stick pen will give you a real good guide, then use the steel straight edge to follow with the plasma cutter and Bob's your uncle and you have what you need.

Do let us see the end product, as it's always great to learn from each others experiences.

TX
Mr fixit for the family
Chris

[Galaxie]

+1

I have used a plasma cutter exactly once in my life but I did as Mr. Fixit suggested and used a straight edge of 1/4" steel. It worked perfect!

[brian Rupnow]

Get half a dozen metal cutting blades for your sabre saw. I have built many hot rod frames from #10 ga. (about 1/8") and a few floor pans from #16 ga. plate, all cut to perfect shape with a sabre saw. Wear safety goggles--those metal shavings are very hot and you don't want one in your eye.

[Noitoen]

I use a piece of steel bar as a guide for the grinding disc. With the 1mm cutting discs it can be used to cut or score straight lines

[deltap]

Clamp or tack weld to a heavy angle. Beat the bend over with a 2 or 3 lb hammer. Work along bending a little at a time. Grind half way through with a cut off wheel to make bend easier. I scribe a line first. Easy to follow after a bit of practice.

[boslab]

As said if it’s too bloody thick for my folder I gash cut with the thin slitting disks at regular intervals, fold on dotted line, weld the slit, just fusion is usually sufficient, filler handy just in case, works great
mark

[Fasttrack]

Metalmagpie,

I have a plasma cutter, and like you I have a hard time keeping a straight line sometimes. The plasma cutter and a steel fence, anything that is 1/4" high or more works perfect for a straight line cut.
I would take a scribe and a straight edge like a level and scribe a line, or even a sharpie marker or a paint stick pen will give you a real good guide, then use the steel straight edge to follow with the plasma cutter and Bob's your uncle and you have what you need.

Do let us see the end product, as it's always great to learn from each others experiences.

TX
Mr fixit for the family
Chris

This. I do it all the time... or at least all the time I have access to a functional plasma cutter. I think it's a skill well worth developing since you have a plasma cutter. Being able to cut fast, clean, straight lines is the whole reason to own a plasma cutter over a gas torch, IMO.

An angle grinder works equally well with a thin cut-off wheel. You just need to be a bit delicate and I find wearing lightly shaded safety goggles helps me see my line better. The trick, I've found, is to score a line with the grinder first. This gives you some opportunity to recover if you veer off at all and then you go back and make the full depth cut. I've ripped 10' long pieces of 1/4" plate this way and you'd be hard pressed to tell it was cut by hand. Really not that difficult - just need to practice on some scrap first to build your confidence. If you're "jumpy", wearing some long sleeves and hearing protection will make the process more comfortable and you'll be less likely to flinch / veer off the line.

[chipmaker4130]

If your material is 1/8" thick at least, you can gouge with a plasma cutter fairly accurately (don't cut through). It doesn't matter if the gouge wavers slightly because the bend will even things out nicely. If you use a fence or guide the line will be straight anyway. If the chute isn't long, you can also drill a series of small holes where you want the bend, then run a bead of caulk or E6000 to seal instead of welding. No weld distortion that way. I've done what I suggest, it works.

[metalmagpie]

I have made thousands of cuts with a plasma cutter, nearly all guided in some way. It's just finicky little cuts which start with a piercing cut .. anyway, I'll give that a try.

So far I have tried two of my methods and am now reporting back.

The first method I tried was by walking the slitting chisel along a clamped-on "fence". What I learned is that apparently the cutting edge on my slitting chisel isn't parallel to the edge of the chisel itself. Rather than getting a single connected line, I got a vaguely sawtooth line. However, it bent OK. The disconnected chisel marks are apparent in this image:



Next I clamped the same "fence" on a different corner of my scrap test piece and used it to guide an angle grinder's cutoff disk. I did get a nice looking straight cut, much better than any I'd done before. Of course, I was only doing a groove. It also bent OK but the kerf was kind of wide. I ordered some .031" cutoff disks and will try again.



Both of these resulted in acceptable looking bends. Remember, the fold line area is going to be welded and sanded to regain the lost strength.



Coming up I'll try plasma slitting and chain drilling. Stay tuned.

metalmagpie

[mattthemuppet]

I use a dremel or angle grinder to grind a line on the inside of the bend. Has the added benefit of allowing a small bend radius in thick material, as there's now no material in the way

[oxford]

If you are going to pretty much end up welding the whole thing up anyways by the time your done, why not just make the whole thing out of flats and weld it up?

Alternative would be cut out the shape you have in your drawing and make the 2 bends directly across from each other on your friends brake. You can then clamp this down to a table with a piece of flat barstock as wide as the bend on your next bend line. The pieces you have bent up already will give it some stiffness and you will be able to make a nice bend by hand that way for the final 2.

[kev74]

I had a sheet metal project recently and used an angle grinder and cut-off wheel with good results (good enough results?).

How about a circular saw with a metal abrasive blade? You could run it with a fence to keep the work straight, and could set the blade depth to just score the sheet metal.

[Edwin Dirnbeck]

SILHOUETT OR CRICUIT MACHINE.My wife has a cnc hobby machine.It will make a series of slits in heavy card stock. You can buy or make your own programs.It can handle a 12x12 sheet.or you can get a role of cardstock that is 12 inches wide and almost unlimited length.She makes some incredible things just by slitting and folding,She makes cardboard houses with 4 sides and roofs and window cutouts. They have tabs that lock everything together.I am shocked that no one has made a bending program for cnc plasma cutters.Take a look at a USPS SMALL FLAT RATE BOX. .It is a flat sheet of thick cardboard. It folds and tucks into a sturdy box in seconds..Edwin Dirnbeck