flamming deal alert- building sheet metal brake

[fairchild1934]

I was in my local Loews today. was in the area in the back of the store-- outside--- out side of the lumber area where the forklift goes out.
I was looking at a 20 foot long 6 by 6 timber. Looking at it to make (maybe) a trailer for hauling steel tubing.

I looked down to the next rack of stuff and I saw some rusty steel laying there. Upon closer inspection-- it was long lengths of 1/4 inch thick angle iron--- 3.5 inches wide and 10.5 feet long. There was a small pile of them. They were a bit rusty from being out side. They claimed they sold those in the concrete section. But when I looked the ones on the shelf were just sheet metal bent into a wavy 90 shape. so It took me about 45 min to get them to figure out the status of this steel. Finally, we found out from the store manager that they used to stock these but no longer. it was no longer in inventory.
So after about another 15 min. of chinese telephone--- the lumber guy came back and said that they wanted them gone. 5 $ each. :-)
So I took all 5 ( I think they wanted them out of their way...... )

So those were about exactly what I thought I wanted to make a sheet metal brake for bending spar blanks. I can get a heavy duty stainless steel hinge from MSC for the pivot point. Im building my 2-nd 9 foot building table now. It can bolt right to the side I think. 25$ for 300 lbs of steel angle.
It appears none of it is bent (like being run over) so that's good too. Check your local stores !

Tim

[Frank]

Yay for scratch-built tools on top of everything else!
Here's my two cents based on experience: use every mounting hole (and maybe even drill extras) of the hinge and use the strongest fasteners you can. The resistance force will try to stretch and pull on the hinge. Also, don't just do short test pieces. In my case the short tests had the perfect bend radius. The long pieces are much much harder to bend and ended with oversized bend radius because there was just enough slop in the system. Beef it up as much as you can. There is a reason industrial brakes are rated in multi tons.

[fairchild1934]

Frank-----
I looked on MSC at stainless steel hinges 8 feet long. They are available in several sizes of varying pin diameters and flange thicknesses.
They has 1/8 inch pins- 5/16 inch pins, 1/4 inch pins and 3/8 pins and I THINK 1/2 inch pins. I was looking at the 3/8 pin model.
I guess the thicker flanges to attach to would help stiffen up the whole rig somewhat.

Can you tell me what size hinge you used ? (and if you think you should have gone bigger ?)

Tim

[Frank]

I used cabinet type stainless steel hinge from home depot, 4 ft. across the middle and 2 ft. at each end. My hinge pins were probably 1/8. Worked okay but the force of bending wanted to pull the two halves of the hinge away from the fasteners. So I don't know if a bigger pin would help. A heavier flange thickness would probably be better in that regard. And I'm not sure how a thicker pin would affect the overall design geometry.

I used an angle grinder to round over the bending edge to the 0.1 bend radius. But in retrospect I should have rounded over the edge to something less than the specified radius to compensate. As a novice I was concerned about minimum bend radius. I should have known in the case of spar webs there would be a maximum bend radius too.

If you have enough .032 material I suggest testing the bend radius on a 6 ft. or longer piece.

[fairchild1934]

I was thinking a big chunkey hinge would resist flex better. However this hinge in the link says its greasable. I assume that means that the pin is loose enough in the knuckles that you can with draw it out the end. If you look at the end view of these-- you can see the iD. of the knuckle is a bit larger than the pin. I am a bit concerned that this slop between the pin and knuckle might allow the two halves to push apart under a load.

3" Wide Continuous Hinge - 6' Long - 3/8" Pin Diameter - Stainless Steel Marlboro Trailer Door Hinges MA94ZR (etrailer.com)

i might call the MFG of the hinge and ask them about that possible problem and see if there is a non-greasable model that is tighter fitted.

Tim

[Frank]

It may be that the bigger the pin, the bigger the slop proportionally. It seemed to me that the bending force wanted to pull the hinge flanges away from the steel angles. That's why a thicker flange may be of benefit more than a thicker pin, if that's an option.

If you can test and control for the bend radius, that will be the main thing. But don't worry, the actual bend is going to be straight and true and you will be pleased with the result. And even if you exceed the maximum bend radius a little (as I did) the Bob-approved work-around is easy: a slight round-over edge of the inside cap strips.

One of my deviations from Dave's Brake was to not remove the pin for placement and drilling. This made the hinge sit up into the work area. I installed 1/8 hardboard on the steel surfaces with adhesive to compensate. In addition to not having to fiddle with the pin, the hardboard surface is easy on the aluminum sheet. As you raise the bar to make the bend, the bender and the aluminum slide against each other. I don't necessarily recommend this deviation from the plan, it's just the way I did it. Glad to have the brake business in the rearview mirror!

https://www.youtube.com/watch?v=PUgFZ8DvDVg

[fairchild1934]

Frank---- where do the bolt head end up on the bottom--- do they go all the way through the table ? or just to the bottom of the angle iron ?
Could I drill the angle iron- tap the holes and red locktite all thread studs in there instead of bolts ? (so the bolt heads on the underside are gone ---)
I am afraid if it welded them under the bottom there would 100% be heat warping---

also - when you mention that your bend radius was bigger- was that due to the diameter of the knuckles on the hinge ? or to the other geometries of the positions of the angle irons -- ?

[Frank]

Those bolt heads are below the surface of the table in shallow holes drilled to receive them. The reason there are so many is to clamp the work as securely as possible.
The brake is fastened to the bench from below, through the side. See photo.
I don't recommend but this is what I did. You'll need to adapt to your bench and hopefully better ideas. Start by following Dave's Brake design and alter as necessary.

The reason I think the bend radius is a bit oversized is primarily because I radiused the bending edge to the desired 0.1 bend radius. In order to actually achieve that outcome I should have radiused the bending edge to something less. Narrow test pieces had the perfect radius but long pieces did not, and I did not think to check them.

Therefore, I think yes beef up the system to a reasonable degree but make sure to sacrifice some long pieces and reduce the radius of the bending edge as necessary.
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[fairchild1934]

My 2-nd table is made as a rectangular box made up of 2 x 6 standing up on edge. That forms the main frame. I thought once the table is done- I would put bolts through the these 2 x 6's and into the lower piece of angle. seems like a natural place to fasten it to the table.

so it sounds like I should grind the edge somewhere between how the angle comes and .1 radius ? does that sound right ?
wouild you suggest doing a long test piece before I even grind it any ?

[Frank]

You're starting to sound like maybe I know what I'm talking about.
But yeah I bolted the setup through 2x6 as you describe.
If I were to use my brake for more spars, I'd grind the edge to 0.05 and give that a try.

[fairchild1934]

there is a lot to be said for "been there- done that" -------- or--- maybe great minds think alike ! :-)

[fairchild1934]

Just watched the video. I see immediately why you r bend radius is too big. watch the video in the section where you make the first bend.
what I see is-- you bend it a little and the metal bends some near the bend line. then that area gets work hardened -- and then when you push up a little more--- the area about 1 inch from the bend line which has not bent--- is softer than the area nearer the bend line which has just been work hardened. So as you push up the 2-nd time-- it bends further out where it is still soft--- which kind of bends a 'bow" instead of forcing the metal to only bend at the edge of the angle iron. (like you want it to) So it appears that yjou only want to apply bending pressure to a narrow band close to the bend line to prevent that.
Im thinking maybe a 3/8 inch wide by 1/8 inch thick strip of something like UHMW That could be placed with one edge all most up against the bend line.
That way the bending face would not be allowed to touch way away from the bend line and cause a french looking curve. Had you noticed that ?

[Frank]

Well, now you mention it yeah. It did seem there was a little added bow in addition to the bend occurring at the bender edge. Kudos to you for precisely identifying it!
I'm convinced that your testing will prove to be successful!
As for me, all's well that ends well... so far.

Screen Shot 2024-03-06 at 8.28.07 PM.png

[fairchild1934]

I cant see that bow on the finished product...... :-) I cant see nay on the top bend. Possibly just a hint on the bottom--- maybe-----

[fairchild1934]

Frank----
I built a 10 inch bender just to bend the stiffener angles on the ribs. I may try adding a narrow bar on it and see if that makes a difference to get rid of the bow problem. im thinking that if the pressure point is forced to be close to the bend line it would have to help. (?)