Box and Pan Sheet Metal Brake Study

[cjtoombs]

I have had a desire for a box and pan brake for some time. I'm not looking for a huge one, I don't have room. I previously built the Gingery brake, which I have used on numerous occasions, but it is a bit limited in size, and doesn't have the box and pan feature. It also has no adjustment for the sheet metal thickness, meaning you have to build it to handle the maximum thickness you intend to bend, with anything thinner being bent in a sub-optimal way. So I've started looking around at some plans that I've found in various places. I have one set from some old issues of Hobby Machinist, and there is one in either book one or two of the Metalworking series from Village Press. There is a set available at Mr Wellwoods Shop of Horrors. There is also a set available from Machineryplans.com, which is rather unique in design. I decided to start with that one and purchased the plans. I proceeded to build it out in Fusion 360. Overall the plans and instructions for it are pretty good, I think a video overview and demonstration of it would have been nice, but after the Fusion build I have a good idea of how it operates and some likely pros and cons. Here is a render of it:


I didn't bother with the stand, as I didn't really need to for the purposes of this study, but it looks to be quite a nice stand. For those of you looking to purchase these plans, be warned that they are metric, as it is based out of Australia. So I'll go into some of the things I like about it as well as what I don't. I like the bending leaf attachment method, as it does away with the need to machine the bending leaf itself, one could just use a piece of cold rolled and call it a day. Overall the machining required on this is fairly simple, although you may need to machine the entire bed if the welding warpage is too bad to use as welded. It does require quite a bit of welding. The unique finger setup is rather interesting as it eliminates the need to have a large number of fingers and allows radius bends with minimal extra equipment. I believe that one could get by without making a lot of mandrels, as the author calls them. I did not model the mandrels, by the way, so one is not shown in the render. One thing I don't particularly care for in this design is the method of adjusting for the sheet metal thickness, which involves set screws in the pressure beam fingers to move the mandrel towards or away from the bending leaf. I think I would look to add an eccentric mechanism to the pressure beam pivot in order to make this a bit less fiddly. While I'm at it I might change the pressure beam adjusters to a turnbuckle to reduce fidling there, as well. Of course, I have to redesign it anyway, as I will be using imperial sized material. The capacity on this is around 2 feet in width. I will be looking at the other designs at some point in the future, but don't hold your breath, it may take me some time to get around to them all.

 

[Winegrower]

Years ago I bought an HF 12" finger brake that has been completely adequate. It has enough adjustments for material thickness and good alignment/setback, and if there's something larger, either longer or thicker, it moves to the HF 20T press where I kludged up a couple of ram and dies out of some angle iron for different width bends. I have to admit most of what I do is not high accuracy bending, so the HF stuff works OK for simple needs.

 

[C-Bag]

Years ago I bought an HF 12" finger brake that has been completely adequate. It has enough adjustments for material thickness and good alignment/setback, and if there's something larger, either longer or thicker, it moves to the HF 20T press where I kludged up a couple of ram and dies out of some angle iron for different width bends. I have to admit most of what I do is not high accuracy bending, so the HF stuff works OK for simple needs.

I found a HF 3n1 brand new still on the pallet from ‘99. After the usual clean up and some mods it has done everything I’ve wanted. I was going to make a brare but really needed a box and pan and realized how much in just metal I’d have spend let alone time I don’t have. For the $230 I paid for it I would had a hard time making just a brake for that, let alone a shear and slip roll. I also think the 30” size is way better than 24”. YMMV.

 

[cjtoombs]

I've looked at the 3 in 1 machines before, my problem with them is the capacity on them is generally spaced at 20 gauge. 18 is about the thinnest that I use. That's also the case for most small box and pan brakes sold commercially.

 

[C-Bag]

originally the blurb on the site said 18ga. I guess it depends on how big a piece or something. I have sheared and bent like 16ga that was way less than 30" wide with no problem. Probably the biggest thing on the 3n1 is make sure you have both handles, one on each side. They typically only come with one. The way it works the actuation goes through one of the rollers to the opposite side and with torque you get the sides out of sync. This lessens the actual torque to like the shear and I think causes the arm to break. This seems to be the most common failure besides not adjusting things correctly as far as I can see. There are other details like the silly spring loaded hold down only obscures your vision to the shear and also adds to the amount of pressure it takes to shear. The other is the crappy "bearings" in the arms that engage the eccentrics. Mine looked like they were installed by a toddler. I took them out and installed roller bearings and the whole machine basically has no inherent drag now. Before it would not let the handles just fall through on their own weight. You had to pull it through. Now they just fall through. Shearing is way easier now. All that internal friction only makes things more hinky. Yeah, it will never be as nice as a stand alone, but it costs a fraction of what one machine would cost and has a third of the footprint of the 3 stand alones.

 

[cjtoombs]

The second one I'll look at here is from Mr. Wellwoods shop of horrors, and can be seen in this YouTube video:

I modeled it as well, here's a render:

This design requires no welding, and most of the work on the flat parts can be done on a drill press and bandsaw, although you will have to notch the bending leaf and the bed leaf to clear the 3/4" pin. These plans have a couple of errors, the first on the Side, the angles on the ends of the part are not defined, which means that the distance between the hole where the shaft goes through is not defined lengthwise. There's probably a bit a wiggle room for that hole, so I just made it look simmilar and the model looked like it would work fine. I did put in the motion, but I have not figured out how to get the nested rotate constraints to work right, so I can't be 100% sure. The other error was on the clamp cam, the bearing surface should be .380, not the .505 it is in the drawing. Other than that they were easy to understand and model. I also modeled the angle parametricaly and I did this with 4" x 3/8" angle as well as the 3" x 1/2" angle, as I happen to have about 10 feet of 4 x 3/8 in my metal pile. In fact, I probably have all the metal I need to build this, if i want to cut it all out, as it is in a 12" flat bar of 1/2". Overall this incorporates what looks to be a fairly easy method of adjusting for the metal thickness in both directions and does not require any welding. The plans and model are for a 36" brake, but it would be a simple matter to make it narrower. The plans can be found by following the link below the video I posted above.

 

[C-Bag]

Interesting design. Surprised there’s no brace across the top to support the middle of the upper brake.

 

[cjtoombs]

Interesting design. Surprised there’s no brace across the top to support the middle of the upper brake.

If you watch the video and read a bit on his website, it is clear he was working within the materials and capabilities on hand. I think adding that feature would not be terribly difficult, if one were to add welding to list of capabilities. At this length, it would probably help, if you shortened it to 24" width, it may not make as much difference.