Post By Bob E
Post By gbent
Question about box pan brake capacity
I have been looking for a box/pan brake for years. In my area used units are hard to find and expensive. I purchased a Tennsmith 48" brake yesterday for $250.00 which is a steal around here and about 1/4 of the price of a new one shipped. It is in excellent condition other than there are a few fingers that are deformed from someone, I suspect, trying to use it for something thicker than the 22 gauge mild steel it is speced for.
My question is what makes a 16 gauge able to handle thicker material than a 22 gauge? Many I've looked at had, what appear to be, hardened or ground jaws. Is this one of the main strength contributors?
I will be using mine mainly for making sheet metal covers for my bee hives so I don't need a heavier duty brake but I am curious about what, if anything, I could do to it if the need arose for bending thicker material.
Lastly what is the recommended fix for the teeth that are deformed. They are slightly rounded up at the very edge of maybe 1/2 of them. The guy I bought it from said that if he was going to repair it he would just grind off the front but I don't want to make problems.
The frame is heavier on the bigger units. IIRC the force to bend material is the thickness squared. So going from 22ga(0.030") to 16ga(0.060") is four times more. The frame and jaws have to be thicker to handle the higher force. Compare the weights on the tennsmith website: The U48-22 is 300# where the HBU48-16 is 500#. Don't try to bend thicker material than rated. It can snap the frame.
To fix the fingers, I'd take them off and press them back into shape.
If you just grind off any raised metal, that will suffice for making clean bends on all but the thinnest material, but if you want perfection, find someone who knows how to make TIG repairs on tool steel and then grind the welds back to flush.
Originally Posted by challenger
edit: oh yeah...great price!
I've got a Roper Whitney 16 ga version of the same brake. No appreciable difference between the R-W brakes and Tennsmith. Actually, when Jet made theirs in Taiwan, it was a better looking brake than either of the above for about 30% less money. Back at the time, I would've bought the Taiwanese Jet over either of the others if I'd seen it first.
There's not really anything you can do to increase the capacity. IMO, the way they deflect when used at their stated capacity, they're already overrated from the get go.
If its just the very end of the fingers that's curled up, that could've been done by bending something with the top frame adjusted too far forward, leaving inadequate space between the leaf and the fingers and pinching the ends of the fingers as a result. Most of the time, if something gets messed up by trying to bend something too thick on these brakes, the result is the fingers get sprung outward up in the area where they attach to the upper beam. That's where the load is transferred into the beam, and due to the construction of the clamping mechanism, its the weak point when the brake is overloaded.
Unless a dead sharp corner is required, these brakes live longer if you adjust the upper assembly back somewhat from the intersection line of the bed and the leaf. It puts a bit of a radius on your bend, but it greatly reduces the load on the various parts of the brake when you make a bend.
And, FWIW, the fingers are just mild steel, so if any welding needs to be done on them you can use whatever process is handy.
Good score. I'd have bought it for that price, and I already have a bigger one.
Leaf brake specifications I've looked at specify the capacity with the top clamp set back from the pivot 2x metal thickness. If you change the set back to 3x and make your bend in a couple of pulls with unclamping and reclamping the top between each pull you will gain a little capacity.
Just a heads-up, the proper way to use a leaf-style pan/box brake is to adjust the fingers AWAY (inboard) of the separation line between the leaf and the body by the same amount as the material thickness you are bending. Super easy to do: lift your upper body assembly with your side arm so it just clears the lower body friction-wise (which should be adjusted so that it stays up in any given position that you put it in, without slamming back down), loosen the fingers you will be working with, push them inboard, stand a piece of material vertically on the bed of the brake with the outer edge of the material on the line where the leaf meets the body, and gently bring the fingers forward to touch the back side of the material (this is if your uppper body doesn't have front-to-back adjustment screws, the larger models have them), and tighten down the screws holding the fingers. The farther the fingers are back, the larger your radius on the part, and less stress on the frame. I have a heavy duty chicago-brand (made in taiwan), I'm guessing late 80's vintage, that will bend 14ga over 6ft no problem, if you have two fat guys to pull down the arms (unluckily i'm starting to classify as "weight-rated" for that duty). If you have the front-to-back body-adjustment screws on you brake, always remember to take out your backlash, b/c the upper body will drift backwards under load. P.S. your clamp position on the upper body should be adjusted according to material thickness for the proper grip (there is some leeway), but I wouldn't use the same setting to grip .032'' aluminum (bent thousands of flanges before we got our cnc press brake), vs. a short piece of 11 ga crs.
They are pretty serious about those ratings a 22 ga brake is not a 16 ga brake. I have had to fix so many of those things because people think that it is 22 ga for the whole 4ft and 1/4inch if they are only bending 12 inches. It is 22ga no matter what. Slip rolls are the worst they get so trashed when people try and roll 1/4 inch stainless through a 16 gauge roll.