PDA

View Full Version : Finger Brake Sizing?



MinnesotaHSM
06-18-2010, 12:28 PM
I have been looking for a finger brake for the robotics team and I am a little confused.

Most finger brake specifications seem to say 16 gauge mild steel capacity. The stuff the team will be working with ranges from .0625" 5052 aluminum up to 37" long all the way to .125" 5052 (most likely not 37" long, but it could be). The most prevalent sizing would be .090" 5052. We also do .125" lexan up to 3/16" lexan.

So, can I buy a 4 foot finger brake with 16 gauge mild steel capacity and use it bend the size of stuff we use, or is that finger brake too small?

Thanks.

- T

camdigger
06-18-2010, 01:54 PM
Most finger brake specifications seem to say 16 gauge mild steel capacity. The stuff the team will be working with .125" 5052 (most likely not 37" long, but it could be). The most prevalent sizing would be .090" 5052. We also do .125" lexan up to 3/16" lexan.

So, can I buy a 4 foot finger brake with 16 gauge mild steel capacity and use it bend the size of stuff we use, or is that finger brake too small?

Thanks.

- T

0.125 5051 37" long seems a bit much for a finger brake. Seems up in what would require a press brake. There's a post or two aboeard here re ratings comparisons try a search. Press tooling will allow tayloring the bend radius to avoid cracking at the bend which could be an issue, too.

kf2qd
06-18-2010, 04:00 PM
For that thicker stuff the finger brake probably won't work, though it can go a bit thicker on narrower bends.

Do you have access to a hydraulic press? You could make a set of dies to use in the press and then be able to bend thicker stuff. You might haver to settle for a larger radius on the bend, but that does require a bit less force.

Ries
06-18-2010, 07:59 PM
Finger brakes are made that will handle up to 1/2" plate.
Here is a 1/2" powered leaf brake- this one doesnt have fingers, but I have seen em with fingers- they made em. Note- it weighs 30,000lbs...
http://www.locatoronline.com/machinery/detail.cfm?adid=350724

The designation "finger brake", or, more commonly, "box and pan", is totally seperate from capacity.

It is true that on thicker material, you need a radius nose bending bar- you cant expect to bend 1/4" aluminum 90 degrees with a zero radius bend- but there is no reason that you cant bend all the material you want with a finger brake.

It just will need to be a bigger one than a cheapie 500 lb tabletop chinese special.

I have a 4' 12gage Chicago D&K finger brake. It easily bends 48" of 1/8" aluminum. (Okay- "easily" might be a bit of an exaggeration- but it will do it)
In fact, although its a bit of a workout, I can bend 48" of 1/8" hot rolled steel on it, even though that is technically beyond its capacity. But a good made in america brake like my old Chicago is built just a bit heavier than the cheapo 16 gage machines- it weighs an honest ton, and is made of thick, heavy steel everywhere.

There is a grizzly/taiwan copy of the Chicago, and it would do what you want- and its pretty reasonable, considering a new chicago is well north of $5k.
http://grizzly.com/products/48-Pan-Box-Brake-12-Ga-/G0542
You may need to fuss with it a bit to get good bends in the 5052, though- either make a radius nose bar, using round bar for the tip, or just do a series of bends, making your bend radius bigger that way- do a bend of ten degrees, slip it out a sixteenth of an inch, do another one, and so on.

Rich Carlstedt
06-18-2010, 11:31 PM
Time Out fellows

Finger brakes are rated for Steel !
Aluminum is 3 times easier to bend than steel !
Careful of ratings from the imports ! they fudge

Rich

Rich Carlstedt
06-18-2010, 11:44 PM
Duplicate posting sorry

Ries
06-19-2010, 12:30 AM
Actually, Aluminum can vary quite a bit, but almost none of it is "3 times as easy" to bend as steel.

Mild steel has a tensile strength of about 55 ksi/kpsi

Here is a chart showing the tensile strengths of stainless and a wide variety of aluminum alloys.

Its absolutely true, 1100 full soft is about 1/5 the strength of mild steel.

But there are several hardnesses of 5052 that approach 40 ksi- which means they are 4/5 as hard to bend as mild steel, not 1/3.

which means you most definitely could not bend twice the thickness of 5052 as mild steel. At 80 ksi, on a brake rated for 55ksi full width, thats brake breaking time, right there. And also remember, those chinese brakes are pretty optimistic when they say "16 gage".

Most common aluminium has gotta be 6061, T5. Which is also around 40 ksi.

7075 in a T6 has a way HIGHER tensile strength than mild steel.

http://www.americanmachinetools.com/tensile_strength.htm

So its true, aluminum is softer than steel, and you could upgrade your brake's capacity a bit- but cheap import 16 gage brakes still are usually not built to bend 1/8" material very well- they dont have the range of adjustment of spacing for the bending leaf and the top leaf that a good brake like a Chicago does. On a Chicago, you can adjust the height of the top leaf, to accomodate a thicker material. And you can adjust the spacing out from the top leaf of the bending leaf, to allow for added thickness as well. This also means you can make an add on round nose bending bar, like a piece of flat bar with a round bar welded on its long side, and clamp it AND the aluminum down. This allows nice radius bends, and avoids cracking the aluminum.

Bending thick stuff on a small gage brake, even if its soft aluminum, will end up springing the brake sooner or later- they just aint built for it.