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777drvr

Well Known Member
Hi Guys,

I've used the search function and also Googled a bunch of terms and haven't found very good resources for this technique .

I want to add footwells to my purchased RV-4 and am working up to it by making some smaller parts out of .032" 2024 . I need to find a way to make neat , constant radius bends in aluminum sheet . I'm not satisfied with my results so far .

I'm aware that there are bending brakes that can be purchased or homebuilt . Can anyone recommend a product or plans ?

How is a bending brake used to make a box type structure ?

Thanks !
Marc
 
Marc,
If you want my little aluminum economy brake (Spruce 12-02800 MB-18 18" SHEET METAL BENDER $39.75) you can have it for half price, $20 plus shipping. Should be ok for .032, not very good for thicker materials.

Boxes are made with a "box and pan brake", aka a finger brake. Type it into Google Images.
 
Pan Brake in Action

Here's a picture from this weekend where I'm using my pan brake with one tooth removed to form a steel part with flanges on two adjacent edges:

100_2048a.JPG


That photo is from the 3 January 2010 Update of the HP-24 kit sailplane project website.

Note also the short section of radius shoe between the part and the teeth of the pan brake. It keeps the inside radius of the bent piece generous to prevent cracking.

In just about every town there's somebody with a pan brake. Just find the one nearest you and bring them some coffee and donuts.
 
Dan,


If Marc decides he isn't interested in your sheet metal brake, I'll take it.

Let me know!
Phil
 
You can also make bending blocks from wood. usually hardwood works best. Put the inside radius on the block, and the side of the wood that you're bending towards should be an acute angle to allow for springback:

______\


With the radius at the point, in this crude sketch.

Then make another block the same size. This one doesn't need any radius or springback allowance.

Place the workpiece between the blocks, line things up well, clamp, and use a third block and a mallet to make the bends. With a bit of practice you'll be able to make very nicely radiused bends.

A typical gotcha is to bend the metal a bit here and a bit there. That will stretch the edge of the metal and you'll never get it to become straight. Practice and you'll get it right.

You can make curved flanges the same way, with curved forming blocks.

David Paule
 
Bend radius is actually published

I am not near AC 43.13-1b, but I believe minimum bend radii are there. I recall it is a simple formula based on sheet thickness, like 2x or something like that. I am sure one of the guru's here can point you to it.
 
Thanks for the info ! I guess I have a pretty good idea of what I need to do . I thought there might be a little more info about basic metal working floating around . I did find some videos on Youtube that explained a few things.

Dan,
Thanks for the kind offer but being up in Canada , postage would be a bit high and I could buy that unit at the local'ish ACS for not too much more . Let Phil take advantage of your great offer !

Marc
 
Marc,

Up here in Canada you could try Princess Auto. They have a 36" bench mounted brake that works well. I've bent up to .125 alum with it! You'll have to round off the corners of the clamp bar when you get it and don't forget to use the proper SET BACK for the size of metal your bending.

regards,

Pat (acwrench)
Calgary, AB
 
Would that be the 24" box and pan brake for $350 ? Can you put an appropriately radiused piece of aluminum under the fingers before bending ?

Do you wrench for AC ? I drive for AC..

Marc
 
Another small point:

Always try to bend "across" the grain. Bending with the grain is asking for cracks.

BTW, I'm in the market for a 4' finger brake at a good price.
 
marc,

yes i do twist wrenches for ac in yyc.

the brake is 36" wide and about $100-$125, real simple design, but works well.

Pat
( in Calgary)
 
Small DIY Bending Brake

I need to make a few bends in some smaller parts but was too cheap to go buy a brake. I used some scrap aluminum from the local home improvement store that was leftover from building my trailing edges and also a piece of leftover hinge. It's 13" wide and I've bent some test pieces of 0.032" with really good results, although I'll probably add a handle to make it a little easier. I need to get a thicker piece of angle for the top to make a larger radius for bending 0.063".

bending_brake.jpg


brake_underside.jpg


close_up.jpg
 
Bum and aircraft and fly down to St.Thomas and I will bend them up for you and give you a basic metal bending lesson to boot!
 
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