anyone tried building the home made 8 foot metal brake

[fairchild1934]

Thought I might try this in expectation of the spar webs. I am concerned about letting someone else doing the bends-- im in a small town with few
machine shops. A computer controlled press brake would do the best job--- but the simple folder types are more likely what we have here and prob many would have beat up blades which would create imperfections in the bend line.

wondering if anyone had tried the home made version. wondering what hinge size was used---- how heavy duty does the hinge need to be for .032 T3.

Tim

[Chris In Milwaukee]

It's been a while, but I used a proper 10-foot brake to bend my spars and it took two people and it took a fair bit of serious clamping pressure to make sure nothing slipped. I'm have a doubt that the average homemade brake would do the job. .032 2024 is some seriously tough stuff!

[Bcone1381]

Are you attending Oshkosh this year? Maybe you could use their brake.

[fairchild1934]

not quite ready yet-- and I could not leave town right now anyway.
I made a little one for doing the rib stiffeners- they are about 5 inches long. Yes--- clamping pressure will be a challenge there. I might be able to make some kind of stop piece that lay under the top piece so that the work would butt up against it. Maybe some hardened steel tabs .032 thick.
I was thinking of using toggle clamps but the flange on the spar may be too wide to allow it.
Most of them have a V shaped tensioner that goes above the hold down and has a turnbuckle. That transmits some pressure from the ends to the center areas so clamping pressure is more constant down the length.

T

[Chris In Milwaukee]

Are you attending Oshkosh this year? Maybe you could use their brake.

Interestingly, theirs is the one I used.

[alaskabearhawk]

There is a reason why brakes are built like a tank, especially long ones. The force required to hold and accurately bend a long length of sheet metal, especially 2024T3, is huge. The bending forces on the brake necessitate thick steel and the huge counterweights help our puny arms complete the task. I’m with Chris on this one, even if it means driving a long distance to have it done on a proper piece of equipment.

[fairchild1934]

if Ican find someone who has an 8 or 10 footer in town- I will have to carefully inspect the blade edges to see if they are dent/ gouge free----
My idea was to bend sone pieces as wide as the spar but only an inch wide to use in setting up the full sized piece. (so they match my ribs exactly)
I will have to calculate how much rear clearance I need for the flanges behind the hold down. Some big heavy c-clamps every 2 feet might be enough pressure-- ????? (if they are deep enough---)

Did yall try to leave some extra material left to be trimmed down on the ends of the flanges--- so the only dimension to be held was the distance between the bends ?

Tim

[Frank]

After seeing another LSA builder successfully built "Dave's Cheap Bending Brake" I did the same. My efforts were less than perfect. (see my previous posts)
I rounded off the bending edge to the specified bend radius with an angle grinder. The test pieces looked great. The aileron spar bends looked great.
But the eight foot pieces ended up with a slightly larger than specified bend radius. The .032 puts up a lot of resistance. And just enough slop in the system to matter.
This created a problem for internal dimensions within the spar webs. But I have a Bob-approved work-around. (again, see my previous posts)
Bottom line, a heavy commercial brake will a better job no doubt. But the DIY brake will get it done.

[Chris In Milwaukee]

Did yall try to leave some extra material left to be trimmed down on the ends of the flanges--- so the only dimension to be held was the distance between the bends ?

Tim

I cut up a few scraps the same width as the spar blank and a few inches wide so I could get the offset just right. Didn’t take too much finagling.

[Sir Newton]

Yes I did build a brake. Pain in the ass with limited success. You need a 8 ft hydraulic press brake with overing 90° dies to bend up the spars. Keep bend radius over 0.125 - 0.188
Any self respecting HVAC shop will have this type of brake. Expect $80 -$100 per hour.

[geraldmorrissey]

Might ask the local EAA chapters if they have a brake. I see them all the time on Craigs list. Usually $1,500 for a 8', a little more for 10'. Buy, do the job, store it for a year while you try to sell it for $1,500 or a little more for a 10'.

[fairchild1934]

Thanks for the feedback-----

Frank------ did you have the turnbuckle rods installed on the hold-down and on the "folding" leaf ? Those are supposed to help with the problem you mentioned... I see even the heavy commercial ones have those tensioning rods..........

No one in my EAA chapter is scratch building--- so they havnt been the answer man on too many of these type of fabrication issues.....

[Frank]

Turnbuckle rods not part of Dave's Cheap Bending Brake plan, which I basically followed.
Reach out to johnb and read his posts. He voiced no complaints using the same plan.
This plan relies on stainless steel piano hinge and multiple bolts through the hold down bar.
Use ss fasteners. Use every hole in the hinge. Maybe even add extra fasteners for the hinge.
I used a six foot hinge cross the middle and one footers at the ends. Use multiple bolts for the hold down.
Find a way to measure the inside radius of the bend. Don't be fooled by short test pieces.
LSA plans call for a bend radius of .10 but you may need a bending edge radius even smaller.
As part of testing, measure resulting cap strip top to bottom distances.

[sjt]

As an aside, Bob told me not to pre cut rib to accommodate cap strips. Not cutting early was very important in my build.

I do not know for a fact Bob's reasoning, but this is why it helped me:

I used a real 10 foot brake. My son and I both had to lift - I think it is called the "leaf arm"

I found that even with best effort you will not get a uniform bend along the entire length of the spar - and that is with a real brake.

This is where Bob's do not cut early helped.

I took all of my ribs (aileron center flap) and sorted them to where they gave the best average fit to the non uniform spar web.

I was only able to do this because I had not pre-cut them to a specific location.


My theory as to why ribs are different one to the next has to do with the grain of 2024 sheets. I cut my blanks at what ever angle to the 2024 grain gave me the most useful number of ribs per 12 foot sheet.
The end result is that when you bend the ribs over the same mdf form block, the material will bend differently one to the next. Not much, but enough that you will like them at different locations along the length
of the spar.

angle.jpg


I taped my shoes to the brake to give me the radius that I wanted. I had shoes over shoes to create the bend radius.
shoe4.jpg

One other thought, If you to to the trouble of finding a 10 foot brake, make sure and do the trailing edge - like in Bob's booklet
trailing.jpg I used drill rod to help form the trailing radius.

The plans also call for stiffener on the trailing wing skin
stiffener1.jpg


More recently, Bob recommended c shaped stiffeners for the wing skin - This also needs a 10 foot brake.
l1.jpg

l2.jpg

https://bearhawkforums.com/forum/bearhawk-patrol-plans-build/52865-plans-update-wing-skin-stiffener

Also there is a false spar for the gas tank support that can be done on the brake.

[fairchild1934]

Stan--- is this stiffener--- a single piece with the flanges cut away where it clears the rib flanges ? or are they short pieces - one for each bay---- ???

also---- where are you making "a cut" to accommodate a particular location ? are you talking about the front of back where they all most butt up against the spars ? I THINK--- all of my nose and main ribs are identical---- is THAT a problem ?????

PS---- just checked the height of the rear of my nose ribs and the fronts of my main ribs--- they seem to be uniform to within plus or minus the material thickness..... not too much variation----