Sheet metal bends and brakes-

[fairchild]

This is probably a "beginner" question- but here goes-
Thinking about the C spar sections. How to bend them-
I remember there are two basic types of brakes- one type which is called a press brake - has male and female dies and the upper die is often a "rod" type cross section- and the
size of the "rod" determines the bend radius.
The other type brake is the manual "leaf" type where it has a set of jaws which clamp the surface and a rigid blade which is offset from the clamp- and the leaf rotates- and brings the material
around to make the bend. If I remember correctly- there is an adjustment to vary the distance from the clamp to the leaf-

My question- is this distance adjustment used to vary the bend radius ----- rely that the material in the bend area will naturally form a "regular" circular bend though there is no support
to force the the bend to conform to a particular shape ???? I immediately noticed that Bob's plan show constructing a aluminum sheet metal "shoe" that slips over the leaf to give the
work something to backstop the bend area against. I THOUGHT this shoe idea wasnt something that non aircraft sheet metal guys use normally. I think its a great idea-
The reason I am asking about it---- I may have a chance to get a used 8 foot brake fairly cheap--- the leaf type--- but I wanted to find out if that type should work fine for bending
the spar C sections. (assuming I make the extra shoe tool to go on it) I assume I would want to go down the leaf and the clamp jaws inch by inch to check for dents or offsets of
any kind of discontinuity (where some ignorant goon tried to bend something stupid with it) Its previous owner was an aircraft restorer- so I dont expect HE hurt it any---
It looks like an older unit from WW2 era maybe. Cant remember the brand but one of the major ones. i am thinking if I could get it for 1000$ that would be doable. ( If I buy the
prebent spar parts - they will be about 1500-1600$ ) So if it is a useable unit with no major defects in the leaves----- wouldnt that be OK ?
I am sure there are places here in town that will have CNC hydraulic press brakes---- but-- there might be advantages to having your own tool ......
I would just as soon do the "work" myself too. I think I have room for it too.....
Just depends too if they guy wants to sell it too--- havnt asked yet....
Opinions ?

Tim

[BTAZ]

I had the blanks sheared out at a local HVAC place for $40 cash and I used a well worn 8' leaf brake(was at the local CAF hangar) to bend my spars with a "shoe" as you described.

Make a few trial bends and adjust the brake as required.

Put a digital level on the leaf or arm so you have a way to measure leaf movement vs resulting bend angle.

The movable leaf was "sprung" a little bit so the bend wasn't 100% consistent over the full length.. Easy to correct by putting a shim as required between the leaf and the spar material to add a little more bend to the "under bent" center area.

Worked just fine.

Note only issue with buying it is that it will take up floor space and is bigger then you need for everything but the spars. If the price is right and space is limited, buy it, use it for your spars, and then possibly sell it at a profit(or at least break even)

[fairchild]

I have a 4 foot jump shear. (probably needs to be sharpened...)
I cant think of any (non-chinese made) tool i have regretted buying- new or used-
Tim

[S Lathrop]

Other than the spars, I have done all my bending with a 4 foot box and pan brake and a 4 foot press brake. The trailing edges of the ailerons and flaps will require more than a 4 ft. bender. Again a long press brake is the best tool to do those parts as well.

I had my spars done on a press brake. The quality of the bent and accuracy is way better than a leaf brake. It may be a case of being too particular with the spar bends but those are probably the most critical bends to get right.

I would say that a 4 foot box and pan brake will be the most useful tool to have in the shop.

[BTAZ]

good point regarding what to try to get bent when having access to the large brake.

I had sheared and then bent all the front/rear wing spar channels as well as the aileron spars and the trailing edges(no flaps on the LSA). Those were the only things that needed an eight foot brake.

As mentioned in other posts, I used my modified small HF leaf brake for the hundreds of stiffener and rib attach angles Lots less labor then working a larger brake.

An 8 ft brake would be great to have if you have the room for it but it is only needed for about a days worth of bending. A four foot shear and a four foot box/pan brake would be much more handy to have for all the other bending to be done.

[Bcone1381]

An 8 ft brake would be great to have if you have the room for it but it is only needed for about a days worth of bending. A four foot shear and a four foot box/pan brake would be much more handy to have for all the other bending to be done.

In Oshkosh, the EAA's Kermit Weeks hanger has a 10 foot brake and an 8 foot brake. The Patrol has a flap spar that is almost 9 feet long. I suspect that the Model B has a similar length flap. A few bearhawk builders have used it to bend all the spars.

[BTAZ]

As Bcone pointed out, you might need a brake longer than 8' for the Model B wing(you will need to check your plans). I know that's the case for the Patrol and it might now be the case for the four place.

In the end, you need to make roughly 18 "long bends" per wing(four for the front spar, four for the rear, two each for the aileron and flap plus three each for the aileron and flap trailing edge, perhaps a couple more if there is a false spar behind the fuel tanks)) so roughly 36 to 40 total "long bends".

You will need to make approximately 400 bends for the rib stiffener and attach angles(somewhere around 10 angles per rib location, roughly 20 rib locations per wing, likely more). Working the leaf on an eight foot brake to bend nominally 6" long angles more than 400 times wouldn't rate high on my fun scale.

Again, if the price is right and floor space isn't an issue, buy it. Like you, I have never regretted picking up quality tools when the opportunity presented itself. There were lots of tools(like a small corner notcher, my router table, a small power hacksaw, oddball reamers, etc.) that I had acquired over the years that hadn't seen extensive use until the airplane project and are again patiently waiting for the next time

But keep your eye out as well for something smaller.

[fairchild]

Thanks for all the responses---
I am just starting to study the plans...... didnt realize there were 9 foot parts. Im not an experienced blue print reader so it may take some time to understand the
interrelationships of the parts. Good thing that its possible to order .025 and .032 in a rolled up form ! Lots to study and think about ! This forum may be a lifesaver for many.
Tim

[BTAZ]

The cap strips need to be shipped flat and will be oversize so have to go as a truck shipment. Since I was already paying for a truck shipment, I ordered the spar aluminum as flat sheets as well to ship at the same time..

Didn't add to the cost of the truck shipment and probably was easier to shear and work with for the spars.

All the other aluminum sheets were purchased rolled.

I also ordered the longerons at the same time as they to exceed the 8' limit. However, I purchased a tubing kit from AviPro so they ar sitting up in my rafters.

The original four place only needed an 8' brake. The updated B version might need a longer brake.

[Foxes Hollow]

I have a 10 ft sheet metal brake like the vinyl siding installers use for soft .025 aluminum. Is this brake strong enough to bend the .025 and .032 2024T3 aluminum.

[sjt]

I do not think so. 2024 is hard stuff, and you also have to use some sort of shoe on the brake to get a radius for aircraft work.
shoe.jpg

Use of a protective shoe requires that the brake can be adjusted back.

real brakes have this feature:
b2.jpg

I copied the concept and remade my 4 foot brake to do the same:
b1.jpg b4.jpg off the shelf it looked like this but not enough adjustment for a shoe.


I can not find it now but another builder was able to make a custom shoe without having to modify his brake.

I do not have access to a machine shop so I tried to make a shoe out of mdf with a drill rod insert.
It did not work.
mdf.jpg

More recently I have had more success buying 1/4 and 3/8 black iron pipe and welding up shoes.
p.jpg