Building the Po' Boy Bending Brake

How do you think the wooden brake would do on 8 foot lengths of .032
2024t3? I suggested something almost identical a while back on the
Bearhawk list for bending the spar webs and was met with much skepticism.

-------------------------------------------------------------

Dear Del,

'Think' or know for a fact? :-)

As a general rule the upper limit for wooden brakes is about .063 for tempered
stock but a lot depends on the quality of the wood and workmanship.

Although the load per unit of length remains the same the overall magnitude of
the load naturally increases with the length of the bend. It also becomes more
difficult to keep the leaf in the same plane as its length increases. There
are fairly simple solutions to each of these problems and I would have no
qualms about making up a long brake for .032 myself but I've got a lifetime of
mistakes behind me :-)

I couldn't find any .032 scrap but I did come across some .040 under the bench
and put a 1" flange on a piece just to give you some idea what a wooden brake
will do. (See the pictures WOODEN_BRAKE 05 thru 08 in the file previously
mentioned.) Other than adding a bar and a couple of clamps this is the same
set-up for .016 meaning the radius is all wrong. But what I wanted to
illustrate was the fact that a wooden brake is more than adequate
strength-wise. The real problem is maintaining the uniformity of the bend as
the length increases. It can be done but the solution will depend on your
tools and experience, the quality of the wood you use and how well the brake is
secured. For an eight footer you're talking some loads that will throw the
typical workbench all over the shop; it needs to be secured to the deck.

-R.S.Hoover

In Veeduber wrote:

Dear Del,

'Think' or know for a fact? :-)

As a general rule the upper limit for wooden brakes is about .063 for
tempered stock but a lot depends on the quality of the wood and
workmanship.

Although the load per unit of length remains the same the overall
magnitude of the load naturally increases with the length of the bend.
It also becomes more difficult to keep the leaf in the same plane as
its length increases. There are fairly simple solutions to each of
these problems and I would have no qualms about making up a long brake
for .032 myself but I've got a lifetime of mistakes behind me :-)

Thanks for posting the info and the additional pictures. Since this
would be for the wing spar webs, the dimensional uniformity is kind of
critical so I am still going to try to pursue other options before
trying a wooden brake. I may have a line on a real 8' brake I can
possibly use, and I'm seriously considering just taking the plans across
town to Atlee Dodge and having the spars bent there. It will cost me
some labor but at least any mistakes won't be on my nickel.

If I go with the wooden brake idea, I'm thinking along the lines of a
4x6 treated beam for the leaf if I can find one straight enough.
Treated only because they seem to be less warped by the time I get my
hands on them.

----------------------------------------------------
Del Rawlins-
Remove _kills_spammers_ to reply via email.
Unofficial Bearhawk FAQ website:
http://www.rawlinsbrothers.org/bhfaq/

If I go with the wooden brake idea, I'm thinking along the lines of a
4x6 treated beam for the leaf if I can find one straight enough.

--------------------------------------------------------

Dear Del,

Consider a couple of different lines :-)

The point of contact with the metal is seldom more than half an inch wide and
usually less. The only thickness consideration in the leaf is to accommodate
the fasteners.

The leaf is a LEVER. You should be more concered with its depth; 2x10 or
2x12... something along those lines.

You only need one square edge to accomplish the bend. Doesn't really matter if
its warped, bowed or BOTH... so long as you square it up before attaching the
hinge.

Drawing from the knot-hole collection at the local Home Depot, the best leaf
material is often 1x12 pine shelving... albeit cupped, bowed, twisted & warped.
Simply pick a pair of complimentary boards, REVERSE their defects, slather on
a good coat of urethane glue on both surfaces, clamp them together and secure
with one deck screw for about every 9 square inches of surface. Then leave the
thing to cure, well supported and out of the weather. True up one edge and
there's your leaf.

There's a lot less to accurately bending tin than most folks realize. The
problem is that most homebuilders have no experience doing repairs in the
field, where your only option is to use whatever is available to accomplish the
task. Bending one airplane's-worth of tin isn't anything to get excited about
and even a rather casually built Po' Boy brake is capable of producing better
accuracy than the average homebuilder can utilize.

-R.S.Hoover

"Veeduber" wrote
Dear Del,

Consider a couple of different lines :-)

The point of contact with the metal is seldom more than half an inch wide
and
usually less. The only thickness consideration in the leaf is to
accommodate
the fasteners.

The leaf is a LEVER. You should be more concered with its depth; 2x10 or
2x12... something along those lines.

-R.S.Hoover
????????????????????????????

Perhaps I missed it. Where are the pictures?
--
Jim in NC


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Most roofing suppliers or contractors have sheet metal breaks. Most
of these place will do your bends for you(10' long, upto .063")for
about a buck a piece plus $0.15 cents for additional bends on the same
pieces. If you tell them you only need 10 to fifteen pieces and its
for a homebuilt airplane, they might even bend them for free.

Bryan

(bryan chaisone) wrote in message om...
Most roofing suppliers or contractors have sheet metal breaks. Most
of these place will do your bends for you(10' long, upto .063")for
about a buck a piece plus $0.15 cents for additional bends on the same
pieces. If you tell them you only need 10 to fifteen pieces and its
for a homebuilt airplane, they might even bend them for free.

Bryan


True, but most of the operators know nothing about aircraft tin
bending. Get them to bend up a small piece first and check the bend
radius before you give them your good spar material. Drip rail and
heating ducting don't care if they get bent a bit tight. 2024 tends
to complain.

"Morgans" wrote in message


Perhaps I missed it. Where are the pictures?

http://groups.yahoo.com/group/Fly5kf...SIC%20BENDING/

Or

http://25th.com/t2/viewfull.php?index=621
http://25th.com/t2/viewfull.php?index=622
http://25th.com/t2/viewfull.php?index=623
http://25th.com/t2/viewfull.php?index=624

For a brake I built with Veeduber's inspiration. This is an 8 ft'r.

Veeduber wrote:
How do you think the wooden brake would do on 8 foot lengths of .032
2024t3? I suggested something almost identical a while back on the
Bearhawk list for bending the spar webs and was met with much skepticism.


-------------------------------------------------------------

Dear Del,

'Think' or know for a fact? :-)

As a general rule the upper limit for wooden brakes is about .063 for tempered
stock but a lot depends on the quality of the wood and workmanship.

Although the load per unit of length remains the same the overall magnitude of
the load naturally increases with the length of the bend. It also becomes more
difficult to keep the leaf in the same plane as its length increases. There
are fairly simple solutions to each of these problems and I would have no
qualms about making up a long brake for .032 myself but I've got a lifetime of
mistakes behind me :-)

I couldn't find any .032 scrap but I did come across some .040 under the bench
and put a 1" flange on a piece just to give you some idea what a wooden brake
will do. (See the pictures WOODEN_BRAKE 05 thru 08 in the file previously
mentioned.) Other than adding a bar and a couple of clamps this is the same
set-up for .016 meaning the radius is all wrong. But what I wanted to
illustrate was the fact that a wooden brake is more than adequate
strength-wise. The real problem is maintaining the uniformity of the bend as
the length increases. It can be done but the solution will depend on your
tools and experience, the quality of the wood you use and how well the brake is
secured. For an eight footer you're talking some loads that will throw the
typical workbench all over the shop; it needs to be secured to the deck.

-R.S.Hoover
Why not visit your local scrap yard & pick up a couple of
large-dimension steel angles in the length you need. At under 20 cents a
pound, you probably won't spend much more money & the strength would be
a lot higher.

Charlie

Why not visit your local scrap yard & pick up a couple of
large-dimension steel angles in the length you need. At under 20 cents a
pound, you probably won't spend much more money & the strength would be
a lot higher.
---------------------------------------------------------

Dear Charlie (and the Group),

In fact, most guys probably do, as I alluded to in the original article. Of
course, this assumes they can weld (and cut) steel, have access to suitable
hinge(s) and so forth.

The result is a more or less permanent part of your shop. Which can get a bit
silly if you're only building one airplane and only need to brake a couple of
bends.

-R.S.Hoover