For what it's worth

[geraldmorrissey]

I have been having trouble bending the most outbd horizontal stab ribs. Unlike the other stab ribs, these ribs have straight edges and go from 7/8" aft to 1/2" fwd at the squashed leading edge tube. The flanges are 9/16" and I have not been able to get an acceptable part using a conventional pan/box brake. The edge of the flange bumps into the leaves before I could get a 90 degree bend on the small end. So I turned to my trusty Harbor Freight 30" mountable brake. I have used this tool alot so far. I had some left over .190 4130 plate from the wing strut attach fittings. Cut off a 3"×24" piece and made a new leaf. The reduced leaf thickness should give me the clearance I needed to get that extra wide flange. Should help with the bends on the ribs that have to fair into the .375 trailing edge tubes. Initial test samples are promising At $69.95 this brake is worth every penny. Plus you can get 15% off with a coupon. The image shows the brake with the new leaf installed.
Gerry
Patrol #30$

[geraldmorrissey]

Still no joy with the 3/8" wide channel, but close. I need to cut a longer bevel on the .190 leaf. This combined with a 1/16" radius (2.5 material thickness) should do it. Right now the radius is 3/32" (4T). Material springback is preventing me from getting 90 degrees on the second bend of the channel cross section. When I get this dialed in, empennage ribs should be dead easy to bend. I like building tooling.
Gerry
Patrol #30

[fairchild1934]

I had the exact same problem on the rudder ribs. The 3/8 hold down was hitting the flange on the work near the last bit of the bend. I took the factory hold down off and used a piece of 3 inch by 5/16 cold roll and then on top of that i laid a piece of 1 inch square stock. I laid the square stock about an inch back from the edge to keep it clear of the material being bent. That seemed to give the upper leaf a little extra rigidity. That allowed the 3/8 width at the small end of the rib-- but just barely. It still hits just a bit but it is in the spring-back zone--- so it does not block the bend now. It looks impossible with the factory hold down leaf. I considered milling a taper or a step-down at the edge -- but as long as it is- that would be a time consuming PITA.
i find I need 4 of the very heaviest bar clamps to get enough pressure to keep the work from sliding during the bending..
Another possible way to prevent the sliding -- would be to use a dummy piece of the same sheet as the work --- under the hold down leaf--- and have it up against some kind of stop screws on the rear side of the hold down leaf. but so far -- 4 big bar clamps have worked OK. Were it seems to want to slip is where I am trying to hold the narrow little edges where that 30 degree bend is. Not much area for the hold down to press on. Also those bends are where the hold down leaf hits the most on the small end of the ribs. ( I am using .030 soft steel sheet-- 1008 I think or 1007--)

[SpruceForest]

Before picking up the 50" 16G Jet brake, I modified a 30" Harbor Freight to do simple 90 degree stuff. One thing you might consider is mounting the brake to two separate pieces of 2x material running the short axis of the tool such that the brake can be mounted off the rear edge of a bench with access to the underside. That should let you use some Bessey-style F clamps with the operating end under the brake where you need the additional down-pressure. Not a great production setup with all the clamp/unclamp, but should get that additional down-pressure on the leaf to prevent slippage. On the returns, if the brake cannot be made to hold the work without slippage, an oak or rock maple mandrel fitted to the interior the rib allows hammer forming on the bench.

[fairchild1934]

I do use 3 bessie F-clamps and a 4-th clone from lowes. Tried oak and rock maple inserts to bend the 30 degree lip against--- sort of worked but it refused to make a clean bend line. kind of wavy and indistinct. as I expected. The HF brake does a better job. My setup looks all most the same as yours -
:-)

The blue lowes looks like it might be thicker than the bessie. I think it said 1200 lbs.

Tim