Thorp Air Command - T18.net

I have now trashed 4 #574 bulkheads. I can not get the bulkheads to lay flat after I cut them and bend the inside flanges. Once I take them out of the form blocks, I can not flute them to get them to lay down. I end up fluting (and more bending) until it cracks at the inside flange in the curved portion.

I am missing something. Please help this idiot. Shouldn't I be able to flute the bulkhead flanges until it lays flat???

Shorten up that flange just a bit on the curves Ryan, this is the inside curve your having trouble with? Dan

yes, its the inside curve that always cracks. But, I cant get the dang bulkhead to lay flat after I take the form blocks off. I always crack the inside radius while attempting to get the bulkhead to lay flat.....

Like Dan says -- Allow for no more material for the flange than it requires. Polish the edge so there are no nicks or other stress risers. You must stretch the metal on the inside. Start in the middle of the curve with a plastic hammer and knock it down a bit, then work on either side 'til you get to the straight part. Work a little at a time. don't worry about getting a full 45 degrees. If you are successful in getting the edge stretched, the bulkhead will lie flat. While you are at it, do not stretch any of the straight parts of the flange. This will make the edges longer than the parent metal and it has no choice but to raise up and not lie flat. You should not need to flute any of this.

_________________
Bob Highley
N711SH
SN 835
KLAL

i'll give both of yalls suggestion a try. thanks for the input.

I'll give you another...........I used a finger break and bent up the outside flange. Cut the center out and as Bob suggest, filed and sanded the edge to eliminate any stress risers. Clamped one side of the flange with a 1" board, leaving the cener protrude out from the table. Now, using 1" roller bearings on a 16" flat bar rolled the inner flange.

thanks Bill.

After reading this topic I was motivated to give it a try myself. I used the 2 form block method with the bulkhead sandwiched in between. I cut a 45 degree chamfer on the inside flange of the form with a router and used a hard rubber mallet to form the inside flange, starting in the corners and then the straight sections, forming a few degrees at a time. After a few passes it was forms all the way down against the chamfer minus a few degrees for spring back. When I removed it from the form it was nice and straight, no warping or waviness at all. I credit it to the helpful tips here or just dumb luck, but I couldn't be happier with the results. The only problem I see is that it's not quite 45 degrees per the drawings do to the spring back.

Nice job! Remember to make the 45 degree flange on the bagage compartment bulkhead bend to the rear instead of forward. This will make installing the luggage compartment rear panel so much easier.

_________________
Bob Highley
N711SH
SN 835
KLAL

Bob, thanks for the tip. I think you told me the same thing when I posted the video the forms being cut. I have it it in my notebook so I won't forget.

Brad Moore
Columbus, IN

now that aint right! dang!.......im kidding, of course. That does look nice.

Dick-I got your PM and I appreciate the tips.

I regret posting my bulkhead attempts. I am not really building a Thorp. I just bought the sheet of aluminum ($11 from spruce) so I thought I would try it. After I screwed up several times I got frustrated. After I thought about it for a while, I didn't understand why I got frustrated since I'm not even building anything.

But, now I gotta get the 574 done just to say I did it.....I have another $11 sheet on the way.....

One piece at a time, Ryan... one piece at a time.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

Ryan,
That's what this hobby is all about. We all like to learn new skills. Keep going!
Cubes

You should have seen the pile of scrap/incorrectly made parts that I took to the aluminum can recycler ! BOOM !

RB