Building a Flue Pan

[Big_Eddy]

In a previous thread http://www.mapletrader.com/community...ead.php?t=4532 I posted my home made brake for bending flues. Now will post the process I followed to make a flue pan. It is not done yet - so this will be a work in process.


Design.
I bought a 4x8 sheet of 20 gauge mill finish stainless for my pan, and I wanted to use it to the best advantage. I had a 9" strip sheared off the long edge, leaving me with a 39"x96" and a 9"x96" piece.

The pan is 39" long x 19" wide, with 9" sides and 6@5" flues, 2 in each of 3 sections.

I carefully marked both the top and the bottom side of the sheet at every bend location - some marks are on the top, others on the underside - along both edges of the sheet. I have a sketch somewhere that I will scan later and attach that shows the design.

First - Pictures of the brake (again)
The brake is primarily made of 3x3 angle with a 3" x 1 1/2" channel for the bed so that the flue can slide over it for the next bend. I have 2 hold down bars - one a 3x3 angle which permits overbending, and the other a 3/4"x 2" bar to fit down in the flues. The first shows on 2 of the pictures, the second on the last. Since this picture I modified the 3/4" bar to add a strip of 1"x 1/4" flat bar offset towards the front to provide some stiffening and allow a slight amount of overbend. It helped but was not enough - see below for the solution.

[Big_Eddy]

After a lot of bending and a lot of flipping of the sheet, this is the end result. (Sorry about the bad lighting - only picture I have of this stage)

Note how the previous flue is now over the 3" channel so that we can bend up for the flat. Then we lift the tail up and bend the next down leg. Flip the sheet, bend the bottom flat, then again lift up the tail to bend the up leg. We had to do it out in the driveway, not enough clearance in the garage.

We had absolutely no problem bending 39" of 20 gauge stainless in this brake. It did not take a lot of effort, and there was little if any flexing of the brake. I did add a stiffening triangle to the front member prior to starting, but I'm not sure it was needed. The only issue was the lack of overbend created due to the tall narrow flues.

[Big_Eddy]

Because we were bending narrow flues and the hold down bar prevented overbending, after springback the end result was more like this \_/ than the |_| we were looking for. I made a tweaking tool to tighten up the bends. I can't find my picture of the accordian - I will add it later if I find it. The tweaking tool is nothing more than a T made of bar stock for the inside of the flue, and 2 pieces of square tubing on the outside. Using nuts and bolts on the ends and a big C clamp in the middle, I squeeze each joint closed to square them up. You'll see in the picture how the upper bends are tight while the bottom ones had not yet been tightened up.

[Big_Eddy]

To weld on the flue ends, I clamped the material to a piece of light plate, to ensure the pan stayed flat, then cut sections of stainless to fit the ends. I purposely cut each piece a bit long and allowed it to hang down (upwards) when I filled the ends - to ensure there will be no gap later when we go to put the end on the pan itself. I considered trying to cut one single end piece, but decided I'd rather weld more than try to cut a complicated shape like that. Note the high tech "jig" to ensure that the flues stayed straight. That stayed on each flue during welding too to try and reduce movement.

Welding was TIG using a Miller Maxstar 150 STL set at 30 amps, but controlled down from there. 0.020 Stainless Mig wire was used for filler, but whereever possible I avoided filler by fusing the joint. Tight fitup is critical and weld in short sections skipping around. I'm a proficient welder, but this is at the edge of my abilities. Back gassing is needed to avoid sugaring. I ended up using LOTS of argon as it is hard to tape off those flues from the underside.

Once the flue ends were welded on, I bent up the sides of the pan ready to add the ends to it. And that's where I am at so far.

[SeanD]

That is the best how-to for making a DIY flue pan I have ever read. I'm especially blown away by the simplicity and genius of the tweaking tool. I've got to show this to the guys in my class. I'm going to save this and give it another whack some day. Thanks for sharing it!

Sean

[KenWP]

Should have told me what you were doing and I would have bought shares in a vise grip factory. Pretty neat work. Time consuming I bet. What is a sheet of SS worth. I would be happy with a flat pan right now and then figure out how to put tube flues on it later. I am wondering if a person could get 1/2 or 3/4 SS tubes and then bend and weld the ends to the pan. Hope I don't get old to fast and forget all these ideas.