Building a Flue Pan

[Big_Eddy]

In a previous thread http://www.mapletrader.com/community/showthread.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.

[Big_Eddy]

Ken - that's only half the Vise Grip collection - once you get welding you will end up with a continually increasing collection of clamps and Vise Grips.

Sheet of 20 gauge mill finish set me back a bit under $250 CDN. I didn't shop around too much, and only have one metal supply business in town, so likely could have done better in time, but I had it in 2 days and I've always had good luck with this vendor. They quoted me a cost to shear it, but waived it when I picked it up.

Bending up the sheet took place one afternoon while the FIL and I were chatting and boiling sap. We were not in any hurry and probably spent 2-3 hours total. That includes tweaking and making the tweaking tool.

Probably have another 2-3 hours into welding in the ends of the flues - haven't been keeping track. With work and the kids, I fit it in when I have spare time, tacking them in one time, welding them up another.

I have one end cut, fit and mostly welded in place - another hour or so into that. I expect to have 10-15 hours into it when I'm done - certainly not a production pace, but even at the rate I'm going, expect to have it done before next season ;) plus a syrup pan and arch to go with it.

[WF MASON]

No one can ever say you an't clever. But wow what alot of work , but I'm sure it'll be worth it. Theres nothen like doing it your self.

[moeh1]

Eddy,
great ingenuity and really fine description as well. I've never seen a drop flue pan and I really am intrigued about following your approach.:D

[PARKER MAPLE]

ok guys call me stupid, but i have been reading about these drop flue pans a have a question. how in the world do you know if the sap your boiling in the bottom of the flues isnt turning to syrup with out you knowing it?? and also how do you draw off this pan, because the heaviest sap is going to be at the bottom "right" and if so how does it make it you to your draw off valve?? sorry for the stupid questions, but im new at this and this one was killing me.. thanks m.r.

[Fred Henderson]

The cooler sap coming in pushes the hot up and out to a flat bottom syrup pan.

[PARKER MAPLE]

Ok So Its The Opposit Of What I Was Thinking. The Cooler Sap Flows In And Goes To The Bottom, In Return Pushes The Hot Sap Up In The Pan, So When You Are Drawing Off That Pan You Are Drawing Off The Cooking Sap.. I Think I Understand Know.. Thanks

[RileySugarbush]

Rook,

The other thing to keep in mind is when you are boiling in a drop flue, there is violent mixing going on at all times. There is absolutely no separation of density vertically and only some due to the separator that runs down the middle of the flue pan to keep the sap from running straight across from inlet to outlet to the syrup pan.

[Fred Henderson]

Ok So Its The Opposit Of What I Was Thinking. The Cooler Sap Flows In And Goes To The Bottom, In Return Pushes The Hot Sap Up In The Pan, So When You Are Drawing Off That Pan You Are Drawing Off The Cooking Sap.. I Think I Understand Know.. Thanks

I think it would be very diffcult to draw syrup off on a flue pan, if not darn near impossible. A flat bottom syup pan is usually used in conjunction with a flue pan.

[ibby458]

Absoloutly WONDERFUL work on that flue pan. Back before I bought my evaporator, I tried to make a single flue out of galvanised as a test before I bought stainless. I had a 48" box & pan brake, and took care bending it, but the warpage as I tried to attach the flue ends kept me from getting it tight enough to hold water. I gave up and bought an evaporator.

I do occasionally reconsider the project. (Good excuse to buy a TIG welder, right?) I have seen a set of cooling fins on an electrical transformer that were closed off at the ends by folding the bottom of each fin (flue) up into the center then camping the sides down onto it and welding closed.

I imagine you would have to have a shaped wood form inside to keep it from closing in further back than necessary. I could also forsee problems at the top of the flue where it joins the rest of the pan.

An interesting thing to consider, but I have no idea if it's doable with normal shop skills and equipment.

[PARKER MAPLE]

I think it would be very diffcult to draw syrup off on a flue pan, if not darn near impossible. A flat bottom syup pan is usually used in conjunction with a flue pan.

I DIDNT MEAN DRAWING SYRUP OFF THE FLUE PAN BUT DRAWING OFF SAP FROM THE FLUE PAN TO THE SYRUP PAN...

[Big_Eddy]

IBBY

Before I started this - I tried a number of things to validate my ability to weld up these flues. I started with a pile of mild steel strips, welding 1"x6" coupons into a staircase.

I tried folding up the edges on the ends so the one piece fit like an L up agains the other ( |L ) then welding either the lower corner of the L or the top of the L - neither worked anywhere near as well, primarily because with the thin material - if you are welding the edge of one piece onto the flat of another - the edge will pull away and melt back rather than fusing.

I tried MIG welding at the lowest settings on both my MIG welders - quickly determined that TIG was a better option - both for the ability to control the heat, and the fact that no filler was being added.

After about 100 steps on the staircase, I determined that the best way to get a good watertight joint was to butt the edges together and fuse the 2 pieces from the outside of the corner. No filler. You need tight fitup, tack at the ends and the middle, then fuse into the center. Keep the pressure on the joint edges with the off hand to keep them together. More heat and more speed seems to work better than less heat and slower. The idea is to get a small puddle going and flow it forward to the center tack. Vertical down or horizontal - not vertical up.

Short story - warping has not been an issue for me - but I ensure tight fit up, I move fast to reduce heat build up, and if I do build up too much heat, I immediatly move to another flue until the heat dissipates, then come back, close the gap by tapping with a hammer and resume where I left off.

Wood form - I used a wooden fork on the outside to keep the flues square while I welded - I used the Vice-Grips on the plate to keep the spacing correct until welding was complete. No need for a form inside - but a cardboard dam to contain the argon was required.

Because I am using seperate pieces for the pan end as the flue ends - I have to seam along the top of the flues. What I did was leave the flue end pieces slightly long, allowing them to overlap the pan end by about 1/8". This gave me something to register the pan end against while I welded it to the flats between the flues. Then I welded that 1/8" flue end extension to the outside of the pan end leaving a small gap at the radius of each bend where the flues were formed. For those I needed to use filler to build across the hole.

[steamvalleyFarms]

Big Eddy I have been intrigued reading your post on making this pan, gets me thinking about trying to make my own. Can you tell me what size flue pan you ended up with. Also did you put any type of drain pipe across the bottom of your flues to drain them. Thanks.
Rob

[Big_Eddy]

I'm not done yet - but the flue pan is ~18" wide x 39" long - I will be building a 18"x 21" syrup pan to go in front of it. Will give me a 18"x60" evaporator - roughly modelled on the 18"x60" models that are sold as hobby evaporators for up to 150 trees. I do 100 trees a year on a 2x3 flat pan now - will stay at 100 for so this should be a huge improvement to me.

The 18" width was governed by the 96" length of the sheet. 2x9" sides + 6@5" flues uses 78" of the 96, leaving 18" for the width. There are 2 dividers with 2 flues in each section. Flues are roughly 1" wide and 1" apart.

I did not put any drains in the flues - I considered it and decided it would be easy enough to siphon out if needed.

[Sugarmaker]

Big Eddy,
Very good educational post. May help me if I get into a project this summer.
Regards,
Chris

[Chris Kervatt]

Very helpful. I'm going to build my own flue pan

[noreast maple]

Cool!!! nice build and good photos and explanation!!!! Congrats. Must feel good when someone of bill masons caliber congradulates you :)

[Big_Eddy]

As an update after 2 seasons on this flue pan with a 18x21 syrup pan on a home made arch, I can boil 14-18 gals/hr with a natural draft and no preheater. It's a huge improvement over the 2x3 flat pan I was using before that maxed out at 6 gals an hour. We increased to 150 trees last year and I was easily able to keep up. I'll see if I can find some pictures to post of the arch, pans and float box.

[Big_Eddy]

Some pictures.

1) First fill with Sap.
2) Top View of the first boil. This was maybe 30 mins into it. You can see the gradient starting to develop from back right to front.
3) Second Boil - Geysers at the front of the flue pan. The splash shield was added after the first boil.
4) Syrup pan and pan connections
5) Float box - off-the-shelf plumbing valve, home made float and some other fittings.

Both the flue pan and the syrup pan are reversible but I have not found it necessary to swap them around during the season. To drain the flue pan, I use a piece of hose and siphon out each flue channel. Only takes a few minutes and for once or twice a year I don't see any need to add a drain. At the end of the season I close the valve between flue and syrup pans, siphon out the flue pan, pour it into the syrup pan and backfill the flue pan with water while I finish off the last boil in the front pan.

The arch is angle iron, lined with fire brick and skinned with stainless from some flip top garbage cans I scrounged from the dumpster at work.

[Ekrueger]

Big Eddy,
I am looking to build a drop flue pan similar to your setup. I have a few questions form reading your posts.
1. For the brake press, would it have been better to make the moving angle iron out of the channel iron and use the angle iron on the stationary side? This seems like it would work better so that you don't have to cut out the channel for relief. Do you think it would be strong enough this way? Maybe both the stationary and moving part would be better out of channel.
2. I was thinking about making the flues 1.5 inches wide so that it would easily fit over the channel iron with your current design of the brake. Is this too wide? You used 1 inch wide flues and this would decrease the amount of sap needed to fill the pans. Maybe this is better to reduce the volume of liquid in the pan.

I really enjoyed the details and pictures in your post. It has given me a lot of ideas.
Erik

[Big_Eddy]

1. For the brake press, would it have been better to make the moving angle iron out of the channel iron and use the angle iron on the stationary side? This seems like it would work better so that you don't have to cut out the channel for relief. Do you think it would be strong enough this way? Maybe both the stationary and moving part would be better out of channel.
I don't think so. The moving leg needs a lot of stiffness in the middle to create sharp bends. The angle provides strength in the correct direction and a reasonable lever arm to bend the steel. The truss added later helped a lot with crisp bends. I did not cut the channel for relief



2. I was thinking about making the flues 1.5 inches wide so that it would easily fit over the channel iron with your current design of the brake. Is this too wide? You used 1 inch wide flues and this would decrease the amount of sap needed to fill the pans. Maybe this is better to reduce the volume of liquid in the pan.
Erik

The goal is the most surface area for the volume of sap. Narrower flues transfer more heat to the sap. 1 1/2" will work, but 1" is better and squeezes more flues into the same pan width. The 1" flues fit over the 1 1/2" brake channel easily enough, and deeper flues would be easier still. The tradeoff is material. More or deeper flues require a longer sheet of steel. I used a full 8' to make an 18" wide pan with 6 x 5" flues. Deeper flues or more flues would have required a longer sheet of stainless.

[Yellzee]

Big Eddy, if you are out there the system says your mailbox is over the size limit and you cant get any new messages. You need to delete some.

Was curious if you are interested in bending up a piece of 2 foot wide stainless on your jig as a side business if I brought one out? Was looking to do the 6 flues at 6 inches. I go down your road on my way home from work most days. I can handle all the tig welding.