The Replacement Forge Flue

The current coal forge flue and accelerator sections have been used since January 1999 - over 14 years.  It is deteriorating and may fail soon. From time to time sheets of rust fall off the inside surfaces onto the ash pile in the smoke collector.

I made the original flue from 18 or 20 gauge sheet and MIG welded all the seams.  I don’t have the time to do that again so I’m asking Kan FAB to cut and bend 16 gauge panels which will bolt together to form the flue.

This will be an experimental design. The smoke chamber was replaced several years ago with bolt-together 10 gauge panels and angle. That design has worked very well. http://persimmonforge.blogspot.com/2012/05/my-side-draft-forge.html

I designed the new flue panels so they can be assembled from the bottom, where they attach to the smoke collector, upward to terminate in a Vacu-Stack chimney topper. There will be five sections; the smoke accelerator, three rectangular duct sections and the adaptor section to mount the Vacu-Stack topper.  Angle tabs will be welded to provide linkage between the sections.  I plan to seal any gaps with silicone caulk

I haven’t decided whether to make the flue sections with four separate sides or with two-side units which would require just half the seam sealing but double the weight of the panels.  Another alternative  would be to form the back and sides as one piece and just bolt on the front.

Also, I haven't made a final decision about incorporating a damper.  With the ability to remove individual panels that could be added later.

The way this year is working out I will not get this job done until it is cooler and drier in the fall.  I plan to borrow a scaffold  from a chimney sweep friend and set it up outside the shop.

10 gauge and angle smoke collector.

Five-section replacement flue.

Vertical flange and angle-tap joinery.

Smoke accelerator

Vacu-Stack mounting section

The Smoke Collector Damper

Sometime this summer I’m planning to replace most of the coal forge flue.  Essentially everything above the smoke collector box will be new.  The original sheet metal was 20 gauge and it is rusting away after many years of use.  The smoke collector box is modular and made of 7 gauge and only a few years old.

The new flue will be the same size and shape as my current one but it will be 14 gauge and modular so the front, back and side pieces will be removable.  The current flue was MIG welded but the new one will be hex bolt joinery.

I will make a new type of topper to deal better with our regularly strong wind and I will add a smoke shelf and damper.  I drew the damper plan this morning but the dimensions are not yet a settled issue.  I will have a few more months to think about them.

My sketch is not very accurately done either at this point.  I plan to make the smoke shelf out of 14 gauge and it will be bolted to the back wall so I can remove it if I need to make a modification.  The damper will also be 14 gauge but I may encounter some warping issues from the heat.  The axel and handle will be something like 3/8” round pivoting in a couple of 3” pipe or tube sections welded to 1/4” x 3” x 3” flanges and bolted to the front wall.

The next thing to think about will be how to lock the damper in the open position.

More on Flue Downdraft

When Ken came to help me Monday afternoon I told him about my experience with the downdraft in the high wind.  When we started discussing a Venturi effect solution he said he recalled seeing some devices for chimneys whig worked like that.

It was one of those cases where their is a hiatus in my knowledge.  Sure enough, when I looked for information it was right there.  These are two references and there are a lot more.  If I do decide to eventually change the flue cap, I won’t have to reinvent the wheel.

http://www.volko.com/vacustack.htm

http://www.luxurymetals.com/chimneycaps.html

Flue Downdraft

Kansas has a reputation for being windy.  Yesterday was a prime example.  A strong west wind blew all day, with few moments of calm and hundreds of strong gusts.  It was a good day for cleaning gutters.  Most of the leaves are down now and the wind blew streams of them across the yard.  I hope most of them reached the Neosho River and won’t return later.

Dustin Michelson, photographer for the Emporia Gazette, had made arrangements to visit the studio and take some images for an articlein a future edition of Emporia Living Magazine.  http://emporiaksliving.com

I was going to get the coal forge fired up so I could demonstrate how my hot work is done but as soon as I opened the door at the bottom of the flu a strong gust of ash and soot blew in and covered me in an instant.  I closed the door and washed up before he arrived.

In spite of our reputation for being windy, there probably are only a handful of days in a year when the wind is so strong I can’t get the forge to work because of the downdraft.  Yesterday was one of those disappointments.  We’ll get another opportunity soon.

The downdraft has never been inconvenient enough for me to think much about and fix and I’ve never actually tried anything beyond making a door to fit in the opening of the smoke collector.  I originally made it for use in the winter so that cold outdoor air doesn’t enter at night.

Now, I’m wondering if I can design a fitting which will allow me to make use of the wind to create a Venturi effect and actually suck air up the flu.

The flue is on the west side of the building and the prevailing west wind moves from left to right .

The door has an almost "air tight" fit.  It seats in two pockets at the bottom and is locked by a drop pin from the top.  I did not add those details to the drawing.