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BUILDING

A

SAWDUST BURNER

Every model of an early sawmill needs a saw dust burner, as they add so much character and atmosphere, so when I was building my 'Driwrott Saw Mill', I just had to include one. They varied in size and shape as most were built on site and had to suit the saw mill's requirements

Below is how I designed and built my burner. You will be surprised how easy it is.

Note: All dimensions are for an 'O' scale model

For 'HO' scale multiply the dimensions by 55%

BUILDING THE SPARK ARRESTER

First impressions are that the domed wire mesh on top of the burner will be the hardest part to achieve. But, this is the easiest part - go to your supermarket and buy a plastic tea strainer. For those building in 'O' scale, there is one that has a 3" diameter, which is the perfect size.

After the handle is cut off,  glued two strips of thin styrene across the wire mesh at 90 degrees to simulate joins in the burner mesh - see the photo above. Spray paint the whole mesh matt black inside and out, and when dry, brush on rust and black chalks to complete - how easy is that!

The burner attached to my saw mill ('Driwrott Saw Mill') has a bottom diameter of 5" while the top diameter is 3" (same as the tea strainer) and the height (excluding the strainer) is 6"  -  I played around with various heights and angles of the side and this seems to me to have really nice proportions. Click on the cross section plan opposite for a larger view.

BUILDING THE BURNER

1. THE FORMWORK

The first step is to build an inner formwork to form the overall shape of the burner. To do this I drew an angled rectangle (if there is such a thing - maybe it's a logging term!) with the bottom 2" (half of the 5" diameter bottom), a vertical side of 6" and a top of 1" (half of the 3" diameter top). I then completed the angled rectangle by joining up the two horizontal lines. This gave me half of a cross section thru the burner. Click on drawing 1 below for a bigger view.  I cut 8 of these out of some stiff cardboard, plus a disc with a 5" diameter and one with a 3" diameter. I then glued the half cross sections to the 5" disc at a 45 degree angles. Click on drawing 2 below for a bigger view. The 3" disc is then glued to the top to give the basic shape of the burner. Click on drawing 3 below for a bigger view.

If you want to get really prototypical, you will need to have a draft gap at the bottom of the wall to allow air to be drawn into the burner. Click on detail drawing 4 below for a bigger view. This small cutout needs to be done on each of the 8 rectangles before you assemble the formwork. It is to allow for a short piece of 'H' girder ('Evergreen' make a range of sizes) which simulates the base framework of the prototype burner. This forms a gap to allow the burner to draft air. You need to make the bottom disc slightly smaller to accommodate this feature. Subtract twice the 'H' girder from the diameter of the bottom disc.

2. THE INNER COVERING

From a local art supply shop I bought a large sheet of artist water color paper. Place the burner form on the edge of the sheet and roll the full 360 degrees of the former to ensure you can form a one piece wrapper around the form. Mark this spot on the sheets edge. I then run wood glue down one of the angled rectangle sides and place on the edge of the paper and allow to dry. Once dry, I roll the former over the paper and mark where to cut the paper ( always allow a bit extra which can be trimmed off later). Glue is then put on all the remaining angled rectangle sides and the two discs, and the former rolled over the paper. Hold until the glue dries. Trim off any excess paper.

3. THE OUTER COVERING

All that needs to be done now to cover the burner with simulated sheets of flat iron. I used flat sheets that were about 4 feet wide. However, because of the tapered shape of the burner, the sheets have to reflect this taper. To do this, I drew another angled rectangle (this one has both tall sides angled in).

At 5" diameter, the bottom disc has a circumference of approximately 18", while the top at 3" diameter has a circumference of approximately 9". If your burner is a different size to this one, and it's been a long time since you did maths at school, the formula to find out the circumference of a circle is 3.14 multiplied by the diameter.

Click on the cross section plan below for a larger view.

To work out the sheet sizes, with a pencil and paper, draw a horizontal line 1" long (approx. 4' in O scale), then a line vertically from the center of this base line to a height the same as the height of the burner wall. Then divide the diameter of the 3" diameter disc by 18, which is just over ". I centered this on top of the vertical line to form a tall H on its side. Then join the two outside vertical sides to form a tapered rectangle. On my burner, at just over 6", these sides are 24 scale feet high, so I divided the tapered rectangle into three. This meant I could use approx. scale 4' by 8' sheets to cover the burner walls This drawing now gives you the three sizes of tapered sheets needed to cover the burner - you will need 18 of each, which I cut from the left over artist water color paper. Make the sheets slightly taller to allow for some overlap.   If you are adding the draft detail you will need to cut pieces to cover this area at the bottom of the walls. There is no easy way to work out the size required. I didn't try and do this in 4 foot sheets, but cut them to reach between each  vertical angled rectangle. Only trail and error will give you the size required, but using three of the bottom sheets lined up long side to long side will give you a good starting point, and you can't see he top of these sheets once the burner is complete, so they don't have to be totally accurate.

These sheets can now be painted a rust color and highlighted with rust powders  I do this before I attach them to the sub-wall  so each is slightly different. Now comes to job of gluing each sheet onto the skin of the burner. Once this is completed you should have a good looking saw dust burner.