Making Gussets for the CNC Router,

 Using a Wood Pattern.

By
Ron Thompson

6-16-2010


While the lost foam casting was usable (with plenty of machining), I wanted something a little lighter and with better dimensional stability. Hopefully, this will just require light machining to make the sides square and true.

I made a quick pattern using thin plywood and MDF, cutting with the table saw and gluing with Elmers white glue. Click a photo for a larger view.

The plywood is 3/16 (.187) inch thick. The MDF was 3/4 (.75) inch thick, so the total height is just under an inch, plus a few coats of rattle can paint. The MDF is tapered about 5 degrees per side. The wood screw is a handle to pull it from the sand. The triangle of plywood started out at 6 inches on a side, but the trimmed pattern is more like 5 1/2".
I used diesel fuel for this pour. Diesel is much hotter than propane, and you can buy it on Sunday or in the middle of the night.

This is my standard Becket gun burner, with a piece of clear tubing (yellowed with age) going to the gas can holding the diesel fuel (NOT GASOLINE!). I like this because it will self start. I don't bleed the line. I stick the tube in the can, plug in the burner and it picks it up after a few moments and then lights itself. Re-lights are instantaneous, as long as there is fuel in the line. There is soot from this burn. I had a small amount of black smoke indicating unburned fuel. Probably because this furnace was designed for a propane burner and the hole is too small for this burner. I also think the nozzle is starting to clog a little from not running a fuel filter.
Here is the result, straight from the sand. I think I poured too hot, as the casting shows every grain of sand.

The pattern is wholly in the drag. I cut the sprue and basin and dug a small trench to gate to the mold. The idea was to make it easy to trim the sprue with a bandsaw. The sand is Kbond, oil bonded sand.
These shots show the pattern verses the casting.

I tried to show every view.
The sprue was easy to remove.
    
The first shot above shows how small the gate actually was. In the last photo, if you click to enlarge it, you can see the casting even picked up the wood grain through the paint.