I have decided to make use of the fretsaw before putting it away after making a couple of wooden toys for my grandchild. I need to have two castings for the Seal that are handed different from the norm, allowing one engine to run in reverse, allowing contra-rotating propellers in the boat (Fairey Huntsman) being built by one of my brothers.
When phoning Hemingway's, the supplier of Westbury's Seal castings I found out that whilst Edgar T Westbury designed the engine to work in either direction, no patterns for the 'other' way exist. So I am making a couple of patterns to cast the two parts needed. This is my first attempt to produce patterns to the quality required so it is interesting to say the least.
I have started by looking at the plans and comparing the existing castings to them. Remembering to allow for shrinkage and having the sides sloping, I made a start by tracing the outline then reversing onto wood and rubbing the reverse side, transferring the shape seen in the photo below. One the outline was done it was over to the fretsaw and cutting outside the line the basic pattern produced.
My next stage is to use filler to get the shape I want before spraying in one colour, sanding/filling then spraying in a different one to get as good a finish as I can. Of course the final test will be when they are cast.
29th June 2010 second session
Work continued on the pair of patterns for the Seal engine. I am now at the stage of painting to get a good finish. To help me I use two different spray colours so I can see clearly the areas I am covering. This works well and after making a few more adjustments, seen because of the paint finish, I am not to far away from finishing these patterns before casting some to see what lessons I can learn in pattern making.
Whilst I will need to dust off the furnace I thought it would be sensible to complete all the different project patterns making best use of the furnace time. I must admit to being a little surprised at just how many different jobs on the go (or waiting for me to cast the part). These include a pen stand to display the pens I make (I hope to try a local Saturday craft fair in Brixham soon), a casting of the 3 pronged bracket to run the power feed to the milling table project (I will try first to use the metal p[art it will mate with before seeing if I need to make a wooden one) and a more substantial table for my Clarke bandsaw (for use when operating vertically).
I am quite happy I have the system of melting the aluminum sorted now but am not so sure about my patterns but the only way to find out is using them. We shall see. I expect to use the furnace the end of this week if I am lucky so watch this space.
