EASTON & ANDERSON

GRASSHOPPER ENGINE BUILD

Part six by Jason Ballamy

The old photos show a piece of diamond chequer plate below the beam support pivot that is missing from AM's model, this was most likely to give access to the air pump below the base. There are some sheets of so-called chequer plate sold for models but they are not that accurate and even the ones for 7.25" locos looked too small so I had to make some.

Starting with a piece of 1/8" brass I used a 3/16 cutter in the mill to make passes 0.020" deep with a rib of 0.020" wide between at an angle of 15deg, its not that easy to see due to reflections and tool marks but hopefully the second shot shows what’s going on.

Next the piece of brass was stood up in the vice at an angle of 15deg the other way and a 0.025" slitting saw used to cut grooves at the same spacing that teh milling had done cutting through the ribs and into the base metal by another 0.020". Thats a bit of 1/2" flat bar I have got the brass clamped to as it would flap about too much on its own.
Some 0.020" brass sheet was held between scraps of MDF and the same slitting saw used to cut narrow strips off the brass, these were over height at about 1/16" wide.
These strips were then given a light coat of soft solder paint pushed into the saw slots and heated to melt the solder
After a clean up they were machined back to height, the stray ends removed and the plate cut to final size
A quick spray of primer and it looks half decent.
Next job was the base, built from aluminium bar. First job was to machine a 1/16" rebate into the top edge to locate it against the edge of the steel plate, I could then attach the ali with some countersunk screws.
Following that the mill vice was clamped down with a bit of packing under one end so that it was slightly tilted, this gave me the desired ‘draught’ angle to mimic a casting and the majority of the waste was machined away with a 5/8 end mill.
That was followed up with a 1/2" ball nose cutter to put the cove on the bottom edge, the top was rounded with a home ground cutter.
This left the ends square so they went back into the mill to have the profile put on the ends.
I also cut some pockets into the edging under the bearing supports to take brackets which were given a shallow concave face. The rebates of the four edgings were coated with a slow set epoxy adhesive and screwed into position, the joints and screw holes filled with JB Weld which was also used to stick the brackets in place.
Once set the JB Weld was cleaned up, fillets added with Milliput and then the whole thing given a quick blast of primer, here it is with a few of the other parts in place.