EASTON & ANDERSON

GRASSHOPPER ENGINE BUILD

Part seven by Jason Ballamy

Next up is the beam or, more precisely, the beams as there are a pair mounted back to back with all the rods etc fitted between. I started out with two pieces of aluminium flat bar 3/8"x 2" just over the required 11" long and squared off one end.

They were then blued and stood vertically on the squared end and clipped to an angle plate to mark out the hole positions. Mostly now I don't do this preferring to just locate an edge/end and use the DRO to position the holes but I wanted to mark in the outer diameters of the bosses.
Here the bosses have been scribed in and the outline drawn to touch the various radii
The beams were then clocked true on the mill and the holes all drilled using the DRO, the largest hole was finished with the boring head. I tend to use stub length drills in the common sizes as it saves having to crank the mill head up and down so much, they are also more rigid so tend not to wander.
The vertical bandsaw was used to trim off the waste from around the outside and then the edges were flycut back to the layout lines.
I set a pair of buttons in the back tee slot of the mill with a parallel against them, this then gave me a reference face to set the beams against rather than having to clock them in for each of the eight edges. I then used a 3-flute FC-3 type cutter to remove half the thickness of the plate. The edges were offset from my ref parallel and I stopped just clear of the scribed boss outlines.
With as much metal removed as possible I setup the rotary table and using various mounting mandrels proceeded to round off the two ends and around each boss.
Rather than use a ball nose or radius corner cutter to do all this milling I opted for a square edged one as they are far quicker at removing metal and there were also several cutter diameters needed but only one fillet radius. I put all the fillets in using Milliput putty as there is no need for any structural strength here, its just cosmetic.
A good heavy coat of primer was stippled into the recesses to give a little "cast" texture followed by a blast from the spray can.
The remaining work was just careful turning to produce all the various spindles and spacers, this used about 18" of mostly 5/8" dia steel rod and luckily it all went together without getting jammed.
With the beam and end support frame done I decided to tackle the cylinder next as this will eventually allow me to support the other end of the beam. I started with the base flange, this was sawn into a octagon from some 5/8"x4" flat brass bar and held in the 4-jaw to trepan out the centre. I went almost half way from each side then took it out of the lathe and gave the middle a whack with a hammer and the central disc dropped out.
The bore was cleaned up and then used to hold the flange by while the outer edge was machined round.
I then proceeded to do the same for the top flange but from 1/4" thick material, it was just as I finished trepanning out the middle that I remembered I should not have cut the corners off  so substituted a piece of 1/4" steel as I did not have another piece of brass large enough.
The main tube of the cylinder started life as a length of 2 1/2" hollow cast bronze
The outside was turned down to 2.375" and spigots formed on the ends for the flanges to fit onto. At this stage the bore was left undersize for finishing after fabrication, the overall length was also 1/16" bigger than needed so the flanges could be skimmed back true to the finished bore.
A lump of bronze was sawn to give me a finished block of 3.25 x 1.5 x 1.75 and this was flycut to get all faces square.
Finally a bit of 1/8" brass sheet was cut to make the flange for the valve chest cover to bolt to and here are the roughed out parts.
I used a boring head to cut the curved face of the valve chest
The chest was then cut off at 20degrees, the chamber roughly hollowed out and the angled face flycut. I also cut a matching hole in the bolting flange and added a few 10BA CSK screws to hold the two together when soldered.
As the cylinder was coming together it became obvious that I would have difficulty holding it to take any heavy cuts off once assembled as I could not get it into my fixed steady so I decided to do a bit more work on it before soldering. Also the valve chest needed quite a bit of heating to get the solder to flow and by removing any unwanted metal the bulk would be reduced making for slightly easier heating. Here is the cylinder barrel getting opened out.

See part one here     See part two here    Part three here    Part four here   Part five here     Part six here      Part seven here     Part eight    Part nine   Part 10     Part 11   Part 12   Part 13    Part 14    Part 15   Part 16