ETA 15D MK 3 AND ELITE  5cc ENGINE BUILDS

Part two by Ramon Wilson

Machining began on the crankcases and, as usual, an extra case is being done in case of mishaps, which means four this time. If they all come out okay the spare may be used for a fourth but modified engine and maybe actually use it as it should be. That, however, is a big ‘maybe’.

With regard to complexity these should not be much more challenging that the previous Mks1 and 2 cases but it has these very prominent protrusions which is going to make for some interesting set ups to get to the end result. As with the Mks 1 and 2, however, some compromise will have to be made but it should be possible to arrive at a reasonable representation of the original.

To give some idea this pic is an original diecast Mk1 and 2 case.

And these two the Mk3 and Elite series.

The intention is to make the circular area above the bosses as a secondary part which should allow shaping of the bosses and the front/back of the case by milling.

It all began like this .....

Four blocks of HE30 (6082) Aluminium each weighing 605g (the other blocks are for the front housings and backplates).


And after finally making the first swarf the initial blocking to size and the bore for the front housing and backplate was finished.

The front part of the bore was opened up (this will be machined away at a later stage) and the bores proper were sized to a plug gauge made for the Mks 1&2 which will allow the drill jig to be used again.

Realised these top plates would need making before cutting the transfer passages so stopped to turn them up first so the passages could be cut with them bolted in situ.



Once again another small cutter was required and this worked really well plunging in sideways with ease despite the straight cut flutes. I know that some are a little wary in attempting cutter making so I include these following pics in the hope that they might help overcome any doubts. It really is quite a straight-forward process and providing the cutter is not going to be used for long repetitive work in tougher steels will stand up well providing speed and feeds are kept low.

After turning the profile on a piece of silver steel (drill rod) - 10.0mm dia and 25deg angle - the teeth were gashed on the mill - five teeth to keep the tooth land small and the odd number to help prevent chatter.

Back on the lathe the teeth were inked up (felt tip)
Then the teeth backed off with a needle file
The parted off cutter was reversed and held on its shank with a 4BA bolt and the teeth undercut before heat treatment
After H/T - which as usual for me on cutters like this, a nice bright red, quenched in oil, no tempering  - the teeth were sharpened on their edges only using a well worn diamond file
The cutter was a pleasure to use and the surface finish from it (no coolant or cutting fluid) on all sixteen passages was very acceptable
Roughing out of the main profile has begun but there's a lot of swarf to make as yet, though, as most of that block is due to disappear.


See part one here  part two  part three  part four  part five  part six  part seven  part eight 

part nine  part 10  part 11  part 12



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