Craig, Roger and Zee - thanks for the encouragement, it really helps to know that people are following along!
The two manifolds (combined inlet and exhaust) didn't generate anything like as much swarf in volume but there were a lot of little bits of Al stuck to the mill with WD40. Also some little bits of carbide from the two 2 mm cutters that died in the first attempt at the fins.
Here is what I was aiming for:
The exported images from Alibre aren't the best so I've attached a .pdf as well.
The manifolds started as two bits of unknown alloy which turned out to be both soft and sticky. After milling to size and turning the exhaust outlets the bits looked like:
Note the labelling, handed pieces like these have caught me out in the past! The various passages were drilled or milled to size:
The burrs raised by the cutters seemed to be work-hardened as it was difficult to get rid of them without damaging the remaining surface. The exhaust passages were connected via cross-drillings that needed blanking plugs in brass:
With these fitted temporarily the bits were ready for the fins to be cut. On the starboard one you can see where the card that was supposed to be protecting the work from the chuck jaws has slipped without me noticing:
Drawing the fins in the computer was easy, cutting them required more work than I anticipated. Its no use the shop floor cursing the drawing office here!
The first plan was to run a 2 mm cutter (of a type advertised for working ally) in the Aciera high speed head and make quick passes, first to clear the middle then each side to form the slopes. In less awkward material this might work but the fine swarf just clogged the cut and wouldn't wash out quickly enough. Two cutters later I decided to make a form tool.
This came out of gauge plate and the teeth were formed with the Aciera dividing head driven from the stepper motor system I described in an earlier post:
After an early scare the vice was added to make sure the work couldn't slip on the mandrel and 14 teeth roughed out with a 6 mm ball-ended cutter:
and the major backing off done:
Based on previous experience the steel was left un-hardened. The tips were ground with an 8 degree rake but the sides were left alone. Three 1 mm deep cuts followed by two at 0.5 got each fin groove to depth without drama. The lack of relief on the sides of the cutter meant that the finish wasn't perfect but was acceptable:
The blanking plugs have been fixed with JB Weld and I can move on to tidying up the blocks and heads to their final external shapes.
David
