The machining of the parts is by bread-and-butter means – turning in a lathe and milling in a mill. I am relatively fortunate here, as over the years I’ve accumulated a number of quality English, German, Swedish and Japanese machines. Even though some are up to 50 years old, they are in good condition, and will hold tight tolerances and give good finishes. (No Chinese machines here – if there was a machinery snobs site, I would be a founding member.)
When starting with bar stock, there is a lot of meat to remove. I think 60% of the aluminium ended up as swarf and chips.
Everything was machined with more care than usual, with critical bores and faces mostly completed in single settings. I machined the discharge path in the body today. It is at a tangent to the outside diameter of the grind chamber, and exits the main body at the centre. I will probably end up fitting a chute from a Rancilio Rocky, so made the final width of the port to suit.
Well, so far, so good. Everything is coming together OK. I made a couple of temporary nylon bushes slightly smaller than the bearings, which allowed a quick and easy assembled of the parts to double check the design. I didn’t want to use the ball bearings as they are an interference fit in the body, and I want to install them once only, after everything is complete.
I still need to make the thrower fingers on the spindle, these will be made from a fancy plastic called PEEK, which has a combination of mechanical strength, resistance to chemicals, wear, and temperatures up to 260°C. These will locate in slots in the spindle flange, and will be secured with M4 cap screws. The material is ordered, and should arrive next week. I made the height of the grinding chamber 20mm - about the same height as the burr set plus a little bit. Hopefully this will limit the amount of old grounds which will accumulate in the chamber.
I had a chat to a few anodising companies yesterday. As there are none in Canberra, I'll have to use one in Sydney or Melbourne. (If anyone can recommend a company I would appreciate it.)I was advised that before I send it, to make sure that I've got all of the machine marks and scratches out of it, as anodising is a pretty unforgiving finish, which will show up all the imperfections. I was also warned about acid from fingerprints, which can leave invisible pitting which makes the final anodising blotchy. Woops, I probably messed that up.
I did run into a problem with the Mazzer burrs. After they were bolted to the spindle, I did a trial assembly, and found that they were not quite parallel. It turns out that there are some ugly little burrs at the back of the three mounting holes, enough to stop them seating flat on the spindle. I'll need to stone these off tomorrow and check it again.
And finally, this is the last thing a coffee bean will ever see - Arrrrrrrrrrrrrr, munch, munch, munch, munch. Bwahahaha!
Well, time for a beer. Cheers, Steve.