Bob on

Here is the first RepRap part that HydraRaptor has milled :-



It is the extruder barrel clamp as shown in the previous post. As you can see it is dimensionally correct to two decimal places! It's not a fluke, the height is bob on 45.00mm as well. I have been getting pretty good accuracy with my previous milling attempts but this is astonishing.

I used a smaller end mill (2.22mm) in a collet chuck which is more accurate than the three jaw chuck I used before. The plastic is a sheet of 9mm Delrin or Acetal which I used because I read somewhere that it was a good plastic for machining. It did machine well but all the edges were left with a thin burr. This was fairly easy to remove with a fingernail.

This is not the latest version of the RepRap design but I decided it would fit my machine better. I added two more mounting holes and changed the central hole diameter to match my PTFE barrel which is 12mm rather than 10 or 16mm in the original design. The central slot is 2.5mm rather than 2mm because my bit was too big. Obviously I will have to drill the horizontal hole for the clamping bolt with a drill press.

Here is an edited video of it being made, it took around 20 minutes to make the part :-



And here is an amusing out-take if you listen to the sound :-



So having achieved perfection on this first part, things can only get worse when I attempt to make the rest of the extruder.

End of play

You may recall that I said my replacement spindle motor, AKA Minicraft drill, had a bit of end play due to the bearing moving. This evening I made some shim washers by milling a thin piece of hard plastic that I got from the inside of a PC power supply. They are 11mm diameter with a 8.5mm hole and about 0.2mm thick. They were a bit ragged round the edges due to the plastic burring quite badly but it didn't really matter. I made three but two were enough to stop the bearing moving.



This is what the inside of the drill looks like. I added the capacitor myself to keep the radiated emissions from the cable to a minimum.



The result was very pleasing and I now have a working milling machine again. My next job will be to mill an FDM extruder. I plan to start with the clamp as this looks the easiest part.




Obviously I will have to modify it a bit. For example I can't do sharp internal right angles due to the tool's radius.

Bodge it and move on

The I²C nightmare continues. I thought slowing the clock of the MSP430 had fixed the problem. However, it still locks up after a few packets. The symptoms are that the MC9S12NE64 decides that the MSP430 has not ACKed the address byte. At this point both clock and data are low. The MC9S12NE64 sends a stop and both lines go high. It then thinks the bus is permanently busy. If I reset the MC9S12NE64 then it works for a while again so the MSP430 is not locked up.

So my first bodge was to detect the MC9S12NE64 thinking the bus is busy when it should not be and reset its I²C module. This caused it to lock up thinking the bus was not busy when it should have been. In desperation I added a 100us delay after the reset and now it works.

It looks like my digital scope will not arrive for at least a couple of weeks so I can't really get to the bottom of this until then but at least it is working with retries. I haven't done a lot of I²C stuff in my career but it looks like a really clever protocol. Less wires than SPI but has defined start and stop codes, multi-master arbitration and auto clocking down to the slowest device. As both ends implement it in hardware I just expected it to work. I should have known better as most hardware has bugs these days like all software.