Too thick

I decided to order the parts to make the extruder so that they could arrive while I was writing the firmware. The official RepRap design I am working to is here. Forrest Higgs has a simpler design here but as I have a lathe and I don't have a blowtorch I decided to stick with Adrian Bower's original for my first attempt.

I got a lot of the mechanical parts from Farnell and was most impressed with their free next day delivery.



Some of the part numbers had gone obsolete, mainly due to ROHS, so I made the following substitutions :-

Description	Original	Substitute
Steel M5 Studding	517343	517409
Steel M3 Nuts	758796	8861250
Steel M3 Washers	149687	8861447
Steel 25mm M3 cap screws	100165	8838887

10mm PTFE rod was out of stock but I found a cheap source of 12mm rod on eBay at Fantastic Plastic.

I also ordered a 5Kg reel of HDPE filament to get started with. It cost £85 including shipping. I plan to recycle milk bottles eventually but that will require a grinder. A four pint milk bottle weighs about 25g which makes them worth about 42p each. They must cost a lot less than that to make so the implication is that this stuff, sold as plastic welding rod, is overpriced.



The reel is a bit big and heavy to mount on the machine so I will probably have to re-spool it somehow.

It is a good job that I bought the filament before I made the extruder. The instructions specify to drill out the barrel to 3mm but my filament measures 3.2mm! I have ordered a 3.3mm drill from www.toolfastdirect.co.uk.

I also bought some nichrome wire to make the heater and some J-B Weld to attach it to the barrel and provide the electrical insulation and thermal coupling.


This stuff is rated up to 600°F. It is a departure from the original design which uses PTFE tape so it will be a bit experimental. I am hoping the thermal coupling will be good enough to allow me to use the resistance of the nichrome wire to measure the temperature rather than having a separate thermistor.

A lot quicker

Here is somebody that works a lot quicker than me: reprap-wasnt-built-in-day.html !

Slow going

Not much to report as I have had little time to spend on HydraRaptor this week, should get more done this weekend though.

On the firmware front I got as far as writing the Ethernet PHY driver. This is the part of the Ethernet controller concerned with actually sending the signals down the wire. Back in the days of 10MB Ethernet this was a relatively simple line driver. With 100MB it is a lot more complicated and generally involves a DSP to compensate for signal distortion in the cable. Quite often these are separate chips but the MC9S12NE64 has one built in.

Despite the internal complexity, the interface to a PHY is straightforward. The driver just has to configure it and then wait for it to report that the link is up. One slight wrinkle I came across is that there is a bug in the silicon that drives the activity LED. Apparently the pulse it generates is too short to be seen. You can either stretch it in hardware or disable the hardware control of the LEDs and do it yourself in software, using the pins as general purpose I/O.

The next thing to do is write the MAC driver. This part of the chip is responsible for sending and receiving Ethernet packets.