Sunday, 22 April 2007

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 :-




Steel M5 Studding517343517409
Steel M3 Nuts7587968861250
Steel M3 Washers1496878861447
Steel 25mm M3 cap screws 1001658838887

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

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.

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