Prusa Mendel building begins

This is the first post in a series which will cover the build process of a Prusa Mendel 3D printer.

The Prusa Mendel is a fully open-source 3D printer. Its main features are its low cost relative to other 3D printers out there right now, its many interchangeable modules, as well as the fact that one printer can print the required plastic parts for subsequent printers. This last point is where I begin my building work log …

I’ll start off with the plastic parts, which have all been printed using our first printer.

RepRap #1 – The mother

RepRap #2 – The soon-to-be son(?)

The first RepRap has given birth to the (mostly) green parts you see above. Next step, gather all the pieces (easier said than done)!

A collection of almost all of the required RepRap parts and tools.

While I was waiting for the final pieces to be delivered (mainly the long treaded rods and M3 bolts) I decided to start off with the hot end and the extruder.

The hot end main components are a PTFE thermal barrier which attaches to the extruder, the brass barrel which acts as the output nozzle for the melted plastic, the nichrome wire which will provide the heating, and a temperature sensor.

Hot end parts.

Some good instructions for the hot end can be found here (even thought the page is deprecated, it has good instructions on how to construct the thermal barrier and brass barrel, as well as how to wire the up the nichrome wire and temp. sensor). The hot end took a few tries before I was happy with the result. A useful modification we have added is the hex bolt and brass washer with two drilled holes that you can see in the pictures. I’ll later show how these provide a good resistive force which holds the brass barrel firmly into place inside the thermal barrier. From experience we found that the force from the incoming melting plastic tends to push the brass barrel out of the soft PTFE barrier, so this mod solves the problem!

A drawing of the extruder tip assembly.

The assembled hot end.

Another view of the assembled hot end.

The images above show the final assembly (the black insulating tape was replaced with some more high-temp. resistive Kapton tape as it would melt from the high temperatures generated by the nichrome wire). Getting the nichrome wire and temperature sensor to fit around the large washer resulted in an extruder tip which might not look refined, but should get the job done!

The extruder model is an upgraded version of the original Wade’s Geared Extruder (not sure of the exact iteration number, but it’s the the one with the hinged extruder idler block and spoked large gear, but without the filament guide of herringbone gear).

Beginning of extruder assembly

Green Sugru.

Green Sugru opened.

Aligning hobbed bolt with 608 bearings and filament guiding hole.

Large extruder gear with Sugru used to fill in imperfections and hold bolt in place.

Hobbed bolt and large gear in place and correctly aligned.

The hex nut placement on the large gear was slightly out of place. This was promptly fixed by filing down until the bolt fit. Luckily I had some Sugru lying around (and in the right colour!) which worked perfectly in holding the bolt in the correct place with the gear aligned straight. It also helped to keep one of the 608 bearings firmly in place.

This concludes the first post on the build process. Stay tuned!

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