608 bearings | Cognitive Dissonance

Continuing from the first post, I made some progress on the extruder while also starting construction on the RepRap frame.

For the extruder idler block, a piece of threaded rod was cut down to size. Based on instructions this should have been smooth rod, but since it simply sits through a bearing there isn’t any issue of friction.

Fitting two hex nuts to the top of the extruder where the idler is attached required some extensive filing which ended up in the plastic splitting at the weakest points and a small part of the plastic breaking off, but the issue was easily fixed with some two-part epoxy. Once the epoxy has set and I get the required M3 bolts, the extruder assembly can be completed.

Extruder idler block, 608 bearing and a threaded bolt piece sawed to the right size (2 cm).

Fitting the M3 nuts into the top of the extruder (drill bits used as rough guides).

Repairs on one of the bolt holes using epoxy glue..

Switching to the frame construction for a change of scenery, the first task is to put together the two “frame vertex triangle”, i.e. the triangular frames which make up two opposing sides of the printer.

The first frame vertex triangle

Both frame vertex triangles completed.

Next, the frame starts taking shape by connecting the two vertex triangles. A few more threaded rods attached and it starts looking like an actual printer!

The frame taking shape

Close-up of one side.

Close-up of side with bracket where y-axis motor will be mounted.

Top view of the frame, with z-motor mounts on either side.

Basic frame connected, before calibrating and tightening.

The frame remains untightened for now, as I need to replace the large washers (M8, 24 mm diam.) on either side of the 608 bearings with even larger ones (M8, 30 mm diam.).

Next step will be to calibrate the frame, start attaching the remianing rods and complete the extruder. Coming up soon!

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!