RepRap: Blog

this is probably one of the most common cries of anguish heard from new RepRap owners. The picture on the right shows two common modes of extruder failure. In each case, the symptom is that the filament cannot be pushed through the extruder, or requires enough force to damage the filament even when the nozzle has been removed and the barrel is hot enough for molten plastic to dribble out of it.

To find out what is going on, take the cooled extruder apart and look at the filament inside. If you can't get the filament out of the PTFE or PEEK spacer, the chances are that your spacer has got hot and the filament has bulged inside it. Use hose clamps or a metal sheath to stop the spacer from deforming. You will probably need a new one.

If you see a blob of plastic sitting directly on top of the heater barrel, you have a gap. Any space between the top of the barrel and the end of the hole that it fits into will accumulate plastic. This plastic will not all be molten, and will cause a lot of friction on the filament as it enters the barrel. Typically the extruder will run for a while, but mysteriously clog up if you let it cool and restart it. Or it may just jam solid.

The cure is to taper the top of the barrel to ensure it is driven into the PTFE or PEEK spacer, and to remove the thread from the top 1mm or so of the heater barrel. If the hole has not been tapped all the way to the end, this will let the heater barrel reach the bottom of it. It is important to clear any remaining melted filament before fitting the barrel back!

Vik :v)

Labels: extruder, fail

While preparing the Mendel files, we’re all building prototype machines in the Bath Uni RepRap lab to get a mini factory up and running. Whilst the other guys are building three standard issue Mendels, I’m going to scratch an itch I’ve had for a long time: it’s that "how big can this thing go", itch ;-) My single motivation is to have a large enough build volume to manufacture all of the printed parts in one single shot. This, in my mind, makes for a much more independent self-manufacturing machine.

I laid up what a single shot build might look like and found the area for printing all the parts, with enough spare room for evolutions, to be 440mm square (marked with a blue line in pic below). That’s 5 times bigger than the standard Mendel build area.



I’m going for a build area of 350 mm x 550 mm. Whilst this achieves the same area as 440mm square, it yields a more manageable footprint out of the Mendel architecture and caters for the fact that most print jobs are rectangular, not square. I modelled the variant design (I’ve dubbed it Mendel Apollo after the 440 coincidence) and here’s a pic comparing the two volumes. Note: the Apollo model is fairly naked: electronics/brace plates need to be added.


So the Apollo’s a big machine, and with its size will come all sorts of wonderful problems. Structural for sure… how will the M8 components fair? No doubt reinforcements will ensue. Will NEMA 17’s pull the bed around OK? There will also be a huge test of reliability for the one-shot build, specifically for the software and extruder mechanics.

I think this will be interesting. I believe it will be a bit of a milestone if we ever get that single shot replication and in doing so it may establish some mechanical limits. But before I can scratch the itch, I need to keep going on getting the standard Mendel files finished… grrr

RepRap relies heavily on free software to drive the RepRap itself, create the models of the components, design the circuitry, build the software, and run the websites. Software Freedom Day is about supporting and raising awareness of Free and Open software around the world, so find out your nearest local event and get down there to support all this wonderful stuff. Oh, and show off your RepRap or RepStrap :)

I'll be at events in Albany and Auckland in New Zealand, with even bigger events being held in our Capital, Wellington.

Vik :v)

Labels: day, freedom, software

I've just finished a parts list analysis on the two models: Darwin 1.0.6 (left) and the Wedge prototype (right). Here's some graphs:




So to very briefly summarise, with the use of bearings the wedge attracts a higher proportion of fasteners. I consider this a small price to pay for much smoother running. The volume of RP parts is the same, as is the area of sheet used in the construction, however the number of structural components is significantly reduced. The assembly has been simplified using only a third the number of different bolt types, and the total assembly volume has halved whilst maintaining a similar build volume.

Here's an analysis of the RP parts in the Wedge design (nod to Forrest for the suggestion). Clearly we could save some volume by optimising the vertices etc etc

Here's my toothed belt design for Mendelssohn using the Darwin-style moulded gear. I've turned Mendelssohn on its side, so you can see the Y axis workings clearly. I'm just using the NEMA17 to drive this at 250mA, so it won't get hot enough to melt the CAPA. The belt is the E-SKY model helicopter belt, and there is just the right length once you've cut the loop.

The big silver idler is a 608 bearing and 2x ridiculous washers as per the Z idler. The less heavily loaded small belt guide is an M4 soft, black plastic spacer between two M4x11 washers (plenty of lubricant). The belt is clamped by printed pillars (shout up if anyone wants the design files BTW), each held by 2 M4x40mm screws.

The base itself is 230x230x9mm MDF, supported on 16 x M4x40mm countersunk screws clad in 20mm lengths of stiff rubber tubing. These go into 4 PLA pads, which can also be hand-formed from CAPA. These pads have a very low friction, and can be levelled individually to cope with quite gross manufacturing flaws :) The axis moves at 50mm/s very smoothly with plenty in reserve even at 250mA. Yes, bearings will move much smother and faster with less wear. But this seems to work for now so I'll move on to butchering the X axis.

Vik :v)

Labels: helicopter belt, Mendel, Mendelssohn, y-axis