Tuesday 6 October 2015

End Game

Since my last post there have been many expressions of sadness in the comments here and here. I'd be lucky to get so much mourning at my funeral I think! Yes it may be sad for potential customers that missed out, but not for us. Fortunately we are at a stage in life where time is more important than money to us. It does feel a bit weird though as the house is now silent after having three or four machines printing solidly for about five years.

The harsh reality is we always planned to stop selling kits before demand dried up completely because otherwise we would be left with unsold stock. In order to to get volume discounts and cover long lead times we needed to carry around £12,000 - 15,000 of stock.

As we didn't hire premises or staff, and had enough capital to cover cash flow, the only business risk we had was being left with stock. It was very hard to predict future demand because it fluctuates wildly with currency changes and, with a new 3D printer coming out nearly every day, there is a risk sales could suddenly dry up if a better cheaper kit emerged. For example, a £40 Prusa I3 from China with 2 rolls of filament and LCD, bargain!

In the end the issue with Dibond made the tricky decision of when to stop for us. This happened a few months ago and we synchronised most of our stock to all run out together.

Yes we could have used other sheet materials, solid aluminium and steel were suggested. However, these are more expensive to buy and machine, much heavier and therefore more costly to ship. Although they are a bit stiffer there is no real advantage to the frame being stiffer because the forces due to accelerating the axes is along the plane of the sheets, where almost any sheet is very stiff indeed. As long as the machine sits on a solid work surface it doesn't flex at all when printing, unlike some of the triangular prism machines.

The good thing about an Open Source product is that the design and instructions will always be available, so people can still self source, or another company could pick up the baton. We will always be able to supply printed parts and, fastener kits, wire and sleeving, hobbed bolts and the extruder PCB. See the RepRap forum for prices. Everything else can be self sourced.

Friday 2 October 2015

No More Mendel90 kits

We sold our last Mendel90 kit today. We found it increasingly difficult to get Dibond that wasn't scratched and after going through four different suppliers we eventually gave up and synchronised the rest of our stock to the number of good Dibond sheets we had managed to get.

The problem is we don't have room for an 8' x 4' router, so we get the sheets cut into smaller blanks that fit on my A2 router. The sawyers that cut them keep forgetting that, unlike other materials like wood and acrylic, the aluminium chips that come off Dibond are sharp enough to cut through the protective film and damage the surface. That means that all the chips need to be cleaned off the cut pieces before they are stacked. You would think that companies whose main business is selling cut to size sheets for decorative use would know this, but they all seem to make the same mistakes over and over again, wasting my time and their money.

Many thanks to all our customers for all their kind words and recommendations.

Back to experimenting and blogging ...

Wednesday 30 July 2014

PLA pipe cleaner

Yesterday one of my machines stopped extruding ABS mid print. I immediately suspected the filament as faulty filament is my main source of unreliability these days, having eliminated other things like push fit connectors and wires that break.

I removed the hobbed bolt to clean it and found that I could not feed filament forward by hand but I could pull it back easily, a sign that the nozzle aperture was blocked by something. I spent a long time trying to clear the blockage with several attempts that failed. Here is the method that successfully cleared it in the end: -

I pushed the shank of a 0.4mm drill up the nozzle aperture while it was hot. That cleared the blockage enough to be able to extrude but the particle of contamination kept finding its way back into the aperture causing the plastic to come out in a flat turbulent ribbon instead of a cylinder. That made poor prints with rough surfaces and strings.

PLA has a useful property that you can heat it to a temperature between its glass transition and its melting point where it becomes a rubbery solid. When you pull it backwards it stretches and becomes thinner, so it peels away from the walls of the melt chamber and comes out in one piece. Anything in the melt chamber is pulled out with it leaving it completely empty and clean.

ABS does not have this property and is more like chewing gum above 105°C. It can be pulled back at around 130°C but it usually does not all come out because it is a super viscous liquid rather than an elastic solid.

Because of this I decided to flush out the ABS with some natural PLA. I did this at 240°C until it was extruding clear PLA,. then I cooled it to 80°C and pulled it out. This is how it looked: -

As you can see it stretches until the last bit comes away from the walls of the barrel and the shape of the end matches the cone leading to the nozzle. The problem is this did not get the particle blocking the nozzle because that was pressed into the aperture by the flow of PLA when I inserted it.

The final trick was to push a drill shank up the nozzle to force the contamination into the melt chamber before cooling it to 80°C. That ensured it was embedded in the PLA when I pulled it out. Here you can see the particle that caused all the trouble.

So to recap:
  1. Heat to extrusion temperature and pull out the filament being used.
  2. Use a 0.4mm drill shank to clear the aperture.
  3. Insert PLA (preferably natural so you can see the contamination) and flush through the remaining original filament. You may need to keep clearing the aperture with the drill shank.
  4. Cool the extruder to 80°C with the drill shank in place to ensure the nozzle is clear.
  5. Remove the drill and then pull out the PLA.
  6. Inspect the end that comes out to see the culprit contamination.
Of course if you are using PLA you can just do steps 4 and 5.

This method of cleaning with PLA is much better than using solvents or burning out nozzles that I often see recommended as it can be done in situ and doesn't risk damaging anything.