RepRap: Blog

It's been a while coming, but at last I have managed to do multiple layers. The big question is: How many? Well, about 10 before things turned to custard on this attempt. But the custard was very informative. Take a look:

There are three major objects, and some insignificant little lumps that are me checking probe height. In the foreground, slightly fuzzy (sorry, depth of focus is not a well-known trait of microscopes), is where I started printing a 200μm long "test lollipop (a 100μm circle with a similar size line coming out the side). It became apparent pretty darn quick that Probe 9 was depositing bigger blobs of "Top Coat" nail resin than it had in dip testing, so I aborted that one.

In the middle we have a 400μm long (i.e. 200μm diameter) lollipop made with layers 4μm high and assuming a 30μm wide dot size. I got a few layers in before I noticed irregularities around the circumference which you can just make out. This was where the probe was not touching the surface below and so no resin was transferred.

A few notes:

First, it is really, really hard to see the layers or indeed what is going on. So it is not obvious when the RepRapMicron is not working. Consequently things can go hilariously wrong and you can't tell until you take the slide off, tilt it sideways, and shove it under the big microscope.

Secondly, it appears that any defect in the layer tends to accumulate resin. This means that if all your print seams line up, a really big defect will happen (I'm looking at you at the back). So, lesson learned, stagger your print seams. When the probe goes to dip and recharge with resin, that can create a seam too - that's where the biggest blob came from. It may be that making sure the probe runs out of resin will lessen this problem.

Kinda related to that, the first resin drop is always a bit big. It may be necessary to make some form of print tower ("The Tower of Ooze" as we called it way back) to get rid of that.

Finally, the probe is not just brushing the upper surface. It is stabbing in to semi-set resin. On that scale the resin doesn't just run downhill because surface tension is having a massive effect on the resin - far more than gravity. So your resin will stick to the top surface, the side of a surface, or any damn where it comes into contact. This may be useful for bridging later.

Back to our picture.

Bringing up the rear is a 500μm diameter single-walled cylinder with some kind of blob sticking out the top. That was done at 3.5μm per layer with an assumed dot size of 40μm ,and a dot spacing of 15μm. It was depositing 60 dots between dipping the tip. Every time it was dipping, the dip code briefly turns the UV LED on to gel the already deposited resin.

That one got to about 10 layers. You can see the top surface (ignoring the darn blob from the seam problem) has a square edge, not a rounded one. This indicates that layering is happening rather than I'm just making a thick line - there is no surface tension curving the upper surface.

So by that reckoning that cylinder is roughly 35-40μm high, and the deposited line is roughly 40μm wide. Which looks about right.

For a first stab at a multi-layered object from an STL file I'm pretty pleased with that result. A slightly thinner or more steeply angled probe tip, staggered layers, a more accurate measure of how many dots per dip, some kind of method of knocking off the first dot from the probe, and I think we can get better resolution and significantly more than 10 layers out of this. Maybe overhangs too.