Sunday, March 17, 2019

405 Nanometres

As most of you will know I like 3D printing, I've been a convert since I got my first print back in August 2012. One thing I worked out quite quickly was that while I really enjoyed designing the parts and receiving the prints (usually from Shapeways) I had no interest in having a printer of my own.

The main reason for not wanting my own printer was a simple cost versus quality trade off. All the printers I could contemplate affording couldn't get anywhere near the quality of the prints I could buy via Shapeways who could afford to buy very very expensive printers. Over the last year or so a couple of things have changed that caused me to rethink my stance.

Firstly Shapeways are no longer the friendly, open, and helpful startup they once were. Don't get me wrong they are still producing high quality prints, but they've made a number of changes to their platform that make it a lot less fun to use. First they hid the pricing formula and a lot of the related details which made it difficult to print items without them becoming more expensive than necessary. Then they increased the prices, with some models seeing price rises of over 30% and they doubled the shipping costs. Added to that they changed the website layout making it so much harder to simply order a print.

At the same time as Shapeways were doing their best to alienate their customers there was a significant change in the home 3D printer market. Until fairly recently almost all the printers that I'd consider affordable for home use were based around Fused Deposition Modelling (FDM); essentially a nozzle moving in three dimensions depositing melted plastic. Whilst these printers can be used to produce great models, they tend to be quite large, and the quality, especially on small details, doesn't match up with what I'm used to getting via Shapeways (the process there is also FDM but again it's the cost/quality trade off issue). An alternative approach to printing is to use light to cure a resin, often referred to as stereolithography. Traditionally this involved a laser and mirrors and was an expensive approach, but there are other ways of achieving the same result. One such way is often refereed to as Digital Light Procssing (DLP) printing, where the light for a single layer is projected onto the resin. Depending how this is achieved it can be done relatively cheaply while still producing high quality prints. More importantly it can be done cheap enough for home use.

As you've probably guessed by now I've gone and bought myself a 3D printer. Specifically I've bought an Anycubic Photon (best price I've found for a UK seller is Amazon, and they seem to have fairly regular offers on, I got mine for quite a bit less than the current list price in one of Amazon's "Lightning Deals"). The printer has a relatively small build volume (i.e. the maximum size of object you can print) of 115mm x 115mm x 65mm but that's plenty big enough for the models I usually print. The small size is actually an advantage as it takes up very little space (22cm x 20cm) on my desk. It works by using an LCD screen, at the bottom of the resin vat, to act as a mask for a UV light. After each layer has cured the build plate is moved up a tiny amount before the next layer is made.

This means that essentially the printer boils down to a UV light (with a wavelength of 405 nanometre), an LCD screen, and a single stepper motor (plus the control electronics obviously) making it fairly cheap to produce. Of course the approach does have some limitations. For example, the XY resolution is dependent on the resolution of the LCD screen, and the smallest detail you can produce is therefore the size of a pixel -- 47 microns in this case. Also with the LCD essentially acting as a mask there will be some bleeding of light which can make producing small holes an issue as they tend to close up slightly. So the question becomes how good can printers like this be for the price.

Well there is really only one way to find out, and that's to print something!

Okay I didn't just print one thing, but three things. Specifically I started by printing a sprue of 40 L&B roof finials as they didn't need any supports adding. I used the default settings with a layer height of 0.05mm and the finials look perfect; no obvious print lines and nice crisp details. Of course they are not the most complex or detailed parts so next up was the 6.5mm gauge chassis for the peat wagon I'm currently working on. This was a bit more involved as it required supports to be added. Even so it came out really well. A few lines on the print (possibly because of the orientation) and the fit of the wheels is ever so slightly tighter than I'd like but usable as they are. The final test print that I've done so far was the kit of parts for the K12 diesel loco.

This is a much more complex model with lots of parts requiring supports adding and a number of small holes and tight clearances (as it was designed to minimise the build volume to keep the price on Shapeways down). I altered some of the automatically generated supports which caused a few problems; the bottom of the buffer beams drooped downwards and half the power retaining clip is missing. Also the small slots for the etched parts to fit into are a little undersized. This seems to be a known issue with the printer and is probably a combination of light leakage on the LCD and the viscosity of the resin. There are a number of ways to work around the issue so it's not the end of the world. More importantly, I gave the part a quick waft of primer to get a better look at the details; I made no attempt to smooth the surface all I did was remove the supports.

Now this does highlight the drooping issue with the buffer beams but, look at the axle box detail, and how smooth the sides are! In this area, the print is better than the last print of this I got from Shapeways where I had to do lots of careful sanding around the axle boxes to remove the print lines.

All in all, I'm exceptionally happy with the printer so far. Yes I have work to do in order to fix a few issues (mostly around small holes and sorting out the best way of putting supports etc.) but I don't think it will be too hard to move to the point where I'm happy to use the prints for my own modelling. It might even be that I start printing parts for some of my kits as well. This isn't to say I'll never use Shapeways again as I'm sure I'll want to print in other materials (like brass and stainless steel) or I might decide that in some cases the prints from Shapeways are better for some reason (maybe something is difficult to support and print) but if nothing else I should be able to prototype new models a lot quicker and cheaper than before, and if nothing else I'm going to have lots of fun.


  1. Well no one could ever accuse you of not being adventurous. I actually understood some of that too!

  2. That does look like a nice bit of kit. Still a learning curve to get the best from it, but lots of potential.

    1. Yes, the learning curve is going to take a bit of time to work along, but I think I'm getting there slowly. One of the things I like about it though is that it looks the part; I guess being solidly constructed from metal and looking like a piece of consumer equipment rather than something I've assembled myself helps.