Any recommendations on an FDM printer? I've been looking at the Anycubic Kobra Max, which has a 400 x 400mm print area, seems ideal for timbering bases.
@Nick Allport
Hi Nick,
Congratulations on your hi-res photo of the chairs. I find it extremely difficult to photograph the translucent material and capture detail, but you have managed for the first time to show the random rotations on the square screw heads in 4mm/ft scale:
Many thanks for posting that.
The rail seats do look rather angular, but they get mostly hidden under the rail, and a good scoosh of paint will fill the corners to replicate the fillet radii on the prototype castings. The paint is needed to protect them from long-term UV exposure which may cause them to become brittle. This might be another reason to prefer the ABS-Like resin, although no-one has been doing this stuff for long enough to know for sure. Yes, that resin uses the same print settings as the standard resin (as far as I know).
Regarding FDM printers, it is a constantly moving feast of new printers as the various manufacturers try to leap-frog over each other. I can't make a recommendation because I can't possibly buy them all to try! In any event all the latest printers appear to be currently out-of-stock in the UK after the recent Black Friday frenzy, and are quoting deliveries into February.
But a few of the relevant points which we have been discussing here.
1. For a timbering brick we must be able to create a flat print of constant thickness all over. Which is not a typical use for these printers, so doesn't feature much in the specs. It relates to the levelling of the build plate.
Some printers claim to be "auto-levelling", but are no such thing -- nothing gets changed. All that happens is that the Z height of the nozzle is adjusted while printing the first layers to compensate for any variations in the surface of the build plate. Which itself tends to be a flexible tin sheet with nothing to hold it dead flat. This "auto-levelling" ensures that the first layer adheres properly to the build plate, but does nothing to ensure the dimensional accuracy of the finished part over a wide area.
For the test timbering bricks I have been using a rigid glass build plate with manual screw levelling at the corners (on Neptune 2S). By this means I have managed to produce timbering bricks which are a constant thickness within about +/-0.025mm (+/- 1 thou) all over, and repeatable.
It seems that Elegoo have recognised the need for manual levelling by re-introducing it as an option on their latest
Neptune 3 Plus and
Neptune 3 Max printers, having removed it on the previous Neptune 3 and Neptune 3 Pro printers. They call it "
Auxiliary Levelling":
"Auto Bed Leveling + Auxiliary Leveling: The non-contact high precision sensor automatically scans 63 points of the hotbed to compensate for any unevenness and inconsistencies of the printing platform. You can also use the hand-twist knobs under the build platform for auxiliary leveling to achieve a nice first layer."
I can't find whether other manufacturers are or will be doing the same, but if not that would be a definite vote for the Neptune 3 Plus and Neptune 3 Max printers from me. On a printer without screw adjustments it's possible to level a rigid build plate by using card packing under the corner clips, but a screw adjuster is much easier to use and repeatable.
2. Z-precision. For accurate Z thickness dimensions it needs a twin Z-screw. The Neptune 2S has only a single Z-screw and I have had to modify it to be sure of getting consistent results.
3. Extruder. The Neptune 2S has a bowden-tube extruder, unlike my older BIBO printer which has a direct-drive extruder. I was expecting that the bowden tube might cause problems with stringing from the nozzle, but I have found that by using an aggressive retraction setting it produces results just as good as the BIBO. The snag is that this stresses the bowden tube end fittings, and I have already had to replace one of them. I wondered why there were 2 spares included with the printer!
So I would definitely go for a direct-drive extruder if possible. Again this is a change for the Neptune 3 range from the Neptune 2S. In theory the heavier direct-drive extruder head means a slower printer, but it's hardly relevant when printing precise parts. It might make a difference if printing large chunky parts as fast as possible. FDM printing is slow regardless, but runs unattended for hours while you get on with some modelling.
4. Build plate area. The bigger the better, but it does increase the cost! The larger printers are also taller, which might be a nuisance and you may not have any use for the increased model height in 4mm/ft scale.
cheers,
Martin.
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