Tuesday, 7 February 2017

3D print graveyard

As I posted, I have a new 3D printer. The Lulzbot TAZ 6 is much like the Makerbot Replicator 2 but with a lot of refinements. So now I am looking at the software you use with the printer.

With the Makerbot, you use their software. It just works, and does so very well. Some models need "support" material and some do not (you cannot print in thin air, so overhangs need support). But models tend to print well, and there are a lot of models designed and tested to just work on a Makerbot.

The TAZ 6 is usually used with Cura, which is free software and there is a profile for the TAZ 6 (i.e. all of the various settings) to allow printing in PLA, ABS, etc. It offers much the same in simple settings - fast/medium/fine print speeds, with supports or not, etc. Again, for most things, it just works.

However, Cura, unlike the Makerbot software, does allow a lot of advanced options. For a lot of people you do not need to touch these.

One thing I tried to print, what with Valantine's day coming up, is the Secret Heart Box (on thingiverse). This is a very impressive 3D model, which is designed to print on a Makerbot.

It opens, and can fold to a non heart shape. Quite clever, with hinges built in and printed as one.

I tried on Cura and TAZ 6 and it did not "move", the parts were fused. Thankfully they publish the OpenSCAD model, which, after some updating, allowed me to change tolerances, but still it tricky.

So I thought I would experiment with some other software, and have bought a copy of Simplify3D ($149). For a start, it is quicker and easier to use than Cura. The print preview is really impressive and quick.

Simplify3D has way more fine tuning options, and in fact has allowed me to make a much better "profile" for printing on the TAZ 6. What seems odd if the profile for the TAZ 6 as supplied was still somewhat lacking. Here are just a few things I ended up fine tuning...
  • To get the first layer to stick better I am heating the bed more (100C) just for first layer
  • Printing first layer slower (25%)
  • Printing first layer 200% thickness
  • Printing a brim at 0.1mm spacing for small footprint objects
  • Horizontal adjusts of -0.05mm
  • Extrusion multiplier 1 (why was default 0.9, odd)
  • Fewer base layers (2)
I also tried a few other tricks, and reverted them. One trick is printing at a small negative Z offset to force first layer in to the bed, and hence allowing 100% thickness, but that was not as reliable as just printing first layer 200%.

There are still many more features I could adjust, and I can tell it to print using different processes for different layers if I want.

Brims, Skirts, and Rafts

One of the things that 3D printing often needs is additional adhesion to the print bed - the TAZ 6 helps a lot by having a heated bed. In an ideal world you just want to print the model exactly and no extra bits (many models do not need support material).

However, if you are not careful the model comes unstuck during the print.

A raft is the normal solution on the Makerbot (I do not think it supports a brim). This means printing a thick layer on the bed (sticks well) then some thinner layers, then the model.

A raft is important if the bed is not smooth or exactly level. The TAZ 6 is very good with bed levelling and the bed is (so far) very smooth and flat. The Makerbot can easily be slightly off level and can easily be marked or pitted by previous removal of prints.

There are downsides with a raft. It sticks very well to the bed. Well, you want this while printing, but afterwards it is very easy to injure yourself trying to break the raft from the bed (on a Makerbot). Less of an issue on the TAZ 6 as the cooled bed tends to allow things to unstick. Also, separating the raft from the print can be tricky. and has same risk of injury! It can also leave some raft on the model which is almost impossible to remove. Rafts also use time and plastic, and for small models can be more plastic than the model itself! As a rule I dislike rafts!

A brim is a simpler solution. This is an outline, several layers wide and usually one layer thick that touches the model. This simply makes the base layer much larger, and is easy to break off after printing. Indeed, I have set it 0.1mm from model, which creates that slight weak point and makes it ever easier to separate. Brims work well but only really needed on models with small footprints.

If the footprint is big enough you do not need a raft or a brim, but you may need a skirt - this is an outline or some such that simply gets printed first to ensure the extruder is extruding and printing cleanly. The makerbot uses a long line at top of build plate for this, the TAZ 6 typically uses a skirt (outline away from the model).

Building bridges

One issue with all slicers (the software to turn a model to a tool path for printing) is where there is a lid on something, i.e. a print layer between the sides. You have to extrude filament to span over thin air from one side to the other.

The cura code coped with the top of the heart model perfectly, spanning over the thin walls each side.

The Simplify3D was stupid. It plotted the border for the top over the thin walls, and then tried to print the bridge totally over thin air, unsupported.  I had to tweak the model to make thicker walls so the bridge was supported on something. It tool several latest to actually build up a layer on top of a load of spaghetti, and even then it was not complete.

This is a poor design in Simplify 3D which Makerbot and Cura manage with no problem!

Time (and plastic) consuming

Each time you try something you can spend hours waiting for the outcome. It is a good job I have real work to do whilst it is printing another broken model for the grave yard.

Important tip: If you have a heated bed like the TAZ 6, always wait for it to cool before removing the model, else your perfect flat base gets all warped as you remove it, D'Oh.

Some times you can test something with a small test model, that helps a lot. To get the -0.05mm horizontal adjust I printed a small test cube, and measured it carefully.

P.S. I finally ended up with layer one done as a separate "process" for the first layer with 1.75 extrude factor (i.e. more plastic) but same layer thickness. This means not having to skip a layer by making first layer 200% thick.

P.P.S. I redesigned the heart from scratch - which was, in itself, quite fun. Just in time for Valentine's day. http://www.thingiverse.com/thing:2097443

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