Wednesday, October 28, 2009


Colour Printing - the next step

To follow on from the basic twin extruder test in the last blog, here we have the results of my first test using support material

The machine is loaded with two colours of ABS, mainly for convenience at this stage, Black for the object and Yellow for the support material.

The file chosen is a bearing cap, printed from the bearing axis up, this has a semi-circular void that runs front to rear of the part. Actually this file prints very well without support material but it is a small part suitable for testing the head change.

Small it may be, but it still contains a fair number of layers and therefore lots of head swapping!

The first test was done with a hand edited file, I added several new lines of G_Code to manage an orderly change over from one head to the other. On more complex parts, it would not be practical, the new codes need to be added by Skienforge.

Skienforge already deals with support material by issuing a temperature change to flag the start and end, I need several other codes inserting at this point. To do this I have made a simple modification to Skienforge to pick out the support material, then insert my new codes as required.

The image shows the first complete part made by running the file from Skienforge.
Finish on the part is crude as the G_Code has been generated with 0.4mm layer thickness, this ensures a relatively quick build and gives a manageable file size.

The print is far from perfect, but I have to say I am encouraged by the results.

I'm curious to see printing with two different plastics.
Has anyone considered this PVA for support material? It appears to dissolve in plastic.
We will be giving PVA a try, it does extrude and yes it does dissolve in water.
Having said that PVA comes with its own set of problems so its not perfect.
Most excellent.

A couple of quick questions.

How was seperation and if the yellow is support why was the raft in black ??

The idea and work is great it resembles some work I did on a Dimension machine with snap off support. I guess this takes the whole thing to the next level.

Given that the pigments in the plastic act as dope-ants is temperature change actually necessary ?
Great progess!

Smart thinking about the temperature change as a trigger for inserting your own code to switch heads. You can use my (GPL'd) 3D-to-5D-gcode.php script's action engine to do the find-and-replace for me automatically.
Another reason for me to get my second extruder working (more) reliably!

Regarding sacrificial materials it might be interesting to know that PLA (polylactic acid) dissolves in lye. Lye is not expensive and can be bought to remedy a congested sink's drain chemically. It does require a lot of care while handling because you can get blind if you get it in your eyes and it also dissolves skin and other body parts.
Maybe the majority of separation of PLA and ABS could be done by heating it to 80-90 degrees Celsius and pull off most of the softer PLA. This could be reused in other projects or perhaps even formed into a filament again. It would also reduce the amount of lye used up and the time the process takes.

@AKA47: What do the pigments as dope-ants do? Increase/decrease separation or the melting temperature? Or something else? I did read somewhere that they can influence the time it takes for plastics to degrade. B.t.w. did you work a lot with Dimension/Stratasys machines?

No I only did a little work as part of a uni project/hand in. I shudder to think of the costs involved in doing a lot of work with one, The consumables are hideously expensive as are the machines.

It used two heads that looked like they were part of the same heater block. The support material looked to be grey ABS and the component was made from what looked like virgin ABS. The grey stuff snapped off (with varying degrees of ease).

Re Dope-ants. You are pretty much there with yout understanding. Nopheads experimentation with different plastics and with Green & Black versus Virgin ABS showed that they have different melt points, most likely as the pigments dope the plastic. (a bit like you change the melt point of ice to water if you a dope or impurity like salt)

If you have a common print head heater (nozzles are closer together) having two plastic feed-stocks that differ in temperature characteristics sufficiently would allow you to have one that stuck to the other but not that well. ie it would be a good candidate for snap of support material.

An easy hit with minimal changes to the code but a slight tweak of head design.
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AKA47 Yes the raft would ideally be printed in the support material but my quick hack in Skienforge only put it in the object layers.

By the way, I sent the modified Skienforge file to Enrique last night and today he tells me there are two file templates in the tool section, guess what?
support_start.gcode and support_end.gcode!
It was fun having a play with Python but it looks like I wasted my time. I have tried putting my additional codes in these files and it works well.

The black and Yellow seem to extrude OK at very similar temperatures and as such if both are printed with the same temp the layer adhesion is very good.

I have finished doing the work with two ABS colours for now, I was only looking to sort the code and see it all work before I try some other material combinations.

We have experimented with PVA and it will extrude, I hope to run some 3mm stock next so I will post pictures of the mess it makes!
For info: I cut off a 300mm length and placed it in a glass of water overnight, the following morning only a small tail of the filament was left above the surface of the water, all the rest had gone!

The issue I expect to have when printing PVA and ABS together is the differential in print temperature. PVA is significantly lower and as such is very hard to get a raft stuck down to acrylic. If you manage to get a raft down, hot ABS melts into it more than I would like. I have no idea if this will work so there is no short cut - just try it and see how I get on
@Tony: Is ABS melting the PVA that much of a problem? From the pics of some prints in pure ABS, overhangs are not really a tremendous problem. Take for example that book on the statue of liberty or Bre's half-a-Disney-head. In both situations the printer was printing way beyond 45 degrees - but it sorted itself out by printing a little more on the last edge of solid ABS.

Thus, my question is that as long as ABS had a little support from PVA rather than hanging out in mid-air, shouldn't it print reasonably well?
@ Tony: I got myself a BfB control system. You are also using that, right? Is it equipped to run two extruder stepper motors AND three axes? Or do I need to make a breakout board for powering a second extruder? (similar to what I need to do in my current setup)
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