3D Printing (Part 7)

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After many hours of parts design and many rolls of ABS fused in our Makerbot Replicator 2x, it is time to write a little review on this nice printer, just be before it comes obsolete because of the new announced Makerbot products.

The Replicator 2x is doing what it was supposed to do. It is definitely an experimental printer which means that it is a good basis for printing all sorts of parts, but it suffers from uncontrolled performances which result in many printing failures and big need for improvements in part design and parameter settings.

The most critical aspect of the Makerbot 2x is the temperature control of the whole printer. I do not even care about the mod applied to the extruders thermocouple which is, to my opinion, a straight design error more than an uncontrolled function. Printing a simple ruler, 2 x 2 x 15 cm illustrates very well the major flaw. In most cases, this type of print will fail because of corner warping. This is very frustrating phenomenon because it happens  late in the printing process which means a loss of ABS and and a loss of time.

I read here an there many comments and suggested tricks to overcome this problem: Use this brand for acetone, use this type of Kapton tape, rub the Kapton with sand paper, do not rub the Kapton, change the heated bed temperature, spit on the Kapton tape (Oh nooo) …

I personally identified two causes for this defect. One is the heat balance of the part, the other is more mechanical. My assumption is that both causes have approximately the same weight. As the heat balance is pretty complex to handle and would require significant mods to the printer, I suggest that we concentrate on the second cause.

Here are few points to keep in mind while tweaking these warping issues:

  • ABS does not have sticking properties. If it would, it would not flow through the heated extruder, would it?
  • Acetone does not have sticking properties, neither Kapton
  • Putting the top cover on or off as no effect on the warping. Except that printing large flat surfaces with the cover on will lead to filament drive problems.

So how come my part stick on the heated Kapton coated bed?

The absence of air between the Kapton surface and the ABS film deposit (in other words, vacuum) is responsible for the “sticking” of the part on the bed. It is the atmospheric pressure which pulls the part on the Kapton surface. Thus the following thoughts and hints:

  • The larger the printed surface, the more the force as F= P.S where F is the force applied to the part (in N), P is the pressure (in Pa/m^2, with atmospheric pressure = ~100000 Pa) and S is the (contact) surface (in m^2). For example, the atmospheric pressure will exert a force on a printed part which contact surface is 10 cm^2 identical to a weight of 10 kg. Adding mouse ears to the part corner increases the contact surface and thus the pressure exert on the part.
  • The better the surface of the bed, the lesser the air leaks. Scratches on Kapton tape will create the so called capillary leaks. Poor bed and nozzle adjustments will also lead to multiple air leaks because the ABS will be deposit as rolls and not as a layer.

I am currently experimenting and testing heavily an alternative technique which really solves elegantly and efficiently this question. However, I am immensely curious to see the new Makerbot Replicator printer. From the pictures on their web site, I clearly see a fan which indicates that the heat balance within the printing chamber as been reworked, probably with the hep of the Stratasys R&D people…

3D_printer

The contribution of  Stratasys to Makerbot is clearly visible on the announced Makerbot Replicator Z18 !

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