Saturday, June 30, 2007


Printing the night away

After demonstrating that I could print 20+ layers with infill in HDPE I decided to take a crack at printing a polymer pump again, this time starting from Art of Illusion rather than building an XML transfer file from scratch.

Heretofore, Slice and Dice has been a once-through routine that simply takes a STL file of an object that you want to print and slices it at a given thickness and creates a STL print file that can be used in the Tommelise Control Panel. While it gives a graphical display of what is going on while it is processing I typically haven't got the patience to sit down while it grinds through 30-40 slices.

Since I haven't been trying to do anything too complicated printing out a layer or two to check to see if anything is amiss has been no big deal. With more complicated object, however, you are talking about 15-20 minutes/layer. That's slow. What I needed is a simple graphical method of displaying a print layer-by-layer. I'm not trying for anything as grad as what Adrian is doing in Java, just a 2D display of a slice or several slices so that I can see how the infill is fitting together.
Here are two overlain slices of zone two of a polymer pump that I designed in Art of Illusion. This cheap little bit of code is letting me spot problems in a layer without having to spend half an hour watching Tommelise print. Once I can see where they are it is a relatively simple matter to edit them out of the XML transfer file.

Can you see the problems in this view?

Looks beautiful :-)

Just as a matter of interest, though: why cross hatch in that direction though? Why not horizontally and vertically?
I think I might see the issue that you refer to... Is that 2 layers, or 6? Or 12? Methinks a little tag with the layer number on it might be helpful, a well as alternating colors.
I see 4 little ticks, two of which are outside the outline, unless you are also concerned with the minor discontinuities (just mentioning I see those, but don't think they are what you would be worried about). I'm guessing the 2 outside are what concerns you.
Bart: You got it! That was the problem. Little short extrusion segments are generated by some software bug I haven't trapped yet.

Eric: I did two layers this time. I'll be showing the range as soon as I get a moment to work on the GUI.

Diagonal cross-hatch lets you use both the x and y axis motors which meant that you get an aggregate speed of 2^0.5 times what you would get with only one axis.

Right now I get 1.7 mm/sec on one axis. When I use both I get 2.4 mm/sec. :-D

If and when I decide to shift over to 3/8-16 studding from the 3/87-24 that I'm using now my diagonal speed will push up to 3.6 mm/sec.

Mind, since I'm using HDPE with a 50% infill which I can get by with because of its strength I'm getting effectively twice that speed.
Forrest, why is this kind of speed relevant at all? Amount of extruded material for given time is the same, so the only difference is track thickness (difference is now fourth root of 2), which can be compensated by more sparse grid. Surely intersections of tracks affect form much more than that.

If your one-axis speed is a limit (although I agree with Vladimir in that I'm not sure how it could be) why not turn the whole part diagonal-wise as you print it, and make the whole thing, crosshatching and all, 45deg from the axis?

Vladimir: You adjust the polymer flow for head velocity, so it's not necessarily the same at all. Intersections at the tracks in a sparse fill just mash out to the sides a bit. You don't get z distortion unless you are extruding pretty cold. When you do that you don't get good welding between tracks.

Kyle: If you rotate the object 45 degrees you are able to extrude the perimeter faster but you've translated the infil into pure x and pure y movement. That slows down the print dramatically.
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I meant that it doesn't _depend_ on movement speed (and so if your objective is to complete the extrusion faster, this given action in inefficient, giving rise to wander what said objective is).

Kyle's point was that you can rotate detail 45 degrees _and_ make cross hatch parallel to the sides.

(And even extruding 45 degrees-turned detail according to your interpretation wouldn't slow down extrusion if you make traces sparser as per my first point.)
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