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Challenge

Posted: Fri Apr 10, 2015 10:16 pm
by DIY3D
Guys, I have a challenge and a question :lol:

In the link below you find:
  • A picture of a small object. The top of that object has a grid. The grid is 0.5mm ^ 3. When I print this object, the grid is not open but filled, as you can see in the picture:
  • The settings I used in Cura, I've also tried to Slic3 with a but the same result
  • The .stl file if you wanna give it a try ;)
http://1drv.ms/1NmgCNJ

Is it possible to print such a fine grid and how do I get the best result?

Kind regards,
Marco

Re: Challenge

Posted: Fri Apr 10, 2015 10:47 pm
by insta
Make your printer's resolution work for you -- print it on edge with a 0.1mm layer height. :)

Re: Challenge

Posted: Sat Apr 11, 2015 2:19 am
by ednisley
DIY3D wrote:Is it possible to print such a fine grid
Basically, no.

The problem is that the size of the printed thread is larger than the features you want to print. Think of trying to draw a grid of 1 mm squares using a 3 mm marker: the marker can't draw anything smaller than 3 mm.

In round numbers, the smallest possible square must have two threads. For a 0.4 mm thread width, the square must be 0.8 mm on a side... but it will look like a circle, because there's no way to fill the corners. So you can't print a 0.5 mm square: each one would come out as a 0.4 mm dot.

Even if the slicer can figure out how to emit a 0.5 mm dot, that will hammer the filament drive with one extrude/retraction cycle per "square", each cycle emitting a single dot without moving. If you have retraction set up perfectly and the filament drive doesn't chew through the filament, you could get a bunch of dots.

If you have a 0.25 mm nozzle and select a 0.25 mm thread width (rather than the usual 0.3+ mm for that nozzle size), then you might be able to print a 0.5 mm square-ish blob, but the overall grid won't work for another reason...

The gentle surface curve means the slicer must produce each cube using slices that aren't parallel to the top surface. The slices intersecting the top of each cube must be smaller than 0.5 mm in the direction of the curve, but 0.5 mm is already the bare minimum the nozzle can produce.
insta wrote:print it on edge with a 0.1mm layer height
Alas, that won't work, because the nozzle can't draw those little 0.5 mm "square" protrusions on each layer. It might come heartbreakingly close with a 0.25 mm thread width, but ...

In short, fused plastic 3D printers have a fairly large minimum feature size: just under 1 mm. For most human-scale objects, that's not a problem. For the highly detailed miniature objects and mechanical features that we techies would really like to produce, it's a showstopper.

Re: Challenge

Posted: Sat Apr 11, 2015 5:15 am
by jsc
ednisley wrote:Alas, that won't work, because the nozzle can't draw those little 0.5 mm "square" protrusions on each layer. It might come heartbreakingly close with a 0.25 mm thread width, but ...
You'd think that, but:
holes.jpg
holes.jpg (237 KiB) Viewed 11585 times
Here's what the slicer is doing to it:
holes-sliced.jpg
holes-sliced.jpg (167.68 KiB) Viewed 11585 times
Here's a macro shot of the holes:
holes-macro.jpg
holes-macro.jpg (188.15 KiB) Viewed 11580 times
(What is this thing, anyway?)

Re: Challenge

Posted: Sat Apr 11, 2015 5:59 am
by jimc
man i had to look at that top photo for a min. i thought you had some fancy new type of chrome filament or something. after i scrolled down i see its just black. its so shiny though it does look like some glossy stainless steel filled plastic.

Re: Challenge

Posted: Sat Apr 11, 2015 6:10 am
by jsc
I had a flashlight raking across it to bring out some detail.

Re: Challenge

Posted: Sat Apr 11, 2015 12:01 pm
by DIY3D
Hi All,

@Ed
That was exactly what I thought, I couldn't imagine how that should works, anyway thanks for the reply!.

@jcs
Great result and clear photo's :o !

I have made a testprint and you're right, that looks much better then my first attempt:
http://1drv.ms/1yfgHvu

Thank you for trying out, it's the top part of a press mold.

Kind regards,
Marco

Re: Challenge

Posted: Sat Apr 11, 2015 2:05 pm
by ednisley
jsc wrote:You'd think that
And, indeed, I did! I saw bumps, not dents... [sigh]

Just to show how wrong I was, subtract that thing from a rectangular solid and print the resulting bumps emerging from a concave arc. They're small enough that overhang droop might not be a problem.

It looks like the difference between hole and wall widths depends critically on the printer setup, but at least it's possible to get close to the goal: your printer produces wider walls, Marco's generates wider holes.

Well done!

Re: Challenge

Posted: Sat Apr 11, 2015 5:45 pm
by jsc
It looks to my eye like the walls are thinner than the holes, so I think the inverse object would print out okay.

I understand your argument, but it seems like the slicer is doing interesting things to invalidate it. Maybe backtracking with half extrusion? Wonder what Cura or slic3r does with it.

Re: Challenge

Posted: Sat Apr 11, 2015 6:43 pm
by ednisley
jsc wrote:it seems like the slicer is doing interesting things to invalidate it
Believe it or not, I really want to see the day where "If you can dream it, you can make it" actually works like that, minus all the tedious screwing around with orientation / alignment holes / adhesives / tweaking. [grin]