Improve Dual Material print quality esp. for front panel marking

[Jez (in his) Shed @jezshed High Peak, UK]

Hi all,

After my fast-fill head decided to burst it’s innards after 407 hrs of use, I’ve just invested in a dual material upgrade and full “MOT” of my Cel Robox. It wasn’t a cheap exercise, but I hope it will be worth it.

I’d like to use the Dual Material capability for doing front panels of my electronic projects. I notice that the DM alignment test print looks really good and I’d like to get that kind of definition and quality for my own panels, but what’s the secret?

How can use I SketchUp to apply markings and text efficiently? I’ve tried added markings and text as separate objects (with a depth of 0.5mm for example) and selecting the appropriate material in AutoMaker but I can’t really work out the best combination of text size (or feature width) and depth to obtain a neat finish.

My attempts (although reasonable) do show some blobbing and joining of features. The best results so far use a simple font (Dosis) with approximate feature width of 2mm and a depth of 0.5mm, but it’s not as neat as the Alignment Test Print. I’m sure a font that results in a single pass outline rather than a “fill” will yield better results but I don’t know how I would ensure that a font (or marking) uses only a single pass rather than attempting a fill. To be honest, a font with a feature (line) width of 2mm is way too big, so I need to be able to get down to a feature width of 1mm like the Alignment Test Print, but my attempt was horrendous!

Also, really stupid question here but I’m missing something obvious here. What’s the most efficient way to assign materials to certain parts of the print. So far I’ve tried importing the whole STL and then using “ungroup” and then selecting individual objects to assign the correct material. That takes ages and is not always possible. I’ve also tried exporting the various objects as separate STL files from SketchUp and then assigning the desired material when importing them into AutoMaker. Sadly any imported objects get positioned to Z=0 (flat on the bed) so the relative Z positions are not correct.

Finally, is there a general tutorial here for Dual Material printing? I feel a little lost although I’ve loads of experience with single material design and print.

Thanks all,

Jez

• This topic was modified 4 days, 10 hours ago by  Jez (in his) Shed.

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[Mike @17bt CHORLEY, Lancashire]

@jezshed I think you might have nozzle calibration issues, because although the calibration test is OK, your text is stop start, whereas that’s a long perimeter. Also you might need to tweak the the line width of your fonts as the calibration test is two lines wide, and the lettering more. I personally think you are getting poor adhesion with the second colour on the red “fingers” around the knob, so maybe you might want to add some draft angles, so the red layer is bigger underneath, and the black layer on top masks it smaller.

I’ve had success using that technique on smaller two colour parts.

[BHudson @bhudson I have both RoboxDual and other Robox versions Arizona, USA]

@jezshed Your results are about what I would expect. Dual-color printing isn’t as simple as just putting two parts next to each other. There is a getting started article on it, but it only covers the points you have already figured out.

One of the things to keep in mind is that you will always be at the mercy of the size of your nozzles relative to the size of your parts. The rule of thumb in general is that your part smallest dimension should be a multiple of your extrusion width. If your extrusion width is set to 0.45 mm, your features should be multiples of two: 0.9 mm, 1.8 mm, etc. for any closed feature. The wall of an enclosure, where the nozzle will make a closed path around the wall, can be multiples of a single pass - 1x, 2x, 3x, etc. The material also needs time to cool and harden before the next layer, and the layer needs to have enough thermal mass to absorb the subsequent layer without loosing its structure. For the tiny text and the knob lines you are seeing two things happen:

1. The feature is too small for the number of passes. This causes the filament to remain soft, to stick to the nozzle, and to remelt. This is why your text isn’t crisp.
2. The heat of the nozzle is staying in one place too long. This melts the material around it and the nozzle starts to pick up the neighboring color.

The larger Hello text shows the number of passes issue in the open gaps between the passes. In addition, it shows some of the same point in number 1 above with the feature size. At the bottom of each “L” is a spot of material that is pushed out when the nozzle opens or closes. These values are controlled in the print profile. When I did a job like this it took about five hours to fine tune the profile to give sharp, consistent letters every time. It is also material sensitive, so all the work I did can’t be transferred to you unless you are using the same material. Each head can be unique; some heads will push a slightly higher opening or closing volume. This is a complex issue and not one that I can explain in detail. It can be solved for the most part with the above testing and fine tuning of the profile. This spot of extra material is what causes the stringing.

I think the nozzle opening calibration is correct on this print head. I would not change it based on the calibration print and the other indications I see on the printed results.

I operate two Betas and four Production Robox.
I am the US/Canada Technical Support engineer for the Robox.
See my 3D Hub site at https://www.3dhubs.com/phoenix/hubs/ben

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