Settings to print parts designed for injection moulding

[PeterM @petermaries My Robox is a Blue Commercial Version]

I’ve been using rapid prototype bureau services to make samples of parts for more than 20 years. Processes employed: LOM, SLA, SLS and FDM (aka FFF). Mostly the parts I had made were prototypes of things designed for injection moulding or die casting. I bought a Robox about 5 weeks ago and I’ve spent most of the time since working through 1-2 reels of material in the pursuit of knowledge - how to get the best out of Robox when printing parts intended for injection moulding.

Tips:

Don’t use slic3r. The Robox version always wants to build bridges for elevated horizontal surfaces. There are always sagging threads under the elevated surface and the result looks quite unlike an injection moulded outcome. Angling the part to make the elevated surfaces not horizontal in any plane will prevent slic3r from building bridges, but it also causes all those surfaces to be banded - again not much like the injection moulded result. So use Cura.

When Cura is selected as the slicer of choice in the Robox settings, you will loose acces to a range of slicing options which are only avaialable in slic3r. Don’t worry, this reduces the number of ways in which you can screw up a print! They’re not all bad options by any means - just too many for the learner driver.

Download the freeware version of Cura so you can use it to preview how it is going to slice and support your part. Robox doesn’t have a print preview, so you cannot see how it will print until you commit time and filament to the job.

The default supports in Cura are rectilinear lines running from front to rear of the Robox. This works well if your part has a foot print which is roughly rectangular and you line up the long dimension of your part across the width of Robox. However if your part has features than then run from front to rear of Robox, rectilinear lines may leave poorly supported.

One solution is to simply rotate your part a few degrees so the front to rear supports now do support your vulnerable features. However, this effectively reduces the maximum part size that Robox can print.

Front to rear rectilinear support lines may also need support! If the part to be printed is quite deep (front to rear), then the rectilinear support line will be long and they may sag in the middle of their length and provide little support.

I have read comments from others recommending rectilinear support lines because they are relatively easy to remove after printing is finished. I want good parts ahead of easy support removal.

Use rectilinear grid supports in Cura. Now the supports support themselves as well as your part.

Robox / Cura doubles your support spacing parameter. If you have set support spacing to 2mm this is what you will get with rectilinear lines. However, when Rectilinear grids is selected, the result will be 4mm square cells.

Enough for now. More to come on shrinkage, temperatures and filament feed matters.

 

[Pete @pete My Robox is a Blue Commercial Version CEL HQ Bristol UK]

Good advice, thanks for sharing and I look forward to seeing more.

We are aware of the limitations of Cura which is why we chose Slic3r initially. Cura does to a good job in many situations and at a basic level can create cleaner prints than Slic3r. We allow users to choose between them in the settings page to try and get the best of both.

Gcode previews are very useful, the software team has an outline of how we would like a custom AutoMaker version to work and it is discussed quite often, it would be of great benefit to us as a development tool as well so I expect it will come fairly soon but keeps getting pushed back as we make changes and improvements to the other systems. We often use Repetier to view gcode.

We have also discussed support generation at great length. Again the software team has some pretty cool ideas and the next release of AutoMaker is already able to generate new .stl files by breaking up loaded .stl files. We have found that the best support is designed in but this is time consuming, we hope to have semi automated support structures giving the user hints but allowing them to choose the way the support is structured, not using gcode but actually generating some geometry.

One tip for support using the current system is to reduce the Support Spacing to 1mm for small sections which need support.

For official support please visit www.cel-robox.com/support/ and create a ticket

[gid @gid My Robox is a Green Kickstarter Beta]

@petermaries Good tips! If you haven’t found it already, you might want to look in the CEL/AutoMaker/PrintJobs folder. You should find a subfolder for each print you do that contains a few files including the .gcode file that Cura/slic3r generated, and the modified _robox.gcode file that actually got sent to the printer itself after AutoMaker sprinkled some fairy dust on it to handle the Robox’s unique features.

So, to preview a print, you can print it, then as soon as slicing is complete, pause the print (which hopefully won’t have started) and use Repetier or another GCode viewer to visualise the file. Some more tips here: http://www.roboxing.com/gcode

Tom Gidden -- Bristol, UK

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