Strong anchoring a protrusion on a 3d printed surface

[bergie5737]

Sometimes I need to 3d print small protrusions on a flat surface. The problem is that the protrusion only rides on the top layers, it does not "anchor" into the material. This method I use is to ensure the protrusion goes into the print for a deeper foundation type anchor.

In a nutshell I create a small offset between the faces which my printer will never be able to print, so it just welds it together. I add Cura examples of before and after. The effect now is that the protrusion does not break off so easily - especially small protrusions that is typically used in mounting holes for PCB's. This is akin to planting a pole in a deep hole and not just sitting at grass roots level.

Anyone with abetter method, please please help me out!
Regards

[etfrench · Accepted solution]

I suspect the problem is in your slicer instead of Fusion 360.  You might try increasing the hotend temperature when printing the small protrusions layers. 

One possible way to trick the slicer is to add an internal hole that extends down into the main body.  You'll need to experiment to find the minimum size hole the slicer will recognize.

p.s. Definitely work on calibrating your printer as the layer to layer adhesion is not good.  Temperature could be too hot or too cold. You could be under extruding.  I only print ABS and use a heated bed and also enclosed the printer.  I don't have any issues printing standoffs for PCBs.

You can also change your designs to give the standoffs more area at their base.  I look at the bottom of the PCB and measure the area around the hole to see how large the top can be made without hitting a component (or solder). If the area is really small, then I taper the standoff so the base is larger.

I don't have any images of an unpopulated enclosure, but this one may give you a few ideas:

[lichtzeichenanlage]

@bergie5737: Unfortunately your attachments are missing.  

[davebYYPCU]

Your system seems to work, 

I normally add a fillet to the base for normal load transfer through the fillet, or 

If you split the body at the top surface, some slicers will carry top and bottom layers right through - solid layers internally, but I prefer the fillet.

My  2 cents.....

[TheCADWhisperer]

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@bergie5737wrote:

...Anyone with abetter method, please please help me out!

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Can you File>Export and then Attach a *.f3d example file?

[bergie5737]

Hi, for some reason my screencast did not attach.

I will try and add a hole down into the lower layers. The fillet option usually works, but for a few recent designs, it interfered and the actual pins was a minuscule 2mm and 3mm in diameter and a good 8mm above the surface. This was a "clip-on case" I made that hold a battery and boost converter. With the first fit one pin broke off as it need quite a bit of work to clip it on securely. I second pin snapped, but with epoxy that sort of fills up the infill, it became incredibly strong. A lower layer height or more top layers would helped as well, but a fillet was not an option.

So I am looking for easier or simpler ways to make the print stronger. It would be great to see an option to combine only specific faces when combining bodies and leave the other faces unconnected. But I suppose there is not much of a real world use for such a feature.

Regards

[etfrench]

For standoffs/protrusions that small, I'd add a mechanical stiffener by creating a center hole and pressing in a metal rod .  Piano wire or inexpensive drill bits would work for this.

[bergie5737]

 I'd add a mechanical stiffener by creating a center hole and pressing in a metal rod

Good idea.

I understand Cura 3.2 can change infill in some areas with the "per model" tag, but I I have no idea how to actually do it. Or maybe I just misread the description. In effect if I can make a denser or 100% infill below the skin that extends down a few layers, should help strengthen a model and not increase print time by much. (A print that snaps in two when using add some print time though...! )

[bergie5737]

I've used the small hole in the middle method with success. It's much easier than my wasted method, and the small hole is not at all visible as I made it 0.1mm big and Cura is happy with that size.