I use FreeCAD for quite a few things. I mostly use the RealThunder link branch, simply because it changes some things I find advantageous to my workflow, though of course I keep an unmodified version on hand as well.
Most of what I do relates to 3D printing. Either as a method of rapidly proofing a design, or for the final object.
A common issue is that round holes as side features often have trouble printing the top of the hole. It tends to sag. A typical way to solve this is to make that hole a teardrop shape.
The process for that is quite involved when creating dozens of those features, so my thought was what if Part Design had a teardrop shape option included. That could make it a significantly less complex feature to use regularly.
I don’t know what it would take to add that, so perhaps the request is unreasonable.
I hope I am posting in the appropriate section. I tried to get a feel for what was appropriate for the topic category, but if I got it wrong, feel free to move my post, or even delete it without concern of offending.
IMHO an ellipse wouldn’t be suited. First there’s a positioning issue: do I need to vertically offset the hole in relation to where a cylindrical hole would be? How wide and tall should it be? Then there’s the fact the bolt going through would not have a proper fit (not being an engineer, I wouldn’t know if it could create problems mechanically, but that could be a possibility).
Also, whether using any of the current or future assembly modules to build an assembly, creating ellipse-shaped holes on a part would preclude from using axial relationships. That’s a huge shortcoming.
The teardrop shape is a simple and elegant solution that the RepRap community came up with a long time ago, to FFF/FDM printers’ inability to print overhangs below 45 degrees, and the fact that if you print midair, the filament will sag until it cools, and thus will obstruct the hole. The teardrop retains a cylindrical face of 270 degrees which still allows for axial assembly relationships.
This image found through a web search should be self-explanatory.
It’s not unreasonable, it’s just that it’s a matter of time and resources. I’m guessing the people actively working on FreeCAD at this time have many other priorities. Also, even though many people probably use FC to design 3D printed parts, you may be the first to request such a feature.
Regarding the elipse idea, M4x, that would help with material shrinkage as it cools, but that rarely is the issue for home-users. Aerospace and that sort of use where they are I’m guessing not using FreeCAD as often, certainly would consider things like that to more of an extreme, since the difference for non-commercial grade materials in shrinkage just isn’t that much (maybe 2% shrinkage, and the delta between the planes is probably even smaller). But, it would not solve the material sag issue.
Support material can be used, but using support material to prevent sagging and deformation not only uses more material and increases print times (sometimes significantly), but sometimes the hole will be in a location support material either cannot reach, or cannot be effectively removed from.
I am not 100% on what you are asking for, Shalmeneser so I threw a photo together just to get things moving, and if it isn’t what you are looking for, give me some clarification and we’ll go from there if/as needed. The forum isn’t letting me upload any project files, so if you know of a format it accepts I’ll do that.
My thinking is ideally, it could include a line from the center of the circle to the tip of the teardrop, to give a point to orient the teardrop by setting the angle of the line. Often, things are printed in orientations that do not match the orientation in which it was drawn, and the teardrop would need to be oriented correctly to have any positive effect on outcome.
A new teardrop geometric shape in the Sketcher. You create a sketch containing one or more teardrops, then pocket it.
A teardrop option in the PD Hole feature. Would require selecting an axis for the “up” direction. Sketch would only contain circle(s), the hole feature would automatically add the teardrop tip.
A tool that modifies existing holes on a part to add the teardrop tip. This could be part of a “3D printing” workbench with other useful tools to check overhang angles and 3D printability in general.
Personally, I would go with the third option. I’d prefer to keep a pristine model with proper cylindrical holes, and have a tool generate a “3D printable” copy.
But we’re in the hypothetical…
Alternatively, a FC user competent with python macros could probably create a macro that would do option 3. Sadly I am not that person.
That’s what I would prefer to see too. Then you wouldn’t have to decide during modeling how the object will be manufactured. It would be similar to Path workbench, which does some sort of post processing to an object (beyond its own postprocessor step).
I agree with what has been said about making it a component in its own workbench.
Ideally, with the ability to select all holes on a particular plane, or select specific holes.
Then you wouldn’t have to decide during modeling how the object will be manufactured.
This has been a common issue with 3D models. Many are designed around a specific machine, with gcode created by a specific slicer. I design everything as if it is the finished product, and tune the slicer and printer to meet those dimensions, but most adjust the dimensions in their model. It’ll bite them when they purchase their next model and it doesn’t add 100-300 micron to every round hole anymore (or the slicers finally start correcting for it out of the box), or they want to send it out to have it printed or machined by someone else.
It almost works with some manipulation of the existing slot tool in Sketcher*.
Create a slot, remove the two tangency constraints from one of the arcs, coincindent constrain the unattached ends of the straight lines and delete the superfluous arc.
Maybe it would be possible to start from that in a macro. One thing the above does not do is guarantee 270 degrees of arc.
I came to this by considering that a teardrop is a slot with one end having zero radius.
My printer can do better than 45° - depending on material, layer height, size it can even go up to 60° - so that should be configurable. Be it with a special “circle” in sketcher or in a dedicated workbench.
Is there really a need for this with modern printers and slicers? I print holes with overhang all the time on my voron 2.4 and only use a small support in the middle for holes over 15-20 mm diameter.
Most printers are not modern. And even then, most are not of Voron quality. It also is application dependent. How true to round are they, really. If you had to print a 10 mm hole and fit a precision 10mm steel dowel in it without slop or post-processing, what would be the result?
Most printers have inadequate part-cooling, and are horribly tuned by the manufacturer. Its quite rare a printer owner knows how to correct for it, or even has access to source code to be able to correct for bad firmware settings.
While an option to implement modification in a 3d printing wb certainly would be nice, I do agree that as an interim a macro would seem to make the most sense.
Good idea. As shown in Shalmeneser’s screenshot, you simply add a perpendicular constraint between the two lines.
But come to think of it, it would be quicker to just keep the second arc and make its radius small, but non-zero. I’d say it could even have a radius as large as say, 1/4 of the bottom one. You’ll get filament sagging, but not low enough to obstruct the theoretical fully cylindrical hole.
Back when I was still using my now 11-year old 3D printer (a MendelMax-based Lulzbot AO-100), I sometimes made teardrop holes with a flat top.
Last night I visited the old RepRap.org website trying to find info on teardrop holes (I couldn’t). I was saddened to see it’s now a ghost town, with “state of the art” printer designs being a few years old. Forums are dead.
I guess the makers are now on f…g Discord. (I know the migration started long ago - I was on the Google+ 3D printing community. And look where that got us. )
It’s pretty sad honestly. Forums are one of the best community mediums of the internet. the reprap forums/wiki are still a great source of information for those willing to search them.
(I know the migration started long ago - I was on the Google+ 3D printing community. And look where that got us.