Hole Accuracy

So I've been experimenting with various options with Slic3r to try and make it extruder the proper hole dimensions when the hole is perpendicular to the bed. As best as I have gotten, the only real improvement came when I went from a 0.4 nozzle to a 0.3 nozzle. Holes parallel to the bed come out perfect size. I've tried numerous extrusion width settings, speeds as low as 5mm/s for everything, I even changed the filament diameters up and down to 1.5 to 2.0 with various stops in-between, changed various extruder steps, I even changed my filament size to 1.128 and did the whole machine in the volumetric E units setup to see if it would make any difference. I've tried infill first, I've tried infill last, if it was changeable on Slic3r, I've tried several variations for each option primarily to see what affect it has over the final gcode and print.

Word of caution, I know this is possible with FDM technology as the Stratasys uPrint SE Plus printer will print the exact dimensions from the source file, but what I'm wondering if this is not possible with the RepRap machines, but the Stratasys uPrint SE Plus uses a special piece of software from Stratasys to create the gcode it uses which is actually some cmb.gz file rather than gcode. Regardless of orientation, the dimensions printed on the Stratasys printer are perfect every time.

Attached is the test file I'm working with. Outer dimensions are coming out perfect every time, but the hole in the middle is only come out at 4mm with my 0.3 nozzle and at best 3.9mm with a 0.4 nozzle rather than the 4.3mm. If I print it on it's side, my hole dimension is perfect at 4.3mm. Same hold true if I print it on my CoreXY with the Duet 0.8.5 and the CoreXY with Mega/Ramps.

So, I've started to wonder, is Simplify3D any better with hole dimensions that are perpendicular to the bed? Are the current "free" slicer applications not taking into account the proper elements for paths and plastic squish that are covered in the commercial applications?

FDM technology can do this, but what I'm leaning towards is current reprap based setups with the software of today can't.

Edited 1 time(s). Last edit at 08/05/2016 04:03PM by PDBeal.

I have used Simplify3d for the last 2 years and even when it is lights years ahead of the free slicers, and probably will do better jobs with circles, it won't fix your problem.

To create perfect perpendicular holes, you need to account for several factors:

1 At which layer it will start.
2 How many layers will be needed to cover the right dimension.
3 the use of a good quality cad program.

I use inventor for my designs and the quality compared to free cad programs is huge, even solidworks don't get close. But understand is quite expensive an not everyone can have access to proprietary software, so the best next option is trying to increase the number of polygons created on the stl file in order to increase the quality.

I don't think the cost of the CAD program has any bearing of whether the 3D printed hole size is accurate. I suspect that the software that drives Stratasys printers applies some scaling factor to hole sizes to make sure they print accurately, something that could be but has yet to be added to the free slicers.

This is part of the reason that 3D printing isn't for everyone. It takes intimate knowledge of the printer's and slicer's behaviors to get really high quality prints.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I was curious enough to print this on a Flashforge Pro that has been fairly accurately calibrated.

Doing nothing special in Simplify3D over my normal settings i got a hole size from 4.18 to 4.26, so slightly oval, an M4 bolt slides through the hole with no binding.

Base speed 55mm/s prior to slow down for small object, actual may well have as low as 30mm/s

I now use Fusion 360 and find small holes are within 0.1mm and anything large than about 6mm is exactly right.

Cheers

I get fairly accurate dimensions with my prusa i3 and solid edge. Dimensional accuracy is all about the proper steps, xyz and e, as well as jerk, acceleration and mesh resolution. I can print some parts at 100mms and be very accurate. Holes parallel to the bed require higher resolution, thoughtful placement and all travel steps to be set properly for perfect accuracy since they are dependent on all axis. All quality parts need high resolution meshes as well, I set solid edge to be accurate to .001mm. The files are big, and take a bit longer to slice, but they have all turned out dimensionally accurate, with in .14mm, if printed with the right nozzel and layer height. I could get the dimensions tighter if I were to continue adjusting my steps, but I think that I have good enough accuracy for manufacturing prototypes. Especially since I would have a hard time getting production parts with that level of accuracy for a good cost.

I may have accidentally stumbled upon the source of my non-accurate holes..... PLA shrinkage.

I was playing around with one of my CoreXY machines printing PETG with a 0.4 nozzle. With it being PETG, I'm still tweaking the parameters a little bit, but as I was lowering the printing temperature my prints became a lot more accurate (it might be worth noting, I'm not printing PETG any faswter than 20 mm/s which would also play a part). So trying this lower temperature thing (and the 20 mm/s speeds) didn't help my issues with PLA, but I'm now beginning to wonder if 90% of my hole accuracy issue is with PLA shrinkage.

The Stratasys uPrint SE Plus prints what it calls ABSPlus in a heated chamber, and as far as I have seen, does not shrink when cooled. This would contribute to the proper hole dimensions, and would also explain why my PETG prints are also almost as accurate since PETG doesn't shrink either or if it does very slightly.

I believe PETG is about .4% shrinkage
ABS depends also but I think its more like 2-4%

I dont mind holes coming out a little smaller if I want to thread them, and when I want nice fit or through hole I make it bigger, though i've not scaled whole part to account for shrinkage as advised in some places.

I design my parts with extra tolerance in the holes for just such limitation as of the moment.
Honestly +/- .5mm on a hole is not that bad IMO.

Quote
Floyd
I design my parts with extra tolerance in the holes for just such limitation as of the moment.
Honestly +/- .5mm on a hole is not that bad IMO.

1/2 mm tolerance is not even vaguely acceptable really and designing the tolerance in may work for you it would be better to make your prints more accurate.

Personally I get +0 to -0.15 above 2mm and design all holes to the exact required size.... Anything undersized is easy to fix with a drill in real life though

Tell that to shapeways

Meh, its a known issue with all the free slicers and we have to deal with it for the time being.

From what I've seen, the issue is with the slicers not taking shrinkage into account when it prints, which might be near impossible with the number of different brands of plastic out there. When I run PETG, the hole dimensions are almost exact, but when I run PLA, the hole dimensions are way too small. Physical external part dimensions are accurate on either plastic apart from the corners of PLA occasionally lifting.

There was a long thread about this a while back in the Slic3r forum here.

One issue brought up is that smaller holes have less facets - more strait lines around the hole - effectively making it smaller.
Another issue is that filament being dragged around the hole may be pulled slightly inward.

One thing that was recommended was to print outside perimeters first. This will actually print the inside border of the hole first - which is more accurate, as prior "inside" perimeters will not push it inward (if there is over-extrusion).

As you noticed - the particular hot-end and extruder setup affects the outcome.

I think there is more in play than has been discussed - having to do with pressure regulation (lack thereof)
In my opinion, a worst case scenario has these three features:
1- A bowden extruder (which has more spring pressure stored in the filament between the extruder to hot end)
2- Printing a high volume (mm3/sec) area, and then immediately a small perimeter.
3- Slic3r then uses your speed setting for Small perimeters.

I believe what happens is this:
- When first printing a higher volume (mm3/sec) area (perhaps infill at a higher speed * extrusion width, or ever regular perimeters) the extrusion system is more highly pressurized in order to print at that higher MM3/sec.
- When next printing in the low volume area - at a much slower speed and narrower extrusion width - the difference in mm3/sec can be as much as 4x.
- The excess pressure bleeds out as over extrusion - so wider extrusion - and a smaller hole.

You could test this by setting perimeters = 1, and stopping the print as soon as it has completed the higher speed perimeter around the whole part, and one around a hole (only if they print in that order). Measure both perimeters and see if they are as they should be.

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My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
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