OK print but the dimensions are a bit out
March 26, 2015 08:38PM
Hello

I printed an open cylinder sliced using Slic3r's Spiral vase tool.

PLA 190° Bed 60° 0.1 layer height 0.4 nozzle

It should have been 16mm OD with a 0.5MM wall

It came out at 15.68 to 15.74 OD (avg 15.71) with a wall of 0.43

The mid point of the wall thickness should have been at 15.5MM dia but from measurement was average 15.27

Not much to see;


I also printed a couple of 50mm cubes, I can't remember settings now. They measure 0.1 to 0.2 oversized.

Good tolerances for an ornament, but not great for an engineered component.

I'll try again with the cylinder with a regular slice and see how that compares.

Does anyone have any suggestions to tighten up the tolerance?
Is there any slicers than may perform better for this kind of print?
Also is there any way to increase the number of sides to the polygons that make up the circle?

Ideally, I'd like to print bush components using tribo filaments if anyone has any experience of that.

Thanks

Regards

a
Re: OK print but the dimensions are a bit out
March 27, 2015 02:04AM
Circles because of the way they get printed will always be smaller than original size. Only way is to design them oversized or move up the scale factor in the slicer. Now if cubes are coming oversized then you might have to revisit your steps per mm settings, but then again you cilinders will be even smaller. Get your cubes to perfect size and then just oversize your circles.

Assume those files came out of sketchup? You might try different cad programs: freecad, etc. They might be better at circles. I use inventor for cad and Simplify3d for slicer so can't help you much with free software suggestions.
Re: OK print but the dimensions are a bit out
March 27, 2015 03:25PM
Thanks for the answer.

I think steps/mm are fine as travel moves seem correct.

Objects were drawn in AutoCAD so should be dimensionally correct.

I understand the reasons why holes end up undersized but as I say the cylinder wall midpoint has ended up undersized too which would be a different issue.

Is Simplify3D worth paying for would you say?

-a

Edited 1 time(s). Last edit at 03/27/2015 05:24PM by alan richard.
Re: OK print but the dimensions are a bit out
March 27, 2015 06:44PM
Oh yeah, I don't regret paying the 150 for the software, the slicer have so many options and slicing is fast and accurate, the guy always update and add stuff requested in the forum. (Neither Cura or Slic3r get close to the quality i'm getting from this software) .

Now that you mention AutoCad and dimensionally correct, well they are not. I have had so many parts that once converted to STL loose their accuracy (specially in circles). now what I don't understand is the polygons count? Inventor makes them perfect, maybe the 2D to 3D feature of AutoCad isn't great? .
Re: OK print but the dimensions are a bit out
March 28, 2015 08:32AM
That's Interesting ggherbaz.

I do have a 'copy' of Solidworks. I'll give it a shot.

ACad does export .stl files but can't import them to check them again. I don't think the software is really optimised for producing printed parts. Its more a 'jack of all trades - master of none'

I've not been printing long. So for a first attempt I am quite happy with the overall tolerance - 0.06mm deviation on a 16mm part. I think there's scope to tighten that up as well with feed rates, better quality hotend/ nozzle etc.

It would be nice to print to size rather than have to put in a 'fiddle factor'.

Thanks

a
Re: OK print but the dimensions are a bit out
March 28, 2015 02:39PM
Converting curved surfaces to polygons is always lossy. Most programs can be configured for how much tradeoff you want between accuracy and polygon count. Not having used native AutoCad I'm not sure if it is one of them. SolidWorks is.

Edited 1 time(s). Last edit at 03/28/2015 02:40PM by IMBoring25.
Re: OK print but the dimensions are a bit out
March 29, 2015 07:49PM
Hi.

I imported the acad .stl into solidworks and the dimensions are correct.

I note that by default the AutoCad cylinder is more 'polygonny' than one produced by solidworks, I believe that is adjustable in settings.

The increased number of vertices produces a smoother cylinder as you'd expect. It seemed slightly smaller though. I only printed 10mm long sections so it was hard to measure without it flexing. I'll try with a thicker wall.
I had similar results with a regular non-spiral slice.

Time to try another slicer program.

I just noticed that Solidworks has a 'Print3D' option that requires a printer driver. Has anyone got anywhere with that with a reprap?


-a
Re: OK print but the dimensions are a bit out
March 30, 2015 02:51PM
I always scale the model to 1.03 in cura if i'm using PLA. Seems to work it most cases.
Re: OK print but the dimensions are a bit out
March 30, 2015 04:47PM
I'll try that.
Bit of a work around. But if it works it works

Thanks
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