Accuracy

[ex-egll]

Well, now the fun of building and setting up is over, and son (30 years old) has finished printing dinosaurs I decided to do some more accurate projects.


Prints of simple objects e.g rectangles, cubes etc. came out fairly accurate:


on the x axis a 20mm side printed at 20.39mm = +.69%
on the y axis a 2.075mm side printed at 2.09mm = +.72%
on the z axis a 1.35mm side printed at 1.36mm = +.74%


I am not sure whether to be happy with the above accuracy, or whether to play around with calibration to see if I can improve it.


Printing circular objects is a different matter e.g. a ring:
Outside diameter 40mm prints at 39.7mm = -.75%
Inside diameter 20mm prints at 10.36mm = - 3.13%


Given the linear objects printed slightly larger in all axis, I was surprised to see that circular ones printed smaller. This was consistent.


What sort of accuracy do others have?
Any ideas on the difference between linear and circular accuracy?


I am using the 13v 12", Solidworks to design the parts and Cura for the slicing.


Thanks

[dunginhawk]

that accuracy is not bad. what layer height did you print those at?

from my experience SO FAR with my 12" .1 is what you need to go with for accurate prints. .2 seems to be not nearly as good. as expected.
.2 on my FFCP is quite good, .1 on my FFCP is UNREAL good.

Also remember that given smoosh factor on your first layer, the bottom piece will always be off in the horizontal direction, meaning 20mm cube may show up as 22mm cube, or something, but the rest will be fine.. thats dependent on a few variables.

im still trying to get my quality back after i changed my x carriage etc to work with cloughs cooler, abl and layer fan. I need to figure out why my quality has dipped since i put that in.

[printbus]

Compare your 20mm cube results to another size before jumping to calibration conclusions. Unfortunately, too many people adjust steps per mm to get the 20mm cube printing exactly right, only mess up the scaling for anything other than that 20mm cube.

A lot of factors come into play in managing extrusion width, and this has an effect on dimensional accuracy. Not every exact dimension will be achievable due to limitations of the printing process. Like dunginhawk said, a smaller layer height helps because it gives the slicer/printer a finer resolution for at least that variable. I may not scrutinize as much as some, but if my results come out within a nozzle width of being right, I don't fret over it.

The accuracy of circles are notoriously troublesome. Holes almost always come out undersized. Determining whether to print external perimeters first vs. last makes a difference. In openSCAD, guru nophead came up with a polyhole method that improves on the accuracy issue by forming small diameter cylinders/holes from a polygon with varying number of sides. In my openSCAD designs, that leads to holes for screws and such that are far more accurate than just using a simple cylindrical hole.

Although they can likely all be tuned to identical results, between slic3r, Cura Engine, and Simplify3D, I have found Simplify3D to be more "accurate" in controlling extrusion overall.

[dunginhawk]

i use simplify 3d as well and I love it... Ill never use another slicer (of course unless something comes out that trumps it). its easy, the supports are great. its a perfect slicer in almost all cases.
I need to start tuning again.. ive not 3d printed anything in weeks... my interest is waning i need to print a full size storm trooper mask for a customer that is a SW nerd.. so i need to dial it in.

[ex-egll]

Thanks for the responses. The figures I quoted in the original post were representative of ones I got from a number of different sized prints.

I started using S3d, but found I was not getting as good results as I did with Cura, but now that I have a week or so of printing under my belt I have gone back to it and realised that the original problem was almost certainly operator incompetence! Glad to hear circles are a problem for others as well (not glad as in pleased, but glad it's not just me. The good news is, the inaccuracies in the circles are fairly consistent so I just take them into account when I draw the solidworks part. Not the ultimate solution, but it works, and after all it's only a hobby!