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Mike01Hu
(@mike01hu)
Active Member
Mk3 Printed model accuracy

Since building my Mk3 I have been using it for printing fun models to get used to its functions and tweaking the available calibrations. Last week I started to use it for its proper use, for me, to produce mechanical parts and was surprised to find larger dimensional errors than I experience with my BigBox and Vellemann printers. For these printers I produced a model to check a range of common shapes of cut-outs I use, so that I could build in adjustment to the CAD model. Before adjustment the outside errors are +0.05mm per 100mm, so no adjustment was made, but all internal diameters are around -0.3mm for any diameter, allowing for an easy adjustment in the CAD model; this worked for models sliced in Slic3R and Simplify3D. In all cases, overall height is extremely accurate allowing for the variance in first layer to main layer height.

The Mk3 produces errors of around -0.4mm per 100mm in all dimensions, including internal dimensions, and is +0.2mm in height for any height despite first layer calibration being good across the bed at 0.2mm. Squareness is excellent at within 0.02mm across the diagonal of the 100mm square. Using Angus from Makers-Muse's clearance check model, it easily achieves the 0.15mm clearance with PLA.

In general, the errors are consistent in both X and Y, so my suspicion is that the X/Y problem is a firmware steps/mm issue, although I can't account for the height error but it may also be a Slic3r PE issue (or user error 😯 ), so I would appreciate some views here.

I have included the STL here ( https://1drv.ms/f/s!Ai92-5dj3h20iL5OyociAF0TrXcH8Q ) for anyone who wants to check. It was printed with 2 perimeters, 3 top and bottom layers and 15% rectilinear infill, using the Prusa default for PET in Slic3r PE. All dimension are obvious when checking with the small holes 1mm, 2mm, 3mm and 5mm. If you can see the 1mm hole let me know how!!! 😛

Just to say, I am not a new user for 3D printing and have been using the tech personally for over four years for engineering projects and involved with it for several years before . . . but I admit to being an "old fart" at 76. 😎

Posted : 22/10/2018 11:00 pm
atair
(@atair)
New Member
Re: Mk3 Printed model accuracy

I print mainly mechanical / functional parts and just started out with my mk3. Before i used a makerbot for many years. Also i never used slicer, only Simplify3d.

First order of business was to get the Simplify3d profile up to speed for the mk3. There are a few in the forum, but none of them worked out of the box.
I think the main source of errors are the extrusion multipliers in Simplify3d - had to go down to 0.96 at 0.45 width to get good results. Still in the process of tweaking and testing, but i am getting close to press-fit parts. Not sure how Petg 'ages' - first time using it, but i know from PLA that it can shrink over time and press-fitted parts become loose.

One important Value that has to placed manually in the Simplify3d Script section is the 'K900' value:
https://help.prusa3d.com/l/en/article/t5w9VsdVai-linear-advanced
It can make quite a difference for fitting, as corners become exaggerated if not set properly.

Bottom line - its all about tweaking the Simplify3d profile.

Also i never try go get the dimensions 1:1 - its about finding a good offset value that corresponds with good print quality. For now i have to offset everything 0.1mm x/y in my 3d model and get good results in prints.

Posted : 26/10/2018 11:37 am
rob.l6
(@rob-l6)
Honorable Member
Re: Mk3 Printed model accuracy

Not sure what you were expecting from a sub-1K printer, but have to say that out of all the "issues" with mk2/3 family mechanical accuracy does not appear to be on our list. Of course it will depend on how accurate your prints need to be, but I think it does a pretty sterling job in this regard. Precision has also impressed us.

...
Posted : 26/10/2018 12:24 pm
Phil
 Phil
(@phil-4)
Trusted Member
Re: Mk3 Printed model accuracy

Have you printed a standard 20 mm XYZ calibration cube? What are your actual measurements? If I follow your math, you say +0.2 mm / mm in height, which would mean your 20 mm cube would be 24mm?? If true, that is WAY off. I just measured my latest one and my measurements are

z= 20.04
y = 20.01
x = 20.00

This is what I think is probably fine for this level of printer. If you are getting much worse than +- 0.05 / 20 mm you should check into belt tightness or perhaps over/under extrusion settings.

Posted : 26/10/2018 3:20 pm
Texy
 Texy
(@texy)
Reputable Member
Re: Mk3 Printed model accuracy


Have you printed a standard 20 mm XYZ calibration cube? What are your actual measurements? If I follow your math, you say +0.2 mm / mm in height, which would mean your 20 mm cube would be 24mm?? If true, that is WAY off. I just measured my latest one and my measurements are

z= 20.04
y = 20.01
x = 20.00

This is what I think is probably fine for this level of printer. If you are getting much worse than +- 0.05 / 20 mm you should check into belt tightness or perhaps over/under extrusion settings.

OP said " -0.4mm per 100mm in all dimensions", that's not 24mm for a 20mm cube 😉

Texy

Posted : 29/10/2018 4:26 pm
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