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Size of model vs size of printed item.  

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Owt From Nowt
 Owt From Nowt
(@owt-from-nowt)
Active Member
Size of model vs size of printed item.

HI,

I'm very much a noob with this 3d printing thing.

This item a=13mm and b=14.8 in the physical printed item, but in sketch up these same lengths are different, a=13.16 and b=14.92. I'm using sketch up to draw the thing and slic3r to slice, and a Mk3 to print it with the standard setup / 0.4mm nozzle.

Is this expected or (more likely) am I doing something wrong?

Thanks for your help.

Posted : 03/10/2018 2:10 pm
Neal
 Neal
(@neal)
Reputable Member
Re: Size of model vs size of printed item.

Hope I'm understanding so here goes:

Due to the nature of FDM printing you have to allow for the contraction and expansion of the filament being melted and hardened. This is affected by temps of the machine and the environment. How well your cooling fan works or doesn't . Most usually print a calibration cube and measure it with a set of calipers. From there they adjust their settings.

Neal

Posted : 03/10/2018 2:36 pm
Pathogen
 Pathogen
(@pathogen)
Estimable Member
Re: Size of model vs size of printed item.

I happen to have recently printed a part provided for a kit, to ensure the printer is accurate. The part is expected to be 106mm:

Posted : 03/10/2018 6:45 pm
rob.l6
 rob.l6
(@rob-l6)
Honorable Member
Re: Size of model vs size of printed item.

Some variance is expected. You will really notice it when printing small things like standoffs for screws etc.

Posted : 04/10/2018 4:56 am
bobstro
 bobstro
(@bobstro)
Illustrious Member
Re: Size of model vs size of printed item.


[...] Is this expected or (more likely) am I doing something wrong?
If you haven't yet fully calibrated your printer, I wouldn't worry about it too much just yet. Perhaps the most important it to ensure the extruder actually pushes the amount of filament the gcode is telling it to -- the extrusion rate. There are many good guides available on this process.

  • The procedure on Matt's Hub is highly recommended, but is not Prusa-specific. Prusa-specific discussion can be found on these forum pages. That process describes how to ensure your extruder pushes as much filament as it's told to regardless of software settings.

  • Prusa has a quick-and-easy process that is based on tweaking the extrusion multiplier in your slicer.
    • That approach requires tweaking in every software setting, but might be more flexible if you use filaments that vary considerably.

    You can try either approach to see if it affects your print accuracy.

    My notes and disclaimers on 3D printing

    and miscellaneous other tech projects
    He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan

    Posted : 04/10/2018 5:08 am
    Owt From Nowt
     Owt From Nowt
    (@owt-from-nowt)
    Active Member
    Topic starter answered:
    Re: Size of model vs size of printed item.

    Thanks everyone ... I'm relieved its not me doing something wrong. 🙂

    Posted : 04/10/2018 10:58 am
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