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Scaling factor shrinkage compensation under


tombmatt

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Posted · Scaling factor shrinkage compensation under

i was trying to set a percentage for deminsion accuracy found "Scaling factor shrinkage compensation" under Preferences, settings, material, howerver it has a note that states "this setting has beenbeen hidden by the active machine and will not be visible. So i added a different machine since i couldn't erase the only machine i had. the new machine had the same note attached so i deleted cura and reinstalled, with no printer set up on a fresh install i still have the same note so i assume (i know assumptions etc) it is a feature that is not actually programed for? or is it? does anyone have a work around?

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    Posted · Scaling factor shrinkage compensation under

    You can scale the model in Cura.  If shrinkage is 8% then scale the model up 8% and then slice it.

    If you de-select "Uniform Scaling" you can set each axis to a different scale factor.  That could be useful if (for example) you found that a particular infill caused the Z to shrink differently than the X and Y.

    You could also scale the steps/mm of the X, Y, and Z with an M92 line in the beginning of a Gcode file.  Without an M500 to save the changes, they would return to your default values when the printer cycled on and off.  Not all printers allow that though.

    You could scale the model up in the native design software before exporting the STL file and then use the Undo function to negate the change.

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    Posted · Scaling factor shrinkage compensation under
    12 hours ago, tombmatt said:

    i was trying to set a percentage for deminsion accuracy found "Scaling factor shrinkage compensation" under Preferences, settings, material, howerver it has a note that states "this setting has beenbeen hidden by the active machine and will not be visible. So i added a different machine since i couldn't erase the only machine i had. the new machine had the same note attached so i deleted cura and reinstalled, with no printer set up on a fresh install i still have the same note so i assume (i know assumptions etc) it is a feature that is not actually programed for? or is it? does anyone have a work around?

    It's still disabled because it's not done yet.

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    • 1 year later...
    Posted · Scaling factor shrinkage compensation under
    On 11/1/2020 at 11:11 PM, GregValiant said:

    You can scale the model in Cura.  If shrinkage is 8% then scale the model up 8% and then slice it.

    If you de-select "Uniform Scaling" you can set each axis to a different scale factor.  That could be useful if (for example) you found that a particular infill caused the Z to shrink differently than the X and Y.

    You could also scale the steps/mm of the X, Y, and Z with an M92 line in the beginning of a Gcode file.  Without an M500 to save the changes, they would return to your default values when the printer cycled on and off.  Not all printers allow that though.

    You could scale the model up in the native design software before exporting the STL file and then use the Undo function to negate the change.

    Scaling does work well. Print a cube of known size, measure it precisely, scale it by the shrinkage factor you calculated, print, measure. 

    Repeat if the scaled up print is off by unacceptable margin.

     

    Problem is you must do this for every time and for new model placed on the plate.

     

    Why not tie the shrinkage factor to material profile and have Cura compensate automatically?  

    Adding this feature would indicate Cura is not just for printing toys where tolerances do not matter that much.

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    Posted (edited) · Scaling factor shrinkage compensation under

    @GregValiant that is helpful but I have alot of dimensions in Fusion that need the modification and I did try that but that threw me off as to wether the model was the problem or my scaling shrinkage factor was the problem. I am almost at the point of switching materials ( even though I know what's going on) as I am printing with a lower quality nylon. My question is "Does horizontal scaling factor shrinkage compensation make ID holes larger or smaller?" I have tried to use horizontal expansion thinking that was the resolution to horizontal shrinkage though my model was scaled up on the OD of my circular tube but the diameter was scaled down on the ID of the inside of the tube, then I thought "so now I have to add a horizontal expansion of .15 mm AND a horizontal hole expansion of .3 or .45?!?!(to make up for the additional .15mm which wrongfully reduced on my ID) Inside diameter holes NEVER shrink outward (larger) they always shrink inward, even with foamy materials, so, @nallath does this setting (horizontal scaling factor shrinkage compensation) need some additional work, or am I crazy for not seeing another setting which can negate this scaling problem. All in all I need to know what polygons are affected, weather it be by radius or diameter

    Horizontal expansion - I assume its diameter mm because its scaled as a whole on x + y

    Horizontal Hole expansion - I know its radius mm

    Horizontal scaling factor shrinkage compensation - I think its radius but also think it shrinks the ID when you make a + value (not sure if the ID is decreased by the added% or double because of radius/diameter in coding)

    Horizontal scaling x + y - I think it is a size percentage as a whole

    Edited by GoguyT3d
    added details
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    Posted (edited) · Scaling factor shrinkage compensation under

    I think I can address a piece of this.  The above comments are from a year ago and there were no "shrinkage factor" settings in Cura at that point.

    I've designed a few molds and the customer would inform me of the shrink factor since it was based on the material being molded.  I'll use 8% shrinkage as it was an oft-used number.

     

    When the part was released from the mold, everything was 8% smaller.  To compensate in the design of the mold, I would design the part and then scale it up 8% (to create the "hob") before subtracting it from (what would become) the mold cavity.

    FDM is different.  The parts created are "non-homogenous" and so shrinkage is different not just "XY vs Z" but also from one Z height to another dependent on the density of the infill and other factors.  It's possible that the X shrinkage could be different than the Y shrinkage dependent on both the designed internal geometry and/or the printed internal geometry.

     

    I did an experiment a couple of years ago and printed a hole chart.  I found that Hole Horizontal Expansion is not linear.  Small holes suffer severely as the nozzle drags the molten material in towards the centerline (the "Snot Factor").  On large holes (above about 30mm with PLA) there was no significant change of the diameter.  Where a 3mm hole would print to 2.7mm, a 30mm hole would print at 30mm.  Square holes and Hex holes don't suffer from the problem.  A mix of small round holes and holes with straight sides is really tough to compensate for.

    Every model is different and will require trial and error (sometimes lots of errors) to get a "perfect" print.

     

    Then I take that perfect print out of the air-conditioned room and put it in the bright Florida sun whereupon it will expand differently dependent on the factors noted above plus which side is facing the sun.  Everything affects everything.

     

     

     

    Edited by GregValiant
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    Posted (edited) · Scaling factor shrinkage compensation under

    Up until recently I hadn't really put much thought into "same material but different manufacturer" until I tried materials made from 3 different countries. With that said I'm assuming my difficulty in printability is largely related to quality of filament. Yes all which you have said is correct and I have a horizontal hole expansion test of my own which also tests horizontal hole expansion, scale, z accuracy, top surface quality ect which I've noticed the diameter does change via the size but since I mostly print .125 - .5" holes which have tight tolerances in regard to fitment, I do a .75 x .75 x 2" block with 4 holes .125, .25, .375, and .5 , print with zero expansion settings,  calculate the difference in hole from model in Fusion360,average all 4 hole offsets added together, divide by four, convert to metric for cura, and divide by two for radius which usually gives me a value that is very close to all needed holes which complies with my acceptable tolerances. I am currently on a nylon 6-66 from 3dx tech and it is proving to be much easier than the other that I was using.

    Edited by GoguyT3d
    Missed a word
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    Posted · Scaling factor shrinkage compensation under

    @Juzer99 your theory for cura is exactly what I thought "horizontal expansion" did, until I tried to use it for my shrinkage compensation for nylon, considering that it in fact horizontally contracts ID holes 🤔 so you need to double down on your Horizontal hole expansion for it to work together with Horizontal expansion. horizontal scaling factor shrinkage compensation is just the same as modifying the scale, but also not helping the ID holes yet compromising them like H.E. does (yet another 😕)

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