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Prints just a bit smaller than what they should be  

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SteveSzu
(@steveszu)
Active Member
Prints just a bit smaller than what they should be
I have two Prusa i3 printers, a MK2 purchased in November 2016 and a MK2S purchased in June 2018.  I use them exclusively for printing models of teeth which I then use to make clear retainers.  
 
A problem just started with the older printer, the models are just a little bit smaller than what they should be.  This, of course, causes a problem with the fit in the patient's mouth.
I changed the X and Y belts and replaced the nozzle.  After recalibration everything looks good but the problem still exists.  
 
Any ideas for a fix would be greatly appreciated!
 
Images show retainer fit on incorrectly sized model vs fit on plaster model of actual mouth.
 
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Posted : 22/05/2021 1:43 pm
cwbullet
(@cwbullet)
Illustrious Member
RE: Prints just a bit smaller than what they should be

It could be normal shrinkage depending on the filament used.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 22/05/2021 2:14 pm
SteveSzu
(@steveszu)
Active Member
Topic starter answered:
RE: Prints just a bit smaller than what they should be

@cwbullet

Thanks, but I don't think that's the problem.  Been using the same Protopasta HTPLA for years, beautiful prints, no problems.  And no problem with the same filament on the 2nd printer.

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Posted : 22/05/2021 2:51 pm
Diem
 Diem
(@diem)
Prominent Member
RE: Prints just a bit smaller than what they should be

What is the filament?

Is this new filament or old stock?

Is the printer in a draught? or an especially cold workshop?

By how much is it too small?  Is it small in all dimensions? Is there an error in the degree of curvature (XY plane) of the part?

And roughly how many hours printing has the machine done?

Cheerio,

Posted : 22/05/2021 6:10 pm
Diem
 Diem
(@diem)
Prominent Member
RE: Prints just a bit smaller than what they should be
Posted by: @steveszu

@cwbullet

Thanks, but I don't think that's the problem.  Been using the same Protopasta HTPLA for years, beautiful prints, no problems.  And no problem with the same filament on the 2nd printer.

Is that the same spool on both printers or two different spools of the same brand?

Cheerio,

Posted : 22/05/2021 6:12 pm
cwbullet
(@cwbullet)
Illustrious Member
RE: Prints just a bit smaller than what they should be

@diem

Same brand, different colors of Proto-pasta on two different printers running now.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 22/05/2021 6:35 pm
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(@)
Illustrious Member
RE: Prints just a bit smaller than what they should be

What does a calibration cube show?

Posted : 22/05/2021 6:35 pm
SteveSzu
(@steveszu)
Active Member
Topic starter answered:
RE: Prints just a bit smaller than what they should be

@diem

Everything has been a constant for years.  Just now the older machine has started with these prints that are just a bit too small.  Can't really tell with the naked eye and measuring with calipers don't show much difference at all.  I have been doing this for years now, no problems.  Many, many hours on both machines.

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Posted : 22/05/2021 8:11 pm
Diem
 Diem
(@diem)
Prominent Member
RE: Prints just a bit smaller than what they should be

@steveszu

OK, two thoughts:

I have been doing this for years now, no problems. Many, many hours on both machines.

Presumably wear in the drive pulleys, bearings and rods will eventually have an effect, I don't know how long Prusa expect to retain accuracy.  Prusa support will know which parts are most susceptible.

Possible workaround.

Print a calibration piece, a square much bigger than your regular prints (X-Y  200mm at least, Z is probably OK) and measure it.  This should be enough to calculate a calibration value in each axis - then apply the calibration before printing.

Cheerio,

Posted : 23/05/2021 11:12 am
SteveSzu
(@steveszu)
Active Member
Topic starter answered:
RE: Prints just a bit smaller than what they should be

@diem

Thanks.  Did a small cube, I think it's 20mm, looks pretty good. 

I was also thinking the same thing, possibly worn bearings, etc.

I attached photo of the cube.

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Posted : 23/05/2021 11:24 am
Diem
 Diem
(@diem)
Prominent Member
RE: Prints just a bit smaller than what they should be

@steveszu

That cube says there's nothing much to worry about for run of the mill printing.

It would be a pity to retire a basically sound machine and replace it with something new you'd have to attune to.

I would try the calibration route first.

Cheerio,

Posted : 23/05/2021 11:51 am
cwbullet
(@cwbullet)
Illustrious Member
RE: Prints just a bit smaller than what they should be

@steveszu

That cube is really nice.  Looks like you have it dialed in.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 23/05/2021 1:42 pm
vipu
 vipu
(@vipu)
Active Member
RE: same problem

i have same problem now, whatever filament, over 100mm object is 1mm smaller (like something is 95%, not 100%). i think problem is prusaslicer (i use mac version) but i dont understand what i must change. 

This post was modified 2 days ago by vipu
Posted : 31/07/2021 10:35 am
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