Notifications
Clear all

Print calibration size  

  RSS
Mitchimal
(@mitchimal)
Eminent Member
Print calibration size

I just tried to print something with an internal thread and found that the prints are actually coming out at a smaller scale than they should be...

I am exporting a body from Fusion360 in 3mf and everything looks right...

The strange thing is the first few layers actually are the right size- this may be a fluke but then after than everything is smaller than it should be... Any ideas?

Cheers

Mitch

Best Answer by Diem:

I don't use Fusion but the principle is the same.

Design to the theoretical ideal, print a small test part and measure it, calculate a calibration value (you will quickly learn the figures for your favoured sizes), if parts must move against each other they will also need some tolerance.   Return to your design and add, or subtract, the calibration and tolerance. The slicer, any slicer, cannot guess what you are trying to do so it faithfully follows your source file.

If you are printing both external and internal parts then it's usual to apply half the tolerance to each but each part's calibration may be different...

If one part is sourced elsewhere then your part must apply the whole tolerance to the measured value.

This is especially important for print-in-place mechanisms as your tolerance must also prevent the parts printing seized although in this case preventing seizure usually takes enough space that your other requirements are met as a side effect.

Cheerio,

Posted : 12/12/2021 12:40 pm
Diem
 Diem
(@diem)
Famed Member

Any closed curve is calculated by it's centreline but as it is extruded the filament is squished out in all directions.  On the inside of a curve there is less room than on the outside so the squish effect is greater and as the curve continues there is also drag towards the chord of a curve.

So calibrate a small test part and incorporate the calculated tolerance in your initial design.

It sounds like your first layer may have elephant's foot compensation at about the tolerance value you require.

Cheerio,

Posted : 12/12/2021 1:41 pm
Mitchimal
(@mitchimal)
Eminent Member
Topic starter answered:
RE: Print calibration size

Hi sorry, little confused are you talking about an FDM printer? This is the SL1s resin printer...

Posted : 13/12/2021 12:22 am
Mitchimal
(@mitchimal)
Eminent Member
Topic starter answered:
RE: Print calibration size

Hi sorry, little confused are you talking about an FDM printer? This is the SL1s resin printer...

Posted : 13/12/2021 12:22 am
Diem
 Diem
(@diem)
Famed Member

Oops, yes, somehow this popped up and I was talking FDM but resin has similar issues.  You are approximating to pixel width on any curve and with a concave you still have to calibrate outwards by approx one pixel diameter plus whatever tolerance you require for the movement of any inner part/screw/shaft.

Cheerio,

Posted : 13/12/2021 1:36 am
Mitchimal
(@mitchimal)
Eminent Member
Topic starter answered:
RE: Print calibration size

Is it something I should be changing in Fusion? The mesh has the right dimensions in Prusa slicer so I don't know what to try?

Posted : 13/12/2021 10:46 am
Diem
 Diem
(@diem)
Famed Member

I don't use Fusion but the principle is the same.

Design to the theoretical ideal, print a small test part and measure it, calculate a calibration value (you will quickly learn the figures for your favoured sizes), if parts must move against each other they will also need some tolerance.   Return to your design and add, or subtract, the calibration and tolerance. The slicer, any slicer, cannot guess what you are trying to do so it faithfully follows your source file.

If you are printing both external and internal parts then it's usual to apply half the tolerance to each but each part's calibration may be different...

If one part is sourced elsewhere then your part must apply the whole tolerance to the measured value.

This is especially important for print-in-place mechanisms as your tolerance must also prevent the parts printing seized although in this case preventing seizure usually takes enough space that your other requirements are met as a side effect.

Cheerio,

Posted : 13/12/2021 12:09 pm
Mitchimal
(@mitchimal)
Eminent Member
Topic starter answered:
RE: Print calibration size

Ok cool thanks, Threads in fusion are based off metric or imperial without the ability to adjust the size unless I am missing something. I noticed the whole part is smaller so I will just test different scaled variations and see what's good.

Thanks for the help.

Mitch

Posted : 13/12/2021 12:40 pm
MikeH
(@mikeh-2)
Trusted Member
RE: Print calibration size

 

Posted by: @mitchimal

Ok cool thanks, Threads in fusion are based off metric or imperial without the ability to adjust the size unless I am missing something. I noticed the whole part is smaller so I will just test different scaled variations and see what's good.

Thanks for the help.

Mitch

 

Posted : 13/12/2021 9:09 pm
Mitchimal
(@mitchimal)
Eminent Member
Topic starter answered:
RE: Print calibration size

Did you write something?

Posted : 13/12/2021 9:46 pm
MikeH
(@mikeh-2)
Trusted Member
RE: Print calibration size

Meant too, but the forum software (or me) screwed up somewhere and my actual reply got lost leaving just the quote.

Essentially I was saying that I general use fasteners where male threads are needed in 3D prints and print holes the correct size for taps where female threads are needed, especially for sizes 1/4" (6mm) or smaller.

Posted : 14/12/2021 9:35 pm
Mitchimal
(@mitchimal)
Eminent Member
Topic starter answered:
RE: Print calibration size

Yeah I think you're right, the threads just aren't scaled accurately post print so tapping would be better. I'm doing M3 and M4 so too small really to be strong. Installing inserts is doable just more parts to worry about.

Mitch

Posted : 15/12/2021 1:13 am
MikeH
(@mikeh-2)
Trusted Member
RE: Print calibration size

On FDM prints where I need threaded holes I usually drill through the hole with a properly sized bit for the thread form before tapping and use spiral point (gun) taps for through holes and spiral flute taps for blind holes.

Posted : 15/12/2021 9:41 pm
Mitchimal
(@mitchimal)
Eminent Member
Topic starter answered:
RE: Print calibration size

I'm still noticing a lip on the bottom of the print attached to the bed, it's larger than the other layers and has to be sanded off, looks like it's on the longer exposure time layers, is this normal? Does baking longer make the resin expand more or something? It's nearly 1mm thick around the part.

Posted : 16/12/2021 12:22 am
Share: