PLA shrink factor

[t-squareddesign 2]

Hi, 

I’m printing a huge model for a client in PLA. It will imbed metal parts and components that must fit accurately with some tolerancing. 
 

My first sample test part I printed at 0.1 mm resolution and that wasn’t accurate enough to fit the small metal parts. But it worked well at 0.06mm. 
 

However to print the full complete product at 0.06 mm will take 6 days!! That’s too long, and there’s risk for an error in the print. 
 

Only alternative is to print at a lower resolution and expand these features. But by how much? It must fit metal discs that are about 0.08” And a metal bearing spinner at about 0.27” tall by 0.86” diameter. If i am to print this at a lower resolution, I’ll need to widen these dimensions a bit with more tolerance. But how much?

Edited October 19, 2020 by t-squareddesign

[geert_2 473]

In my experience, there are a lot of things that influence accuracy: temperature, speed, flowrate, material, even color (some colors melt better than others, not sure why, maybe due to fillers?), etc. Further there are things like layer-lines (curved edges), blobs, ringing, thickening of corners due to nozzle slowing down,... All these have an effect.

 

The only way to know, is test. Make your typical features in real size in a small test model, and try that. For me, I usually take 0.1 to 0.5mm extra, depending on how tight a fit I want, and whether it are inner openings or outer sides.

 

Be aware that PLA will deform even under moderate warmth. You can not leave it in your car, even not in mild sunny weather in spring or autumn (internal stress relaxation). And it will deform quite fast under continuous load (creep deformation). Don't ask how I know.  :-)  This might not be suitable for every technical application.

 

If the application allows it, I usually go for plenty of tolerance. Otherwise I calculate some post-processing in from the beginning: some filing, sanding, cutting,...