Standard Deviation/Accuracy in Print Quality?


#1

I’m still waiting for my printer to arrive. What deviation are you experiencing on your prints? My first print will have channels in it for copper wire, so I need to make sure the design accounts for the printers deviation in accuracy. Thanks in advance!


Retro Form 1+ Guide
#2

In general, we’ve found dimensions are held to within .010-.020".  Linear dimensions are longer, holes are smaller.  Also, holes are out of round upwards of .010".  This may vary from machine to machine; however, I had to send back my first printer (power issue), and both my first printer and my current one are behaving similarly.

I attached an example of what we’re seeing.  The part on the right is a plastic (Delrin AF) spacer made by CNC machining.  The printed version is on the left.  You can visibly see the difference in hole size and roundness- this picture may exaggerate the differences due to the angle and view of the clear resin, but I can assure you that the difference is real by actual measurement.  I printed this part 6 times with varying resin settings, resolution, print angle, etc. and got similar results each time.


#3

Thanks Jeannine for the output, it seems that’s a “frequent” problem… Maybe all the printers have the same issue. Because it’s a galvo, i understand it’s more difficult to manage than a DLP but at the end we aren’t able to have accurate print.


#4

@Jeannine - are you saying holes are distorted by the same absolute value regardless of their size? eg a  0.1 inch hole and a 2.0 inch hole are both “off-round” by the same 0.01" ?

The reason I (International form backer - waiting) ask is that I saw a post by someone else suggesting the laser spot might not be perfectly round but oval - which would cause that sort of consistent absolute distortion.

I think that would be something Formlabs could fix in the slicing software - or the community could if they documented the format of the file sent to the machine …


#5

@Kevin - I haven’t measured the same absolute value regardless of size wrt out-of-round.  This is more of a general statement based on the parts I’ve been printing- with small dia holes less than 0.5".  In my experience, the out of round condition is consistently present but can vary from .001-.002" to upwards .010".

This is a perfect opportunity for design of experiments.  I may go down that path once I figure out how best to approach it.

The most general statement I can make (based on my experience) is that objects with round/curved features printer “better” than those with flat/linear features.

We are a CNC machine shop and typically work to tolerances of +/- .005".  We were hoping to use the printer for engineering prototypes and throw-away fixtures.  I still need a lot more experience and print time to try to optimize the process, but I’m hoping that future upgrades to the software and resin will get us closer to where we want to be.

Also, I just want to say that I’ve had a very positive experience so far with form labs support.  They’ve been responsive and helpful.  It looks like they’re committed to improving their support group so that’s very encouraging.


#6

Kevin,

I’ve been advocating for an opening of the protocol seens the beginning but that’ not in their plan for the moment.

The deformation of the geometry is a combination of galvo tuning and probably (because it’s only a theory at this moment) laser spot size. Many other factors can explain different non-linearities seen on certain areas (refraction in glass/pdms layers, peeling…).

I’m slowly building an app to deform the geometry to try and correct the result before print (don’t hold your breath on that one), but it’s really not the thing to do, it should be configured at the Preform level…

Cheers


#7

I’ve found my circular bosses and holes to come out somewhat elliptical. I’ve been printing at a 30 degree angle to fit the part in the build envelope. I’ll try to document this on the next print. I’ve been too busy dremelling bosses to stop and take pictures so far.

I would definitely add tilt angle and orientation relative to peel direction to the list of factors in a design of experiments.

It would be slick (and much appreciated) if Formlabs would work out a calibration feature in the software to correct distortion in critical geometry. For now, I’m loosening tolerances where I can.