ABS size adjustments
Let's assume i need sub-millimeter precision ABS print. ABS has quite high linear temperature expansion coefficient (78-110 e-6/K, according to my sources). My math says that i need to scale print up to 102.25% to get dimensions I want in room temperature.
But 3D printing is quite complex process, there are lot more factors in it. My calipers say that printed object should be resized by 101.0% XY and 100% Z. This is based on one quite small print (44mm), so probably wildly inaccurate.
Then it hit me - I can't be the first one to try to get size-exact ABS print. So, what are your experiences? How do you scale your ABS print to fit?
Re: ABS size adjustments
Unfortunately, it's even more complicated than you suggest.
The initial layers adhere to the bed and shrink less, causing what is know as "elephant's foot".
I don't know too much about this, so over to you for further investigation...
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: ABS size adjustments
Unfortunately, it's even more complicated than you suggest.
The initial layers adhere to the bed and shrink less, causing what is know as "elephant's foot".
Agreed - I have also experienced it. But I can't be a first one who needs precise ABS prints. I figured it's prudent to first gather other user experiences prior wild experimentation.
Re: ABS size adjustments
Yes, and it's true you are not the first to notice this.
Jonathan (whe develops KISS and prints exclusively in ABS) is working on something that will both counter and correct this problem.
You just need to be able to use KISS and wait for the release which will contain the solution.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: ABS size adjustments
I print excusively in ABS. Depending on the colour I use and the height of the print, I scale between 101 and 102% for the same brand of filament. Or better, I scale it directly in my CAD program.
What you are saying about kiss is very interesting for me PJR. Do you have a date for this new release ? I actually use slic3r or kiss depending on the print.
My youtube channel about the Prusa I3 MK2 https://www.youtube.com/channel/UCz-zQZcKcvEDdd9C9hOKYWg
Re: ABS size adjustments
What you are saying about kiss is very interesting for me PJR. Do you have a date for this new release ? I actually use slic3r or kiss depending on the print.
Cyrille The new KISS beta is due in a couple of days, but that will include only XY and Z shrink percentage factors; the full compensation will not be available for a while.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: ABS size adjustments
Hi guys!
I spent awhile dialing in my workflow to get good precision with ABS. I'm on using a Taz 4 and am using Prusa Slic3r 1.36.1. Nozzle is 0.34 mm and layer height is 0.28mm.
I ran into this problem in a big way when trying to print ABS keycaps for cherry keys. I found lots of information about how to tweak things here and there and to use magic to dial things in, but that didn't satisfy my brain at all :-).
Using the process below, I was able to print out a full set of keys repeatedly that all fit nicely. I don't recall the accuracy, but I _think_ it's somewhere around 0.1mm (+/- 0.05mm for the keycaps). The parts are also really strong. I use a
The downside is print speed, but I'm ok with that (personal hobby use) in order to get good parts. I generally use a "relatively" large larger thickness (0.28) to speed things up (a little) and to make sure my layers are good and strong. I think I used thin layers for the keycaps. Anyway, I _don't_ think those details matter in terms of the details below.
Below is (roughly) what I did:
* Calibrated the printer using calipers and a good ruler using large distance differentials in the print volume. I figured stainless steel would change size much less than ABS, so I didn't base this calibration on plastic.
* Calculated the approximate size compensation I needed for ABS at the print temperature It was awhile ago, but I'm pretty sure I looked up some coefficient of thermal expansion values and calculated compensation based on the temperature differential between printing and room temperature. I may have also simply used a caliper. Anyway, I apply a 100.55% compensation to each print and that seems to work well.
* By far, the biggest improvement I got was changing my way of thinking about printing. I got away from focusing on speed, and focused on filament flow rate! I eventually realized that a lot of problems I was having was due to die-swelling effects at different flow rates (and transitions between flow rates)! Perhaps there is some die-swelling modelling built-in to some of the slicers, I'm not sure. Anyhoo, I decided to "get rid" of the effect as much as possible.
I have a 0.34mm nozzle and I calculated/figured out that a maximum volumetric flow rate of 5mm^3/sec would mean die-swelling effects were made negligible (for me at least). That also means that print speed is almost always limited by the max volumetric flow rate. The settings appear to be in both in filament settings / advanced AND print settings /speed. Not sure why, but I have them both set to 5.
* I set my max print speed to 150 (bridges and gaps are 20, travel is 50, and first layer is 15). I think travel is the only one that is impacted. I think the rest are limited by max volumetric print rate. My minimum cooling print speed is 20.
That's all folks!
Edit: For 1st layer squishing, there is also now elephant foot compensation in Prusa Slic3r. Loot at print settings/advanced. Also, I wonder if a raft would help with first layer dimensional issue.