Video: How to determine exposure settings using a working curve


#1

To help you figure out exposure settings for new resins, we made a video and Instructable that demonstrates how to generate a working curve from multiple exposure settings on a single slide.

A “working curve” describes the thickness to which a resin cures as a function of the light “dose” for a given light source. While this may sound unexciting, understanding this concept is key to understanding SLA and DLP 3D printing. With the working curve, one can quickly generate printing settings without a lot of testing. It also allows one to quantitatively compare the curing properties of one resin versus another.

Read the full Instructable


UV Blocker
Alternative clear resin
#2

I might be missing something… Once we have filled in the spreadsheet with measured values, how do we convert this data into a useful exposure time?

All I see is dose per thickness - which I am sure will correspond to the exposure time in the print settings, but why not finish the calculation for us?


#3

The video tells you how to do it at 2:44 – divide dosage by projector irradiance to get the absolute minimum exposure time, then multiply by 120-200% to get a usable exposure time.


#4

In the spreadsheet, what do the “Model ha” and “model t” columns represent?


#5

Those three columns on the right (Dose, model ha, and model t) represent the working curve model you’re using, which is what generates the line on the graph. Model ha and model t are the penetration depth and thickness that can be expected given the value in the Dose column.

Your questions are making me think that we could make this spreadsheet a little more user-friendly. It was made by materials scientists who live and breathe this stuff, so please keep up the feedback, and I’ll see if I can make some adaptations to make it more intuitive.


#6

I think I’m working it out but agree it could be a lot more user-friendly.

Ultimately, we would put in the measured values and all we see in return is the recommended exposure time for a given thickness. I know it’s a bit more complex now - as it seems we have to tweak Dp0, dDp/dE, and Ecrit Test values to try to match the projected curve with the data points.

I’ve just completed one for Fun To Do Snow White, but found that I also had to play with the Dose starting value and increment (column Q). The FTD resin cured so fast the results at first appear to be a verticle line. By playing with all these values I was able to get a decent match. Then I used my brain when selecting an appropriate exposure setting and it worked great. (.6sec for 100um slice for a first pass).


#7

Is there a way we can get a link for the spreadsheet?


#8

It’s also in the full instructable mentioned in the OP.

FX543A2IUSLOOON.xlsx (24.5 KB)


#9

Thanks a lot!


#10

Since you guys have been ‘living and breathing’ this for a while longer than the rest of us, has anyone already captured the working curves for a bunch of different resins? Would certainly save me the time!


#11

Unfortunately most of our working curves have been for resins that aren’t compatible with Ember. But which resins are you interested in? I could look into making some kind of database where everyone can contribute their results.


#12

I was looking for any / all resins. I am slowly working on and FEP solution, and I know others are as well. Having all these resins available (or at least the knowledge of how they cure) would be helpful in deciding which to try next.

Example from my experience:
Fun to Do - snow white - NOT compatible with PDMS. However, has a very fast reaction time with a shallow cure depth. The result is a pretty flat curve. This would indicate a faster print with very good detail.
CPS SW-472 - compatible with PDMS. Moderate cure time, moderate cure depth (has a balanced curve). High viscosity, very ‘sticky’. Should cure similar to PR57-K, but will need extra time between layers due to its viscosity. Should be good for steeper overhang angles, but not sure by how much. Needs lots of post curing.
MakerJuice G+ black - NOT compatible with PDMS. Faster cure time, depth of cure is also deep (Has a pretty steep curve), and it has very low viscosity. This should print thick slices well, but details may suffer.

EDIT - MakerJuice G+ Black is NOT PDMS compatible.


#13

I would be interested in knowing the working curves for Formlabs clear, tough, flexible, and durable resins. I may contribute to this database myself too, but it would definitely save me time if someone has already done it or is planning to do it.


#14

The Instructable tell us to place a layer of resin “several mm thick”. I am worried about consistency here. Shouldn’t we use a very specific amount of resin every time? Otherwise, if we use in one test say 5 mm and in another one 3 mm, wouldn’t that have a huge impact in the final thickness of the cured resin that we are measuring?


#15

We haven’t found that to be hugely important, because the thicknesses of the cured panels only matters relative to the other panels in a given test. It’s more important to make sure you don’t use too little resin.


#16

Got it!

One more thing… In step 5 of the Instructable we are told that the top left corner has only received 0.6 mJ/cm2 while in the Excel spreadsheet it says 6.00 mJ/cm2. I think the value in the Instructable is wrong and it should say 6 instead of 0.6, right?


#17

I also noticed that in the Instrucatble, they tell us that the top left corner is cell #1 and the bottom left is #32. Wouldn’t the bottom right be #32? That would be the more intuitive numbering in my opinion, and it is also the one that matches the data in the provided spreadsheet and in my own measurements best. I attach a picture of how I am thinking the numbering in the Excel spreadsheet is happening. Could someone please confirm that?


#18

No - they have randomized the exposure across the field in an effort to minimize the effects due to projector light intensity variations. You measure in-line, but the excel sheet maps it corrected.


#19

But you are correct about the 6 mJ/cm2 – 20mw/cm2 * 0.32s = 6 mJ/cm2, so the Instructable is wrong.


#20

are these values resin dependent or should these remain fixed for each printer?

I find that I am adjusting these for each resin… not sure if that’s what I’m supposed to do or not.