How to Tune Ember's Print Settings for New Resins

Do you have a new resin your want to try using in the Ember printer, or is a particular print giving you problems? In either case there is a good chance that changing the default printing parameters will allow you to get better results. Currently there are more than user adjustable 30 settings. Changes to these parameters can lead to better resolution, reduced jamming errors, or significantly faster prints. This Instructable will attempt to explain what these parameters do and why one would want to change them. It finishes with examples of developing parameters to print with MadeSolid Black,DWS DC500, and a high speed printing resin (200 mm/hr!). Due to Embers unique sliding mechanism we are still learning what works best, so some advice may change over time.

Updated on 7/23/2015 to include information on new parameters and better advice on choosing the overlift.

Step 1: How to Change the Settings

There are several options for changing the settings:

1) SSH into the printer and change the settings on the fly.

You can connect to the printer via wifi, USB, or a local network and edit (and update) the settings while the printer is running. This is very useful for testing new changes.

2) Unpack the .tar.gz file using from PrintStudio and edit the "printersettings" file.

The print file generated by Print Studio for Ember is just a compressed file that can be extracted with 7zip or another program. This file consists of a bunch of 1280X x 800 .png files and a "printsettings" file. This file can be edited with any text editor (like Note Pad). This is useful for creating test files.

3) Create a Custom Print Profile in Print Studio.

One can create a custom print profile in PrintStudio by editign any of the "Advanced Features". A .json file can then be exported to easily share the settings with other users. This .json file can also be opened in a text editor or browser and directly edited as well.

Step 2: Layer Thickness

Why it is important ?

The layer thickness is one of the most important parameters. 3D printing resins typically incorporate light blocking components to keep the printer from curing material above the layer currently printing. Consequently, when a resin designed to work for thin layers is used to print thicker layers, the light cannot penetrate far enough into the resin to adhere to the previous layer. While Autodesk Standard Clear (PR48) is designed for 25 micron thick layers, 100 micron layers can be printed using a longer exposure time. Thicker layers require a new resin.

Why change it ?

Changing the layer thickness is the easiest way to increase printing speed. Doubling the layer thickness cuts the printing time in half. Going to 250 microns layers (10X the default speed) the whole build volume can be printed in about an hour! The two down sides are that the prints look alot rougher, and at the moment you need to make your own resin. The commercial resins with the least amount of UV blocker that I am currently aware of are Made Solid Fire Cast and Made Solid Vortex.

Step 3: Greyscale and Anti-alizing

What is it ?

The greyscale setting controls whether the image sent to the projector is a uniform intensity (right slice image) or whether it is darker in the middle (left). Prints with a large cross section tend to cause the printer to jam if exposed for too long, while those with tiny cross sections tend to require more light to fully form. This means that optimally different features in the same model require different doses of light. To get around this problem the slicer varies the light intensity across the print. The edge pixels get full power, those in the middle get about 10% less light, and it varies approximately linearly in between.

Why turn it off ?

If your prints are entirely smaller features (~ less than 1 mm) turning off the greyscale option will allow a shorter exposure time, and a faster printing speed. However, for most prints you probably want it enabled. Note, if you are trying to measure the light intensity of the printer, you definitely want to turn this feature off.

NOTE: I would currently recommend not using greyscale, we have only seen benefits from in some specific cases.

Really advanced settings

The greyscale algorithm can be altered by using another slicer. In this slicer the radius is the number of pixels the change occurs over, the Outputmin is the fraction of the max light intensity at the edges, and the Outputmin is the fraction of the light intensity in the bulk. The default values are based on experimental results that gave the best results for high aspect ratio positive features.

As this is a deprecated slicer, after the file has been sliced using this file the tarball needs to be unpacked and the images from it combined with the settings file from the current slicer. This process is described in another instructable.

Anti-aliasing

coming soon

Step 4: Types of Layers

Ember currently breaks the slices into three types: the 1st layer, burn in layers, and model layers. There is only one 1st layer, but the remaining layers can be split between the burn in and model layers (there has to be at least one of each).

Why use two different types of layers?

In the above prints the bases have large cross sectional areas, while the rest of the prints are more sparse. One approach to print these geometries would be to use the burn in layers for the base, and the model layers for the rest. By decreasing the exposure time, reduce the rotation speed, and increasing the overlift in burn in layers jamming is less likely, and by increasing the exposure time in the model layers finer features while typically be produced.

Can you change the settings for each individual layer?

Per greener1:

Optionalper-layer overrides of all print settings. This is intended for those who are creating their own print data .tar.gz files and want to be able to adjust print settings for particular layers. While they can be used to override the settings for First and BurnIn layers, it's recommended that they only be used to override Model layer settings, with BurnInLayers set to 0, such that all layers but the first will be Model layers, and with the existing First layer settings not needing any overrides. The settings may be overridden by including a CSV file named "layersettings.csv" within the print data .tar.gz file. I've attached an example Excel spreadsheet that can be exported to CSV in order to generate such a file. It only overides model layer exposures and layer thicknesses, but any print settings may be overriden in this way. Please note:

a. The first column must be the number of the layer (where 1 is the first layer) to which any overrides in that row apply.

b. The remaining columns are optional and may be in any order, but their headings must be exactly the same as the name of the setting to be overridden.

c. Layer numbers may be given in any order and no entry is needed for layers or cells in which the settings will not be overridden.

d. Any of the override values may include decimal points, and none of them needs to, regardless of whether or not the particular setting is an integer (unlike entries in the ‘printsettings’ and ‘settings’ files).

e. Rows may be left blank, or contain comments only, and comments may also be entered in cells that do not contain overrides, as long as those comments can’t themselves be interpreted as comma separated values.

f. After your print data .tar.gz file has been loaded, you may also edit the CSV file on the printer itself (at /var/smith/print_data/layersettings.csv). Any such changes made before starting a print will take effect in the next print (with no need to refresh).

g. Although a LayerThicknessMicrons override may be entered for layer 1, it will have no effect because only the (manual) calibration process determines the thickness of the first layer.

h. The estimated remaining print time shown on the front panel and at emberprinter.com doesn’t take into account any changes due to overrides in the ‘layersettings.csv’ file.

Step 5: Print Parameters Summary

What can be changed ?

In a typical cycle the printer rotates to the PDMS at the Approach slide velocity, lowers into contact with the PDMS at the Approach Z-axis velocity, irradiates the layer for a set Exposure time, rotates back thru the specified Angle of rotation, and finally lifts the print head to the height specified by the Z-axis overlift at the separation slide velocity. Additionally, pauses can be inserted into the cycle after the exposure, separation, or approach. There are 10 parameters that can be changed for each layer type, these are:

Exposure Time (seconds)

Separation Slide Velocity (RPM)

Approach Slide Velocity (RPM)

Z-axis Overlift (microns)

Separation Z-axis Velocity (microns/s)

Approach Z-axis Velocity (microns/s)

Angle of Rotation (millidegrees)

(After Exposure) (milliseconds)

(After Separation) (milliseconds)

Wait (After Approach) (milliseconds).

New (2.0 and higher firmware)

Maximum Jerk (degrees/s^3)

Overpress (microns)

Overpress velocity (microns/s)

Overpress return velocity (microns/s)

New firmware allows the printer to squeeze resin out from between the print and the window (and allows the acceleration to be set). Both features are useful for printing parts with large cross sections. In addition to the above motion, after the build head moves to the printing position it can then be set to move the "Overpress" distance below the print height at the "Overpress velocity", the build head then returns to the printing position at the "Overpress" return velocity. By moving down the build head displaces the resins tray and forcing resin trapped between the print and the PDMS window to flow out.

Step 6: Recommended Starting Points

Exposure Time

Resins tested to date have cured and not jammed using times ranging from 1.5 to 5 seconds. Some resins have a very small window where they will cure, but not jam, while others have a much broader region. For example for Autodesk Standard Clear (PR48) requires a minimum of 1.5 seconds to cure, and some prints with very small cross-sectional areas may permit exposures as long as 4.0 seconds. Typically, small positive features are best produced using longer times, while large cross sectional areas print more reliably with shorter times. Often 0.5 seconds may be the difference between some prints jamming or sticking to the PDMS. Changes as small as 0.25 s may be the difference between the smallest (positive) feature being 150 or 250 microns. If lots of floating material is forming in the resin tray (or nothing forms at all) the exposure time is too short. If the printer jams the exposure time is too long.

Separation Slide Velocity

With lower viscosity resins (100-300 mPa) the rotation speed can be increased to 15 RPM (maybe alittle faster) before the printer will jam from the force of the resin alone. Higher speeds may also lead to resin spills and other problems. More viscous resins may require slower rotational speeds (down to maybe 4 RPM). If lots of floating material is forming, turning down the rotational speed may be an alternative to increasing the exposure time.

Approach Slide Velocity

When the tray is returning the print is further away from the PDMS reducing the shear stress on the part, and a slight increase in the rotation speed may be possible.

Z-axis Overlift

The overlift is a very critical parameter. If this is set to large the build head has to displace alot of resin trapped between the build head and the PDMS window. If it is too small the build head may run into the PDMS window (particularly during the first few layers). For resins with a viscosity of ~ 300 mPa*s I would recommend an overlift of 750 microns for the 1st and burn in layers, and 500 microns for the printing layers. For more viscous resins (400 - 500 mPa*s) 1000 - 1500 microns is a reasonable starting place. This parameter has a surprisingly large effect on the print speed, so it is advantageous to reduce it if it is possible for the types of prints you are doing.

Separation Z-axis Velocity / Approach Z-axis Velocity

Here be dragons. The default is 5000 microns/s and is already the maximum for the stepper motor. REdued speeds seem to give more accurate movement with the linear drive, but moving to slow increases the printing time dramatically. I typically choose a speed such that the movement takes 0.5 s, so for a 750 micron over lift, 1500 microns per second is a good starting point.

Angle of Rotation

This value is pretty much fixed. If you are printing only a fraction of the bed this value could conceivably be reduced to the minimum rotation for the print to clear the PDMS.

After Exposure Pause, After Separation Pause, and After Approach Pause

Viscous resins need time to flow out from underneath the part after the build head is lowered. The more viscous the resin, the more time is need after the approach. For prints with small cross-sectional areas no pause may be needed, but other geometries may require one. If you notice significant dimensional deviation in the z-direction or that the tray being pushed down during the printing process a pause is likely added. However, this relaxation is exponential in nature and a pause greater than 1.5 seconds typically does not yield a large improvement. If you are running into jamming problems with large crossections you may need to investigate the over press settings.

Overpress, over press velocity, and overpress return velocity

This is still an active area of research for me and others. The overpress required to get the tray to return to the zero position after the build head has moved to the printing position depends on the viscosity of the resin, size and shape of the print. At least 1 mm is needed to see any results, but be careful you could break a tray playing with theses settings. I have attached a short technical paper on the background fluid dynamics and the results of some simple ODE based models of the system if you want a deep dive.

Step 7: An Example

Why change the settings?
There are several reasons to consider making changes. Often the exposure time is not correct. Different resins require different exposure times. Some models also benefit from longer or shorter exposure times. If the most crucial aspect of a print is lots of tiny positive features that are well separated (like hair) longer exposure times also for the printing of smaller features. If the model is has important negative features (embossed writing or channels), shorter exposure times can better preserve these types of features. Resin viscosity varies significantly from resin to resin. More viscous resins generate greater forces, and may even produce bubbles under the build tray that may need time to flow away. Slowing down the rotation (particularly on the separation rotation, as opposed to the approach) can preserve delicate features. Adding a pause after the approach can give bubbles time to flow away. Finally, because the exposure, rotation, and lift/lower steps all represent a significant fraction of the print time, significant improvements in speed can be gained for some types of models by adjusting any of them.

How to change the settings

Tuning the parameters is simply a matter printing your model, observing the results, and writing them down for future reference. In some cases the observation may be whether the printer jams, or if there is alot of unattached layers floating around in the resin. Other times a model may have some fine features that may either be lost to over curing or not produced. Like most experiments in involving alot of parameters its best to make big changes in the first few experiments to see if any change occurs, and then make finer adjustments only if necessary.

Test print print geometries

Because a number of prints can be involved in the process I like to use a fairly short test print that will be done in less than 1/2 an hour. The above test geometry has small posts ranging from 50 to 500 microns in size that rest fine feature resolution and a series of ladders (75 - 1000 microns) to test z resolution. The whole build area is printed to both test the feasibility of prints with large cross-sectional areas and to hold everything together.

Step 8: MadeSolid Black

To determine the printing settings I started with the defaults for Autodesk Standard Clear (PR48), but with the rotation speed cranked up a little. This caused the printer to jam, so I began decreasing the exposure time, until layers stopped forming during printing (1.25 s). Any attempt to increase slightly lead to jamming, so I then began exploring decreasing the rotation speed during the separation step (6-8 RPM), and increasing overlift height (back to 2000 microns). This gave my first successful print with 250 micron sized features. I was able to slightly increase the exposure time by further decreasing the rotation speed during separation to (6 PRM for all steps).

With parts like this test print that have a very large base ( ~ 40 x 60 mm) one useful strategy is to use a different exposure time for the base and rest of the part. By using only a 1.75 s cure for the base, and a 2.25 s exposure for the rest I was then able to eak out slight smaller features, in this case print 200 and 150 micron posts. I was also able to produce very fine 100 micron thick overhangs, better than either of the other resin in this Instructable. However, adhesion between the layers in the base was a problem, and which caused them to separate. These conditions would probably work fine for prints with smaller cross-sectional areas, but printing the whole build area is challenging.

Step 9: DWS DC 500

Unlike the MadeSolid black which had a small window between curing and jamming, the DWS resin was easy to find conditions where it would cure, without jamming. However, the resin has a tendency to form bits of polymer that are not attached to print, and make a real mess.

Like the MadeSolid black I started with the Autodesk Standard Clear (PR48) settings, and adjusted the exposure time, until I was able to get the resins to cure, and not jam. To get rid of the floating material I turned the rotation speed way down (2 RPM) during the burn in layers (again all the way thru the base). Increasing the exposure time when the fine features were printing gave very good results ( 150 microns features). However, most of the fine negative features were lost on this model.

Step 10: High Speed Resin

This was a mixture we prepared in house using commercial materials from Esstech, Rahn, and Mayzo. The last three ingredients can also be acquired from chemical suppliers like TCI America and Sigma Aldrich. The formula uses significantly less of the UV blocker than a conventional resin, and allows very thick layers to be quickly printed.

The formula is:

Esstech Exothane 10 24.9 % wt./wt.

Rahn tripropylene glycol di-acrylate 74.8 % wt./wt.

TPO (Esstech,Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide) 0.20% wt./wt.

OB+(Mayzo, 2,2’-(2,5-thiophenediyl)bis(5-tert-butylbenzoxazole)) 0.016 wt./wt.

This resin was very easy to print with, there was really no adjustment as the resin easily cured without jamming using exposures between 2.5 and 5.0 seconds for 25, 100, and 250 micron step sizes. By setting everything on the machine to make it print as fast as possible some of the prints were faster than 200 mm an hour using 250 micron steps (17 mm is standard with PR48 and 25 micron steps).

The downside is that fine negative features were easily lost if they were under 1 mm, however, as the photo shows the x and y resolution was still excellent for fine features, and posts 250 microns thick were printed.

Surprisingly, we were also able to print a solid brick using this resin, something no other resin has done on Ember.