What does it mean to Calibrate your 3D printer?

Subjective or Objective Methodology

As I mentioned before “Not all methodologies are equal.” Some are based on purely Subjective principles, others Objective.

For example:

• To calibrate your 3D printer based on measuring a part that must measure exactly 6mm x 8mm this would be an Objective Calibration. Verifiable information based on facts and evidence.

  • This methodology is called Dimensional Accuracy.

• In contrast, if you could only observe a pattern and visually determine when it was about 6mm x 8mm this would be a Subjective Methodology. Information based on perspective.

  • This methodology is called Visual Accuracy, or just Accuracy.

Subjective or Objective Design
The design has to follow the methodology used. However that does not mean it can't be independently Subjective or Objective.

For Example:

• If the Calibration part has a section that will Fail until the methodology is satisfied. Even if the method is Subjective, the design is Objective. 

  • Fail = the methodology has not been reached.

  • Success =  methodology has been reached.

• In contrast, if a calibration part had a Pass/Fail section, but also had a Visual Accuracy section. This would be a subjective design, for more reasons than you may consider.

  • The user must determine if they focus the calibration to pass the Accuracy section, the Pass/Fail section, or somewhere in between as you will most likely never achieve both.

  • Visual Accuracy is subjective.

Part 7: The Four Calibration Methodologies

There are four Major Methodologies

1. Accuracy

2. Dimensional  Accuracy

3. Strength

4. Tensile Strength

There are hybrids that combine two or more. Most hybrids tend to pick one as the primary focus with smaller elements of other(s). Some have two primary focuses and allow the user to lean into one or the other.

Examples:

Accuracy - The hits are lower on the target to imply lower exposure and less accurate. 

Visually, you can get close to Dimensional Accuracy but never perfect. 

Dimensional Accuracy - The hits are lower on the target to imply lower exposure but very accurate.

What's in your slicer is what you print. You say use a 0.3mm support tip, that's what you get. Requires a precise instrument to confirm with repeatable consistency. 

Strength - The hits are mostly high and a few low. As strength is purely subjective some calibration will be under exposed, but most will be over. The accuracy is all over as each calibration will have massive variation. Strength based calibration should not be used as it does not meet the minimum requirements to be defined as calibration. 

 As you add UV exposure time to cure resin two things happen. 

1. The part will physically grow on all axis as the UV light penetrates the resin curing more of it.

2. The resin becomes harder as more of the polymers and monomers combine to solidify.

3. Both of these functions are utilized until a test of strength is passed.

Tensile Strength - All the hits are on target. This is imply that dimensional accuracy is used as the control to fine tune all other settings to reach the highest strength possible.

Must be testing strength under "Dimensional Accuracy" and other controls.

1. The resin becomes harder as more of the polymers and monomers combine to solidify.

2. The part CANNOT be allowed to physically grow beyond the design.

   1. Example: A pillar that measures 1mm made of material A is stronger than a 1mm pillar made of material B.

   2. If A and B are not the same size at time of testing, it's not "Tensile Strength".

3. The designer cant have control over the difficulty of the pass/fail parameters.

4. Elongation must also be observed.

   1. Consider how the resin being used, Flexible, High Accuracy or Speed can affect the Tensile Strength of supports or smaller details.

Design (Subjective)
Visual based dimensional accuracy VS Strength with several smaller zones to inspect different aspects of each.

Methodology (Subjective)

Because Town and Starship are hybrid calibrations. You can focus on (visual based) accuracy OR strength.

You do this by observing many different tests presented all over the chassis. Each test will help you understand if you’re under exposed by elements failing. Or over exposed, elements closing up or filling in.
Because of this, it’s up to each user where they end up, when you stop is entirely subjective.

Function(s)

Primary(s) - Strength vs Accuracy - Subjective

• You can focus on strength by getting the smallest pins to print.

• You can focus on visuals by allowing for more pins to fail but achieving better visual accuracy.

• Has several visual aspects that help you identify blooming(Over exposure) or failure.(Under Exposure) 

  • I need to state, using only exposure time to calibrate your resin will often lead to suboptimal results.

  • Click here to learn more about Blooming..

• In this way you can visually see what you give up as you go for one or the other.

• Z-Blooming visuals

  • Also known as cross curing, this is what happens when the UV light will over-penetrate the layer being cured into the previous layers and cause additional blooming on the Z axis.

  • It must be pointed out that the resin being used and the layer height will have more impact than any setting you can adjust in the calibration phase, making this section more interesting than functional.
    
    

Pros:

• Being able to visually see the effect of Accuracy VS Strength will give you a balanced and guided calibration.

  • For this reason this type of calibration, especially Town, is the 2nd most used calibration, used and trusted by many professionals.

• Has an aspect of Z-blooming observation, but can be influenced by XY blooming.

Cons:

• Larger file - Longer print times and higher resin usage.

• Can be hard for new users to read, often requiring asking for assistance.

• Your results are based on your preference and may behave differently from others and other tests.

J3D-Tech -  Boxes of Calibration - (Boxes of Calibration is my own design, the methodology is as old as time.)

Links: Instructions & Download

Primary Methodology - Tensile strength

Secondary - Accuracy

Tertiary - Strength

Hybrid - Yes

Design (Objective)
Obtain Dimensional Accuracy (DA) though measuring, or obtain <=0.04mm of accuracy though stacking the boxes inside of each other. 

At (DA) obtain as many pillars as possible to achieve peak Tensile Strength of your resin.

Methodology (Objective)

• You can always confirm Dimensional Accuracy.

• The pillars have no weights and so are not stress tests. Because you're only looking at them after achieving dimensional accuracy and Elongation can be observed they are in that moment a Tensile Strength Test.
  
  

Function(s)
Primary - Tensile strength - Objective

• Print 10/10 pillars at dimensional accuracy means that the resin has achieved high tensile strength.

• Print less than 8/10 or lower suggests you can calibrate other settings such as delays and speeds to allow for more UV exposure time while maintaining dimensional accuracy to achieve peak resin hardness.

• Observation of elongation of the pillars and measuring of the boxes can be observed before and/or after post curing.

Secondary - Accuracy - Objective

• Ignore the pillars, measure or stack the boxes to get within 0.04mm.The accuracy or as accurate as your printer and resin can possibly achieve.

Tertiary - Strength - Subjective

• Ignore the boxes and just increase exposure time till all the pillars print, measure the boxes to observe how much accuray you gave up.

  • Up to the user to balance accuracy vs strength.

  • Very similar calibration to Town/Starship with an "objective" aspect as you can measure the boxes.

Pros:

• Can be observed before or after post curing to test pre and post shrinking.

• Can be used for testing and not just calibration.

  • Some resin have less tensile strength then others: Example: ABS like vs Flexible. Because all data (pillar success rate) is recorded at dimensional accuracy, it's a valuable comparable data point.

• Has all three major functions allowing it to simulate all other calibration methods.

• Tensile Strength is the holy grail of calibration, giving you both accuracy and printability.

• Digital calipers not required for <= 0.04mm of accuracy.

• As temperature effects cure time you can precisely measure and record how this affects size and then tensile strength.

Cons:

• Fitting the boxes is based on feel and can be considered subjective.

• Some resins, such as very flexible resins, can be difficult to calibrate.

• New users find it intimidating.

• For the best accuracy, Requires digital calipers and understanding how to correctly use them.

• ACF can cause micro fractures in the pillars, causing the 0.1mm and 0.12mm to break more often.

• Printing at very fast speeds and no wait times can give the smooth surface of the boxes a warped texture making them harder to measure. (Could be observed as cause and effect.)

Table Flip Foundry - Cones of Calibration (I am the core designer of Cones V2, NOT the inventor of Methodology.)

Link: Instructions & Download

Primary Methodology - strength

Secondary - NA

Hybrid - No

Design (Objective)
Cones have a clear objective, get all the success cones to fully print. Get all the fail cones fully fail. The smaller the fail cones are the better. Fairly simple and easy to read.

Methodology - Strength - Subjective
With a focus on strength over accuracy the core design assists you to stay within a predetermined range.

Utilizing UV exposure time to harden and physically expand the resin to obtain success.

Function(s)
Primary - Strength - Subjective

A range of pre-calibrated weights (cones), balanced on small tests, the short cylinder between the cones.

Adjust the exposure, altering the resin hardness and physical size of the weights to land in a range between Success and Failure. 

Pros:

• Very easy to read & understand

  • I find Cones to be the most visually easy test to read of any calibration on the market, in this they achieve the top award.

• Some resins/printers/settings will achieve high Accuracy and Strength.

• Aimed and succeeded at solving the issues with 100% accuracy based calibration. The issue was causing supports to have no strength and fail.

• A 2nd fence to help prevent overshooting. A pre-programmed limiter on the range of success and failure.

• Due to the sensitive nature of the invented cone, they will show Z wobble or an unstable printer. Allowing the user to identify and resolve the issue.

Cons:

• The final calibration is double subjective. (Refer to the double fence reference below.)

  • This locks the calibration into a range that may not be ideal.

  • Some resins/printers/settings will be under exposed.

    • Prevents you from achieving peak resin hardness.

    • Some users may utilize larger supports to compensate.

    • Some smaller details may fail to fully form.

  • Some resins/printers/settings will be over exposed.

    • The part physically grows on all axis as the UV light penetrates the resin curing more causing details to be consumed, and support tips grow causing more damage.

    • The resin becomes harder as more of the polymers and monomers solidify, too hard and support tips can be harder to remove causing more damage.

      • This can lead some users to under size supports to compensate.

      • Users that print pre-supported files that utilize larger support tips can leave excessive damage and be very difficult to remove.

• Your result may behave differently from others and other calibration methods.

• The invented cone design is unstable and can bend over during the print causing inconsistencies.

  • Printing it with other items on the printer can cause the angle of FEP pull to push the cone over causing false failures.

  • Does best when centered to keep FEP pull as consistent as possible. (Mitigated in V2)

• V1 

  • High print times and resin usage (fixed in V2)

  • Cones can break off falling into the VAT causing damage to the FEP or LCD. (Fixed in V2)

  • The roof is held up by the cones, this can cause it to rip the cones off when printing causing a false failure. (Fixed in V2)

  • Should not cure, warping of the roof can pull on the cones causing a false failure (Mitigated in V2)

Double Fence Reference:
I know this can be confusing, please allow me to explain this in a way to give a visual.

Visualize that you're in a large field, there is a fence about 20 - 25 feet in front of you. About 5-6 feet behind the first fence, there is another.

The objective, toss a rock to land between the two fences. The 5-6ft foot gap between the two fences is the range of success. If it lands in front of the first fence or after the second fence you fail.

This is subjective in two ways:

1. There is a 5-6 foot gap between the two fences. The ball can land anywhere in that range and still be counted as a win. Why is the gap around 5 feet, Why not 2 or 10 feet? Both the size of the gap and that you can land anywhere within it is the first way this is subjective.

2. Why is the first fence 20-25 feet away from you, why not 10 or 30 feet. Remember the distance of the first fence also sets the distance of the 2nd fence. Hence why it's double subjective.

In this example the first fence presents the Success Cones and the 2nd fence the Failure Cones.

Hopefully with this analogy you can see the power the creator has with the Pass and Fail conditions within the Strength Methodology.

Phrozen - XP Finder / Photonsters - XP2 (Validation Matrix)

Links: Instructions & Download / Links: Instructions & Download

Primary Methodology - Accuracy
Secondary - NA
Hybrid-  No

Design (Subjective)
Visual based accuracy.

Methodology  - Accuracy - Subjective
Adjust exposure till the print visually looks like the 3D file.

Function(s)

Primary - Accuracy - Subjective

Has several visual aspects that help you identify blooming(Over exposure) or failure (under exposure.)

Pros:

• Low resin usage

• Easy to understand

• Very fast print

• Can get close to dimensional accuracy just using visuals

• Quickly find a UV exposure rough estimate before moving to a precise calibration model that takes longer to print.

Cons:

• No mechanism to assist you with strength causing some resins/printers/settings will be under exposed.

  • Prevents you from achieving peak resin hardness.

  • Some users may utilize larger supports to compensate.

  • Some smaller details may fail to fully form.

  • This can lead to a calibration that may have a higher failure rate.

    • Remember Strength is how the resin becomes harder as more of the polymers and monomers solidify.

• Affected by burn in layers

  • You must adjust your bottom layer printer settings or you will get false failures. 

• Can’t be measured and will warp if cured making post cure accuracy calibration impossible.

• Can be hard for new users to read, often requiring asking for assistance.

Siraya Tech Test Model V5

Links: Instructions & Download

Primary Methodology - Accuracy
Secondary - Strength
Hybrid - Yes

Design (Subjective)
Getting the best visuals without losing the cube.

Methodology - Accuracy - Subjective
Adjust exposure till the print visually looks like the 3D file. The added test of resin strength in the shape of a Cube that must not fail.

Function(s)
Primary - Accuracy - Subjective

Observe the different patterns to obtain the best appearance.

Secondary  - Strength - Subjective

Don’t decrease exposure so low that the cube does not fully print.

Pros:

• Low resin usage

• Easy to understand

• Can get close to dimensional accuracy just using visuals

• Has a strength test to prevent you from going too low.

• Has a place to measure 10mm to test DA and shrinking.

• The arch has a 5mm clearance to measure Z accuracy.

• Gives elements of AA testing with the Arch.

• Flat section to mark the print for notes.

Cons:

• Longer print time than other visually based calibrations.

• Some of the visual aspects are harder to read than other similar tests.

• Affected by burn in layers

  • You must adjust your bottom layer printer settings or you will get false failures. 

  • Has a place to measure 10mm but because it’s so close to the raft it can be inconsistent due to warping.

• Can be hard for new users to read, often requiring asking for assistance.

J3D-Tech Build Plate Calibration XL - RERF & Normal

Links: Instructions / Download

Primary Methodology - Accuracy
Secondary - Leveling and Z-Offset
Hybrid - Yes

Design (Subjective)f
Visual based accuracy.

Methodology  - Accuracy - Subjective
Adjust exposure till the print visually looks like the 3D file.

Function(s)

Primary - Accuracy - Subjective

Has several visual aspects that help you identify blooming(Over exposure) or failure (under exposure.)

Secondary  - Build Plate Calibration - Objective

Allows you to confirm that your printer is level and your Z-Offset is set.

Pros:

Low resin usage

RERF and normal versions clearly marked for location on the build plate.

Very fast print

Can get close to dimensional accuracy just using visuals

Sphere and 2 ramps to visualize stepping.

Quickly find a UV exposure rough estimate before moving to a precise calibration model that takes longer to print.

When combined with REFT can do this even faster, prints clearly marked with 1-6.

Test your Build Plate Level.

Measuring the two sides marked 1mm. Each plate in each zone should measure about the same thickness.

Lock them next to each other and use a pencil to draw between the “1mm” sections on the plates, you will feel it is shorter.

Test your Printers Z-offset.

Measure the 1mm sections with digital calipers, or slot them into the groves marked “Raft is 1mm”.

The total height is 2.5mm, the height at the 1-6 logo is 2mm.

Cons:

No mechanism to assist you with strength causing some resins/printers/settings will be under exposed.

Prevents you from achieving peak resin hardness.

Some users may utilize larger supports to compensate.

Some smaller details may fail to fully form.

This can lead to a calibration that may have a higher failure rate.

Remember Strength is how the resin becomes harder as more of the polymers and monomers solidify.

Affected by burn in layers

You must adjust your bottom layer printer settings or you will get false failures. 

Can’t be measured and will warp if cured making post cure XY accuracy calibration impossible.

Can be hard for new users to read, often requiring asking for assistance.

The maze section can be more difficult to clean.

• Not everyone has access to 3D software that can do the correct type of scaling, as traditional scaling will volumetrically grow an object on all 3 dimensions.

  • This can cause details of a print to be out of place during assembly.

• If you don’t first compensate for blooming you may still have issues with keys or pinholes not fitting, even if the perimeter of the object is scaled to compensate for shrinking.

My final thoughts on Compensating Resin Shrinkage: 

1. Don't expect a man counting steps to give you an accurate distance measurement between NYC and LA.

2. Don't expect 3D printed plastics on a Desktop 3D printer to give you the level of accuracy to make NASA drool.

3. If you need a high level of accuracy for prototyping or assembly parts. Calibrate for True Resin Tensile strength and use a low shrinkage resin such as the Siraya Tech Build and others like it. This will have the most positive impact.

In this example there are 6 zones with Zone-1 (Z1) being in the top left and Zone-6 (Z6) being in the bottom right.

Some Anycubic printers can run REFR natively. For others you will need to use UV tools to edit a slice. See this video on how this can be done. I am not sure if all printers on the market are compatible with this type of test. But finish reading this entire article as there is important information about the different Calibration test.

RERF is advertised* as a way to quickly find your UV exposure time. This is accomplished by splitting the build plate into zones typically 6 or 8 zones. Each zone is exposed to a different exposure time per layer. For example, Z1 could be exposed at 1.3s per layer, Z2 at 1.5s, Z3 at 1.7s and so on till Z8 is exposed at 2.7s.

* "Greatly saves your time and resin to calibrate your printer with less trial and error, as the test prints with different exposure times in just one print allow you to compare and decide what will be the best exposure time.” - Anycubic.com

There are three ways that this can be done, spoiler: this is where the issues with this type of system are introduced.

The Domino Method - All zones will be exposed at once, but will fall off after their timer runs out. 

All zones will be exposed for 1.3s then Z1 will turn off.

Z2 will drop off after 1.5s, Z3 at 1.7s and so on till Z8 is exposed at 2.7s

This will repeat till all zones have been exposed for their set time. Once this is finished that layer is completed. The printer will lift to remove that layer from the FEP and do it again till the print is finished.

The One by One Method  - Each zone will be cured one at a time. 

Z1 will be fully exposed at 1.3s and Z2 - Z8 won't be exposed at all. 

Z2 will then be fully exposed at 1.5s. Z1, Z3 -Z8  won't be exposed at all.

This will repeat till all zones have been exposed for their set time. Once this is finished that layer is completed. The printer will lift to remove that layer from the FEP and do it again till the print is finished.

The Strobe Method  - A combination of both methods as every layer is exposed multiple times with a Domino effect.

Zones 1-6 will be exposed for 1.3s and the UV array will turn off.

Zones 2-6 will be exposed for 0.2s and the UV array will turn off.

Zones 3-6 will be exposed for 0.2s and the UV array will turn off.

This will repeat till all zones have been exposed for their set time. Once this is finished that layer is completed. The printer will lift to remove that layer from the FEP and do it again till the print is finished. 

Wait times and REFT:

There are two different types of wait that come into play with REFT.

Wait Before Print

After the build plate is in position to start printing the system will wait (x) seconds before the UV light will cure the resin.

This is used to allow the resin to stop moving before curing to GREATLY help accuracy and quality. 

Wait too long and you start to get negative effects. The recommended time is 2s. 

Wait After Print

After the resin is cured the printer will wait (x) seconds before it lifts up, peeling the now cured layer of resin off of the FEP sheet.

I’m not aware of any value to this and only a negative

Waiting too long will cause the previously cured layer to cool and bond more to the FEP sheet making it more difficult to peel

The overall peak temperature of resin will be reduced during the print. Printing at a different temperature will dramatically change the UV exposure time and strength of the resin. It’s recommended to print at a consistent 20-26 degrees celsius or 68-79 Fahrenheit.

Method 1:  Z1 will have a total of 1.6s of waiting time after the print. Z8 will have 0s of wait time after the print as it’s the last to finish.

Method 2, will introduce massive wait times both before and after the print. For Z1 it will have 0s of wait before print. If can imagine each zone. forced to wait their turn? Imagine waiting at the DMV, with a single clerk, but no one can leave till everyone has had their time at the counter. The wait times before and after your turn are excessive. 

3. In Method 3, the worst of them all, exposing resin multiple cures will dramatically change how it functions. This method should never be used.

Pros and Cons: 

Con:

1. All this extra wait time to both before or after the UV exposure means that REFT can never simulate how you actually print. Where Method 2 the The Domino Method is the clear winner making the least amount of changes to a real print.

2. May not be supported by your printer forcing you to use a 3rd party tool like UV tools that has its own learning curve. 

Pro:

1. When paired with a “Flat Calibration Print” that can be completed in 15-20 min it can be a good way to quickly find a rough range of where to begin for the longer more accurate calibration prints. 

2. Must be followed up with a more accurate calibration tool once you find a rough estimate of a starting point.

3. One Calibration print (Build Plate Calibration XL) will allow you to pack multiple functions into REFT, such as testing your printer's level and Z=offset. All into a single print getting you the best bang for your buck, read to the end for more details.