Get the size right

Before you start

You need a printer and a resin set up (Your first print) and exposure that already gives clean prints: size errors measured on an under- or over-exposed part tell you about the exposure, not the resin (Exposure). Have calipers and a test part with a flat-sided length you can measure across on each axis.

Everything here is per resin on one printer. Encrust keeps the numbers on the resin you added under that printer, so a second printer, or the same bottle from another maker, starts again from neutral. Treat every figure as a starting point for your own printer and resin, and follow the resin maker’s instructions first. Resin safety, including handling an uncured part, is covered by the maker’s safety data sheet.

Know what you are correcting

Three different errors get called “wrong size”, and each has its own setting.

• The whole part is smaller than drawn. The resin shrinks as it cures. The fix is a scale: Shrinkage X, Y and Z.
• Holes are too tight, or outer walls too fat, while the overall size is fine. Light bleeds past the edge of the mask. The fix moves walls: Holes and Outer walls.
• The print takes longer than Preview said. That’s the time estimate, not the part. The fix is Unaccounted per layer.

Don’t use shrinkage to cure a hole problem: scaling a part up also scales its holes, so you trade one error for another.

Print and measure a test part

1. Slice a test part with every Compensation value neutral: Shrinkage at 100 %, offsets at 0 mm.
2. Print it, clean it and cure it as you always do, and let it cool.
3. Measure each axis with calipers: across the plate for X and Y, up the build for Z.

Measure it cold: the calculator’s own note asks for that.

Work out the percentage

The formula is:

percent = 100 x drawn / measured

A 20 mm bar that measures 19.90 mm wants 100 x 20 / 19.90 = 100.503 %. Above 100 slices the part larger so that it measures right after the resin pulls in. A part that came out larger than drawn gives a figure under 100.

Encrust does the division for you:

1. Open Settings (Cmd+, or Ctrl+,), pick your printer’s resin in the Machines list and scroll to the Compensation card, below Waits and Motion.
2. Click “Work it out from a measured part”. The window “Shrinkage from a measured part” opens.
3. For X, Y and Z, type Drawn (the size in the model) and Measured (what the calipers read).
4. Read the line under the fields, for example “100.503 %, …” for the three axes, and click Use these.

The three Shrinkage fields now hold the result. You can also type them straight in: the fields accept 95 to 105 %. The app’s reasoning for that limit is that a resin off by 5 % is one to replace.

Leave Z at 100

Set Shrinkage Z to 100 unless you have a reason. Along Z, a layer’s shrinkage is taken up by the layer cured on top of it, so the error that survives lands in X and Y. A Z figure is for a machine whose Z travel itself is off, a different fault with the same symptom: a part that measures short in height.

The calculator offers a Z row because it fills all three axes. Enter the same number for Drawn Z and Measured Z, or retype 100 afterwards, if you only want XY.

What the scale does to the plate

Encrust scales each model on its own, about the middle of its footprint and about the plate. A part shrinks towards itself and is held at the plate while it prints, so the correction doesn’t slide neighbouring parts apart or lift one off the plate. Supports are scaled with the part they hold. Preview and the sliced file both use the scaled geometry.

Move walls for tight holes

The tolerance fields move each layer’s walls by a distance in millimetres. In the Compensation card:

Field	Moves
Holes	the wall of a hole, inwards
Outer walls	the outer wall, outwards
Holes, bottom block	the same, for the bottom layers
Outer walls, bottom block	the same, for the bottom layers
Every second layer	added to both offsets on every second layer

A positive value leaves more material: a hole closes, an outer wall grows. A negative value takes off what the light bled past the mask. For holes that are too tight, enter a negative number under Holes. On the bottom block, a negative Outer walls value is what takes off an elephant foot.

A wall moves by the offset, so a hole’s diameter changes by twice it. By that arithmetic, a hole that measures 0.10 mm under its drawn diameter wants about -0.05 mm under Holes. Change one field at a time, print again and measure again. The fields go to 0.2 mm either way, and the app notes that past a tenth of a millimetre the model is wrong, not the printer.

The panel can’t draw an edge finer than one pixel (0.019 mm on a Saturn 4 Ultra; the card shows your panel’s value under Every second layer). A smaller offset only exists as an average over alternating layers, which is what that field is for: it adds its value on every second layer, so 0.01 mm there on top of an offset of 0 gives half the layers a 0.01 mm move and the other half none.

Two things follow from the geometry. A hole narrower than twice its offset closes, and a wall thinner than twice its outer offset disappears. Corners are cut square, not carried to a point, which avoids a spike on a sharp corner. The offset is applied before Preview measures the layers, so what Preview says the print cures is what the file carries.

Correct the time estimate

The time Encrust predicts leaves out a few things the machine does on each layer. You can measure the gap from one print.

1. Slice a print and note the Time in Preview’s column on the right, in the section headed with your printer’s name. Note the layer count too.
2. Time the print on the machine, start to finish.
3. In the Compensation card, click “Work it out from a finished print”. The window “Unaccounted time from a print” opens.
4. Type Predicted (hours, minutes, seconds), Actual and Layers, and read the line “… s a layer”.
5. Click Use this. The result goes into Unaccounted per layer.

The formula is seconds = (actual - predicted) / layers. A job predicted at 35 m 49 s that took 60 m 50 s over 200 layers gives (3650 - 2149) / 200, about 7.5 s a layer. Both times must come from the same print. The setting moves the estimate only: no exposure, no motion, nothing the part is made of. The estimate then shows it the next time you slice, and the written file’s header carries the same time.

If something goes wrong

The part is still the wrong size after entering the percentage

Check that the part you measured was printed with Shrinkage at 100. If it was already corrected, the new figure is on top of the old one: divide again using the corrected print’s drawn and measured sizes, and type the result over the field. Then check that the resin you edited is the one chosen in the Print block.

Holes are right but the outside is now too big

You scaled to fix a hole. Put Shrinkage back to the figure from your measured bar and fix the hole with the Holes field instead.

The new time is still off

Check that Predicted, Actual and Layers all come from the same print, not from two different models.