Squish!

Printing the first layer can be frustrating for the do-it-all hobbyist since everything is always changing

Beginner squish

Perform leveling, adjusting, calibrating the printer
Print a Single Layer large box, (most of build plate) outline, or something similar and let it complete without intervention
Inspect the single layer printed object while it prints (or immediately after)
- Too close?
  - Smearing
  - Stringing
  - Dragging - stuck better to nozzle than bed
  - Pulling - stuck to nozzle
- Too Far Away?
  - Not sticking
  - Dragging - not stuck to bed
  - Pulling - not stuck to bed
Adjust nozzle height and print again until it looks good enough!

What IS good squish?

My Opinion - It depends... seriously!

When the material leaves the nozzle it's cross section is roughly circular but once touching the bed is deformed and hopefully stuck to the bed. The resulting oval shaped filament string will have a flat bottom if it sticks to the bed at all, but the top of that oval and any other deformations from this point are exactly what we are discussing here.

Printing whatever filament successfully on a given printer can be performed over a fairly wide range of "filament squish levels", but the best performance, reliability, and quality come from dialing it as close to the middle of the range as possible which I believe helps to account for variations in filament diameter and build plate inconsistencies.

The extremes are easy; if the top if the oval almost looks round it means the nozzle needs to be closer to the bed, or if the oval is deformed to look completely flat, the nozzle needs to be farther from the bed. The middle ground is tricky because each material being printed on each printer will have slightly different preferences.

I begin with the nozzle well above the level I expect to actually print at, then dial it down while printing in the air until the material sticks nicely and has a visible flat on the top... this is the minimum squish, or highest Z offset if you prefer.

Materials prefer different heights

This is not based upon the material such as PLA vs PETG or ASA, but might be more individual to the specific color of each material from a given brand and how well that color wants to stick to the build surface being used.

When the best possible reliability and quality are desired, we need to calibrate each printer for each new material

Print a test part
- Warp testing - Long & thin part, to check for warping and adhesion issues
- Tolerance testing - Known easy to measure features, most useful general test since it gives many measurable details
Start with less Squish for a new material
- If there are ANY adhesion issues with a print line that just has the top flattened, squish a little more
- Starting with too much squish can cause some materials to become permanently bonded to some build surfaces
  - In my experience, this can make repeat prints difficult prior to removal ;)
Big changes are OK at the beginning
- If there is an adhesion issue with the first "lightly flattened" test, I tighten the squish significantly
  - This is often too much squish, but should FIX the adhesion problem, letting us concentrate on any other issues that come up
    - Too much squish can cause smearing and stringing among other issues
If we STILL have adhesion issues, its time to go back to cleaning the build surface and maybe reapplying adhesives for those extra troublesome materials

No PETG on PEI / PEX?

Some claim PETG should not be printed on PEI or PEX build plates without adhesive separation layers, and I believe they say it for liability reasons.

Many PETG filaments have a higher coefficient of adhesion at ~85c when compared to ABS or ASA at ~100c with the same nozzle/bed offset, but raising the nozzle height can alter this significantly. Raising the nozzle to a point of just flattening the top of the print line, seems to allow the same material to stick to the same sheet and pop off nicely after cool down like PLA in most cases.

Simply lowering the bed temperature typically reduces the post-print adhesion to the bed. Printing PETG onto a WhamBam Smooth PEX sheet at 60-70c has a very good possibly of destroying the build surface when removing the part. When I lower the bed temperature ~20c PETG no longer seems to bond with the PEX/PEI surfaces during printing. I still have perfectly adequate stick without warping, but the part is now removable without damaging the build surface.

No Silver Bullets!?!

Unfortunately this is a trial and ERROR process that requires failing regularly before mastering the techniques. Yes, there is a trick to it, and if we keep trying we WILL get it. Don't give up!