Supports That Won’t Come Off Aren’t Too Dense — Your Z Gap Got Rounded

A support welds itself to the underside of a bracket. It takes pliers to remove, and it tears the surface on the way out. The usual fix is to turn support density down, and the next print has a rougher underside and a support that is just as stuck. Density was never the problem. How hard a support holds on is decided at the contact, in a gap one or two layers tall, and most slicers do not print the gap you typed.

The Gap Is Whole Layers

Supports work because the slicer leaves an air gap between the top of the support and the overhang, the top Z distance. Bambu Studio and OrcaSlicer default it to 0.2 mm on a 0.2 mm layer profile: exactly one layer. Cura rounds the value up to a multiple of the layer height, so 0.15 mm at 0.2 mm layers prints as 0.2 mm, and 0.2 mm at 0.16 mm layers prints as 0.32 mm. OrcaSlicer also snaps both top and bottom Z distance to whole layers unless independent support layer height is on. PrusaSlicer is the exception: it prints the first layer over support at whatever thickness the gap needs.

So at 0.2 mm layers there are only two real choices: one layer (0.20 mm) or two (0.40 mm). For PLA, one layer is about right. PETG, PCTG and ABS bond to themselves much harder, so one layer is close enough for the first line over the support to fuse into it. Two layers frees it, but the first layer now bridges 0.4 mm of air and droops. The 0.25–0.30 mm gap most people actually want for PETG does not exist at that layer height. Typing it in only changes the number in the box.

In This Order

1. 1
   Read the preview, not the settingScrub the layer slider to the first layer of the overhang and count the empty layers between it and the top of the support. That count is your real gap. If it is zero, you are in contact mode; if it changed after a profile switch, rounding did it.
2. 2
   Pick a layer height that makes the gap you wantFor a PETG part that wants about 0.3 mm, 0.15 mm layers give exactly two layers, and 0.16 mm layers give 0.32 mm. In OrcaSlicer, independent support layer height lets the gap stay off the layer grid. In PrusaSlicer, set the contact distance you want directly.
3. 3
   Set XY distance for side contactIf the support sticks to walls rather than undersides, raise support/object XY distance from the 0.35 mm Bambu default in 0.1 mm steps. Z changes will not touch this.
4. 4
   Keep the interface sensibleTwo top interface layers is a sound default. A very dense interface (0 mm spacing) gives a better underside but grips harder, so only use it with a gap that can take it.
5. 5
   Use a release interface for materials that self-bondPLA and PETG bond poorly to each other, so a PLA interface under a PETG part (or PETG under PLA) can run at 0 mm top gap and still peel cleanly, with a flat underside. With an AMS or tool changer, this is the best fix of the lot, because it removes the gap trade-off entirely.

A Worked Example

A PETG bracket at 0.2 mm layers, top Z distance set to 0.15 mm. Cura rounds that to 0.2 mm, one layer, and the PETG fuses across it. Density goes from 15% to 10%: no change at the contact, worse sag in the middle of the overhang. Raising the gap to 0.25 mm rounds it to 0.4 mm and the underside droops. Reprint at 0.15 mm layers with a 0.3 mm gap, and the support comes off by hand with a clean underside. Same file, same density as the first print. The only change was making the gap a number the slicer can actually print.

Less Support Does Not Mean Easier Removal

Lower density and fewer support walls make the support body easier to crush, which helps when the body itself is the problem. They do nothing at the contact, because the interface layers are printed at their own spacing regardless. What they do change is how well the overhang is held: sparser support lets the first layer sag between the lines, so the underside gets worse and the bond stays the same. Fix the gap and the interface first, then thin the body only if it is still hard to break apart.

The same logic is why a stuck support often goes with a curled or blobby underside. Both come from how the first layer over air is laid down; the cross-links below cover that, and why fusion between layers depends on heat and time rather than settings alone.

If a part needs clean supported faces in an engineering material, ask before you order. DuffAM chooses support gaps, layer heights and interface materials per part, which is part of how we work.