Bottom layer squashed

I have assembled a prusa i3 and have got it working (I think), but I have an issue that I would like to have fixed, even though I recognise it might be more of a feature.

The bottom layer of any print gets squashed a bit, so that it does not keep its intended dimensions, and this means gthat I cannot rpint something like a set of custom dice or similar, where all dimensions must be controlled.

I am using 225/110 and 180/60 as extruder/bed temperatures for ABS/PLA, and both of them show the same result, albeit the ABS is slighty less squashed.

My guess is that the bottom layer is kept so warm by the bed that the weight of the upper layers pushes it down during printing.

Can I change this by reducing the bed temperature after the first layer?
Is there a way to avoid it or do I have to live with it?

The below picture shows two cubes, the orange is ABS, white is PLA.

I just edit the gcode file with a text editor and insert M109 commands at the appropriate palces,

You will have probably have M109 S110 T0 in the startup code (assuming you have set the HBP temperature to 110)

Now search for the beginning of the second layer - you can tell by the Z parameters in the gCode

for instance in the first layer you might find:
G1 X-109.740 Y-71.516 Z0.125 F252.000 A3.939 (Z is 0.,125 here)

If you are using 0.25mm layer height then the next (second) layer will have Z0.375, so you can just search for the first occurence of Z0.375

You will find something like this:
G1 X-109.060 Y-71.097 Z0.375 F9000.000


Insert a new line before that with : M109 S080 T0

This will cause the HBP temperature to reduce to 80 degrees at the beginning of the second layer.

If you want the machine to wait for the temperature to reach 80 degrees before printing the second layer (as opposed to letting it decrease while printing the second layer) then just insert this after the M109 S080 T0 command:

M6 T0


I actually prefer to lower the temperature gradually in steps of 5 degrees each layer without waiting for the decrease. I start at 110 degrees and decrease in steps of 5 until I reach 80.


However, that being said, you will always get some squahing of the first layer (or even first few layers). Lowering the HBP after first layer does help but does not fully solve the problem, at least that is my experience.

Whenever I need to print something with an accurate base (which is actually the case for most of what I print) I build a few layers of raft, then 3 layers of soluble support material and only then the actual object to be printed. It is laborious and quite a hassle but it is the only way I found to get it right.

There are probably other better ways that don't need soluble supports but I haven't explored them since I need soluble support for most of my prints anyway (to support overhangs and delicate structures)

The slicers support this to some extent.

Slic3r allows you to have 1 temp for the first layer and another for every other layer.

Skeinforge allows you to gradually lower the temperature to whatever level you want ot spread evenly over as many layers as you want to.

Not sure about cura or kisslicer.

Slic3r allows you to set the trace width for the first layer. By default it's set to 200% for the first layer for better adhesion, so you may have to change that if you want an even first layer. Also, in my experience, when printing to a heated surface the bottom layer always seems to be squashed, but when printing onto a non heated surface (PLA on blue painter tape for example) the bottom layer is more even. On my ABS prints to heated Kapton coated glass you can definately tell where the "bottom" is, but on my PLA prints to blue tape with no heat it's difficult to tell unless you know what to look for.