THC cutoff % when using multiple feed rates

I’ve been looking at some gcode generated from sheetcam (1.5 post) and wondering how the THC cutoff % calculation works when you have multiple layers with different defined feed rates. Sorry if it’s already been asked - I couldn’t find a post similar.

For example, I have a simple 2 layer drawing. First layer is some letters that I’ve defined a tool at 150 IPM. Second layer is an outline using a tool at 201 IPM.

When I look at the post, I see the last few lines as:

G0 Z1.0
M5 M30
<end of file>

In the first layer I see sections that start:
G3 X1.2944 Y0.6363 I-0.0 J0.064 F150.0
The F150.0 being the feedrate defined for that layer.

In the second layer I see sections that start:
G3 X1.165 Y0.035 I-0.064 J0.0 F201.0

F201.0 being the next (and highest) feedrate…

From what I can tell from looking at the post file logic, the fastest feed rate / program speed is what is written to the last line (PS XXX) - in this case 201 IPM. I did see in the manual it says the program speed is set when the program is loaded - guessing firecontrol uses the PS201 value.

The initial feed rate for layer 1 (150 IPM) is under 85% of the max feedrate (201 IPM) so it seems the THC would be inactive for that whole section even though I wanted THC on.

Is there a way to define multiple cut speeds for THC cutoff purposes or is this just a one shot deal? For example if slower sections are first will they get 85% of 150 and later sections will get 85% of 201.

At this point there is only one cutoff value per program. You can change it on the fly while cutting (via the THC module) or select a value that is lower to have THC on in the letters- something like 70%.

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Thanks for reply! Adding to the knowledge bank…