Ability to enter the absolute overall print speed in mm/s

[laptop-laptop]

Is your feature request related to a problem? Please describe.

Feature request: Ability to change the overall print speed to a specific speed in mm/s.

Asked Prusa support and three agents could not provide an answer on how to change the overall print
speed of the i3MK3S+ to a specific speed in mm/s. For example, I want to change the overall print speed to
20%. Two agents told me to use the dial to change it. However, the dial is in percentage, not in absolute
value. They also could not tell at what speed does such percentage is based on. All three of them don't know the default overall print speed of the printer. They also mentioned about changing the speed in the slicer but could not tell which parameters to change.

In Super Slicer, there are many speed settings. Some of them are also in percentage. If I want to change the overall print speed to a specific value, say at 20mm/s, which parameter(s) should I modify? As I don't know the default print speed of the printer, I cannot use percentage correctly.

Describe the solution you'd like

In the slicer, allow the users to enter the desired overall print speed in mm/s.

Describe how it would work
See above

[Area5142]

A suggestion:

If you like to change the overall speed of all print moves, the dial on the printer can be used or gcode M220 can be inserted into the print file. To reduce all speeds to 20%:

M220 S20 ; Reduce print speed to 20%

The effect of M220 is until changed or restart (power on/off).

I use this method to reduce travel speed for the first layer to prevent small details detaching from the build plate and stick to the nozzle. In SuperSlicer (or PrusaSlicer) this is the only way I can reduce travel speed for only first layer.

[laptop-laptop]

I know about M220 and the dial but the problem is it is expressed as percentage. So percentage of which speed parameter? For example, if the printer prints at 100 mm/s, 20% means 20 mm/s. If the printer prints at 200 mm/s, 20% means 40 mm/s. So just M220 S20 could be speed other than 20mm/s.

If I want to print at a specific speed of 20mm/s, what should I do?

[Area5142]

Absolute speeds (mm/s) can only be set in the g-code (by the slicer program).
There are more than one specific speed to set: Travel speed, perimeter speed, first layer speed, external perimeter speed, infill-speed and a lot more.

Which speed do you want to set?

Slicer profiles can always be defined for different job types, setting the required speeds for that job type.
The physical printer may run slower than specified in the g-code due to physical limits as acceleration, motor power or limits in the firmware.

[supermerill]

You can use the auto-speed: set everything to 0 (but gap fill and thin walls), and set the max speed at the bottom (max_print_speed).
Set the max_volumetric_speed to 0 if you don't use it.
It won't print everything at the same speed, as it will try instead to keep the same volumetric speed for everything (but gap fill and other very thin things)

[laptop-laptop]

Thank you. There are two cases. Case 1 is to set the speed of the overall print job. For example, some filaments or downloaded prints require different print speeds. Case 2 is to set the speed when printing specific parts.

Let's separate them for the following discussions:

I guess your suggestion is for Case 1. Under Speed- for print moves->Thin extrusions speed->Gap fill, I have 40 mm/s and under Thin walls, I have 30 mm/s. When I use your method to set everything else to zero and then the max_print_speed to the overall print speed I want, what should I put under Gap fill and Thin Walls? Under Max print speed, I have 200 mm/s. I don't recall entering such value myself.

In Case 2, is the special layer that is in between the top of Support and the Overhang surface (i.e. the special layer that is made up of the Overhang Perimeter and Bridge Infill) part of Support or part of the model? If I want this special layer and support interface layers to print at 20mm/s, what should I do?

[laptop-laptop]

Under High Range Modifier->Add Settings->Speed, there is an option called "Default speed". What is that for? Default speed for which setting(s)?

[supermerill]

Under High Range Modifier->Add Settings->Speed, there is an option called "Default speed". What is that for? Default speed for which setting(s)?

It's a typo, should be "Perimeter speed", will fix that.

Case 1. [...] what should I put under Gap fill and Thin Walls?

I don't know, whatever your printer is capable of. Default values should be okay in most printers.

In Case 2, [...] what should I do?

you can add all speeds in the modifier and set them to the value you want.

[laptop-laptop]

Thank you. In the slicer, does the layer that is made up of the Overhang Perimeter and Bridge Infill part of support or part of the actual model?

[supermerill]

model.
support things are colored to support color

[laptop-laptop]

Thank you. I can see that without support, the Overhang Perimeter and Bridge Infill parts are still there. So they became part of the model.

Here is the confusion: Supposing that I am printing an inverted L-shape consisting of a vertical and a horizontal bars. Now the Bridge Infill and Overhang Perimeter show up at the bottom of the horizontal bar. Does that mean SuperSlicer modified my model by: a) replacing the bottom flat surface of the horizontal bar by a series of Bridge Infill parallel lines along with an Overhang Perimeter as the outline of the rectangular shape or b) added an extra layer of 0.15mm (my layer height) consisting of Bridge Infill parallel lines and Overhang Perimeter at the bottom of the horizontal bar of the inverted L-shape? Accuracy is very important for me as I join various parts together. I need to know.

[supermerill]

It extrudes the unsupported layer with more flow, as you can't squish the filament against the previous layer, it stays as a cylinder.
I'll add an option to get the bridge flow equivalent to the current layer height after prusaslicer merge.
Currently, you have to compute it yourself.
current 100% bridge flow is a circle of nozzle diameter diameter. If you want it to be of your layer height, you have to reduce the flow to get the bridge flow diameter equal to the layer height.

formula : ratio = 100 * layer_height² / nozzle_dimeter²
If you have 0.4mm nozzle and 0.2mm layer height, you have 100 * 0.04/ 0.16 = 25, so you have to set bridge flow to 25%

[laptop-laptop]

Thank you. I am using a 0.4mm nozzle and 0.15 mm layer height. So ratio = 100 * 0.0225 / 0.16 = 14%?

If I use water soluble on support below the horizontal bar of the inverted L-shape object as well as on the layer with Overhang Perimeter and Bridge Infill to avoid seeing those parallel Bridge infill, the horizontal bar of the inverted L-shape model will be 0.15mm less thick?

[supermerill]

yes
no bridge flow if using soluble support interface.

[laptop-laptop]

Thank you. I will try both methods and see which is better for my case.