Bottom Layer Speed

[rachael7 74]

I'm working on a print that has quite a bit of support. The supports start both from the buildplate and from the model. Filaments are ABS and PVA. I'm having some trouble getting the ABS to stick when it goes down onto the support interface. Having checked temperatures and fan speeds, my next thought for this is to decrease the speed of the ABS layer that is directly on the support. So I went to the speed section, looking for the bottom layer speed, and I was surprised to find that top and bottom layers share a single speed setting. So if I lower the speed, it not only slows all the layers of the bottoms, but also all the layers of the tops, and it adds an unacceptable amount of time to the print. Is there any way to get each first bottom layer to print slowly without slowing down all the top/bottom layers?

[GregValiant 1,412]

There are at least 3 ways.  I think this is the one you are looking for.

In Speed - set the "Number of Slower Layers" to 1.  That will make the "Initial Layer Speed" setting visible and you can enter whatever you like for the first layer.

[rachael7 74]

19 minutes ago, GregValiant said:

There are at least 3 ways.  I think this is the one you are looking for.

In Speed - set the "Number of Slower Layers" to 1.  That will make the "Initial Layer Speed" setting visible and you can enter whatever you like for the first layer.

Thanks for the reply. As far as I understand though, that only applies to the first layer against the buildplate. If the first layer of the material is not on the bed, as would happen if  you printed a raft from the other material or when it is a bottom layer that occurs higher up (like an overhang), then the initial layer speed does not apply. Is that understanding incorrect?

[GregValiant 1,412]

The initial layer is Layer:0.  The raft layers are negative numbers so your first slow layer would be the first layer of the part.

 

In higher layers then yes, that setting wouldn't work for you.  Instead, you can find the layer (minus "1") in the gcode and manually add an M220 command.  (M220 S50 would tell the printer to compute all of the speed entries at 50%.)  At the next layer you would add M220 S100 to return the printer to 100% feedrate.

 

The Search and Replace plugin will accept multiple commands as replacement text so long as they are separated by "\n" (backslash+n) the new line character.  You would want two instances of Search And Replace active.  (Extensions menu, Post-Processing | Modify Gcode and then Add a Script).

 

So you are looking at your preview and you see that at layer 29 a feature starts on top of the support and you want to slow down to 33% for it.  (Again - remembering that Cura is base 1 and gcode operates from base 0:

Search = ;LAYER:28

Replace = ;LAYER:28\nM220 S33 

(By putting the "LAYER:28" comment line back in the gcode it remains easily searchable.)

The next instance of Search and Replace might be configured:

Search = ;LAYER:29

Replace = ;LAYER:29\nM220 S100

 

For each layer you want to slow down for, you can add two more Search and Replace instances.  One will reduce the speed at the layer of interest, and the next will return the speed to 100% at a later layer.

Edited December 8, 2021 by GregValiant

[rachael7 74]

12 minutes ago, GregValiant said:

The initial layer is Layer:0.  The raft layers are negative numbers so your first slow layer would be the first layer of the part.

 

In higher layers then yes, that setting wouldn't work for you.  Instead, you can find the layer (minus "1") in the gcode and manually add an M220 command.  (M220 S50 would tell the printer to compute all of the speed entries at 50%.)  At the next layer you would add M220 S100 to return the printer to 100% feedrate.

 

That would indeed work. If there were only a couple of spots, it would be a very elegant solution indeed. Unfortunately, this part is pretty tall though, almost 1000 layers, and there are overhangs that put "bottom" portions on probably 1/3 of the layers or more, so it would slow down the print a tremendous amount, almost as much as if I just set the top/bottom speed for the whole print. Thanks again for bouncing it around with me though, most appreciated!

[GregValiant 1,412]

I'm right at the bottom of the list of people around here for coding but within the gcode a ";TYPE:SKIN" is a skin whether it's on the top or the bottom or a fill for an angled feature that is trying to maintain wall thickness.  So searching for TOP or BOTTOM won't work.  It would take as long to make a list of layers and to hand code each occurrence of the "bottom of interest" as it would to just print the thing at the lower speed.  Then there is the outer and inner walls that go around the "Bottom of Interest".

I'm sorry I couldn't be more helpful.  Maybe someone else will have a different take on it.  I seem to recall that there was a request on Github for a new feature that would split Top/Bottom speed into two settings.  I don't know what the Cura team has in mind about that.  That wouldn't really help a lot in your case but post-processing might be a tad easier.  It would have to be easier than manually adding 300*2 M220 lines.  It would be really easy to get bored and make a typo or ten.

Good Luck.