Printing a part with multiple extruders

[Abinav_Shankar 0]

Hi,

I am trying to print a CAD model with two different extruder nozzles - AA0.4 and AA0.8. I need to print only the first few layers with high quality because of some text in it. After the first few layers, I don't need high accuracy. So, I am trying to print them with 0.8 nozzle to speed up the process.

 

I read somewhere that, I can just change the extruder at the specific point. But I don't see how that will change anything because the layer heights still remain the same. Also, won't that cause an issue because of extrusion volume being mentioned in each line? 

 

Is there an other way to handle this? Any suggestion would be greatly helpful.

 

Thanks!

Edited January 24, 2022 by Abinav_Shankar

[gr5 2,172]

I don't understand your point about extrusion volume.  The extrusion volume is calculated based on each "line" that is printed by multiplying layer height by line width by line length.

 

You do have an issue as you can change many things for just one area (volume really) of the model but not layer height.

 

The AA 0.8 can indeed print a little bit faster with the wider lines.  About twice as "fast" because if your walls are 0.8mm wide then you are printing 2 passes on the shell with the 0.4 and one pass with the 0.8.  But if your wall width is 1.2mm then you save nothing.  The big savings with a 0.8 - half of that comes from thicker layers which you can't really do.

 

[Abinav_Shankar 0]

On 1/24/2022 at 3:22 PM, gr5 said:

I don't understand your point about extrusion volume.  The extrusion volume is calculated based on each "line" that is printed by multiplying layer height by line width by line length.

 

You do have an issue as you can change many things for just one area (volume really) of the model but not layer height.

 

The AA 0.8 can indeed print a little bit faster with the wider lines.  About twice as "fast" because if your walls are 0.8mm wide then you are printing 2 passes on the shell with the 0.4 and one pass with the 0.8.  But if your wall width is 1.2mm then you save nothing.  The big savings with a 0.8 - half of that comes from thicker layers which you can't really do.

 

 

So, if I understood correctly, the extrusion volume only depends on the line being printed and is independent of the extruder nozzle size. So, I can just change the extruders without altering any "E" values and it should speed up the printing process as expected if the wall width is appropriate, is that correct?

[gr5 2,172]

5 hours ago, Abinav_Shankar said:

I can just change the extruders without altering any "E" values and it should speed up the printing process

what?  So far the answer is no.  If you slice for 0.4 core with line width set to 0.4mm and you put  in a 0.8 core it will not speed up anything - the AA 0.8 core will be printing 0.4 lines.  But then there is more to your sentence - which doesn't seem to change the answer but I'm not sure I understand you.  So I think still "no".

 

The AA 0.8 core tends to print 4X faster because of the cura settings - because you are going to do 0.8mm line width (instead of 0.4 or so) and because you are going to print doubly thicker layer heights.  Twice as wide, twice as thick, gives you 4X speedup.

 

The AA 0.8 can print thicker layer heights for any given "print speed" partly because it has much larger hole in it so the friction is lower getting that volume of plastic through the nozzle hole.

 

But in your case you are trying to print the lower half 0.4 and upper 0.8 and cura won't let you change the layer height part way through.  It lets you change the line width, but not layer height.  I could explain why but it won't help you.

 

If you are only printing one part you should "bite the bullet" and just print the whole thing with a 0.4.  If you are printing 100 parts you can fudge things.  You can slice for each nozzle and splice two jobs together.  With tricks to fix the jump in E value at the splice.  But it's a little tricky and not worth the trouble if you can print this thing in under 4 days.

 

 

 

[Abinav_Shankar 0]

On 1/26/2022 at 3:14 PM, gr5 said:

what?  So far the answer is no.  If you slice for 0.4 core with line width set to 0.4mm and you put  in a 0.8 core it will not speed up anything - the AA 0.8 core will be printing 0.4 lines.  But then there is more to your sentence - which doesn't seem to change the answer but I'm not sure I understand you.  So I think still "no".

 

The AA 0.8 core tends to print 4X faster because of the cura settings - because you are going to do 0.8mm line width (instead of 0.4 or so) and because you are going to print doubly thicker layer heights.  Twice as wide, twice as thick, gives you 4X speedup.

 

The AA 0.8 can print thicker layer heights for any given "print speed" partly because it has much larger hole in it so the friction is lower getting that volume of plastic through the nozzle hole.

 

But in your case you are trying to print the lower half 0.4 and upper 0.8 and cura won't let you change the layer height part way through.  It lets you change the line width, but not layer height.  I could explain why but it won't help you.

 

If you are only printing one part you should "bite the bullet" and just print the whole thing with a 0.4.  If you are printing 100 parts you can fudge things.  You can slice for each nozzle and splice two jobs together.  With tricks to fix the jump in E value at the splice.  But it's a little tricky and not worth the trouble if you can print this thing in under 4 days.

 

 

 

 

I am going to print 100s of parts, that's why any improvement on speed is important.

 

But thanks for the info. I'll try slicing for two nozzles and put that together and see if it works. Looks like a really clever workaround.

[gr5 2,172]

Okay so you need to read and learn about the G92 command.  So you can reset one or multiple axes.  You will have to reset the E axis to a specific value.  So...

 

In the gcode for these prints the E value will just keep getting larger.  For example E1000 is when you have printed 1 meter (1000mm) of filament.  The next E value in the file might be:

G1 X100.13 Y75.33 E1000.2  (this says move X, Y and E axis to these new positions)

 

That would mean it will be extruding 0.2mm of linear filament on the next "line" of filament printed.  This is called "absolute position" on the E axis.

 

So the 2 gcode files you are merging will be off by E and if you just start the next file on  aprticular layer one might end around E500 and the other start at E470.  The problem is it will back rotate the extruder by 30mm.  Or if it's say 500mm you will run the filament backwards right out of the extruder.  Or it might *overextrude* if the values are off in the other direction.

 

So you hadd a single G92 command in between at the splice of the two files.  If one is ending at E100 and the other one starts at E200.734 you can just add a 

G92 E200.734      <-- this tells the printer that the extruder is not where it thinks it is but is actually at location 200.734mm.

 

In between the end of the first gcode file and the start of the next.  Even better - use the E value that was the most recent just before the splice on the new file - so if this line of code gets thrown away just before the splice on the new file:

G1 X100.33 Y134.3 E75.3

You can delete that line and all above before you add to the end but insert the G92 like this

G92 E75.3

 

[gr5 2,172]

If you don't understand my post above 100% do not do the splice!!!!!!!!!!!1   Just read it a few times until you understand or ask questions.

[Abinav_Shankar 0]

On 1/28/2022 at 8:38 PM, gr5 said:

If you don't understand my post above 100% do not do the splice!!!!!!!!!!!1   Just read it a few times until you understand or ask questions.

Thanks for the detailed explanation. It's clear what you are trying to explain.

 

I just have one question. Does making the extruder think that it is in a different feed position and giving it a new value, also affect the filament quantity that is shown on the 3D printer? Say, I jump from E100 to E200, does the printer think, the 100mm of filament skipped as already used and reduce that from the quantity left?

 

Because it's a common printer shared by multiple people at office, I don't want to confuse them with these kind of work.

[gr5 2,172]

Ah!  I don't know.  There are comments among the gcode at the top of the file that say how much filament will be used in total.  But I'm not sure the printer displays remaining filament?  does it?  I forget.

 

There are also comments on each layer estimating how much time to print the rest of the print.  So those numbers will probably help the printer show accurate times when it gets past layer 100.

 

In theory it should use about the same amount of filament either way.  You can mess with that comment at the start of the file that says how much filament it will use such that it comes out perfect at the end but I don't know how that works exactly.

[GregValiant 1,251]

Hi @gr5 and @Abinav_Shankar.

I thought I'd stick my nose in for a second as I've printed quite a few "file-on-file" projects.

 

"G92 E0"

Cura always resets the E number when the volume approaches 10,000mm³ during any print.  From what I've read it's because the constant rounding off of the E value starts to produce significant errors.  For 1.75mm filament the max "E" would be 4158 and for 2.85 filament it would be 2233mm of filament.  So if a print is large enough there will be a few "G92 E0" lines present in the Gcode.  I don't know how an Ultimaker keeps track of the total filament used.  If it is by the total steps sent to the E motor or if it reads "filament used" from the file then the G92's wouldn't matter.

 

File-on-file.

I spent more than a little time writing some code to splice files automatically.  It was a pain.  It finally occurred to me that Pause at Height always calculates a restart position for all 4 axes.  So I enter a pause at the layer I want and slice the file and create the Gcode for the bottom half of the print.  Then I change the layer height, line width, or switch to extruder 2, etc., and re-slice the model and produce the second gcode.  I open the second gcode file look through it to find the layer at the correct Z (or close enough) and adjust the Pause at Height Layer number, and slice again.  In the base file I discard everything below the line ";Current Layer" (that Pause at Height adds) and discard it.  Then in the second file I select everything from the "resume temperature" line through the end of the file and copy it into the first file.

The restart position XY of the first extrusion are present as well as the G92 to sync the extruder and the resume Z height.  A check of the XYZ is just prudence and there might be an adjustment that has to be made (usually the Z) but with a bit of practice the system works very well and the transitions are seamless.  In this case you would want to make sure that the Tool switch occurs and that a purge happens (if required).

 

At any rate I hope that helps (or at least doesn't hurt).

Edited January 30, 2022 by GregValiant

[Abinav_Shankar 0]

3 hours ago, GregValiant said:

Hi @gr5 and @Abinav_Shankar.

I thought I'd stick my nose in for a second as I've printed quite a few "file-on-file" projects.

 

"G92 E0"

Cura always resets the E number when the volume approaches 10,000mm³ during any print.  From what I've read it's because the constant rounding off of the E value starts to produce significant errors.  For 1.75mm filament the max "E" would be 4158 and for 2.85 filament it would be 2233mm of filament.  So if a print is large enough there will be a few "G92 E0" lines present in the Gcode.  I don't know how an Ultimaker keeps track of the total filament used.  If it is by the total steps sent to the E motor or if it reads "filament used" from the file then the G92's wouldn't matter.

 

File-on-file.

I spent more than a little time writing some code to splice files automatically.  It was a pain.  It finally occurred to me that Pause at Height always calculates a restart position for all 4 axes.  So I enter a pause at the layer I want and slice the file and create the Gcode for the bottom half of the print.  Then I change the layer height, line width, or switch to extruder 2, etc., and re-slice the model and produce the second gcode.  I open the second gcode file look through it to find the layer at the correct Z (or close enough) and adjust the Pause at Height Layer number, and slice again.  In the base file I discard everything below the line ";Current Layer" (that Pause at Height adds) and discard it.  Then in the second file I select everything from the "resume temperature" line through the end of the file and copy it into the first file.

The restart position XY of the first extrusion are present as well as the G92 to sync the extruder and the resume Z height.  A check of the XYZ is just prudence and there might be an adjustment that has to be made (usually the Z) but with a bit of practice the system works very well and the transitions are seamless.  In this case you would want to make sure that the Tool switch occurs and that a purge happens (if required).

 

At any rate I hope that helps (or at least doesn't hurt).

That's some valuable info, Thanks!.🙂