Raft Gap from Model

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Targo
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Raft Gap from Model

Postby Targo » Wed Nov 22, 2017 10:35 am

Hello,
When I print ABS with raft, I often have problems solving the finished model of the raft. The parameter "Raft Gap from Model" shows no effect at all, no matter if I enter 0.2 or exaggerated 0.5. Is this a mistake? Alternatively, I can retract the flow rate for the first layer, but what's this parameter for?
I have tested this with the current V2.6 as well as the current beta.

Frank

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John@Raise3D
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Re: Raft Gap from Model

Postby John@Raise3D » Wed Nov 22, 2017 9:28 pm

Targo wrote:Hello,
When I print ABS with raft, I often have problems solving the finished model of the raft. The parameter "Raft Gap from Model" shows no effect at all, no matter if I enter 0.2 or exaggerated 0.5. Is this a mistake? Alternatively, I can retract the flow rate for the first layer, but what's this parameter for?
I have tested this with the current V2.6 as well as the current beta.

Frank

Less flow rate will make the first layer less dense and it may help. Further model to raft gap may help as well. However, there are a few others factors you may want to check.
1. what is your nozzle temperature?
2.Nozzle size?
3. Layer height?
4. nozzle to bed gap?
5. filament brand?

Targo
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Joined: Fri Aug 25, 2017 9:09 am

Re: Raft Gap from Model

Postby Targo » Thu Nov 23, 2017 10:21 am

Here are my parameters for ABS
1. nozzle temp 245°
2. bed temp 110° all closed
3. nozzle size 0.4
4. Layer height 0.15
5. ABS from material4print

The printing works perfectly, mostly I print without a raft directly on a FR4 plate. I only wonder that the parameter "Raft Gap from Model" has no influence whatsoever. Even in the preview, nothing can be recognized, here actually a gap between raft and model should be seen.

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Vicky@Raise3D
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Re: Raft Gap from Model

Postby Vicky@Raise3D » Fri Nov 24, 2017 2:27 am

The gap wont be shown in Preview, but it should work during real printing. If you have any interest, you can try even larger gap to check the result more clearly or share your gcode file with us, we'd like to help check.

Targo
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Joined: Fri Aug 25, 2017 9:09 am

Re: Raft Gap from Model

Postby Targo » Fri Nov 24, 2017 6:28 pm

Here is a test file. Once with gap 0 and once with gap 1. At layer -1, everything is exactly the same. In layer 0, Gap has 0 Z at 2.02 and Gap 1 Z at 3.02. That's clear to me. But in Layer 1, the Z height is exactly the same again for both variants. Should not the Z height incrementally build up?

lay-1.JPG


lay0.JPG


lay1.JPG

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Vicky@Raise3D
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Re: Raft Gap from Model

Postby Vicky@Raise3D » Mon Nov 27, 2017 8:42 am

Normally the Z should not change from Layer 0 to Layer 1 under the default settings.
But your gap is too big (gap+ first layer height >= first layer height+ layer height), so that the filament of Layer 0 (the first layer of model) will drop off from the Z height you set to stick to the top surface of Raft, so Z value of Layer 1 will drop a little to match.

Targo
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Re: Raft Gap from Model

Postby Targo » Mon Nov 27, 2017 7:23 pm

I just do not understand. If I enter a layer thickness of 0.2 and gap between Raft and model of 0.2, G code layer 0 and 1 is output with the same Z-height. This means that two layers with the same height are printed. Try it. Or have I thought incorrectly about that?

I'm sorry if I bother :-)

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Vicky@Raise3D
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Re: Raft Gap from Model

Postby Vicky@Raise3D » Tue Nov 28, 2017 3:09 am

As the gap you set is 0.2mm, and the layer thickness of the Layer 0 is 0.2mm, then the nozzle will move to 0.4mm far to the Raft to start print the Layer 0. And the thickness of Layer 1 is 0.15mm, which means in total, there will have 0.2+0.15=0.35mm thick filament be extruded from Layer 0 to Layer 1. And the nozzle is already at 0.4mm, the space is enough to extrude these two layers.

Targo
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Re: Raft Gap from Model

Postby Targo » Tue Nov 28, 2017 5:03 pm

Vicky@Raise3D wrote:As the gap you set is 0.2mm, and the layer thickness of the Layer 0 is 0.2mm, then the nozzle will move to 0.4mm far to the Raft to start print the Layer 0.


That's how I would understand that, but it's not like that. Please try it out and have a look at the GCode.
If the gap is the same as the layer thickness, layer 0 is driven at the same Z height as layer 1. So the two layers are at the same Z height.

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Vicky@Raise3D
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Re: Raft Gap from Model

Postby Vicky@Raise3D » Wed Nov 29, 2017 3:52 am

The two layers are not at the same height, the first layer will drop to the surface of Raft from 0.4mm-height. The rest space is enough to print another 0.15mm-thick layer.

rbosworth
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Re: Raft Gap from Model

Postby rbosworth » Thu Oct 03, 2019 1:58 pm

I'm not seeing how the current implementation of raft gap from model is intentional from this conversation.
This explanation is not clear: "The two layers are not at the same height, the first layer will drop to the surface of Raft from 0.4mm-height. The rest space is enough to print another 0.15mm-thick layer." If you set a raft gap model equal to the layer height, so both a 0.1mm as an example, the gcode prints layer 0 and layer 1 at the same height (which is what Targo was talking about being a problem).
The raft gap model only creates a useless layer 0 since it just gets overwritten/smeared by layer 1, so I will copy paste from the other thread:

Has this issue been addressed as a software bug yet?

I don't know why the software would decide a raft gap for me instead of the using the setting that's suppose to control it. It seems this issue is being addressed as "You shouldn't use that raft gap value" (this should be entirely the users decision), but there's clearly a bug in the gcode beyond the software deciding a raft gap for you.

I set "Raft Gap from Model" to 0.35 mm and the Gcode contains the following:
Layer -1 (last layer of raft)
Z1.42
Layer 0 (First layer of model)
Z1.87 (The correct value according to the raft gap model and layer height=0.35mm+0.1mm)
Layer 1 (Second layer of model and the problem)
Z1.62 (This is using a raft gap model of 0.1mm after already printing a raft gap in layer 0)
Layer 2
Z1.72 (Continues on as if layer 0 never happened)

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Vicky@Raise3D
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Re: Raft Gap from Model

Postby Vicky@Raise3D » Tue Oct 08, 2019 1:18 am

rbosworth wrote:I'm not seeing how the current implementation of raft gap from model is intentional from this conversation.
This explanation is not clear: "The two layers are not at the same height, the first layer will drop to the surface of Raft from 0.4mm-height. The rest space is enough to print another 0.15mm-thick layer." If you set a raft gap model equal to the layer height, so both a 0.1mm as an example, the gcode prints layer 0 and layer 1 at the same height (which is what Targo was talking about being a problem).
The raft gap model only creates a useless layer 0 since it just gets overwritten/smeared by layer 1, so I will copy paste from the other thread:

Has this issue been addressed as a software bug yet?

I don't know why the software would decide a raft gap for me instead of the using the setting that's suppose to control it. It seems this issue is being addressed as "You shouldn't use that raft gap value" (this should be entirely the users decision), but there's clearly a bug in the gcode beyond the software deciding a raft gap for you.

I set "Raft Gap from Model" to 0.35 mm and the Gcode contains the following:
Layer -1 (last layer of raft)
Z1.42
Layer 0 (First layer of model)
Z1.87 (The correct value according to the raft gap model and layer height=0.35mm+0.1mm)
Layer 1 (Second layer of model and the problem)
Z1.62 (This is using a raft gap model of 0.1mm after already printing a raft gap in layer 0)
Layer 2
Z1.72 (Continues on as if layer 0 never happened)


Would you like to share your gcode and data files with us? So that we can find more information from there.

Stevie
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Re: Raft Gap from Model

Postby Stevie » Fri Oct 18, 2019 6:11 am

As I already figured out this is definitely a bug... And very easy to reproduce... Second to last layer does completely ignore the gap layer - only the first model layer is at correct z level...

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Vicky@Raise3D
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Re: Raft Gap from Model

Postby Vicky@Raise3D » Sat Oct 19, 2019 12:40 am

As we have explained above, the first layer of the model has a gap with Raft, but the filament will still drop from the height nozzle extrudes the filament onto Raft. If keeping on letting nozzle moving up and printing from that height, the each layer after first layer will be extruded in the air and drop to the last layer placed. If so, the bounding among all the layers on model will be very weak and loose.

Stevie
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Joined: Tue Sep 24, 2019 8:44 am

Re: Raft Gap from Model

Postby Stevie » Mon Oct 21, 2019 8:16 am

Vicky@Raise3D wrote:As we have explained above, the first layer of the model has a gap with Raft, but the filament will still drop from the height nozzle extrudes the filament onto Raft. If keeping on letting nozzle moving up and printing from that height, the each layer after first layer will be extruded in the air and drop to the last layer placed. If so, the bounding among all the layers on model will be very weak and loose.


But that should exactly be what I would expect if I set a GAP between raft and model...

And sorry to say but it can NOT be intended that the second layer lies deeper than the first layer... this HAS to be a bug...

The nozzle should constantly get higher on each layer to get a decent quality... and not to jump up and down and up again on different layers...

Did you ever try to load the generated gcode with a (too high but illustrating) gap into some software capable of showing gcode like simplify3d? This is so very obvious that there is something wrong - I am a bit suprised that we discuss this topic for so long...

Here are some lines I copied from attached GCODE file - extreme gap with 5mm... :
;LAYER:-2
;Z:0.500
;HEIGHT:0.500
G0 F300 Z0.500

;LAYER:-2
;Z:1.000
;HEIGHT:0.500
G0 F300 Z1.000

;LAYER:-1
;Z:1.380
;HEIGHT:0.380
G0 F300 Z1.380

;LAYER:-1
;Z:1.600
;HEIGHT:0.220
G0 F300 Z1.600

;LAYER:-1
;Z:1.820
;HEIGHT:0.220
G0 F300 Z1.820

;LAYER:0
;Z:7.020
;HEIGHT:0.200
G0 F300 Z7.020

;LAYER:1
;Z:2.220
;HEIGHT:0.200
G0 F300 Z2.220

;LAYER:2
;Z:2.420
;HEIGHT:0.200
G0 F300 Z2.420
...
Attachments
RaftBug.gcode
(947.95 KiB) Downloaded 54 times
RaftBug.data
(84.05 KiB) Downloaded 60 times

rbosworth
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Re: Raft Gap from Model

Postby rbosworth » Mon Oct 21, 2019 11:09 pm

I'd post my Gcode, but Stevie perfectly illustrates the problem again. The next layer should be 7.220, and not 2.220.
What purpose does this setting serve when it's immediately overwritten by what the software thinks is the "right" layer height on the very next layer?
The simple fact is that it's not the correct layer height and makes it extremely difficult/impossible to remove from the raft and ruins the bottom layer quality.

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Vicky@Raise3D
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Re: Raft Gap from Model

Postby Vicky@Raise3D » Tue Oct 22, 2019 12:58 am

In real print with the gcode you attached above, at which height does the first layer print? At 7.02mm height or some other height? How does the first layer look on Raft before printing the second layer?

rbosworth
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Joined: Thu Oct 20, 2016 2:25 pm

Re: Raft Gap from Model

Postby rbosworth » Thu Oct 31, 2019 1:53 pm

Vicky@Raise3D wrote:In real print with the gcode you attached above, at which height does the first layer print? At 7.02mm height or some other height? How does the first layer look on Raft before printing the second layer?


It's shown in Stevie's gcode. The first layer prints at 7.02, but the next layer prints at 2.22. Given this was extreme to illustrate the problem.

From my own experience with my raft gap the first layer prints perfectly, but the second layer just smears it and fuses the print to the raft. I've developed my own program to iterate through the gcode to increment every layer to continue after the raft gap layer instead going back down. Went from failed prints fused to the raft with poor quality bases, back to good quality prints.

Example of my Gcode reposted:

I set "Raft Gap from Model" to 0.2 mm and the Gcode contains the following:

Code: Select all

Layer -1 (last layer of raft)
Z1.42
Layer 0 (First layer of model)
Z1.72 (The correct value according to the raft gap model and layer height=0.2mm+0.1mm)
Layer 1 (Second layer of model and the problem)
Z1.62 (This is using a raft gap model of 0.1mm after already printing a raft gap in layer 0)
Layer 2
Z1.72 (Continues on as if layer 0 never happened)

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Vicky@Raise3D
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Re: Raft Gap from Model

Postby Vicky@Raise3D » Fri Nov 01, 2019 1:05 am

We will consider to add an option for a compensate height for the layers after the second layers. So that the second layer will be printed out at higher position.


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