Raft separation distance and next layer height problem

[jomireyn3]

Thanks for your efforts on this, Doug. That seems to confirm what I'm seeing in the print previews, despite the support team telling me that the preview doesn't represent what actually happens

To reiterate what I said......the preview DOESN'T represent the end result of the extrusion process, quite correctly as the S3D support staff say. It does, however represent EXACTLY what the slicer code is telling the hardware to do.

What is in question is the reasoning behind extruding the first layer in fresh air a certain distance above the raft....the possible theory being to allow the layer to "rest" on top of the raft - and thus not adhering strongly,....and then ramming the layer down into the raft by extruding the second layer of the model as if the first layer had been extruded normally.

Using common sense, I would work on the principle that the first layer having been "rested" on the raft, then the height of the nozzle for extruding the second ( and subsequent layers) would be very slightly higher....to take into account the non-squished first layer. The alternative would not to bother at all with trying to allow any separation at all!

Got it. . It seemed to me that the preview and the printer's action were very similar, if not the same.
Thanks for the clarification

[billyd]

fwiw I agree rafts are broken in version 3. I thought there was something wrong with my settings, but I never had to touch them in prior versions so this upgrade has clearly broken the raft function. Kind of irritating to see people claiming it's supposed to work this way and it's not a bug. And preview shows exaclty what the tool head is doing, so if preview is wrong the gcode is wrong period.

[dkightley]

And preview shows exaclty what the tool head is doing, so if preview is wrong the gcode is wrong period.

Would it be cruel of me to ask you to explain what you believe is wrong....and what needs doing to correct it. I've given my thoughts....and I'd like to compare mine with others'.

[PPLDC3]

What I would like it to do is this. Let's say that we have a standard layer height of .2mm, and a raft separation of .15mm.

Instead of printing like this....

Layer 1 Height (Raft): 0mm
Layer 2 Height (Raft): .2mm
Layer 3 Height (Raft): .4mm
Layer 4 Height (Raft): .6mm
Layer 5 Height (Raft): .8mm
Layer 6 Height (Raft): 1mm
Layer 7 Height: 1.35mm
Layer 8 Height: 1.4mm
Layer 9 Height: 1.6mm

In the above example, every layer except layer 7 comes out at the exact same height that it would have if we'd had absolutely no raft separation distance at all. And with Layer 8 squishing down the filament while it's still hot, down to the same height it would have printed without any separation, the raft separation setting basically becomes useless.

What I would like it to do is print like this:

Layer 1 Height (Raft): 0mm
Layer 2 Height (Raft): .2mm
Layer 3 Height (Raft): .4mm
Layer 4 Height (Raft): .6mm
Layer 5 Height (Raft): .8mm
Layer 6 Height (Raft): 1mm
Layer 7 Height: 1.35mm
Layer 8 Height: 1.55mm
Layer 9 Height: 1.75mm

Yes, in the second example, Layer 8 would be printing with slightly more of a gap than it should above Layer 7, because Layer 7 has dropped down onto the raft. However, this effect would be negligible, and all but insignificant by the time you print a few more layers.

[dkightley]

Taking this a step further, I see two parameters.....a Drop Height and a Settlement Height. The drop height would determine how high the first layer is "dropped" from, which would affect how the first layer of the model would stick to the top raft layer...and the settlement height would be the height at which the slicer would consider the "dropped" layer to be at so as to determine the height of all following layers. Testing would need to be done to determine either if the settlement height can be derived from the Drop Height and filament type/temperature, etc, or whether adjusting the Drop height is irrelevant or not.

Using the above as a reference, with a Drop Height of 0.3mm and a Settlement Height of 0.5mm, the print would now be:

Layer 1 Height (Raft): 0mm
Layer 2 Height (Raft): .2mm
Layer 3 Height (Raft): .4mm
Layer 4 Height (Raft): .6mm
Layer 5 Height (Raft): .8mm
Layer 6 Height (Raft): 1mm
Layer 7 Height: 1.50mm
Layer 8 Height: 1.45mm
Layer 9 Height: 1.65mm

Of course, the preview would still look as if its wrong....unless the first layer is shown at it's "dropped height", in which case it would appear to reflect real life - and not what the slicer is actually doing!

[jomireyn3]

What I would like it to do is this. Let's say that we have a standard layer height of .2mm, and a raft separation of .15mm.

Instead of printing like this....

Layer 1 Height (Raft): 0mm
Layer 2 Height (Raft): .2mm
Layer 3 Height (Raft): .4mm
Layer 4 Height (Raft): .6mm
Layer 5 Height (Raft): .8mm
Layer 6 Height (Raft): 1mm
Layer 7 Height: 1.35mm
Layer 8 Height: 1.4mm
Layer 9 Height: 1.6mm

In the above example, every layer except layer 7 comes out at the exact same height that it would have if we'd had absolutely no raft separation distance at all. And with Layer 8 squishing down the filament while it's still hot, down to the same height it would have printed without any separation, the raft separation setting basically becomes useless.

What I would like it to do is print like this:

Layer 1 Height (Raft): 0mm
Layer 2 Height (Raft): .2mm
Layer 3 Height (Raft): .4mm
Layer 4 Height (Raft): .6mm
Layer 5 Height (Raft): .8mm
Layer 6 Height (Raft): 1mm
Layer 7 Height: 1.35mm
Layer 8 Height: 1.55mm
Layer 9 Height: 1.75mm

Yes, in the second example, Layer 8 would be printing with slightly more of a gap than it should above Layer 7, because Layer 7 has dropped down onto the raft. However, this effect would be negligible, and all but insignificant by the time you print a few more layers.

Your second example is exactly what I would expect to happen - if I have specified a gap of .35, I would expect the nozzle to be .35 mm higher for the next layer,, and since I know that the nozzle is pushing out molten plastic, I understand that it may not stay there, and I'm ok with having to experiment a little to see what works best for my printer and the particular filament for that job.

[billyd]

And preview shows exaclty what the tool head is doing, so if preview is wrong the gcode is wrong period.

Would it be cruel of me to ask you to explain what you believe is wrong....and what needs doing to correct it. I've given my thoughts....and I'd like to compare mine with others'.

In a nutshell, anything printed on a raft in version 3 becomes one with the raft. I have never had such good adhesion between layers as I do between a part and the raft in version 3 lol. And the settings for gap above raft don't seem to change anything with respect to sticking to the raft. This never happened in prior versions with the stock settings.

[krouviere]

IMHO, all of this just goes away by returning to the way it worked in 2.x.
I doubt anyone has benefited from the way this has been changed for 3.x.
The feature is broken. I've been hoping to see a new release with it restored to the way it worked before in 2.x, which was logical and sensible.
The generated g-code shows pretty clearly that it's being stupid. The preview agrees accurately enough to show the same thing.
All of the talk and theory about the drop height, falling, etc is just not necessary and is just a distraction.
I'm disappointed that the dev team hasn't just come out and admitted it was a mistake. That I can accept.

[jgrouse]

I'm getting around this bonding issue by inserting a pause after the raft to let the raft cool and allow me to apply a very light and very quick swipe from a distance coat of hairspray. This light dusting of hairspray allows the object to come off the raft easier without it popping off during printing. Combined with a breeze free enclosure I'm getting good results.

[Tesse]

Hi,
i think there is a bug in the software when using rafts.

The issue is with the placement of the 2nd object layer (layer 6 on the pictures below).

To visualize the problem, I used a seperation distance of 1mm. The same issue apears on a smaller distances, but it would not be as easy to detect on the pictures. Yet you can see the issue clearly in every gcode.

The Problem:
The 1st object layer (layer 5 on the pictures below) is placed correctly, according to the choosen seperation distance.
The 2nd object layer (layer 6 on the pictures below) is then located underneath the 1st object layer. BUG!
The next layers build up ontop of that.

I hope this will get fixed soon. Any help?

~ Tesse

layer1-5: So good so far.

layer1-6: 2nd object layer not placed correctly.

layer1-7: the next layers build up ontop...

[/i]