Raft separation distance and next layer height problem

[jomireyn3]

Hello -

I have a MakerBot Replicator 5 and have been using it with good success for several months. I got Simplify3D because I needed better control over small part tolerances such as holes and parts that need to be assembled together after printing. I'm getting much more accurate parts with S3D, but much poorer removal of parts from the rafts. I'm printing with PLA and find that I get much better adhesion with a raft, especially for very small parts.
I've tried various raft separation distances with minimal success. I've tried replicating the MakerBot raft settings, since its rafts are fine.
The Simplify3D software doesn't seem to be handling the separation distance properly, though, for distances more than .18mm or so.

The first layer after the raft prints at the right height, but the next layers print at a lower height, then move up from there.
I'm including an example with a 1mm separation height (just for illustration purposes, so it's easier to see what's happening. I know that's not a reasonable height to actually use.) I'm actually trying to use somewhere between .22 and .35)

raft settings

raft_settings.png (7.22 KiB) Viewed 25186 times

The last layer of the raft (layer 7)

The next layer, shown printing below the last layer of the raft (layer 8)

Layers 8 and up print from where layer 8 starts.
So two questions
I don't think this is how the separation layer distance is supposed to work. Is there another setting I'm supposed to change, or is there a bug that needs fixing?
Also, can anyone recommend good raft settings for a Makerbot 5th gen using PLA?

thanks

[KeyboardWarrior]

A raft separation of 1 mm is a lot, I would recommend a range of .1 to .35 mm for the separation distance. The second layer on top of the raft is not offset, because the idea is that the filament "fell" onto your raft and therefore is not elevated. The separation distance hopefully though will lead to a bit less bonding which allows for raft removal

[JATMN]

I haven't done testing to -this- extent..

I have also noticed issues with raft printing after v3 (and v3.0.1) releases.. in v2.2 I didn't have raft issues at all they worked flawlessly without any changes needed so I never bothered tweaking the settings aside from turning them on or off..

[razster]

I didn't notice any changes from v2.2 to v3.0 with the raft. Mine still works and looks exactly the same as how it did in earlier version.

[jomireyn3]

I never had v2. I bought 3.0 and had this problem from the start. I didn't test it much on 3.0, but did get the same difficult raft removal. I'm getting the same error results on 3.0.1
Looking at the preview, it looks like the 1st layer is printing correctly but then the subsequent layers are being pushed down with the hot extruder nozzle, making it stick to the raft.

When you say it works like it did before - does that mean it works well with PLA rafts or works poorly?

[jomireyn3]

A raft separation of 1 mm is a lot, I would recommend a range of .1 to .35 mm for the separation distance. The second layer on top of the raft is not offset, because the idea is that the filament "fell" onto your raft and therefore is not elevated. The separation distance hopefully though will lead to a bit less bonding which allows for raft removal

I think I mentioned that I would not use 1mm separation distance, and that I'm actually trying to use .22 to .35, and that I used the 1mm distance for illustration purposes.

"I'm including an example with a 1mm separation height (just for illustration purposes, so it's easier to see what's happening. I know that's not a reasonable height to actually use.) I'm actually trying to use somewhere between .22 and .35)

It does the same thing at any height above .2 (approx) it's hard to tell

So given, that information - any suggestions on if the software should be behaving this way or how to work around it?

[JoeJ]

That is normal. As people mentioned above, even though the plastic is extruded at the elevated position, gravity will pull it down to the surface of the raft. So when you actually print it, the next layer is in the correct position for where the plastic ends up. So what you are showing is normal.

[jomireyn3]

That is normal. As people mentioned above, even though the plastic is extruded at the elevated position, gravity will pull it down to the surface of the raft. So when you actually print it, the next layer is in the correct position for where the plastic ends up. So what you are showing is normal.

I guess I'm not expressing my question properly. I know the separation layer is elevated. That's how it is supposed to work, and it is supposed to make the subsequent layers easy to separate, but it does not.

My concern is that the next layers seem to be printed LOWER than what is supposed to be to the bottom layer of the object. The result is that the hot nozzle pushes down the next layers (layers 8 and up in my illustration) and the next layers of extruded plastic into the raft, negating the effect of inserting the separation layer. At least that's what it looks like from the tool path illustration.

Are you saying that layer 8 (and following) are supposed to be printed lower than layer 7? Or that the illustrated tool path is not correct?

In either case, at any separation distance - and I have tried everything from .1 to .4, (in .02 increments) with nearly identical results - the top layer of the raft sticks to the bottom of the object tighter than the two sections of the raft do to each other. Needlenose pliers and sandpaper are required to remove the raft.

Still looking for suggestions for settings that will let the raft be removed like it does with Markerbot Desktop

[KC_703]

What's your layer height? I find that a separation distance set to 1.5 to 2 times the layer height seems optimal for my machine. I'm guessing it may also have something to do with the extrusion temp... an extrusion temp which is too high may not set on top of the raft, and bond too well. I normally use a rectilinear external infill, this bonds the edges of the model to the raft... because more filament is deposited when the infill overlaps with the perimeter. A concentric external infill could help resolve this...

Regarding your original question, its probably best to print a test cube and measure the Z height for accuracy... it shouldn't printing the layers lower or shorter than set.

[JoeJ]

Yes, that 8th layer should be printed lower than the 7th because the 7th layer doesn't stay at the exact height where it was printed. It falls down to the surface of the raft due to gravity. So the layers are being printed at the correct height.