Start print higher than buildplate

[3DPiper 0]

I have a large format printer with a removable magnetic flexible build plate.

I need to print two parts that will precisely fit together.

The sides that should fit together are printed down touching the build plate.

The build plate is not exactly level, so fitting the parts together is not good.

I have auto-leveled the print head, but that just makes it follow and print on the un-level bed.

Can I start printing the parts a few mm above the build plate and print exactly flat?

I have tried a raft, but that still just follows the un-level bed and my parts still come out warped on the bottom.

I need the bottom of the parts to be exactly flat, not warped because the bed is warped.

 

[GregValiant 1,258]

The Z=0 is set by leveling.  If the bed isn't flat, and all your mechanicals are always at 90° to each other and stay "in plane" while printing, then you really need to fix the bed because you have a hardware problem.  You cannot print in the air.

 

Some of the upscale ABL systems will compensate for an uneven bed over the first couple of layers so that by (call it) layer 3 the print is leveled out.  There will be areas of over and under extrusion because of that.  The reason is that the E values in the gcode were calculated for a level surface and not one where the Z keeps changing randomly.

 

You need to address the bed problem.  If the waviness is random it's tough but if you know the low spots then stick a custom cut-out piece of aluminum foil (or 3) under the magnetic surface to shim certain areas up.

 

An alternative would be to go with a glass surface even if it's just for this one job.

 

Edited September 11, 2023 by GregValiant

[3DPiper 0]

Sorry, I may have misspoke. I didn't mean floating in the air, I meant force supports etc so by 3mm above the bed everything should be level and flat and start printing the actual model there. I guess I can model my own supports externally?

We have the bed close to level by shimming under the flexible sheet, but I don't think we will get it glass smooth flat and level.

If the two halved didn't have to exactly mate, it wouldn't matter. We use it for other prints all the time and are very happy with it. We assumed it to be level until we did this print and were surprised to see they would not mate.

[GregValiant 1,258]

Ah.  That's better.

In the Cura "Preferences" turn off "Automatically drop models to the build plate".

In the "Mesh Fixes" settings make sure "Remove empty first layers" is disabled.

That will allow you to move your model up off the build plate by any amount.  With proper support structure it will print there.  This is up 3mm.

[3DPiper 0]

Awesome, thank you!

Will try this tomorrow at work 🙂

[GregValiant 1,258]

I've taken to writing "niche" post processors and I happen to have one that you might find handy.  I call it "Very Cool".

I have found that a cool Support Interface releases from the print both easier and cleaner.   So the Very Cool script:

• Retracts
• Lifts the nozzle 1mm
• Runs back and forth over the area bounded (approximately) by the skirt / brim with the fan running.  It indexes 10mm in the X each pass.
• Then the print continues.

It's part of this collection of 7 fairly useless (until you need them) post processors.  Unzip the file and put it into your Configuration Folder in the "scripts" sub-folder.

The settings are for the layer(s) you want it to run, the travel speed, the fan speed, and a second pass that would index in the Y.

 

LittleUtilities.zip