Tried to print without raft, nozzle plowed into bed. What am I missing?

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2CNK
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Tried to print without raft, nozzle plowed into bed. What am I missing?

Postby 2CNK » Sun Nov 06, 2016 4:37 am

Some time ago (a few months probably) I decided to experiment with printing with no raft.

I turned Raft off and made no other changes, and tried to print a 20mm calibration box.

Printing started but I could tell it didn't look right -- nozzle way too close to the print surface. I stopped the print and when I removed it to look, I could see that the nozzle had in fact damaged the BuildTak. The perimeter was "printed" (really just the nozzle deeply indented the surface) and the print stopped shortly after trying to fill in the first layer corner - ripping up some of the build surface in the process.

I stopped my attempts to print without raft, and printed happily with rafts ever since, but I am recently thinking about it again and realized I never solved that mystery :(

These photos are of that spot. I have been using the BuildTak since then, so it is a little worn but the damage is clear.

The ragged part is where I had to cut away a piece of torn BuildTak, then use emery paper to smooth away the roughness.

Can anyone help me understand why this happened? It was a perfectly fine printing profile that I successfully printed 20mm boxes with, I simply de-selected Raft, saved and sliced & tried to print.

2016-11-05 22.25.27.jpg

2016-11-05 22.25.20.jpg

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Trhuster
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Re: Tried to print without raft, nozzle plowed into bed. What am I missing?

Postby Trhuster » Sun Nov 06, 2016 7:13 am

It is no mystery. When using raft nozzle is further away from bed so the plastic has more room to expand. You have to adjust your bed height. Use the thumbscrew on the front left side off the printbed. If you turn it anti clockwise gap between nozzle and bed will be bigger.

Mabey you have to lvl your bed too, if so follow this guide. https://www.raise3d.com/pages/bed-leveling-instruction

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2CNK
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Re: Tried to print without raft, nozzle plowed into bed. What am I missing?

Postby 2CNK » Mon Nov 07, 2016 4:41 am

Are you saying that the bed's zero position (in the Z plane) is different - from a software perspective - between Raft enabled and disabled? I didn't expect that.

Nozzle-from-bed distance (adjusted via the screw) when this happened was set to zero at close to 0.2mm - the factory default. But the nozzle was much lower than that when I tried printing after dis-abling the Raft. It was low enough to damage the buildTak.

I had expected that if Raft was disabled, the bed's Zero (and therefore starting height when printing) would be unchanged. Is that not the case?

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Trhuster
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Re: Tried to print without raft, nozzle plowed into bed. What am I missing?

Postby Trhuster » Mon Nov 07, 2016 6:42 am

No. Z position is the same with or without raft. If you had the gap between the nozzle and the bed at 0.2mm when you started print without raft it is not possible to get to low. In software when using raft first layer is 0.5mm or somthing like that. When raftless it is 0.2 or 0.3 normally, depends what setting you put in for the first layer in ideamaker.

So your nozzle is to close to the bed. And mabey your bed is out of level.

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walshlg
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Re: Tried to print without raft, nozzle plowed into bed. What am I missing?

Postby walshlg » Mon Nov 07, 2016 2:02 pm

remember to wait when adjusting Z since home first moves Z rapidly then goes very slowly for another 30 seconds or so. I have plowed into the bed a few times because I set Z too quickly. Watch the Z axis screws to make sure they stop rotating.

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2CNK
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Re: Tried to print without raft, nozzle plowed into bed. What am I missing?

Postby 2CNK » Mon Nov 07, 2016 4:50 pm

From what is described, what happened should not have happened. Disabling Raft alone (as in, making no other changes) should not have resulted in putting the nozzle closer to the build plate.

I recently did some maintenance and had to adjust Z home, so I can't confirm the original setting from when this originally occurred but Z home is currently set to 0.2mm. Bed is level, or close enough to not tell a difference with feeler gauges.

I was very hesitant to replicate the experiment since it had damaged my build plate, but it sounds like I need to try it again in some other safe way to confirm what is going on.

Just to make it very clear to me: I am not "missing" anything, am I? It should be OK to print raftless simply by disabling Raft in the slicer? (Except perhaps for some fine tuning of the first layer thickness and other such fine tuning details?)

Thanks for helping me understand!

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walshlg
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Re: Tried to print without raft, nozzle plowed into bed. What am I missing?

Postby walshlg » Mon Nov 07, 2016 9:18 pm

IMHO: something must have changed your Z. (I also have this problem right now where one of the heads has just gradually vibrated a bit lower in the set screw.) So I suggest you screw out your Z-stop screw a turn. re-tighten all the set screws holding the isolation tube/hotend assembly in place. Then re-set Z.

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2CNK
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Re: Tried to print without raft, nozzle plowed into bed. What am I missing?

Postby 2CNK » Thu Nov 10, 2016 4:25 am

I did some tests (first by adding some spacers/shims to the top of the Z adjustment screw, just in case) and I have concluded that either a glitch or some other thing happened to mess up the Z zero when my original problem happened. I can't replicate the problem, so whatever happened that led to it remains a mystery.

However I'm happily printing raftless for some larger quick-and-dirty prints with my 0.8mm nozzle so all is well.

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walshlg
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Re: Tried to print without raft, nozzle plowed into bed. What am I missing?

Postby walshlg » Thu Nov 10, 2016 4:23 pm

After my last printing messup one of my heads was off by a good 250 um. Doing well after another dual head alignment. IMHO set screws aren't great for holding the isolation tube/ hotend assembly in place - they always slip in time and change position every time you try to tighten the set screw. Not sure what is better.


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