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AeonDG
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Dense Objects Slide on Print Bed

Fri Mar 11, 2016 12:13 pm

I could use some advice. When I have dense item to print, the part sometimes curls up and slides around the bed, causing the print to fail. I am printing with PLA.

I may need to adjust the temperature / cooling in the gcode - I have made one attempt since I first posted this. I did figure out how to slow the cooling process. Improved a little, but still a problem. I am guessing that the part is cooling so much that it slides. Perhaps I need to turn the fan down as time goes on?

I am not using a raft and i have considered it. going to try that next.

print profile:
bed heated to 85 degrees, consistent throughout the print
extruder heated to 210 degrees
first layer speed is 50%

layers: 6 top, 6 bottom, 5 perimeter shells
30 percent infill

Here is a video from my last failed print, https://youtu.be/pzEJEz5Q9aE
1:33 is where things start to go very much awry!

I have used this print profile on other prints with no issues, it seems to happen when the part is dense.

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AeonDG
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Re: Dense Objects Slide on Print Bed

Fri Mar 11, 2016 6:06 pm

ok i made one change: in cooling tab in simplify 3d I changed the printing speed for layers from 15 seconds to 10 seconds. and dropped the speed reductions down to 18 percent.

i really need help! i am just making wild guesses at this point. I did have much greater success though, even tho this part has the same issue, it printed roughly 1.5 inches tall before the flaw, rather than the half and inch result from before...

danielhenley
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Joined: Fri Sep 11, 2015 1:27 pm

Re: Dense Objects Slide on Print Bed

Fri Mar 11, 2016 6:40 pm

You're prints aren't sticking well enough to the bed. Looks like you're printing directly on glass, try adding some blue painters tape.

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AeonDG
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Re: Dense Objects Slide on Print Bed

Fri Mar 11, 2016 6:47 pm

danielhenley wrote:You're prints aren't sticking well enough to the bed. Looks like you're printing directly on glass, try adding some blue painters tape.
Thank you! May I ask a further question? My print bed is heated. I wasn't certain about using tape with a heated print bed. Is painters tape safe on the heated bed, or should i drop the temperature of the HPB or turn it off completely?

Heutinck
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Joined: Thu Mar 03, 2016 2:14 am

Re: Dense Objects Slide on Print Bed

Fri Mar 11, 2016 11:38 pm

I think that 85 degrees is a little high for PLA. You should try around 60 degrees. I also agree you need something to help adhesion to the glass. You could use Kapton tape, the Elmers purple glue stick (my personal favourite) or you can use certain types of hairspray ( think they need to be of the kind that contains plastic in them).

I don't think you have a cooling issue. Normally the calling fan is off for the first layer and then it should be turned on after that. There are several ways to do it. I'm not sure which one is best. Simplify3D defaults to turning it on to 100% on layer 2. Cura starts it at 20% on layer 2 and ramps it to 100% by the time the layer height reaches .5 mm.

Tim

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AeonDG
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Re: Dense Objects Slide on Print Bed

Sat Mar 12, 2016 5:57 pm

Thank you all so much! I appreciate all of your advice and input. :D

In between the first post and now, i had one test print in the middle. In that attempt before this last one, i did change the rotation of the item on the print bed so it wasn't as top heavy. had a 90 percent success rate. and then I read the messages about tape.

I wasn't able to buy printing tape right away, so what I did was follow the tips that were posted - I lowered the head bed to 70 degrees. and since the curling up was happening later in the print, close to finishing up the last several top layers - I also modified the cooling tab a little more - where I adjust the speed for prints below 10 seconds and allow reductions down to 18%.

I was able to print that same piece, I just had a nearly perfect result from all these changes. I would call this one a 98 percent success rate! :P I will still pick up some tape as well, but I am looking for sheets online that are already made so I don't create issues with layering tape on the surface or throw calibration off.

super excited to have finally gotten a denser smooth part in PLA!!! This DaVinci Duo 2.0 is kind of limping along, but its still possible to get decent results from it.

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dkightley
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Re: Dense Objects Slide on Print Bed

Sat Mar 12, 2016 7:02 pm

I have a BuildTak sheet on the bed of both of my Makerbot Rep 2s...and I've actually had difficulty get printed items off the bed!! In fact the only reason I use BuildTak is because the plastic sheet beds have become damaged with trying to remove prints!! And the beds on Makerbots are not heated!


I even had a time when I tried a glass sheet....but didn't get on with it, as it seemed to sap the heat out of small parts too quickly.
I'm actually surprised nobody has suggested your nozzle may be too far away from the bed when printing the first layer....which is a prime culprit of non-adhesion. Having said that, putting a layer of tape on the bed will bring the bed closer to the nozzle....achieving the same thing as tweaking the global z offset, but at a considerable inconvenience!

I would try the global z axis tweak. On the GCode tab....adjust negatively for starters by approx. a quarter of the layer thickness (even making the value negative) may be worth a try. If you look at the quality of the bottom surface, you'll get an idea of whether the nozzle is too high as the surface will not be smooth. Get too close....and the nozzle will be prevented from extruding.

EDIT: And the other thing to try to help with bed adhesion is to add a brim...which increases the surface area in contact with the bed, and the brim will separate easily leaving next to no scarring.
Doug Kightley
Volunteer at the National Tramway Museum http://www.tramway.co.uk
Railway modeller and webmaster at http://www.talkingtgauge.net

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AeonDG
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Re: Dense Objects Slide on Print Bed

Sat Mar 12, 2016 7:29 pm

dkightley wrote: I'm actually surprised nobody has suggested your nozzle may be too far away from the bed when printing the first layer....which is a prime culprit of non-adhesion. Having said that, putting a layer of tape on the bed will bring the bed closer to the nozzle....achieving the same thing as tweaking the global z offset, but at a considerable inconvenience!
.
Actually the problem was much later, long after the printer lays down the first layer perfectly. So it wasn't an issue of the first layer adhesion, in fact the curling of the edges and loosening of the prints were occurring constantly into about hour 5 of a 7 hour print. Reducing the cooling speeds and lowering the heat bed produced a near perfect print. I am happy to say this problem is solved!

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