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Raft detachment

Andrew
(@achan1369)
Distinguished Member

This model has a lot of sharp corners on the leaves so I used a raft. The edges of the raft are adhered well but the model shrinkage was strong enough to peel the raft off the bed in the local area. The print finished but it's no longer flat. 

The build plate was cleaned and the temp was 60C the entire time. Does this model need a thicker raft? 

IMG 2327
Quote
Topic starter Posted : 19/09/2021 5:36 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Andrew,

Welcome to the community!

Can you list what filament material and slicer you're using and post a screenshot of your raft settings? Also could you post an image of the non-flat parts of the print? Did the print detach itself from the raft or did the raft just detach from the bed?

If it's the latter, my first suggestion would be to try upping the bed temperature to 70°C. Raft layers consume a phenomenal amount of print time and material for something that's going to be thrown away, so increasing raft thickness is a last resort to try only after all other avenues have failed.

Looking forward to your feedback.

Regards,
Luke

ReplyQuote
Posted : 20/09/2021 5:41 pm
Andrew
(@achan1369)
Distinguished Member

Hi Luke,

The print is firmly attached to the raft. Almost too well because they're hard to separate. Here is a photo of the bottom of the raft. You can see the areas where it pulled up from the bed. There must have been significant thermal strain to pull up the raft in areas away from the edges.

I started with the standard Cura slicer settings for the raft then increased the margin and first layer jerk. 

I'm using Overture brand PLA filament. It's a budget brand. 

IMG 2330
image
image
ReplyQuote
Topic starter Posted : 20/09/2021 6:38 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Andrew,

Your raft is already 4 layers and 0.94mm thick, representing a significant use of time and material. Moreover the first raft layer is printed with a very large line width and large line spacing - this would tend to make it more detachable. One quick way to improve that would be to lower the base line thickness like so -

Before (raft base line width 0.8):

image

After (raft base line width 0.4):

image

 

However that would make raft printing even slower. Ideally you should try and find settings that enable you to print directly on the ultrabase without so much warping.

Here are some suggestions for improving bed adhesion:

  • Make sure the bed is clean. I use a dry paintbrush to remove loose dust fibers between prints. Every few months I use surgical spirit (rubbing alcohol) to clean the base
  • Make sure the bed levelling is correct. If the nozzle is too far from the bed you will lose adhesion. The most reliable way to ensure the spacing is correct is to print some bed levelling squares (without raft), such as these - https://www.thingiverse.com/thing:2789086 - and measure the thickness of their perimeter using a vernier caliper with 2 decimal places or a micrometer. With a first layer height of 0.2mm in the slicer you should be measuring a real-world thickness of 0.15 to 0.25mm for all the squares (the closer to 0.2mm the better).
  • Check that the extrusion multiplier is correct. Your prints seem to be very, very slightly underextruded. You might benefit from raising EM by 1% or 0.01 (in Cura this is Flow, under Material settings)
  • If all of the above was already correct, raise nozzle temperature to 210°C and bed temperature to 70°C. 70C is just above the glass transition temperature of PLA so it would reduce residual thermal stresses in the base layer to almost zero. Of course the layers above the base wouldn't quite reach this temperature, so you'll still have the stresses from the upper layers (starting from approximately where the temperature dips below Tg of ~60°C). But this will be less than what you have now so it might be enough to save the corners.

Generally speaking, other users have reported an increase in print quality and performance by shifting to PrusaSlicer - so if you want to invest some time in learning this I would recommend it (we have a great series of guides on PrusaSlicer on the main page). The learning curve is quite a bit easier than cura because there are much, much fewer settings. It also has more features (like paint-on supports and paint-on seam locations) and significantly faster slicing. If you decide to make the switch we will support you too 🙂

Let me know how it goes with the recommended adjustments. Looking forward for your feedback!

 

Regards,
Luke

ReplyQuote
Posted : 22/09/2021 9:09 pm
Andrew
(@achan1369)
Distinguished Member

Hi Luke,

The bed is already levelled from your advice on another post a few months ago. It's going to take a few days to finish printing another one.

What makes the model look underextruded? There are layer lines visible everywhere because there are no flat surfaces.

ReplyQuote
Topic starter Posted : 23/09/2021 4:53 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

@achan1369 Hi Andrew,

It's lines like these here -

image

It's hard to tell for sure from the picture, but those lines may be a slight underextrusion. Your print is almost perfect, but given the adhesion problems and the appearance of those lines, you might get better results by bumping the extrusion multiplier upwards a very tiny amount (0.5 to 1%).

If you last leveled the bed a few months ago, it's a good idea to re-check with a piece of paper. The brass nozzle wears out over time and tends to get shorter. You might find yourself about 0.05 to 0.1mm too high after printing a couple of kilos of filament. If you just meant my post was a few months ago and you level your bed regularly then disregard this paragraph 😇 .

Let me know how your testing goes!

Regards,
Luke

ReplyQuote
Posted : 23/09/2021 8:34 pm
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