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I've been having a hard time lately getting the raft off of my ABS prints.

Is that a symptom of either a nozzle or bed that are too hot? Or is there some other factor I should be looking in to?

I have an UP mini that I've modified both the nozzle and bed to customize the temperatures on.

Bed gets heated to 100˚C and nozzle is either 266˚C for UP ABS filament or 236˚C for off-brand ABS filament.

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  • $\begingroup$ Hotter ABS is less viscous, so it can get into smaller microscopic cracks and holes in your bed and therefore be harder to remove later, as well as join the layers together more. This might be it. This is also the theory why ABS slurry (abs+acetone mixture) works so well for bed adhesion. $\endgroup$ – Leo Ervin Jun 6 '16 at 20:57
  • $\begingroup$ @LeoErvin I could be misinterpreting your comment, but I don't think an ABS slurry is meant to stick directly to the build plate. Usually the acetone in the slurry helps break down a bit of the Kapton tape (for ABS printing), allowing the slurry to bond easier to the surface of the tape (maybe the microcracks you mentioned?). Then, as the HBP heats up, it creates a more native surface for the ABS to bond to. $\endgroup$ – tbm0115 Jun 7 '16 at 14:09
  • $\begingroup$ @tbm0115 I don't know what acetone does (or doesn't do) to kapton, but what I described is the reason abs slurry sticks to bare glass so well. The mixture is far less viscous so it can get into tiny cracks in the glass. However, once the acetone evaporates, the printed ABS sticks to the ABS left from the slurry which itself is stuck to the build plate much better, hence why ABS slurry helps so much with glass beds. This is the reason why ABS left from evaporated slurry is so much better stuck to the glass than an ordinary 1st layer which can easily lift. $\endgroup$ – Leo Ervin Jun 7 '16 at 15:02
  • $\begingroup$ Add your settings if you want a good answer. Following. Increase raft seperation distance, and buy simplify 3d? $\endgroup$ – StarWind0 Jun 16 '16 at 13:33
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A couple things to consider:

  • Ensure that your build plate is flat and level. An un-parallel HBP could result in the object "welding" to the raft.
  • Turn down your nozzle temperature. It is likely that the material is hotter than it needs as it is extruding. This results in a slower "cool-down rate". So, if it takes longer for the filament to cool between the raft and the first layers of the object. Therefore, cooling together in a manner that somewhat binds them.
  • Personally, 266C seems VERY high to me. I've primarily only used ABS on my MakerBot and have successfully printed with 225C +-5C nozzle temperature and 110C +-2C HBP temperature.
  • Typically you want to extrude slightly above the melting point. You don't want to liquefy the material, but make it pliable enough to bond it to other layers of material (or a BP).
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You could try reducing the temperature of the hotend. If you are using too high of a temperature, the ABS will "run" and over-adhere to the raft.

What slicer are you using? I have found that raft quality is drastically affected by the slicer I've used. In my experience, MakerBot and Simplify3D produce the nicest, easiest to remove rafts. I've also had success with Cura.

Barring changing the temperature of your hotend or switching to a new slicer, you could always try printing without the raft. From the sound of it, your bed is hot enough. Do you have Kapton on the bed? If so, give printing without a raft a shot. If sticking is an issue, try painting a slurry of ABS and Acetone onto the bed before starting.

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Do you allow the filament to cool completely (5-10 minutes or longer after printing) before you begin to remove the rafter, or do you remove the printed piece immediately after finished printing and begin to remove the rafter?

In my experience, I have noticed that the rafter is easier to remove if the piece is still somewhat warm from the heated bed.

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I haven't got a printer with a heated bed so have only tested this on PLA but I have found editing the G code so the printer cools the nozzle down and then heats it up again gives the raft enough time to cool down so that it peels off easier when the print is finished.

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