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medicalmodeller

Print failure possibly because the bed not hot enough

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I have been printing large models of bones. The prints have been failing due to failure of the print to stay stuck to the heated plate (UM2). I have wondered if this is partly to do with keeping the UM2 in a room with the heating on low so that the room is rather cool. Anyhow, I increased the bed temp to 70 degrees and the print came out perfectly (showing the fracture nicely)

Is there a way to make the default bed temp anything other than 60 degrees to avoid having to tune every print??

Thanks

MM

 

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I have been printing large models of bones. The prints have been failing due to failure of the print to stay stuck to the heated plate (UM2). I have wondered if this is partly to do with keeping the UM2 in a room with the heating on low so that the room is rather cool. Anyhow, I increased the bed temp to 70 degrees and the print came out perfectly (showing the fracture nicely)

Is there a way to make the default bed temp anything other than 60 degrees to avoid having to tune every print??

Thanks

MM

 

You can save a custom material profile in the UM2 machine with things like bed temp, nozzle temp and other settings. You do this in the menu from I think the materials setting (then choose customise or something similair?) I'd check for you but my UM2 is in the middle of a long print right now.

 

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Basic steps are "customize" then change the settings for pla then "save" then select "pla". That last step I never quite understood at first.

Also a year ago the firmware had some bugs regarding changing custom settings and you had to change led brightness also or something bizarre but if you have a machine from the last 6 months you should be fine or if you updated marlin in the last 6 months.

70C definitely sticks a bit better (I usually print PLA on a 50C bed). There are two effects here.

First of all I hope you are putting some kind of PVA glue on your bed. I use wood glue mixed with water but glue stick works pretty well also. The layer should be so thin you can't see it. If it is thick enough to see then wet a tissue and spread it around a bit (and remove some in the process).

The first effect is that the PLA needs to flow well to stick well. It needs to hug that glass surface completely and not act as a cylinder touching just along a line. So you want it to cool slow enough so it has time to spread. 1 second is plenty. The threshold temp for this is typically around 35C to 45C for a room at 20C and PLA at 220C. For cooler air or cooler nozzle you might need to raise up to 50 or 60C. There is a very sudden transition between too cold and too hot.

The second effect has to do with warping and not sticking power but it may seem like the same thing. PLA has a glass temp of around 50 or 60C so above those temps it acts more like clay than a solid. It can be stretched and molded (like a non-solid) but it pretty much stays where you leave it (like a solid). This is the glass phase. When you print large parts it helps to keep the bottom layers of PLA above glass temp such that if there are strong pulling/shrinking forces on upper layers they are allowed to warp the "glass phase" PLA below a little. The amount is small enough that the distortion is minor to the bottom layers of PLA.

To get this to work you should use a minimum of 70C and possibly even 75C for the bed.

There is a problem with this however. Bed temperatures of 65C and hotter make the bottom of the part curve inward a bit. But the effect is not nearly as serious as having your part lift from the surface. See 5th picture down on left side:

http://support.3dverkstan.se/article/23-a-visual-ultimaker-troubleshooting-guide

 

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Basic steps are "customize" then change the settings for pla then "save" then select "pla". That last step I never quite understood at first.

 

You don't need to overwrite the default PLA setting, there is an option to save the new settings as a completely separate entry.

Edit: My print just finished. Menu item is:

Material/Settings/Customise and then "Store as preset" :smile:

 

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Dear All, Thanks for the support/advice

I have not been using glue on the bed! In fact I have been cleaning the glass with isopropyl alcohol and almost all the prints seem to work fine. But as I posted, not all prints stick.

I will try a thin layer of PVA glue.

As as aside I wonder why the nozzle blocks after the print becomes loose. Is it because the PLA accumulates around the print head and so it does not get hot enough and the filament then solidifies inside the print head? Certainly I have become expert of the Atomic unblock method!

Thanks

MM

 

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