Parts have started lifting

[jasperash]

Hi all, Hoping for some general advice here. I have had my Rostock running for about a year and have had some great small prints. Inititally I had no luck with the glue on the bed, so I went to Kapton tape and have had great success. However a few months back I put an aluminium plate under my glass to more evenly distribute the bed temp as I did have parts warping issues. That fixed that problem and I'm now trying to move to larger parts is 150mm diameter. But I'm having issues with the parts lifting from the bed and warping then becoming unstuck and trailing the nozzle around the bed until they become a big pile of goop.

I'm in Oz, so its winter here. I have my rostock in a cupboard with a small space heater in there with it (not a fan type, so doesn't cause a draft.)

I am printing in ABS running the bed temp at 92 deg C. I can't seem to get it any higher than that, 93 at best.

I've attached the gcode of the part that I am currently printing in case that helps. I've tried 3 times and it seems to get about 5mm of build height before the part starts to come off and then all hell breaks loose! I've tried both with and without a raft also.

Any ideas would be greatly appreciated.

Thankyou!

[Qdeathstar]

Make sure you have a good calibration, bigger parts seem to be more affected my slight imperfections in your calibration.

Also, try abs juice for bed adhesion (abs print failures fully de solved in acetone)

[jram]

ABS juice will hold ABS most of the time but it sticks so well that sometimes you will pull up shards of glass. I just upgraded to PEI and haven't had an A B S print come up yet with the bed set at 90-95. I really wish I had not waited to upgrade, it was worth every penny! The room with my printer no longer smells like Aqua Net and acetone.

[IMBoring25]

What temperature is the heater getting the ambient environment? I've found 25C helps but high 30s to low 40s makes a lot more difference for ABS.

Do you have the ATX power supply or the newer OEM style? If the former, some of them really struggle to power the hot end and bed simultaneously. A load on the 5V rail may help, or an upgrade to an OEM-style power supply or a dedicated PSU for the bed. I'm running my bed through an SSR to a dedicated power supply and, despite it being a 12V dedicated supply at the moment (my new 24V power supply is dimensionally different than my first 24V power supply, so the cover I made doesn't fit) it's making enough difference that I really don't feel the urgency to get the 24V capability up.

[Captain Starfish]

You're fighting physics.

As the melted plastic cools, it tries to shrink. ABS is particularly bad for it. Because each layer trying to shrink is bonded to the layer below, it gets held by the adhesion force to the bed. In small parts it doesn't matter so much but, in big parts, it gets more and more important. The first thing to go is usually the edges, as you're seeing. If you increase the bed adhesion to stop that, the tension can exceed the strength of the glass and you get chunks out. Many of us have experienced that headache.

What is causing the curl-up effect is that, looking down the part, you have layers which are building up tension based on layers under tension below them and it stacks high. You can verify this by printing a part which is only (for example) a couple mm high but out to 150mm wide. It'll print fine if you have some half decent bed adhesion and alignment. Now make it 2cm high and it's corners up everywhere.

Another symptom of this issue is part cracking further up the piece. The same forces build up until they exceed the inter-layer bonding strength and then something gives way.

How to fix it? Well, it's a function of width, height and temperature delta. So you can change your part, make multiple smaller bits and join them together post print. Which sucks. You can change your material to something with a lower coefficient of expansion. Hint: nylon's just as bad. I believe PLA is a lot better. You can improve your bed adhesion strength and the strength of the bed itself so that the part won't pull. But those internal stresses will relieve as soon as you pull it from the bed and it will still curl somewhat then. Or you can limit the temperature differential by getting the build airspace up nice and warm. This means the shrinkage of cooling happens simultaneously across the part when you pull it off the bed, and (hopefully) everything stays straight.

A combination of all of these things is probably in order. Use mouse ears and a big skirt to spread the force over the bed and help with adhesion, be careful of the design you send to the printer knowing that height*layer width will get you into trouble, and look at getting that enclosure nice and toasty.

It's a pain in the butt, but it can be worked around.

[jasperash]

Thanks all for your replies. IMBoring25, the ambient appears to get around 31 degrees. I could pump it a bit more as there is one setting higher. I am a little lost on your powering description. What do you mean by a load on the 5v rail? Also I'm not sure of the terms PSU and SSR. I'm not sure of the power supply but given your description, I've probably got the ATX.

I will pull out the old instruction manual and re-do the calibration tomorrow. Has anyone tried ABS juice on the kapton tape bed. jram, What is PEI?

Has anyone tried printing straight to the aluminium plate on top of the heat bed?

Thanks again?

[Qdeathstar]

I do abs juice right on the glass bed then just use the scraper to get it off the bed once the print is cool. I don't have an enclosure and I run at 80c on the bed and 228 as extrusion temp and rarley have have an issue, though the tallest thing I've tried to print was 8cm tall. I have printed several large/short things in abs w.o issue though.

[IMBoring25]

PSU is Power Supply Unit. SSR is Solid State Relay, which is used to get the high bed currents off the circuit board.

Some people have found that the ATX power supplies will limit the 12V power supply if they don't also have a power draw at 5V. They've improved power delivery by adding a light bulb or some such draw on the 5V wires.

[VAXHeadroom]

Thanks all for your replies. IMBoring25, the ambient appears to get around 31 degrees. I could pump it a bit more as there is one setting higher. I am a little lost on your powering description. What do you mean by a load on the 5v rail? Also I'm not sure of the terms PSU and SSR. I'm not sure of the power supply but given your description, I've probably got the ATX.

I will pull out the old instruction manual and re-do the calibration tomorrow. Has anyone tried ABS juice on the kapton tape bed. jram, What is PEI?

Has anyone tried printing straight to the aluminium plate on top of the heat bed?

Thanks again?

I use kapton with ABS juice on all my printers for both ABS and PLA. Never had a problem with it. Needs to be renewed every few prints.
Recent video I did showing it: https://youtu.be/1CitQhP9wh0

[jasperash]

Hi VAXHeadroom, Yep, that's the way I went and its been amazing! I've managed to patch bits of Kapton so far but will need to replace a section from the centre soon. Perfect stick every time so far which I'm so happy with.

[geneb]

*mumbles something about Dec Vadic and Luke Vaxhacker, then wanders away*