That would sound pretty odd anywhere else but on a 3D printing forum...
I have been applying and re-applying the usual Aquanet super hold on my borosilicate glass bed for many months now, just spot spraying locations where parts were removed.
Yesterday I printed a body for the "Itty Bitty Belted Extruder" in ABS. I have a fully enclosed Delta machine so the chamber keeps pretty warm. A minor goof on my part had the bed start at 100C and drop to 60C shortly thereafter, I print eSun ABS at 245 for the best layer adhesion that I can get. I did a 12 line brim as well, call me paranoid.

Long story short.
The darn thing would NOT come off the bed! After 10 minutes of effort with a super-thin pallet knife and a putty knife, I almost broke the piece and DID leave plastic still attached!
Normally, once the bed cools, an ABS part just pops off after listening to several minutes of alarming "pings" and "pops" while the parts cool.

Not this time. I wonder which it was, multiple and perhaps uneven layers of hairspray or the "start at 100, drop to 60" bed temperature that caused my bed-adhesion-from-hell experience. I will have to experiment with this. Not that I want parts to never come off, but to see if I have accidentally found a first layer adhesion silver bullet that I can tune.
Normally I put my hair-sprayed bed in the sink under hot water and clear the old stuff off with a toothbrush, I had neglected this bed for quite a while. If a part gets super-stuck next time I can just soak the glass plate with hot water until the part releases (with gunk attached...)

I once pulled glass off of my plate after a part cooled, but it wasn't super stuck, like this one.

Has anyone else ever seen this kind of behavior?

have fun,
DLC

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Kits: Folgertech Kossel 2020 upgraded E3Dv6, Anet A8 upgraded E3Dv6, Tevo Tarantula enhanced parts and dual-head, TronXY X5SA Pro(E3DHemera).
Scratch: Large bed Cartesian, exchangeable heads, Linear slide Delta, Maker-Beam XL Micro Delta, 220x220CoreXY.

Maybe if it happens again, heat the bed up to soften the part to try and pry it off, simply to get it off the bed without causing possible harm to the bed ?

If it still won't come off, turn the bed temp right up and cut your losses with a melted lump

I had the same on numerous occasions with PVA glue or varnish and nylon. I now get the same with the BuildTak surface and ABS. What I do is put the plate on a table that's against a wall, then put the edge of the plate against the wall so it won't move when lateral force is applied. I use a sharpened putty knife, like really sharp with a whet stone and polishing compound, the same way you sharpen chisels and wood planes, with the corners rounded so it doesn't damage the surface. There are youtube videos that show you the technique.
Now you can apply sufficient force without having to worry of cutting yourself on the glass or buildTak edge when the part decides to suddenly let go. It also prevents chipping the glass or breaking it. Just put the knife edge along the glass surface. It's sharp enough to just cut through the first printed layer if you have to. Then clean off the residue with the same putty knife.
It' also handy to take off the brims from your parts, bevel edges and remove burs from aluminium parts (if you own a cnc it works great, but you'll have to regularly resharpen it). Resharpening is easy with a fine file, just move the knife over the file with the beveled edge, then the back of the blade. A thin bur should come off the blade. Then polish it with a piece of cloth or leather with polishing compound (lapping).

I use a putty knife like this, though half the width of the one in the picture:
[cdn.toolstation.nl]

You could slightly increase the z offset so that less plastic touches the surface on the first layer. There's a sweetspot of good adhesion and being able to remove the part after printing. If you look at the 3D printed parts bottom, if you can still see individual extrusion lines, even in the corner it's ok, but if it's a single squished surface you may have to adjust z offset.

I do think that the drop in temperature make a big difference. If plastic is known to shrink when cooling, a larger temperature difference will increase this effect. ie there's considerable tension in the plastic if its surface its printed on doesn't shrink as much. This could also warp the plastic, making the outer edges release before the centre. It's best to gradually cool the part within the 3D printer enclosure rather than blowing fans at it or removing it from the printer to cool quicker.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

Dried hair spray can be dissolved with acetone.

I'd try pouring a little acetone around one edge of the brim and then getting a putty knife or similar in under it. Don't get any acetone near your ABS part.

Don't leave it too long to soak in... if you leave it long enough for the acetone to evaporate, you're back to square 1.

Sometimes a really sharp knife (Stanley knife, scalpel) can get in where a putty knife won't. But the blades are brittle and break if you try to lever with them.

Maybe try putting bed and part into the freezer? That may give enough differential shrinkage to pop the part off?

Edited 1 time(s). Last edit at 04/26/2019 10:24PM by frankvdh.

I use hairspray on my printers' beds all the time. Most times the part will come off without a struggle, but occasionally extra effort is required. On those occasions I try (1) just letting the bed cool down - often there's a loud 'click' and the part is freed, or (2) put the bed's glass sheet in the freezer for 10 minutes - has worked 100% so far.

I'm printing PLA directly on kapton tape that's put on an aluminium plate. The tape has been on there since 2014 and it has gained some small dings last month from rebuilding the printer but it still works fine. Wipe it every week with some acetone and it's clean and tacky.

However... I recently bought new PLA and started printing with it, the prints were stuck and wouldn't want to come off! I let the bed cool down and the tension didn't release. It was so bad that once I got it off, the kapton had been pulled up with it. Luckily I could press the kapton back to the aluminium plate and it has been flat again ever since, no marks on new prints whatsoever but I notice the new PLA has a crazy attachment to the kapton tape. I am afraid I'm breaking my print bed construction some times, especially with objects that have a large surface area attaching to the bed.

My only solution was to print with a raft for those kinds of prints.

I have bought a new Prusa i3 print bed with the removable spring steel sheet for my other printer so I'm very curious to see if that holds up. Should be easier to remove. I'm afraid to use the supplied PEI sheets though as I've seen that PLA can actually bond with PEI surfaces. Maybe I'll just put kapton on the sheet.

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http://www.marinusdebeer.nl/

Try reducing the bed temperature if the stuff sticks too well.

I've been printing some TPU parts recently and found that my 60C bed temperature was sticking them to the PEI surface too well. I have since dropped the bed temperature to 45C, but may go lower yet. They still stick quite well but not quite as hard as they do with the bed set to 60C.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
Try reducing the bed temperature if the stuff sticks too well.

I've been printing some TPU parts recently and found that my 60C bed temperature was sticking them to the PEI surface too well. I have since dropped the bed temperature to 45C, but may go lower yet. They still stick quite well but not quite as hard as they do with the bed set to 60C.

Normally that is what I thought, but in this case I accidentally dropped from 100C to 60C after the first layer.
It required a court order to get it off. Subsequent prints (with new hair spray ) and 100C bed acted normally.
Go figure, I wonder if I have found some kind of "secret sauce" for troublesome ABS parts...

Hmm,
DLC