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Heated print beds - are they overrated gimmicks? Answered

For years now I use my old, trusty Mega Prusa with the bare basics in terms of hardware.
But basically every new printer out there comes with heated print beds and most users "upgrade" to one to get better quality prints.

So I started to to check the reprap forums and other websites to find out why a heated would be a "must have".
Quite a simple task you might think, but not so for someone who prints every material on a cold bed with success...

What are the official pro statements for a heated bed?
1. Better bed adhesion of course.
2. Less warping of parts.
3. Far less problems with layer seperation.
4. Better print results.
And of course there are a few more but not worth listing them.

Why do I think most of the four statements are actually unrelated to using a heated bed?
Bed adhesion is a matter of print material and surface of the bed / bed preperation, like tape, glue and such.
If you filament peels off a cold bed with no adhesion at all it simply means the surface is either unclean or unsuited for the print material.
Warping of parts happens because the material shrinks when it cools down, a heated bed is only able to keep a certain height of the print warm.
Higher prints won't have any benefit in terms of better layer adhesion with a heated bed.
Same goes for seperating layers.
Unlike the common believe a heated bed does not fix this problem - it only masks it!
Layers seperate because there is not enough bonging between them.
This can be due to insuffient extrusion width, too high print layers, wrong print temperature and of course wrong z-axis stepping and wrong extrusion multiplicator.
And how good a print comes out of your printer depends on a good calibration and proper print settings - again a heated bed only masks problems ;)

Ok, so heated beds are nonsense, right?
Well, wrong again ;)
They take a lot of worry out of the daily print life to start with.
Especially prints with big foot print will benefit, although PLA should never be a problem on a cold bed.
If you print long parts in ABS or even Nylon you can have a hard time forcing the plastic to stay on the bed all around the print.
A heated bed, with the right settings of course, can make sure your print keeps the shape until it is high enough so the bottom part won't be affected by shrinking anymore.

My opinion on how to get the best results...
Manage to print on a cold bed first!
Smaller parts don't need a heated bed anyway, so use them to improve on your skills of finding the perfect bed material / coating!
You will find that once you have really optimised your printer and settings most parts won't need a heated bed anymore.
Once you are really happy with the result of smaller prints on a cold bed try something bigger and pay close attention to any problems on the way.
For example a big print might start out perfectly but after about 5-10mm of print height you see the part starts to warp and slowly peels of the print bed - especially long parts or thin areas are affected.
The infill also affects how a parts reacts during the cooling, so try the same problem print with solid infill as well as only 15% infill to compare - you can stop the print once the problem is identified, don't waste filament.
Now comes the magic of the heated bed...
You want the temp as low as possible but still high enough to prevent the warping!
Why go low if high would help more??
Simply said: If the bed is too hot the part stays soft for a long time, which can badly affect layer bonding and shape.
Imagine you squish the plastic on an already "hard" layer - the plastic is pressed flat to be within the set specs.
Now if the the layer is still too hot and soft the plastic will push the lower layer in - which of course will expand outwards.
So the layer can actually end up to be lower than it should be - layer will still peel ;)
Start with around 50° C for ABS and turn the heat down gradually every 10 layers or 25 if you print really thin layers.
If the part still prefers to warp go 10 degrees higher.
But again: If the stuff would not stick properly on a cold bed work on that first!

How do I print on a cold bed and claim it works fine?
To be honest, with a lot of time spent on trying, calibrating and finding the right "magic" to put on the glass to make things stick.
Nylon, if the part is big, can still be a frustrating task unless cardboard or Bakelite is used but I still prefer the glass bed.
I no longer bother with tapes as it can be costly and I hate changing the entire setup just because I use a different material ;)
As said, the main key is a proper calibration of hard- and software!
If your prints look messy and you spend as much time cleaning your parts as printing them you know what I mean ;)
At the moment my "bed magic" is a clear craft glue with methanol as a solvent, mine is from Aldi but similar products can be found in every craft store.
The bed is sanded with 600 grid diamond blocks to be as flat as possible and to provide a bigger surface area for the glue.
When mostly printing Nylon is first clean the bed with alcohol and put a layer of plastic primer on it before re-applying the glue.
With the right temp settings this glue surface can be reused several times with increasing bond to the part.
Once the glue start peeling off the bed it cut the area clean and apply another coat just in the spot.
A single bottle of craft glue, diluted down by 20%, lasted now about 3 rolls of filament - not too bad for a 2$ investment LOL
Seriously though, squeeky clean your glass bed using alcohol and / or acetone and play with different types of craft glue.
You want the stuff that is clear and uses either methanol or ethanol as the solvent, don't bother with water based glues!
If the glue sticks well to your part but peels off the bed easily try a layer of plastic primer on the bed first - do this outside!
However, if your printer is only capable of using PLA anyway you might not want to bother at all and stick to tape ;)


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