Friday, October 2, 2015

3D printing basics: bed adhesion

One of the important things that FDM 3D printing hobbyists have to figure out is how to get their plastic to stick to the bed reliably, but lightly enough that it can be removed without the use of power tools and/or demolition charges. (Seriously, I've had prints stuck so tight that I had to use a chisel and hammer to get them off).

I'll start out by saying that my experience is fairly limited, but I've tried a few things and had some failures.

PLA

I print pretty much exclusively in PLA these days. It suits my needs, it's really easy to print with, it produces pretty looking prints, and most importantly it does not smell too bad. The downside being mainly that it becomes soft at lower temperatures than its main rival, ABS. This is not generally a problem for what I do.

You can theoretically print on heated Kapton at about 60*C, but that has led to ruined prints way too often for me.  These days I rely on blue painter's masking tape.


I've tried a few blue tapes. The canonical blue tape to print on is 3M original 14 day tape. This works pretty well and if it's all you can get, go for it. I find that there are some tapes that provide just a bit more adhesion to the plastic and I've had prints come off the 3M stuff.

Two tapes that I've found are good are Duck brand 14 day blue painter's tape, and Blue Hawk brand blue tape - I think this might be a house brand of Lowes home improvement stores. Both are a darker blue than the 3M stuff, and in fact I think they may be the same thing.

No matter what tape I use, I clean with isopropyl alcohol on a paper towel first. Not a thorough scrubbing, just enough to take off residual material and perhaps raise the fibers in the tape a tiny bit.

I've used blue tape for dozens of prints, but I think it's probably actually a better idea to replace it every 5 or so prints, because the surface starts to get a little grunged up and I've had bits of blue tape get permanently into the bottom of prints before.

With a trusted blue tape on the bed and the bed properly levelled, I'm perfectly comfortable hitting "print" on a 10 hour print and walking away.

ABS

When I started out, it was all ABS and the standard "knowledge" was that you put down Kapton tape, heated the bed to 110C and the ABS would stick beautifully and release when the bed cooled again.

This is bunk. I've had more prints break loose on bare Kapton than I care to think about. Certainly I've wasted entire spools of filament on ruined prints.  I no longer trust bare Kapton with any material.  

ABS slurry

A while back someone came up with an excellent method for ABS. Dissolve a bit of ABS in acetone and use that as a bonding agent. I actually stopped using ABS because I couldn't get good bed adhesion, but since trying this method I may start doing ABS again.  I found some little squeeze bottles in the camping section of the local hardware store and they work very well. Obviously be careful what containers you use, make sure that the acetone won't dissolve them.


I just cut up a failed print with diagonal cutters, crammed it in there and poured in some acetone. As you can see from the photo, the only ABS I have on hand is purple. It would probably be better to use clear/natural so you don't discolor other filament colors.

It took about an hour for the ABS to all dissolve. To use it, I just put a few drops on the print bed (on top of the Kapton tape) where the print will be done, smear it around with a fingertip, then start the print. The print bed still should go to 110*C for printing - this will evaporate the acetone quickly, before the print starts.

NOTE that this method WILL NOT WORK WITH PLA because acetone does not dissolve PLA. There are things that will, but those solvents are expensive and IMO this is just not necessary because blue tape is pretty much perfect anyway.

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