3d Printing

3d printing – working with ABS and making the first layer stick

This article is a follow up to my previous article, where I discuss some of the challenges of 3d printing with PLA. The material that I print with most commonly these days is ABS, which is a lot more difficult than PLA. I’ve found that if you get the first layer right, that’s the biggest problem over. But it can be a big problem.

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So why is ABS more difficult than PLA?

Basically it’s a different material, with different properties – so the solutions that work for PLA aren’t going to necessarily work for ABS.

First thing – the melting temperature for ABS is significantly higher than for PLA. You’ll need to get your printer’s hot-end up to about 230C, and some people find that they need it to be even a little bit higher than that.

Secondly, when ABS cools down, it shrinks. This property causes problems for 3d printers in two ways:

  • The first layer really really doesn’t want to stick to the bed. Even if you get it to attach to the bed as the plastic comes out of the extruder, after a few seconds it cools down and starts to shrink. When that happens, it starts to curl and peel off the bed.
  • When you do get the plastic to stick for all of the first layer, your shrinking problems still aren’t over. Individual layers might shrink so much that they don’t want to stick to the layers above and below, and this is when delamination occurs – your 3d printed object starts to crack and split.

Why should I bother with ABS?

LEGO is made from ABS – a lot of us will know that as a pretty tough, durable material.

Because it has a high melting temperature, it’s more useful for building something that’s going to operate in a warm environment (like the inside of a car).

It’s also a little bit more flexible than PLA, which can sometimes be useful. A good example is the parts on a printer which hold ball bearings – that extra bit of flexibility allows the printed part to deform just enough for you to push the bearing in, where it forms an interference fit.

But if you do decide to print with ABS, remember to do it in a well ventilated area – when molten, it gives off a pretty unpleasant fume.

So what’s the answer?

First – a heated bed

For my Sintron i3 Prusa printer, getting the hot-end up to about 230C isn’t that big a deal. The Sintron has a heated bed, which is good because it’s basically impossible to print ABS without a heated bed. Most of the research I’ve done suggested that the bed needs to be about 110C – 120c to have any success at all.

Also, I’ve found that a glass plate on the heated bed also helps distribute the heat more evenly.

However, I had a problem. My Sintron is a great value printer and I have very few criticisms – but I just could not get the temperature of the heated bed past about 60C. This was not close to hot enough to get the ABS to adhere to the glass surface.

I needed something else to make this work.

Second – an ABS and Acetone mix

An interesting – and useful – property of ABS is that it dissolves in the chemical Acetone. Acetone is liquid at room temperature, and is a household chemical most commonly used as nail varnish removed. It’s usually possible to buy this chemical by the litre at a hardware store or chemist.

If you mix ABS and acetone to create a chemical slurry, and smear this over the cold glass plate on your printer bed, this makes a huge difference to the print results. This cold slurry really sticks well to to the cold plate. When the printer extrudes hot ABS to this thin ABS film, this bonds much more tightly to the ABS film than it would when it’s going straight to the glass. Suddenly the first layer ceases to be as much of a problem.

To do this, remember safety first – don’t get acetone on your hands. Wear some rubber gloves to protect your skin.

Find a container which doesn’t dissolve in acetone – for example, a HDPE container – with a lid that closes tightly. This kind of plastic container is often used for holding milk or cream, and has the symbol shown below.

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Now add some acetone and ABS to this container – there’s not really a formula for this, but I’ve found that mixing 40ml of acetone and about a metre of 1.75mm ABS gives a pretty good slurry. Cut the ABS up into short lengths and put it into the acetone. Then put the container lid back on and close it tightly. After a few hours, you’ll find that the ABS has dissolved, and the acetone has changed from a clear thin liquid into a thicker liquid, which has the same colour as the ABS plastic that you added.

I get best results when the constituency of my ABS and acetone mix is like syrup, but your mileage may vary.

Finally, pour a small amount of this slurry onto the glass plate, and using a paper towel smear the slurry mix over the glass so that the print area is covered with a thin film. Try not to leave any gaps.

Third – use a brim

I’ve found this isn’t entirely necessary, but it helps. As with PLA (or any other material), if you increase the amount of surface area in contact with the heated bed, you’re going to increase how well it’s attached to the bed.

Summary

ABS is a bit more difficult to print with than PLA, but since it might be a better material for your needs, it’s worth trying to overcome the challenge. Even if you have a printer that doesn’t allow the heated bed to go up to 110C, you can still print PLA using these three tips:

  • Get your heated bed to 60C, and use a glass plate;
  • Coat your glass plate’s printer surface with an ABS/Acetone slurry;
  • Use a 10mm brim.

I now mainly print using ABS. Whereas my first few attempts were pretty disasterous, with lots of problems with warping and delamination, I rarely (if ever) have this problem now.