ABS on FR4

I have been printing both ABS and PLA on PET tape for more than a year now. It works well and lasts for many months, but eventually the silicone adhesive fails and it blisters. Applying it is fiddly to avoid any overlap but also not leave gaps between the adjacent runs of tape. I have been on the lookout for a solid material to avoid these pitfalls.

Stoffel15 (Wolfgang) told me that FR4 fibreglass PCB material works well. FR4 is the most common PCB material and is a glass fibre and epoxy resin laminate. It will handle solder re-flow temperatures (~ 240°C) for short durations and can be used continuously at 140°C. As I haven't worked on single sided PCBs for many years, I had forgotten what the surface of the raw material looks like. It is actually smooth and glassy, so ideal as a bed material.

I ordered some single sided PCB material from Farnell. It works fantastically well. It seems to have a bit more grip than PET and has the advantage that there are no lines on the part from the joins in the tape. It also has no give in it, so I don't get any blistering at sharp corners like I did with tape, sometimes leaving shallow dimples.

Another advantage is that when the object cools it tends to break free because it contracts more than the bed does. With tape there is some compliance, so it usually stays stuck when the object cools and it is often hard to remove parts. With FR4, if you get the layer height spot on, the parts break free of their own accord, and if not, are very easy to snap off. This vertex bracket was loose after the bed cooled to 50°C.

Yet another advantage is that I stick the tape to a steel plate 0.9mm thick that weighs 280g. The FR4 is 1.6mm thick but it only weighs 134g, so less than half the mass.

I also tried some plain FR4 without copper and that seems to work just as well. It is 0.9mm thick and weights only 75g. The disadvantage is it is bright yellow, which makes it hard to see the white plastic on it.

I have printed a full set of Mendel parts so far on FR4 and every part has come out perfectly flat, and was easy to remove.

I don't know if it will degrade over time, but there is no sign of surface damage so far. The dark features on the picture above are marks on the aluminium plate underneath.

The nice thing about the z - probe I have on HydraRaptor is that I can change the bed without any calibration.

This is what the underside of an object looks like.

I used the same temperature I used for PET tape, which is 140°C for the first layer and 110°C after that.

I haven't tried PLA yet, but my guess is it will stick because it seems to stick to a superset of things ABS sticks to.

Great tip Wolfgang!

In the past I tried FR2 (SRBP, Paxolin) but that did not work, probably because it had a matt surface. I also tried some CAT7FR, which is another type fibreglass PCB material, but again it had a matt surface and did not work very well. I was able to build a flat object on it, but the first layer outline did not stick properly, so some holes were a bit scrappy.

The copper on the bottom of the single sided material could be used as a heater like the Prusajr heated bed design.

FR4 fail

Well it seems that FR4 only lasts for about a week. The grip slowly fades making the parts very easy to remove. In fact they all pop off as the bed cools below 60°C and slide about due to the fan and the bed's final movement to the front. The odd small part falls down inside the machine.

If I mounted my machine so it was inclined at 45° they would all fall out the front and could be directed by a chute into a hopper and the machine could then build continuously unattended. Who needs a conveyor belt! The only problem is the grip is now not enough to hold the bigger parts during the build.

I have tried cleaning with acetone but it doesn't seem to help. I suspect the high temperature is making the epoxy more brittle and less sticky. I will be able to prove that when the FR4 without copper on HydraRaptor fails. If I then turn it upside down and it still works on the under side then it is not a temperature ageing effect. If the other side is still working then it must be a reaction to the ABS or the acetone that is the problem.

It is shame because I much prefer a solid substrate to tape. Something like polyimide and fibreglass laminate would probably be ideal but it is hundreds of dollars for a piece big enough.

Wolfgang has posted a mystery material to me that sounds promising, so back to PET tape until it arrives. My friend Tony found that Farnell sells it in wider rolls. It seems to be a bit thicker as well, so is easier to apply, but a lot more expensive than the stuff from BestOfferBuy.com.

CU + PLA

Vik Olliver asked for a volunteer with a heated bed to see if we can extrude onto copper clad board. I didn't think it would stick, but gave it a go anyway.

I first tried ABS onto double sided copper clad FR4 taped to a bed at 120°C. The ABS stuck well enough to extrude the first layer of a 20mm square, but when it cooled down it had no adhesion at all.

PLA at 55°C did exactly the same, but PLA at 130°C stuck very well, so well in fact that I can't get it off with my fingers (the blob was where I aborted the print after the first layer).



Maybe ABS would stick in the same way at an even higher temperature, but maybe not as it is less like glue than PLA. The 120°C / 55°C temperatures are what I use for Kapton, which is why I used them as the starting point.

An interesting aside: I had to measure the PCB to work out the z-height. It is only 1.4mm thick, whereas a standard PCB is 1.6mm. You can also see the grains in the FR4 showing through the copper. This means the board I bought in Maplin for home PCB use is actually the same stock material that they use for the first part of a commercial production process, but when they plate thorough the vias they increase the thickness of the copper all over to get the standard 1oz/inch². I don't know if this is always the case, i.e, that all home made PCBs have less copper than a production one, or whether you can get bare board with 1oz on it already.

Anyway a good result, assuming PLA will resist PCB etchant. Also, it seemed like a potential bed technique. I.e. do the first layer onto hot copper and then cool it to about 50°C for the rest of the object. I tried it with this butterfly: -



It worked perfectly. After the first layer I blew it with a fan to cool it down to 50°C. It took about four layers to get down to that temperature. Since I added the insulation under the bed it takes longer to cool it than it does to heat it.

After it had finished and cooled down to 40°C it was still firmly attached, so I removed it by flexing the PCB.



The base of the object is perfectly flat.



I think for PLA this might be a better technique than Kapton. I can't imagine the PCB wearing out. It could also be self heating with a serpentine track on the other side. I don't know that just taping it down would be strong enough for making large objects. I could solder fastenings on the back if not.

I don't know if there is anything special about copper and PLA, or whether other hot metals and plastic would work . I tried similar things with ABS on AL, but may not have had it hot enough.