It is already a couple of weeks since my heated print-bed from László arrived. I was busy so I didn't find time yet to update the blog, but finally here is my experience with building and installing it.

The print-bed is made of aluminium. It's heated from the bottom side using power resistors. The print is done on a Kapton-covered steel sheet which lies on to the of the aluminium bed and which is hold in place by powerful magents.

The bottom side has threads to attach 9 power resistors and pits where the magnets will find it place. First I covered it with Kapton tape, cut out holes for the resistors (I only used 5 in the beginning) and the magnets:

Then I added the magnets.
U/D stands for up/down for the orientation of the magnets.

László recommends to add iron bars on top of the magnets. This makes the magnetic force stronger. Neodym magents don't stand heat that well, but short-cutting them with the iron bars also seems to improve this.
I decided to mount all 9 resistors I ordered at that point, so I added the remaining ones too:

Then I wired the resistors. For a start I was only using 6 of them, this is why the middle 3 are not conencted. Here the 3 mounting screws an the z-switch holder are already added as well.

I tested the bed in this configuration, but it was not getting hot enough. Even with all 9 resistors it hardly reached the temperature where ABS sticks to the steel sheet, which should be at about 100-110°C.

So the next step was to add heat insulation. To prepare that I added the heat-resistant insulation for the connecting wires. I chose not to wire all the resistors together but have two groups with 6 and 3 resistors to have more possibilities later.

Then I covered the bottom side with the rock wool. I also attached a thermistor to the bottom side of the bed, so there are now 5 wires coming out there.
Shouldn't have done this in our living room really, it's quite a mess. I'm lucky I have an understanding wife.

OK, now the bed was ready to be installed. Removed old bed, replaced it with the new one, attached the power transformer, covered the steel sheet with Kapton.
I wasn't happy with the z-switch holder, so I replaced it with a newly designed one (more in an extra post later).

Turned out that the temperature now was ideal for printing ABS. I now always switch the print-bed on about 5 minutes before the print and leave it on for the whole print. With all 9 resistors connected (all parallel) the power transformer which comes with the kit is a bit too weak by specification. It gets a bit hot, but it works fine. I'll probably add a fan for it later.
I didn't measure the temperature, but the ABS sticks very well on the Kapton. I didn't have to do anything (like sanding) to improve the adhesion.

Here's a finshed print (lots of strings, but that's not the fault of the print bed). I'm using the scraper which came with my RapMan to remove the steel sheet (it's not that easy, the magnets are really strong). I added small pieces of card-board on both sides of the scraper so that I do not burn my fingers.
When the print is cooled down a bit you can remove it from the sheet.

Right now am really happy with the print bed. Its a bit costly, but it is nicely made and very flat. And it probably cannot be made cheaper really. You would have to go for a different approach like a circuit board, but I haven't seen one which covers the full RapMan print area.

I do not sand the Kapton, so the bottom faces of my prints are really nice, flat and shiny. I did not have any warping issues any more when using it.
I didn't print really big objects yet, this is one of the next things I will test, but I do not expect problems.

 

 

I had a couple of objects where I wanted a really flat, clean bottom side, which is hard to archive when printing on a raft with your RepRap/RepMan. So I wanted to have one of these heated printbeds where you do not need a raft - the objects stick to it directly and due to the heat they do not shrink while printing avoiding the warping problem ABS has which would cause the edges to come off the printing surface otherwise.

But I did not like spending lots of money in a machined metal table. I'll probably will get one now, but for trying it out and playing around I looked for something cheaper.

So here is my (roughly) 10$ heated printbed design. You need:

• flat piece of wood board
• a proto-board with stripes (something like this)
• Kapton tape
• old PC power supply

I soldered bridges onto the protoboard so that the whole board is covered by one long zig-zag ciruit. With my board size of 160x100mm (Euro card size) this resulted in about 2.5 Ohms. Attaching that to 5V resulted in about 60°C which is is not enough, but with 12V it was at about 90°C, which proved to be enough.

I covered the board with Kapton so that the holes are covered and ABS sticks much better to it. I mounted the proto-board on the wooden board using little wooden pieces as spacers which I covered with a few layers of Kaption tape for insulation. I wrapped some Kapton all around the proto-board and the wooden board which proved to be enough to hold it in place. I glued the wooden board onto the print bed mount of the RepMan using double-sided take. Pay attention to what take you use, mine was really hard to get off again.

In case you wonder, my proto-board was broken, so I soldered it together again. Made a bit of trouble, because it was not flat any more.

 

So does this work? Yes, I was able to print a couple of nice objects with it.
However, there are a couple of cons:

• The prints stick really well. This is good, but you have to wait for the printbed to cool down before attempting to get the print off, otherwise the object will get bent. Once I was ripping the proto-board off the wooden board while trying to get the print off. Also the Kapton tape came off easily.
• I had problems to get the printbed flat. Mostly because of the broken proto-board so that probably a problem that could be avoided easily.
• 100x160mm is enough for many objects, but if you have a RepMan you could do much larger prints. When using larger proto-boards the resistance will be different, so you need either a higher voltage or you need a different way to connect the stripes on the board. Either way you probably need a higher rated power supply.
• The proto-board started smelling funny. I think it was a really cheap one (don't know, I used one I had lying around) so this could be avoided by using a better, more heat-resistant one.

It was a fun experiment and useful for smaller prints. But I guess I get something better now.