Printrbot – heated bed

The break in posts on 3d printing does not indicate that nothing has happened in the time passed. On the contrary, I have been too busy exploring various smaller problems and ways to improve.   The most important improvement is the installation of the “heated bed” upgrade that has been waiting since I got the printer. I left it alone for a while because I wanted to get some experience with printing on the unheated standard bed. I think now it was a good idea, because I can see the benefits in better perspective after installing the upgrade.

So what exactly is the “heated bed”? It means that the print surface is heated by a heating element so that the plastic parts do not warp as easily (or at all). With the unheated bed there will be temperature gradients in the parts causing warping, especially when the print surface is relatively large, i.e. longer than just a couple of centimetres.  With the heated bed the temperature is more uniform through the part and you can then create more geometrically accurate parts. Since I am mostly interested in mechanical parts, it is important.

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The upgrade kit contained a machined aluminium print surface (bottom right). Being machined, it also provides a flatter surface than the standard bed, which can be slightly non-flat. The other main parts are the 2 black aluminium “wings” that are needed for the X belt after removing the standard non-heated bed. At top left is the heater element with 12V wires and next to it is a sheet of heat resistant Kapton tape which will be fastened to the aluminium print surface. In the bag is a thermistor that will be used for monitoring and controlling the bed temperature. Both the thermistor and the heat element power wires connects to the board under the printer. The bag also contains delrin parts to help insulate the “wings” from the hot print surface.

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On the underside of the machined print surface, there are grooves that must be electrically insulated using Kapton tape. The biggest groove will contain the soldering points on the heater element and the smaller groove is for the thermistor.  After placing the thermistor in its place, the heater element is put on top (i.e.  under it, since the print surface is upside down still). The black & white wires are for the thermistor.

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Over (i.e. under) the heater plate comes a reflective sheet that is simply screwed into the corners. I added some Kapton tape pieces to secure it. I am not sure this is sheet very effective, heat is lost not only via radiation. It would make sense to let the sheet cover the whole plate also. But this is according to the kit.

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What remains after this is to turn the heated bed around and connect the X-belt to the wings and then connect the wires to the board. But I also added an update of my own. Under the 4 corners of the heated bed I put a flat and a split washer so that it is possible to manually adjust the “bed level”, i.e. manually make the print surface as perpendicular as possible to the print Z-axis of the printer.  The goal is not to replace the Z probe which accounts for unlevelled beds automatically, but  to ensure the adjustments are very small.

Once installed, we have a new and shiny printer! Notice also the Raspberry Pi  Model B in the background, that is the other important upgrades that the recent weeks have seen.  Instead of connecting the printer to the main computer, the Raspberry PI is committed as a wireless printer server, running OctoPrint . OctoPrint provides a web interface, so you can access the printer via any browser, anywhere. This is now the standard mode for how I  operate the printer, it is very convenient.

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Also in the background is the new power supply serving the printer. The standard laptop-style power supply that came with the printer cannot be used with the heated bed, you need a power supply with more “grunt” as the heated bed draws about 7A  at 12V.  The power supply I use is rated at 10A and seems to be working fine for the job.

Below is how OctoPrint reports the temperatures of the bed and the hotend. The bed can reach 100C in about 14-15 minutes from a starting point of ~20C which I find adequate.  100C is required for ABS, but for PLA 60C is sufficient, it achieved in about 5 minutes.

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The temperature curves above are not really reflecting the standard heated bed upgrade shown above. It reflects an additional modification. I noticed that the black “wings” of the heated bed got quite warm, they acted as heat sinks and radiators, even with the delrin pieces in the kit that were supposed to insulate the “wings” from the machined print plate.  It probably has some effect, but a lot of heat is lost that way still.  The curve above shows the effect after installing the “blankets” described below.

It seems like a good idea to put a “blanket” over the wings to reduce the heat loss. I did that by designing hollow covers to go over the wings. They are designed as solid parts, but printed with “hollow” infill and 0.8 mm skin. Below is how it looked during early print, there are for parts since each of the two wing covers are split,  you cannot print a part covering the whole print surface on the same print surface…

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After completion, you get this nice looking view, four parts complete with holes for screws and belt tensioners.

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These parts simply “snap” onto the wings, the heat loss is now much reduced.

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I am very happy with these changes. The power supply is working, the Raspberry PI with OctoPrint is the perfect way to operate the printer, it works flawlessly even with the older Raspberry PI model B. It also frees up the main computer during long prints.  The heated bed itself works fine, I can now print large parts without warping and I am also ready to consider printing ABS.

4 thoughts on “Printrbot – heated bed”

  1. Hi,
    Just read your post about the heated bed wings insulation and I’m interested in trying them out. Any chance you can share your wings design?

    Thanks!

  2. Hi

    I have a printrbot play and I’m going to install a heated bed.

    I have two questions. I guess the aluminium bed is 6mm thick, but how deep is the machined section where you put the heat plate? I will make a larger aluminium bed to cover the PCB heat plate which I have since before.

    How much of the heat goes downwards? There are belts running directly under the bed and i dont know if they will be affected?

    Thanks, in advance

  3. Hi Richard, I don’t have a printrbot play, so I cannot answer for that, I will try to check my simple metal bed and give you some numbers. I think my bed is thicker than 6mm, but I am not by my printer now. I think you should aim at machining to the depth of your PCB heat plate.

    There is a reflection sheet as you can see from my post, but this does not help much. I think you should aim for cardboard insulation under the bed. The cardboard may of course be covered in reflective aluminium. Then you insulate for both radiation and convection, much more effective. But you need to have some space for it.

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