P3Steel Build Log (#14) – Heated Bed / Build Plate

Choice of Print Beds and Heated Beds for 3D Printers

When building a 3D printer, there are lots of options you can go with for a build platform, and whether to have it heated or not. I will not go into all of them, but simply state what I am going to use compared to Toolson’s designs. Toolson ended up using a 6mm custom cut Aluminium bed with a silicone heater and a solid state relay to power it. I am far too frugal to go with this option, but did want an Aluminium bed, to work with a glass as a print surface, and to have the option of heating it. Turns out there is a ready built solution for this which is highly used – so that is what I went with!

MK3 Aluminium Print Bed

This is my bed I am going to use. The “MK3 Aluminium Heat Bed” – a 3mm Aluminium bed with a copper traced heating element on one side (covered by the black and white paint job!). I purchased this from AliExpress (where else!?) as a whole unit which included the heater cables, 100K Ohm thermistor and board LED which lights up when it is activated (and heating). The heater cables were also pre-soldered onto the board. If these joints look dodgy if you get a pre-soldered board – re-solder them, as they need to have a good thick and reliable connection.

You can find my exact listing here – MK3 Aluminium heatbed.

With the whole unit provided it was easy to assemble it and get it mounted. I planned on having the silk screen print face up (as I am going to use glass as the print surface) so I needed to route the power cables and thermistor from the underside. I may well change this configuration in the future and print directly on the Aluminium bed on the other “plain” side… we shall see.

To route and mange the cables you need to stick them down, and as this bed is capable of going up to and beyond 100°C we need some proper tape – in comes some polyamide tape, aka Kapton tape.

The MK3 bed has a small hole in the middle of the Aluminium sheet, ideal for a small 100K Ohm thermistor to sit inside. I like this idea as it sits within an air pocket and is not in direct contact with the heating element or heated Aluminium. Whether this was the intention I am not so sure – but it works for me!

So with the silk screen facing down I routed the power cables around and to the plain side. (I also intend to have the silk screen text facing me so it reads correctly when looking at the printer, pure vanity!). First tap down the power cables so they are secure to the bottom side. Then I routed them down to what will be the back of the heated bed and taped them down with more strips of Kapton tape.

I then installed the 100K ohm thermistor in the hole in the middle and routed that down next to the power cables. I added extra tape and secured those lines too. You can see my neat tape job below – don’t ask me to wrap any Christmas presents for you….! 🙂

Silicone Dampeners, not Springs

Hey – remember this post? Here are the silicone dampeners now in place below:

The bed screws (M3) just slot straight through the silicone moulds and fasten up with the bed frame. You can add in an M3 nut here, but to be able to adjust the bed level via the corners with ease I have opted for some M3 knurled knobs. They screw on and with a few extra turns the silicone gives sufficient resistance to push back and hold them all in place without vibrating loose.

Fitting the Heated Bed and Borosilicate Glass

Better shot of the bed on the bed frame is seen below – Purely for aesthetics I have gone for the silk screen to be readable from the front, so as per the wiring of the heater and thermistor above, they loop under and to the back of the printer which you are looking at below.

Next on top of the bed is the glass build plate, the borosilicate glass bed (borocilicate to help with the heat and less likely to crack and shatter!). Don’t just just window glass here!! It will be fastened to the bed with some bull dog clips and maybe some of those clip frame photo frame clips. I’ve not made up my mind yet, but I don’t want the clips to interfere with the hotend in any way, so I want them to be as low profile as possible.

And seen from the front – the finished heated bed and glass build plate.

The heating wiring and thermistor wires will be covered in protective tubing, but for now a few cable ties help neaten up the wiring and keep them together. You can use the additional (unused) mounting hole at the back of the bed frame to zip tie the wires to the bed frame. This will stop them from pulling on the Kapton tape and solder joints when the bed is going back and forth. When you can, you should always go for physical fastenings with moving machines to limit wear and tear on weaker parts.

Glass Build Plate and Polyamide/Kapton Tape

Now that the heated bed is all sorted and I want to print on the glass plate for ease of use and a smooth flat surface – I want to help my parts stick to this glass plate. Again – there are lots of different methods to do this with varying degrees of success. I have always liked the idea of using Kapton tape as a replaceable, strong and flat surface. Ideally I would like to use PEI – which seems to be the latest surface which sticks well and is almost indestructible. But is it costly, difficult to apply and hard to source here in the UK. So I am stuck (happily) with Kapton tape for now. And to help improve the application and final finish of the tape I also didn’t want lots of small strips of it – so I went with some large “A4” style sheets, rather than a roll of it. To get the sheets I got, click on this AliExpress link – 3d Printer Kapton Sheets from seller yihong (http://s.click.aliexpress.com/e/rzzVRnY). I got a pack of 10, so it should last me a long time, even with the mess that lies ahead! 😱

Behold.. the glass and the Kapton sheets below. (you try photographing glass….!)

And speaking about that mess – Have you ever tried to lay down a sticky piece of tape 200mm by 200mm perfectly flat?! Turns out it’s quite tricky, and results in lots of bubbles! I give you exhibits A, 2 and D!

There has to be a better way, and turns out it’s much like applying transfers and other sticky things – you need to get wet.

Applying Kapton Tape Sheets to a Glass Bed

The trick, which is an old trick for applying large transfers, installing anything that is a tight fit etc – and that is to get things wet and slippy. I think the first time I came across this was when my dad taught me how to get new handle bar grips onto my BMX bike, by applying some “fairy liquid” dish soap. With that lubed up the grips slipped on, and then you just go off and wait for the soap to dry and evaporate.

Same principle here, you need something wet and slippy which will evaporate without trace. Turns out window cleaner, aka Windolene here in the UK works a treat!

You cut your square of Kapton as per normal, start to pull it away from it’s plastic cover at one corner and then apply it to the glass which is now covered with a light spray of Windolene. The more Windolene you have on the glass, the less likely it is to stick, but the longer it will take to evaporate and adhere the tape to the glass. Pull all the Kapton tape off it’s backing and down onto the glass. Try not to crease the tape as you will struggle to get any crease marks out!

You need to hit a happy medium here – but you should be able to move the full square of Kapton around the glass with ease and squeeze out any bubbles with a dull edge blade like a credit card. With the adhesive not working, the Kapton will want to curl up and the edges. I found after squeezing all bubbles out and getting it perfectly flat and bubble free I would lay up several glass “place mats” I have on top and then just leave it for several hours, or overnight.

The end result – A Kaptop surface that is free of bubbles, edges or creases, stuck like 💩 on a mattress! See below for some better examples of how I got on. And you get better each time you need to replace the tape!

Now that the heated bed and build platform are in place, we’re just one more step closer to finishing this beast! Next stop – we’re going to hop up to the top and sort out the extruder.


18 comments on “P3Steel Build Log (#14) – Heated Bed / Build Plate

  1. Hi,

    I really like your blog, and I use it as “manual” for my current build: An upgrade from an Prusa i3 to a P3Steel Frame with Toolson Parts (Which I have printed on the Prusa i3). So thanks for that effort!

    I am questioning myself why you added Kapton to the glass. I am using a borsilit glass on the heated bed of my i3 without any addons. As long as the glass is clean (I use window cleaner before each print) and heated to the right temperature, I have perfect adhesion of the printed part to the glass with PLA and PETG, and as soon as the glass gets cold, the parts are very easy to remove.


    • Hi Chris,

      Thanks for the comment, much appreciated! Sorry it’s not fully written up!

      You know – I have no idea why I use Kapton tape?! I assumed it was the norm for glass plates, but maybe it’s more for Aluminium plates?! I am getting annoyed with it – as I seem to “nip” or “nic” it in one spot (usually the middle!! 😭) and it ruins the rest of the plate until I replace it. I use window cleaner too and it really works wonders. I think with your suggestion, when this latest tape wears away, or I bite into it with some pliers – I will try just bare glass as a surface. Sure would beat faffing with the Kapton tape!

      I do have one last experiment with the Kapton tape, fore which I will need it. I am not always happy with the super shiny surface it produces (glass too) compared to the rest of the print. Blue ‘painters’ M3 tape always gave a good ‘similar’ texture and shine to the rest of my print surfaces when I used that, and I miss it. I was going to experiment “sanding” the kapton, with some very fine sandpaper or even rough “wet and dry” to lose it’s shiny surface. This may lose it’s ability to hold prints?! We will see….

      Thanks for the suggestion though. I will give it a go!


  2. Hello Steve,

    Thank you for the blog on building the i3 Steel Toolson. I’ve selected it as my build too and I’m now sourcing materials, getting the metal parts cut as well as getting the 3D printed parts printed as well.

    I’ll be doing my own blog on building my printer and where to source stuff from here in Holland. I’ll make sure to add the rightful owners of the stuff I buy and source on my blog.

    Again thank you, best wished for the holidays and a happy new year!


    • Hey Leon,

      Thanks for the comment, and glad you like my build log! I hope it will be of some use to you when you start to build! Best of luck with your build – what is your blog name so I can check it out?!

      All the best for the holidays!


  3. Hi Steve
    Loving this blog so much that I have ordered a Cheap Chinese Prusa i3 clone to print and build my own P3steel.
    I have one question/request would be possible to show in the blog how to set up Arduino and the printer with a slicer?
    Thank you very much for this build blog really looking forward to read new posts!
    All the best

    • Hi Francesco,

      Thanks for the comment, and best of luck with your build of the P3. Buying a cheap Chinese clone to print your own parts is a good route. You will learn a lot about 3D printing as you go and the skills are transferable to your new printer. And then you have two printers to work with!

      Regarding the setup of Arduino – I have not finished the write up of my P3Steel build and there are still a few more build log updates to go. Arduino, Marlin and possibly a slicer blog are all on the cards – I just need to get round to finishing them!! I got a laser engraver for Christmas, and my P3Steel has been built, finished, working and upgraded (already!!) for some time – so I REALLY need to finish off the build log!

      You can sign up to get email alerts when I post a new blog, there’s an email form on the right hand side widget sidebar.



      • Hello Steve, can you tell us more on the upgrades you have made ? I am building the same P3Steel Toolson and it would be great if i could include the improvements !
        And keep up the good work, your build logs are great and i can’t wait for the next steps ! (hotend assembly, wiring ?)



        • Hi Michael,

          Thanks for the comment. My upgrades are all usually just in ‘testing mode’ at the moment – probably best if you read “upgraded” as “repaired”!! 😄

          I do use Octopi and am still in the middle of choosing a case and where to place it on the frame. I have also (again, not finalised) printed a case for a 12v->USB adaptor that will be bolted to the frame of the P3Steel and will power the Raspberry Pi and maybe even my GoPro when taking timelapses – I am sick of having so many plugs in use, and the PSU is rated high enough to take an extra amp or two (blog post to be added!).

          I am also replacing the X and Y pulley idler bearings for actual GT2 20 tooth idlers rather than the flanged bearing setup. The GT2 idler doesn’t fit in the idler bearing blocks, so tweaking these as we speak (blog post to add!).

          Biggest upgrade really, which isn’t really an upgrade but more for reliability is the re-print of all parts from PLA to PETG. I did not have a heated bed till this P3Steel so could not reliably print PETG. A lot of my PLA parts are cracking and you will have seen in other posts I have had to tweak some of the STL’s to be beefed up around the nut parts which broke using building. PETG is stronger and will last much longer. Got the replacement orange in PETG and plan to do this soon – bbbuuuutt…. my z-axis threaded rod went horribly wrong recently and I am trying to eliminate a tiny (TINY!) z-wobble I can see in my prints. Once this is resolved the PETG parts will be printed out and replaced.

          And then following on from my z-axis issues – I am no longer happy with my M5 threaded rod for the z-axis and looking to upgrade to 8mm trapezoidal lead screw – it is overkill in terms of trying to improve print quality, but does improve reliability and maintenance (just finished a 30 hour print for a 3D Hubs customer, I need reliability!! 😅).

          IT…NEVER…ENDS!! 😂



  4. Thanks Steve
    Subscribed on both Blog and Youtube!
    Looking fwd to the new posts
    Have a nice one

    • Thanks Fran! Much appreciated!

      Just posted the next blog update, you inspired me to crack on with the rest and get it finished! ha!! 😂


  5. Hey,

    Thank you for sharing your build; it’s an asset to the community. I am wondering if it might be possible to constructs a P3Steel (Leonardo V2.5 frame) with an MK42 -size heated bed.

    • Hi Iden,

      That’s a good question, and one I have been wanting to play with. The MK42 bed looks great, and is really only a little bigger than the 200*200mm standard bed you can usually get. I think it would fit width wise, as the 2.5XL frame is a little wider than the standard 2.01 frame. The issue may be the length – I think the new MK42 bed uses a new y-axis bed frame which reduces the distance between bearings to allow for longer travel before the bearing hit the end and the endstop(s).

      After looking further with the MK42 bed – it looks a little more complex to use and you would need to know the Prusa version of Marlin to take full advantage of all the extras the bed uses (proximity spots, alignment, heat zones etc)? This is a little further than I wanted to go – so I (and you) may want to look at some of the 300*200mm Aluminium beds out there? These beds would require amending the y-axis bed frame and the length of the y-axis increased. There is a “plastic” extension of the y-axis on Thingiverse which requires you to only buy new 8mm rods, not any new Steel frames.


  6. Having gone through the 12V shenanigans of powering the heated bed, I quickly adopted the 24V approach.
    A 230V – 24VAC, 250VA (secondary 10.42A) safety transformer sets you back roughly € 45,- and a Solid State Relay just a few quid.

    I’ve wired the SSR to the secondary wiring of the transformer and use bang-bang control for it.

    It heats up the bed within 8 minutes to 90 degrees, haven’t gone higher but I think it’ll do much more. At 90 degrees, the duty cycle of the SSR was 10 seconds on / 10 seconds off with a hysteresis of 0.5 degrees C.

    Hope it helps.


    • Good info Leon, much appreciated! I do see my 12v bed struggle to keep temp. One of my many upgrades would be to swap to a 24V system!



  7. Please do put things in proper context. You’ve flipped the heated bed because the Swiss clips you’re using will damage the heating element.

    • Actually no Bernard. There is no right or wrong side to flip these beds, but as I was using a glass plate, and like the look of the silkscreen, I wanted it this way. With the heating element against the glass I found it gets to temperature quicker. Good point on the Swiss clips scratching through the solder mask, but that wasn’t my reasoning.

      Thanks for the comment.


      • Thanks, Steve, for the clarification. You may want to note the reason for flipping the bed, as technically it’s upside down—you can print directly onto the aluminum. To add, I am unaware of glass as a good thermal insulator. How much of a difference in heating time have you noticed? Lastly, it would be apt to explain the choice to use Swiss clips (as they’re are uncommon) and the caveat that their sharp edges damage anything they contact.

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