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.