T3P3 Kossel Mini Kit

Assembly Instructions

Chapter 23 - Heat-Bed Upgrade

Creative Commons License

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Think3DPrint3D Ltd


NOTE: This Chapter applies to heated beds supplied as an upgrade kit for existing Kossels after 23 January 2015. If you purchased a Kossel kit together with a heated bed then please refer to Chapters 15, 17 and 18

2301 Standard Components



200m diameter x 4mm thick aluminium plate with 3M ™ Kapton adhesive heater pre-applied. The heater is rated at 10 A, giving an output of 120W at 12V, and supplied complete with a MF58104F3950 thermistor taped to the centre of the aluminium plate.  Wires are prepared for fitting to RAMPS.

We have run these heaters continuously at 125ºC for 24 hours on our Kossel prototypes without any problems, and find that they heat up significantly faster than PCB heatbeds because of the higher power density (6kW/m2 vs 3kW/m2)

NOTE: The aluminium heat-bed as supplied may have some minor surface imperfections and scratches. You may care to rub it down with very fine (600 or 800 grit) emery paper to remove these and provide the smoothest possible surface for contact with the print glass, if used, or for printing on directly. The picture shows the top surface of a prepared plate.

Heatbed Mounts

12mm M3 plated brass M/F PCB standoffs x 3

M3 x 10 countersunk socket screws x 3

M3 penny washers x 3

M3 flat washers x 3

Z-probe retractor

Printed replacement for the standard Z-probe retractor bolt and penny-washer, with M3x30 socket capscrew to attach it. The height of the pillar can be increased if necessary by using the M3x12 penny washers previously used to attach the mirror glass print bed to its mounting tabs


Electronics cooling fan

40mm cooling fan with Molex SL-type connector

M3x16 socket capscrews x 2

M3 washers x 2

12mm M3 Nylon M/F PCB standoffs (may be black or white)

Fan splitter cable

Bulldog clips

3 x 19mm bulldog clips for attaching print glasses to the heat-bed.


Aluminium tape

Approximately 800mm of self-adhesive aluminium foil tape for covering the cardboard heat insulator

Cardboard insulator, pre-cut

185mm diameter cardboard insulator disc

Power Supply Unit

Dell DA2 power supply brick.

You are free to use an alternative power source that has 12V and 10A, for example an old laptop power supply or an ATX PSU. Just ensure that both power supplies are plugged into the same mains extension lead to avoid ground loops

Power/USB plate and cable


see Chapter 15

Replacement for the standard Kossel kit Power/USB plate, with a second jack-plug and cable for the heatbed PSU

2303 Dismantling

Start by removing the existing mirror-glass print-bed with its mounting tabs, and the Z-probe retractor bolt.

Retain the glass print-bed for re-use.

If you are going to use the optional 10 amp PSU described in 2302 above: 

remove the Power/USB plate, retaining the screws for re-use, and…….

remove the power lead and USB socket from the Power/USB plate.  The USB cable can be left attached to the RAMPS but the power lead should be unplugged from the RAMPS to fit a second lead.

2304 Fan

Assemble the fan mounting bolts , nuts and washers as shown:-

Insert the bolts in the 2 top holes from the label side, with the fan wires exiting bottom right.  Fit 2 flat washers and 2 nuts on the other side of the fan case, but do not tighten fully at this stage. Then fit the remaining items to each bolt in the sequence nut/washer/rubber ring/washer.

The rubber ring washer is to reduce fan noise being amplified by the frame.

Rotate the fan so the bolts are now on the bottom, being careful that the washers do not fall off. Locate the spare nuts you fitted in the bottom inside channel of the X-Y side of the frame base (Chapter 2 Section 207), slide them to the middle of the channel and screw the fan bolts into them as shown. Do not screw the bolts in too far past the captive nuts in the channel - they should not touch the other side of the groove.  Position the fan centrally behind the LCD controller.  Tighten the nuts to compress the rubber sound-dampening rings, and the nuts at the back of the fan.

Unplug the existing hotend cooling fan from its RAMPS pins and plug the splitter cable 2-way female plug in instead, observing the same polarity.  Plug the fan and extruder cooling fan plugs onto the 4-way male end of the splitter cable, again observing polarity.

2305 Power cable and Plate (optional)


See Chapter 15

   2.1mm            2.5mm             2.5mm        2.1mm

Fit the wires from the second 2.5/5.5mm jack to the 2 unused ways of the RAMPS power plug as shown,  and tighten them up very well - they carry a lot of power and will burn out if not fully tightened.


Fit the USB port and the 2 power jacks to the replacement Power/USB plate, remembering that the green RAMPS power plug will not fit between the beams and so the jacks have to be pushed through from behind. Observe the labelling: the left-hand power jack is the 2.5/5.5mm one, labelled HB above for Heat-Bed and 10A below. The original jack on the right side is labelled P for Power above and 5A below.

Plug the RAMPS power plug into the controller and fit the new Power/USB plate using the original fasteners.

2306 Heat-Bed Mount

Fit the 3 new heat-bed mounts centrally on each of the 3 extrusions, using the original captive nuts and new M3x18 socket capscrews. Do not tighten fully at this stage.

2307 Cardboard insulator

Cut a 165mm diameter cardboard insulator disc from a piece of scrap double walled corrugated cardboard (like the box your kossel kit was shipped in) If you only have very thin corrugated cardboard (<2mm) then you can use two layers, however only bother with aluminium tape on the layer next to the bed.)

Cover the top only with the aluminium foil tape provided.

Note that the total thickness of cardboard and aluminium foil should not be thicker than the first step of the stepped tabs, as a small air gap is required.


2308 Fit heat-bed

The aluminium heat-bed as supplied may have some minor surface imperfections and scratches. You may care to rub it down with very fine (600 or 800 grit) emery paper to remove these and provide the smoothest possible surface for contact with the print glass, if used, or for printing on directly. The picture shows the top surface of a prepared plate.

Note: we recommend using a mirror glass or other print surface, rather than printing directly on the aluminium plate.

Attach the 2 heavy red heater element wires to screw terminals D8 on the RAMPS. Make sure you tighten these fully and firmly because of the large current they carry.

Plug the black thermistor wires onto the T1 thermistor pins - the center pair immediately next to the T0 hot-end thermistor pins.

Guide the heat-bed power and thermistor cables out of the way and fit the cardboard insulator to the bottom tabs on the heatbed mounts. It is not fixed in any way, but just rests loose on the tabs.

Fit the heat-bed to its mounts, aligning the countersunk holes in the aluminium plate with the tapped holes in the mounts. You may have to move the mounts slightly to get them to line up, but try to keep them central on the extrusions.

Fit the M3x14 countersunk screws and tighten up  until you feel the printbed firmly in contact with the mounts. Do not overtighten as you may strip the threads tapped into the printed parts.

Print Surface:

You may print directly onto the aluminium plate with your surface preparation of choice, but we recommend clipping a prepared glass mirror plate to the aluminium plate with bulldog clips. This takes slightly longer to heat up but allows a hot print to be removed immediately it is finished - carefully, with gloves!

We then fit a spare glass plate and start preheating it at once, for the quickest possible start of the next print. The clip positions need to be carefully chosen so they are not hit by the hotend - those shown work best for us.

The picture shows a blue tape covered glass plate for printing PLA, but internet research will show a plethora of available print surfaces and treatments depending on the material.

2309 Z-Probe retractor

Fit the replacement Z-probe retractor as close to the original one as possible. It will probably be slightly towards the Z-tower to accommodate the bulldog clip, and will need to be recalibrated following the procedure outlined in Chaper 19, section 1905 - Set and test Z-probe retract position

2310 Update Firmware

If you are retrofitting the heat-bed to an existing Kossel then the Marlin originally supplied will not have the correct thermistor table for the thermistor supplied with the Kapton heater.  You will need to use the Marlin version now distributed on the T3P3 Github.

Download the Marlin zip and extract, transfer your printer calibration settings in configuration.h and check that the heat-bed is enabled as below:-

#define TEMP_SENSOR_BED 11 // T3P3 alu heatbed with Kapton heater and 3950 thermistor

(Thanks to Chirpy’s blog for publishing the required thermistor table)

2311 Connect Power Supplies

Connect both power supplies , making sure you use the correct jacks, then power up. You should be able to hear the electronics fan come on, and feel a slight draught from the gap between the Y-Z base extrusions.

NOTE: Ensure that the heatbed PSU is firmly plugged into the jack and try not to disturb it too much. It is carrying a heavy current and poor contact between plug and socket could result in the plug burning out.

2312 Test

If you have successfully modified and uploaded Marlin with the heated bed enabled then the bed temperature will show up on the top line of the LCD display, to the right of the hotend temperature.

Test the bead heating by selecting Control> …….

Temperature> ……..

Bed>  ……..

and setting it to a suitable temperature for PLA, e.g 80ºC.

The temperature should rise to 80ºC in 5 to 6 minutes and settle there.

That concludes the heat-bed installation.

We have done a significant amount of printing in ABS since fitting the prototype heatbed and find that it is easily able to reach and maintain 125ºC. One of the first items printed was a pair of eggO egg-cup “seats” by Mageli, seen right. These were printed using the Kossel_medium Slicer configuration  with appropriate temperature changes and came out as well as the PLA ones previously printed (below)

PLA egg0 eggcup