Building a second 3D printer - mounting, wiring up and configuring the heated bed

For the filaments I use, PLA and PETG, a heated bed is more a nice to have than an absolute necessity. That is why it is one of the last things on my list. And was the reason that I had the heated bed mounted to my printer MacGyver style for so long. I used clamps to mount the bed to the printer frame and bulldog clips to hold the glass to the bed. Especially with larger prints I always had the check that the end effector would not hit one of the clamps.

Clamps and bulldog clips holding the glass and heated bed to the printer MacGyver style

Design of the heated bed holders / adapters

These clips and clamps not only made my printer look cheap, it also made it impossible to connect the heated bed. The soldering connections were clamped to the printer frame. The holes in the heated bed are not suited for my Kossel XL 2020. They were intended for 15 mm bars. OpenSCAD to the rescue. I designed some heated bed holders/adapters to:

• mount the bed to the frame
• mount the glass plate to the bed
• wire up the heated bed

Lowest part is for mounting the bed to the printer frame

The holder/adapters I design do all of the above. They consist of an lower and upper part. The lower part connects the bed to the printer frame. One of them has room to wire up the heated bed. The upper part connects the glass plate to the bed.

The upper part mounts the glass plate to the bed.

Close up of the mounted heated bed holder/adapter

With these adapters, you can mount and wire up the heated bed, and the printer instantaneously looks 500€ more expensive :-)

Pile of prototype material

Wire up the heated bed

To wire up the heated bed you need wire, a thermistor and kapton tape. I ordered an 3950 NTC thermistor. You can find plenty of those cheap on ebay and chinese web shops. To mount the thermistor to the bed, first solder one of its legs. Cover that leg with some kapton tape, to mount and isolate it. Solder the second leg and cover the whole with another piece of kapton tape.

Thermistor soldered and mounted using kapton tape

Note that because of its size, the 3950 is not suitable for a hot end.

Thermistor and wires mounted to the heated bed.

Because of the current, you need thick wire to connect the heated bed. I had some beefy speaker wire laying around. The image above shows the wire attached for 24 volt usage.

Wire up to the RADDS-controller

I am using the RADDS controller. In the schema above, you can see how to connect the thermistor of the heated bed, and the heated bed itself.

Configuration

Configure the firmware

I updated three values in the Repetier 92.9 firmware that I use:
#define HAVE_HEATED_BED 0
#define HAVE_HEATED_BED 1
To let the firmware know there is a heated bed.

#define HEATED_BED_SENSOR_TYPE 1
#define HEATED_BED_SENSOR_TYPE 14
To configure the correct thermistor (the 3950).

#define UI_SET_PRESET_HEATED_BED_TEMP_PLA 60
#define UI_SET_PRESET_HEATED_BED_TEMP_PLA 30
For the UI controller; according to my PLA specification a bed temperature between 20 and 35 degrees Celsius is enough.

Also update the configuration string:
- "hasHeatedBed": "1",
- "uiPresetBedTempPLA": 30,
- "bedSensorType": 14,

Compile and upload the new firmware.

Configure the slicer

Also the slicer software has to be aware that the printer has a heated bed.
Update the configuration of your slicer software for that.

Configuration of the slicer software, Cura 15.04.6 in this case