I’ve been interested in 3D printing for a while, but could never justify spending hundreds of euros on something I potentially only would use a couple of times a year. Until I was browsing an online second-hand marketplace and saw a second-hand 3D printer, that was so cheap, I couldn’t pass on it. It is a basic model from the German electronics retailer “Conrad Electronic” released in 2018. Its features are fairly limited, especially the maximum build area is tiny with 10x10x10cm, but I thought it’s probably good enough for the things I’d need a 3D printer for: mainly small cases, mounting brackets etc. for electronics projects.
I was having some initial success with small and simple prints, but I experienced massive warping and bed adhesion issues when printing larger objects.
After trying out different settings with various degrees of success. I decided to upgrade my printer with a heated print bed. Heated print beds are a standard feature in newer/better 3d printers, they help mitigate warping, by preventing the printed parts from cooling down too quickly. Additionally they help with bed adhesion, by softening the material slightly in the first few layers allowing it to stick better to the print bed. In order to print more advanced materials they are a necessity.
Later it turned out, that the root cause for most of my issues was the fact, that the filament I was given from the seller, was in fact ABS and not PLA as I thought. Since ABS requires higher temperature settings on both the nozzle and the print bed for successful prints and is nonetheless quite prone to warping, the initial results make total sense in hindsight.
Heating the Bed Link to heading
The printer uses a 150x150mm glass plate as its build plate. It comes pre-applied with a textured sticker that is supposed to help with bed adhesion. Glass has good thermal conductivity properties, hence it should be able to distribute the heat evenly. I don’t know the maximum temperature rating of the specific glass used, but it should be fine for the relatively low temperatures required to print PLA (around 60°C).
In order to heat the glass I decided to use 0.5mm NiChr resistance wire. The wire was laid out on the glass in a regular pattern and is held in place by Kapton tape.
Temperature Control Link to heading
To achieve good results it is necessary to control the temperature of the print bed, especially it is important that the temperature can be kept at a constant value.
In order to control the temperature, I attached a temperature probe to the bottom of the glass build plate.
The initial plan was to build a simple thermostat using a microcontroller that can be set to a specific temperature so that it controls the heating such that the temperature is maintained. I quickly realised, this it is not really necessary.
I’m powering the heater using a Lab-power-supply, which allows me to control the current limit in a fine granular way.
With this I can use a high current to heat up the build plate quickly to the desired temperature and then lower the current limit to a value, that sustains the temperature on a nearly constant level.
Setting the current such, that the output power reaches 150W allows me to heat the build plate to 60°C within a minute.
In order to maintain the temperature, I need approximately 20W.
Naturally this is not ideal by any means and is especially not suitable for unsupervised printing, but it’s good enough for my needs.
Results Link to heading
With the heated print bed I am now able to get significantly better print results. Even when using ABS, bed adhesion issues are gone and warping is minimal.
After some test runs it was clear, that the adhesive of the original print surface sticker was not suitable for higher temperatures, as air bubbles started to form under it, leading to an uneven print surface. I exchanged it for a magnetically attached PEI sheet which gave me good print results. Additionally, I added a display to show the bed temperature, so I don’t need to use my multimeter for it, this is wired directly to the printer’s power supply, so it turns on with the printer.
