- The original aluminium plate was far away from being even. In the center of the bed there was an air gap of around 1mm between the aluminium and the glass plate – estimated at room temperature. In hot state it was much more. As air isn't the best heat conductor, it took a long time to get the glass plate on print temperature. If I was printing PC (bed set to 110°C) I had to wait at least half an hour – anoying!
- A leveled bed at room temperature did not mean, the bed was still leveled at 90°C.
- Leveling the bed was still improvable. It was much easier and faster than adjusting the original bed, but still took a few minutes.
The heater is an silicone heater glued on the bottom of the aluminium plate. There are versions for 12V, 24V, 110V and 220/230V supply available. Because of the bad performance of the original bed, I decided to increase the heating power – I have chosen a 220V, 750W version. If you are not familiar with installing components on mains voltage level, I strongly recommend to choose a 24V version (with the same power rating as the original bed)! It would also make the mod much easier, as the original power supply and wires are still usable.
In any case you should be prepared for modifying the printers firmware, as the built in thermistor is most likely of another type. At least that was the case here.
As I've chosen the high power variant, the heater is switched by an Solid State Relay which is controlled by the original heater output of the mainboard.
The springs I've used have the same dimensions as in my first mod, but are a little bit stronger. Maybe it's not really needed, but it helps stabilizing the bed as I'm using only 3 springs (and 3 thumb nuts) for the easiest possible handling.
I also designed a new set of stabilizers for the springs, these needed to be a bit smaller, as the bolts are mounted on the very edge of the aluminium plate.
At the beginning, my aim was also to have changeable bed surfaces by using some cheap window glass plates. But currently I think, I don't need this feature anymore because a colleague of me recommended to use a thin sheet (0.5...1mm) of Pertinax as print surface. After my first trials with this surface I'm really impressed. I was able to print immediately every filament I normally use (PLA, PETG, PC). My colleague is also printing ABS, TPU and others on it for years. The best is, this material is cheap and durable. If better sticking is needed, just do a light sanding (but do not breathe the dust!). The only disadvantages I know are: It takes some care on attaching and you shouldn't heat it above 120°C as it would produce toxic fumes. Also it smells a bit at the first few times of usage.
Overall there are a a lot of advantages and I wonder, why this material isn't recommended more often? Most likely I will stick a new Pertinax sheet directly on top of the aluminium plate later, I think I don't need any other print surface anymore.
Here is my shopping list:
- Silicone Heater 300x300mm, 750W, 220V with NTC:
I requested to get the heater with wires at least 100cm long, but still needed to extend the supply line.
- Solid State Relay:
- Heatsink for SSR (most likely not really necessary, but just in case...):
- Mounting hardware for SSR and heatsink, 0.5mm silicone pads for better heat transfer
- Casted, precision milled aluminium plate, 320x305x8mm:
- 3 pcs. countersunk head hex screws M3x40mm (from ebay or local shop)
- 3 pcs. M3 Thumb nuts:
- some washers for M3 (from ebay or local shop)
- some countersunk head hex screws M3x14mm (from ebay or local shop)
- 3 pcs. Compression springs 1x10x25mm (wire x OD x length): http://www.ebay.de/itm/121806473705
- Option: Glass plates 305x320x3mm:
(Not in stock currently, but there are other sellers.)
- Option: Paper Clamps for fixing the glass plates:
- Option: Pertinax 1220x915x0.5mm:
1mm should work as well, but I selected this to get a higher surface temperature.
- Option: 3M 467MP tape for sticking the Pertinax to glass or the aluminium plate. First, I ordered a 400x400mm sheet from ebay (http://www.ebay.de/itm/112239962371) but it was tricky to bring the pieces together without bubbles and wrinkles. My colleague is using smaller stripes, like this one:
I think this is easier to handle, but I didn't try it by myself so far.
- Aluminium plate:
Here is also an comparision of the original (red) and my new bed (green):
- Option: 3D printed corners (2x) for fast aligning of the glass plate:
Regarding the firmware, the most important thing is to select the right temperature sensor, in my case:
Code: Select all
#define TEMP_SENSOR_BED 11
Further, I found that there were relatively large fluctuations in the displayed bed temperature. This can be explained with the higher heating power. Even if this is more a cosmetic issue, it was easy to solve by decreasing the bed hysteresis and the control interval:
Code: Select all
#define BED_HYSTERESIS 1
#define BED_CHECK_INTERVAL 500
Below are some fotos from the build:
The heating pad arrived:
to be continued...