Heat Distribution on Heated Bed

[printbus]

The voltage loss is less towards the front since the traces there are only carrying the current for the forward section of the heater. Traces towards the rear are carrying more current for more of the heat bed, and likely explains why there's more voltage loss there.

Whether beefing up the distribution traces should be needed depends on whether the PCB layout person knew what they were doing. Trace resistance is a factor of trace width, trace thickness, and trace length. It would have been possible in the PCB design to tweak the trace widths or trace lengths in the different heater sections as required to achieve equal heat dissipation throughout the board. The reprap heat bed Wiki says the original MK1 design by Prusa should be within +/- 3 degrees C across the bed. Of course, the MK1 used by MakerFarm is custom, so what Prusa did may mean diddly-squat to the MakerFarm variants.

Note that you can't reliably use an IR thermometer on glass unless the thermometer has a setting for the emissivity of the surface being measured. Search on IR thermometers and emissivity for an explanation. Here's one reference.

How do you have the hot end fan oriented? A lot of people, including myself, flip the hot end fan around from the MakerFarm recommendation so that fan exhaust goes to the front of the printer. The bad side of this is that it can create a major draft across the heat bed in front of the hot end. I used to add a piece of painter's tape across the bottom of the hot end fan, shaped in a bit of a U to channel the airflow upwards. Now my fan mount angles the hot end fan upwards 10 degrees to help with this. A bit more of an angle would be even better.

IMO the forward part of the heat bed is naturally more prone to drafts in the room environment than the rear part. Most of my printing is done on a cold bed, but when I run the heat bed I *always* cover the heat bed with something like a piece of cardboard and let the heat bed soak at temperature about 10 minutes before starting the print. Regardless of how even the heat distribution is across the heat bed, I think that's important.