PCB Heatbed MK2a
I have made a number of small design changes to the MK2 heatbed. These are as a result of feedback from customers and advice from members of the RepRap community, especially thanks to Nophead for his extremely helpful comments.
The resistance, track layout and dimensions of the board are unchanged, the improvements can be seen in this close up of the connection area:
Bed levelling. I added another mounting hole mid way down the front side. This allows for three point mounting and a much simplified bed levelling. I got the idea from Nophead in conversation and his blog post on bed levelling. It is worth noting that this idea has been addressed a number of times before using three points between the bottom and top plate on a Sells/Prusa Mendel: see Kritzinger.net and NumberSix's blog. The advantage of having it on the heated bed is machines like the Mendel90 with one platform under the bed can also benefit from the point mounting and easier levelling.
Cable soldering. On the subject of the Mendel90, soldering ribbon cable to the big exposed pad areas is much easier now (previously I had scraped an area to solder onto, once again copying Nophead, in this case in the Mendel90 build instructions). In addition the through holes are larger to allow for thicker cable to be fed through from the other side if not using ribbon cable. The redundant pads have been removed from the other side of the board as, with no plated through holes, they were not electrically connected.
Surface mount component sizes. The pad dimensions for the LEDs and resistor are enlarged to take 1206 surface mount components. These should be much easier to solder, I will post an update once I have assembled some boards and have some pictures)
The Eagle board file is available on the reprap wiki,and the boards are available through our webstore as well as eMakershop and eBay.