Got the heat bed done. Was a little complicated due to its size. I got it flat (checked with a precision straight edge) but will lap the build surface to eliminate the facing tool marks. Running my finger across it I can not feel the tool marks, it feels completely smooth. Specs: 1/2" MIC 6 18" sq.
You people and your CNC machines make me so jealous! That looks awesome Kyle!
Beautiful surface finish!
Now PEI coat it! Looks good
Thanks guys!
Step - I am having a very difficult time finding any one in the US that does PEI coating on aluminum. I’m stumped…
I know… I too has done my research and my conclusion is the same… no one here in US seems to be practicing this PEI coating method… I ended outsourcing from Germany…
Looks great! I did a bed like this a few years ago using Mic 6. I machined a cavity like you did, leaving a bit of a flange all the way around. It was really great for a while, then it became slightly domed in the middle, a little over 0.2 mm above the corners. I had probably put a couple hundred hours on it by then, printing ABS with the bed 90-110 C. This was horribly disappointing of course.
I looked at some similar stories from the manufacturing world where Mic 6 plates were used for cooling production parts. They were complaining about a similar problem where the repeated heat flux in one direction caused the Mic 6 to distort.
I decided that if I make another Mic 6 heated bed, I will make it reversible, and I’ll try flipping it every so often. I hope you get better results than I did!
@Robert_Swarner Or try to use better aluminium, e.g. EN AW 5083
@Kyle1 PEI coat it yourself… Dissolve some PEI in chlorophorm (go outside and use proper gloves) and tint the previous eloxed alu with it. Done.
@Rene_Jurack That was the point of using Alcoa Mic 6 cast tooling plate, like the OP has done. It is the better aluminum for this application. Extruded, or rolled material like you suggest, contains residual stresses from the manufacturing process that cause it to distort when machined. Mic 6 is cast, then stress relieved in an expensive process so that it won’t.
EN AW 5083 is cast too. Didnt know Mic 6 was cast.
Step - So you do feel my pain lol. My google searches for PEI have indicated that mainly labs are using the process to do something with cell cultures. Very little info about it being used in industrial applications. I have thought about sending it off but would like to see if I can do it myself.
Rene - I cant seem to find any info on a DIY process or where to source the coating from. There is a large anodizing plant here in town that I have done some work for so they maybe able to help with the process. Any info you can share would be appreciated.
Robert - That is an excellent idea. I did not think about it warping from being heated in one direction. This was my first time working with MIC 6 and was not that bad just the size was a pain. I know what to do now when I need to make another bed. My bed is 0.33" thick center and the sides I left at 0.5" My thinking was that the 0.5" web around the bed would help eliminate any possible warping.
Nathan - You are right. That is probably why it is has been very difficult to find a PEI coating service and why only labs are implementing the process because they have access to such chemicals.
I tried pei coating briefly last year. Didn’t really have time to pursue the method to get it perfected. I might come back to it when I have time.
@Step_Cia Hi, where in Germany did you get pei coating ?
We have produced a LOT of mic 6 beds over the years. The Printrbot plus uses a 11"X11" mic 6 bed for a 10x10 build plate. My machinist and I have talked a lot about it. Adding the pocket on the back can certainly cause the metal to move in some cases. We reduced the depth of our pocket as much as we could. I even had some made without any pocket. But when you heat it from one side- it does warp a teence and relaxes as it evenly spreads the heat over time. Heat beds tend to heat most rapidly in the middle and also cool more in the corners making the problem worse. Maybe we should all have circular beds. 
The warping on mic 6 is very very slight and almost imperceptible when all is said and done. We attach our linear rails to the bed in y axis and had to spring the carriage in one side in case someone tried to print while it heats up- it would bind. We solved it by using every other hole in the rail, insulating between the rail and bed and springing one carriage. Funny how I expected 1/4" mic 6 to be problem free, but physics is powerful… Metal moves when heated and it is a powerful force!
Best of luck
Brook
You can easily find German online retailer selling 3mm-5mm thick pei coated aluminum. But only a handful that would want to ship to US with reasonable rate… Use “dauerdruckplatte” when you search prepare to turn Google German translation to English on. Good luck.
@Step_Cia Thanks for the quick answer. I am from Germany But I had no luck finding someone to coat my 1.2mx1.2m 12mm thick aluminium plate ;-(
because you would not want that coated.
In this size, it’s much easier to go with a different print surface… and maybe cheaper too…