Better Heated Bed? (Page 1 of 2)

Sure you can. 

200mm x 200mm is the most common size.  I have a MK2B on my SD3 and so far it's been the best heated bed I tried.

dont know if it will help you any, grob, but our Folgertech 2020 Prusa came with a MK2B bed - for the glass topper I simply laid down some Kapton tape on the MK2 and hairsprayed the glass to that to avoid using clips.

Been considering stealing the Mk2 from the Prusa and installing it on the SD4... LOL

Happy 1,000 Pirvan

Didn't even notice until you guys pointed it out...

... I guess that makes this one 1001 

BTW, here is a link to the original post on my MK2 installation

http://www.soliforum.com/post/58679/#p58679

I would hope my comment was taken to mean that it doesn't matter if the platform is Aluminum, or Copper.

I'd like to think folks here are smart enough to figure that part out.....

Correct me if I am wrong but most kits and builds I have seen that use a pcb type heater have nothing under it. It is used to heat a plate of glass or aluminum placed on top of it. My last two printers I had where made that way as well.

3mm thick glass is not going to flex so the pcb would not flex either. The perimeter of the pcb can be drilled if needed, the etchings are usually a quarter to half inch in and only on one side. But whatever works best for you, I was just pointing out the normal use of the pcb type heaters.

So tidy - the VHB tape will have a tiny amount of give in shear so it will probably not do the whole bimetallic-strip flexing thing when it heats up. So sensible, and think of how easy this would be to assemble for a manufacturer...

My plan is now to keep the existing alu bed, but assemble my MK2 on top exactly how you've done with your copper plate. Thanks Pirvan!

Here's a good thread you may want to read.
http://www.soliforum.com/topic/9004/sd4 … tallation/
On the third page, I had come to the conclusion that SD was on the right track with their design.  Just needed beefing up (thicker Aluminum plate, higher wattage heater).

Hi veehoo,

I've got the same setup, and seems to be working well. A couple of application notes if they're helpful to anyone:

* I drilled a reasonably-sized hole (8mm or something?) in the middle of the aluminium to pass the thermistor cable through, thermistor was glued in place in the middle of the MK2B with RTV silicone. Once I'd taped the MK2B down, I then taped the thermistor cable under the aluminium so it doesn't pull out.

* I let the power connections to the MK2B overhang the edge of the aluminium plate a little, so they didn't short. Otherwise was looking a bit close to the plate for comfort, especially considering a head crash or a bit of mucking around could compress the VHB a bit...

* My MK2B had a bow in it, which I had to flatten out by clamping it to the glass initially, and heat cycling. The flexibility of the VHB meant it was stretching up in the middle and compressing down at the edges, and remained a fairly poor contact with the glass initially. Now it's settled down and I'm back to hairspray attachment, which is a relief.

15-20 mins doesn't sound extraordinarily slow to go from 20Cish to 100C stable. I'll probably do 10-15. My plate does get warm, I tend to avoid touching the whole thing anyway. Slowness and heating of the plate is not necessarily something to be alarmed about unless they're preventing you from reaching the required temperature (or you're impatient enough! haha) - losses will contribute to stability and enclosure temperature. At the moment, with ambients of about 22-25C, I'm getting a steady-state enclosure temp of a happy 40-45C with bed heater set to 100C, enclosure heater off. While this means my bed heater is losing quite a lot, probably from both sides, I'm not particularly concerned as the losses are going somewhere helpful, and this setup is achieving a real glass temperature much closer to the indicated, unlike the solidoodle pad previously.

Are you sure the PCB isn't slightly bowed and contacting the aluminium at the middle of the plate? Is there a piece VHB tape in the middle (I did this to help flatten the thing a bit)?

How is your thermistor attached? If the thermistor is reading low (i.e. is not very well bonded to the plate) then the PCB will be at an extra-high temperature and may be the cause of the surrounding stuff being surprisingly warm too. You can sanity-check with a multimeter and thermocouple taped on top of the PCB, and go for a test run.

I've thought an alternative could be maybe a bit of 3-6mm fibro board or similar between the PCB and the aluminium, use the double-sided tape on both sides, or maybe even epoxy the PCB to the fibro (I think they have similar thermal expansion coefficients).

Hi grob,

Thank's for your helpful answer, gave me lots of info and thoughts. I'll start by explaining my build:

I also had a similar bow in my mk2b so that the middle part of the pcb was higher than the corners, so I screwed the pcb to a flat wooden plate before attaching the alu bed with pads of vhb tape. I got it reasonably flat but maybe not perfect, so I'm hoping it'll also settle down straight in time. I put small tape pads on corners, sides, the middle and a few in between. Before that, I glued the thermistor to the mk2b with this: http://www.amazon.com/Arctic-Alumina-Th … B0009IQ1BU . And I also drilled a hole to the alu bed for the thermistor wire to run through and taped the wires on the alu bed. The pcb is definitely not touching the alu bed.

I took your advice and measured the temperature with my (VC99) multimeter, and it shows the same temp as the thermistor so I think I'm good there. Also, i think my thinking has been clouded by the crappy SD4 heater, and maybe I don't need 110C on the thermistor reading with this setup. It'd also help with the heating time, I do get from 20C to 100C in about 12min, the last 10 degrees to 110C is very slow.

So, all in all, maybe I need to stop worrying and start printing First test prints @100C came out fine at least.

Thanks for your help,

veehoo