http://forum.seemecnc.com/viewtopic.php ... nyx#p52767
The majority of us have the R2 bed. It is a great design, but there are 2 things that I don't like about it.
1. The heating traces are spiraled with an even spacing which makes them less concentrated the further you spiral out towards the perimeter. R3 and beyond fixed this problem by varying the spacing of the spiral to cover the whole bed more evenly.
2. The thermistor hole is in the dead center of the bed which isn't the most accurate spot to put it. It's also where every single piece is going to print over, and it tends to give you false readings that throw off the bed temp for that critical first layer. Later versions improved this as well.
The R3 bed fixes the heat consistency issue, and it can easily be drilled off center for a better thermisor location. And best of all IT'S ON CLEARANCE because its resistance is a tad high. For me, the resistance is a non-issue because I've either been printing low temps for PLA or I've been plugging in 24v for higher than usual ABS temps. So, for my purposes, an R3 bed with a modified thermistor hole is every bit as good as an R7 for half of the price.
Here's my build.
First I marked out the furthest location from center that my thermistor leads would reach without hitting a trace and drilled a new thermistor hole. I used a 5/32" drill bit which is a much tighter hole for the thermistors I had. My theory is that the smaller the hole, the closer the temp reading would be to the actual bed material. (note, I drilled 2 holes in my bed... I found a thermistor with slightly longer leads that allowed me to reach further)
[img]http://i.imgur.com/W0A9MVG.jpg[/img]
[img]http://i.imgur.com/xOGdbnK.jpg[/img]
Next I put a piece of tape over the top of the holes to keep silicone from oozing through, stuffed the hole with silicone using a toothpick, and inserted the thermistor as far as it would go (lightly). I also taped down the leads to hold them in place while drying (not pictured) and squeezed a glob over the top to make sure the thermistor was really secured in there. After it dried, I soldered the leads to the pads.
[img]http://i.imgur.com/ADFsGhR.jpg[/img]
Make sure you get a piece of dog hair in there. It helps
[img]http://i.imgur.com/GfmErwP.jpg[/img]
I wanted to make the main power leads on my bed disconnectable. To do this, I flattened the crimp sleeve from a male spade connector into a tab that I could solder to the pads on the bed.
[img]http://i.imgur.com/EFgzZxB.jpg[/img]
For my resistor, I used a 1Kohm 1W. It's a higher resistance and wattage than the "stock" resistor because I do run 24v occasionally. I bent the leads to hold it off of the surface of the bed in case it would warm up and cause a hot spot. Then I soldered it on, and put a bed of silicone under it. I put silicone around all of the components on my bed after they were soldered on. The idea was to "shock proof" everything since I move my printer and throw it in the car so often.
[img]http://i.imgur.com/lNEsAgC.jpg[/img]
[img]http://i.imgur.com/e6TSYX1.jpg[/img]
I mocked up my LED and bent the leads just right so that the LED would be flush with the top of the hole in the bed and still contact the solder pads evenly.
[img]http://i.imgur.com/gHydP87.jpg[/img]
Also soldered leads the the thermistor pads that terminate at a JST connector, to make the thermistor disconnectable as well. Covered everything exposed with a glob of silicone to shock proof it, and let it all dry. Then fitted up the snowflake to make sure that everything cleared.
[img]http://i.imgur.com/tsLosht.jpg[/img]
It all fit, so I put her together. Printing again, yay! One more note, if you're using a heat spreader that covers up the heat indicator LED (I've got Brian's Trick Laser heat spreader prototype on mine) you can still see the glow of the heater light from below (my LED was leftover from a variety pack from Radio Shack, so it may be brighter than stock).
[img]http://i.imgur.com/SoDlwch.jpg[/img]
Anyway though, I'm up and printing again. I like the new bed quite a bit. Nice upgrade for an evening's time and not a lot of money.
