Full glass hotbed conversion by ArtemKuchin

Last crawled date: 3 years, 1 month ago

Please, read and understand everything before you do anything.
Skills needed: hand cutting and hand drilling aluminum, basic soldering, basic gluing.
I was very tired of how uneven aluminum plates was. Cast and cnc-ed aluminum is very expensive and hard to find. Also, since my printed has a moving bed, I am always finght the bed weight. Most people use aluminum and then put glass on top. Too heavy. Some just use heater plate as a base and clamp glass on top. Okay for not moving bed, but too flimsy for a moving one.
So, I though why I need the aluminum bed at all? Just for the screws? Then let’s find way to screw the glass the carriage and not even damage the top side of the glass.
Usual window glass is no good. Maybe even maybe not. So, I tested the method on usual glass and then used a 4 mm mirror. Mirror is good because it can be visually controlled for any distortion. Eye is very sensitive instrument, can see holes up to 0.01mm and detect very small distortions.
Using a mirror, I also increased the printable area to 230x230 mm.
Tasks list
1) Cut mirror
2) Attach heater
3) Attach screws
Cutting mirror
Very easy. Just use hand glass cutter of any time. Then use 150-200 grid sand paper to clean the edge. Easy.
Attaching the heater
Complex tax. Need to make cut outs for the screws and glue and resolder connection. Nothing too difficult, basic soldering skills. The problem here is that I used my original aluminum table as a carriage, so the whole are still like for 214x214, the same whole distances in the heater. Also, I wanted to make 3 screws attachment, not 4. So, I made all cutout, resoldered with thick wire. Next I used thin layer of thermal compound in some pattern (see photos) and then silicon glue (pure silicon, hold up to 250C and conducts heat a lot better than air). Then I attached the mirror and heater together and put 5kg load on top for 3 days. Done.
Attaching screws.
Worst part. Took me some experiments to choose the right glue and the gluing method. The glue must be hard enough to avoid any detectable movement during direction change, but elastic enough to withstand some thermal and mechanical deformations. Also, must withstand temperature up to 100C. Must bind very good to metal and to glass.
Pure 2 component epoxy does not work well. It breaks of the glass and breaks too easily. Does not tolerate temperature change very well. Since I am in Russia I found local glue called TITAN 6http://anles.ru/product/%D1%8D%D0%BF%D0%BE%D0%BA%D1%81%D0%B8-%D1%82%D0%B8%D1%82%D0%B0%D0%BD-%E2%84%966/
It is a epoxy rubber glue, which is hard enough and can work up to 120C. Amazing glue. Very strong. Use google translate and find something like that in your area.
But still, it does not hold very good to clean glass. Hold very strong to the screw head, but can be detached from glass with no so much force. However, even like that I printed for 4 month without problems.
But eventually I dropped the bed when I was changing two wheels and all screws detached from the glass. No problem. This time I took a glass drill (4mm) and made 6-7 indentation in each place about 1-2mm deep. And glues the screws back. Now the holding force is amazing. Just make sure you clean the indents very well.
When gluing you need to place the screws as precise as you can. For that I used my old table as a template. Out the screws into it with two nuts and tightened it on the screw end. So, screws was sitting tight in the template plate sticking out the head as much as possible. Before that I made a whole where a new screws possible will be (I used 2 old whole, and one new, because switched to 3 point attachment).
Place glass table upside down. Clean the gluing places with IPA. Wait for it to evaporate. Put some glue onto the places and push some into the indents with a toothpick. Then just place the template plate with screws on top of it. After about 30 minutes I used toothpick to bring some more glue from bottom onto the screw heads and even a little on the thread. After 24 hours it is ready to be used.
Assembly
I hate springs in the table assembly. It is always a problem. Everything must hold tight. So, My assembly (from top to bottom) on each screw is like this: Screw-nut-washer-carriage-washer-lockwasher-hand nut. See photo – you will understand.
If all three screws do not want to go into the wholes at the same time, then they were places not very straight. I solved this problem just by using 4mm metal drill to enlarge one whole in the table carriage base.
Results.
Since I do not print ABS I don’t need to head by bed to 100C. I tested it up to 80 about 10 cycles and it now heats a lot faster even without any heat insulation underneath. I checked it with a pyrometer. This is obviously due to better thermal connection between heater and the bed.
I used a lot of force when detaching some PETG models and even PLA with big bed surface and did not have any problems.
The bed is now extremely flat. Here is G29
At 25C:
0 -0.060 -0.085
1 -0.045 -0.045
At 50C:
0 -0.037 -0.055
1 -0.035 -0.035
As you see the height difference is within 0.03mm. With 0.2mm first layer gives perfect 1st layer.
As you see the heater does not cover full areas of the print bed. That’s ok. Full area only needed for rare cases and even using heater 40C will give me about 33C on the edge, so PLA attached better.
I also tried glass with PEI on top. It is more problems than advantages. Now I used just clean glass with some glue stick dissolved in water. Good for PLA, PETG, SBS.
Good luck.
ADDED 2018/09/17
One mirror has cracked after too heating too fast to 80C with cold wind around. I thought i need a new heater, but luckily, the heater detached from glass very easily. So, i just cut new mirror and reattached the heater. Works perfectly.