So I stopped by the hardware store last weekend, interested in picking up some glass to experiment with for a print platform (It looks like the laser-cut plywood might be starting to warp, I live in a humid place). They guys there were nice enough to just cut me a 6" x 6" piece of scrap window glass for free, since I'd have to pay for the whole sheet (24" x 24") otherwise.

After three generations of so-so results (lots of slippage, and they tended to reduce my X-Axis travel by getting in the way), I've settled on this to mount it. It also uses some of those little Goody brand rubber bands to keep tension, something like $2 at the grocery store, some springs I found at Home Depot (8mm ID / 20mm Uncompressed Length), and some #4 nuts and bolts.

Printing directly on to the glass has had mixed results. Since I don't have a heater, I've tried both with and without PLA "Juice", bare glass, and on painters tape.

Printing on bare glass makes for beautiful print surface results. The bottoms come out looking like a mirror. The problem is the parts don't stick very well. Tried smooshing the bottom layer, still dislodges whenever there is too much sideways force.

With the PLA Juice (elmers glue + water), it printed okay. I still had issues with sticking on longer prints. I heard I'm supposed to use PLAc glue, but I have no idea what that is. Might try it next time I stop by the hardware store.

I'm currently running with the blue tape, so this gives it a little extra bite around the corners.

In the end, I got a super-flat build platform that is way easier to clean and retape compared to the plywood. I also don't have to worry about the warping issue I had before, though with the added X-Y tension, it may migrate down the to X Carriage.

Ingredients

4 x #4 Bolts (Similar to ones that came with the Printrbot Jr.)
4 x #4 Nuts (Same thing, similar to the ones that came with it.)
4 x Springs (I got a little baggy of 6 springs from Home Depot, smallest ones I could find, I.D. of 8mm / height of about 20mm).

Instructions

1. Print. I used 10% Infill, 2 Perimeters, with support.

2. Clean off the support structures, file down anything that gets in the way.

3. Assemble them.

They are laid out int he STL the same way they fit on my Printrbot Jr. I placed the #4 bolt in the clip first, then the spring on the bottom, the spring holder, then the knob and the bolt underneath.

I found that without the spring holder, the bottom of the spring would move around after long prints and throw my level off. I also had to cut off the bottoms of my #4 bolts so they wouldn't get stuck on the screws underneath the X Carriage. Depending on the screws you use, you might have to do the same.

1. Add the rubber bands.

They use 4 rubber bands to keep tension on the glass plate, stretched around each of the outer pegs (you can see them in the picture).

On my previous builds, they'd start to wander and the glass bed would end up sliding around. Sor far, It's worked pretty well. You might want to stretch them out first, to get them easier to put on.

1. Add glass.

I just fit the left side in, then the right, and pressed the front and back sides to get a good hold of the glass.

1. That's it!