Predator Glass Bed

In order to protect the existing Predators heated bed I have placed a sheet of glass on top of it. I had the glass cut by a local supplier close to where I live as such I can not provide a link for purchasing on-line. There is nothing special about the glass it is a standard piece of plate glass 4mm thick cut to a diameter to exactly match the predators existing bed 380mm Diameter, it is not tempered. I had the glass supplier aris the edged to make it safe to handle without the risk of cutting myself.
I wanted to have a way to ensure my bed temperature was correct. So I am using a separate little temperature display on top of the glass. What I found was that with the glass I am getting about a 10deg differential than without the glass. So if I want the glass surface to be 60deg I set my bed temp to be 70deg. In fact what I do is initially set the bed temp in the gcode for the print to be 80deg for the first 3 layers then back to 70deg for the remainder. As the glass does take longer to get to temperature doing this allows for the latency.
I did a test at 50deg and the difference was about 5deg at the center out to about 10cm from the center. At the outside about 8deg differential. However this is with the bed on for 15 to 20 minutes so it had plenty of time to stabilize. While heating the differential is much greater (it can be 15deg or more initially). That's what has to be allowed for especially getting those first few layer down with the glass at the temperature you want.

The glass itself has enough weight to ensure it sits flat on the predators bed but to prevent it from slipping sideways I made some cam wheels that are placed around the outside using existing screw locations. The only thing is that the existing screws are much too short and will need to be replaced with longer ones, M3 30mm. The first cams I designed were round then I later re-designed them to have flat sections around the circumference. The .stl files for the cams can be downloaded via a link at the bottom of this page. They are printed in two sections so that the screws can be firmly tightened with the cam still able to be rotated. These screws used actually are the ones that hold the existing heated bed to the predators base. I placed a cam at all six securing points.

I found that the adhesion was really good (PLA all I have tested) and the glass has to be down to room temperature before it will release the print.
I clean it with Isopropyl Alcohol. I really like the bottom side finish as it is clean and somewhat glossy.