Quote
calogerom

Quote
Ohmarinus
Did my images help a bit with looking at how an aluminium plate would function on a printer?

I saw your images. Can you tell me about warping with Al plate?

Quote
Ohmarinus
Did my images help a bit with looking at how an aluminium plate would function on a printer?

Quote
calogerom

Quote
DonaldJ
That's a good suggestion, but a nice piece of .25" Mic6 aluminum plate would weigh more than twice as much as the glass I'm now using. And cost twice as much.

Performance would suffer as the printbed moves back and forth in the Y direction, don't you think?

I agree with you. Unfortunately, there are advantages and disadvantages.

Quote
DonaldJ
That's a good suggestion, but a nice piece of .25" Mic6 aluminum plate would weigh more than twice as much as the glass I'm now using. And cost twice as much.

Performance would suffer as the printbed moves back and forth in the Y direction, don't you think?

Quote
calogerom
Have you ever thought to replace glass plate with Al plate? I think that with Al plate there would not be problem of "divots". That's right?

Quote
DonaldJ
I have five borosilicate build plates, and they all have those kind of "divots." I asked my glass guy about it, and he said it was due to microscopic imperfections on the surface of the glass. Remember, this glass was probably not designed to have stuff stuck to it.

This has happened with both ABS and PLA, using either hairspray or ABS juice directly on the glass. As near as I can determine, it is caused by forced cooling without letting the glass cool to room temperature. The sudden change in contraction causes the break.

My work-around is to use the other side of the glass, or arrange the parts on the build plate to avoid the divots.

I consider it a minor annoyance, considering the extensive use the glass plates have provided.

Quote
calogerom
But my glass is in borosilicate. This is the problem!

Quote
Vjk
On my heated bed there is a resistor and set of LEDs attached to one surface. These would be the most obvious high point as they are quite tiny and can create the pressure point. I originally had my bed set up with these pointed upwards because I prefered the look on that side of the pcb. The glass did not sit nicely on the bed this way, so I flipped the bed over. I also am only using two clips to hold the glass on.

To find any other highspots, take the glass/whatever you are using off the heated bed and use some sort of flashlight that is on the same level as the board. Shine the light across the board and any high points should leave a shadow. You can deal with those as they appear. I doubt there to be any, but I have found them in other pcb projects (basically left overs from manufacturing).

Finally do a good clean of the bed with a lint free cloth or soft tooth brush and something like methyl hydrate. Be careful what you use. Acetone and similar solvents can dissolve the pcb. I find methyl hydrate works well enough and doesnt leave a residue. Be sure to follow the safety instructions on whatever you use.

At this point I am suspecting that you just had some bad luck with your glass. If you haven't already decided to go with the Al, check it out and let us know how well it works. I will probably go and find some in the next few weeks to try out.

Quote
calogerom
How can I find an hypothetical high point in the bed?

Quote
Vjk

Quote
Ohmarinus
No trouble here with the Alu expansion, the bed stays flat too. Also, it seems that it actually doesn't need more heating to stay on the same temperature for my experience. The bed heats up fast and maintains a good heated surface during the whole print.

That is interesting. What thickness of Al are you using? How is adhesion? Is something like painters tape needed?

I will have to check this out and pick some up next time I am at the metal supplier.

Quote
Vjk
if you don't recall any impacts, then there is either a high point in the bed applying pressure to that spot or a defect from manufacturing the glass.

I dont think that the binder clips would have much of an affect on the glass other than if there was a high point. These would increase the pressure and result in glass failure.

Quote
Ohmarinus
No trouble here with the Alu expansion, the bed stays flat too. Also, it seems that it actually doesn't need more heating to stay on the same temperature for my experience. The bed heats up fast and maintains a good heated surface during the whole print.

Quote
calogerom
I don't remember any impact of hot end on the glass. Maybe did I use many binder clip and its have generated the break of the glass?

Quote
Vjk
Something that occured to me after I posted last night was that I have a similar looking crack on my vehicles front window that came from a rock impact at highway speeds.
Is there a chance you rammed your hot end into the glass at some point in the past creating a micro-fracture? I did that once already because I had not noticed that my z endstop had slipped down.

As for switching to an Al plate for the bed, I have no experience with that. My opinion is that there is a chance for creating a circuit which would create a fire hazard and the possibility of electrocution. Depending on the thickness of the Al plate, the hot bed pcb may not be powerful enough to get to the temperatures required for printing ABS. Finally something that may or may not be an issue is that Al expands more readily than glass. (PM me for the science)

Quote
Vjk
Something that occured to me after I posted last night was that I have a similar looking crack on my vehicles front window that came from a rock impact at highway speeds.
Is there a chance you rammed your hot end into the glass at some point in the past creating a micro-fracture? I did that once already because I had not noticed that my z endstop had slipped down.

As for switching to an Al plate for the bed, I have no experience with that. My opinion is that there is a chance for creating a circuit which would create a fire hazard and the possibility of electrocution. Depending on the thickness of the Al plate, the hot bed pcb may not be powerful enough to get to the temperatures required for printing ABS. Finally something that may or may not be an issue is that Al expands more readily than glass. (PM me for the science)

Quote
Vjk
The pictures did not seem to show how the glass was attached to the heated bed. How did you have the glass attached? My first thought is that the glass had a pressure point on the heated bed where the break is. You may have had the glass clamped down too tightly?