Glass Type - Heated Beds

Is there a type of glass better suited for heated bed applications than others? Sources?

For the sake of an example, I have a piece of platen glass, about 3-5 mm thick, taken from a scanner/printer. I have not used it yet. If I do use it, I may need to get it cut by the local glass shop, if it's even possible...

Is there better glass, or worse glass that one could use, and why?

I've heard of people using borosillicate glass as it won't shatter as easily as regular glass. However if you can get polished granite tiles that are thin they work great as well. On my printer I use a 1/2 *12*12" granite tile it retains the heat very well, and won't ever crack due to uneven heating like glass.

Edited 1 time(s). Last edit at 12/13/2013 12:56AM by aduy.

Wow! 1/2" granite?! Doesn't that take a while to heat up?

I'm using the glass bottom of a "spring form" (a form for baking cake). It's only 10€ on Amazon and the glass is heat-proof. Anyways, i guess no type glass will take harm of the little heat from the heatbed - it could crack though if it is much larger than the heatbed and there is only a small part of it heated.

I checked out "spring form" glass on Amazon and they are all circular in shape so will not fit my printer.

Got me thinking. How about a glass chopping board? Smaller ones are 20cm x 30cm and they are made of thin toughened glass.
One side is usually a dimpled finish which might help adhesion.

I'm using a 3 mm thick mirror cut to size. Works really well for PLA at 65 degrees (iirc) and ABS at 125 (coated with diluted PVA glue for ABS, no coating needed for PLA). Never had any cracking issues, even with some rough head crashes.

There is a hypothesis about the mirror reflecting heat back up from the part itself, but not so sure if there is a real difference compared to plain glass. It's dead flat though, any unevenness would distort the mirror image. I think finding a flatter bed than a mirror would be challenging.

I suppose even heating is important for the crack resilience. I use a thin aluminium sheet smeared with heatsink paste directly on the back of the mirror. Kapton heater attached to the bottom of the sheet.

/Andreas

Borosilicate glass (Pyrex) is more tolerant of thermal shock so it's safer to use and it's stronger so you can use thinner glass. ebay or most open source printer sellers carry it with beveled edges so it's also not sharp. Yes you can use pretty much any glass and lots of people swear mirrors are best as the mirrored surface has some effect on heat.

Personally I use borosilicate 3.3mm glass.

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anwe79
I'm using a 3 mm thick mirror cut to size. Works really well for PLA at 65 degrees (iirc) and ABS at 125 (coated with diluted PVA glue for ABS, no coating needed for PLA). Never had any cracking issues, even with some rough head crashes.

There is a hypothesis about the mirror reflecting heat back up from the part itself, but not so sure if there is a real difference compared to plain glass. It's dead flat though, any unevenness would distort the mirror image. I think finding a flatter bed than a mirror would be challenging.

I suppose even heating is important for the crack resilience. I use a thin aluminium sheet smeared with heatsink paste directly on the back of the mirror. Kapton heater attached to the bottom of the sheet.

/Andreas

I could debunk that hypothesis in 3 seconds.

Aside from the fact that the power radiated electromagnetically is going to be tiny, the peak wavelength at 100C is around 8 microns, which is absorbed very well by glass... i.e. no infrared light will even reach the metallic surface.

On the other hand, it may help to spread heat that is applied to the backside of the glass which could make it have slightly better temperature uniformity.

I've been using mirror tiles cut to fit for the last year. Before that I was using picture glass. Have never had an issue with the glass breaking and have never really understood why people spend so much for a piece of borosilicate. I even take my glass off the hot bed and put it in the freezer to help get stuck prints off. No cracks, nothing.

this was the piece i had that broke, I had kapton tape on it too.

Edited 1 time(s). Last edit at 12/15/2013 05:09PM by aduy.

i use borosilicate glass i got from ebay, it has been working great for me.

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[mike-mack.blogspot.com]

i applied pva-water mix to my mirror glass at 100 instead of 60 degC by accident and it cracked. dont know if pyrex would do any better. its still useable, just has a crack in it.

borosilicate (aka pyrex) was made to be much more shock tolerent than normal glass, it is the type of glass used in cook wear and i think a good chunk of lab glass.

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[mike-mack.blogspot.com]

Awesome dialog everyone!

It sounds as though any type of glass will do, as long as you protect it from physical and thermal shock. Of course, borosilicate glass is extremely resistant to breaking due to it's low thermal expansion coefficient. I can certainly attest to it's resilience having immersed borosilicate Erlenmeyer flasks with boiling liquid directly into ice baths with no issue.

I have no idea what type of glass they use for the platens on consumer grade HP flatbed scanners, but that's what I have, so I'm going to try it out. I also have to get it cut to size, so I hope my glass guy is able to work it out. I'll write back if I have any issues with the platen glass.

Thanks again everyone

Edited 1 time(s). Last edit at 01/31/2014 04:29PM by RossWindows.

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dissidence
borosilicate (aka pyrex) was made to be much more shock tolerent than normal glass, it is the type of glass used in cook wear and i think a good chunk of lab glass.

Most Pyrex that's made in the US hasn't been made of borosilicate glass since most of the industry switched sometime in the 80s, instead using cheaper and slightly less strong soda lime glass. And it's definitely been the case for all Pyrex since at least 1998 when World Kitchen bought the name Pyrex from Corning.

I have been using 1/8" window glass with Prusa Mk1 PCB heat bed for over 3 years and I've not had a single one crack except when I crashed the nozzle on one and I broke a couple from the stress caused by a thick heated bed (Panucatt) that warped upon heating.

I use borosilicate at home on the printer, and in the lab at work, It is very durable, Can withstand reprap temps easily...iv used normaly glass before and it warped on me