heatbed cover ..... Glass or mirror

Hi guys

i had a nice mirror attached to my heatbed it was a littl heavy for its use (around5mm thick) and i got some backlash from it. So it was in my thoughts to remove it and get something else instead, but for the time being it worked.....

yes you are reading it worked, as for my first practice with ABS (was printing PLA) i raised the printbed to 100 degrees, as lower temps didnt really stick. I printed my first 15mm box what was quite nice. but after i setup for the next one (changed some stuff in slic3r) it suddenly cracked when i set the heatbed to 105 degree. 3 nice pieces of mirror were the result...

now my question is do other poeple have more experience with there glas or mirror cracking? at the time it cracked it was unstressed and i wasnt printing i was just getting the temp up 5 degree. My thoughts its not really in that 5 degree....
It was a pieve of really old mirror as i cut it from a leftover mirror I salvidged from my house when i bought it. probably dating back to 1980 or smt.

I thought of replacing it with a sheet of 3 mm glass but now because of the cracking im in doubts, do i have to replace it with maybe hardened glass or even heat resistand glass. If so the price will go up.....

So what do you use? what kind of glass and how thick? i have tried the Ikea mirrors wich were ok but they dont really fit my Heatbed wich is 23 x23 cm

Tnx in advance

Im guessing the expansion/contraction of 2 different materials in the mirror caused it to crack easily. Plus being thick added to the problem.

I had a 6mm mirror made (it was really nice) for my heated bed and the same thing happened - broke after a few prints. switched to 3mm glass/mirror and a lot fewer problems. You could always look for some borosilicate glass, or an 8x8 glass trivet at a home store.

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

I have been using the same 2 pieces of 3mm picture glass for over a year and printed at least 50 sets of Prusa parts on them

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Experimenting in 3D in New Zealand

you have 2 pieces of glass on top of them ?

so the tickness has resulted in the cracking? also i remember that the back side was painted so that could prolly cause it...
so 3mm will not brake that fast

Probably not. Swapping the glass out to start the next print is a common practice.

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

I have a local shop that orders to Atlanta and gets my glass back in 2 or 3 days. It is Safety glass and they will cut to fit and that stuff is strong as it gets plus it handles heat really well (I know up to 425f at least). A tad expensive but not overly as a 3'x4' 1/8" was 80 dollars (was my screen door that the wind blew and shattered the glass 2 years ago).

A little 9"x9" (23cmx23cm) would be so cheap I dunno how much it would be. Might charge the 30cmX30cm (12"x12") price then cut for you before they cook it.

Nope I swap them at the end of a print as they need to cool before the prints will lift off

Weedz Wrote:
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> you have 2 pieces of glass on top of them ?
>
> so the tickness has resulted in the cracking? also
> i remember that the back side was painted so that
> could prolly cause it...
> so 3mm will not brake that fast

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__________________________________________________________________________
Experimenting in 3D in New Zealand

When I said safety I meant tempered glass.

NelsonRap Wrote:
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> Nope I swap them at the end of a print as they
> need to cool before the prints will lift off


sounds logical i am not arrived at that state, as with the pla heating the bed up to 60- 65 C it cools down pretty fast and is reheated pretty fast.
So thats a good tip to take then several pieces of glass.

but the real question is and i think its ansered does it need to be safety glass, no it doesnt but makes it fancy

Tempered Glass is really not that much more (safety glass is that stuff used in cars that has tiny metal wires in it and is bloody expensive) than standard glass and if it breaks it doesn't cut you but breaks into tiny little squares. Tempered glass is what they use in oven doors, for instance, so it can take the heat and is stronger than glass due to having to cook it (once cooked it can't be cut so they cut first then cook it). I asked about the price when I had to buy mine and the real reason the cost is higher is that regular glass is 1/16" whereas these are 1/8" so twice as much glass. I figure 3-4 times the cost of regular glass but oh so much better, and safer.

just a thought when i saw your say stuff used in cars lol

has anyone ever tried glass with conductive paint or copper directly on the glass, like car rear windows?

be interested to see how that worked

that sounds like a plan!