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Thanks Gene - but they're 6mm not 3mm and WAshington, not Western Australia.

The more I think about this the more I'm leaning toward Aluminium. But would appreciate some feedback first. Or are guys throwing glass on top of the aluminium?

speaking of broken glass... [youtube]http://www.youtube.com/watch?v=xe-f4gokRBs[/youtube]

Cool video!

A 6mm glass plate won't hurt - just remember to adjust your Z height.

There's GOT to be a glass supplier in WA that isn't a total prat and won't charge you and arm and a leg for a stupid disc of glass...

g.

geneb wrote:A 6mm glass plate won't hurt - just remember to adjust your Z height.

There's GOT to be a glass supplier in WA that isn't a total prat and won't charge you and arm and a leg for a stupid disc of glass...

g.

Do you use regular glass on your printers? I was going to buy the five pack of mirrors you found but Michael's comment about glass
flying around the room made me think twice and I would like your opinion and experience.

I cracked a mirror when we were doing bathroom mirrors and if that type of fracture happens during the cool down due to grab and thermal stress etc, I don't want to be in the room and I don't want to have to try and clean up the splinters and mess afterwards, either.

So I'll probably go for 4mm toughened glass as a first choice if I can't get boro or soda glass locally first.

Only supplier I've found so far is on the other side of Oz.

A mate suggested buying a glass saucepan and taking it to a glazier to get the arse cut out of it, I might investigate this too - depends if I can find a saucepan with an un-contoured bottom which I doubt.

That video was awesome!

Normal plate glass is not made to withstand the thermal cycles we need for printer hot beds. Borosilicate glass was EXPLICITLY formulated to withstand the thermal stresses during heat up and cool down. It scared the crap out of me when my plate fractured. I implore you to spend the time/money to find the right material.

Captain Starfish wrote:A mate suggested buying a glass saucepan and taking it to a glazier to get the arse cut out of it, I might investigate this too - depends if I can find a saucepan with an un-contoured bottom which I doubt.

I just checked over my glass and ceramic cookware, even a Corelle dinner plate, and didn't find anything that was sufficiently flat. They all seem to dip oh-so-slightly in the middle. My glass cutting board is flat, but it's also tempered...not so easy to cut.

Guys, you're making this more complicated than it should be.

A brand new plate of boro glass will not crack or break under printing stress/use. But when you start scraping off your prints with a paint scraper or other metal utensil, or scrub it clean when it has particles on it that can scratch it, then eventually you'll crack it. Just part of the deal.

If you get a new plate from SeeMe and want it to last, then put PET tape on, and never print directly on the glass.

Otherwise, factor in $50 or so every 800-1000 hours of print time because that's probably how long it'll last before you get cracks like mine in the original post.

Hopefully today I'll have better luck finding a supplier.

Have a few leads now.

My understanding was that borosilicate and soda glass have very low thermal expansion coefficients and so will tolerate hot spots (eg flame on the bottom but not on the sides of a beaker or pan) well. Normal glass doesn't care much about temperature if it's heated and cooled gently and evenly without hotspots across the surface or through the thickness of it. And that's the case with the hot bed, so Pyrex probably is overkill for the application. More important I reckon is that, when it DOES go, how safe is it going to be and how hard is the cleanup going to be?

Boro came apart cleanly, toughened glass might well do the same but a lot cheaper. John @ SeeMeCNC suggested the mirror glass was worth a try too and that they've had some success with it.

Anyway, will see how it all plays out today.

Once again though - you guys using aluminium plates, are you printing straight onto them or do you have a sheet of glass sitting on top?

Printing on aluminum plate with glass on top. Never tried to print on the aluminum and don't intend to. Glass is a lot cheaper than aluminum and I don't want scratches all over it
from removing parts.

I also have borosilicate glass over aluminum for the same reason as Eagle. I printed on aluminum (with hairspray) for a short while but it started to get scratched up easily.

You are right on about the thermal expansion properties of these glasses. I was a glass blower in graduate schools (Chemistry, made all my own glassware). Even heating and cooling is fine for normal glass but as you say, hot spots cause problems. Borosilicate has a much lower coefficient of thermal expansion and handles hot-spot stresses. We also made quartz ware but that was very difficult to work and expensive but very durable.

Sapphire crystal bed, anyone?

At least that would take care of the scratching. But I suspect a sheet that big would cost enough to buy half a dozen Maxes.

Grrr

For any other Aussies that encounter this issue, this may help:

Nothing in Perth, Helm Australia sent me to Glasslite 02 6658 5234, I spoke with Barry who said they had exactly what we needed in good flat 3mm boro they could cut to whatever size I wanted. In 300mm dia:
1 piece $55.
5 pieces $34 each.

Shipping to WA $50, YMMV.

A local glazier has offered to cut a piece of 4mm toughened glass for $25.

Decision time.

I didn't have much luck with the glue stick but that was before I calibrated everything so it might work better now. Would prefer not to introduce the extra hassle of Kapton if I can avoid it. Mostly printing ABS but intend heading down the nylon road eventually (not with the PEEK hot ends though). Apparently the boro will fail just like plain float window glass in shards usually, no difference at all. The toughened will shatter into cubes.

What do, gurus?

Boro is the best glass to use on a heated bed. Do people use other types? Yes they do but not for long.
The danger in using glass that is not Boro is when it shatters, shards can fly off the bed and if you are in
the way..................
The toughened glass you speak of is most likely tempered and like the others it is not recommended for heatbeds.

Interesting, the boro supplier said that the shatter characteristics of borosilicate were almost identical to that of float glass. It too will splinter and shatter if it fails in the usual manner. Our boro chipping experience could well be showing a failure the way it does because of the mechanism of failure (shear stresses etc rather than the impact shattering we're used to seeing on glass) more than because of the type of glass being used.

Talking with a local guy about glass that fails safely, he suggested tempered glass but then pointed out that tempered glass is much more prone to scratching, which takes us back to the original surface degradation which may well have started this problem in the first place.

Bugger it. If I'm going to have to treat this stuff as a consumable, I'm going to see if the cheap local stuff will work before I fork out two hundred bucks on a year's supply of bed glass.

Have ordered a $25 cut and safe edged mirror to try per John's suggestion, will report back how it goes.

The other option that's not glass is a sheet of polyetherimide (PEI). There are a few hardware manufacturers using it for their beds, and it works really well, but it can be tough to source and a little bit pricey. The results I've seen with it are pretty great, though, and it's got some desirable properties over glass.

This happened to me as well. Printing ABS with a bit of glue. Pulled the print off and there was a crater in the glass. Found the shard a bit later. John from SeeMeCNC sent out a replacement. The glass was still usable as it wasn't cracked but I fear it will eventually break.

Dan

Yeah, John didn't want to play replacies with me, I guess when it costs $50 to ship $20 worth of glass that's understandable. First I've heard of PEI, but I suspect if I'm struggling to source boro here then PEI will be impossible.

Captain Starfish wrote:Yeah, John didn't want to play replacies with me, I guess when it costs $50 to ship $20 worth of glass that's understandable. First I've heard of PEI, but I suspect if I'm struggling to source boro here then PEI will be impossible.

I'm confused, as usual. Some of your posts seem to indicate you are from Australia, others seem to say Washington.
Do you mind clearing my confusion?

WA = Western Australia on the other side of the planet

Bah

Cleaned the glass, flipped it and tried some school glue stick. All aboard the boat of fail, by layer 3 half of the brim has pulled up and is waving around.

I might try being a little more precise with the juice on the next piece - it could have been a little strong because the pickle jar I used to mix and store it allowed some evaporation.

Could we imagine putting a sticker on the bottom face of a cheap glass, to prevent it from explosion ?

Or maybe it could be prone to warping, or the sticker could not stand on the heat ??

Any ideas ?

There is a very active RepRap community in Australia. Have you asked on the RepRap forums to see if someone can point you to a source?

If you are printing below 100°C or so, you could cover the bottom of the glass with blue tape. It might help some but not really sure how much.

The other thing I've seen used is a ceramic floor tile. It's square but might get you up and running.

Ran a print this arvo with the cleaned and flipped plate, I don't trust it but it went ok. Glue stick didn't really work that well for me.

Given that through other interests I'm already pretty much a permanent posthoor on 6 forums now I'm kinda loathe to add more to the list, so I'll leave the RepRap kids alone for now but thanks for the pointer - I know it's there now if I get stuck again for suppliers of stuff like glass, tape, filament etc.

I'm picking up the mirror tomorrow and will see how that goes. No point putting tape on the back of it because that will only stick to the silver which, according to the glassy, is sprayed on and won't hold the glass if it lets fly.

So we'll see what happens. Thanks for the ideas peoples, most helpful and instructive!