Another reason not to use a glass bed

We have a Taz printer at the makerspace that has/had a glass bed. A couple days ago someone was printing with glue stick applied directly to the bed without the PET tape that's normally on it. It has been reported that when the print cooled, the shrinking plastic broke the glass.

I believe I'm going to replace it with cast aluminum tooling plate. It will be twice as much mass which may limit maximum print speeds, but heating will be more even and there will be no danger of it breaking no matter what people do to it. I'll use a 3 point leveling system instead of the dumb 4 point system that was used with the glass.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

What kind of glass was it normal picture frame glass or borosilicate?

ive never had a issue using borosilicate as its made to help thermal expansion normal glass will crack best idea is to go aluminium bed as people state glass is rubbish although i have never had a problem with parts sticking (pla) with hairspray

Edited 1 time(s). Last edit at 04/10/2016 10:33AM by chris33.

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Check my rubbish blog for my prusa i3

up and running
[3dimetech.blogspot.co.uk]

Borosilicate. The replacement part from Lulzbot is $35 plus shipping. I can pick up a piece of cast aluminum tooling plate locally for $40.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

1 - Heating element directly on the glass? - bad
2 - glue stick for anything but what is absolutely necessary? - bad
3 - prying parts off of the bed without waiting for it to cool down COMPLETELY - doubly bad

Unless it is nylon, pretty much EVERYTHING will stick to a CLEAN, finely tuned/calibrated/leveled, heated piece of glass.
Are you SURE that was boro glass?
It is always advisable to wait for the bed to cool ALL the way down before removing prints.

Get that piece of aluminum anyway and put it between your heater and your glass build surface.

PET doesn't shrink much if at all. I doubt it was the PET shrinking that broke the glass. From the looks of it, someone was prying that part off and broken the bed.

Edited 1 time(s). Last edit at 04/12/2016 06:41PM by MrBaz.

I print ABS with normal glass and glue stick for what its worth.
I have no issues with prints sticking or releasing when cool. Im using the same glass for more than a year without issues.

The only thing I really want to get away from is the 4 point leveling. 3 point is SO much easier to setup and maintain.

Quote
the_digital_dentist
Borosilicate. The replacement part from Lulzbot is $35 plus shipping. I can pick up a piece of cast aluminum tooling plate locally for $40.

What was the size of the glass? I got some glass for less then 10$ to support my PrintBite.
My own design will use a 6mm Aluminium-plate with a silicone heater and a PrintBite on top, maybe BuildTak.

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Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

The failure mode for glass is catastrophic - it does not get a little gouged or have a tiny bend. I ran two of my printers for years with only a heater directly under a 3mm glass plate without trouble until I changed the cooling of another part of the printer which was directed over the build stage and got a whole series of broken glass plates [forums.reprap.org]
My guess is that the failure reported by DD is caused by one edge being cooled far more than the others.

One option that I have found is to use 3mm anodised aluminium sheet. It seems to be consistently of a harder temper and flatter than readily available un-anodised aluminium. If your build stage is larger than 200mm by 200mm then thicker aluminium is needed.

Mike