Heated Bed Question

Quick question, does the glass pane that covers the PCB heated bed need to be heat treated? Like Pyrex? Or can I just use any old peice of glass. I ask this becuase I have an old scanner bed piece of glass that will work perfectly, but I'm not sure what will happen when I heat it up.

Thanks!

PLA: Any old pice of glass will work.

ABS: At least tempered glass or other heat treated glass. Regular glass will usually crack at these temps.

ABS Juce: Regular glass coated with ABS Juce is known to work at lower bed tempratures. Cool enough not to crack.

Hope this helps.

I am using 3mm float (i.e. not treated) glass on my Reprap.

I regularly use it at temperatures of 100c and 60c (ABS and PLA respectively) and have had no cracking incidents at all. I have had it up to temperatures of 125c without damage, at this temperature ABS prints shrunk anyway.

As far as I understand it, as long as you heat the glass evenly it should not crack. Laminated glass (toughened glass) should be avoided as the tension between the layers of the laminate is highly likely to stress.

I just use plain 3mm window glass on my printer. I have been using the same glass for 6 months with no cracking but I also have a 5mm aluminum resistor bed that heats even and fairly slow. I have put it up to 135C.

When I use ABS juice I do not paint it on until the bed reaches 100C then I usually print between 110 and 130C depending on the plastic.

---

----------------------------------------------------------------------------------------------------------------------------
www.Robosprout.com RepRap Mendel parts and accessories.
Message if there is anything you need...I have more than what is listed on my site.
Located in the Spokane, WA / Coeur d'Alene, ID area.
Contact: Robosprout@gmail.com Flickr: [www.flickr.com]

I like to use picture frame glass for PLA because it is usually much flatter than pyrex and produces a better surface finish on the bottom of parts. Like Komb said, if you want to print with ABS, you can use ABS juice at 90 C or you can get a sheet of pyrex glass and set to 140 C.

I don't have any problems with 2mm picture frame glass even up to 130C, as long as it is heated evenly. I have never had any glass cracked through heating.

Ya I ended up just using a picture frame glass since it fit almost perfectly without having to be cut, I put kapton tape on it and its been printing beautifily all day. I'm very interested in trying plain glass and PLA, can someone tell me what the procedure is for switching between ABS and PLA? I remember reading something about washing out the hot end with acetone, but I'm not quite sure how to go about it.

Thanks for the help! Realy appreciated.

I also use 2mm picture glass at 130C. I haven't cracked any due to the temperature but I have broken it removing parts occasionally. As it only costs £2.50 from a local glass shop it is not a problem.

To switch between PLA and ABS I just run the filament at the higher of the two temperature until it is flushed through and then switch to the correct temperature. It can take a while to flush it though. PLA to ABS is the most difficult as you get shiny ABS that doesn't stick to the bed properly for a while.

---

[www.hydraraptor.blogspot.com]

i use a replacement 8x10 picture frame glass I got at the homedepot for 1.98

---

Ryan
Quality Engineer & Hobbyist
thingsandtrains.blogspot.com

Conventional wisdom is that glass cracks when heated, but a lot of people use regular glass and I don't hear many reports of problems. It seems the key is even heating and avoiding stressing the glass. If it does fail, it may crack but since it is lying on a bed you don't get pieces flying everywhere.

Tempered glass is heat proof, but can not be cut once tempered, so you need find the right size or have it made to size, which is not cheap. As far as I can tell, tempered glass is not necessarily made to be flat, because it is used for shelving, chopping boards etc. Cheap window glass is not only cheap, but usually quite flat, which is a bonus.

I think the key issue about cracking is that the glass is without extra drilled holes.
All the pictures that I have seen had cracks that passed through (originated at) the drilled holes.

Drill holes in glass !! I think it will always crack if the glass can not expand, as I understand it most people just place the glass on top of the heated bed aand hold it down with bulldog clips this way the glass can move a little on heating.

I will post some pictures when I update my site (hopefully tonight or tomorrow) of my new heat surface. A flat ceramic plate 8"x8" ontop of the heatbed. It is ground flat and parallel to within .0002" and costs $1095. Now before you have a cow on the price, I got it free as I work in the Quality Department of a ceramic company. This part failed due to a large chip on one of the edges and and was dumpster bound. I got all required permissions to use it for this project [as they all know about my printer ] It works awesome, way better heat distribution than glass, and it holds the heat very well and wont vary much if a cool breeze blows by. I no longer have insulation under the heatbed and it still performs beautifully.

I still use Kapton tape as the ABS refused to stick to the ceramic(maybe partially because the surface finish is so high it had nothing to grab on to) I havent had any warping yet [fingers crossed]. After a print is finished I shut off the heatbed and my print pops off after the temp drops a little. Then to cool the heat bed back off I throw a bunch of scrap ceramic on it to pull all the heat out.

Like I said, hopefully have some pics up tonight or tomorrow as my blog is a week and a half behind!

---

Ryan
Quality Engineer & Hobbyist
thingsandtrains.blogspot.com

Has anyone had issues trying to get PLA to stick to the glass? My Prusa worked great for several months, the prints stuck like glue to the glass at 60 deg. Now, I can't get anything to stick at all. The temperature, PLA, and heatbed are all unchanged. Any ideas? I've tried to clean the glass with 99% rubbing alcohol and acetone, but there is no improvement. My bottom layer seems to be squishing down as it should, and my temperature is unchanged at 185 degrees. I do have a new J-head hot end.

I don't know if it is a good idea, but I was wondering about roughing up the glass with 600 grit wet/dry paper. Thoughts?

EDIT: I scratched the glass with 400 grit paper, just lightly so that you can see scratches if you hold it to the light. Wow. It sticks like it's been crazy glued in place, I had to pry it off with a knife. Problem solved ><

Thanks.

Edited 2 time(s). Last edit at 04/25/2012 12:31AM by peterrash.

@banthafodder7400

Interesting I seen some pictures on your blog, what type of ceramic it is ?
(as I was considering a ceramic plate of aluminium-nitride instead of alu+glass, since it wouldn't shatter like glass on uneven heating and spread it well, for a small huxley bed)

---

about // liberapay // flickr // wiki // thingiverse - github

peterrash Wrote:
-------------------------------------------------------
...
> there is no improvement. My bottom layer seems to
> be squishing down as it should, and my temperature
> is unchanged at 185 degrees.I do have a new J-head
> hot end.
>
> Thanks.

Do you see the filament going on the glass and then peeling right off? This usually indicate that there's some residue on the glass or the temperature is not high enough.

Have you adjusted the clearance between the nozzle and the glass bed after warming both the bed and the extruder at operating temperatures and waiting for 5 minutes or so? You can use a sheet of paper as a feeler gauge. Adjust the endstop switch or flag position until you can feel a slight resistance when pulling on the paper after homing the z.

It *usually* sticks enough to make a couple layers, and then starts to slide around, wrecking the print.
I will re-adjust my Z-position, and play with the temp some more.

Also, does anyone have recommendations of something to clean the glass with that is better than alcohol or acetone?

Thanks.

@ Emmanuel

96% alumina (cant reveal the other 4% its our trademark )
density 3.71
Hardness Mohs Scale: 3.71
Waterabsorption: 0%
flexural strength: 52,000 PSI
Tensile Strength: 29,000 PSI
Compressive strength: 300,000 PSI
Shears Modulus: 19 PSIx10^6
Thermal Conductivity: 23 W/m-K
Max Temp for nonloaded: 1700 degrees C

I have some more data but thats all i will include for now. Cant wait for some much bigger prints later this week to see how it does.

Edited 1 time(s). Last edit at 04/24/2012 08:55PM by banthafodder7400.

---

Ryan
Quality Engineer & Hobbyist
thingsandtrains.blogspot.com

After some sticking problems with PLA I have just frosted my glass and the results seem better.
Method I used was to put a small amount of carborundum grit on the glass and a little water then use another piece of glass and rub the two together.
This created a very fine frosted finish and also removed any small irregularities in the glass. I guess you could use wet and dry sandpaper if you had no grit I just happened to have some around from my pepple polishing phase.
As regards the question about cleaning, I use methalated spririts.

My PLA sticks to heated glass great.... until the humidity gets above 70% or so. Then it won't stick worth a darn. Did you problem start after a rain? Are you in an air conditioned environment, or a garage?

gtg252b Wrote:
-------------------------------------------------------
> My PLA sticks to heated glass great.... until the
> humidity gets above 70% or so. Then it won't
> stick worth a darn. Did you problem start after a
> rain? Are you in an air conditioned environment,
> or a garage?

That is interesting. As a matter of fact, it has been below 70% in my basement for most of the winter, but with the arrival of spring, the humidity has increased. Perhaps that is my problem.

@Bantha
Thanks for the answer, it's always helpful to have some elements to compare to (I was especially interested by the thermal conductivity)

peterrash Wrote:
> Has anyone had issues trying to get PLA to stick
> to the glass? My Prusa worked great for several
> months, the prints stuck like glue to the glass at
> 60 deg. Now, I can't get anything to stick at all.

I've had the same issue. With a new glass plate PLA stick extremely well at 40C, but with use it slowly gets worse and I have to increase the temperature. Then after a longer while at 65C it also started to fail. I cleaned it regularly with acetone, but It seems like there is a slow build up of a thin film of PLA residue on the glass that needs a good scrubbing to get rid of.

The solution for me is to clean the glass plate in the kitchen sink with dish washing liquid and a lot of water (ending with a dash of vinegar to avoid water spots when drying). This solves it perfectly, and I can once again print with the bed at 40C.

---

--
-Nudel
Blog with RepRap Comic

Thought I'd share this with folks as I have had a glass failure! However, this glass was 3/16" thick window glass. Perhaps the thinner glass that folks here are using is better able to handle the stress - that and this is also a very large diameter (12"). The table does heat more in the center. I had intended to add a layer of aluminum to dissipate the heat more evenly but this is a new printer and had not made that yet. The bed had been used for several hours at 100°C and it had just reached this temperature (measured in the center hot area) when I heard the SNAP.





There was no obvious stress site at the edge where the crack seems to originate.

Cheers,
Michael