jcabrer Wrote:
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> For ABS, you can use the Red PCB @120C with bare
> glass, at any speed. The ABS extrusion
> temperature should be around 250C. When the glass
> cools, the part will already be free. Same for
> PLA on bare glass.
>
> One more thing. I use Pyrex Glass AKA
> Boro-Silicate Glass, so your results might varry
> with other types.

I cannot recreate this. I bought a piece of borosilicate glass 150x150x2.2mm (very expensive, almost £50!). I have tried ABS at 250C, bed at 120C, 140C and 160C and it does not stick at all. It won't even do the outline square. This is in line with my previous experience of ABS on glass. I have tried ABS from reprapsource.com and makerbot.com, which are quite different. What short of ABS are you using?

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[www.hydraraptor.blogspot.com]

Have a look at my camera for the details of the bed setup

Camera 1

Camera 2

My heated bed is the red PCB type that you get at Ultimachine. The thermistor is mounted on the bottom, in the center. The glass is mounted right on top of the bed, held on with four strips of Kapton tape at the corners. Other than this, there is nothing else on the glass. I do not use a fan. Since the heated bed is mounted above my old acrylic bed, I have placed four pieces of corrugated card board sandwiched between the two. This helps insulate the bottom from heat loss, and speeds up the heat up time. From time to time, I do clean the glass with 70% Isopropyl Alcohol.

The ABS and PLA that I have used on this have come from Ultimachine (Red ABS, all the Translucent PLA they have), and MakerGear (Royal Blue ABS, Emergency Orange ABS , Glow In The Dark ABS). There was a roll of black ABS that would not work at all. Something was wrong with it, and MakerGear gave me a credit for it. They said the batch was bad.

I'm going to have a look through your blog and see if I spot anything that might be giving you problems.

The first layer needs to be essentially nozzle to glass. I lower the extrude rate multiplier and I don't go particularly slow either. I usually just extrude at high speed right before starting the print, to make sure there is some slight pressure there in the tip. After the first layer, I bump up the extrude rate.

Edited 1 time(s). Last edit at 07/26/2011 08:41AM by jcabrer.

I put up a video of a print that I started this morning. I demonstrates GREEN TRANSLUCENT PLA on borisilicate glass.

I do not have the embedded link at the moment, so search for wildseyed.

I have no problem printing PLA on glass but ABS does not stick at all for me. I start with a blob and do the first line moving away from it. As soon as it turns the first corner the filament comes loose. There is absolutely no adhesion, whereas on Kapton or PET tape, under the same conditions, the first layer sticks like chewing gum.

I do my first layer at the correct height, but quite slowly. If you do yours lower, but with lower flow rate to compensate, then it should amount to the same thing pretty much. Maybe a bit more contact area due to squashing the filament more, but this isn't in anyway a borderline situation. It doesn't grip enough to turn a corner, let alone hold down an object that wants to warp.

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[www.hydraraptor.blogspot.com]

Well, I can suggest what I have done in the past. When I would start a print with ABS, they nozzle would always be too high, so I would just turn the z axis screws by hand until I could see the filament stick.

I would not use the starting blob method on bear glass with ABS. When the tip comes off the blob, it tends to roll a little, and then the whole thing gets dragged by the tip.

What you say about turning corners has happened to me as well, but not frequently. A drafty room, or cold ambient temperature will cause the ABS to not stick. In fact, I can blow on a hot part while it's printing, and it will start to peel off the bed. My house is usually a little warmer than room temperature, and low humidity due to the Southern California climate. These may be factors as well.

I think a big problem when comparing notes is that we all just assume that our temperature readings are accurate, but in fact my 250C may be someone else 235C.

Keep an eye out later tonight. I will load up some ABS Glow, and record my results.

I put up a couple of ABS heated glass print videos for encouragement.