Heated bed & Glass

I've built a nichrome wire/aluminium sheet heated bed which I'm using to print ABS on with the bed running at 120 to 125 C (which is about as hot as it gets). I was wondering whether to top it off with a glass sheet to make sure it is perfectly flat.

To those of you using glass on heated beds, what sort of glass do you use, of what thickness, have any of you had any problems with cracking / breaking and do you take any precautions (such as ensuring not too fast a rate of heating)?

Any advice appreciated.

HI

I have been using glass for months with no problems. I use just exeryday house 4mm glass and hold it on the bp with bulldog clips.

Auzze

Auzze Wrote:
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> HI
>
> I have been using glass for months with no
> problems. I use just exeryday house 4mm glass and
> hold it on the bp with bulldog clips.
>
> Auzze

Are you printing with ABS or PLA? I think that the question is for ABS. For ABS, most people can print on heated Kapton or PET. Jcabrer is the only one I know that's able to print ABS on heated borosilicate glass (pyrex) at 120C or so. I tried with window glass and failed. Nophead tried a while ago on plain glass and tempered glass and then recently on borosilicate glass and also failed.

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__________________________________________________________________________
"I like to be, what I like to see, in you and me.
I am the Stallion, Mang."

ISTAR Scope Club

I think the question was what heated surface to use for ABS, not PLA.

For ABS no for PLA yes

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__________________________________________________________________________
Experimenting in 3D in New Zealand

CeeThreeEs Wrote:
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> I've built a nichrome wire/aluminium sheet heated
> bed which I'm using to print ABS on with the bed
> running at 120 to 125 C (which is about as hot as
> it gets). I was wondering whether to top it off
> with a glass sheet to make sure it is perfectly
> flat.
>
> To those of you using glass on heated beds, what
> sort of glass do you use, of what thickness, have
> any of you had any problems with cracking /
> breaking and do you take any precautions (such as
> ensuring not too fast a rate of heating)?
>
> Any advice appreciated.

I've read that 100 C is the safe limit for plain glass and that you have to use pyrex or tempered glass above that temperature. But I along with others in this forum have heated plain glass to 120C on an aluminum plate without it cracking.

As I wrote before, ABS doesn't stick to glass very well but you can put Kapton or PET over it. It works but it's not as good as aluminum since it's not a good conductor. What I found is that I can't get the surface of glass as hot as aluminum with the same temperature setting on my heated bed.

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

Please excuse my off topic post, but how are you able to adjust printing speed in the middle of a print? I have just started printing things with my repstrap. I use Skeinforge to slice and send it to the printer with Pronterface. I'm using the Sprinter firmware RAMPS 1.2 and was thinking that a speed control knob would be great. I watched the videos and saw you change the speed and flow rates on the fly. Am I missing something?

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[dankimble7.blogspot.com]

Yeah, I'm using Repsnapper, and in the Interactive Tab there are two controls labeled Speed Multiplier and Extrusion Multiplier.

These two controls allow you to tweak the speeds during the print. I havent used Pronterface yet, so I don't know if there is an equivalent there.

I was planning on using kapton (which I have) or PET (which I don't at the moment) on top of the glass. Currently I'm using kapton on the aluminium bed and the print outline keeps peeling off in the corners and ruining the print. I think part of the issue is that the aluminium isn't quite flat so some parts of the outline are not as squished into the surface as others.

I'll keep trying and maybe buy some glass at the weekend.

Thanks.

jcabrer Wrote:
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> I put up a couple of ABS heated glass print videos
> for encouragement.
>
>
Thanks for posting this. What's the clearance of your tip from the bed on the first layer? If it's closer than the layer thickness, did you compensate by reducing the flow rate? I have my first height set the same as the layer thickness. Considering that I also see ABS sticking to glass but then peeling off easily, you may be right that it's not hot enough. I am also using the PCB headted bed but I have a 4 mm aluminum build plate between it and the glass. I thought that this would distribute the heat more evenly but perhaps I'm also losing more heat this way. I also haven't tried pyrex yet and I've only tried window glass.

Would it be possible to put a glass sheet on a Aluminum bed?
What would be the best way to attach it? Should I use heat contact paste?

I suspect that aluminum being such a good conductor, and glass being such a poor one, the having the aluminum in the middle actually prevent the glass from getting as hot as it should. Probably loosing heat to the edges, instead of into the glass.

I've seen some using the paper clips to hold the glass to the print bed. If you notice in the video, I'm just using strips of kapton in the corners. The PCB heat bed becomes slightly convex on the solid copper side (top) when heated, so this helps press the PCB into the glass without additional fixturing.

brnrd Wrote:
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> jcabrer Wrote:
> --------------------------------------------------
> -----
> > I put up a couple of ABS heated glass print
> videos
> > for encouragement.
> >
> >
> Thanks for posting this. What's the clearance of
> your tip from the bed on the first layer? If it's
> closer than the layer thickness, did you
> compensate by reducing the flow rate? I have my
> first height set the same as the layer thickness.
> Considering that I also see ABS sticking to glass
> but then peeling off easily, you may be right that
> it's not hot enough. I am also using the PCB
> headted bed but I have a 4 mm aluminum build plate
> between it and the glass. I thought that this
> would distribute the heat more evenly but perhaps
> I'm also losing more heat this way. I also haven't
> tried pyrex yet and I've only tried window glass.

I am gathering bits for a heated bed as you describe, I will use a dibond sheet and fasten Nichrome wire underneath. On top i have got hold of a sheet of glass from an oven door.
The question i have is the thickness of the nichrome wire, I have some that is 0.8mm thick, as it appears the thinner the wire the better it would work.
Is this the case or am I totally stupid and should get thicker wire?