My last issue with my printer since i've built it has been trying to get my print bed right. I've tried just about every combo of hot and cold beds onto glass with kapton, blue masking tape and various other suggestions without any luck (everything either sticks too hard or doesnt stick well). But after stumbling onto Nophead's blog entry about pva i've had zero problems.

Im using 1:2 PVA:Water onto a cold glass bed, extruding at 195c and i get no problems with it, no warping, doesnt lift off the bed and it comes off with a small click (doesnt affect the PVA either). Been through about 10 prints so far with this and its just brilliant (from 0.1mm to 0.25mm layer heights and various fill levels).

The PVA washes off with a 5 minutes soak in warm water. The PVA im using is aquadere (the cheap non-exterior stuff, [www.selleys.com.au]).

Figured i might post cause its worth trying if your having print bed issues.

Sorry but it wasn't me who blogged it. I haven't tried PVA yet as plain glass works fine with PLA for me.

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[www.hydraraptor.blogspot.com]

Sorry your right, i had your blog open in the next tab, its actually from here (http://richrap.blogspot.com.au/2012/06/more-scrap-art-gearboxes-and-panelmax.html).

Just to clarify, after doing a google search for my local PVA adhesive supplier, we are talking about regular old Elmers white glue? From the wiki entry: "The glue is based on an emulsion of polyvinyl acetate, derived from petrochemical sources."

Will definitely have to try this out tonight.

Yes, thats the stuff, this is a print i did yesterday that i photo'd just cause of what it was, but you can shes quite well attached (pink panther woman, so not safe for work i guess?)...

[dl.dropbox.com]

Theres another one coming out the printer now i'll do a video of me taking the print off the bed. I printed some mendel90 z-axis clamps earlier, they would have been good to video in hindsight cause there quite wide/long and not very high, but they came off beautifully, completely flat too.

Looks interesting might have to give it a go once I get up and running again

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Experimenting in 3D in New Zealand

I keep meaning to take a video but always forget to, but one word of caution. I originally tried 100% pva on the glass bed and this stuck so hard to the bed i had to stick the whole thing in the oven until the pla was soft enough to twist off the bed with a pair of plyers, it wasn until i stumbled onto the blog post that mentioned diluting it that my bed started working for me.

finally remembered to take a video [www.youtube.com]

Though i forgot to put the lens back on autofocus...

Edited 1 time(s). Last edit at 07/17/2012 08:04PM by Takigama.

Hi there,
Just clarifying... are you printing to an unheated bed? What's the general room temperature? Are you in a warm climate?
I've been using a PVA coating for the past few weeks and it works very well, but I use a heated bed. The PLA doesn't well at all when the bed is cold.

Regards,
NumberSix

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[numbersixreprap.blogspot.com]

Im on an unheated bed, I find when i switch my heatbed on, i need to dilute the PVA a bit more (1:6-1:8), but as the PLA im using is printing without warping on 1:2 PVA, im quite happy not having to use the bed.

Im in Australia, which is generally a warm climate but its winter atm and the general room temperature during prints would be somewhere between 8-14 celcius.

Im about to switch to a new PLA provider, so i'll be curious to see what that might do to my prints.

Hi Takigama,
That's very interesting. I'll have to try that out, the trick appearing to be a more concentrated solution of PVA when printing to a cold bed. My coating on the heated bed was about 1:8, and believe it or not I found that almost too strong a grip, and a challenge to remove once it had cooled. I've recently posted some detail and a short video on my blog: [numbersixreprap.blogspot.ie]

My suggestion when printing to a heated bed was to dilute further for easier removal when cold.

Have you tried many prints with larger footprints? The general logic seems to be that the heated bed prevents warping by maintaining the base PLA temperature at around 60Deg C and keeping it in a relaxed state, if I'm describing it correctly. What's interesting is that the concentrated PVA solution could have the strength to adhere the work to the surface even as it cools and attempts to curl up (due to contraction of the upper layers), but still allow the piece to be detached easily when finished.

What thickness of glass are you using? I'm using a very light glass, <2mm (actually a cheap mirror). My concern when removing pieces that have stuck too well is that I'll crack the glass.

my largest footprint print would be this one: [www.thingiverse.com] (my own design), its about 110x60 (2 of those), which is reasonably large. I've also printed an M90 x Carriage which is quite large and thin-ish. Im printing onto 1mm picture frame glass (i have a few of these, so not worried about breaking the glass). My main reason for wanting a cold bed is cause my printer has quite a large print area so heating it becomes a little difficult (or limits the build area). I find though that if im at a point where i feel like the print is stuck on just too hard to remove, i shove it in the oven @ 100c and take it off with plyers with a twisting motion (destroys the print). Tends to come off quite easy that way. Theres been a few times i've printed on the wrong (uncoated side of the glass) and had to do this.

I've experimented with the PVA solution a fair bit now and i find one of the more important variables in the print is actually the extrusion temperature. The PLA i have will extrude starting at about 185. Printing onto PVA i find at 185 it'll warp, once i get to 195 though it no longer warps, but at 215 it sticks too hard. With the heated bed on, i can drop back to 185 and it wont warp.

The PLA concentration does effect it but i think it has more to do with how thick the layer is when its dried on the glass.. i.e. pure pva is quite thick so it produces a much thicker (also hard to keep it even) surface (though why this makes prints hard to remove, i cant quite figure out).. once i get down below about 1:6 on a cold bed, i think the PVA is getting too thin to really produce decent results. I've noticed even with 1:2 if i paint on a layer and then tilt the glass so it ends up drying thicker towards one edge (i.e. the pva solution slowly creaps down the glass while its drying), the closer i print towards the thick edge, the easier the print is to remove. Atm, im using 1:3 and literally pouring it on the glass to the point where its almost like holding a tray of water. Multi-coating the surface i have not had any real success with, just seems to make the surface a little uneven.

I've tried different drying techniques also and this doesn't really seem to have any impact other then how quick it dries (normal drying, cold fan, warm fan heater, fan forced oven @ 100c) - though the fan forced over seemed to cause the pla to pucker in parts which actually didnt have any effect, theres just a slight rippling in the surface you can see but has no impact on the prints itself.

That's very interesting. You have done quite a bit of experimenting with pva coatings and cold bed printing.

Can I just ask you to clarify some detail in your third paragraph above? You say a pure PVA coating is thick and hard to remove prints from, but then you say it's easy to remove prints from the thicker end of 1:2 coating. This seems a contradiction, but I'm sure you can clarify.

When you print at 195deg C or above is it just for the first layer? Do you then lower the temperature back to 185deg C then or keep it high?

I suspect my failed attempts to print to a cold PVA coated print bed may be a combination of PVA dilution (too weak) and too low an initial first layer.

What might be your guideline dilution ratio and initial print temperature setting following you experimentation? (and do you reduce your hot-end temperature after the first layer?)

I'll be happy to coat a new sheet of glass and do some testing.

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[numbersixreprap.blogspot.com]

Sorry, poor wording on my part, what i meant was that undiluted pva has a reasonably thick consistency, so spreading it on the glass is quite easy and you can produce quite a nice thick (as in layer height) of pva when it drys. But this doesnt seem to work (print sticks too hard - even with a thin layer of undiluted pva i get this). But with diluted pva, the thicker the layer you can produce on the glass, the better the end result (i.e. sticks well, removes easiily and lasts longer), but making a thick layer with diluted pva is a little harder cause its more like water.

I havent experimented with first layer temperatures yet really, i'll throw a few prints thru today with 195/185 and see how they go.

Im typically using 1:2 or 1:3, i find with anything more diulte then that i cant get a very good layer of pva on the glass. Pretty much everything i print im printing at 195-200. I did a few prints today at 198 and really didnt see much difference.

I recently switched to diamondage pla (also have impla but havent tried it yet) and im half way thru a 100m roll of 3mm fillament, still working very well with pva, so highly recommend diamondage pla for printing on cold pva/glass.