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Confused About PLA on Glass

Posted by ajayre 
Confused About PLA on Glass
August 05, 2012 06:07PM
I initially tried printing small objects (4cm width/height) in PLA on glass at 60C and observed warping. I then reduced the temperature to 55C and the warping went away. Based on advice I read somewhere I changed to printing the first layer at 55C and the reducing the heatbed to 45C for the rest of the layers. Still no warping.

Now I've tried to print a larger part - 8cm by 14cm and by the time it was on the third layer (so 0.9mm high) it popped right off the heatbed.

I am confused as to what to try next. Keep reducing the heatbed temperature? 45C seems low already to me. The "brim" doesn't seem a solution because my part at 8cm x 14cm x 0.9cm is really just like a large brim anyway. I clean the glass using window cleaner with vinegar as recommended by RichRap.

Thanks, Andy
Re: Confused About PLA on Glass
August 05, 2012 07:03PM
It's odd that you would get warping at 60C but not at 55C. 45C is almost definitely too cold for PLA to stick properly. You can try a PVA solution. (Elmer's white glue is PVA glue if you are in the States).


Cameron

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Re: Confused About PLA on Glass
August 06, 2012 01:44AM
Chances are, something else is the issue.

Maybe your heat bed is not regulating temperature properly (loose connection on the thermistor, poor contact, draft)

Maybe the first layer height is not remaining constant. surprisingly small changes in the 'squish' of the first layer can make a big difference in part adhesion. Check your endstops perhaps.


www.Fablicator.com
Re: Confused About PLA on Glass
August 06, 2012 07:16AM
i use PLA all the time on glass and i have the same issue prints would lift while printing (mainly due to the fan blowing on the print)

i use watered down PVA glue on the glass (apply when glass is hot) at 52C and print have the hotend at 185c

print never lift and also have a nicer matching finish to the bottom.

to lift the print let the glass cool to around 25c should then pop off nice.

if you really really want to test it i tried using a watered down polymer based primer on glass.

this stick like crazy ! only problem its near impossible to get it off the glass smiling smiley and you are left with the primer on the print.

just to note this does not work with ABS (from the little tests i did)
Re: Confused About PLA on Glass
August 06, 2012 06:12PM
I went back and looked a bit more closely at my small parts and I noticed that they are shaped a bit like the Eiffel Tower - instead of being the same width at all heights, it is slightly largest at the first layer and smallest at the last layer. I have a minimum 15 sec layer time in Slic3r.

I understand that a cooling fan can fix this but perhaps it is related to the problem of my large parts popping off the bed in some way?

Andy

Edited 1 time(s). Last edit at 08/06/2012 06:22PM by ajayre.
Re: Confused About PLA on Glass
August 07, 2012 07:49PM
PLA on glass is a vicious cycle friend.

The glass must be hot enough that the plastic sticks...

But then after enough layers, the upper layers of the print are cooler than the bottom layers (due to the heated bed) and the print will then curl and lift. This is because the bottom layers are softer than the top layers; the rigid upper layers are exerting a force on the squishy bottom layers.

You will see this even more readily with cheap Chinese PLA.

You can use a "Brim" to help minimize this warping.

Read about the brim here [forums.reprap.org]

If you use a brim and blue painters tape; a hammer and chisel might be needed to,get the print off of the plate winking smiley
Re: Confused About PLA on Glass
August 07, 2012 07:56PM
Attempt a brim on glass; if that does not work, do this:



When you are ready to beat this print and move on with life, use a brim and blue painters tape winking smiley

I feel for you; I spent weeks attempting to unlock the glass temp at various layer heights mystery; unfortunately, the shape of the object plays a huge role.
Re: Confused About PLA on Glass
August 07, 2012 08:08PM
Although everyone seems to print on glass I found that putting a covering right on the surface of the heated bed works great. The heated bed surface gets hot fast but it doesn't have to work hard to also heat a plate of glass. I use airplane covering over the bed that can be cut to any size and easily removed if it rips. The bed surface is flat enought for what I do. I also don't have to worry that much about dragging the tip of the nozzle along glass and potentially damaging something. I also don't have to juice up the glass because PLA and ABS sticks well to the covering. This is all based on not having to print beyond the standard red beds that can be purchased on ebay.

I know glass works. I'm just not sure why its better, with the potential issues.
Re: Confused About PLA on Glass
August 07, 2012 08:22PM
The issue with printing right on the bed is it warps when it gets hot, depending on which way up you have it the center will either rise or fall quite measurably.
If you printing a raft or with thick enough layer heights it might not matter.
Glass is predominantly useful because it's very flat.
Re: Confused About PLA on Glass
August 07, 2012 08:37PM
OK. My bed is mounted on a thin layer of cork. If it does rise the printing action easily pushes is down. Up to 50mm across the bottom of my prints seem perfectly flat. The message is that if glass is giving you a problem, this method is easy to try.
Re: Confused About PLA on Glass
August 08, 2012 01:59AM
dean448 Wrote:
-------------------------------------------------------
> Although everyone seems to print on glass I found
> that putting a covering right on the surface of
> the heated bed works great. The heated bed
> surface gets hot fast but it doesn't have to work
> hard to also heat a plate of glass. I use
> airplane covering over the bed that can be cut to
> any size and easily removed if it rips. The bed
> surface is flat enought for what I do. I also
> don't have to worry that much about dragging the
> tip of the nozzle along glass and potentially
> damaging something. I also don't have to juice
> up the glass because PLA and ABS sticks well to
> the covering. This is all based on not having to
> print beyond the standard red beds that can be
> purchased on ebay.
>
> I know glass works. I'm just not sure why its
> better, with the potential issues.


Hi Dean,

Do you have a link to the "airplane covering" you use?

Sounds neat smiling smiley
Re: Confused About PLA on Glass
August 08, 2012 04:26AM
Idolcrasher Wrote:
-------------------------------------------------------
> You can use a "Brim" to help minimize this
> warping.

However when my part popped off it was large, very thin and almost completely filled with the infill of the first three layers. So it was already like a massive brim itself. I don't see how added even more surface area would help. Instead I think it is a temperature problem in some way.

Andy
Re: Confused About PLA on Glass
August 08, 2012 05:51AM
Surface coverings have been discussed in the past. The favorite tape on this site is Kapton used for electronics. I'm using Monocote, or something similar which is heat resistant. Any hobby shop that sells model airplanes has it.

I really don't see any warping on my heated bed. I wonder if the difference is that I'm using 10V AC power it instead of DC. I'm using a transformer plugged into 120V line current. Could AC cause less warping then DC?
Re: Confused About PLA on Glass
August 08, 2012 08:05AM
As long as the Wattage is the same AC or DC will not make any difference. The thermal time constant of the bed is massive compared to the frequency so it gets smoothed out.


[www.hydraraptor.blogspot.com]
Re: Confused About PLA on Glass
August 08, 2012 02:58PM
Got a picture or thingiverse link of what you are printing?

I bet we can come up with a solution smiling smiley

ajayre Wrote:
-------------------------------------------------------
> Idolcrasher Wrote:
> --------------------------------------------------
> -----
> > You can use a "Brim" to help minimize this
> > warping.
>
> However when my part popped off it was large, very
> thin and almost completely filled with the infill
> of the first three layers. So it was already like
> a massive brim itself. I don't see how added even
> more surface area would help. Instead I think it
> is a temperature problem in some way.
>
> Andy
Re: Confused About PLA on Glass
August 10, 2012 03:20PM
Idolcrasher Wrote:
-------------------------------------------------------
> Got a picture or thingiverse link of what you are
> printing?
>
> I bet we can come up with a solution smiling smiley

This: http://www.thingiverse.com/download:39776 (here is a render: http://www.thingiverse.com/image:77905) and it is part of this: http://www.thingiverse.com/thing:11447.

Thanks, Andy
Re: Confused About PLA on Glass
August 18, 2012 05:58PM
I've cleaned the glass with methylated spirits. I've tried a heatbed temperature of 55C, 60C and 90C. I've tried a hotend temperature of 185C and 195C (too much drooling).

Now the PLA won't stick at all - even on small parts that previously printed fine! The problem starts on the perimeters of the first layer.

I've checked the nozzle is clean and doesn't appear to be dragging. I've checked the heatbed is flat with a piece of paper. I use a 80% squish for the first layer and I can clearly see the squishing. The glass is squeaky clean. There is no blobbing of the plastic. I slowed the printing of the first layer down to 20% of the speed of the other layers.

I don't want to cover the heatbed because I believe this should work, otherwise why would Dr. Bowyer sell me a machine that claims direct printing on heated glass with PLA works fine? If he can do it why not me?

Any suggestions or hints on what to try next?

Thanks, Andy

Edited 1 time(s). Last edit at 08/18/2012 05:58PM by ajayre.
Re: Confused About PLA on Glass
August 18, 2012 06:58PM
NVM. Already mentioned.

Edited 1 time(s). Last edit at 08/18/2012 06:59PM by NewPerfection.


Cameron

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Re: Confused About PLA on Glass
August 18, 2012 07:04PM
How are you measuring the hearted bed temperature, I've been told that the temperature of the bed is somewhat critical when printing PLA directly onto glass, I know my bed thermistor is miles off (about 30 degrees) because of it's placement, but it's repeatable so I just take it into account when setting temperatures.
Re: Confused About PLA on Glass
August 18, 2012 07:06PM
have you tried altering the Z height (heigher and lower) while trying to print to see if this helps? I normally do this and when i get it right just start alerting the Z stop untill you get it right.

maybe a pic of the problem or even better a video will help us diagnose the problem

only other thing i can think is that your temps are reading wrong ? (wrong thermistor selected in firmware)
Re: Confused About PLA on Glass
August 19, 2012 02:54AM
ajayre Wrote:
-------------------------------------------------------

> I don't want to cover the heatbed because I
> believe this should work, otherwise why would Dr.
> Bowyer sell me a machine that claims direct
> printing on heated glass with PLA works fine? If
> he can do it why not me?

On the long run you will find out that "PLA" isn't necessarily PLA. As everyone likes to buy cheap PLA quality decreases. Unfortunatly there is no way to ensure that quality. That's why the german section has started a thread to point out good sources. [forums.reprap.org]
Re: Confused About PLA on Glass
August 19, 2012 08:04AM
I'm using Faberdashery Arctic White, same as Dr. Bowyer.

I've found out that even though Methylated Spirits are recommended by some people and it makes the glass squeaky clean, PLA hates it and won't stick at all.

Don't use Methylated Spirits with PLA on glass!

I switched back to the cheapo supermarket glass cleaner with Vinegar that I was using before and there was an instant improvement. I've also noticed that my bed was not completely level - I didn't realize what an incredibly small difference can make to adhesion. I also plan on trying 1:8 PVA glue solution.

Andy
Re: Confused About PLA on Glass
August 19, 2012 08:44AM
Odd, I wonder if the additives in meths have changed over the years. My bottle is more than 20 years old!


[www.hydraraptor.blogspot.com]
Re: Confused About PLA on Glass
August 19, 2012 09:30AM
nophead Wrote:
-------------------------------------------------------
> Odd, I wonder if the additives in meths have
> changed over the years. My bottle is more than 20
> years old!

For the record I have a new bottle from Wickes. It doesn't list the ingredients... eye rolling smiley

Andy
Re: Confused About PLA on Glass
August 19, 2012 11:24AM
I have the same experience with far less adhesion for PLA on glass when cleaning with acetone. Dish washing liquid, vinegar and a thorough rinsing in the sink works for me.


--
-Nudel
Blog with RepRap Comic
Re: Confused About PLA on Glass
August 19, 2012 02:44PM
I just read this topic and want to share my experiences:

I use an aluminum 1,5mm thick sheet. Thoroughly cleaned with an abrasive sponge and some glass cleaner. Then I place the plate on the machine and treat it with 1:5 PVA. Within a few minutes it dries at 80 degrees. When dry I start printing large PLA parts. First layer 80degrees, the rest on 55degrees.

After the print finishes the reason for using the aluminium becomes clear: the aluminium can be bend a little so even when the PVA sticks to much, the print still pops of easily.

Even with prints of 200mm x 50mm x 100mm high this works flawless. So definitely worth the try!
Re: Confused About PLA on Glass
September 03, 2012 03:29AM
Enlightx Wrote:
-------------------------------------------------------
> i use watered down PVA glue on the glass (apply
> when glass is hot) at 52C and print have the
> hotend at 185c
>
> print never lift and also have a nicer matching
> finish to the bottom.

Hello. I've now tried this and it works - kind of. I've put PVA diluted 1:6 on there and I don't get warping, however I still need to squash the first layer otherwise it won't work and I don't get a nice finish to the bottom of the part. I think the glue might be a bit uneven. Also when removing the part it seems to weaken the PVA solution for the next time so I have to keep touching it up. When touching it up it creates while flakes of dried glue mixed in with the fresh glue.

Do you have any hints and tips? Could it be that my PVA glue is weaker than yours?

The strange thing is once a part is finished if I let the heatbed cool I sometimes have difficulty getting the part off.

What I would really like to aim for is what RichRap found - that he could print without squashing the first layer and get a perfectly looking surface.

Thanks, Andy
Re: Confused About PLA on Glass
September 04, 2012 02:24AM
You must also consider other factors in play.

Try using a wider width over thickness ratio for your first layer (slic3r has options for this).
Re: Confused About PLA on Glass
September 04, 2012 10:02AM
here is a video i took a bit ago, posted it recently. it shows pla sticking to glass. i have had it work some times and not on others. what i think is needed is for acrylic residue to dry, then sand paper the glass with dry acrylic on it. this method works well for abs, pla only if it is ruffed up after spreading acrylic floor wax.





when object cools and bed is off, it snaps off. same with abs. the thermal shock breaks it free. i am using glass from a picture frame.
Re: Confused About PLA on Glass
September 04, 2012 10:56AM
That's very strange how the results vary between users here.

I have good results with PLA straight on heated glass (60°C).
From time to time I clean the glass plate with dish washing "soap" and hot water. This might not be very helpful for some of you, I've learn that dish washing products are different among countries (for instance in england it seems they never rinse their dishes while we do here in france).

I even sometimes have a hard time detaching the object from the glass ! It seems to depend on the plastic source. The stickier I've ever seen is diamond age "High Impact PLA", I resorted to heating the bed again to soften the object a bit by fear of breaking the glass plate.


Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.
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