I found a piece of glass the same size as HydraRaptor's bed that was 5mm thick. It used to be the platform of a kitchen weighing scale. It has nice rounded corners, the only problem was that it had an aluminium boss glued to it. I tried to remove it first with a hammer, then I tried acetone and finally I tried a hot air gun. None of these methods worked so I put it in the oven at gas mark 6 for 10 minutes. It then just lifted off with a pair of tongs.
For a quick test I just taped it down with some Kapton tape. It holds firm as long as you do all four sides.
As you can see ABS does not stick to glass at 140°C.
Next I moved the glass onto my Mendel as it was set up for PLA at the time and I couldn't get PLA to stick to PET tape.
I printed a frame vertex on glass with the bed starting at 120°C for the first layer, dropping down to 45°C for the rest of the build.
That stuck well but came off easily when the bed was cooled. Next I tried a new piece of 4mm glass cut to the size of the bed.
That stuck so well that it took several blows with a hammer to to remove each object. One piece chipped when it hit the wall behind! For some reason the new glass seems to stick much better than the old.
The objects come off perfectly flat and glassy.
I dropped the bed temperature to 100°C, which makes them a little easier to remove, just a sharp tap with a hammer rather than a heavy blow! Any lower than that and I have trouble getting the outlines to stick. Jordan uses only 65°C and reports the objects are easy to remove, so I am not sure what I am doing wrong, different PLA perhaps. If I start with the head lower then the plastic rucks up during the first layer infill.
So glass looks like a good bed material for PLA as it comes completely flat and hopefully should not degrade. Jordan reports that finger prints prevent objects sticking but they can be removed with alcohol. Copper clad PCB material has the advantage that you can flex it to remove objects but doesn't give as good a finish.
This is so awesome. We have been looking to use glass as a printing surface. Nice job man.
ReplyDeleteThe temperature discrepancies are probably due to the glass being a poor conductor and quite thick so the surface temperature is a lot less than the aluminium bed which is what is being controlled.
ReplyDeleteTo increase the adhesion of the glass, you could try spraying it with a glass frosting spray like Krylon or Rustoleum. This is from:
ReplyDeletehttp://www.ehow.com/how_4857796_create-frosted-glasseasy-inexpensive.html
Krylon is available at:
http://www.krylon.com/products/glass_frosting
Rustoleum is listed at:
http://www.rustoleum.com/CBGProduct.asp?pid=106
You could etch/frost aluminum or steel using equal amounts of anhydrous copper sulfate (technical grade or industrial grade) and cooking salt, as described at:
http://www.nontoxicprint.com/etchzincsteelaluminum.htm
You could etch/frost copper using four parts ferric chloride solution and one part citric acid solution, as described at:
http://www.nontoxicprint.com/etchcopperandbrass.htm
Enrique,
ReplyDeleteThanks that would be an interesting experiment. A lot of the force that holds objects onto perfectly flat surfaces is atmospheric pressure. When I tap a part on glass with a hammer it sometimes slides but does come off. I think that is why shiny surfaces stick better than rough ones. E.g. although others have reported that sanding Kapton improves its grip I find exactly the opposite.
The vacuum theory also explains why if there is the slightest gap in the outline the part will come unstuck after two or three layers.
I have yet to find a 100% reliable bed material. When doing multi-part builds the odd one will lift so I have quite a high reject rate.
Hello, can you write me at andrew.answer at gmail.com ? I want to ask several questions about CNC machines you have, but not here.
ReplyDeleteAndrew, maybe some of nophead "fans" will even be able to answer your questions for him. He has a lot of long-time loyal blog readers. Moreover, the answers are also interesting for all of us... So unless there's a legitimate need for secrecy it's probably counterproductive :)
ReplyDeleteOf course I have no idea what you want to ask or for what reasons, so maybe I should mind my own business. In that case, my apologies!