Friday, 12 February 2016

Glass 3D Print build surfaces - are not all the same - and a solution for PETG

Glass damage with PET is not fun :-(

In this post I investigated some common glass build surfaces - Starting with a little history to see how we ended up using borosilicate glass and why that's not always such a good choice for 3D Printing.

Many years ago when 3D Printing material choice was more limited than today, enormous amounts of effort went into testing and experimentation of surfaces to print on. Take one look at the RepRap forum archives and you will see that people tried almost every type of material known to man as a 3D printer build surface.

The heated 3D Print bed solved many of these issues, and many people opted for a glass surface to print on.

Over the years I have always used standard mirror-glass as my printing surface of choice. I like that you get a reflection - it's easy to see the state of your nozzle. And I found that they heated up evenly and produced fantastic results.

Over time many people have started to specify the use of borosilicate glass surfaces in 3D printers. While they do have some good properties and can be ground and polished very flat, they also have some limitations that are not always great for 3D Printing.

One of the biggest issues of borosilicate glass is that is can scratch easily, you can dig out chips with a metal scraper and generally cause damage just from normal use.

This is a stunning example of exactly the problem with PETG - Image supplied by Ante Vukorepa

I had plenty of damage - even with small parts, borosilicate glass can get chipped easily.

Often the glass chips are also almost impossible to remove from the printed part.

Borosilicate glass is also starts to get fragile when it gets damaged, and if you decide to print in PET or many of the filled materials you can take massive chunks out of your glass bed.

This problem seems to be something that has not been addressed, other than coating the nice smooth glass surface with uneven gluestick, sprays, sheets of tape or films.

I'm at the point where I no longer want to re-coat build surfaces, mess with glue or generally do anything other than clean the glass every 10-15 prints. And for the last few years using the mirrored-glass surface and some standard window cleaner with vinegar that's worked out well.

My mission was to find a universal build print surface that can also handle more materials and work with IR detection systems.

I have used PEI sheets quite successfully, but they slowly deteriorate and do not seem to like wood-filled and other filled materials.

Tufnol was a fond favorite when the first round of Nylon materials were released back in 2011, Taulman Nylons stick well to natural materials like wood, Tufnol, paper tapes and even cardboard. But they all soon deteriorate too.

Copper FR4  - PCB material works quite well, but it's hard to keep clean and oxidises very quickly.

The only build surface that seems to carry on print after print is glass. But not everything likes to stick to 'normal' or toughened glass.

Recently various surface treatments (for glass and other materials) have made it much easier to print with many different materials, but again they all have a limited life and need to be constantly re-coated or patched up. Airwolf Wolfbite is a good example of a great surface treatment I use it on glass for ABS and PCABS.

BuildTak is another good sheeting material, and for some 3D Printing plastic's is simply too strong - NEVER, ever try to print with TPU materials onto BuildTak - there is a very good chance they will bond permanently to the sheet forever.

Until I had the BigBox I always used standard mirror-glass. Unfortunately because the BigBox used an optical Infra-red (IR) level detection system you can't use a mirror surface.

Adding glue, sheets or tapes does make a difference to the IR sensing Z offset, and a change of glue thickness or a missing patch can cause issues. I specifically wanted a clean sheet of glass to print with as many materials as possible - without damage.

And that's where the trouble started. My borosilicate glass sheet started getting damaged and with the use of PETG materials became quickly destroyed with missing chunks of glass.
It's also quite easy to dig a scraper into the glass and cause a nick or scratch.

The issues are not because of bad or low quality borsilicate glass, in fact E3D commissioned an optical instrument company to custom make the sheets of flat borosilicate glass for the BigBox 3D Printer. It's an expensive, and very good quality sheet of glass!

But I want a solution that does it all, and has no maintenance apart from a quick wipe down.

I made a video talking about some of the issues, and a solution using a tempered glass protector, seems to work exceptionally well - view below or in HD on Youtube here - 

To cut a long story short - I went around the same loop again I did in 2010 testing a lot of different materials for use as a surface - Copper clad PCB (FR4) material - glass fibre sheets, sanded Aluminium, Polycarbonate, Acrylic...

I was about to buy an A4 sized sheet of toughened glass (300mm x 200mm) and I found sheets of thin glass protectors designed for tablets and phones. ('Gorilla glass' - and many copies that are basically a laminate of toughened glass and probably polycarbonate with some coatings. They are also very thin usually around 0.3mm and have a convenient silicone adhesive backing.

The silicone adhesive backing allows it to stick easily to glass without any bubbles.

The glass protector is only 0.3mm think - easy to compensate in the Z offset and still allows you to use the other side if you want clean borosilicate glass for other materials.

I was concerned that the “Oleophobic” coating they add to these sheets to stop fingerprints and repel oils and almost any type of liquid would stop the thermoplastic extrusion sticking to the sheet.

I also wondered if it would bond and not release after cooling down - or worst still totally shatter when using PET/G/T.

My borosilicate glass sheet was already damaged beyond use, so I decided to try out a toughened gorilla-glass screen protector. In hindsight this was not ideal because I now have gaps under my laminated sheet, but I'm still using one of the good properties of the borosilicate glass - that it's very flat.

Some research into common size protectors and the iPad pro was too big but the Surface Pro4 was almost perfect sized for the BigBox bed (2 ) - I found them on eBay for £7.30 (under $10). From a UK seller including free postage.

You can get the exact same thing from China for under $5 with free postage.

I believe this glass laminate sheeting protector is mass-produced in China and laser-cut to size, with various cut-outs for phones and tablet computers -  so it's possible that a keen manufacturer could have some cut to exact size for use in 3D Printing...

In short it seems to be a total success - especially for PETG materials - of any size print - in fact the bigger the better.

PLA and various filled materials all seem to stick well too.

I found that I needed to increase my heated bed temperatures by +5 degrees C and Eureka! - this works.

I didn't use a brim with the PETG materials, and some were over 150mm in size with 45% rectilinear infill - (that's nasty and would take great chunks out of my bare Borosilicate glass sheet).

Some key points - 

The the “Oleophobic” coating should last a very long time, but you need to make sure not to use aggressive chemicals or alcohol based cleaners. It's designed to be easily cleaned with just a dry standard microfibre cloth and nothing else.

I also believe that when the coating does start to vanish, that will only help other materials (like PLA) stick just a little better things - time will tell on that.

You do get slightly less stick with PLA, so for very small parts (20mm or smaller) I found that a brim was all that was required to keep them stuck. It was more of an issue with transparent PLA's I didn't see any issues at all using Opaque PLA materials.

I have not yet done any testing with Nylon or woodfilled / other-filled materials.

Other PET (G/T) based materials Like Refil, nGen, _XT and T-glase all seem to work well.

Why not use a thick sheet of toughened glass? - Yes you could, but it's often not all that flat and many 3DPrinters now come as standard with a heated borosilicate glass surface. That's great for PLA, and with a 'Gorilla glass' style protector on one side, you can still use the other side for other materials if you need.

Thanks for reading,

Please leave me a comment and get in contact. If you try out a sheet of toughened glass - 'protector' do let me know how you get on with it.

Until next time.


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