IPad Glass As 3D Printing Build Platform

Are you tired of scratches on your Kapton tape, or the bubbles that show up when trying to remove your parts?
Are you fed up with having to change your tape after every 3-4 builds to get optimum results?
Are you having trouble with your parts warping and delaminating?
Do you want a reliable 3D printing build platform which is durable and low maintenance?

Then this is for you!

I was inspired by the work of others who have tried printing on sheets of glass and mirrors, yet at the same time I wanted to have a flexible platform that I could bend to release the parts (like NinjaPlate from adafruit). Gorilla Glass from Corning looked like the perfect candidate. After searching for thin sheets of the stuff that I could cleave down to size for my MakerBot 2X, I realized the iPad screen is the closest thing and fits all the requirements:

Thin, yet flexible tempered glass
Scratch-proof (well, scratch-resistant, but the only thing I found to scratch it was diamond or tungsten carbide tip scribers)
Great thermal conductivity (for uniform heat distribution)
Very low thermal expansion/distortion (at the usual printing temperatures of 110-120C)
Resistant to pretty much all solvents I could find (Acetone safe)
Pretty cheap (bought mine for $15 on Amazon)
Not too hard to hack it into a build plate (see instructions)

Step 1: What You Need

You need a very flat surface in a well ventilated area. I wouldn't do this on a surface that you may later prepare food on!

Here is the shopping list:

Generic replacement iPad screen (I got mine for $15 on Amazon)
Single sided razor blades (or a sharp flexible scraper)
Acetone and IPA (rubbing alcohol will also do)
Lint-free cloth (TexWipe works great)
Binder clips of the right size depending on your hotplate thickness
Disposable gloves and eye protection

Step 2: Removing the Touch Sensitive Circuitry

This step can get a bit messy! There is a second glass sheet glued to the back that I believe acts as a capacitive plate. I don't know the exact specs for the adhesive spacer used, but the way it smells, I would guess it is a cyanoacrylate derivative and would produce toxic fumes when heated. So it must come off!

start by removing the wires and the button and the camera fixture.

Fortunately the second sheet has similar properties to sugar glass, so it breaks into small pieces quite easily. Be sure to wear eye protection as the needle-sharp pieces fly everywhere. Don't use any solvent at this stage as the glue will help keep the glass shards bound when they shatter.

Step 3: Cleaning the Glass

When all the capacitive plate and the double-sided tape on the edges have been scraped off, it's time to remove the residual glue.

What I found to work best is to first cover the surface with IPA and scrape off the glue with the razor blade.
Then put acetone on your rag and start rubbing off what is left.
Finish by putting IPA on a fresh piece of TexWipe and rub off the acetone smudges.
Wash the whole thing with warm water and dry.

You could even scrape off the paint around the edges, the glass is pretty tough and won't scratch as I attacked it with a chisel! But you have to be very careful not to put a dent on the sides or your glass will start to shrink (happened to me on the first attempt ... towards the very end ... Facepalm!).

Step 4: Measurements!

You don't have to do this but since I had a very precise height gauge I wanted to test the thickness variation across the whole thing. It turned out to be around 19-25 microns bending up from the center, which is pretty decent. The plate thickness is about 1.6mm.

Step 5: Mounting the Glass

You are almost done!

I used large binder clips to attach the glass to my heated plate. You can either bend the handles in a vice or remove them after placing the clips in the right place or they will get tangled up in your extruder assembly. I am not planning on editing the gcode for every build to make sure the extruders don't hit the clips but it is pretty easy to squeeze 3 clips in there (see the intro picture as a guide).

The glass is very thin so you don't need a custom spacer, but I strongly suggest that you lower the plate by 2-3mm before alignment to prevent the extruder nozzles from crashing into your glass. Also, I suggest heating the plate up to your usual printing temp and then doing the build plate alignment. For MakerBot users, I would manually jog to each position instead of using the "level build plate" option so I can control the travel paths.

Step 6: Printing Prep

I got good results with just printing on the glass with nothing added (no raft either) but you can also use hair spray or glue stick to increase your filament adhesion for peace of mind. I spray onto the TexWipe and dab the surface. You can also try spraying a couple of coats directly on the surface. I usually print 2-3 times then clean the surface with acetone/IPA and re-apply the spray.

Remember, no matter how hard the part is stuck to your glass you can still scrape it off without having to worry about scratching your plate!

Hope you enjoyed this instructable and best of luck printing :)

A.S.