3D Printing - Replacing The Fluorinated Ethylene Propylene (FEP) Sheet

My twelve-month old FEP film is badly scratched, scuffed and starting to crack

Recently I've noticed that the number of failures with my trusty Mars 3 Pro 3D Printer have started to increase. In my experience during the past twelve months, this issue usually boils down to the "Elegoo" Water Washable Resin getting too cold (during late night sessions), the build plate being unlevel/overloaded (preventing the resin from flowing into the gaps between each exposure), or the models having insufficient supports.

The underside of my Resin Tank showing the wear and tear upon my FEP Sheet

However, the fact I was simply getting shapeless splodges where my miniatures should have been, especially when the figures were positioned close to the centre of my build plate, made me think it was probably down to my Fluorinated Ethylene Propylene (FEP) Sheet finally 'giving up the ghost'. This non-stick transparent film stretches across the bottom of a 3D Printer's resin tank, and needs to be scratch-free so as to best ensure successful prints. It's replacement is arguably one of the scariest pieces of maintenance a user must carry out, so I thought some might appreciate a guide as to how I do it.

To begin with I simply wanted to ensure my current FEP sheet was as clean as possible so I could visually check it over for faults. To do this I used the Mars 3 Pro tank clean function to create a thin film of cured resin on the bottom of my resin tank and then simply peeled it off. This operation not only showed that the FEP was so badly scratched in places that they had created non-transparent, smudge-covered areas. But that the plastic was actually cracking in places too. These faults didn't come as much of a surprise though, as it's probably been close to a year since I last changed it - having really struggled to complete the task the first time round.

My Resin Vat with its four large corner screws removed

With my mind made up I unfastened my resin vat and set about freeing the FEP film from its bottom by removing the four large screws which sit in the rectangular-shaped tank's corners. I currently use a sheet from the "Elegoo" Five Piece Release Liner Film PFA for the Mars Series LCD 3D Printer as it can supposedly last up to "50% longer than the regular version of release film." I don't know about that, but this last piece has been merrily mullered over the last twelve months without too many woes so definitely has stood the test of time.

My Resin Vat with its ten medium-sized screws removed

I also utilise a set of hex screwdrivers by "Engineer", which come in the required sizes of 2mm, 2.5mm and 3mm. In addition, the kit contains a useful 1.5mm head too, which is great for piercing the new FEP whenever a screw struggles to penetrate its surface. These are so much better than the Allen keys which come with the 3D printer, and make disassembling/reassembling the resin vat so much easier - albeit I do like to still use the Allen Keys at the end to really tighten up screws.

With the four main screws sorted, it's time to remove the ten (slightly smaller) screws which fix the squash in place. This should then allow you to completely remove the FEP sheet and its two-piece metal frame from the bottom of the resin tank, before tackling the fourteen (even smaller) screws keeping the structure together. Once this has been completed you can now separate the film from its mounting and replace it with a fresh one.

My FEP Film after I've removed the fourteen small screws and separated the Squash.

Peel the protective film off of the new FEP sheet and place it over the squash allowing a little 'give' in the tension. This 'give' has caused some considerable consternation in the past as "Elegoo" themselves recommend deploying a 50x35x5mm piece of foam underneath the FEP film - a clearly useful item which doesn't come supplied with the 3D printer. I however, simply use 32 playing cards as my spacer, having picked up the tip from a fellow hobbyist. Whatever you use, ensure the FEP sheet is carefully placed between the two-piece metal frame and fasten the smallest screws back in position.

My new FEP Sheet being screwed in place over my 'spacer' and then cut to size

This is where the aforementioned 1.5mm hex head I bought can come in useful, as you're twisting the screws straight through the FEP film - something which is almost impossible to accomplish if you're just using the Allen keys supplied. So whenever I struggle, I just pop the 1.5mm hex head through the hole first and then fasten the screw. With the fourteen screws now in place, it's time to carefully trim the excess FEP sheet flat against the frame with a sharp modelling knife.

Next up is to attach the entire squash back to the bottom of the resin tank using the ten medium-sized screws. This is probably the most dangerous part of the process as sometimes I find the screwdriver can occasionally fail to push the screw straight through the FEP and resultantly its head will flail towards the pristinely taut sheet threatening to pierce or badly scratch it before you've even printed a single miniature. This part does produce a highly satisfying popping sound though, whenever a screw successfully penetrates the sheet. Lastly, fix the four corner screws back in position and the resin tank is once again fully assembled and ready to be filled for 3D printing.