Like a lot of folk right now (mid Covid-19 lockdown), I'm using a 3D printer to produce face shields. I started from scratch and with little experience of using a 3D printer. This post will detail some of the issues I had and my solutions, in the off chance that this information could help somebody else.
Please see my HSE manager testing one of the completed face shields in the picture below so you know what I am talking about. These face shields are requested by front line workers as there is a scarcity of off-the-shelf personal protective equipment (PPE) . I print the yellow clip at the top. The face shield is an A4 clear plastic sheet bought from an online stationery store. The holes are punched using a four hole A4 punch. The design comes from the national 3D printing society.
I work through a couple in Ulverston who set the scheme up at https://www.facebook.com/F3Dprinting. They received some funding through donations and kindly sent me some filament and the pre-punched sheets. Requests for the face shields go straight to this couple. I try to fulfill some of the orders that they receive.
I bought a Creality CR10-Mini 3D printer the same day I read of their project. Why this printer? There's quote "There are two types of fool, one says 'This is old and therefore good'. The second says 'This is new and therefore better' ". I went for the 'old and therefore good' option. The CR10-Mini is a printer that came out a few years ago, so there are many videos on YouTube to show me how to set up the printer and trouble-shoot inevitable problems. The CR10-Mini gets good reviews for the beginner, which I most definitely am. Maybe a more recent printer would give me more for my money, but I needed to get into production as soon as possible. Some of the reviews of more recently produced or cheaper machines showed that simple bodges were necessary to get them running. I can't nip down the local hardware store to get some washers or a spring at the moment. This YouTube video , comparing the Creality CR10-Mini with the Creality Ender 3, convinced me to spend the extra to get a printer that lookes easier to get into production than a cheaper model that may take some extra time and experience to set up. However, if you don't have the extra money, the Ender 3 looks to be a good printer.
The CR10-Mini was straight forwards to set up. Most of the online reviews are made by people who have substantial experience of 3D printers and may have forgotten what it is like to know almost nothing about them. Even so, bolting the printer together while following this YouTube video was not difficult. An experienced 3D printer guy would laugh, shake the parts a little and have a machine ready. I didn't find the manual too helpful, so stuck with the video guide.
Watch this video on levelling the printer, download and edit the G code as suggested by the presenter. Then run the code to check your levelling and nozzle clearance. I check this levelling about once a day now.
Problems encountered and solutions
Prints not sticking to the glass plate
Check the plate levelling and the clearance between the extruder nozzle and the plate. Get a good tight clearance as suggested in the video linked in the Tips section.
Use decent filament - not the sample that came with the printer.
Decreased first layer print speed to 20 mm/s. This gives the plastic more time to melt and stick to the glass plate.
Increased glass plate temperature from the suggested 60C to 70C. This worked well. I stepped the temperature back down to 60C as my experience and confidence increased. A higher bed temperature increases the chance of the plastic melting and bonding to the plate against using a lower temperature. The higher bed temperature increases the start up time, as the bed has to get to the higher temperature and uses more electricity.
Smeared the glass with a film of UHU glue stick. I was shown this trick by a friend some years ago when having an induction on the lab 3D printer, which I then did not touch again.
After about 100 prints, I was getting the hang of things. So I cleaned off all the UHU glue stick from the plate and found that the prints stick straight to the glass. I guess that I got my nozzle clearance good and tight so that the base layer of plastic squishes down and sticks. Maybe smearing the glue on for a while then cleaning all of this off removed any residual grease on the plate. I will never know.
Knocking sound and a decrease in print quality.
This happened after about 100 hours of printing. Please see the photo below. The layers of filament are not as tight as they should be on the part shown on the top of the photo. The part on the bottom of the photo was printed after I fixed the problem. Note that the prints were both made at low resolution and high speed. The machine is capable of a smoother finish if you give it the time.
I found that that the little gear wheel-shaped filament feeder was slipping on the filament. So less filament was fed to the extruder than intended, leading to material missing on the final print.
I fixed this by cleaning the teeth on the wheel. Please see the photo below where I indicate the component that needed cleaning. In the photo it is shiny and clean though.
The feeder wheel is toothed and metal, so inevitably the teeth gum up with bits of plastic from the filament, allowing the filament to slip. I should also look at how my filament reel is mounted, in case there is excess drag on the filament entering the printer, leading to it slipping in the feed mechanism.
To clean the wheel, I first preheated the nozzle to PLA temp, then pulled out the filament. I unbolted the plastic feed tube. I cut a short length of filament and fed it through the feed mechanism. Then I pulled this filament rod back and forwards while holding a toothbrush against the gear wheel teeth.
I reassembled the printer and tried again. Instant fix! A video showing how to do this in detail can be found on this YouTube video.
Printer not levelling correctly
One of the wires connecting the printer to the control unit snagged above the contact switch on the Z-axis controller. This switch is used to help the machine reset its home position. When the printer was resetting, this wire pressed onto the contact, triggering a false home position. The incorrect wire position is shown in the photo below.
I print two nested head-pieces at a time as shown below. I tried some stacked prints, but they didn't come out as well as the single-layer prints. My lack of experience and the need to maintain production stop me from trying more. A year from now I'll laugh at my not printing stacks, but right now, I'm running with what I know works. As always 'Experience is something you get after you needed it'.
I printed off about 145 clips for local care home and hospice orders and sent a batch of prints to the NHS scheme, for a grand total of 200 prints. Then I was asked to return to my paid work offshore, so my PPE manufacturing came to an end. Until the next pandemic...