One of the 3D printers the Ely Makers has was donated by my Dad. After decades of running an injection moulding firm, he was interested in getting a printer to prototype parts for plastic model kits – his main hobby. The problem was that he couldn’t quite get it to work so he donated it so it didn’t sit gathering dust in his garage.
So when he heard that we had the 3D printers running, my Dad was straight over with one of the jobs he had wanted to try.
The plastic modelling club he is a member of seems to have a recurring theme of dressing up the minion characters from Despicable Me to fit the theme of the competition. Normally he has been using epoxy putty to make the hands.
So my task was if I could create hands for the Minion characters for a model he was building.
My Dad had an existing model figure, a minion in Napoleonic uniform. This was the scale he was aiming for. So I took rough measurements of the wrist and fingers to work with. I also searched for reference pictures of minions and their hands. I ended up with this picture of Bob.
Modelling the Hand
Version 1 – OpenSCAD
The first attempt was done using OpenSCAD. OpenSCAD uses a programming language to describe and generate 3D objects working from either primitive shapes like cubes and spheres or taking a 2D shape and extruding it out into 3D. It’s great if you have a clear idea of what you are trying to do and the object is easy to describe mathematically.
Unfortunately, I didn’t have a clear idea and using spheres and cylinders didn’t work very well at all. It ended up looking like a frog’s foot. There’s a picture of it later. I didn’t like it and it took me the best part of an evening to get a script. Since you write programmes in OpenSCAD, I instinctively made a number of variables so I could tweak the knuckle sizes, finger length, angles. Setting all that up too time but the end result just didn’t work.
I did a 3D print of it and it’s great as a frog foot but didn’t solve the problem. Back to the drawing board.
Version 2 – Fusion 360
I decided to attempt a second version using AutoDesk Fusion 360. They don’t make it very clear on the website but Fusion 360 is “free” to makers (such that if you don’t earn money from it, you can get it free a year at a time). The biggest problem is that it is Windows and macOS only. Which meant I had to rebuild my Windows partition rather than running on my normal Linux system.
I used AutoCAD professionally for two years when I was left school. That meant I was reasonably familiar with things and made it easier to pick up. I had also been playing with FreeCAD for a while which covers most of the same features. Unfortunately, I’ve also had it crash a few times and completely lose my work so I’ve been hesitant to use it recently.
One of the many features in Fusion 360 is you can load in reference images. So rather than do it by eye again using primitive shapes, I used the image of Bob’s hand and loaded it in as a reference image, which is similar to a background but calibrated it to be 6mm across the wrist.
With a calibrated reference, I drew around the outline of the hand with a polyline to get a simple 2D sketch. It took seconds to extrude that 2D sketch to be a 6mm thick to get a big solid block shaped like a minion’s hand. The next trick was to add a 2mm fillet (curved edge) on the front and back. This made them rounded on the front and back. Last I adding a 6mm cylinder as for the arm and joined the models together to make one solid. It took far less time to design than my first effort and look much better.
The biggest challenge was 3D printing it. I printed one hand by itself to make sure it looked okay. This came out looking pretty good. I had unintentionally left it in “Fine” quality so it printed at a 0.1mm layer height which was twice as detailed as my usual 0.2mm.
I decided I didn’t need it quite that detailed so I tried to print a pair of hands at 0.2mm and see how that looked. I sat looking at the printer for most of the print. Went to get a cup of tea and returned to find the print job had finished. But something wasn’t right. The middle finger (or index – had to tell with minions) just stopped and was open to the inside.
Turns out during my cup of tea, the extrusion gear, that feeds the plastic into the end of the printer had slipped off so for the last five minutes, no plastic came out. So I had to dismantle the extrusion head to refit the gear. Then when I tried to test it, the motor was not working. After rebuilding it again and checking the wiring, I eventually found that the 3D printer I was using has a safety feature in the firmware that it won’t run the motor unless the “hot-end” extruder is on and at 180°C.
With the 3D Printer running again, I was just trying to get a pair of hand printed. However, the next printout was directly on the bed and one of the hands slipped during the print but the rest of the print carried on. I let it finish since with the prototype, that at least meant one workable pair. I did several more prints each going wrong it their own ways. Vertical prints would fall over. A large raft structure, intended to hold the hands to the print surface, itself slipped off.
Eventually, I got another pair to actually print successfully. I wasn’t 100% happy because the first print still looked so much better at 0.1mm layers but I knew that my Dad still had more work to do before it would be usable for his model. Sanding, filling, cleaning and painting and modifying to be holding some items. So I sent off the collection, failures as well.
So after a few days, my Dad had taken the 3D prints and cleaned them up, modified them and painted them ready for the model. It turned out that this particular hand was for a minion version of Margaret Thatcher. He sent me some photos of the finished model including modifications so she was holding a little flag and her handbag.
Overall it was quite fun having a purpose to 3D print something rather than just printing fun bits and pieces from Thingiverse. Fusion 360 was familiar enough to me that I could pick it up and get something have decent quite quickly. The quality was a bit lower than I’d like so I need to work a bit more on that aspect of the prints for similar projects. In this case, I knew that there was additional clean up due so I was able to pass over what had been done.
My Dad was happy with how they turned out. Now I’m waiting on details for some small hangers for an airfield diorama that he wants next.