Post 7: Surface Preparation
We currently have all our main armour parts together and segments separated based on colour zones, time to get them ready for paint. This is arguably the longest and most physically demanding stage of a normal armour build so expect to be sore in multiple ways and put on some good music to just flow with.
Tools Overview
-Rotary Tool
-80 grit flapper wheels (25mm height, 80mm diameter)
-5” orbital sander
-5” orbital sander pads 60/80/220/300 grit
-Mouse sander
-Mouse sander pads 60/80/220/300 grit
-Linear pen sander
-Two sided tape
-Sand paper 80/220/300/400/600/800 grit
-Needle files
-Disposable cups
-Disposable brushes
-Mixing sticks
-Aluminium foil
-Fibreglass cloth
-Polyester fibreglass resin
-XTC epoxy resin
-Bondo Body Filler
-Bondo Glazing Putty
A work station where you can be an absolute mess for periods of time
Safety Concerns
-Chemicals and particulate requiring use of a respirator and ventilation
-Spinning tools working to remove material requiring safety glasses or a grinding shield
-Grinding tools requiring ear defenders
-Chemicals requiring use of gloves
-Fibreglass is itchy. Cover literally everything
-Take breaks, your body will thank you
General Approach
You can likely notice that there are multiple sanding tools listed within the Tools Overview, this is due to the fact that although I like sanding, I hate sanding. My back and hands will get tired long before I am mentally done for the day on cleaning up parts so anything to help get to a milestone of “X armour parts sanded to Y grit level” quicker is always needed. For every sanding grit I start with the orbital sander, follow with the mouse sander for sharp corners and finish with the linear sander for small recesses and sharp corners. The goal is to save fingers and arms for the wet sanding later. Let the machines do the work early on to save you pain.
60-80 Grit
The first pass after assembly and deburring is one where we have to trust the process. Stuff left the printer looking nice and glossy coming off the machine but we’re going to mess that all up in the name of getting it even smoother later.
Now is also the time where I’ll remove any remaining contact points from support material. Flapper wheels on a rotary tool get rid of it no problem at all.
If there’s any large surface defects that need to be reshaped or filled, now is the time to fix them and smooth them with Bondo Body Filler. Luckily on this suit there was only two or three spots that called for a body filler repair but the general rule of thumb is that any defect 1cm or less in width and depth can be fixed with body filler without a backing reinforcement, anything past that might need to be reprinted for structural reasons or a metal mesh should be added. For smaller defects (pits or scratches less than 3mm in depth) Bondo Spot Putty works great. This suit was getting an epoxy shell so the spot putty stage was not as important but at the same time there weren't too many locations in need of repairs.
Fibreglass Reinforcement
It is well known that I am a clumsy lad on occasion (parts of this suit have been involuntarily drop tested) and due to that fact I like to add an interior layer of fibreglass. It’s lightweight and adds a bit of extra structure that will help prevent catastrophic failure of parts due to dropping or heat warping which is entirely a positive in my books. The added benefit of resin flowing and accidentally filling in layer lines on the outer faces of the armour is just a bonus.
For doing a considerable amount of fibreglass at once I like to pre-cut squares of fibreglass cloth and store them in a small rectangular take out container to help organize the workspace and limit damage spills can make in a time sensitive operation when odd shapes like armour are being manipulated.
To help further keep things simple and minimize loss when doing things I like an easy repeatable measurement for working with the chemistry of the chemicals.
Most red beverage cups have some sort of marking on the side for specific volumes, and this 60mL marking is a small enough volume that’s easy to work with before the resin gels as well as being a nice round number for the approximate number of drops to get the magic 3-4% catalyst. As always temperature plays into chemistry and I was working in a basement in the Great White North which means adding a little extra kick always helps make sure we can get over the threshold for curing. Nobody likes sticky or smelly armour.
Applying two layers to all suit parts and three to some of the more accident prone parts (boots, shoulders, forearms) took about eight hours of solid work and I can tell you, that much time in nitrile gloves is not the most fun.
The only thing that is less fun than applying a bunch of itchy glass strands with a liquid poison is cleaning up the sharp sections of the hardened itchy glass. I will always advise against gloves when working with any rotating tool but for the sake of trimming excess and cleaning up edges, it was a tuck coveralls into gloves situation and tape the seams to stop as much as possible from getting in and onto skin.
Epoxy Coating
Again it’s more poison, this time with a slightly more viscous resin that has a slightly higher bonding strength and overall resistance to the types of damage that costume armour is expected to encounter (flexing, dent impacts). I’ve used XTC-3D on quite a few other projects and I reserve it for the times that I want to be fancy and not have to deal with chasing drips like with polyester fibreglass resin. It cures quickly (as long as you mix correctly and don’t have old stock) and sands just a little bit more evenly.
The rules for XTC-3D that they really need to print larger or at all on the instructions are as follows.
-Check the date on the box. If the manufacture date is older than a year, do not buy it.
-Shake the daylights out of Part B before use. This stuff separates and will leave you with a mess if you don’t
-Alway B onto A, never A onto B
-The listed mixing time is no joke
For mixing again we have the funny red cups, this time cut down to size for easier handling and mixing. The newly introduced tool is the excuse to have a lot of ice cream (4L recyclable bucket) and aluminum foil to make a wide tray. Epoxies like this are exothermic reactions when mixed with their hardener and spreading out the volume in a wide container like this helps slow the cure while limiting the chance of the mixing cup smoking and wasting a few dollars of material.
Covering the whole suit while carefully avoiding panel lines is a time consuming task and having the constant pressure of a tray of material that is threatening to go bad if you don’t work fast enough is stressful, always have a fun relaxation activity planned for afterwards like building a Brute Shot. Yes, the camera angles were very specific during Mayhem this year to hide the suit of armour.
180-220 Grit
Yes XTC is self levelling and will make a nice shell coat on the armour parts that will look nice but unfortunately some of the sharp edges will have been rounded and potentially some panel lines will have been filled so this stage is more for correcting any defects and helping satisfy any perfectionism. Overall the goal at this stage is to get a good paint surface that’s free of any telltale signs of FDM printing.
As always, continue to dry fit parts and confirm that any added material doesn’t get in the way of proper alignment and fit. Small greeblies that are inset may be the biggest struggle after an epoxy coat since their nests may have been slightly filled in. A linear pen sander is great for clearing out corners with the pointed triangle pads or in extreme cases a pointed grinding bit for a rotary tool can be used.
400-800 Wet Sanding
The first step to this process is to spray a layer of high body filler primer, my personal preference is Rutoleum 2 in 1 Filler/Sandable but depending on where you live that may be difficult to source. If you’ve been a good noodle in previous stages things should already look really smooth but we’re being extra and going for a shine.
Depending on how many little treats you need in your life, another 4L icecream bucket can be used for water during the wet sanding stage. The goal of this stage is for a nice glossy finish on parts that will create natural reflections of light. Yes, you can go higher than 800 grit but overall I’ve found that past 600 grit there is very little benefit for large printed pieces if you’re painting with rattle cans. If you’re planning on using parts for moulding master parts, go higher but for this, save your fingers the pain.
If you can, do better at controlling the weather than I did and spray paint and wet sand outdoors in temperatures above 10°C. Always read the manufacturer's application instructions, they’ve probably tested the product once or twice.
Here the fingernail scratch test is going to be doing a lot of work looking for any small recesses that may not be readily visible. The filler primer will help highlight low spots as you sand most of it away from the surface of the parts. Water will also add a reflectance to the parts that help you spot any surface defects. Switching between colours of filler primer also helps if doing multiple sanding passes but here I was being thrifty and bought in bulk the grey. I’ve included a picture of an
unrelated project to help show the colour switching of filler primers.
For this specific build the majority of the suit was wet sanded to 600 with the vibrant pink sections being sanded to 800 since I was planning on applying a colour shift top coat which likes glossy surfaces (spoilers, the colour shift didn’t end up looking great).
