Genestealer Update 9: Assembling the Arms and Laying up the Back

 When I posted the last update I had a big pile of untrimmed, vacformed arm pieces like so:

So I set to work trimming the edges and getting them glued together.  I also set Jeff to work on some of the rough trimming and cutting:


Once the edges were cut, the next step was to clamp them to their adjoining pieces either overlapping the margins or butting them together with a piece of scrap clamped behind them like so:


The magnets were used along the edges were I couldn't reach with the clamps.

Once everything was securely clamped, a tiny amount of Weld-On #4 solvent adhesive was dripped into the seam.


Capillary action wicks the solvent into the tiny space between the clamped parts and everywhere it touches it dissolves the plastic a little bit.  As the solvent dries out, the plastic becomes solid again, but now it's all one part:


So, tinkering in the background over a couple of days in between projects, the arms start to come together:


Here's one complete set of arms for one genestealer:


They'll look pretty good in paint.

Meanwhile, last time I posted about the back piece, the mold looked like so:


As usual, there were tiny flaws in the surface, so we started by giving them a quick sanding.  Here's Tia working on one of the particularly problematic parts:


A couple of days later, I found a few minutes to finish up the wet sanding of the parts prior to waxing them:


Each segment was given three judicious coats of wax.  To speed the wax drying between coats, the parts were placed in front of the big circular fan:


After waxing and coating with PVA mold release, the parts were bolted back together and a layer of grey gelcoat was applied to the inside:


It's a pretty good-looking mold.  Look at it:


With the gelcoat applied, the mold was set face-down to cure:


First thing the next morning, I laid up the fiberglass inside.  With all of the curves and corners, it was a tricky part to lay up while also keeping it lightweight:


Here's another shot after I'd peeled off all of the release agent:


And the nice, clean inside which I'm very proud of:


Here it is again, weighing almost nothing:


After trimming the edges and cutting out the windows where the fleshy bits will be exposed, I did a quick fitting for the arm pieces with some gaff tape:


Since I had it all set up anyway, I couldn't resist the urge to try it on:


It'll be interesting once I have all of the weight of the head out in front, but for right now it's pretty easy to carry around:


I'm probably going to make up a backplate for the upper body to slot onto once we get the chest molded.  That way I can give the whole thing a rigid mounting system.  It'll be interesting working out a way to balance the weight on the nose and still keep some agility in the waist:


Still, this critter is going to be a lot of fun to perform in:


For now, here it sits while I work out how I want the chest to work:

I'm thinking I'll split off the sections that to under the lower arms and make the rest of the chest attach permanently to the back.  This will provide better strength and simplify the process of getting it on and off.

Stay tuned...

Genestealer Update 8: Vacuum-Forming the Arms

 So as of my last update, Jeff had done the digital modeling to get us to this point:

I had 3D printed the chest and back and started making molds to lay up copies of those parts in fiberglass.  It was important to make the back out of something that would have significant structure to it since there will be a lot of things that get attached to it later.

The arms do not have that problem.  They don't have to hold up anything but a coat of paint.  As long as they're the right shape and can survive being put on, worn around, and taken off, they've done their job.  So there's no need to go through the very labor intensive process of making them in fiberglass.  Instead we can get away with something significantly faster and less expensive.  While I could just make silicone molds of each part of the arms and rotocast them in urethane resin, it would be a lot of work, cost quite a bit of money, the parts would have a tendency to be a bit breakable, and then I'd have four really big molds that I would need to store somewhere afterwards.*  

Fortunately, their mostly smooth organic shape lends itself to an easier replication process: vacuum forming.  

To make the vacforming bucks, I started by filling in the insides of Jeff's arm models to make them solid blocks instead of wearable sleeves.  Then I imported them into the Project Designer software for my Carvewright CNC machines and sliced them up into pieces I could carve out on that 3-axis machine like so:

That's the inside half of the upper arm, mirrored to make the left and right versions.

Once I was happy with all of the parts I'd need, I fired up Lopez the Robot Whittler and left him to run:


In the space of a few hours, the first set of parts was carved:


Somewhere along the way, one of the bearings on the Z-axis truck sheared off it's mounting screw and I got this weirdness:


Weirdness.  Look at it:


Here's a set of properly carved pieces next to the weirness:


I'm a bit embarrassed by how long my troubleshooting process took before I got that little problem fixed.  But since these pieces didn't have any fine details to preserve, I would still be able to use the weirdness and the time and material wouldn't go to waste.

So I started by stacking the slices up and gluing them together:


For the slices with the weirdness, I did a bit of rough shaping with a coarse rasp, then filled any gaps with sawdust soaked in superglue, then worked the roughness back into shape with a flapwheel grinder, rasps, and coarse sandpaper:


The glue/sawdust composite would end up being sturdier than the rest of the MDF board, but since I'm only going to need four or so pulls from each of these bucks, it turns out there's no reason to reinforce the whole surface.  

Here's all four upper arm parts (outsides, insides, left and right) after the initial assembly and reshaping was done:


With most of the shape tuned up, I did a bit of final smoothing with Bondo and coarse sandpaper:


Bondo isn't ideally suited to deal with the kind of heating and cooling cycles that vacforming will put it through, but since they'll only get very limited use, I wasn't worried about it.

So after about half a day of filling and sanding, I had all of the arm parts smoothed out and ready for vacforming:


In order to make a pair of arms, I would have to do two pulls on the forming machine.  Here's half of the forming bucks laid out on the platen as the plastic sheet (0.125" high impact polystyrene in this case) is being heated:


Here's the machine in action:

View this post on Instagram

A post shared by Shawn M Thorsson (@thorssoli)

And moments later, here's the first set of vacformed arm parts:


Schnazzy:


The forming bucks were removed from the sheet and set aside to cool off (to keep the bondo from getting too soft from the heat) and I set up the other four bucks to pull the other half of the first pair of arms:


It turns out I could've spent just a bit more time smoothing out the forming bucks to make the surface smoother, but give the irregular, organic nature of the shapes we're working with, I wasn't too particularly concerned about the little bits of wiggly-ness here and there.  Here's a closeup of the shoulder area that shows the worst of what I'm referring to:

It's fine.

So I forged ahead and pulled four pairs of arms worth of sheets:

So with all of the parts formed, the next step was to trim off the excess plastic and make a nice, neat stack:

Now I just need to do the last little bit of trimming and I can seam the edges together and make them wearable.

I've been putting off posting about this update in the blog, because It feels horribly dissatisfying to not have this step just a bit more done, but I also know that if I post pics of the parts trimmed and glued together I'm going to wish I also had pictures of them all rigged and wearable.  And if I show them rigged and wearable I'm going to wish they were painted.  And if...

The deal is: I resolved that I would post every week no matter what and it's already been twelve days since my last update, so it's time to stop failing at keeping y'all up to date on how this is going.  

Stay tuned for more.  This thing is about to start looking like something.

*I know I'll probably never make any more of these things, but with all of the work that goes into making molds, I hate the notion of discarding them after a project is wrapped because you never know if they'll turn out to be useful at some point.  As a result, I have a lot of storage space that is claustrophobically jam-packed with molds from almost every project I've ever built.  It's terrifying.

Genestealer Update 7: Carapace Molding Completed and a New Approach for the Stilts

I have to admit, I haven't done much on this project since my last update.  I've been distracted with working on some other projects and have mostly been off site and working out of the shop, but I did manage to finish laying up the mold sections for this side of the carapace:

Then I cleaned off the clay parting wall that ran down the length of the spine:


And repeated the layup for the mold sections on the right hand side:


Once I was done with the layup and all of the sections had cured, it was time to demold the whole thing.  I'm happy to say that here, in this moment of truth, the mold separated with no real strain and nothing had to break to take it apart:

It turns out I'm getting pretty good at this.

So in short order, I had all of the mold sections removed:


The master now serves no further purpose, but I'm still hesitant to throw it away.  So for now it clings to the side of my rolling trashcan until I finally acknowledge that it's gotta go:

Maybe I'll turn it into an ornamental birdbath or something.  But probably not.

The next step was to trim the the mold sections to get rid of the fuzzy edges, then smooth the edges out on the belt sander to eliminate any little loose splinters of fiberglass that I don't want to find later with my hands.  Then the parts were taken outside so I could scrub off all of the clay and mold release and various other bits of schmoo that they'd picked up along the way.

That done, they're now just leaned up against a handy bucket to dry until I get a minute (or a couple of hours) to polish them in preparation for laying up my first copy:


Once I have the first carapace out of the molds, I'll finalize the shape of the chest piece so I can be sure they two parts will connect to each other with a perfect snap fit to make it easy to get the piece on and off without having to add any extra hardware or other fasteners.  That's the goal anyway.

In other news, I've decided that the digitigrade stilts I'd already made were going to be way too bulky to fit under the somewhat svelte leg armor of the genestealer.  Fortunately, I'd already been working on a much simpler version of digitigrade feet for my friend Rachel.  

Unfortunately, each pair has to be custom-made to fit only one wearer.  The process starts with slathering the lower legs with lotion:

Then standing in a purpose-built box full of lifecasting alginate:


For a while:


Once the alginate has set, the feet have to be pulled out.  Hilarity ensues:

View this post on Instagram

A post shared by Shawn M Thorsson (@thorssoli)

Then, because the alginate shrinks as it dries out, the cavity left behind by the legs has to be filled with resin as quickly as possible in order to prevent distortion.  So, with no time to stop and put my shoes on, I rushed to mix the resin:

And fill the molds:


Then, just like that, I've got new legs:


Namaste:


We did the same thing to Jeff:


So now I have a variety of legs:

In an economy where everything costs an arm and a leg, it's basically like I'm printing money...

Ahem.

So anyway, these will be wrapped in a layer of clay to give us an offset to allow for padding later.  Then they'll be wrapped in fiberglass and a steel strut will be glassed onto the bottom of the foot:


Once they are trimmed and cut properly they'll be fitted with straps, padded, and then they're ready to go.  Here's Rachel learning to walk in the pair we made for her:

She say's they're not particularly uncomfortable, so once she learns how to balance with these new extra-long feet and her ankles braced in place, she'll be good to go.

I'll be sure to post a video clip of Jeff falling over once he tries his on.

Meanwhile, this guy still sits on the bench in the middle of the room:


I can't help but feel like he's taunting me...

Stay tuned for next week when I dust off the CNC machines and finally get started on the arm parts.