Chris-Craft Cobra pt 2

In the last post, I had just wrapped up the under-planking. Next came the mahogany planking. I began on the keel, running a plank up each side of the center line on the bottom. I also soaked some of the planks, so that they would be easier to bend at the front. Below you can see the darker plank (dark because it is wet), bent around the front of the keel.


After a few rows of planks from the center, I then added one that runs along the edge that forms the border between the bottom and the sides. Having that plank in place gave me something to fit the bottom planks to, so there isn’t a gap.


Below you can see the bottom planking done. The planks are just glued on with thick CA glue, so they go on fairly quickly.


Below you can see a detail shot of the front. I wasn’t too careful about the fitment on these planks, as they will be below the waterline and therefore painted. With a little filler and sanding, this area will be nice and smooth before it gets painted.


The planking continued on the sides of the boat. The planks were long enough to span the length of the boat, so attaching them really just consisted of tracing a line along the edge of each plank on the hull (seen below), and then using that line as a guide for where to apply some glue. With the glue in place, then I can just hold the plank in place until the glue sets.


Below you can see all the bottom and side planks in place.


Here is a close-up showing the relatively rough surface of the planks. This will take quite a bit of sanding later to get it smoothed out.


With all the planking in place, I applied a coat of the wood filler to the lower parts of the hull. This is the area that will later be painted, so having a smooth surface is more important than having good looking wood.


Below you can see the nose of the hull after a bit of sanding and refining of the center line.


It was also at about this point that I realized that maybe soaking the big mahogany planks was not the best thing to do. It seems that while the planks being wet made them easier to bend around a few curves, it also made them swell just a bit. Once the planks had been on the hull for a few days and had dried out, they shrunk back to their original size, leaving a few gaps between the planks. I’m hoping that these will be filled in a bit later on, once I put a bunch of coats of spar varnish on the hull.


Next up was carving the nose from a block of mahogany. Below you can see the starting point, which was two triangles glued together, a mid point, when I had sawn off big chunks for rough shaping, and the point at which I had finished the rough shaping using a Dremel and sanding drum.


In order to reduce the mess from the sanding, I had some luck making a makeshift dust collection system using out vacuum cleaner hose positioned near the sanding. Below you can see an action shot of the sawdust coming off of the sanding drum and into the hose. It looked cool, so I took a photo :)


That completed the underside of the boat. The next step was to cut it off of the build board, sand the ribs flush with the top surface and then start adding the top deck components. Below you can see the edge parts glued in place. This was, unfortunately, where I made a bit of a mistake, placing the side strips a little bit too far inboard. I didn’t notice the misplacement until later in the build, though.


The side strips consist of three layers, each layer overlapping the others differently. Below you can see the second layer being held in place while the glue dries.


There is a strip that runs along the inside of the mahogany parts that provides support for the decking later. Below you can see it being glued in place.


In gluing the above strip in place, I realized my mistake. The rear edge strip was in the correct place, but when I glued the side strips on, I had aligned the outside edges with the outside of the rear strip, when I SHOULD have aligned the inside edges. Once I discovered this, I found that I couldn’t pry off the side strips without doing lot of damage, so I opted instead to make adjustments to the build as I went, in order to compensate for the misalignment. The first thing I had to do was add a few extra strips to the back in order to even out the alignment of the inside edge. Below you can see the two additional strips, before sanding.


While there will need to be more adjustments later, the next few steps were fairly straightforward. Below you can see some decking glued in place, forming the front of the cockpit surround.


Front sub-planking in place, using the same techniques as the lower hull:


I order to provide support for the rear and side decks, I needed to add some support ribs. Theses were just 1/8” basswood, cut to length and tapered a bit so that there will be a bit of a slope to the decks.


Below you can see the side/rear sub-decking in place. I had to do a good deal of trimming and fitting to this piece in order to fit it into a space that is slightly smaller due to my additional thickness on the rear edge piece.


Finally, once the sub-deck was in place, I could start to add the final top decking layer. Below you can see the current state of the boat. Because the side rails should have been pushed just a bit back and out, the center basswood part didn’t reach the full length of the front deck. This meant that I had to add a little piece to extend it, which will be sanded and integrated more later. The thicker rear edge rail also required that the large basswood part be shortened slightly, in order to match up with the edges of the cockpit and still just meet the rear edge. I ended up removing approximately 1/4 inch from the straight section along the edge of the cockpit. I may also need to shorten the plastic molded pieces that form the engine cover and fin, but I was already thinking of cutting those up in order to add opening engine bay covers, so that may not cause any problems.


That is where the project stands now. Next up is applying the striped mahogany and plastic decking, and then a bunch of sanding to even it all out.

Thanks for reading!


1955 Chris-Craft Cobra

Back at the end of 2015, I was in Orlando, Florida, visiting Disney World (taking advantage of a perk of working for the mouse: free park entry!). One of the restaurants in Disney Springs (formerly Downtown Disney) was just FILLED with great looking large scale boat and ship models. I was inspired to take up a wooden model project again, except this time I wanted it to end up shiny. After a bit of research, I narrowed it down to a handful of possible kit options. Mostly I was looking at kits from Dumas, as they have some great looking Chris-Craft speedboat kits. I spent a Saturday morning making the rounds at my local hobby shops (living in the SF Bay Area, there are a few to choose from) and managed to find this kit:


With a length of 27 inches, it’s a fairly large scale project (at least for me and my limited building space).

Like most kits of this type, it comes as a number of sheets of pre-cut parts, some strips of thin plywood, a bunch of strips of mahogany and bass wood, and some cast metal parts.


The instructions had me start by marking rib positions on a building board (spare plywood in this case) and then assembling and gluing the frame to the board.


That was followed by adding a few stringers and the keel boards on the bottom of the boat.


Because of the rapid change in shape between the first rib and the nose of the boat, the front is shaped from balsa. The kit came with a sheet of half-inch-thick balsa that was cut into triangles and glued in place. Below you can see the rough blocks glued in place. I had to use a little bit of spare balsa that I had laying around in order to fill the space all of the way (those thin sheets right at the front).


Below you can see the rough shaping. This was done using first a jewelers saw to cut off big chunks of the wood, then a sanding drum on a Dremel for fast shaping and then finally some 150 grit sandpaper for finer shaping.


Next up was the under-planking. This consisted of 1/16 inch thick plywood strips that are laid diagonally on the bottom and sides of the hull. The instructions said to use a thick cyanoacrylate (super glue), but I found that when the strips needed to be bent a bit, the glue tended to not have the strength to hold the strips in place. I believe that this was mostly because there were fairly small areas in which the strips contacted the frame. I had actually started the planking and then found that I had started laying the planks going the wrong direction (dark spots in photo below was the glue that held them in place). When I discovered this, I tried to take those planks off and discovered that they came off so easily that I lost all confidence in the CA method.

I decided instead to try good ol’ yellow carpenter’s glue. This required that the strips be clamped in place while the glue dried. Once dried, though, the glue was strong and the connection between the strips and frame was solid. I ended up going with this technique for all of the under-planking. Below you can see the transom in place as well as the first few planks.


Below you can see some of the clamping and weighting I needed to do in order to hold planks in place while the glue dried. Those angle blocks weigh 3lbs each, and were providing a great deal of pressure on those planks.


A closer view of the same setup.


As I got closer and closer to the nose of the boat, the angle between the bottom planks and the chine (frame piece that is the line between the sides and bottom) became shallower and the area of contact between the two got smaller. What I decided to do was add a few strips of basswood, trimmed to the correct angle, in order to give more contact area. Below you can see those strips in place.


A different angle on the same strips. You can see that the left side is untrimmed, while the right side is trimmed to the angle of the strips of plywood.


Below you can see the entire bottom of the boat with under-planking on it. The top edge in this photo has been sanded even with the angle of the side, while the bottom edge still looks ragged because it has not yet been sanded smooth.


The planking of the sides was very similar. I did attempt to use straight sewing pins as temporary nails. This worked some times and other times just resulted in lots of bent pins and plenty of cursing.


Using thinner strips of plywood near the front. The thinner strips are easier to bend and can therefore be formed to the sharper curves near the bow.


With the under-planking complete, the whole hull got a first pass of sanding.


In a few places, a plank or two ended up lower than I would like. In the case below, I added another bit of strip on top and then sanded it flush to the surrounding planks.


After that first pass of sanding, I put a thin layer of wood filler over most of the hull. This filled in gaps, leveled out the surface and gave me something to sand down in order to get things nice and smooth before the top plank layer.


Below you can see the filled and sanded result, all ready for the mahogany plank layer.


That seems like a good place to stop for this post. The mahogany planking is nearly done, so look for that in a forthcoming blog post!

Thanks for reading!


Inc in Grey Gallery

As a follow-up to the last blog entry, I’ve put together a gallery of the finished Inc model.

Because of the tight timeline on which I put this one together (in order to make book publishing deadlines), I don’t have any photos of the in-progress build. Fortunately, I’ve still got another kit worth of parts AND the molds to make more parts. So, keep an eye out for future blog posts when I do get back around to making another of this model. Perhaps I’ll even paint that one!

You can find the gallery here, or click the image below.

Thanks for reading!


Inc Project

A little while back, I put the Ferrari Enzo project aside so that I could try something new.

A good friend of mine, Neil Blevins, along with Bill Zahn, Stephan Bugaj, and a collection of concept art all-stars, have been working on an ‘art of’ book of sorts. For those unfamiliar, an ‘art of’ book is usually a book that contains the concept art for a film, television series, or something similar, i.e. ‘The Art of Inside Out’ or ‘The Art of Game of Thrones.’ The big difference here is that this book is full of art for a production that has not yet been made. They’ve been painting images and writing a story for a few years and this presented an opportunity for me to add my own bit of flavor to the mix.

I’d been interested in trying my hand at producing a garage resin model kit for a while, so that I could learn a bit more about the process. I talked to Neil about such a project and we decided that I would take his digital 3d model of the main character, who is a can-shaped robot, and see if I could turn it into a model kit. This blog post is about some of that process.

First off, I received a 3d file from Neil, which was the version of the main character that he was using to digitally render images from. It was set up to look good in pictures, but had lots of fine detail and various features that would be tricky to turn into physical object. Neil and I had agreed that we’d like to aim for a completed model that was 8-10 inches tall, which meant roughly 1/18 scale for this character (it was meant to be a pretty large robot). So, it fell to me to take his digital 3d model and figure out how to shrink it down, alter it and cut it up so that it could both be 3d printed and then replicated in resin, and then actually print it, clean up the prints, make molds of the parts, make castings from those molds and finally put at least one kit together so that Neil could put images of it into the book that they were working on.

Here are a few views of the digital model that I was working from.



Before jumping into the bulk of the work, I did a bit of a test. The robot had a weapon of sorts that was part gun and part spot welder. It was a fairly complex shape, with both thick and thin areas and would make a decent trial for the printing, clean up and mold making. After a few additions in the 3d file, to bridge some gaps, add some support and make it a little more mold friendly (less undercuts), I had the gun printed at Shapeways. Below you can see the print I got back, sprayed with an initial coat of primer.


The print itself was a little rough in a few areas, so it required a few cycles of priming and sanding, in order to fill in and smooth out the striations that the printing left behind. Below you can see a close up of one such area and the ridges on the flat surfaces that should be smooth.


With that test done, and a few lessons learned (how to keep print costs down, basic mold pouring techniques learned, etc), I moved on to a few more pieces. Below you can see the head, split into three parts, as they arrived from the printer. They come in a clear plastic that makes it difficult to see the texture from the printing process. This is why I primed the parts before sanding, as otherwise it was nearly impossible to see if the surface was smooth or not.


Here is how they go together, just press-fit in this photo:


Once the long and dull process of prepping all of the parts for mold making was complete, I split the mold making process into two main groups: single-piece molds and two-piece molds. The single-piece molds are for relatively flat parts, that only have detail on one side. The parts can be attached to a board, have a little box built around them and the silicon poured over them. The two-piece molds are for parts that have detail all around them. Those are more complicated to make molds for and require a form be built up around them with something like clay, defining where the mold seam will be. A pour spout and registration indentations need to be added so that the mold halves align and there is a place to pour in the resin in the finished mold.

First though, a bit about this process: Since the intent here is to make resin castings, using silicon rubber as the mold material, the requirements are a little different than if I were making molds for something like injection molded plastic kits. The silicon has a great deal of flexibility, so there can be some undercuts on the piece to be cast, and you don’t have to worry about the piece getting stuck in the mold. Also, basic molding and casting with these materials don’t strictly require any special equipment, although the addition of a few small machines can help the quality level a great deal.

In my case, I opted to supplement my process with the addition of a vacuum pump, a vacuum chamber, a pressure vessel and air compressor. I’ll go into more detail on those a bit later.

For the mold making, I started by ordering a box of corrugated plastic sheet. This stuff is commonly used for signs, but it is easy to cut, reasonably strong and inexpensive. For the one-part molds, I simply put a sheet down, hot-glued my parts to the sheet, and then built little walls around each part that would hold in the silicon. Those walls were hot-glued to the base and any gaps sealed up with more hot glue.


From what I had read, the mold should be at least 3/4” thick from the highest bit of the part being cast. I measured and marked on the walls of each box so I knew where to pour to. Now, when pouring a silicon mold, you’ll get the best mold quality if you eliminate bubbles from the silicon. Additionally, if you would like to pressure cast later on, you MUST get rid of the air bubbles in the silicon or they will give you a bumpy surface on your casting. There are a few ways to eliminate or minimize bubbles: pouring slowly into one corner of the mold (easy way, but not good for pressure casting), and vacuum degassing (harder, requires equipment, but good for pressure casting).

There is lots of information out there about mold making with silicon and casting with resin, so I’ll gloss over most of this. See the end of this post for links to various information sources to learn more.

The executive summary is that pouring your silicon from a little bit of a height (maybe 6 inches) and fairly slowly prevents bubbles from forming around your object, so you get good fidelity, but it does not prevent bubbles from forming in the silicon itself. So, if you are going to just pour resin into your mold and let it cure, this works just fine. If you are intending to pressure cast, you’ll need to get all the bubbles out of the silicon as well, so that requires another step: vacuum degassing. This is the technique of putting your mixed silicon under vacuum so that all the air bubbles expand and rise to the top, leaving your silicon bubble-free. If you skip this step, and pressure cast later, you’ll get what are commonly called ‘measles’ on the casting. These are when the bubbles in the silicon shrink under the pressure, and make little bumps on the casting, which you have to clean up later.

Since my goal was to be able to make the highest quality parts possible, I decided to invest in a bit of new equipment. This consisted of a vacuum chamber and a vacuum pump. This allows me to mix up a batch of silicon, put it into the vacuum chamber, place it under vacuum for a few minutes, watch all the air bubble out, and THEN pour it into my mold forms. Below you can see my setup and a batch of silicon bubbling away under vacuum.



After the single-piece molds were poured and cured, and a test casting or two had been done, it was time to move on to the larger and more complex multi-piece molds. For these, I got a box of water-based clay to use to build up half of each mold. Below you can see the arms and legs in their molds, ready for the first part to be poured. You can see how there are a few divots and grooves to be used for registration as well as little lumps that will be the pour spouts at the top of each part. You can also see the final state of the 3d printed parts, after they had been sanded and primed a few times and then finally had a gloss clear coat sprayed onto them, in order to get a smoother finish on the cast parts.


After pouring the first half, the molds are pulled off of their bases (but the sides left in place), the water-based clay washed away, some mold release agent sprayed on, and the other half of the mold poured. Below you can see a bunch of the other pieces ready for their second mold halves to be poured. On the lower left you can see the feet and their pour spouts that are plastic instead of clay, and the face plate and mouth in the center lower row, where I’m connecting two parts in one mold for faster casting later.


For the largest parts, including the two halves of the body and the head dome, the molds were still just two parts, but they required a bit more engineering in order to be sure that they could support their own weight later on. My fear was that if they were not thick enough, they would sag and close off the narrow space between the two halves of the mold, thinning the final part. For a few of the halves, I ended up enclosing a few scrap metal rods inside the mold in order to add support, which seemed to work decently.

Below you can see the head dome, getting prepped for pouring the first half of the mold.


Similarly, one of the body halves, on its little bed of clay, ready for mold walls and some silicon.


Once the molds were made, I did a bit of testing with casting. First off, I tried to pour some resin into my new molds to see how it turned out without using any fancy tricks. Below you can see some freshly-poured resin, which pours clear and turns opaque white as it cures.


What I discovered is that while this lazy casting works pretty well for the larger, thicker parts, it doesn’t work as well for the smaller thinner things. Air bubbles tended to get trapped in the thinner parts, resulting in unusable castings. So, the next step was to move on to pressure casting. This entails pouring resin into the molds and then putting those molds into a pressure chamber and cranking up the pressure. This both pushes the resin down into the molds and also compresses any bubbles down to tiny sizes, making them much less of an issue. If this is combined with vacuum degassing of the resin, you get the best of both worlds, with nearly bubble-free resin squished down into the molds.

While I don’t have any good pictures of my pressure casting setup, it was decidedly DIY. I purchased an inexpensive pressure chamber (from Harbor Freight) that is intended for painting and then did all the things that the warning labels tell you not to do. I took most all of the fittings off of it, plugged up most of the holes, and removed the paint intake tube. The end result being a pressure pot that has a fitting to attach an air hose, a pressure gauge, and a valve that can vent the chamber. Combine this with an average-power air compressor and I’ve got a pressure casting setup!

The tricky part here was that the resin I was using has a pot life (time between mixing and curing) of about 7 minutes, during which I needed to vacuum degas the resin, pour it into the molds (which was complicated in a few cases), and then get it into the pressure chamber and under pressure, all before it starts to thicken. To help pack the most into the pressure chamber (which wasn’t very large), I built a little shelf that I could load up and drop into the pot. It was just a couple round pieces of wood held apart by long threaded rods with some nuts on them. Below you can see the shelf (with the top shelf removed), and various molds, after removal from the pressure pot.


This allowed me, if everything went perfectly, to make one kit worth of parts in three cycles of the pressure chamber. Unfortunately, there are a few parts that are tricky to get good castings of (like the hands), so often I’ve got to try those a couple of times in order to get a set of good parts.

That’s the basics of my adventure in building up a model kit on my own. Keep an eye out for a near-future blog post with a bit about the finished parts, some casting tricks and photos of the first finished model in grey primer.

Thanks for reading!


Visiting Tamiya Headquarters!

Earlier this year, I spent two weeks visiting Japan. As part of that trip, my wife and I visited her brother, who was studying in Shizuoka, a medium sized city about an hour and a half bullet train ride south-west of Tokyo. When looking into what to do for the couple of days that we would be in Shizuoka, I discovered that it was home to the headquarters of the Tamiya corporation! After a little research, I discovered that a) At the headquarters, there was a museum that was open to the public. b) The headquarters was a 20 minute walk from where we were staying.

My wife and I walked across town and arrived there around 11am. We signed in at the front desk and were left to our own devices to wander about the first floor, which had a few galleries of models and full size cars. There is a showroom of their full size car collection, a room full of their current model releases and a room that is full of various models of historic significance to the company. There are also a few areas that have original box artwork on display and a few miscellaneous displays scattered about. After we wandered around for a few minutes, the receptionist called us over to a corner of the room that had some seating and a television. Through her broken English and out terrible Japanese, we determined that we should watch whatever she was about to show us. So, we sat and watched a 15 minute video about the Tamiya corporation and their model making process from start to finish, which was actually very interesting (and in English!). We were there on a weekday, and it was pretty much empty, so should you be in the neighborhood, I highly recommend stopping by!

What you see below are some of the photos I took there, along with some descriptions where relevant.

Here’s the view after passing through the main gates:


Right outside the front doors:


Over the years, Tamiya has purchased various vehicles as reference (or maybe just because they wanted to drive them around for fun). As a result they have a bit of a car collection, much of which is on display on the ground floor of their headquarters.


More of their car collection:


I’m sure this was totally for reference and definitely not driven around by the boss at any point ;)


Who knew that Isuzu made a V12 engine? Definitely not me!


Some of the original paintings for box art:



Here are a few photos from the gallery of current plastic models:





I built that Bimota model about 10 years ago!


The whole Calsonic collection:




The wall cases in the background are all of their R/C releases.


These were some models and dioramas that were on display out with the full size cars:





Here are a few from the gallery of models of historical significance (to the Tamiya company). The below ship appeared to be made entirely of paper!




This ship had to be five or six feet long!


I guess the beginnings of Tamiya were in the wooden ship kit business:


This was a pretty nice display of all the parts in a motorcycle kit, put together like this to celebrate the 50th anniversary of Tamiya:


Finally, here’s a photo of the 1/12 scale Ferrari Enzo kit, assembled by their master builders. Hopefully mine will look half as good as theirs does when I’m done:


Thanks for reading, and let me know what you think in the comment section below!