M29C Water Weasel

[Jakko]

It’s been a while, but I’m finally back to this one

After spraying the undercarriage with black primer, I glued the top and bottom together, then began to add a coaming around the hull from etched parts provided in the kit. However, that made me realise I should not have glued the engine cover into the hull yet, but it’s far too late to get that back out again. The reason is that the coaming goes all around the upper hull edge, and the engine cover is supposed to then go inside of that.

The upshot of this was that I had to cut a gap into its front and right side:



It took some trial and error to find a way to do this without damaging the rest of the model (which didn’t quite work, as you can see) but in the end I used an X-Acto No. 13 saw blade:

These fit a standard X-Acto knife handle to turn it into a saw about 2.5 cm long, which is much more controllable than a full-sized saw. It also had the right thickness for the etched coamings, unlike my razor saw which made a cut that was too narrow.

With that done, I could add the coamings on all four sides:

 

[Jakko]

The floatation cell at the front has sheet-metal bits on the side that close the gap between the cell and the hull. These are cast onto the model’s floatation cell, but resin shrinkage (I think) has made the cell the same width as the hull, so they won’t overlap without breaking. I copied the shape onto pieces of 0.25 mm plastic card and glued them to the sides of the cell:



They still overlap the front of the cell because I intend to trim them to size and fair them into it once the glue is dry.

 

[Jim R]

Hi Jakko
The kit is throwing up a few issues for you to deal with. Those saw blades look useful. I have some very fine PE blades which fit into a knife handle. Work ok but are very easily damaged, they kink and then can't be straightened.
I suppose the larger the part the more noticeable resin shrinkage becomes.
Fine job so far.
Jim

 

[Jakko]

The kit is throwing up a few issues for you to deal with.

I’m not overly enjoying the building of this, if I’m honest. It’s a model I want to have finished, but not one I really care for working on

Those saw blades look useful. I have some very fine PE blades which fit into a knife handle. Work ok but are very easily damaged, they kink and then can't be straightened.

These are much sturdier, a proper piece of knife steel with saw teeth cut into one side. I suspect they’ll break rather than bend, though I’ve never had to apply enough force to one to have that happen. In fact I think the one I used is the only one I’ve taken from the packaging, which I’ve had since time immemorial (I get the impression from their web site that X-Acto don’t make these anymore, so I’ll have to be extra careful with them …)

I suppose the larger the part the more noticeable resin shrinkage becomes.

I think I heard once that polyurethane resin shrinks about 3% when it cures, so for larger parts especially it can be very noticeable, yes. This piece is about 5 cm wide, at a quick guess, and the little bits on the sides that I replaced were thicker than the 0.25 mm card I used, but still under 0.5 mm. If the master was made to the correct width to overlap the sides, even 1% shrinkage would then make it too narrow. Of course, the hull would shrink as well and so everything should work out — but what if the solid floatation cell shrinks more than the mostly empty hull does, for example?

 

[adt70hk]

Well done Jakko. Not the most straightforward build

ATB

Andrew

 

[Tim Marlow]

I think I heard once that polyurethane resin shrinks about 3% when it cures, so for larger parts especially it can be very noticeable, yes. This piece is about 5 cm wide, at a quick guess, and the little bits on the sides that I replaced were thicker than the 0.25 mm card I used, but still under 0.5 mm. If the master was made to the correct width to overlap the sides, even 1% shrinkage would then make it too narrow. Of course, the hull would shrink as well and so everything should work out — but what if the solid floatation cell shrinks more than the mostly empty hull does, for example?

You’d like to think the person that produced the master took this into account…..but probably not!

 

[scottie3158]

Jakko coming on nicely.

 

[Jakko]

Thanks, all

You’d like to think the person that produced the master took this into account…..but probably not!

I have this feeling that the shrinkage isn’t the same for all the parts. Still, it’s something I would also expect the master maker to account for, if it’s largely predictable by (for example) whether the part is solid or hollow. But at the same time, the etched parts, which definitely don’t suffer shrinkage, for the coaming around the upper hull fit perfectly in the opening in the hull top, whereas the resin floor was too long to do the same (see near the start of this thread).

That said, I have a different complaint about some of the etched parts, though All but one of the frets are laminated with plastic on both sides for protection, which is a good idea in general. However, the plastic of the largest fret was very hard to remove, so that even though I was being careful, I bent both of the side skirts by pulling them up with the plastic. Not only that, but the plastic left a layer of glue all over both sides of the fret, which I’m having to remove with a cloth soaked in solvent. This is a bit of a chore, as it takes lot of effort and needs to be done carefully to avoid more damage

 

[Tim Marlow]

Sounds a bit like lazy kit production to me Jakko. The photoresist film should be removed before sale??

 

[Jakko]

Oh, it’s not film, I think, but plastic specifically added for protection. You see this in plenty of kits, but not that often in those from small manufacturers.

 

[Jakko]

I finally got the etched fret clean enough to use:



Initially, I began scrubbing it with solvent on a cloth, which worked but was very laborious and prone to bending the larger parts (as you can see). The other day, I instead put it into a stainless steel pan and poured cellulose thinner into that, deep enough to cover the whole fret, and let it sit for a couple of hours. That got most of the glue off, with the fret ended up looking like the lower right corner still does:



Just now, I scrubbed all the parts again with solvent on a cloth to get the rest off, and it’s now good enough to use, I think. Now to try and bend those skirting plates …

Also, I trimmed the plastic I added to the floatation cell, filled the gap and sanded it down:



After taking the picture I painted the filled areas grey, and they look fine, with just a little extra work still needed to blend the new sides into the cell.

 

[Jim R]

Hi Jakko
What a job with the PE fret. I've never heard of that before. At least it's useable now although the bending may be awkward.
Glad the floatation cell filling went ok.
Jim

 

[adt70hk]

Well done Jakko for sorting that out. Can't have been easy.

 

[Jakko]

What a job with the PE fret. I've never heard of that before. At least it's useable now although the bending may be awkward.

I haven’t seen it either, and I wonder if the glue on the plastic was not suitable or if it went off with age. The other couple of frets that had plastic on them, didn’t have this problem.

Well done Jakko for sorting that out. Can't have been easy.

Mostly it was a lot of work that shouldn’t have been necessary in the first place This kit is very slow progress, even by my standards …

 

[Lee Drennen]

Looks good Jakko. Resin can sure be a pain in backside sometimes

 

[Jakko]

Thanks. I’ve built plenty of resin conversions as well as full kits, and this is really an odd one. Usually when the casting quality isn’t great, then neither is the kit in general — detail etc. This one, though, has great detail but fit and especially casting quality aren’t very good. They could have simplified a lot of parts and made the whole thing easier to build, but I guess they didn’t want to. That would have been OK, if they had had Verlinden-type of casting standards, I suppose. This isn’t quite Elite Models in terms of casting (shovels bent into an S-shape, etc.) but it’s not one I would recommend unless you like a challenge.

 

[Jakko]

It’s only getting worse Putting the front floatation cell on was easy enough by doing it in reverse from how the “instructions” recommend. That is, first this:



And then this:



Because that way, you automatically avoid gaps between the etched parts and the cell. After that, though, things didn’t go as smoothly. There also needs to be an etched part along the bow, and bending that to shape is (to put it politely) bloody difficult. I spent at least half an hour on trying to get it right, and ended up with …



It just doesn’t fit. If you put the centre section onto the resin you have gaps on the angled bits, if you put the angled bits against the resin, the etched part overlaps it at the front. And that’s assuming the whole thing is properly flat, which is almost impossible to make it because of lack of strength:



I think I’ve got a solution, though: ditch the etched part and make my own from plastic sheet. I intend to tape a piece of paper to the front so I can accurately mark out the shape of the resin bow and use it as a template to make a new bow plate.

 

[Tim Marlow]

The flared shape of that part looks like it’s impossible to make the corners from a flat etched sheet, as you’ve discovered Jakko. Not sure you can make it from plastic sheet either?

 

[Jakko]

The real thing is sheet steel, so I think it will be possible:



The main problem is getting the bottom edge right, I think, because when that and the height both are, the angle should follow automatically. The paper method will hopefully work to get that correct …

Meanwhile, I went on to the rear floatation cell. It fits like a charm:



A bad luck charm, that is. In the photo above it’s held in place with Blu-Tack at the correct angle (the top being flat) and that puts it about half a millimetre from the hull rather than against it. Still, this is no real problem, because it butting up against the hull is not correct anyway:



On the real thing its sides overlap the hull, and the top also overhangs it, both of which are impossible with the kit part. So, same solution as at the front:



Plus a few strips of plastic to space the cell from the hull, that you can also see in the picture.

 

[scottie3158]

Jakko nice work so far. Can you take that piece off, anneal it then bend it to fit the profile of the resin.