Scratch-built 1/96 Oscar II

[tmsmalley]

Fantastic Kev - I hope

Fantastic Kev - I hope you'll be able to document the making of the molds step by step with pictures.

[KevinMC]

Hi Tim,

While I can certianly

Hi Tim,

While I can certianly field that request, as it stands right now that's the one part of this project I won't be doing myself. Due to difficulties in locally procuring small quantities of the recommended BJB high-temp silicone, David Merriman has kindly offered to cast the propeller molds for me from my masters.

[KevinMC]

More things to show... I

More things to show... I did a "dry run" on the vortex attenuator last night, and I'm all set to go on the real thing. Why a dry run? Unfortunately I only have one photo that shows OSCAR's prop with the vortex attenuator in plain sight, so I wanted to build up a "full sized" model of the final part so I could look at it from different angles while comparing it to the photo to ensure that it looks right.

First, here's the photo that I'm working to]http://www.subcommittee.com/forum/Oscar II prop.JPG[/img]

The blade shape for the vortex attenuator was generated by pulling the above photo into AutoCAD and tracing the outline of the one blade that's conveniently facing the camera at the perfect angle. This was then rescaled to the right size for my hub, and printed off to make 7 little attenuator blade templates. These were glued to card stock, and each was CA'd to one of my aluminum prop hubs. The result, shown below, was compared to the photo above and I think it compares well.



Also shown in the above photo I've begun to putty-in the blade roots of my prop masters. The dome-shaped pieces are the hubs for the vortex attenuator masters. These will be cast separately from the prop, and assembled after casting.

Here's a couple more shots of the vortex attenuator model.





Next comes making the vortex attenuator blade masters. Stay tuned...

[bcliffe]

Kevin,

WooHoo! The snow is melting

Kevin,

WooHoo! The snow is melting the snow is melting!

The Oscar is looking GREAT! I'm hooked .. your coming to the cottage this year ... I want my Seawolf to hunt that beast down.

Actually I am more exicited about getting some underwater photo's and video of her ... wonderful job !!

Let's get her to the cottage get some cool in use shots, and turn this thread into an SCR article.

Cheers
Ben



Edited By bcliffe on 1142527621

[KevinMC]

Now that sounds like an

Now that sounds like an awesome plan Ben. And I'm all for playing a hunting game, but only time will tell who will be the hunter and who will be the huntee.
"Captain Cliffe, sonar reporting sharp metallic transients close aboard. The target may be trying to open his outer tube doors!"

[wayne frey]

Finish it!!!

Finish it!!!

[KevinMC]

Da, Comrade Frey! As quickly

Da, Comrade Frey! As quickly as I can!

[bcliffe]

Now that sounds like an

Now that sounds like an awesome plan Ben. And I'm all for playing a hunting game, but only time will tell who will be the hunter and who will be the huntee.
"Captain Cliffe, sonar reporting sharp metallic transients close aboard. The target may be trying to open his outer tube doors!"

Sounds like I may need to deploy the Trenchant as well just to back the Seawolf up.... game on!

[KevinMC]

Okay, enough banter for now...

I

Okay, enough banter for now...

I used some putty on the roots of the blades to fair them into the hub. This was squeezed into place with a round bamboo BBQ skewer and filed back with a little rat-tail file.



Now back to the vortex attenuator. I did not relish the task of making 14 identical blades, so I came to an alternate solution for this- I have access to a PCB milling machine, which is essentially just a 2D CNC router. Since I had my blade outlines in AutoCAD already, it was a small task to reformat the file into something the PCB machine could use and have it route out my blades. Here is the result- 14 vortex attenuator blades (with 2 spares) all cut from .030" PCB material.



In actual fact, the .030" PCB material was a bit too thick, so I opted to peel away the copper cladding, and reducing my overall blade thickness to just .020". (Note- the blades have still not been trimmed to their final length, this will be done just prior to gluing them in place on the hub.)

[KevinMC]

Now it's time to start

Now it's time to start assembling the attenuator. A jig was fashioned from a chunk of 2x4, some leftove PCB material and paper templates. The jig was used to both mark on the hub where the releifs were to be cut, and to act as a backing for the blade when they get put into place.



The releif for each blade root was cut using a Dremel cutoff wheel on the opposite side of the jig.



Then each blade was cut to the appropriate lenght and Zapped into place.



After gluing the first blade into place, I traced it's outline so that the remaining 6 could be set into the hub to the exact same depth. 5 down, 2 to go!



Here's the result, ready for prime and removed from the jig.



The blade masters and vortex attenuators were then given a good shot of primer in preparation for finishing.



Finally, a coat of gloss black laquer was applied to bring out any remaining imperfections.



Prop masters complete! These are ready for molding, which as reported before will be done by David Merriman. David promised that he'd take in process shots of steps associated with making the molds and casting the parts and painting/weathering the resultant parts.

Now it's back to scribing the hull!

[KevinMC]

Before getting into scribing all

Before getting into scribing all the new detail, another detail photo has come my way which shows that I've misplaced one of the panel lines on the bow. This next sequence of photos will show the steps I used to fill in the unwanted panel line, and hopefully tomorrow I'll have a sequence to show scribing the new one.

The mis-placed panel line is the left-most radial line in this shot. From photographs I've determined that my line sits about 3/8" too far back on the hull. (It should line up with the forward-most hinge on the upper section of the torpedo loading hatch.)



Step one is to boarder the errant line with masking tape. (Before applying to the hull I layed this stuff down on my workbench and cut a clean edge on the tape.)



Next, I squeezed Icing into the panel line using the rounded end of a popsicle stick. Notice that although there is a buildup of Icing on the tape, I've "cut though" it right down to the tape on either side of the panel line. This will ensure that there's a minimal amount of cleanup work to be done once the tape is removed.



And here's the hull with the tape pulled, leaving only enough Icing to fill the line and nothing to clean up around it. Because the repaired part of the panel area protrudes above the rest of the surface by only the thickness of one layer of masking tape, I can go directly to sanding with 600-grit wet paper.



And here's the bow again, this time after the 600 grit paper treatment.



I finally also got 'round to peeling all the other panel tape from the hull. (And the 300-some easy case drain masks!) Here's the result...



So close!

[KevinMC]

Okay guys, I've finally got

Okay guys, I've finally got somehting to show for re-scribing the incorrect panel line.

I made a jig that is comprised of a flat surface that wraps around the hull, backed up by a couple of right angles to keep it square to the building surface. Anyone who's read all the instructions for a D&E WTC will instantly recognise this- that's where I got the idea from. I next made a scribing tool holder from a chunk of 2x4. Both are shown below.



Before actually going at the hull with the scribing tool, I loaded up the tool holder with a pencil to draw out exactly where I'd be scribing.



Then I loaded up the jig with my scribe and went to town re-cutting the new panel line. Unfortunately I missed getting an in-process shot here, but here is the result.



While working with the scribing tool, I also marked the parting line on the sides of the hull. Unfortunately my tool holder was a bit too short for this, so I raised it up with another block cut from 2x4. I used hot-glue to hold these two pieces together so I could still get them apart when I was done.



BTW- what's not shown well with these "crude" 2x4 chunks is the precision height adjustment device- On the bottom of each block is a tripod of wood screws. By adjusting the depth of each screw in the block I can precisely set the height of the tool (be it pencil or scribe) above the height of the reference surface. For a 4 cent tool, this one worked really well.

[KevinMC]

I've also completed the bulk

I've also completed the bulk of the detail scribing on the hull. Detail "bits" were cut into brass templates (by drill and file) and then scribed into the hull.

[KevinMC]

It's molding time!

On Friday I

It's molding time!

On Friday I slipped out to the (sorta) local sculpture supply store to pick up the RTV I needed to make my molds from. Although I'd originally planned on making hard sided molds, I came to the conclusion that all my hull detailing would lock the master in to the mold in such a way that I'd never get my master out intact. Consequently I made an 11'th hour decision to go the 2-part, RTV with hardback mold route.

I built a box to support both the hull and parting board to the appropriate heights. The sides of the box were made from 1x4's from the hardware store, and the parting board (and triangular parting board support gussets) were made from 1/8" melamine finished paper board. Total box cost- less than $15.



The shape of the hull was traced down onto the parting board by raising the hull by the height of my square above the surface of the parting board. The outline was then traced and a hole in the middle of the parting board was cut out using a jig saw. The hull was then carefully placed into the box, the extra space around filled with foam packing chips to support it. The hull was adjusted such that the scribed reference line sits roughly 1/4" above the height of the parting board. With the hull and parting board at the correct level, non-sulfur based clay was worked into the gap between the hull and the parting board.



Now for the detail coat of RTV. I used a Smooth-on product for this, SmoothSil 920. Despite being a platinum catalyzed RTV, it's mixed up in a 1:1 ratio by volume and brushed on to the master. No tales here of chasing RTV around the molding board for an hour or two- despite flowing on easily this stuff stopped running in less than 30 minutes and had completely kicked in about 3 hours. Special thanks to Craig G for putting me onto this fantastic RTV system, and for his assistance in showing me the ropes of laying it down.



Although the sail will see the same RTV process, it's molding board is a little bit different from that used on the hull. It was placed on a 1/2" bed of clay on top of a solid piece of melamine paperboard. This will allow me to run a little scribe line around the base of the sail (in the clay) to denote in the mold where the sail stops. Once worked down onto the board, the sail then received the same RTV treatment as the hull.



After about 3 hours cure time, the SmoothSil 920 was ready to be built up. Great for picking up all the details, this layer will have to be backed up by something a little bit more substantial. The answer to this is Smooth-on Rebound 25, a thixotropic RTV that's specifically designed to be brushed on to vertical surfaces such as those found on the sides of a hull master. I've brushed on the first coat mixed straight from the pails, although I plan to add some additional thixotropic additive to the next two layers. Again, notice that the RTV has not oozed away much from the bottom of the hull, despite not being dammed up with clay.



I should be able to get the remaining coats of Rebound on tonight, then I'll be ready to start making the strong-back.

[anonymous]

Man Kevin I hope you

Man Kevin I hope you did a test patch first. That platinum RTV can react to your sweat dripping into it as my 17 molds did when I did them during summer. Anything with the slightest amount of sulfur will cause it not to cure. Even auto body spot putty will react.

I used the GI 1000. I did a test directly on the spot putty and even some sulfur based clay and it set fine. As long as your services are sealed well you should be ok. Or maybe this brand will fare better since I used the BJB RTV on the 17. But on the blueback I had zero problems with the GI 1000. It's bullet proof.

steve