Need a Technique for Hull Surgery

If I'm envisioning this correctly, you will have a wider beam overall, but will still need to converge each half of the hull at the bow stem and the stern as well, although you may have a squared-off (transom) stern that carries the additional beam as well.  Assuming your hull is one-piece, if I were to attempt this I would probably resort to my band saw with a fine blade and a cutting speed slow enough to avoid melting the plastic.  I would first make a jig that allows me to use the saw's cutting guide.  I think I would take a block of wood slight longer than the hull, and temporarily affix the hull to it making sure that the longitudinal centerline of the hull is parallel to the sides of the block.  You can probably do the same with a small table saw or scroll saw.  If you don't have a band or scroll saw, I would probably try a hot knife or a small Dremel cutting bit and eyeball it.  It will be a bit rough at first but once you get the hull halves spaced the way you want them, sheet styrene and filler could patch that up.

What do you plan to do at the bow, though?  

One way to do it is to tape a metal ruler where you want it cut and scribe the line with the tip of your exacto knife.I use a similar techinique to cut doors out of car models when I want them to open. Works pretty well but it does take some time.The doors were molded closed on this '59 Impala so I used the above method to cut out the doors and hinged them  to open. 

Use some Dymo tape as a guide fence for your cut down the centerline. I would suggest using a micro razor saw to make the cut.

I drew a line and "freehand" cut this fuselage but I usually use the Dymo tape method. 

 

 

Just out of curiosity, what hull, and why? I have to widen the beam of a 1/700 carrier, to match the changes made over the years from the time she was built, to the time I want to model. Becuse of the shape of the hull, I will have to add "thickness", and not just widen the hull. The point of "what about the bow" is a valid one. If there is a prominent stem, it would be possible to laminate the add on piece, so that the stem could remain the proper width, removing the original cast stem. Using an exacto blade to scribe the parting line, with a strait edge as a guide, is probably the most accurate, as the "cut" will be the thinnest possible, and the hull halves can then be sanded to true up the edges.

What I'm attempting to do is to convert the Revell kit of the Red October submarine to the one described in Clancy's book.  According to the book, the Red October had a slightly wider beam (1 meter ?) and was significantly longer than the standard Typhoon class Soviet submarine.

What I figure I need to do is: make one cut from stem to stern to add the necessary increase in the beam from my stash of plastic stock.  Then, I need to make a cut from port to starboard to add the plug for the additional missile tubes. (I'll need two kits.)

I'm not concerned about the bow; I figured I'd just sand/fill as needed to make the bow smooth and match things up as best I could in the stern.

I needed a way to make a straight cut from bow to stern since I know I don't have a steady enough hand to do the cut freehand.

Thanks for the advice.

OK information is helpful, and since you're now in more of my realm, aircraft, I'll hazard some opinions.

First of all ignore the beaminess issue. Who would know? And you're creating more work for yourself than is reasonable, considering all those torpedo tubes, hull plates etc. And threaten the integrity of the end shapes.

Just add length. I'll try my best to describe what to do. Plan to sacrifce one side by side pair of tubes. Starting at the bow, tape where you want your vertical seam to be which I would guess would be midway fore and aft of a pair of doors, with the tape on the bow part, and spray some white on the part towards the conn. Which means you'll be cutting into the next pair of tubes. Likewise fore of the conn, tape where you want the cut to be (on the second kit) and spray forward towards the bow. Likewise into a pair of tubes.

Cut each with a bit of white, like 1/16", showing. Take either scrap and again mask and paint a cross section with the extra pair of doors, plus. Then sand each piece (3 each top and bottom) until the white goes away.

Glue the sections of each half together first, with little tabs of plastic to make them strong. Get one half nice and straight, then glue the other half's three pieces together taped to the finished half, and finally glue the halves together. If you do this right, minimal to no filler will be needed.

I think the movie, which was modelled by Kim Smith, has a bunch of important details of the "induction drive" that the Revell model doesn't have because it's a rerelease of a Typhoon. I'm planning to buy it this weekend, you've piqued my interest.

That would be good stuff to build. Not to just copy Smith, but he's really creative.

 

Okkkkkkkkkkkkkkkkkkk then! "Accuracy" issues aside ... I don't know what scale the kit in question is, but for that kind of major surgery, I would have to question whether anyone but you will ever even notice. In 1/700, 1 meter is 0.056-inches, in other words, not very much! Even at 1/350 it's only 0.11-inches. I'm all for accuracy, but some things fall into the Just not worth it category. I think this is one of those.