U540 - Refurbishing a KRICK type VII U-Boat

[steveuk]

Pics show the relocated rudders and stern planes. Fitted and and operational. Since the rudders are so wide apart and run very close to the outside edges of the hull the usual tiller arm positions wouldn't provide enough throw. So I arranged the tiller arms inward where there is plenty of room. Since they are facing each other one has to push whilst the other has to pull in order to move both rudders in the same direction. Hence the cross bar arrangement. This does exactly that operation. You can also just see the stern plane tiller arm and its stainless push rod which I had to locate outside the hull. Hopefully they will not be very noticeable when all painted up. Final pic shows the soldering jig to hold everything in place whilst soldering the prop shaft A frames. I think some heat deflection will be needed before I apply the pencil torch. I wonder if baking foil will be up to that job? I will let you know...

[steveuk]

Silver soldering...It didn't go well. The baking foil didn't stop the intense heat getting through to the wooden jig, which did actually burst into flames and is now a blackened mess. Whats worse the joints didn't look too clever. The flux bubbled, and then burnt, and the metal still wasn't hot enough to melt the silver solder on contact What do you do when the horse throws you off for the third time? ...No, I retreat to lick my wounds and ponder how to get this damn stuff to work for me. To all those out there who can silver solder I salute you. When I went back to survey the burnt offerings I discovered somehow in the midst of the charred remains some of the silver solder had in fact taken. Both hydroplane guards feel quite solidly fixed. So I have cleaned the parts up and what is left will just have to have normal solder.

[crueby]

For silver soldering (aka silver brazing, not to be confused with the soft solder with a tiny bit of silver) you really want steel or brass fixtures. Using small screws to hold the parts also works. There is a product out there which helps a lot for small parts, sold through jewelry tool suppliers. Its just a set of thin titanium strips that can be bent into spring clamps to hold the parts. Titanium can take the heat without losing the springiness. With a melting point in the 1400 F range, depending on the silver content, wood forms are a bad idea in general. With proper flux and a few simple techniques, silver soldering is easy to learn and very strong.

[steveuk]

Thanks for your advice. I will look for these. It all helps. I learned a few things after the event. - 1) There are different grades of silver solder. Some are lower melt temperatures which have only small traces of Silver and often come in rod form. Others have a much higher melt temperatures and contain lots of Silver, these often come in wire form. I took a look at the info which came with my small purchase of Silver solder wire and read the following " Hallmarkable jewellery quality Silver solder" Great, so I had bought the very high temperature stuff ! I know now for next time... 2) My small pencil torch was too focussed and could not get the pieces all up to temperature and it packed up shortly afterwards so I took to my larger blow lamp - wow the blow lamp got the brass parts up to cherry red hot in less than a minute and at that point the Silver solder flowed like mercury around the joints everywhere I had put the Borax flux. 3) Yes indeed, wood is not a suitable base to hold work even with a baking foil shield. Much better is the plumbers heat shield mat, or even better there are heat proof blocks which jewelers use.


Continuing with low melt solder, I managed to get all of my A frame pieces soldered together. Here is the finished piece. It is now fixed into the hull and everything is moving how it should. Just a few pieces to go between skeg and rudder now.

[crueby]

Glad it worked out!

The high temperature silver solder comes in several grades, usually named Easy, Medium, and Hard. The difference is the percentage of silver, which changes the melting temperature slightly. For times when soldering up assemblies, it lets you solder the subassemblies with Hard, then solder the subassemblies together with Easy, without the first parts coming apart, unless you overheat.
With all the high temp silver solders, keys are clean parts, fluxed, put on some bits of solder on the joints, then heat with the torch from the other side, so the hot metal melts the solder rather than the flame. A pointed rod can be useful to spread the molten solder along a long joint. If you try heating from the side where the solder is, it will just ball up and roll off since the metal is not hot enough yet. If one part is smaller, heat the bigger one more so they both get to temperature together, or the solder will flow just onto the hotter one. Takes a little practice, but the result is parts as strong as welded.

[steveuk]

Thank you for all the advice. I will use all this on my next foray into silver soldering. I now feel educated enough to reach successful outcomes easier. It's all a learning process. With friendly advice like this we can move up the ladder of achieving our end goals.

[steveuk]

Skeg / Rudder wishbone.

More soldering. Here's the wishbone soldered together, and now fixed in place on the skeg Also visible are the shaft logs exiting the hull which I made from the original prop shafts. The prop shafts now have plenty of support. This concludes stern running gear work. Back to detailing. Oh. What you cant see in these pics is the new stern tube tunnel which I have now drilled and filed out.

[David F]

Don't give up on silver solder/brazing it is much stronger and easier than soft solder once you can get enough heat in (Good gas blowlamp and parts put on insulation block) You need to get close to dull red temperature. Once the flux melts and goes brown you are ready to dip the solder wire in. (Smaller diameter wire cools the part less.)

[steveuk]

Thanks David. I will keep trying with it. Insulation block sounds like a great idea.

[steveuk]

Update: Stern flood holes done. Also a little work on the prop shaft exits, now with fairings. This is the view underneath now.

[steveuk]

Saddle tanks: These are being slimmed down. First step.. removal !

[steveuk]

Saddle tanks have now been slimmed down, 5mm strips were removed down the entire length of them, taken off the tops where they appear to have a flat, and then glued back on. Now they look radius-ed and slimmer. I am much happier with these slimmed down tanks. I think this might be the last thing about this model which said "Krick". Now she's starting to look proper U-boat. I also worked on the bow but it doesn't show well in the photographs. There is a mock tower placed on the deck just to see how it is measuring up with the rest of the model.

[steveuk]

Drain slot and deck supports done

Summers over and so it's time to get back on the U boat project..

I decided to cut out the long drain slots which run above the saddle tanks. Seeing as it is quite a long span I figured why not just put the proper deck support detail in there to support the upper structure on the saddle tanks. I cut 5mm strips of 20 thou plasticard for the deck supports. Inside the upper hull I extended the saddle tanks inwards by about 5mm using some plasticard off cut strips. Then I cut notches along the new inner edges of the saddle tanks. The junior hacksaw blade cut just the right thickness slot for the 20 thou deck supports to slide into, and then CA glued for speed.

I'm liking the look, so much so that I am going to have to put this into my 1:48th scale scratch build as well now!

[salmon]

Yeah, I like the look too! It gives it a depth of realism.
As a kid, I enjoyed going to 20th Century Fox or Universal Studios. I remember going to the portion where there were boulders made from foam and they let you pick them up and Jail bars made from rubber and you could look like Superman and bend open to escape. Or buildings that looked like stone blocks, but was mere wood framework and incomplete behind. My point is Hollywood made things look real, but it was a false front to the look. We do the same thing to give a level of reality to our models. That is what you have done. It looks realistic.
Peace,
Tom

[steveuk]

Cheers Tom! It wasnt meant to be so involved when I started the refurbish. One thing led to another though. Still I have enjoyed making these extra details. Because the hull is vac formed plastic it is easier to cut and build than GRP. I think I've got to know type VII's pretty well now and I want to see in my models what I see in ref photos. The net has changed things. We have so much ref to pour over now. So our models can be much more realistic than they used to be when we just had a few military books to go by. The only downside is they all take more time to complete now. ..But the end results are worth it I think.