Scratch Build project SM U-23 Class World war one U-boote. Zero Bubble model design.

[He Who Shall Not Be Named]

Good, sound tool design. Proceed!

David

[Davidh]

Hello all,

Being in Lock down here in the New South Wales has mean't that all my classes have been on zoom for about 9 weeks. This means that I don't have to commute for 50 mins either way each day and thus saving me lots of time that I have been able to convert into workshop time. That all changes next week as schools across NSW resume face to face. The rapid pace of things will slow however I am coming up to the construction of the hull molds. I find this the most tedious and tiring part of the whole tooling exercise and I will generally be glad when its over.

However, before I cut any particle board and start setting up the molding / splitter board I need to think this one through. This will be the most complex mold sequence I have ever done. I have never done a traditional boat hull type submarine and so as a result the molds are going to have areas of undercut and draft angle not seen on a modern nuclear type. This will mainly be at the back and front parts of the boat. The Torpedo tube arrangements at both ends have made me really think about how this is all going to work. I can think it all out in my head but need to put it down on paper in order to not miss anything and also to trigger anything else I haven't thought of that may become necessary or give me an avenue that I hadn't thought of that may prove better than what I was working on at the time.



The mold that I have designed will be a 6 part mold. It will feature 5 parts for the lower hull section which is the biggest part of the operation. The top mold being just the top deck and is a one piece silicon hard shell glove mold arrangement. This above drawing just shows the lower hull and comprises two main hull sections that cover the main hull length and then two bow half sections and a stern single piece. In these drawings it was shown as a split piece making up 6th bottom piece however I saw no reason why I couldn't make it a single small silicon mold with a hard shell. The smallest one I have ever made.

I make my boards out of particle board with a laminate sheet that doesn't stick to glass so when these parts come off the board they should have a really nice finish. I have gone with wide flanges around all the molds and also will incorporate register points along the flanges where any other mold part joins. There is no need to join the lower hull to the top so no register points needed here. The register points are simply a dowel, sanded round and then drilled through at the back. Sealed with resin and applies to the flat surface around the flange. These things are a pain to glass around.



I had to work out the procedure for how I would go about glassing up the sections. There needed to be a definite order. This all came down to which partitions/ splitter needed to be kept in place and which flanges could take their place. Every flange needs to but up against another flange so I needed to make sure I could find a sequence that would need the least amount of re-arrangement of partitions to get all the flanges built. So to do this I worked out that I mold one main half first, then the bow section in front of that (2). Then the other middle hull section. (3) Then the one piece stern silicon hard shell mold (4) and finally the other front bow last (5)



This drawing shows the top hull piece. This is a one piece Silicon mold with a hard shell glove. Unlike my previous models I have usually done this section first, on this model it will be last. After being happy with all this I just needed to then start getting all the sections of sheet board together and start marking and cutting out. This is all the parts that will go into making the molds or become part of the molds themselves minus the silicon and the glass. These include the "egg -crate" box frame that will go over both main hull halves to keep them rigid. The long square strip is the dam wall for silicon on the top mold and then little cubes mold the register points for the silicon top mold to register with the hard shell.



The final hull.



The sides of the box I saved from constructing the Delta IV two years ago. The box frame for that boat is about the same size so I could re-use.


Mark out the position of the hull making sure either side there is plenty of room for the flanges. Then drill holes and get out my Jigsaw. (Some thing that only happens once a year or so).



This is the first time I have molded the underside first. I then secured small cross braces underneath to hold the boat in just the right position. Sealing with Play-doh next week.




David H

[Davidh]

Hello all,

I finally got some pigment for the polyurethane molds for all the parts. I went with standard grey. I think that the railing parts have turned out really well and a second and third conning tower. I just need to drill the holes and start the fine detail. Even though I haven't started the molds for the hull I have enough finished parts out of the mold to start making the actual finished boat. The Bubble catcher and the curves air vent surfaces have been very effective. There are no trapped bubbles anywhere and the conning tower turns out nicely. I am super happy with the texture and feel of the fabric covers over the railing.





The original master in Blue and two cast copies out of the mold. The middle one is just the orange one sprayed and then sanded somewhat..




I will soon be turning attention to the hull and getting it ready for the long drawn out and somewhat monotonous task of creating all the hull molds. This one is going to be involved and much more intricate then all my previous molds. Before doing this I needed to do one more appendage mold so once again I have gone through the same process of setting up my usual box construction technique and then laying down the vents and sprues, Drilling the registration points and pouring the two halves of silicon in the molds. These appendage parts include the stern hydroplane guards, the anchor, the conning tower pieces, the lower rudder support, the rudder push rod exits and hub, and finally the torpedo tube doors.



I also started the molds for the twin screws. U-boats featured three bladed screws. Creating the molds for these is easier than producing molds for the rest as I use a round section of PVC pipe for this. The set up is rather quick. I take the PVC pipe that I always use and find the base that I used for the last set of props that I made which I believe were for the Delta from 2 years ago. Has it been that long. I then place the screw facing upwards on the base. I use play-Doh around the undersides of the curved surfaces to create the parting plane. Great thing is that these screws are so small I can use one mold to do both.




The first pour is made and what you can see below is the underside of what you see above. Clear away all the play-Doh and then you can start on the bottom end of the screws. However, I will need to glue pouring sprues and also some air vents although they will mainly be cut along the plane radially outwards.




Insert the 3 mm bolt to create the thread needed to make the casting a simple screw on affair. Balsa pouring sprue right next to it.



Place the bottom half back in to the PVC pipe and pour the second half. I really need to get some pics of the finished props. More next week. Getting closer to molding the hull.

David H

[Davidh]

Hello all,

David, thanks for the advice, however as at the time of writing I have completed all the molds so any further write up will show molds created before your advice.
I spent some time working out the box arrangement for how i would do the molds for the conning tower. As you can see I spent some time drawing up how this would work mainly to work out in advance any possible problems that could occur. I didn't want to mix up a whole heap of silicon and then realize that there would be a major problem with some aspect of the set up and waste a lot of good silicon.

I created the main box for the mold just out of particle board and some plywood, making sure that there was enough room around all the sides of the box for a decent thickness of silicon. Once I created the box I then worked out the air vent and bubble ring arrangement for the part. I have used a "Bubble ring" on several molds where there runs the risk of getting trapped air along a wide long surface. I used this technique on the propulsor ring of the Borei kit that I produced. The ring is simply just an extension of the edge of a surface and is sacrificial. Any air bubbles will hope full rise up in to the Bubble ring area and will be cut of as flashing after the casting process leaving the proper part beneath it Bubble free.



The "Bubble ring" area is actually the section that connects all the "arches". The curved air vents are curves so that air bubble transit vertically past the bubble ring area and then if the "hit" the lower point of the
inverted arch they then ride up either side of the curve of the air vent and then hopefully up to the surface. this means that that there will be a fair amount of flash, however better than getting air bubbles in the base of the conning tower. The Bubble ring and arches for the air vents are made of cardboard. At either end will be balsa sprues that can be used to pour.



The below pic shows how the piece needs to be suspended. There needs to be a good distance between the base and the top of the conning tower which is upside down. To make sure that the silicon does not pour up into the center of the part a small piece of clear plastic is glued about 2 mm up inside the inside of the part and sealed around the inside edge with some Play-doh. This makes sure that the silicon only goes up a little inside the inner surface of the part. This will help with registry. The mold simply comprises an outside mold and then an inside mold.



The Sprues at either end have a bar placed across that will suspend the part inside the mold. Once the first outside mold is poured and set then the horizontal bars will be discarded.




The first mold is poured with the silicon coming up to a point just below the lower edge of the tower. This is so that no silicon from the first pour gets inside but also acts as a register point for the top and bottom mold and helps to make sure that the two mold parts don't mis-align.




Once the first and outer mold part has been poured then I divot gauges into the top surface to act as register points for the next inside mold about to be poured. I rub the surface with lanolin to act as a release agent and then pour the second half of the mold. It's really important that the air vents come up above the silicon surface.




The mold looks rough, however the important surface is inside the larger outer mold. The front mold is the inside mold and the surface is the inner surface of the molded part.






The batch of Urethane that I bought recently is translucent. I managed to find some pigment and so poured the first part. This is supposed to be a gold flake but looks more like a bright Orange. The part has turned out quite well and I am happy with how the parts have turned out. This photo shows the part still with the inner part. The Sprue funnel gets twisted and pulled off first so that you can release the rest of the cast.








The air vents simply need to be cut off and trimmed to the bottom edge of the part.

David H

[He Who Shall Not Be Named]

Orient your sprues to feed the cavities from the bottom,

[Davidh]

Hello all,

After completion of the railing molds and first parts, I decided to start work on the molds for the stern parts. This includes the Rudder, The stern gland, the shaft brackets and also the conning tower main deck. These parts have been fitted numerous times and adjusted against the hull so they are the right size and dimension. Once again I go through my usual mold box technique where i cut out the profile of the parts on a board and then work out the vent and sprue arrangement that will deliver the best flow of urethane with the best way to push the displaced air outside.



Pouring sprues and vent lines marked out. Yet to drill the registration holes. These parts with the exception of the deck will have brass inserts included.




The completed surface of the mold. The vertical positioning of the shaft brass inserts is critical. They need to be as close to vertical as possible so that when I close up the molds the brass inserts will be able to slide in their corresponding holes. Now I just need to press Play-Doh into the gaps and glue down the air vents.






First half of the mold done.



After this I spent a fair bit of time looking at how to do the molds for the conning tower. I have decided to create a one piece Polyurethane casting. I have not done this before, I had for the delta IV I created a one piece silicon mold for the sail but without an insert so that I just created a one piece fiberglass part out of it. This has worked well but being able to produce a one part casting out of urethane will be less labour intensive and simply easier. I have felt that I have now developed the skills to a point where i am capable of pulling this off.

I asked HWSNBN some advice after looking at his write ups on how he developed two part molds for the sail of the Barbel class. I realized that for me this would need to planned well and i would need the think about the steps taken and how the part would sit in the mold. I created a couple of drawings to show how I intend on doing this asked for advice and guidance with the arrangement.






More next week.

David H

[rwtdiver]

Hi Rob,

Really appreciate the comments. I sometimes wonder if people are paying attention however during the week I see the number of views slowly go up. I post every Friday night ( AEST) and usually after a couple of hours I get bumped off the top spot, invariably by a Skipjack thread. I wish I was on the same building level as David M. It’s been an interesting ride and this boat has been a real challenge.

I do think it will be a great boat when it is finished. I am currently compiling the next video on the build which will deal with all the tooling. This should be coming out on a couple of months.

Thanks, once again,

David h

You are welcome David!

I for one am really enjoying, and most of all learning from your build! Keep it coming!!

Rob
"Firemen can stand the heat"

[Davidh]

Hi Rob,

Really appreciate the comments. I sometimes wonder if people are paying attention however during the week I see the number of views slowly go up. I post every Friday night ( AEST) and usually after a couple of hours I get bumped off the top spot, invariably by a Skipjack thread. I wish I was on the same building level as David M. It’s been an interesting ride and this boat has been a real challenge.

I do think it will be a great boat when it is finished. I am currently compiling the next video on the build which will deal with all the tooling. This should be coming out on a couple of months.

Thanks, once again,

David h

[rwtdiver]

David,

Watching you build your sub using the old tried and true methods is so fascinating to watch! If I had a nice shop, with the tooling to do the type work that you and David M. do, and if I where a lot younger, I would learn how to build subs the way you do! I really admire the old ways and the skill level you have learned and achieved!

Again David, I want to thank you for taking the time to take the great photos and writing up the instructions as to what you are doing!

Rob
"Firemen can stand the heat"

[Davidh]

Thanks Rob,

I haven't seen the Kookaburra for a while. For the moment it has been magpies swooping everyone because its nesting season. I had a dogfight last week with one over the slope at my local beach, I should have been flying my faster glider.

Anyway back to U-23.

So the first mold has been done and with the creation of some extra air vents cut into the silicon, a re-pour of the resin has produced parts with air bubbles of gaps. Really happy with how they have turned out. The Hydroplane guards look really thin however the resin has stiffened and they are rigid enough. The next mold that I decided to tackle is one that I am most unsure about. The Upper conning tower frame of these early U-boats featured a Steel frame railing. This railing was either open as was the case with submerging and for surface running there was a canvas fabric covering that was attached to the railing for protection of the crews on the surface in bad weather. Previously I wanted to re create the sagged fabric look of the canvas. I did this with styrene heated and fitted over a brass frame. Now I was to create the moulds to recreate the texture and the sagged effect of the fabric as it is wrapped around the frame. The below photo of U9 clearly shows the canvas wrapped over the steel frame.



I had spent a bit of time looking at how I would create the molds for this. My main concerns were the irregular shape of the parts and the really thin wall of the fabric/ styrene. I was concerned that the wall thickness being so thin that the silicon mold sides may press down and touch as the gap between then two surfaces is down to about 1 mm. I then had to work out how I would position the frame on the usual wooden base board that I use to create my box molds.



Previously almost all of my parts are relatively flat and don't curve and deviate from a central plane. The curve of the railing frame pieces throws this out. I decided to create sections at either end where the curve dips down below the usual plane that I work with. As a result I then carved down sections on either side to accommodate the wrap around. The raised bulge in the centre will be covered by large amounts of Play doh.



So I use the milling machine to create the two rectangular sections at either end. I have put a tilt on the piece so that the air bubbles will rise up the upper rim of the part and out through an air vent.



Register points have been drilled down and the outline in pink shows the limit of the Play Doh that will rise to meet the underside of the frame part. Air vents are also shown. The air vents will be the usual paper clip wires that will run down from the top and up the sides of the Play Doh.



I have made sure that the pouring Sprue meets the front top of the frame and that it will start at a lower point on the plane. The Play Doh angles down at the front of the frame. The first part mold process often plays havoc with the paper clip air vents. I often try to keep them in place but often they come out and I press some lanolin to the groove to act as a release agent and not allow silicon to not fill the void. I now strip the base down and place the masters inside the mold and repeat the process. I don't need to use the Play- Doh anymore. So far so good.




Rub the silicon mold with Lanolin and make sure that the parts are well pressed down inside the first half.



The completed two part mold. Happy with how its turned out. The big test will be whether the small distance between the two fabric surfaces and a small amount of pressure could make the two halves touch at the middle between the squares of the frame making the fabric appear to have holes in it. I recently bought a batch of urethane resin and it turned out to be colour less and almost transparent. I then found some metallic pigment and added some to the mix. Wasn't enough to give it full colour and i think the parts will come out skin coloured. Oh well...



I like the wrinkled texture of the front top canvas panel on the starboard side. I f it wasn't Fabric that I was simulating, I would be annoyed. I Think these parts have turned out really well. I have since done some more with grey resin and they look great.



Cut out the small little blobs and some slight flashing other wise, parts I am happy with.

David H

[rwtdiver]

David,

I am really enjoying your sub build! But I also enjoy seeing your animal friends! (Bluey & the Kockaburra) Keep the photos coming! The Kockaburra sure has his eyes on you!

Rob
"Firemen can stand the heat"

[Davidh]

Hello Jorg and all,

I haven'y named him yet as I haven't seen him in a while unlike the Kookaburra that parks his but on our back Verandah. He often laughs with his mates over something that's not funny...



Anyway, getting back to the U-23.

So the hull is mostly done, I have just been doing the odd little bit of filler and sanding here and there and some coats of primer just to show up the odd little imperfection that needs my attention. I laid down some styrene strip that emulated a rim that runs along the gunwhale of the hull. I will have to be careful when I mount the hull on the splitter board that I don't chip the styrene off. I also had to replace some last minute access plates on the hull to make sure that I go the full number according to the drawings. Lots of fine imperfections to chase up.



In the meantime It is time to start with the parts / appendage molds. I have the biggest number of appendage parts of any kit I have produced. I will need to create approx 4-5 molds. Plus the molds for the screws and a large one for the conning tower. That should be fun. I have asked HWSNBN for his opinion on how to mold this up as I wanted to do a polyurethane mold unlike my previous ones that have been glass lay ups. I decided to start first with the hydroplanes. The forward and stern hydroplanes look similar but have slightly differently geometries.



in my usual style I like to create a rectangular box. I could do what David does and wraps them in a round container made of tape with a huge central sprue and carve out the vents later. I guess whilst I am interested in doing new things and trying new techniques I often in some procedures like to stick to what I know works. Even though this box is a lot more work. I like it... Here you see the forward guard and both forward and stern planes. The outlines for the vents and also the sprue funnel. Next step play doh...



Recycled side pieces of MDF and plywood screwed onto the base. Vents of paper clip and sprues of Balsa strip and Play Doh.. Pour in the silicon. I have chosen Red as my colour for this job. Once cured you then pull the silicon off the base, remove the parts and rub some lanolin in as a release agent and then pay up the parts and sprue and Ply-Doh again and repeat the process for the second half.




I am quite happy with how this half has turned out. I will re groove the air vents and widen the sprues as needed.



Second half of the mold has been made and the first pour of urethane and pressure pot treatment. First parts out of the mold. I will have to cut some more air vents off the top of the third plane and the side of the second plane as their was air trapped or maybe it thickened a bit too quickly in this spot.




I cut a few more air vents and then the problem disappeared. These planes have since come out looking complete and without air bubbles. I will take on the challenge next, of making the molds for the steel railing and canvas cover. That is going to be fun...


David H

[JHapprich]

Nice pet! What's it's name? Doe's it like subs,too?

[Davidh]

Hi Jorg,

I could have but I really like using Renshape. I had company in the workshop today, a big fat Bluey. ( Bluetongue lizard.) This one was big, about 300mm long.

[JHapprich]

Wow, thats really small! You could have used brass instead.

New 3D-Printer?