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

[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]

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]

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]

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

[He Who Shall Not Be Named]

Orient your sprues to feed the cavities from the bottom,

[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

[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,

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

[He Who Shall Not Be Named]

Good, sound tool design. Proceed!

David

[Davidh]

Thank you David,


We are slowly working our way through Spring, temperatures going up. Hitting mid 20's and early 30's, nice weather for mold making. However I still need to keep building the main mold board for the hull. So after cutting out the profile of the hull, with the hull turned upside down and the board sitting right on the waterline just below the lower deck edge. Once the hull was level fore and aft I then made sure that the hull wasn't listing. Once that was done, I drilled a couple of holes along the underside and placed some blocks underneath to hold the hull in just the right place.



The next major step was to create the register point. These register points are made from wood dowels that are sanded down to a point. I then cut these off and then put a coating of resin over the top to seal them. A light sanding followed. These register points will be screwed or glued down to the mold flanges in order to create the bulges that create precise register points for the mold. Fiber glassing around them can be a pain in the neck but they are necessary.



These register points will only be on the vertical flanges that separate the lower hull mold pieces. They wont be needed for to hold the bottom to the top. They will never need to be joined. Below shows the register points just before the resin is applied. I have used screws to hold them to clamps whilst drying.



The stern section will be a separate mold that straddles the width of the rear. This will be a silicon hard shell mold.



The next major step is to produce the vertical splitter board / partition between the two sides. This board needs to line up with the center of the keel to make sure that the two side molds are the same width. Marking it out accurately to then cut it accurately was a bit of a challenge. I used my depth gauge to try and outline the profile that I would need to cut. Had to make sure that the pencil lead is at just the right height. After several runs and lots of cross measuring I think that I finally got it right. I then took the jigsaw and made the cut.



Because the stern mold crosses the width of the hull, I will need to cut the vertical board just in from the stern so it does not run the full length and will not get support after the stern. The cross piece will support the vertical board on both sides. Once this was cut I then needed to mark the point where the cut would be made for the stern board. once this was done I needed to create the stern profile in order to make a nice flush surface for the cross board and its interface with the horizontal board.



This profile matching device is a cracker!



The only other flange is the forward bow board that will separate the middle hull section and create the bow section. This will be a two part mold and feature a hybrid silicon and hard shell mold in one. I have never down this before and so it should be interesting. The torpedo tubes are just below the equator split between top and bottom. The hybrid silicon mold will be covering the torpedo tube bulges and forward "scoops" where the torpedo comes out. This silicon area will be covered by Play-Doh in order to create the cavity that will be later filled.



Screwing down the boards from underneath and behind. When this side is complete then this board will be applied to the other side.

More next week.

David h

[He Who Shall Not Be Named]

The mold-board with parting planes is coming along as planned. Good work so far.

[Davidh]

Thank you David,

Next video installment.

https://www.youtube.com/watch?v=J_Dz0GmsFkE&t=513s

[rwtdiver]

Thank you David,

Next video installment.

https://www.youtube.com/watch?v=J_Dz0GmsFkE&t=513s

David H.!

That YouTube showing your building process was amazing! You and David M. have really mastered the skills required to truly SCRATCH build a submarine! I truly respect what you do!

Thank you for putting up the video of your work! You and David M. are truly masters!!

Rob
"Firemen can stand the heat"

[He Who Shall Not Be Named]

Beautiful video. Looks like you stuck to the plan presented in those great shop sketches.

David

[Davidh]

Hello David and Rob,

Thank you. If it helps inspire someone to give it a go and clarifies processes then so be it.
The molds have turned out really well. There will be more about that in next weeks write up…
Dave.