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

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  • Davidh
    replied
    Hello all,

    Thanks Scot,

    So once the template was glued in place I cut two brass shafts. One that sits, touching the center of the shaft output from the cylinder template and going to an estimated point where I envisage the shaft output location to be. I then cut another short length of brass long enough to go from where I am anticipating the shaft output to be to where I am expecting the shaft to terminate with a propeller on the end. The challenge being to make sure that the two individual shafts meeting end on end are as straight as possible.

    I measured the distance that the shaft needs to be from the hull plus a little bit more to allow for blade clearance. I am also thinking about how to make the shaft to be as level as possible. The drawings show the shafts to extend out of the hull almost horizontal. I don't know if I can quite get this as it would mean that the shaft would be quite high. The next major step was making a mock up of the shaft bracket. This would hold the shaft in place and give me the precise positioning of the end of the propeller and I could them work out clearance.

    I cut out some small lengths of 3mm brass tube to act as the shaft bracket. I then cut some 1 mm thick styrene sheet to act as the bracket and super glued them on at an angle similar to the drawing section of the U-23 at the stern. As can be seen the lower bracket is almost horizontal and the vertical is nearly, vertical.

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    Mock up bracket. The styrene can be cut off shorter if needed.


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    I slid the bracket onto the shaft and after looking at the drawings I worked out where the bracket should be positioned. This would give me an idea of clearance. In order to hold the bracket in place I have cut out some small strips of tape and stuck down the two bracket arms in various spot to check for clearance and positioning of the shaft output.

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    Here you can see the anticipated exit point of the shaft. I marked the position and repeated the exercise on the other side with another opposite bracket and market the location making sure that they were exactly reciprocal. I checked the position inside and found it was almost exactly where I expected it to be. I then dremelled a hole at an angle into the hull through the resin and balsa layers.


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    Below you can see the tape holding the shaft in the right exit position.

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    I cheated here. I've used a spare prop from the Papa class SSGN to get a feel for the size of the prop. Similar clearance, just three blades. I have also put on a basic mock up of the rudder. I may print off one and use that as the template, or I may just do one out of Renshape. You can see that I have cut the exit shaft position.

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    The last pic, below shows the shaft running through from the center point of the shaft output to the exit point and then onto the stern shaft bracket and ending with a propeller, hopefully. After this I will then push some filler into the hole and use a brass shaft rotated inside the hole to create a curves recess section signifying in the mold the position of the output.


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    David H

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  • Scott T
    replied
    Make you a marking jig from a pair of calipers or something similar.
    Add a tube and drill to mark the location from the motor shafts to the point of the propeller.

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    Leave a comment:


  • Davidh
    replied
    Hello all,

    I have been putting off this next stage for a couple of weeks now as I have just been thinking of how to attack it from various angles and methods to think through and work out which angle might be best. I am determined that the location for the shaft outputs needs to be marked on the mold. Not just for me but to make it easier for any customer to not guess where these outputs lie. I needed to come up with a precise point as to where the shafts exit the hull at a tangent to the general curve of the hull at that point. The shaft needs to intercept a propeller shaft bracket just in front of the screw but also needs to align up with the twin shaft outputs of the ZB-2 and or ZB-1/2. It would be great if the rear section of hull was transparent and completely see through. That would make things so much easier.

    I decided to make a template or jig based on the positioning of the output shafts of the twin ZB's. This involved cutting two small pieces of 6mm stainless shaft. Then I marked a round disc to represent the end cap diameter. I cut that out and marked out the precise placing of the two shafts and glued them on.


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    Here I have placed the MDF sheet disc that simulates the end cap of the ZB. I have needed to go in with a file and the Dremel to clear excess expanded polyurethane foam that was sprayed down earlier in order to allow me to sand beyond the limits of the Balsa sheet. Where the disc is, is the furthest point rearward that the ZB can fit.

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    Template showing precise distance between the ZB shafts. The cut out sections along the bottom allow the discs to fit down snugly into the space where it will reside. The cutouts are to accommodate the balsa stringers that run alongside the bulkheads. Below, glued down with superglue.

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    Once this template was complete the I could insert it into the back of the bulkhead that it buts up against and then need to clear the area and guess where the shafts will output. I needed to align the template to make sure that it was dead level and in the center of the hull. I also needed to ensure that the top of the end cap doesn't exceed the top of the hull. this could occur in the bottom inner corners where the vertical section between the lower and upper hull sections meet. The end cap clears by about 3mm.


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    More next week.

    David H

    Leave a comment:


  • Davidh
    replied
    Hi Jorg,

    Its coming up now. I do have a Sjormen class , (Sjohasten) but the mould you see in the background is the lower hull half mold for the Gotland class. They are great little boats.

    Dave.

    Leave a comment:


  • JHapprich
    replied
    Hello, David! I am seeing your recent post beeing doubled, that might be the problem. Can see all the pictures in post no.1. Well done! What is the square recess just forward of the tubedoors good for? Ps whats that black hull mould in the background? Sjörmen?
    Jörg

    Leave a comment:


  • Davidh
    replied
    Hello,

    I have just posted up my latest build update. It is coming up green with ‘unapproved’ and I guess not showing for everyone else. Could this be fixed please?

    David H

    Leave a comment:


  • Davidh
    replied
    Hello all,

    At this point both tubes are in. They have both had a layer of filler applied around the edges of the Renshape tube forward of the tube doors. Once sanded back and another layer added, more sanding. Then a paint brush with some resin around the scoop area. I will need to carefully add some more filler around the gar between the doors and then scoop. ( This is the space for the doors to open inwards). I will have to get into the square corners and smoothly sand back..

    [ATTACH=CONFIG]n148723[/ATTACH]

    The hull has also had a light sanding back to get out some of the high points and undulations caused by the thicker coat of resin and weave. It is pretty smooth. Once the bumps have been taken out with something thicker I will move through 600, 800, 1000 grit. The formers have received all sorts of spray coats, splatter of resin and splashes of water and as a result look a bit aged.


    [ATTACH=CONFIG]n148724[/ATTACH]

    Primer grey on the other side and repeat the process.

    [ATTACH=CONFIG]n148725[/ATTACH]

    Looking from the front back towards the door show small areas where the filler hasn't quite covered over the gaps. Once tube door is slightly forward of the other, so I will need to address that. I also need to define further and make sharp the bow line. I will still need to add more filler along the edge of the scoop line to get the transition between scoop and hull sides just smooth and consistent.

    For some time I have been working on interpreting the the middle deck section hull detail. Having never built a U-boat before and certain not one that is over 100 years old meant that I was unfamiliar with the layout and parts that would be found on the center deck. Certainly will not find any red and white hatches like I have always worked with on my soviet boats. My inspiration for working out the deck arrangement has come from the main drawings that I have and the images of the U-9 kit that I have had to rely on when the 2-dimensional-ness of the drawings doesn't quite give me enough. The U-9 model has been good for getting the low down on raised items on the main deck. I am going on the theory that from Class to Class there are only incremental changes and wouldn't be a huge change between the U-9 class and U-23 deck arrangements.

    So I have aligned up the middle section of deck that is made of a 4 mm sheet of Renshape and started marking out the placement of hatches and access panels. Once marked out in pencil I could then start on scribing. I have taken a small fine file and have ground it down to a tiny round point. Renshape is fantastic for scribing into. Scribing on a flat surface is definitely easier than trying to with the Renshape strip already attached to the hull.


    [ATTACH=CONFIG]n148726[/ATTACH]

    I have used an array of circle and square templates to attain some consistency. On this boat many of the features seen up front are also duplicated towards the stern.

    [ATTACH=CONFIG]n148727[/ATTACH]

    I now have to work through which parts have raised components and which don't. Any more pics that people have of the front deck space would be greatly appreciated.

    [ATTACH=CONFIG]n148728[/ATTACH]



    David H

    Leave a comment:


  • Davidh
    replied
    Hello all,

    At this point both tubes are in. They have both had a layer of filler applied around the edges of the Renshape tube forward of the tube doors. Once sanded back and another layer added, more sanding. Then a paint brush with some resin around the scoop area. I will need to carefully add some more filler around the gar between the doors and then scoop. ( This is the space for the doors to open inwards). I will have to get into the square corners and smoothly sand back..

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    The hull has also had a light sanding back to get out some of the high points and undulations caused by the thicker coat of resin and weave. It is pretty smooth. Once the bumps have been taken out with something thicker I will move through 600, 800, 1000 grit. The formers have received all sorts of spray coats, splatter of resin and splashes of water and as a result look a bit aged.


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    Primer grey on the other side and repeat the process.

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    Looking from the front back towards the door show small areas where the filler hasn't quite covered over the gaps. Once tube door is slightly forward of the other, so I will need to address that. I also need to define further and make sharp the bow line. I will still need to add more filler along the edge of the scoop line to get the transition between scoop and hull sides just smooth and consistent.

    For some time I have been working on interpreting the the middle deck section hull detail. Having never built a U-boat before and certain not one that is over 100 years old meant that I was unfamiliar with the layout and parts that would be found on the center deck. Certainly will not find any red and white hatches like I have always worked with on my soviet boats. My inspiration for working out the deck arrangement has come from the main drawings that I have and the images of the U-9 kit that I have had to rely on when the 2-dimensional-ness of the drawings doesn't quite give me enough. The U-9 model has been good for getting the low down on raised items on the main deck. I am going on the theory that from Class to Class there are only incremental changes and wouldn't be a huge change between the U-9 class and U-23 deck arrangements.

    So I have aligned up the middle section of deck that is made of a 4 mm sheet of Renshape and started marking out the placement of hatches and access panels. Once marked out in pencil I could then start on scribing. I have taken a small fine file and have ground it down to a tiny round point. Renshape is fantastic for scribing into. Scribing on a flat surface is definitely easier than trying to with the Renshape strip already attached to the hull.


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    I have used an array of circle and square templates to attain some consistency. On this boat many of the features seen up front are also duplicated towards the stern.

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    I now have to work through which parts have raised components and which don't. Any more pics that people have of the front deck space would be greatly appreciated.

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    David H

    Leave a comment:


  • Davidh
    replied
    Hello all.

    Torpedo Time!....


    Torpedo Tubes that is...

    The space for the torpedo tubes at the moment currently is a big oversized rectangular box that is begging for something more in terms of details. As mentioned over previous logs I had the dilemma of not knowing whether the torpedo tubes had a boxy appearance rather than having a half round curve. Bernhard Wenzel to the rescue with a picture showing an early U-boat in dry dock with a curved front section of the torpedo tube. The picture looks doctored or even a hand drawing but it was the best I have. The earlier boats such as U-9 have a box like forward tube structure.

    I decided to start doing some more detail work at the front end of the boat rather than the back end even though I will be going over both. The rear end is especially needing some attention at the moment but I though I would go with the front.

    I measured the area around the box frame that would make up the tube area and measured the width or diameter of the tubes on the original drawings that I was working off. I used various sizes of drill bits to get a feel of the side and dia of the torpedoes and the corresponding tubes.


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    The width of the torpedo tube space as seen here is about 16mm. This varies as it heads towards the bow. I haven't bothered with sanding and getting the width consistent as it will be filled over with the tube details. I then took a couple of drill bits and placed them inside the tube opening to get an idea of the diameter of the torpedo and tried to get it as close to the original size in the drawing.

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    To make the curved outer surface of the tubes I decided to take a piece of Renshape and then machine it down to the 16mm width of the outlet then took it a little further just for good measure. I made this piece as long as the length of the outlet. I then took the drill bit shown here and placed in the tail stock drilled a hole through the Renshape to create the hole for the Torpedo.

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    This is the two turned Renshape pieces that will feature in the torpedo areas to be come the front of the tubes or scoops as I'll call them for want of a better term. The second one hasn't been drilled through yet. Back and front denote the back and front end. Once made I then place them inside the recess area for the tube and mark out the line that will see them sliced in half in a gradual curve to follow the profile of the front of the boat and create the scoop. I had to dremel out some of the recess especially at the back of the box section to accommodate the half tube.

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    I have had to give some though to the geometry of the Torpedo tube doors. On these early subs they seemed to have the door exposed, unlike later and WW2 U-boats there were no outer shutters. As a result it would seem that the doors opened outwards and as far as I can tell they opened inwards with the hinge on the inside of the tube. In order for this to happen then you would need to have space for the door to open which means that you couldn't have the curved section of the tube in the way for this door to open without jamming. As a result I deiced to create a square section immediately in front of the Bow door to give space to the door top open. The torpedo then moves forward sliding past the open door and runs along side the scoop and then on to target.


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    The buried torpedo tube terminates with a bulged section as the outer corner of the tube exceeds the curved profile of the hull. As a result there is the bulge that terminated at the door. This was created by
    cutting a left over piece and shaping it to coincide with the front edge of the tube. I then placed a small Renshape block in place immediately before the tube door outlet and glued into place. This provides the space for the door to swing back. It makes the tube look a bit awkward and not smooth and streamlines but I don't see any other way they could have made this geometry work.

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    The bulge and block in place. The front section needed to be raised at the back end to make sure that it would be in line with the axis of the tube as it comes out of the hull. This meant putting down a bed of filler and at the right time pushing the back end of the tube into the soft filler and aligning it so that theoretically the torpedo wouldn't glance off the scoop as it was heading out of the tube. Then I cut out two small circles of Balsa sheet to cap off the door area and glued them to the bulge sections that would sit as the back of the recess and signify the front of the tubes. Line them up and glue them in place.

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    Early filler, lots more needed.


    Stay tuned, more torpedo's next week....


    David H

    Leave a comment:


  • trout
    replied
    Gantu, that is pretty cool link.
    David, thank you for explaining.

    Leave a comment:


  • Davidh
    replied
    Thankyou David.

    David H

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by trout View Post
    Ah, got it. So, good set of plans is imperative otherwise it is a lot of guess work?
    If guess work, at least the jig will assure symmetry between the two shafts -- they will be wrong... equally!

    David

    Leave a comment:


  • trout
    replied
    Ah, got it. So, good set of plans is imperative otherwise it is a lot of guess work?

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by trout View Post
    David,
    ‘great jigs, but how do you figure or build the jig to get the torpedo doors where they need to be?
    You loft the orthographic 'front-view' onto the face of the jig. find the center of the doors, and that becomes the center of rotation.

    Leave a comment:


  • trout
    replied
    David,
    ‘great jigs, but how do you figure or build the jig to get the torpedo doors where they need to be?

    Leave a comment:

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