Yes, I have already learned a lot, now it's time to put my education to practice. FIRST thing I figured out, make an educated guess on how long it will take to complete a phase, then triple it. Second thing, make an educated guess how much that phase will cost you, then triple it.
Steve, your type XVII thread was the first one that I "stumbled" onto here at Subcommittee while I was searching the net for an r/c sub kit. When I saw your thread I thought, "You mean, guys actually build their own subs from scratch ?" I thought it was a very cool idea and ever since, the gears have been turning to build my own sub. That was over a year ago.
....and now for more.
Step 3: Building the Master Formers.
Time to complete: 16 hours.
Total to date: 20 hours.
On the side view of the plan it indicates where the actual ribs were located for both the pressure hull and the outer hull/superstructure. I decided that I would use the actual rib locations of the outer hull for my hull formers, the question remained, which ribs and how many ribs/formers would I make. After literally examining the side profile for hours (not part of the build time), measuring, calculating, I concluded that I could model every 4th rib. Using a former width of 1/8", this left EXACTLY 3" between every forth rib. I would use extruded styrofoam 3" thick in between each former that I made, and that would recreate the hull in perfect scale. Every 4th rib seemed to be a good compromise as well between having enough ribs/formers to accurately replicate the complicated shape of the hull, and not actually making EVERY....SINGLE....RIB (130). I was quite happy with this discovery. After another hour or so gawking at the plans, I selected the following ribs to model:
-15, -13, -9, -7, -4, 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 55, 59, 63, 67, 71, 75, 79, 83, 87, 91, 95, 99, 103, 107, 111, 115
Couple things of note on the ribs. The "negative" ribs indicate the ribs of the outer hull which are aft of the pressure hull, hence the negative numbers. Number 0 is where the pressure hull begins. As well, right in the middle, the rib #'s change from even to odd starting at rib #55. This is because in the plans, there is a rib 54a. In other words, rib 55 is still 4 ribs away from rib 52. This numbering scheme is part of the Kohl plans and not of my doing. In addition to that, I felt the neccesity to include a couple extra ribs at the stern in order to get more detail on shaping that area of added comlexity. I included ribs -7 and -15 and will simply have to shave down the extruded foam in order to squeeze it in between these formers that are tighter together than the 3". Finally, ribs 44, 48, 52, 55, 59 are all exactly the same which would mean I would only have to build one master for these 5 ribs.
I spent a ton of time on this phase of planning as I knew that getting things right at this stage was crucial, everything else depended on it. I have a paranoia of getting halfway into a project only to discover that I have to restart it due to not thinking things through thoroughly enough at the start. I lost count how many hours I spent looking at, and measuring my plans. I was very happy with my decision to get excellent plans and go the route I did in terms of getting them enlarged and resized. Huge money but.................... it was already starting to pay off. I had no illusions that this sub would be cheap from the get go.
Now to build the master formers. I decided I would build masters to build the actual formers from after realizing that if I simply built one set of formers from the paper templates, all that time and effort (and expense) would be lost once the formers were destroyed in the plug making process. If I kept a set of masters, then, I would always have them and could make another set of formers very easily if the need ever arose or in the event I needed them in later stages of this sub build.
I started by taking my paper plan copies of the cross sections and carefully.....and tediously.....cutting along the line that represented the particular rib I was after. This was a challenge to say the least. There are so many profile lines so closely together, I had my magnifying glass out and was working with the precision of a brain surgeon under my work table lighting. Had my vision been anything less than 20/20 with a 4X magnifying glass, I don't know if I could have done this. The process was very slow and required a very steady hand. I cut one rib/former out of each paper copy of the cross section so that I would have the longitudinal reference lines that the Kohl plans have, on every former. The importance of this will come up later. As a result, I threw a lot of wasted cut out paper in the garbage, particularly on the small formers. My head, neck, and back was killing me by the end of it.
Once the paper templates were cut out, I positioned them on 1/8" hardboard to see how many I could get on a 2' x 4' piece. Once I had them laid out, I drew lines where I would cut the hard board into individual pieces for each former so that they would be manageable with the band saw, then took all the paper templates off to cut. Once all the individual pieces were cut out (my table saw made very quick and easy work of this), I spray glued (Elmer's) the paper templates to their respective pieces, pressing them down flat with another piece of hardboard. I then left them to dry (2 hours).
On returning 2 hours later, I used my bandsaw to cut out each master former, using the paper template that was now glued on top as a guide. At first, I was trying to be bang on with the band saw and cut EXACTLY up to the paper. I found this to be very difficult, my band saw skills not being the best. I quickly discovered that if I just use the band saw to cut "pretty close" to the paper, I could then use my 1" belt sander to bring it up flush to the paper with precision. This technique worked wonderfully as the sound of the sanding would change juuuuust a little when I was nicking the paper, letting me know that I had sanded the former exactly up to the paper template. The rest on the sander ensured that I was sanding at a 90 degree angle as well. It was fast (relatively) and allowed me to shape the 1/8" hardboard perfectly to the paper template glued on top. I was pleased with the accuracy I was getting.
To get all the formers and extruded foam lined up to create a one piece plug, the "Plan" was to use a spine board to hold the formers in alignment as well as an 1/4" index rod ("ready rod" / threaded rod) that would run the length of the longitudinal axis. This rod would ensure that the formers were anchored at the right hight on the spine board. This rod would also act as to compress the formers and foam together to hold them securely in place. This would be done by threading nuts onto the rod every 4th former. In looking at the cross sections, I concluded that if I put the index rod where the longitudinal axis was marked on the plans, I would have a "spine" that ran.......right down the logitudinal axis of the sub, which, I thought would be the way to go. I discovered that if I was to drill holes on the master formers in the EXACT locations where these lines merge at the tip of the bow and stern on each paper template, I would be able to insert the index rod through these points, which would perfectly align the formers. This was possible only due to the reference lines drawn on the Kohl plans. The result would be formers that were alligned to precision on the spine board. I would use my drill press to drill these holes using a wood bit that has a very sharp "tip" on it. I would lower the bit slowly and place the tip of the bit RIGHT where it needed to be, then drill the hole out. I took a lot of time and care with the drilling of these holes, the accuracy of the former allignment, and therefore the shape of the hull, depended on these holes being perfect. Very hard to explain, I hope the photos are of value.
The former masters were now completed. I was now ready to build the actual formers using the masters. I felt good about the fact that I had the masters to work with and would still have them long after the sub was built or in the event I had to remake another former. They MAY come in handy in the sub building process as well. They took a ton of time, effort, and precision to build, it would have seemed a shame to have them destroyed in the plug making process if I would have used them as the formers.
Step 4: Building the hull formers from the masters.
Time to complete: 10 hours.
Total to date: 30 hours.
I don't know why I did this, but I did. I purchased some 2" extruded styrofoam and some 1" stuff ( I could not find 3") in order to be able to put the two together to get 3" stuff, which is, as I mentioned before, the exact distance that I needed between formers. This really isn't very complicated math. What I did was, I decided to put the two pieces together and measure them, to see if they actually were 3" in total. Nope....go figure. 2" + 1" DOES NOT = 3" It DOES = 2 7/8" Now, if you're insulating a house, this likely doesn't matter, but if you NEED 3" in between formers on an R/C sub that you are scratch building, 1/8" off is HUGE. Since there was going to be 39 formers in total, losing an 1/8" on EACH would have put the sub 4 7/8 " shorter than it should have been. In 1:25 scale, that's a scale 3.125 metres (10'), it's no longer a type VIIc/41 as far as I'm concerned. ...THAT's what I mean by "HUGE". It put a wrench in my entire design plan of using 1/8" former widths. However, I quickly realized that since I needed another 1/8" of thickness to make up for it not being there with the foam, I could use 1/4" formers instead of 1/8" formers. Again my ruler and calculator came out and I measured and remeasured. I was right, the 1/4" formers would work great. It turned out to be a blessing that the foam was 1/8" too thin, because I preferred the idea of having the formers 1/4" thick over 1/8" thick, a little more "meat" to work with. I was VERY thankful that I decided to measure the foam before building the formers. If I hadn't, I would have built a ton of 1/8" thick formers that would have been useless for this design.
Using my masters, I traced out all the formers I would need on 1/4" hardboard. Medium Density Fibreboard (MDF) is usually my material of choice to do stuff like this, but I couldn't find it in 1/4" thickness (on the particular day that I was shopping for materials) so I opted to use the hardboard, which is really close to the same thing....only harder. It still cuts and shapes very nicely. Using the exact same technique that I used to make the masters, I made the formers, numbering each one as per it's represented rib. When drilling out the index holes on the formers after marking with the master, I took the master off and simply used the tiny mark in the former to place the bit and drill the hole. I did not want to simply drill the hole out while marking with the master on as I did not want to damage the indexing hole on the master. The holes on the masters were in the EXACT right spot and EXACTLY round, they needed to stay that way if they were going to be of any use in the future.
Once I was done using the masters to trace and mark, I secured them all in order on their own index rod. I did this not only to keep the masters all nicely together. The complexity of the hull shape demanded that a lot of time be spent on the construction process up to this point. This thing was not a "tube" by any stretch of the imagination. I knew that taking on a U-Boat for my first scratch build was quite a bite to take, so I was prepared for things to take a lot of time, and to make a few mistakes along the way. I only had to redo 2 hull formers due to screwing up, adding about 1.5 hours as I had to completely redo the paper template as well. Thankfully, I had a few "spares". I considered this a success.
By some lack of brainpower, I neglected to cut the spine board slots out of the masters. After some further thought, I decided to use 5/8" malamine as my spine board instead of my initial thought of using a piece of 3/8" plywood that I had lying around. I concluded that the plywood simply wasn't rigid enough, even though I wanted to "cheap out" and use materials that I already had. I also decided on malamine because I suspected that the finished surface would be easier to locate the formers onto. I had drilled the index hole for the spine board slot cutout in the master former 3/8" thinking that I would be using 3/8" plywood. Since I would now be using 5/8" malamine, the holes would have to be redrilled to 5/8".
To cut the spine board slots out of the formers, I measured 5/16" from either side of the centre of the 3/8" index hole that was drilled in the former. In total, I would have 5/16" on each side making for a total of 10/16" (5/8"), which is the width I needed to cut the slot to fit the spine board. Using a square, I marked the lines on the former where the spine board slot would be. I would use these same lines as a guide to place my 5/8" drill bit when I redrilled the index holes.
Much care had to be taken with these measurements and redrilling. Once the 5/8" index hole was drilled, completing the spine board slot was just a matter of cutting down the two marked lines up to the hole. I used my table saw, a steady hand, and a keen eyeball to do this. I was lucky to get them all done without losing a finger as I had to take the guard off for such small pieces. In all, the technique worked very well as all the formers fit nice and snugly onto the spine board. The malamine board was a good choice for this purpose instead of plywood.
I had placed the formers onto the spine board without the foam to test fit the formers and spine board slots that were cut into them.
Once on the spine board, the index rod was threaded through by chucking one end into my drill and tapering the other end with a grinder so that if it needed to "find" the index hole, it could do that. The index rod threaded through without any problems, finding each hole easily. As the rod was being threaded through, it was making teeeny tiiiiiny alignment corrections to 3 or 4 of the formers. Once the rod was completely through, the formers were in perfect alignment and very solid on the spine board. After the formers were in alignment, I could see where a couple of the formers needed just a minor sanding to bring them into symetrical form with the others, which was primarily in the centre area of the saddle tanks where the formers are all the identical dimension. The keel section was also sanded down a little to flush up this area nicely.
........more to follow.