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PostPosted: Wed Oct 10, 2012 6:27 am 
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There's a thread about angle cutting with lasers over here:

http://www.rcgroups.com/forums/showthread.php?t=1291976

I think the takeaway message was, angle cutting isn't really practical for model building, or at least not yet. Several responders thought a CNC mill could come closer to a solution than a laser cutter.

For plank on frame, for example, it would be really handy if a CNC mill could shape and bevel each of the many adjacent planks. I have seen a flying boat project in which all the planks were pre-cut by a laser, but then bevel edged by hand. For bread and butter, my guess is you would still end up hand planing and sanding.

But it seems the laser would really minimize the amount of hand work involved. Less like heavy carving and sculpting, more like a quick sanding to shape.

From the photos Dean recently posted of one of his airplanes, it looks like his balsa sheeting technique produces really fine results. Michael


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PostPosted: Sun Oct 21, 2012 7:18 pm 
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Hey guys, it's been awhile.

Michael,

I've seen that thread, and I agree that it's just not practical at this time with what's out there. But maybe in the near future someone will make, or build a 2 axis laser head that will do the things that we've mentioned. Now that would be a milestone for the model builder, and take model building to a whole new level.

And I get the feeling :wink:, you guys would really like to see the hull of the Onondaga get the bread & butter treatment. So I did a quick cut up of the hull, without any inner support frames, to see what it would look like, and it's not looking half bad. It would still need some minor framing to help align it all, but I'm thinking of giving it a go.
More to come.

Image

-Dean


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PostPosted: Mon Oct 22, 2012 4:52 pm 
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Dean, what a beauty she is!

Some years ago my dad and I built a freesailing model using the bread and butter method. It was a model of the National Geographic's far ranging brigantine, Irving Johnson's Yankee. We cut out the interior of each panel with a coping saw. The bottom (keel) layer is solid lead. We painted the hull but used no fiberglass. Worked fine, no leaks. I still have it. The only negative was that we ran through a lot of material. Michael


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PostPosted: Mon Oct 22, 2012 5:34 pm 
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Thanks Michael,

The Brigantine Yankee is a good looking ship, you should post some pics so we can check it out.

I'll try and get the frames laid out this weekend, and post what I come up with. I plan on adding notches to each layer so they locate on the frames to align everything up, that way it should be easy enough to assemble, and add a little extra strength.

Take care,
Dean


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PostPosted: Sat Nov 10, 2012 10:49 pm 
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The B&B hull is pretty much done, except for maybe a couple little tweaks I may add. I decided to use dowels for alignment on this also, which you can see the holes for them in the pics, along with a couple keys, fore and aft. Those keys serve a duel purpose, besides helping keep both ends aligned, along with the dowels, they also act as a guide for sanding the hull curve at each end, and for attaching the keel. Well, I guess that's a triple purpose. :big_grin:
You'll notice I didn't add any frames or longerons, figuring that once it's all glued together, it should be plenty strong and rigid enough without them.
Now the only question is, which hull do you guys prefer, the stringer/frame approach, or the B&B?

I still have a few things to finish on the deck half, but once I get back from my trip next weekend, I'll start breaking down everything for laser cutting. And of course, I'll post a few pics of the cut file breakdown as I go.

Image

Image

Here's a link to a short video of the assembly. http://youtu.be/VmePks96la8?hd=1

-Dean


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PostPosted: Sun Nov 11, 2012 6:43 am 
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Just one thing... How are you going to align all those planks once you've cut them out?

Owen


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PostPosted: Sun Nov 11, 2012 9:08 am 
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With wood dowels, you can barely see the dowel holes in the top pic, near the inner radius, fore and aft. You lay the the first slab down, glue in the dowel, straight of course, :big_grin: then start stacking.

Also, in the video, it's meant to be built upside down, with the top slab being laid down first, then layered up, or down, whichever way you look at it, from there. The keys are added once all the slabs are together. I was a bit tired when I made that vid and didn't feel like redoing it. :heh:

-Dean


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PostPosted: Sun Nov 11, 2012 10:06 am 
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That looks great!

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PostPosted: Sun Dec 02, 2012 4:02 pm 
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Thanks Devin.


So the cut-file phase of this project has begun, and I thought I'd post a very basic overview of how I use the CAD model to produce cut-files.
I'm using the stringer/frame version of the hull for this example.

First, I'll take the basic hull model hollowed out to the thickness I want the frames to be. No need for details on the CAD model at this point, they only make producing your cut files harder.

I try to get as many notches and taps on the CAD model before I start making the cut-file sketches I'll use. Starting with making the stringer notches, I'll use multiple Planes at an angle to the hull, then use those Planes to create Split-Lines on the hull surface where I want the stringer notches.
Image


Next I'll Thicken those split surfaces to form the stringers, and Indent them into the hull to form the notches.
Image


Now a series of Planes along the length of the hull where I want the frames to be. Then I make a Sketch on each Plane and use Intersect-Curves to make the frame Sketches.
Image


You can make the cut-files without Extruding each Sketch into a solid body as I have done, but I like to do it this way for two reasons. It's nice to actually see how everything fits together, plus I use these solid parts to make my assembly drawings.

For the long parts that will not fit on a stock Ply or Basswood sheet, I'll Split these into sections that will fit. Then make Sketches of those parts the same way as the frames, Intersect Curves.
Image
Image


Once all those Sketches are made, I'll just copy and paste each one onto a sized drawing matching the material sheet size, and arrange them to fill out the sheet. It's nice to fill up the space on each sheet as much as possible if you can, but if you are using different materials, sometimes this isn't possible. It isn't such a bad thing though, because you have spare material to use elsewhere.
Image


And here's the Cut-files, which I'll now "save-as" DWG files, then open them in Draftsite to add some holding tabs, then re-save them as either DXF or DWG, whichever the laser cutter prefers. One little trick, save them in the older, AutoCAD 12 DXF or DWG format, this automatically converts Splines to Poly-lines, which the laser cutting software reads better.
Image

Image


On to the B&B cut-files.....

-Dean


Last edited by Roscoe on Fri Dec 07, 2012 10:28 pm, edited 1 time in total.

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PostPosted: Fri Dec 07, 2012 7:41 pm 
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Very cool. It's great to see how these things come together.

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PostPosted: Mon Dec 10, 2012 8:42 pm 
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Dean, this is like a master class in how to produce cut files. Many thanks for this step by step narrative, I am learning a lot of CAD strategy as you go along! Re the beautiful bread and butter version, I think it is perfect for rc . All that free space inside for trial positioning the prop shafts, the turret drives and the batteries and servos -- and everything nice and solid throughout. Not quite as pretty as the bulkhead and stringer technique now in progress, though. Michael


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PostPosted: Tue Dec 11, 2012 8:04 pm 
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Thanks guys, appreciate it.


Michael,

Thanks for the kind words, and I'm glad you enjoyed it. Most of the method I used was borrowed from doing R/C airplane designs, where, after some trial and error, I've learned to keep the workflow as simple as possible. As an example, knowing from the start that I was making the CAD model just to produce cut-files and drawings, all that I really needed to model was a plain hull and deck, no details. So that's how I always start on a project now, with a simple, base model, which I can then either cut up, or detail out. And I always make at least one copy of the model before I cut it up, so I have one to detail out later if I want.
If you, or anyone else, have any questions on anything, feel free to ask, I'd be happy to help out if I can.

So, since the first hull is done, next thing is to break down the Bread & Butter Deck and Hull halves, which I'll post a quick overview on that also. Once everything, cut-files, drawings, etc. is done, I'll have a little surprise for everyone. Ho-ho-ho :big_grin:

Take care,
Dean


Last edited by Roscoe on Wed Dec 12, 2012 5:51 pm, edited 1 time in total.

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PostPosted: Wed Dec 12, 2012 8:53 am 
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Dean,

I just noticed the difference call-outs of wood types. It looks like you're cutting the keel and other main support members out of basswood, but the frames and such out of lite ply. Good thinking!

-Devin

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PostPosted: Wed Dec 12, 2012 6:48 pm 
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Thanks Devin,

Yeah, since the ply has no real grain to it, it works well for frames and internal structure, there's no real bending along the grain like basswood, which I think helps make for a straighter frame. Another benefit is you can lay it out on a sheet anyway you want and cut it, where with the basswood, I try to run the grain lengthwise on the parts, or whichever way gives you the most strength.
But like on a flying model airplane, instead of using lite ply for the frames or former's, I would use balsa to save on weight. And to add strength, I would use two former halves glued cross-grain to each other, which gives you roughly the same strength of ply, without the weight penalty.

Take care,
Dean


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PostPosted: Fri Dec 28, 2012 9:38 am 
Hey everyone! I have a project for school and I chose to make the U.S.S. Onondaga. I am doing pretty well but I am a little confused on how all of you know your hull measurements and angles. If you could help me out I would be soooooo thankful. :smallsmile: so If you could give me the measurement of the hull before it curves down and the angle of the curve and how long the curve goes down that would be awesome!
Thanks everyone!
-Zach


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PostPosted: Fri Dec 28, 2012 8:14 pm 
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Hi Zach,

It sounds like a cool project to have. Like most people that make these models, I used a fairly detailed drawing of the Onondaga that has hull line profiles on it, which correspond to intervals along the length of the hull. Some of the more detailed drawings do have actual numbers to use for these hull lines, unfortunately the drawing I used does not have these. So it's more of a trace and place type process for this one, where your using the drawing profiles, and not actual numbers and angles.
If you can give us some more details, like the scale of your project, how you are doing it now, maybe we can help get you some info that could be useful.

-Dean


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PostPosted: Wed Jan 02, 2013 8:05 pm 
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After breaking down the B&B hull into parts, I realized there are just a few too many to be practical. So I'm going to redo it using double the sheet thickness for each layer, which shouldn't add too much more sanding to shape it. Anyway, here's what made me change my mind, the mega-part version.

Image

-Dean


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PostPosted: Wed Jan 02, 2013 8:09 pm 
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Wow. Yeah, that's a tad much.

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PostPosted: Sun Jan 06, 2013 6:35 pm 
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Yeah, just a bit too many, but that's what happens trying to save sanding time by using thinner sheets. :big_grin:

So, round two, dissected to fit on mainly 1/4"x 6"x 18" basswood sheet, with the very bottom layer, tabs, keel and rudder from 1/8"x 6"x 18" sheet.
6 inches is the widest sheet I found that comes as a single piece and not two glued together, which limit's how it can be split up into parts. So I'm starting to think that this type of Bread & Butter technique might be more practical, laser cutting wise, for the smaller scales. And at these bigger scales, using a router with a bigger cutting area, along with a wood, or plastic that's available in wider sheets, might be the way to go.

Image

-Dean


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PostPosted: Sun Jan 06, 2013 9:00 pm 
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Dean, it looks great!


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