When you model a full fuse you typically draw the outside skin (as that is what most plans show).
Meaning any material thickness will go towards the inside of the object.

There is a minimum material bend diameter so to account for thickness on any hard/sharp bend, separate parts should be used with mitered corners, or butt joints, one side of which takes account for the thickness… The fold tool works well for bends because it effectively miters the corners… to a point. I don’t recommend it for any bend over and approaching 90 degrees.

So for all the normal shapes used in an aircraft body, which are simple round natural curves, you know the thickness is going towards the inside of the fuse… So to make the part fold correctly, you need to adjust your formers. The only question is how much do you take off? Well, you’d think your material thickness is ¼ inch for FFF, but that is not a good number to use.

Through trial and error, lots of trial and error… I’ve found that 3/16 of an inch is a near perfect fit for ¼ blue FFF.

So the solution is to offset your formers that distance to make things fit nicely.

Construction wise, I assemble the sections in parts, using a simple butt joint on the seam. This more or less forms a cylinder, then the formers are worked into the rolled foam. Once I’ve got a few sections assembled, I glue them together aligning the fuse one part at a time.

Again, through trial and error, I’ve found that having some additional way to ensure your fuse is not twisted is a good move. Currently I’m experimenting with tabs and unique features.

I would love to hear how others are doing this.

(I'll get some pics up of this process as well)

 

I design my fuses from the inside skin. The tops and bottoms go inside the two sides. The fuse ends up being 12mm wider than the 3d model. Doing it this way makes making formers very easy. Just take the top line of your former and move it down 6mm and the bottom up 6mm. I hope that makes sense…

 

The blue FFF is marked "6mm" thick which is 6 X 0.03936 = 0.23616. I've measured with my dial calipers and get anywhere from 0.220 to 0.225. I've been designing using 0.220 for the slot widths and even though I have Sketchup set to fractional, it will still take that as a direct input for the slot widths.
Just using 3/16" would make things much simpler for me, eh?

 

Yeah, were talking what 1/32 there? For formers, that would just allow a tiny bit more slop in most cases, for more extream formers that make really funky shapes it may be a bit too much, as 3/16 is border line too much slop. I like my formers to fit pretty tight, and the foam compresses a little bit anyhow.

Now on the other hand, designing from the inside out will work fine as well, but I can not wrap my head around it, do you ever run into problems?

 

I haven’t had any problems designing from the inside out yet but all my planes are “Box Scale”. If you watch my video on my process I note the fuse will be wider than the model and scale the width to compensate before I start making formers or tabs and slots. On the other hand, my only design to use formers so far has been my Space Shuttle for RcPowers.com. My “Box Scale” fuses seem strong enough with out them. I can see if you were building something round, how formers would be a must.

 

Reference this build for more info:
viewtopic.php?f=73&t=129

 

Another really great tip I pulled from the guys who work with depron (over on rcgroups):

With the single sided blue FFF bending one way is fairly easy, there are two issues...
The first you are likely to encounter is bending the opposite way.
This can be fixed by adding a layer of packing tape to the other side of the foam where you want to make the bend, this will keep the foam from cracking and should allow an opposite bend!

The second is when you try to make a sharp bend greater then 90 like I told you to avoid. Well there qare times when yiou don't want to avoid it, besides I generally don't know what I talking about anyhow...
Just add that same kind of tape to the layered side! It will re-enforce the side with the layer and allow for a very hard bend without cracking! Still if you want a good shard 90 edge, or any edge for that matter, you are better off designing to use two parts.

 

More lessons learned...
For bending and rolling very small surfaces, ie the tail area, it's best not to throw out that hobby knife quite yet.

I've found that the challenge in rolling pre-cut part to account for that tail section of an aircraft in the 30-40 inch wing span area leads to more time spent on assembly, with poorer results. Not to mention the time this adds on the sketchup side. Instead, it may be better to put a few guide holes in (and get away from tabbing these critical areas) to allow for "manual adjustment."

This will make rolls easier, modeling easier, and produce a better product.

So far I've had very good luck with pre-cutting the main wing slot, but accurate assembly is a must if you go that route.

 

Hey guys, I picked up a trick in another forum (rcgroups) that I really wanted to share on designing a full fuse in CAD that may simplify the problem (or at least make it easier to understand).

The idea here is to make construction planes at an array of angles (draw a rectangle, make it a group, then rotate it after pressing ctrl about a corner, once you've got your array; scale the whole thing as desired).


From there as you setup your reference drawing (for the formers) all you do is trace the former so that the endpoint falls on the intersection of the construction plane. The result will be a nice evenly spaced model.

Connect the endpoints and you are good to go!
Attached files

 

I got it, how to make the fan form (from the rectangles). I didn't get the part where you transfer the formers into the fan.

 

Man the fan is the hard part!
Ok, let me see if I can explain a little more.
I typically import one image of the plane I am working on. Then I copy that image as needed, that way they are all to the same scale. The reference image imports just like another rectangle, typically on the green red plane. All you have to do is hit ctrl then rotate it around so that it is at a right angle to your construction planes, as shown in the above pic. Now you should have two reference images at a right angle. Pic a former you want to model on your second image and move it to where it goes on the first reference, usually they are marked with a letter or number. Now move those reference images to your fan array…

If you can get that far, most of the work is done, and the rest is easy.

Start tracing (on the vertical reference image) from the green red plane to then next intersection of the fan and the reference image using the line tool. When you make it all the way around, connect the line to make a “D”

 

I tried your ides, tvcasualty, and I found out that I have to select the whole shebang and and then select 'intersect with model' to get the points for the lines you've mentioned.

I also found out that if the bulkhead has an arc and the arc segment (a problem in SU that what already mentioned numerous times) are not the same as the number of fans, that I don't get a face since the endpoint of the segments are not on the same plane as the face I was just making.

 

If I've said it once, I've said it a hundred times now, TigerPilot, don't use the arc tool that's your problem. That arc tool seems like the best way to go at first, but really you need more control.
Curves can be made of multiple line segments, and when it comes out, you can't really see the difference. The arc and circle tool is the devil when used for this part in modeling in this method. ...Not to mention when it comes time to unfold.

Instead use the line tool, you will get an intersect cursor hint as shown.

Don't worry to match those small segment arcs, you don't need to do that! A single line is all you need, and the fan is only to guide you on where your end points of those lines should go.

The model shown above did not use a single arc or circle tool to make.
Let me know how it goes! Good luck! Attached files