Replies

1. 
   Guest_ | Jun 28, 2000 09:25am | #1

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   This one killed me once, too. A cone on top of a five sided quarter round turret. We had ply that was delaminating from all the nails we used to hold the bend to the rafters. We tried the slices, too. I think we ended up wrapping ply around the cone in sheets that spiraled, and then needed to be cut down center of next rafter for the next piece that continued to spiral up the cone. So none of the panel edges were square. It was a terror. I don't ever want to sheath another cone again. For that matter, I don't ever want to be responsible for framing a cone on a building, either, cones are not supposed to go on top of buildings, architects, they look pretty stupid. If you have to draw a big box, and are upset with yourself for the ugly thing you drew, at least don't subject the framing crew to the same agony you felt just before you slapped those hideous things up there with that little pencil or mouse or whatever.

   I'm done. Sorry, no ideas for you Spence.

2. 
   scott_lind | Jun 28, 2000 02:14pm | #2

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   I would like to see if you get any igenious ideas back on this one using panel materials. We disassembled a victorian house with the same type of structure and will be reassembling it. I saved every sliver of lumber off of the tower. It has tounge and groove 1x6 vertical on the tower (blocking between studs for nailing) and then dozens of pieces cut in triangular shapes that are about 4" at the base and taper to nothing at the point of the cone.

   Good luck!

3. 
   Guest_ | Jun 28, 2000 04:54pm | #3

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   Try checking your local library for back issues of Old House Journal. They've had some articles on this.

   Bob

4. 
   Spencer_Withers | Jun 29, 2000 05:06am | #4

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   Glad to know I'm not the only one who's scratched his head over this. Thanks for your help everybody.

   Spence

1. 
   Adam_Greisz | Jun 29, 2000 06:22am | #5

   *Our project (nearing completion) has a full turret and a half turret. Both of these are true radius' cones and were indeed a challenge. Using a full sheet we bent it over the rafters and temporarily nailed it in place at the eave.We then tied a wire to a nail at the peak and penciled the largest diameter arc that would fit on the sheet. Then we scratched another arc at the top of the sheet. After marking the center lines of the rafters we took the sheet down and cut it. Our rafters were about 26 1/2" apart at the bottom and we were able to span three rafter bays with each sheet. Our large turret had 24 rafters all equally spaced (a task in itself). Therefore it took eight pieces of plywood with arcs to make it around the turret. We were able to bend 1/2" ply for the first row (16' diameter 16:12 pitch). For the next row we switched to 1/4" ply using the first row to get the bottom arc and marked another arc maxxing out the sheet (16 of these). After four rows we had approximately 42" left to reach the peak, for this we used pie shaped pieces. It was quite the project, I haven't mentioned that the eaves changed pitch and that it is a tile roof. For a picture check out http://www.Ravenwood.org.. Check out the pictures marked Jan 7 and Jan 31 1999 in the construction journal. Good luck.

5. 
   Guest_ | Jun 29, 2000 05:44pm | #6

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   Adam, how did you figure out how to cut the rafters?

1. 
   Guest_ | Jun 29, 2000 05:55pm | #7

   *here's the bonnet of our town windmill built in 1787..Millwright Andy Shrake has the contract to rebuild it..on the bonnet itself, the rafters were cut just like boat ribs, and then covered with 1/2 inch boards just like the ones that are visible...thirty years or so ago, the bonnet was oversheathed with the 1/2 inch boards you can see, and then it was reshingled with cedar shingles..the original sheathing is still underneath the visible sheathing and is cut and fastened just like the newer ones...this project should be pretty interesting to watch...

6. 
   Spencer_Withers | Jul 01, 2000 01:15am | #8

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   Adam, that is the best idea yet. Did you need to block the seams, or does that not make a difference?

1. 
   jjmk | Jul 01, 2000 02:19am | #9

   *Adam; Very nice job, it is ahead of schedule and under budget?

1. 
   Adam_Greisz | Jul 01, 2000 04:21am | #10

   *Frenchy, The first two rafters were cut to full span on a 16:12 pitch with square ends. For the next two rafters we subtracted 3/4" from the span and again cut the ends square. This gave us our first four rafters, the next four were cut with double 45's. To get the span for these four we subtracted 1 1/8"(the distance from the center point)from the overall span. This gave us eight of our 24 rafters, we then added two rafters to each of our eight bays. To figure out the rafter length I marked each of the bays with a 3" wide block. This told me where the rafters would hit the installed rafters. We then measured the existing rafter and cut sixteen to that measurement. For these we used a square cut since cutting a 75 degree angle on a 16:12 is quite a challenge. For possible wood compression we cut a plywood circle nailed it to the bottom of our point and filled these gaps with a dry mixed mortar. As for blocking with a 16:12 pitch it was not necessary. To make my job easier (figuring rafter spans) I have invested in a construction master 4. It certainly saves times to not need to convert decimal points and fractions using the scientific calculator. And for your knowledge I originally learned how to cut rafters with Reichers rafter tables (the framers bible). Good Luck. Only The Best.

7. 
   Guest_ | Jul 01, 2000 04:57am | #11

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   Adam,

   That is an impressive job, you have some good ideas on sheathing the cone that I think I will try in the future.

   I posted a question on framing a 12 sided turret a while back and received some excellent advice. One technique which worked great for me and I think would simplify things in a situation like yours would be to make up a barrel shaped affair as the attachment point for the 32 main rafters(I guess you could call them hips or commons?). I made a 12 sided hub the depth of the plumb cut, to simplify rafter lengths, plumb cuts and nailing. This arrangement also eliminates the compression issue. Not to mention it looks a lot cleaner. It took me about 30 minutes to fab the hub and allowed me to cut all the hips the same, and cut virtually all the parts prior to assembly. Basically, you divide the 360 by the number of sides, and divide the result by two to get the miter of the barrel "staves". Make the staves 1-1/2" wide on the outside. Subtract the radius of the finished barrel from your common or hip run to get your length and cut them all the same.

   Search the archives for the thread, lots of good advice.

   Tom

1. 
   Guest_ | Jul 01, 2000 02:16pm | #13

   *Spencer,

   You can "figure" how to cut the sheets of plywood by using the length of one of your rafters. This length would be the radius of the arc you would need to scribe at the bottom of your sheet of plywood. This would be a convex curve in relation to the top of the cone. The second arc would be just 4' less then the first, this corresponds to the width of the plywood and would be concave in relation to the top of the cone.This second arc would become the bottom or convex arc of the next sheet going up. The piece formed is in purple to the left.

   View Image © 1999-2000 "Whenever, therefore, people are deceived and form opinions wide of the truth, it is clear that the error has slid into their minds through the medium of certain resemblance to that truth." Socrates

8. 
   Spencer_Withers | Jul 01, 2000 02:16pm | #12

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   We just built a 20' turret, the difference from the turrets I have done is that it was round and not octagonal. My question results from the total pain that it was to sheet it. We put a double layer of 1/4" ply on it and as the wall had about a 6' radius, it was grim duty bending those suckers on. We wondered if there was a more efficient or quicker way. The cone roof was even worse. We're looking for ways that maintain the true round without cutting triangle slivers between each rafter. Anybody have any ideas out there?