Rib Grain Orientation

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Rib Grain Orientation

Postby PeterZ » Mon Feb 06, 2012 5:31 pm

All

Have seen several posts on steam bending ribs, which I need to do. Confused about the proper grain direction of the rib.

So, ... lets say you buy a board that is quarter sawn white oak, 6" inches wide, 1-1/8" thick (5/4). You lay it on a bench top with the 6 inch part laying flat across the bench. The end grain should be perpundicular to the benchtop right - the grain lines on the end of the board are verticle assuming the bench is level and horizontal, right?

So, how do you cut the needed 1-1/8" wide X 3/4" thick rib out of the 6" wide board? According to Danenberg's book (page 277 of the complete Wooden Runabout Restoration Guide), he shows the end grain parallel to the wide part of the rib (the part that touches the strakes). So I guess this means I would cut my 3/4" ribs by setting my table saw fence at 3/4" (might go thicker and plane down to the right thickness to get rid of saw marks), lay the flat 6" wide board on the table and rip away - right? So each finished rib is 1-1/8" wide x ~3/4 of an inch thick, with the end grain parallel to the wide 1-1/8" part (the part that touches the strakes) - is this right?

I am an avid wookworker and feel stupid asking this question, but have seen some conflicting comments in various forums, or perhaps it was the wording I did not comprehend without a picture like in Danenberg's book.

Thanks for reading
Regards
Peter

1965 Thompson Offshore
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Postby richnle » Tue Feb 07, 2012 2:28 pm

Yes Peter - I think you have it right. In your description the grrain should be vertical with the 6" X 1 1/8" board laying flat. Once you cut the boards into the 3/4" ribs, You want to pick out the pieces that have as few of the grain lines breaking through the 1 1/8" wide surfaces as possible. I steamed and installed 38 ribs following this and did not have a single one crack during installation. Good luck!

Rich
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Postby PeterZ » Tue Feb 07, 2012 2:54 pm

Thanks Rich
I assumed you used air dried white oak? I am having trouble finding any of that, ... lots of kiln dried though. So when you say grain coming through the 1-1/8" surface you mean where you see those 'U-shapes'. I think Danenberg points this out in his book as this is a good place for fracture.

Regards
Peter
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Postby richnle » Wed Feb 08, 2012 9:04 am

Yes Peter to both questions. I went to a saw mill and bought boards right after they were cut from the logs. I tried to find the boards with the straightest grain. We roughed out the ribs and then let them air dry on a rack for a few weeks. The wood was so green when we cut it that the saw blade got hot from all the moisture, and we got strings instead of saw dust. It is not optimal to steam wood in this condition, so you want to leave time for it do dry to close to atmospheric humidity.

we roughed out about 20% more ribs than we needed. We later finish cut them and rounded the interior corners. From there, we sorted the ribs to use the ones with the straightest grain for the rear of the boat (tightest bends), and to not use any with Knots or crazy grain patterns . You can see from the U shapes and just from the look of the grain which ones are the best. As I mentioned, not one cracked during installation. I was also glad that we made extras since we used up all of the good material that we yielded after inspection.

One final note, I decided to make the ribs about 1/16th" thicker than the original ribs. Since all my ribs from the dashboard back cracked, I decided it could not hurt to make the replacement ribs a little stronger. I will also be careful to make sure debris does not accumulate at the bends between the ribs and the strakes.
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Postby Torchie » Wed Feb 08, 2012 10:25 am

I am going to add some fuel to the fire . I used kiln dried quarter sawn white oak for my ribs. Soaked them for a couple of days prior to bending and had absolutley no cracks or breaks when steam bent. In my opinion the runout of the grain is much more important than wether or not the wood is air dried versus kiln dried.
If you use a fine tooth blade to rip the ribs you will have little to no blade marks
then just go over them with some 80 grit sandpaper.
Allows for extra ribs as once you cut them as defects will show up(hidden knots,pinholes) etc.
This is the way that I learned from an old timer over 35 years ago. It has always worked for me.
Good luck and have fun. You will get quite a sense of accomplishment steam bending that first rib.
Karl.
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Postby PeterZ » Sun Feb 12, 2012 12:19 pm

Thanks for fueling the fire Karl!!! I appreciate the comments. I think I am going to have to do the old soak and steam method when I get a chance. Right now concentrating on the transom rebuild and getting ready to flip and strip and look at the underside for issues.

Regards
Peter
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Postby Bill E » Wed May 30, 2012 8:44 pm

Torchie wrote:If you use a fine tooth blade to rip the ribs you will have little to no blade marks
then just go over them with some 80 grit sandpaper.
Karl.


Here's another tip along those lines: Put a 7-1/4" circular saw blade in your tablesaw. The arbor hole should be the same 5/8"; you just get less cutting depth. The benefit is that your saw has much better torque with the smaller diameter blade, so it's less likely to bind or stall if it gets pinched. In addition, I'd recommend a 24-tooth Freud Diablo framing blade from my experience, vs. a DeWalt (can't remember which DeWalt). The Diablo ran much more smoothly and made very smooth cuts that generally didn't require any sanding/smoothing afterward.

These circular saw blades also make only a 1/16" kerf, compared to a typical 1/8" on a tablesaw blade. Again, your saw is only pushing its way through half as much oak as with a wider blade, so you have more effective power. Furthermore, you're wasting half as much wood turned to sawdust!
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