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saintjohnbarleycorn

re sawing ribs

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I have a piece of wood for ribs, 

1  do you cut lengths doe full top and bottom, and then lengths for sides ?

2 its 1 3/16" x 54"

3  how much longer do you ( if any) make them then the actual length ?

4. with those dimensions what thickness would you cut minus the saw kerf  1/8 ( not exactly sure about that ) 

 

thanks kevin

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I would approach this task by successive approximations.

Cut one rib to your best guesstimate thickness and as you smooth

the saw marks out to your finished thickness it out it will become

apparent if you have cut it too thick or thin.

Adjust your next cut accordingly.

The same holds true for the length and in both cases it is

better to have a tad too much material than not enough.

Good luck !

 

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I plane one surface of the block smooth to a finished state, and then rip it on the bandsaw to 2mm or so, with the smooth planed surface up against the fence;  This is followed by planing the cut side of the rib strip afterwards.

Then I plane the side of the block again, followed by ripping the rib off the block. Rinse and repeat.

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I usually try to keep the long grain running in sequence from upper bouts to lower bout with an end match at the center of the lower bout. How you achieve this depends on what length wood you have. If you have not bent ribs before you should allow for some extra material incase you break some. I would plan on adding 1/2" to 3/4" on each end of each bout length. Too much extra length can get in the way when bending the tight curves. I pretty much process them the same way Bill does. To finish plane the saw cut side I use a bit of double stick tape on the very end stuck to my bench top which is nice and flat. I plane with a Lie Neilson low angle block plane, straight blade. Use a hair dryer to release the tape from the bench. Be sure and add a little extra length to cut off cause the thickness of the tape will make the rib thin where it is taped down to the bench. 

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I use a low angle block plane too with a real tight mouth opening, or if there is tear out occurring, I use a Lie Nielson scraper plane.

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I cut the ribs with the saw to a thickness of 2.3 mm. After removing the saw marks on both sides with the plane (toothed scraping plane or low angle) and the scraper I get a final thickness of 1.2 / 1.1 mm.

But this depends on how deep the marks left by your saw are, so doing a test as advised above is essential.

As for the length, after thicknessing I cut at 15 cm for C, at 19 cm for the upper ones and at 22.5 cm for the lower ones. or 37 cm for one piece upper rib and 44,5 cm for one piece lower rib.

I also take the actual measurement of the finished ribs for each form as this can vary for different models, to know which is the minimum necessary measure in case of raw ribs strips with short total length (using masking tape on the form with finished blocks to get this measure).

As an  example for my G form these finished measures are respectively : 12.7 - 17.8 - 21.5 - 35.5 - 43.1 cm

Often the blanks for the ribs are not long enough to make the lower rib in one piece or you are forced to accurately calculate these measures to avoid some flaws in the wood (knots, stains, cracks, etc.).

 

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Generally you should be able to get one lower rib and one c--bout from each of two strips and both upper bouts from a third strip  the same length. That is why most dealers sell three pieces to a set. The ends are hard to thickness accurately so best to thickness the strips before cutting the ribs to length and if you have an  inch or so  extra on either end  you can hold the rib for scraping using a teeter totter type hold down made from two pieces of scrap wood with a clamp holding down on the rib side and you press down on the other side of the teeter totter to release the rib as needed. Tooth plane is pretty much required for figured wood and cleaned up with a flat scraper.

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 I found that a half round Iwasaki file can do wonders attacking the high points on ribs.  I like those things.  Flat files are far less useful.  I don't have a toothed plane.

When I got a bandsaw, I did find that when you change blades on a bandsaw you have to adjust tracking.  Who knew?  I didn't. Hah.

Ken

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I usually mark the lining lengths and the rib lengths on the mold itself for future reference.

Since you are using inches.   Most makers use mm for lengths.    Here are the common minimum measurements

LB   9"  (190 mm)          CB   5 1/2" (140 mm)     UB       7 1/2"  (190 mm)

so any combination of these minimum lengths will work

 2  UB    15"  (380 mm)

LB + CB   14 1/2 "  (370 mm)

LB + CB + UB    22"  ( 560 mm)

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