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  #1  
Old 01-23-2012, 01:16 PM
(o)COBRA(o) (o)COBRA(o) is offline
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Question Top Different Shades

Hey everyone,

I'm starting to build my first acoustic guitar and I ran into a problem. Once I glued the two spruce panels for the soundboard and started to plane them down to thickness, I realized they plane in different directions. I believe the grain should be going in the same direction, because at different angles, the two top panels are darker and lighter. I have book-matched the two, so they have the same characteristics on either side. My next assumption is that they were not quartersawn, but I got them from a local tone-wood supplier and trusted their judgement. Any help would be greatly appreciated. Thanks!!
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  #2  
Old 01-23-2012, 01:34 PM
arie arie is offline
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either the wood was not from a split billet and has some runout, or was not bookmatched correctly. slight runout (around 1~5 deg) isn't too bad of a thing as it won't actually hurt the sound of the guitar and many fine instruments have this condition. really bad runout (you'll know it when you see it) is another thing entirely and should be avoided for instrument making

read here:
http://www.lutherie.net/frankford.runout.html

Last edited by arie; 01-23-2012 at 01:41 PM.
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Old 01-23-2012, 01:57 PM
(o)COBRA(o) (o)COBRA(o) is offline
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Hmm if it's runout then why doesn't it all plane in one direction. Either way, my main problem, is how I can plane down the centerline while avoiding tearout on one of the sides, since the grains go in separate directions.
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Old 01-23-2012, 02:17 PM
Alan Carruth Alan Carruth is offline
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(o) cobra(o) asked:
"Hmm if it's runout then why doesn't it all plane in one direction."

Because that's the way runout works. Let's say that the tree grew with some twist, lika an old fashioned barber pole, so that sawing a top out along the axis of the tree will result in the grain 'running out' at some angle to the surface. Start with a piece cut along the radius of the tree, thick enough to slice into two pieces to book match. If you look at the edge on the bark side, where the runout is usually the worst, you'll see that the grain runs at some angle, let's say five degrees, to the surface, and lets say it slopes up from left to right. If you open it out on that side, to make the book match, then you reverse the direction of the slope on one side; where it was going 'up' it's now going 'down'. As you plane it, you're going to be going against the grain on one side or the other.

It often happens that the twist increases as the tree gets older, so there's more runout on the bark side than on the heart side. In that case, a 'heart' match can minimize the appearance of runout. On a top with no runout, if you hold it up with the light behind you, you'll see a line of bright reflected light that runs straight across the top. With runout, the line will run at an angle, say, sloping down from left to right. That's why it shows up on a top: it starts in the upper left, and runs down toward the right until you hit the center line, and then shifts back up toward the top again, to slope down toward the right. The 'heart' match at least gets both sides to reflect in the same place along the center line: most poeple won't notice the tilt of the reflection otherwise. You still have to deal with the runout in the wings, but this minimizes it.
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Old 01-23-2012, 02:20 PM
dchristo dchristo is offline
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cut it down the center, flip the board then reglue
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Old 01-23-2012, 02:50 PM
(o)COBRA(o) (o)COBRA(o) is offline
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Alan Carruth if I understand you correctly, when matching the hearts, this decreases the light/dark effect of the wood slightly. But, when planing, I will still have to plane each side separately. dchristo, that is one way of realigning the wood in order to plane all from one side, but I'd rather keep the bookmatched design of the wood. My next question is, is there any way of telling the extent of the runout before buying a piece?

My options right now include keeping the piece as is or flipping one side to make planing easier, but ruining the bookmatching aspect.
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Old 01-23-2012, 03:04 PM
arie arie is offline
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keep the bookmatching but rough plane at 45 deg to the wood in a cross hatch pattern. a toothed roughing blade can help here. then a standard blade, then move to a a nice sharp scraper. or run it through a thickness sander if you can.

"My next question is, is there any way of telling the extent of the runout before buying a piece?"

just follow the grain with your eyes from one end of the board to the other and look for any that "fall off" the glue joint edge of the board. also look for any twisting of grain from one end to the other.
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Old 01-23-2012, 03:20 PM
(o)COBRA(o) (o)COBRA(o) is offline
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thanks arie,

I didn't know toothed blades existed. I might just end up flipping one side because it seems like the easiest method that keeps the coloration and I don't have a scraper or a toothed blade. Those hints might come in handy in the future though
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Old 01-23-2012, 03:41 PM
arie arie is offline
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you're welcome

honestly were it mine i'd keep the grain orientation and bookmatching in the "correct" fashion and disregard the color issue. imo the structural consistency would be more important to me then a slight change in sheen when the guitar is viewed from the either side.

-i don't know whether toothed plane blades are commercially available but i suspect that they are. another route would be to get a standard blade and cut notches in it with a dremel cutoff wheel being careful not to burn the metal -or it will loose it's temper and wear quickly.

-scrapers are plentiful and inexpensive. you will need one to finish your guitar with. dressing the edge is easy. a single cut mill file and a hardened dowel pin are what i use. true up the edge with the file then burnish the edge with the dowel to curl the burr.

do you have any pictures of this top?

Last edited by arie; 01-23-2012 at 04:22 PM.
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Old 01-23-2012, 05:02 PM
(o)COBRA(o) (o)COBRA(o) is offline
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arie,

my sister is coming up for the weekend with the camera charger, so I will post pictures then. I am really interested in what you have to say, as you seem knowledgeable. I live near rochester new york, if anyone has a good referral where I can buy decent tonewood near here, I would be grateful. Preferably, where they cut wood from a billet instead of a saw. Thanks.
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Old 01-23-2012, 05:05 PM
charles Tauber charles Tauber is online now
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Toothed plane blades are commercially available, but it is probably over-kill given that there isn't usually much to plane off on a commercially-purchased top and spruce is a very soft, easily worked wood.

Scrapers aren't fantastic on soft woods. They work, but there is a tendency to tear the wood. Still, even on soft woods they are a good choice for removing plane marks (tracks), levelling rosettes, etc. Better still is to learn better blade (iron) sharpening technique to eliminate the plane tracks. Skilled cabinet makers have this down pat.

In my opinion, cabinet scrapers are to instrument making what a light sabre is to a Jedi. One should learn how to use one. Inexpensive and indispensable. With good instruction, they are easy to sharpen and use.

I hand plane all my guitar tops. I plane each half along the grain with minimal overlap of the center seam. Tear-out is usually minimal, as is the overlap of the center seam. Then scrape and/or sand. Not really a problem. Also, use a plane with an adjustable throat and close the throat to the smallest setting that just allows the thickness of shaving you are taking. It can make a huge difference in eliminating/reducing tear-out.

Last edited by charles Tauber; 01-23-2012 at 05:17 PM.
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Old 01-23-2012, 05:15 PM
(o)COBRA(o) (o)COBRA(o) is offline
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Charles,

I have waterstones of 800, 1200, and 6000 grit which I use to sharpen my plane blade of the 5 1/2 vintage stanley I own. I also have the 60 1/2 vintage stanley block plane for planing down the bracing when I get to that step. The final thickness of the top is to be 1/8 of an inch. When do I stop planing and start sanding/scraping in order to get to that 1/8''?
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  #13  
Old 01-23-2012, 05:26 PM
charles Tauber charles Tauber is online now
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Quote:
Originally Posted by (o)COBRA(o) View Post
When do I stop planing and start sanding/scraping in order to get to that 1/8''?
It depends on your skills and, to some extent, the individual piece of wood.

A while back, I took a series of seminars with Rob Cosman. They focused on basics skills - sharpening, planing, sawing, etc. (I highly recommend him and his video series.) From rough-sawn lumber, we made finish-ready furniture projects using no power tools, scrapers or sandpaper - 100% handtools.

In answer to your question, it is possible to plane to final thickness and do no sanding or scraping. If one doesn't know how to do that - or chooses not to - how much material to leave depends on how rough the surface is when one finishes planing. You'll need to leave enough that after you remove planing marks with a scraper and scraper marks with sandpaper you arrive at your final thickness.

Not knowing your skills or the behavior of the piece of wood you're planing, it's hard to estimate. Probably .020" over thickness, anyway, for removing marks.

Oh, and to maximize the bookmatch, once the face is smoothed, the excess thickness should be removed from the back/inside of the top.
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Old 01-23-2012, 05:44 PM
tadol tadol is offline
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Not meaning to butt in here, but(t) -

If you can sharpen your iron to 6000 grit with the very slightest of convexity at the corners of the iron, and if you can plane a shaving thin enough that it floats up and away from the plane and leaves no furrow on either side that you can feel, then you can take it to final thickness without any sanding or scraping. But the sole of your 5-1/2 need to be honed flat, and the rest of the plane needs to be properly set-up as well, including the throat and chipbreaker.

Otherwise, you need to leave just enough material to remove any marks left by the plane - and whether you choose to scrape or sand is your choice.

Toothed irons are for highly figured material, with lots of grain reversal, and are usually used at a higher angle than standard. You would be better setting up another plane as a "finish scrubber" - sharpening the iron into a very shallow convex curve so the corners cannot catch, and then using it like a scrub plane, skewed and at a diagonal to the grain, but taking a very light cut, to efficiently remove material until you get very close to dimension -
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Old 01-23-2012, 09:22 PM
(o)COBRA(o) (o)COBRA(o) is offline
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I also have another question regarding the type of scraper that is suitable for guitar tops and backs. I know they range in thickness and also type (card scraper, cabinet scraper). Does it matter how thick it is or the type? Thanks.
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