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  #1  
Old 09-25-2022, 06:44 AM
viento viento is offline
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Default How plane a (jumbo) spruce top

I have never planed a top (spruce) to make it thinner.
I've always taken them to a carpentry shop and they would use their electric thicknesser.
This hasn't happened very easily because the machines normally can't be set that thin ..to 1.06"
So we always put a corresponding panel under the top wood and it worked to some extent.

Since I can't go to the carpentry at the moment, the thinning of the spruce top should also work with a plane.
I don't want to do anything wrong, here to the experienced builders:

Which plane would you recommend?
I have a smoothing plane No. 4 and a smaller hand plane, 12°...
except for a No. 7 roughing plane, which is probably out of the question.

Then my stupid beginner´s question: I want to thin a spruce top of about 1.26 "down to 1.06".
Do I use the plane across the grain or with it?

Maybe someone can share his experiences and give me a good tip?
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  #2  
Old 09-25-2022, 07:25 AM
Fathand Fathand is offline
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1.26" or 1.06" would be like thick enough for a carved archtop. Do you mean .126" or .106".

.106" is a typical guitar top thickness and .126" is on the thick side but sometimes works. Larger guitars tend to thicker tops than smaller guitars, mostly depends on your wood stiffness, is it Sitka? Englemann which is usually less stiff?

As you thin your top you should do the wobble test, hold the top at edges and shake, should make a wobbly sound like shaking sheet metal. Don't forget there is probably finish sanding which will thin it more.

People like #7 planes for tops, a #5 would work. You can pick up a good used Stanley #5 for $50 sometimes. Can you change to a smooth blade in you #7?

Can you take off your .020" by hand with a large sanding block?
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Old 09-25-2022, 08:15 AM
viento viento is offline
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I´m sorry, I meant .126" and .106"...
Taking off .020" with a large sanding block would take some time.
So I better use a plane to do that.
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Yamaha FG-340 (1970)
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  #4  
Old 09-25-2022, 10:34 AM
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Bruce Sexauer Bruce Sexauer is offline
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For the first 15 years of my career I hand planed all of my plates, tops, backs, and sides. My tool of choice was and is a 9 1/2 plane with an adjustable throat. These can be found on eBay for between $20 and $60, made by Stanley or Record. For the plane to work accurately it is very important to have as flat a work surface as possible. Some people use stone, but MDF works pretty well. If your spruce is of the highest quality it will have close to no run out and can be planed in any direction, which makes things easier. If it is more gnarly than that, planing at a diagonal works better. Highly flamed maple can be successfully planed at a diagonal as well.
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Last edited by Bruce Sexauer; 09-25-2022 at 07:39 PM.
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Old 09-25-2022, 11:18 AM
viento viento is offline
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I thank both of you!
I did as you proposed and first sharpened the blade of the No. 4 smoothing plane.
Then I planed very thin shavings at an angle to the grain. Almost like paper (whistle)
Pressed the board against a small stop bar and pushed the plane quickly. Great fun!
Both ends of the board were planed without tearing.
One just has to measure the thickness achieved more often. My thickness gauge only has a depth of about 8cm,
soon I'll get myself a longer one that reaches to the middle of the board.
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Old 09-25-2022, 12:35 PM
Howard Klepper Howard Klepper is offline
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Hand planing a guitar top to thickness is like flattening and thicknessing any board. You go from large scale to small scale irregularities. So first you use a longer plane to get the high spots into the same plane, and then you use a shorter plane to bring those high spots down. That's why the smaller sizes are called "smoothing" planes.

A No. 7 jointing plane has no use thinning a guitar top. A No. 4 smoother can do the whole job. When you have a warped board, it's best to start by going across the grain. That should not be needed on an already flat guitar top. But each piece of wood responds best to slightly different planing. I would tend to go at a slight angle to the grain, and even if going parallel to the grain, angle the plane a little to get a shearing cut. Certainly if there is noticeable runout, you need to be planing more on a diagonal, as Bruce said.
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Old 09-25-2022, 01:42 PM
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If your work surface is absolutely flat and your plane is also flat, razor sharp, and cutting tissue thin, it is not necessary to be able to measure beyond the edge of the plate as the plane cannot cut a significant concave.

I built 50 guitar on that premise, and they are cherished by their owners to this day.
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Old 09-25-2022, 03:28 PM
Alan Carruth Alan Carruth is offline
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In theory you want to hit every part of the piece in every direction the same number of times. There are two ways to do this: you can be perfectly random, or perfectly systematic. Nobody can be perfectly random....

Plane on diagonals, taking strokes side-by-side all the way across. Then switch so that your plane strokes are crossing the ones you just made at 90 degrees. With a good flat bench top you should end up within a few thousandths of the same thickness everywhere, or, at least, a straight taper. I've used the same Record #4-1/2 plane for leveling and joining for several hundred instruments, but the iron has been replaced a couple of times....

I clamp the plate on the near side, and plane away from the clamps, then turn the piece around and do the other end. A thin piece of wood can buckle and break if you're planing into a stop. DAMHIKT
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Old 09-25-2022, 04:49 PM
viento viento is offline
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I used a smooth white coated flat chipboard as a base.
The rectangular top piece of spruce was only a little too thick but completely flat.
At the end of the chipboard I attached a flat wooden board with two cam clamps that held the spruce wood firmly.
It was a bit narrower than the spruce board so that I could slide the plane to the right and left of it.
Planing the paper-thin shavings was great fun and did the job well ,better than electric thicknessers.
Besides the surface is really smooth
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Martin D28 (1973)
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Hoyer 12-string (1965)
Yamaha FG-340 (1970)
Yamaha FG-512 (ca. 1980)
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and 4 electric axes
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  #10  
Old 09-26-2022, 03:24 PM
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Mark Hatcher Mark Hatcher is offline
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I have two tips that I hope will be helpful.
1) When setting up the blade measure each sides thickness of the ribbon you pull with a micrometer and tap the sides of the blade with a small hammer until they match perfectly. This will help eliminate ridges.
2) when you get close to your target thickness adjust the blade back until you are pulling very thin ribbons, like .002" Then finish the surface like that. Glue holds about 30% better on a planned surface than a sanded one.
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  #11  
Old 09-26-2022, 05:21 PM
redir redir is offline
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What has not quite been mentioned is that you will most certainly have to tune up any plane you decide to use to get this type of work as accurate as possible and without destroying it. To do that you need a thick piece of glass or some other dead flat hard surface like a machined piece of granite, wet/dry sandpaper up to 4000 or so and many hours of spare time. The 3M paper that has an adhesive backing is best but I forgot what it is called now...

You need to lap the bottom of the plane till it is dead flat and polished out nicely. While you are at it, the plane blade needs to be lapped perfectly too. Then you need to get a nice sharp edge on the blade before getting to work.

I use MDF and it's typically perfectly flat or easy enough to make it so. With little tack nails I nail down the spruce top to the mdf so the heads of the nails are well below the desired thickness of the top so the plane blade is safe. I also like to have the center hole of the sound hole cut out just to have a point of reference there.

I also like to plane the entire joined top and not the top cut to size.

I struggled with the first several guitars I made until someone told me about tuning up planes, even the good ones are not perfectly in tune. Makes a HUGE difference.
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  #12  
Old 09-28-2022, 09:07 AM
viento viento is offline
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Thanks for your help!
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Martin D28 (1973)
12-string cutaway ...finished ;-)
Hoyer 12-string (1965)
Yamaha FG-340 (1970)
Yamaha FG-512 (ca. 1980)
D.Maurer 8-string baritone (2013-2014)
and 4 electric axes
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  #13  
Old 09-28-2022, 09:17 AM
Alan Carruth Alan Carruth is offline
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This is generally a job for a 'smoothing' plane, as opposed to a 'joiner'. Aside from the length of the plane itself they are usually sharpened differently: the edge of a smooth plane is usually a very shallow arc, while a joiner is sharpened to a straight edge. The smooth plane leaves a slightly scalloped surface, but because of the arc there's no danger of the corners of the cutter messing up the surface. A joiner leaves a flat surface, but is normally used on the edges of boards that are narrower than the cutter, so there's still no danger from the corners.

I like to use a 'modified' edge shaper on my planes; it's straight across except for being rounded on the corners. This allows for use as both a joiner and a smoother. Back when I only had one plane that was handy.

Buyers of old tables are told to look for the wavy surface from the smooth plane as one indication of authenticity. We don't usually take so thick a shaving, especially when finishing up, so that's less of a consideration; the scallops are not deep enough to make much difference.

I usually finish off the surface with a hard scraper; again, a straight cutter that has rounded corners, to level up the scallops. With a very sharp scraper (and you should never use cutters that are not very sharp) the surface is almost as clean as a planed surface. A planed surface shows all the structure of the wood clearly in a microscopic view. A properly scraped surface has a more 'burnished' look, with some crushing of cell walls. A sanded surface looks like a plowed field, with loose fibers and dust scattered around, and not much structure if the sand paper was coarse. As Mark says, a freshly planed flat surface glues best, followed by a freshly scraped one. Sanded surfaces are 'way down the list.
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