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Honestly I think sanding would be more difficult then using a plane. I remember ages ago on my first build I used a level with sand paper taped to it. I think this idea came from Sloans book, I never could get it right. Sanding evenly is not easy though I have never tried a proper sanding jig. Using the plane was tricky at first, still is, but the good thing is that when you get it you really get it right. Even with a well trued sharp plane you still have to make a mental image of where your high and low spots are when shooting and adjust the pressure of the cut appropriately. But when you get that one long thin double curl in one shot and it candles true then you know you are good to go. I use a Record Marples No. 5 for shooting.

It's really not necessary, you'd be wasting your time.
I had problems jointing the tops and back until I adjusted the frog on the plane to get what Arnt Rian described as "dandilion seed shavings".

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We are all in the gutter but some of us are looking at guitars.

fwiw, being an ex-tool and die maker i mill a scarf joint. i throw each piece into the vise on top of an angle block and hit it with a safe-t-plane in my little milling machine. is it traditional? -no. do i care? -no. is it flat and accurate?-a wring test proves it to be flat, and a master grade square shows much less then .001 out of square which plenty good for wood.

now this doesn't mean that i can't use a plane it's just that for me, i can achieve greater accuracy in less time. i have no romantic attachment to expending valuable effort doing something the hard way (IMO). would i sand a scarf joint? no. that fact that one has a lab grade surface plate doesn't mitigate the fact that you need do control the piece you are sanding with a high level of rigidity. your leading edge and trailing edge will be radiused to some degree as your workpiece rocks with your sanding stroke, and the paper moves (yes, even psa shifts) and breaks down.

given that one has chosen the sanding route (and i have no problem with that), let's think about the condition of the surface you've just sanded. take it to a microscope or buy a cheapo 20X jeweler's loupe from ebay. you'll see a raked surface with grit embedded in it, torn fibers, and debris packed into the pores. compare to a freshly cleaved surface. you'll see clean open pores, no embedded grit, no torn fibers.

so with a scarf joint on a neck you have a lot of wood that's going to be cut away so any edge irregularities will most likely disappear. not so much with top and back plates where you have far less real estate. then there's the cleanliness issues possibly robbing the joint of a good adhesive surface. take care of the details and the rest will fall into place.

moving on to the use of a guide rail on a shooting board. i used to use a steel straight edge. after a while as i got better i started using a longer smoothing plane and this helped a lot as well as closing up the frog. i just use a plane, and a cabinet scraper to get a good clean joint.

I generally use a hand plane to join tops(I do very few as I'm more of an electric builder), but another method I have used is to joint with a router. Stack the plates one atop the other as usual, clamp a straight board to them(a piece of mdf works, but what I use is a shelving board which is covered with melomine, or whatever is used to cover the mdf the shelf is made of. Gives a nice, straight edge that is very smooth), and use a bearing guided router bit to cut the joint. Takes mere minutes, gives IME a perfect joint(at least as perfect as I can get with a plane). Not as cool as using a hand plane, shooting board or all the fancy jigs we like so much, but it's the way I join my electric body blanks, and works great. Tried it on the last couple of acoustic tops I joined and will most likely being doing this from now on.

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Mike

The only thing nescessary for evil to thrive is for good men to do nothing.

Coming from a similar background as arie I too tend to take a machine tool approach to things. For me it's quicker easier and more accurate. For joining plates I clamp em down on a mill and run an end mill down the sides. Makes for a nice straight joint. Just have to watch your feeds and speeds so as not to case harden the wood from a dull or slow moving tool.

Hell I even use my mill for neck blanks. chuck it up and run a fly cutter down the neck and I have a nice square flat surface in seconds. Then chuck up the proper sized end mill and mill out the truss rod slot too. To me it's much better this way. But my wood working skills ain't the best seeing I'm new to it. As I gather experience and better tools I'm sure that I'll start to lean more toward the traditional way of things. But at the moment using the skills I already have get the job done better and faster.

I've made scarf joints all along with a plane, and really can't see why any other method would be better. Sanding stuff really flat; now that's hard!

I use a Woodriver #4 for jointing with a shooting board. When I have trouble chasing gaps, it means it's time to sharpen the plane. I usually start a session by sharpening the plane and it makes a clean joint usually pretty quickly. The exception is Osage Orange with it's grain convolutions and chip outs. I've been considering modifying a plane for more angle (not less like in the Veritas) just for doing Osage Orange. It appears from the cited review above that the Veritas plane is more designed for end grain shooting--that's a different problem than we have.

I was considering putting a back bevel on a standard bevel down plane for the Osage Orange. I haven't tried it yet, but I'm procrastinating closer.

I've got a bit of a back bevel on the Hock iron in my old Record; it makes life easier with figured wood all around.

Fwiw, I use a jointer then sand with a sanding beam. I do not have a problem with visible joints and I do not think I have seen a top joint "fail" that was not a result of the guitar being dried out. I have noticed a renaissance towards hand tools and I agree the "old way" is rewarding and sometimes more effective (scrapers for me) than power tools but a poorly planed joint is worse than a well executed sanded or milled joint. Again as most discussions go, what works for you is generally the best method

So Flipo likes mass in him tools and jigs...

well me too, is simple, me hold a plate in me hands, shoot it down a # 8 plane thats held in a vise, bolted to a 500 lb. bench thats lagged to the walls and flour of me house. Couple of passes over a sharp blade and them plates are good to glue.

Must be all that concrete in the foundation eh Flipo. Who wooda thunk.


blessings

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Audiences and dispensations on Thursdays ~ by appointment only.


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Back to the question of the OP, it would seem to me that the reason that none of us have heard of a 45 degree join on the top is for a couple of reasons;
1) much easier to ensure a 90 surface. If you were to try a 45 degree joint, it would need to be exactly 45 degrees to join it. Any error might make it impossible to get a good joint.
2) with very tight grain on spruce, you'd be planning through a number of growth rings as you make that 45 degree angle. I would imagine that you'd end up with "ridges" in the planed surface which would resist a perfectly tight fit.

As to the plane versus sand debate, I find planning a perfect joint a challenge, but see it as one of those tests in this process which is worth spending the time to get really right. Scary sharp planes, and absolutely flat shooting boards made it easier.