Glued 2 Piece top joint question

solteroblues

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So I bought this HIGHLY flamed maple top set for a guitar build from Northridge. Normally, every top I've bought from them has been jointed already, and this one was too, but you could see a little light through the joint. So, I tried jointing it again with my old crappy jointer, didn't fare much better, then I tried using my nice finish blade on my table saw, no better, then I tried a couple times with a factory straight edge piece of MDF and my router table. So finally, I found a local professional woodworker and paid him to joint it with his fancy helical head jointer. THere's still light shining through the joint.

Am I just being too OCD and this is fine? I mean it's not noticeable along the joint unless I hold it up to the light, so there's no noticeable gaps. I'm afraid if I keep cutting away I'll lose too much width, even if it is only a hair at a time, jointing it over and over 10 times will take it pretty quick! My next course of action is trying the router table again, but this time I'll use my whiteside spiral trim bit and a precision ground straightedge that I just ordered. But do I need to go this far?
 

Michael Matyas

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Is your top flat or cut into wedges? If it's flat you could try planing one side of the joint upside-down. If the edge of whatever tool you're using is not exactly square, then flipping one piece of wood over before planing or routing might work. If the wood is already wedge-cut I don't know what else to try.
 

solteroblues

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it's flat, not exactly sure what you mean by cut into wedges. It's one piece that was bookmatched...
 

Michael Matyas

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Some wood suppliers sell arched top wood cut so it tapers in thickness from the edge you are supposed to join. For instance, each half might taper from about 3/4 inch thick to about 3/8 or so. If your wood is the same thickness from center joint to edge, you can flip one half over before planing. That way, any defect or misalignment of the blade will tend to cancel itself out when you flip the wood back over the right way. I don't have a jointer in my shop so I have to hand-plane a blank when I make the joint. I have a shooting-board clamped to my bench and I always flip one piece of the wood over when I plane the edges to be joined. I hope this helps.
 

solteroblues

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ah I know what you mean now, I've seen those. Thank you!

The guy I took it to actually jointed the boards together, but flipped. I just don't know if the figuring is what's causing the issue, surely all of the different tools aren't just all making the same issue.
 

ARandall

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Proper jointing means there is no light visible anywhere along the two bits.....because by definition the two pieces should be mating perfectly to be properly jointed.
Light showing will mean very visible glue joint at the point, so its worth being OCD with that part of the build for sure.

Very flamed maple can often tear with a long handplane (the typical way most experienced people joint), so in those cases you can put sandpaper onto a long beam you know to be straight (like a newly bought straightedge). And if you position both sides of the top (as evenly level at the jointed edge as you can make them) into whatever you are using to hold them in place for this process, then you will be levelling the two mating sides together.
 

the great waldo

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Randall got it right. I used a metal spirit level with self adhesive abrasive on it which worked fine and the very slight roughness from the abrasive helped to make the joint invisible. I got myself a spiral jointer which solved my problems of jointing highly figured maple. You said that someone jointed it with a helical jointer, If the jointer was properly setup you should have a perfect joint ! I wonder if maybe the wood is not properly dry ? this can cause all sorts of problems with highly figured wood.
Cheers
Andrew
 

Lester

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Long level, apply double sided tape, stick sandpaper to level. Place top wood near the edge of a table and use several long strokes to flatten one side (the repeat for the other). Hold level at a very slight angle (like a couple degrees) so that the top joint is the meeting of just the upper edges and the wood below doesn't prevent the top edges from meeting flush.
 

ARandall

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^ Thats fine if its a drop-top and will remain flat.
Be aware that for a carved top you must have all the depth jointed flush, or you'll end up with a visible glue line once you start carving.
As the OP has not yet told us what type of build he is doing and what the top profile is we cannot specify certain specific techniques
 

Michael Matyas

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^ Thats fine if its a drop-top and will remain flat.
Be aware that for a carved top you must have all the depth jointed flush, or you'll end up with a visible glue line once you start carving.
As the OP has not yet told us what type of build he is doing and what the top profile is we cannot specify certain specific techniques
I agree with arandall. A thick top will cause the joint to show as the wood is carved away. But I like the suggestion about the long level and sandpaper. You could try this: fold the book matched wood back up with the edges to be joined lined up and parallel. Stick them together with double-side tape, and sand them together with a board wide enough to cover them both. When the edges are straight according to your level, open them back up like a book and then check for any gaps.
 

ARandall

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^ Yep, and given the face that needs to be flat is the lower one, have that lower side innermost should mean your resulting joint is referenced by the 2 bits meeting flat and level on the bottom
 

Ripthorn

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How much light? Light is able to pass through a gap of less than a thousandth of an inch. It's also common in some areas of woodworking to "spring" a joint, where there is a hollow of a couple thousandths in the middle. This is then clamped out and helps ensure that ends don't come apart.

In short, if it's the faintest amount of light and in the center, you could probably go with it.

For perfect joints, nothing beats a sharp hand plane.
 

tabascom16

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If it is just a wee little bit of light coming through when you clamp it together the clamps will pull the wood together. I had actually heard the argument of setting up a jointer to make an ever so slight dip in the middle of the board (so when book matched would have light coming through the middle). The theory here is that it will help keep the edges from separating in a finished piece.

When I joint a board I make sure to maintain downward pressure on the outgoing table which helps keep the edge referenced to that table in case there are issues with the two beds being out of line.
 

moreles

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I think A Randall said it all. This is a joint that really needs to be right. I have generally had to use sandpaper on a dead-flat surface and finish the job by hand. And yes, light shows through pretty readily, which means you have to do a great job. I claim no special skill beyond patience and attention to detail, and even so, I've always been able to get a fine fit and no glue line. A visible join would bug the hell out of me -- it's the axis of the whole guitar. I suppose it is conceivable that the wood itself is moving after being worked... just to drive you nuts! I admire you jointer-users and planers... I could never finish this off with either one.
 

nuance97

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I think A Randall said it all. This is a joint that really needs to be right. I have generally had to use sandpaper on a dead-flat surface and finish the job by hand. And yes, light shows through pretty readily, which means you have to do a great job. I claim no special skill beyond patience and attention to detail, and even so, I've always been able to get a fine fit and no glue line. A visible join would bug the hell out of me -- it's the axis of the whole guitar. I suppose it is conceivable that the wood itself is moving after being worked... just to drive you nuts! I admire you jointer-users and planers... I could never finish this off with either one.
Same...I have to finish off a top seam with sandpaper and a straight beam, but they do come out perfect in the end
 

the great waldo

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How much light? Light is able to pass through a gap of less than a thousandth of an inch. It's also common in some areas of woodworking to "spring" a joint, where there is a hollow of a couple thousandths in the middle. This is then clamped out and helps ensure that ends don't come apart.

In short, if it's the faintest amount of light and in the center, you could probably go with it.

For perfect joints, nothing beats a sharp hand plane.
I think a spring joint is ok for a piece of wood that is 10x10cm but a wide board like a maple les paul top means your'e going to have to clamp the hell out of it to get it to glue correctl. A good joint with no light showing through is the way to go. Using a sharp plane (i've got a pile of those wonderful veritas low angle planes) will get you there although with figured wood I always liked to finish with a sanding beam. The spiral jointer pretty much solved all my jointing problems with curly maple. I think the slight roughness finish from a sanding beam (depending on which grit you use) gives a little bit of a cushion to glue with, giving a tight joint (thats just my theory)
Cheers
Andrew
 

pshupe

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The more I learn about woodworking in general the more I know what is acceptable and what is not. There have been a lot of posts lately, or maybe I am just noticing them more now, that deal with degrees of accuracy. I think we tend to over think things and in some cases way over think things.

The first few tops I glued up I was using the light method and struggled slightly to get the joint perfect. After quite a few more tops and bodies and other general woodworking joints, I never check with light. I use the same method every time and it does not fail me. I joint both edges making sure the fence on my jointer is perfectly square, once set I find I do not move it or even check it. Setup my clamps and dry fit my joint. Where I used to take 3 or 4 passes with my jointer and check with light, now I only take 1 or 2 passes and just dry fit. I apply a little pressure to the clamps and I can tell instantly if the joint is good enough or not. Would I see light through that joint, I don't know, probably in some cases. Carve tops are quite thick and as long as the faces are square you can apply a lot of pressure with bar clamps. Depending on grain orientation my joints are almost invisible.

IMG_0695.JPG


This is my typical setup and I have glued up dozens of tops without issue. With the clamps on the joint at each end I ensure the mating surfaces are flush and I have a nice flat surface. Also on thinner material like 1/4" it holds the flat surfaces together so you can get decent pressure on the thinner material.

The take away is the joint does not have to be absolutely perfect but it is somewhat subjective as to "perfect".

Cheers Peter.
 

dcomiskey

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A perfect joint, IMO, should not have ANY light coming through. I have a new jointer with spiral head and it's the best machine I've ever bought, outside of my band saw. Set up and used properly, you should have absolutely perfect joints. I now get perfect joints for tops and bodies.

One issue I've had many times in the past is that I'll buy a bookmatched top and they'll sit on the shelf for months/years and I notice that they all tend to bend/warp slightly in that the joint is open slightly in the middle. Worse case is I just re-joint it and it's good to go.

Anyway, if there's light coming through, it's not straight.
 
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VancoD

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If you run a piece through the jointer repeatedly and still find you're getting "light in the middle" I'd suggest that you insure you are only applying pressure to the workpiece on the outfeed table side. If you're pressing it down on the infeed side as you joint it's possible you're actually inducing the defect every time.

A shooting board for sanding isn't a hard tool to make - I'd suggest that too. I went to my local Menard's and got a nice piece of Corain countertop from their odds-n-ends department and it was a great base for a shooting board. If I were doing it again I'd probably use MDF - the Corian isn't quite thick enough to sink T-track into it and maintain structural integrity, and that would make clamping much easier.
If you do go with Corian and decide to route a channel for the "shooter" (as you should) be sure to have a really good vacuum setup on your router - because there will be an absolute BLIZZARD of Corian chips and the static from routing will make them stick to everything in a 5 foot radius.

YMMV.
 


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