best way to join wood

[Larry Wyble]

I'm new at wood working and have a question.
I have 2 pieces of 6" x 4' x 3/4" that I need make one piece of 12" x 4' x 3/4"
out of. What is the best joint to cut on the edges for this operation?
And what is the best proceedure. IOW, how to actually do the cutting?


Thanks

[glenn bradley]

Depends. Don't you hate that answer. If the 12' span will be supported (like an apron or backed with studs) a simple opposing 45* edge will give you some increased glue surface. This type of modified butt joint will not take free weight stress however. That is if the joint will be in the middle of a 10 foot unsupported span, it will fail.

We can help better is you can describe what the 12' piece will be used for and mounted too?

[John Hain]

I think he's making a 4' long 12" wide board.

In this case, just a standard long-grain to long-grain joint will be fine.

You need to choose whatever tools you have to give you 2 parallel surfaces, whether that be a jointer, TS, CS with straight edge, or handplane.

[glenn bradley]

Oooops. Read Bradley, read! Second cup of coffee kicked in. John's got it.

[Shane Newlin]

What are your options? Table saw, biscuit joiner, router, jointer, etc.?

[Andrew Williams]

This may be a neanderthal answer but the cheapest way is with a long handplane. Just put the two pieces in their glue-up orientation, fold them closed like a book, and plane the mating surfaces at the same time. The resulting edge joint will cancel out any error making a perfect flat joint. Test the joint by eye to make sure there is no daylight coming through, then glue and clamp the boards. I don't feel that biscuits are necessary with a well-jointed long-grain to long-grain adhesion.

[Larry Wyble]

What are your options? Table saw, biscuit joiner, router, jointer, etc.?

I am building a guitar body the joint has to be strong. I have table saws, routers and 6" x 4 ' jointer. What I was thinking was to cut a groove in one piece in the center and a land in the center of the other and glue/fit the 2 together. Sorry if groove and land isn't the right words I'm more of a gun barrel proficianado. :D

But I'm not sure how to center things up for the cuts so the edges fit perfectly together in the end.


Thanks

[Ellen Benkin]

If, as we assume, you are joining edge grain to edge grain, this is a relatively common procedure. For example, most table tops today are made from several boards that are glued up. First joint (flatten) the two edges that will be joined. You can do this using a joiner or a plane. The two edges really have to mate together very well to hold the join.

Put the boards in the orientation you want and mark them with a couple of lines going through the joint to make sure you get them where you want them when you finish.

Now you can just glue them together using standard wood glue and lots of clamps. This will make a good joint, but not the strongest. You can reinforce the joint with dowels or with biscuits. If you have access to a biscuit joiner, that is probably the easiest way because the machine automatically lines up the slots and the biscuits give you a little wiggle leeway to get the boards exactly where you want them. If you use dowels, you should probably have a doweling jig to make sure the holes are straight and line up vertically across the boards.

Good luck with your project.

[James Phillips]

Depends. Don't you hate that answer. If the 12' span will be supported (like an apron or backed with studs) a simple opposing 45* edge will give you some increased glue surface. This type of modified butt joint will not take free weight stress however. That is if the joint will be in the middle of a 10 foot unsupported span, it will fail.

We can help better is you can describe what the 12' piece will be used for and mounted too?

I Disagree. If it is unsupported the wood will fail, but not the glue joint. A long grain to long grain glue joint is stronger than the wood it joins.

[Jim Becker]

IMHO, a simple glued butt joint is the right method for the need described. If the edges are properly jointed, the glue-up will be invisible outside of grain differences between the two boards.

[John Michaels]

Two different ways I might do this.

1. Cut a piece of plywood about 12 or 14 inches wide and 5 feet long. It's important that one edge of the plywood is very straight because it needs to run against your table saw fence. Use a hot glue gun to adhere one of the 6" X 4' pieces to the plywood so it hangs over just a hair opposite the straight edge of the plywood. Now cut it on the table saw (sharp blade is important). Now you should have one very straight edge on your 6" X 4' piece. Pry off the board and repeat procedure to the other board. Now it's time to glue them together. I'm not sure if using a biscuit joiner really makes the joint any stronger, but it does help with alignment.

2. Buy a glue joint router bit (sometimes sold in pairs) and make the glue joint. If your boards don't already have at least one very straight edge on each, go through step 1 above.

I also have a 6" jointer and have found that step 1 yields better results than what I can accomplish on a small jointer.

[Andrew Williams]

If you are building an acoustic guitar then you absolutely must not use anything but a butt joint. by the time you carve the plate out of your back or top blank, the biscuits or splines will show, ruining your piece. If you are building an electric guitar, it might be ok to use a reinforced butt joint, but I have never heard of a 3/4" thick body on an electric guitar. They are usually much thicker than that. Besides, after routing out all of the guts and the dovetail for the neck, you will have splines showing everywhere.

just my .02










I am building a guitar body the joint has to be strong. I have table saws, routers and 6" x 4 ' jointer. What I was thinking was to cut a groove in one piece in the center and a land in the center of the other and glue/fit the 2 together. Sorry if groove and land isn't the right words I'm more of a gun barrel proficianado. :D

But I'm not sure how to center things up for the cuts so the edges fit perfectly together in the end.


Thanks

[Larry Wyble]

If you are building an acoustic guitar then you absolutely must not use anything but a butt joint. by the time you carve the plate out of your back or top blank, the biscuits or splines will show, ruining your piece. If you are building an electric guitar, it might be ok to use a reinforced butt joint, but I have never heard of a 3/4" thick body on an electric guitar. They are usually much thicker than that. Besides, after routing out all of the guts and the dovetail for the neck, you will have splines showing everywhere.

just my .02

Actually it's a semi hollow body, I'm using 3/4" x 8" boards put together to form 1-1/2" x 16" body that will have the innerds routed out except for the center where the neck, bridge, and pickups will go. then there will be a carved top of 3/4" that will be glued on after the routing of the interior. I'm having to use 3/4" x 8" x 4' boards to build all this because there are no quality hardwoods that are thicker than 3/4" unless you want to pay like $ 300.00 for it, and I don't. ;)

These are tone woods and large chunks of this stuff are costly. That's why it's best to buy the smaller pieces and build up from there.

Thanks

[Fred Voorhees]

This may be a neanderthal answer but the cheapest way is with a long handplane. Just put the two pieces in their glue-up orientation, fold them closed like a book, and plane the mating surfaces at the same time. The resulting edge joint will cancel out any error making a perfect flat joint. Test the joint by eye to make sure there is no daylight coming through, then glue and clamp the boards. I don't feel that biscuits are necessary with a well-jointed long-grain to long-grain adhesion.

Andrew, I'm not taking you on personally, but you bring up a theory that maybe I've never completely understood, or maybe I just have a different opinion of it. You say to take the two boards and put them in the proper orientation and then fold them closed like a book. Using a hand plane, on both edges at the same time.....let's say as in the first picture below, you have a depression, ever so slight, but a depression all the same. You claim that it would cancel each other out. I beg to differ. Any variance from perfectly straight will, when aligned with its mate, serve to open up a gap that is TWICE the amount of the variation from straight. I fail to see, how planing two boards together side by side will allow any differences to "cancel each other out". It just doesn't seem right and I have seen this theory mentioned time and time again and I just don't subscribe to it.

If I'm wrong, someone point it out and explain.

[Greg Funk]

Andrew, I'm not taking you on personally, but you bring up a theory that maybe I've never completely understood, or maybe I just have a different opinion of it. ...It just doesn't seem right and I have seen this theory mentioned time and time again and I just don't subscribe to it.

If I'm wrong, someone point it out and explain.

It won't cancel out depressions but it will cancel out edges that are not perfectly square.

Greg

[Bryan Berguson]

Larry,

I'll add to what Ellen wrote. Lay your boards together the way you want to join them. Mark them in some manner so you put them back together that way. When you joint them on your jointer, one board should have the good face against the fence and the other board should have the "bad" face against the fence. This way, if your fence and table aren't perfectly 90 degrees, it won't matter, the difference will cancel out and you'll have perfectly parallel edges.

With flat boards and the right clamps, you may not need dowels or biscuits. Start clamping in the middle and make sure your edges are together. When you get to the ends, you can always put a clamp directly on the joint to make them perfect.

Bryan

[Randal Stevenson]

Doesn't anybody watch Red Green?



Duct tape.:eek::D

[robert micley]

i have used biscuits and dowels for many applications.when gluing boards together for panels in doors or table tops i just use glue and clamps.i have never had them fail.it is great to have a perfectly joined edge but even if it is alittle off i have not had a problem with failed lines.you can see daylight through 1 thousand of an inch so a few spots with a little light like 1 over 200 of an inch has not been a problem with my glue ups.more important to me is to have a 90 degree angle to the face.otherwise the two edges will not be touching completely or you will bow the wood and change the flatness of the top.

[Shane Newlin]

Larry, if there is one thing I could tell you to do, it would be to spend 4 to 5 times as long making a jig for whatever you do, as you do making the joint. Support support support. A well made jig will pay for itself, especially considering what you are doing. Kudos to you for aspiring to be a luthier. I am a guitar player myself, and consider it an awesome project. Play on!!!

[glenn bradley]

Correct James. I misunderstood it to be an end grain to end grain joint to create a long board. Again, my apologies.

[Andrew Williams]

This is too complicated to describe when I am sure that a video would make all the difference. It may seem counter intuitive, but believe me when I say that I have successfully jointed edges on many many boards this way. The only time when I have to do any additional work is if each board has a convex bow on the joining edge. The bow must be removed before anything else. Once you do it a few times it becomes faster than setting up the power jointer.





Andrew, I'm not taking you on personally, but you bring up a theory that maybe I've never completely understood, or maybe I just have a different opinion of it. You say to take the two boards and put them in the proper orientation and then fold them closed like a book. Using a hand plane, on both edges at the same time.....let's say as in the first picture below, you have a depression, ever so slight, but a depression all the same. You claim that it would cancel each other out. I beg to differ. Any variance from perfectly straight will, when aligned with its mate, serve to open up a gap that is TWICE the amount of the variation from straight. I fail to see, how planing two boards together side by side will allow any differences to "cancel each other out". It just doesn't seem right and I have seen this theory mentioned time and time again and I just don't subscribe to it.

If I'm wrong, someone point it out and explain.

[Eddie Darby]

I am building a guitar body the joint has to be strong. I have table saws, routers and 6" x 4 ' jointer.
Thanks
I would set-up my router in a table with a fence and have the fence set for joining. I would have the difference between the infeed and outfeed set at a very thin amount, so you are taking a very thin chip. Set the router on the highest RPM setting that is safe for the size of bit you run, and feed it in slowly.

The advantage of the router method is the high RPM that it offers over the lower number that a jointer offers.

Hold the two plates together, up to the light and see if any is coming through. There should be none. This is perfect wood to wood contact.

Since a guitar top is very very thin, the glue will be so much stronger than any force that you can apply to the top. The weakest link will be the wood itself, which will break way before the glue even knows it.

Do a test run with some small pieces of wood and try breaking the joint. You won't be able to. The wood itself will break.

To check a glued joint after glue-up, take a gouge and remove a chip that goes across the glue-line on one of the waste ends that will be cut away later, and bend it and see where it breaks. It should break in the wood and not at the joint.

Here is a forum that has a lot of good info on making instruments that might be helpful to you.

http://www.mimf.com/

[Dennis Peacock]

Wow.....ask 25 woodworkers about a glue joint and you can get over 50 different answers. :rolleyes: :p :D

Y'all keep on goin'.....I'm getting a little more edumuhkation here. :D

[Howard Acheson]

To add to Jim's answer. there is no edge to edge joint stronger than a flat, smooth edge to edge to edge joint. No reinforcement addes to the strength.

[Joe Spear]

If you have a good glue-joint rip blade or a Woodworker II, just doublestick tape them flat side to flat side and rip one edge of the double layer. Unstick them, flip the two pieces open as described by Bryan Berguson, and glue them up. Clamp moderately tightly every 6 inches or so. You don't need biscuits, dowels, or anything else besides the glue. I've done it that way 13,475,816 times (a slight exaggeration). Acoustic guitar tops and backs are joined that way, and they're roughly only 1/8 inch thick. You can also plane or rout, but the secret is doing both edges sandwiched together at the same time, face to face or back to back, so that any slightly deviation from 90 degrees will be canceled out.