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Hi.

Quick Question. I joined a test top - all looked pretty good. The next day, I was flexing the top, and the joint popped loose. I figured 1 of 2 things happened:
- I flexed the top too much
- Or, My joint was never very good.

Should I not flex the top until the bracing is on? or should I just go on to another knowing my joint wasnt good, and to try to get it tighter.

Thx!

Glenn

Sounds like a poor glue joint....Curious, what type of glue did you use? How did you prepare the edges, and what method did you use to clamp them? How thick were the 2 plates when you joined them? When the joint popped loose was it strictly glue failing or did any wood pull off as well?


GG

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Gwaltney Guitars

It sounds like a poor glue joint to me too. Greg G. asked all the right questions Glen.
You must have a perfectly tight joint with no light whatsoever getting through .

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Anderson Guitars
Clearwater,Fl. 33755

Good questions

I used Titebond

I used a Record #5 and shooting board

I clamped using the method found here: http://soundsalon.com/2007/02/12/make-a-joining-board/

I was fooling around with the thicknessing (as this was just a test top). I never looked at the thickness, but it was ~.150

When the joint failed, it was glue, no wood pulling off

After answering the questions, soounds like a bad joint. It looked pretty darn tight though - no light showing through. I will chaulk it up to inexperience, and do another test join (I have another defective top). I think I will join the top thicker.

Thx!

Glenn

Just keep using this first top. 0.150 is fine for the thickness to join. Keep using this top till you get it right. Than if you want to, cut the top in two and join it again, than again etc... If the top is just practice, keep cutting it apart and joining it again. It will help you get your jointing done well, you gluing and clamping too.

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"There's really no wrong way, as long as the results are what's desired." Charles Fox

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I always try and get an off-cut of the centerline area above and below my body outline. I will then test the glue joint - if it breaks cleanly, then the top needs to be rejoined.

Does the dried glue look chalky? If it does, then your glue was bad. The first time it happened to me I figured that I left the bottle in the shop one night when it dropped below freezing. The second time it happened, I knew it wasn't what I had done. Someone pointed out that it might have frozen during delivery to the store or just been old.

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Aoibeann

It does sound like a bad joint. Test or just toss out that glue and get fresh. Glue is cheap, no reason to risk bad joints due to glue that has gone bad.

Rich

Thanks Lillian - if the joint candled well, was clamped correctly and still failed the Titebond is suspect. Good call!

Glenn, I rigged up a light table, a piece of plexiglas over a fluorescent work light, and when just the slightest hand pressure closes off the light leak, I con sider the joint ready for glue.

Then there's clamp pressure. The titebond website says tb wants from 100 psi (low end with softwoods) to 250 psi (high end for hardwoods) in the joint. Now, people have sucessful joints clamping with masking tape - I have, or maybe they are merely adequate for the application - but I think these pressures are good to shoot for.

The problem is, that floppy sheet of spruce just won't survive those bar clamps. 0.150 is only 15% of a square inch per linear inch of joint, and you're going to want about a 100 psi for every 6 inches or so of top joint.

This is my clamp. Four plywood bars are set into dados in a 2 X 6, and long low angle wedges tighten the twisted ropes. All the glue contact surfaces are covered with packing tape for glue resistance.

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Dan
http://www.acme-archtops.com

I am about 1000% sure it is not the glue. If the joint was prepared properly even stringy old yellow glue would most likely work fine. (Don't recomend it, it is just that the glue is very low on the list of potential problems) One thing that is very important and I don't see it done enough is to wet out both sides of a glue joint. You need penetration and by wetting both sides you go a long way to insure that. You use less glue with less sqeeze out as well. Slapping a bunch of glue on one surface is not a good practice.

The thickness or thinness of the wood is not a issue. I regularly edge glue 1/16" veeners with yellow glue and plain masking tape to clamp with joints that are as strong as the wood. With the thickness of a top or bottom plate of a guitar I would use a simple system of wedges to clamp.

I don't get this candleing thing. Holding two thin boards up to a light is awkward at best. I don't see it as that reliable and the angle you look at makes a difference. Maybe the slide table light thing might work but I don't see the point when all you have to do is lay you two boards on a flat surface and with light finger pressure push together. You will see a thin black line if your joint is not tight. If you push or tap on the joint and the two pieces move without binding then your joint is bad. I like for there to be the slightest opening in the middle of the edge joint. Such that very light finger pressure will bring the joint. I mean slight and light pressure. When your joint is right you can not see the seam, even with magnifing glasses. It is easy to see when it is not together.

You scare me with the shooting board thing. What do you mean. If by a shooting board you are using the edge of some wood or plywood to guide the plane I think this is a mistake. Lie-Neilson went to great effort to make the sole of the plane flat. Use the plane sole on the wood to be jointed. Let the nice machined flat sole of your plane do it's job. I have seen it recomended to use a shooting board for edge jointing. Not a good idea. Shooting boards are typically used with a stop and used to shoot the ends of boards. Mostly end grain. Usually just a few inches of board.
For edge jointing all you need is a flat surface for the side of the plane and another board to elevate the work high enough to contact the cutter.

Are you jointing the boards so that any angle of the cutt by the plane is complimented on the other half of the edge joint ? Lay your two boards down so that they are as they will be on the guitar. Mark the faces. Now fold them together so that the two faces that will be the top of the sound board are next to each other . In this arrangement you could joint them both at the same time. If your plane or jointer wasn't set to exactly 90° it doesn't matter. When you unfold them the two edges will compliment each other. One might be 92° the the other would be 88°. But you can see if you don't arrange them properly and your plane or jointer fence is off you will have a gap. So get this part right and concentrate on shooting the joint.

As you start to plane the joint put pressure on the front of the plane, then center your pressure, and as you exit the end of the board move the pressure to the back of the plane. This will become automatic after a while and should be a habit for any type of hand planing. If you are still having problems with this after a few more attempts P.M. me and we can talk on the phone. I can definitely help you. It is a lot easier to explain verbally. My writing skills are not up to my verbal skills. I haven't done a very good job of explaining I know. Lets not even talk about my spelling.
Link

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Cut to size.....Beat to fit.....Paint to match.

Does anyone have a light table built into a workbench? There is a guy in Minnesota who did that. Hoffman I think.

I like Kinkeads method, you put a 3/8 bar under the plates so they match up and clamp side bars down, then remove the 3/8 bar, and weight down. Easy to do.

I think I would like a light table also at this point.

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Here is what a Parlor Guitar is for!
http://www.youtube.com/watch?v=oEa8PkjO6_I

For my light table if it is dark out I candle on my wide screen HD TV while watching Fargo...... Seriously.

Thanks for all the replies and suggestions.

Is there any preference for either LMI white or titebond? I have both (fresh bottles).

Thanks again!

Glenn

No - both are great glues. The only thing to know is that LMI has half the shelf life, 6 months, as Titebond. I think that LMI dries a bit harder then Titeblond too.

I would have used LMI more often except I always kept forgetting to order it from LMI and I can't get it anywhere else.

Consider using HHG as well - it's not difficult, has advantages over both of the above, and IMHO is a joy to use.

Don't you ever go to bed Hesh?

Dave F.

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Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

So, uh... that yer top in d' chipper, there?

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Jim Howell
Charlotte, NC

Oh, how long was it glued up until it broke during the test
? My test top did the same thing, although I got some wood along the joint, and it was a week old at least.

I'm wondering about the basic rule here:

The WOOD should fail somewhere along the grain, NOT the joint, if its a good joint? I will be testing out my glue up skills with a test top, breaking the joint.

Also: What is considered extreme in terms of flexing?

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Here is what a Parlor Guitar is for!
http://www.youtube.com/watch?v=oEa8PkjO6_I

Yes is the joint is good, you need to see a lot of wood fibers ripped from either side, or likely a completely new break line.

As to what is extreme flexing. Usually, a thin plate of wood will bend with some very moderate pressure. It will move for a while under that pressure and at a certain point, you will feel it suddenly because much harder to bend. This is the point where adding more pressure will give you only a very small amount of movement - while the wood feels quite rigid - at this point continuing to put pressure will likely snap it.

And in other words, take it very slowly, and don't fight it

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Build log

Yep bad glue joint. enven if the glue was old and somewhat week. if it broke on the seam then the joint was not properly fitted and clamped. when 2 pieces of wood are glued up, cured, then stressed to the breaking point the wood should break one side or the other of the glue joint and never in the glue joint its self. Heat stress is a totally diffrent issue but in tension, compression a and radial stress, a glue joint will be stronger than the wood unless the joint is fitted.