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Keep getting gaps when laminating necks


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Mating surfaces (one or both) on the left hand laminate could be slightly convex.

Could be some foreign material contaminating the joint before clamping, stopping the two pieces from meeting flush. Maybe some wood shavings, dried glue from the bottle, dirt etc?

Insufficient clamps or uneven clamping force distribution.

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On 4/24/2021 at 9:58 PM, curtisa said:

Mating surfaces (one or both) on the left hand laminate could be slightly convex.

Could be some foreign material contaminating the joint before clamping, stopping the two pieces from meeting flush. Maybe some wood shavings, dried glue from the bottle, dirt etc?

Insufficient clamps or uneven clamping force distribution.

Looks like I needed to plane multiple passes after jointing slightly bowed boards.  More even glue coverage probably helped. I did another neck and it has came out well.  Will post pics tonight.

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  • 3 weeks later...

Did another few necks, trying to get good/consistant/eliminate variables. 

Last two necks have the same gap as the first pic.  I wonder if I'm using too much glue?  I lay down 5 * 2mm beads of glue over each piece of 2.5" wide  wood, then spread it with a spackle tool/joint knife.  

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There's a million ways to spread glue, most of which are correct. Fingers, brush, credit cards, joint knives... You mention it.

If you're uncertain, a toothed joint knife of sorts is your friend. Builders use glue spatulas all the time as the glues used for flooring can be pretty stiff and the amounts are huge. The right amount is measured by the size of the teeth. For guitar building the tooth size of the spatula should be something like that on a hobby saw, about 15 tpi. You can easily make one yourself of an old credit card.

The right amount of glue is when you get a thin bead of squeeze out all along the seam. No squeeze out means there's no glue there. Lots of squeeze out means lots of extra work to wipe the excess off plus wasted money since you can't usually put the glue back into the bottle. Also remember that wood glue isn't a filler. Perfectly matching surfaces with an invisible film of glue in between is what we're after. Some pressure is needed to keep the pieces together while the glue dries. In theory it's possible to squeeze all of the glue out of the joint so don't overdo it.

Clamping is not the right cure for curved boards unless you can squeeze the gap tight with your fingers when dry fitting.

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Posted (edited)
16 hours ago, Bizman62 said:

There's a million ways to spread glue, most of which are correct. Fingers, brush, credit cards, joint knives... You mention it.

If you're uncertain, a toothed joint knife of sorts is your friend. Builders use glue spatulas all the time as the glues used for flooring can be pretty stiff and the amounts are huge. The right amount is measured by the size of the teeth. For guitar building the tooth size of the spatula should be something like that on a hobby saw, about 15 tpi. You can easily make one yourself of an old credit card.

The right amount of glue is when you get a thin bead of squeeze out all along the seam. No squeeze out means there's no glue there. Lots of squeeze out means lots of extra work to wipe the excess off plus wasted money since you can't usually put the glue back into the bottle. Also remember that wood glue isn't a filler. Perfectly matching surfaces with an invisible film of glue in between is what we're after. Some pressure is needed to keep the pieces together while the glue dries. In theory it's possible to squeeze all of the glue out of the joint so don't overdo it.

Clamping is not the right cure for curved boards unless you can squeeze the gap tight with your fingers when dry fitting.

Thanks man.  I'm never sure just how complimentary they should be.  

 

I just processed wood for a neck yesterday.  I jointed each piece while checking in between passes by drawing a squigly line on the face I was jointing.  I have not done this before but I think this is going to help a lot more than relying solely on my 4' level to test for straightness.  After I got one face of each board jointed this way, I planed them in my planer using the same squigly line method.  Then I finally planed them to the desired thickness.  All in all, it seems the boards sit very tight with no cupping or warping.  I buy s3s poplar so I expect to have to process it quite a bit.  I numbered the boards so I knew the orientation in which I checked fitment.

 

This time I used a contact cement adhesive roller to apply the glue across all boards simultaneously accept one.  It looks very consistent.  Hopefully all this effort will result in a better neck.  

Additionally I used my bad neck blanks to make multiple neck jigs, so now I got clamps on top and bottom.  I got about 32 clamps on there, but that's because the 4" clamps I use will only do about 300lbs of force.  

 

I really hope this works lol.  I started with a 12'x12"x7/8" board that was warped quite a bit.

Edited by thekt88killedjfk
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Posted (edited)

Okay okay okay looks like I did not use enough glue on the previous necks but this one came out great.  For whatever reason, I struggle with getting the right amount of glue but it looks like I really should be applying a 3/32" to 1/8" bead for every half inch width.  I've seen some youtube videos advocating for as little glue as possible, but they were probably assuming people were putting down larger beads.

 

I built a 12 ton neck press out of 4x4 steel square tube and bottle jacks and even that wasn't enough to squeeze all the glue out.  12 tons at ~200 square inches still is on the low side of the recommended pressure by glue companies, so I'll probably add more bottle jacks lol.  Unfortunately the square tubing I am using is slightly bent, about a 1/16" over 48" so I can't really use any neck I press on it.  I just wanted to eliminate pressure as a variable.  

 

Last night I didn't use the press at all.  I just used the two neck jigs I mentioned and 32 clamps.  Neck is straight and gap free.  I'm gonna machine that neck press down flat and parallel, though.  It was too easy to use.  

Edited by thekt88killedjfk
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2 hours ago, thekt88killedjfk said:

looks like I did not use enough glue on the previous necks but this one came out great.

That's good news! You're learning! A semi-see-through film on both surfaces is fool proof, the same on one surface should suffice when you know how much is enough. Rather a bit too much than too little. And I repeat, don't overdo with the pressure. For what I've heard a perfect joint should be doable even without clamps! That said, even high end professionals use them just for sanity as you never know how the wood will react with the extra moisture of the glue. The high pressure clamping systems are for industrial thicknesses where 2x4" blanks are glued to beams up to 10x50" or even bigger.

 

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  • 2 weeks later...
On 5/15/2021 at 1:27 PM, Bizman62 said:

That's good news! You're learning! A semi-see-through film on both surfaces is fool proof, the same on one surface should suffice when you know how much is enough. Rather a bit too much than too little. And I repeat, don't overdo with the pressure. For what I've heard a perfect joint should be doable even without clamps! That said, even high end professionals use them just for sanity as you never know how the wood will react with the extra moisture of the glue. The high pressure clamping systems are for industrial thicknesses where 2x4" blanks are glued to beams up to 10x50" or even bigger.

Oh yeah no way I'm gluing two pieces of wood together that I didn't think jointed perfectly before.  We're on the same page on that.  Thanks man.  

 

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