One more time, singlecut

[Andyjr1515]

I've been umming and ah-ing about a proper mitre box for a while....I think this has convinced me that it is something I need.  Not want, you understand....need 

[Prostheta]

Agreed. I recommend them, especially Carlos at Guitars and Woods. He's done a lot to build his business and he's really putting out quality stuff at prices which are reasonable. Check out his radius beams. I got one of those and they're gems.

[Andyjr1515]

2 minutes ago, Prostheta said:

Agreed. I recommend them, especially Carlos at Guitars and Woods. He's done a lot to build his business and he's really putting out quality stuff at prices which are reasonable. Check out his radius beams. I got one of those and they're gems.

Yes - that's where I got my acoustic neck templates,,,very good quality and super-fast delivery 

[Prostheta]

Yeah, he's communicative as well. That makes the key difference with vendors. If they take the time, it makes a world of it.

[psikoT]

That was the shop where I bought it, also the radius beam and some other cool stuff... I highly recommend it, if you live in Europe.

The mitterbox is the most expensive thing they have, but it's worth every cent. 

[psikoT]

So finally I could manage to get a 0.8mm stripe of mahogany to bind the fretboard. The outer binding is wider than needed, I will trim it together with the neck once it's glued, I think...

Next step is cutting the shape of the headstock before gluing the fretboard.

I really would love to cut the joints at 45 degrees, but I have no time for such details...

[KnightroExpress]

This is going to be a stunner, I can already feel it.

[Prostheta]

Definitely. That's a classy look to the binding with the accent line. Always looks good.

[ScottR]

I love the wood choice for that fretboard!

SR

[psikoT]

Thanks guys!

I'm currently the hell busy at work, but still scratching some spare hours here and there to continue with this. The neck is waiting for me to print the headstock and make the template (the easiest tasks always require more time) so I've switched to the body.

Looks like I did nothing, but there are a lot of hours behind these three pieces, and still need some more... now they have a regular thickness and the halves are glued. They "just" need the final sanding before gluing. Not sure if I've already mentioned, but the top will be a 3 piece sandwich (rosewood-mahogany-rosewood) with a subtle carving.

My main concern now is about how to glue them together in a nicely way, without any gap. I was wondering if it's better to glue them as they are now, in a square shape... or should I cut the rough shape of the body contour before gluing? Another question I have is if it's better to glue them at once, or one after the other... 

And of course, any advice, warning, suggestion, trick or opinion about the clamping process is very welcome. I was thinking on the curved sticks but that requires a lot of work. I have a bunch of clamps and an old heavy 20 kg. mac pro... I was even thinking on putting a board and sit myself over it for 30 minutes, which is the time that Titebond needs to dry... 

[ScottR]

I would cut them roughly to shape first--less to sand and less to clamp.

SR

[Norris]

15 hours ago, ScottR said:

I would cut them roughly to shape first--less to sand and less to clamp.

SR

Plus you can clamp them near the final edges - where you would see a glue line if there is any gap

[Prostheta]

You're laminating three boards together? That's not an easy task. Remember that clamping hardwoods needs around 100-300PSI depending on species and growth ring orientation. In that respect, reducing the footprint helps apply more pressure to the end product and not the waste. Still, a guitar body has a significant area which still requires several tons of clamping pressure to be "perfect". Since they're thin boards, you'll need thick clamping cauls either side to ensure good distribution of pressure.

If I were laminating three boards onto a body blank using clamps only, I would do them one at a time. That way the clamping pressure is working on one glue line at a time, rather than being frittered across many.

I wouldn't cut the boards too close to the finish size in case of any slippage. Hydrostatic pressure and glue lubrication makes the workpieces very slippery and prone to misalignment, especially under high clamping pressures. A little additional material also helps if you are hand-sanding the surfaces between glueups. Invariably you get a little rounding over at the edges which can result in glue lines or gaps.

The alternative is to leave the laminations as they are without cutting them up, and simply shape your caul a little larger than the body. It'll apply pressure where it's needed rather than diffusing it over a larger area where it isn't.

Dowelling the glueup into the neck pocket, pickup holes or in the waste areas will help prevent slippage of course.

[Prostheta]

Quick illustration; let's say that a guitar body is 300mm x 400mm. That's 1200cm² or 186in². At the lower end of the clamping pressure (100PSI) that's 8,4 Metric tonnes. A little more than your Mac Pro.

A medium-duty Bessey F-clamp is rated at 1000lbs-1320lbs of pressure. You're going to need over a dozen of them around the glueup.

http://www.besseytools.com/en/product_details.php?ASIMOID=000000010003893000020023&ASIMOID_SC=000000000001f21d00030023&ASIMOID_MC=000000000001f3f000030023

 

Remember that I am speaking only from the standpoint of how the numbers stack up. Going lower than that will likely still produce a good end result. In my opinion, it's good to know how far one is from the ideal in order to do the best with what one has available at any given time.

[psikoT]

Hi guys, thanks for the input... that helps a lot.

I'm gonna cry to a corner and think about, I'll come back in a while. 

[Prostheta]

Better than jumping into the job and letting it do what it wants. I think that you can leverage more pressure using those convex wooden cauls....the tension in those is quite high.

[psikoT]

15 minutes ago, Prostheta said:

Better than jumping into the job and letting it do what it wants. I think that you can leverage more pressure using those convex wooden cauls....the tension in those is quite high.

Yeah, it seems to be the best option... got a bit shocked with your numbers and need some time to recover. Never realized that clamping pressure was so high, and that changed my mind completely. Thanks very much for the info!  

[Prostheta]

It's simply a good guideline to aim for. Doubling surface area halves pressure, so you can see how several tons soon no longer feels "massive". They're just numbers. A dozen medium duty clamps easily do what you're needing.

[Prostheta]

F clamps are powerful things.

[psikoT]

Ok, so I just tried to figure out how it should be... 8 pine cauls, about 30mm width, separated enough to place a clamp in between and also those areas which can not be covered by them. Am I in the right directon?

[Prostheta]

I don't think they'd all need to be concave. Only the longest six. The other two are fine flat. The most important factor is that the pressure is high enough at the edges where it would be most visible. I think 30-20mm is a large convexity to be using, however I have yet to put any of this to practical test as of yet. Making convex cauls is a bit of a crapshoot unless we know the length, cross sectional area ofthe caul, and the material's compliance. Check these out for a better idea (about 0:35 onwards):

 

The compliance of the metal used in those cauls will have been precisely calculated to produce 220PSI of pressure at the centre when forced flat by the two edge clamps. 220PSI is right in the middle of the 100-300PSI rule of thumb that most hardwoods are within. Softwoods likely top out around 200-250PSI. Not sure of their general range.

Marketing wank for Bowclamps. Same kind of idea:

 

The problem is that unless we can calculate the compliance and point where the Pine exceeds its optimal range in its modulus of elasticity (I think that's right) we can't tell whether it's applying the right amount of force in the centre.

 

We're certainly in danger of overthinking this, and I hope I haven't opened a can of worms that didn't really need to be....however you know what I'm like. I love ideal like the convex clamping.Often simpler (but well considered) solutions are the best solutions. If you're going to use that convex caul arrangement, you've obviously got 12-16 clamps? A large flat caul over the entire thing is more than satisfactory. Just place the clamping points a few of centimetres in from the edges where it's most important. The caul should be stiff enough to distribute the pressure around the area well enough, even if not perfectly evenly.

If the thin boards are being laminated on top of a thick body blank, then a large thick flat board as a caul on top with a thin protective caul under the blank is as simple and predictable as it gets.

[Prostheta]

Incidentally, if I could figure out a way of selling a stick of wood at a few thousand percent markup....

[psikoT]

Thanks very much for the info, I really appreciate it. If you don't open that can I probably would have wasted a bunch of euros in wood.

I was worried about that because in the last (and first) top I've glued, I got a gap in the edge at some point, but now I'm checking the pictures and noticed that I didn't use enough clamps and focused mostly on the inner part than the edges. I think I can solve it just covering all the perimeter - as you guys said - with my small clamps and buy some wider ones to make pressure in the center.

Those commercial cauls are too big anyway, maybe you can patent a smaller one specially for guitar building and sell the idea to Stewmac. I can see you enjoying your retirement somewhere in the Caribe, just think about... ^^ 

 

[SIMpleONe89]

So what's the minimum number of cauls for clamping a top? And should they arranged length wise or width wise?

[Prostheta]

11 hours ago, psikoT said:

Those commercial cauls are too big anyway, maybe you can patent a smaller one specially for guitar building and sell the idea to Stewmac. I can see you enjoying your retirement somewhere in the Caribe, just think about... ^^ 

 

What? Invent something and make it so that it is not possible to use it unless you pay a third party a huge amount of money to access it? That's totally the opposite of what ProjectGuitar.com is about! I'd rather open-source the idea so that it can be accessed, improved and developed by all. Not interested in retirement on a beach. Just not my thing, man.