Further J45 questions

You can ask questions here about Trevor and Gerard's exciting new book on Luthiery.

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Richardl
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Further J45 questions

Post by Richardl » Sun Jun 17, 2018 5:18 pm

Hi again

I'm in the process of making the headblock and have been following the book, very slowly and to the letter - as much as I'm able. I keep running into questions, and being new at the game, I never really know which aspects are absolutely critical and which have some flexibility in their interpretation. So, I'd really appreciate some guidance on some probably pretty basic questions please.

1 I'm assuming the dimension of the bolt on/off headblock are a bit bigger that actually required and the 100 mm depth is to be trimmed to fit to the brace (78 mm or something like). The plan seems to indicate a 30 mm thickness while the book requires 35 mm. Is this thickness actually critical as long as there is 12-15 mm of wood in the platform the neck bolts to? If it really needs to be 35 mm, I will have to laminate some. I have some 32 mm thick sapele that would do otherwise.

2 Jumping ahead to the neck joint, I've been hunting down a mortiser. The only one I have come across in NZ (at a reasonable price) is the Carbatec one which is a drill attachment. https://www.carbatec.co.nz/product/1098 ... cl-chisels
Is this likely to be any good for a small numeber of guitars or should I take the neck to a pro who might have a commercial mortise machine?

3 Following the instructions I was very particular about the RH when gluing the front and back bracing. I think, via several measurement methods, it was 42-44%. I have noticed, while waiting for my bending iron to arrive from Luthiers bench the UK (which I'm really pleased with BTW), at slightly higher RH (45-50%) that the back and front now have a significantly tighter radius than the radius dishes (like Fig 11-2 but a bit more pronounced). I guess this is to be expected as the wood has expanded a little but how critical is it that I get them bang on the same RH/shape as when they were glued up - I'm assuming if don't then the angle sanded onto the side linings will be slightly different - again - I just dont have a feel for how critical this is. I'm hoping that when I drop the RH to 42% again during assembly, they will come pretty much right. Is that likely?

Hope those questions aren't too stupid.

Thanks

Richard

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Boe Jonamassa
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Re: Further J45 questions

Post by Boe Jonamassa » Mon Jun 18, 2018 7:12 am

1 I'm assuming the dimension of the bolt on/off headblock are a bit bigger that actually required and the 100 mm depth is to be trimmed to fit to the brace (78 mm or something like). The plan seems to indicate a 30 mm thickness while the book requires 35 mm. Is this thickness actually critical as long as there is 12-15 mm of wood in the platform the neck bolts to? If it really needs to be 35 mm, I will have to laminate some. I have some 32 mm thick sapele that would do otherwise.


I think you will find the dimension for the headblock is ~110mm X 75mm X 45mm. Ideally you would want a solid block but I can't see a problem laminating 2 pieces to get the required thickness. The height of the block depends on the depth of your sides plus 5mm.

2 Jumping ahead to the neck joint, I've been hunting down a mortiser. The only one I have come across in NZ (at a reasonable price) is the Carbatec one which is a drill attachment. https://www.carbatec.co.nz/product/1098 ... cl-chisels
Is this likely to be any good for a small numeber of guitars or should I take the neck to a pro who might have a commercial mortise machine?


Mcjing sells a kit with a 3/8 chisel bit included for $99, not sure if they send it to NZ. https://mcjing.com.au/categorybrowser.a ... oryid=1183

Following the instructions I was very particular about the RH when gluing the front and back bracing. I think, via several measurement methods, it was 42-44%. I have noticed, while waiting for my bending iron to arrive from Luthiers bench the UK (which I'm really pleased with BTW), at slightly higher RH (45-50%) that the back and front now have a significantly tighter radius than the radius dishes (like Fig 11-2 but a bit more pronounced). I guess this is to be expected as the wood has expanded a little but how critical is it that I get them bang on the same RH/shape as when they were glued up - I'm assuming if don't then the angle sanded onto the side linings will be slightly different - again - I just dont have a feel for how critical this is. I'm hoping that when I drop the RH to 42% again during assembly, they will come pretty much right. Is that likely?

The top radius is the most important, you want it to be pretty much spot on or you make it difficult for yourself down the track. You check it after the sides have been profiled a bit later on by placing the top on temporarily and measuring the depth at the bridge with a straight edge, it should be 2.5mm. If it is slightly out you can get away with it, but if it is significantly different like you say, you will want to investigate why. The books explain it very well.

Cheers

Col

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Trevor Gore
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Re: Further J45 questions

Post by Trevor Gore » Mon Jun 18, 2018 10:20 am

Richardl wrote:
Sun Jun 17, 2018 5:18 pm
1 I'm assuming the dimension of the bolt on/off headblock are a bit bigger that actually required and the 100 mm depth is to be trimmed to fit to the brace (78 mm or something like).
Yes. The timber sizes in the book cover all the build options (4 models) in the plans. You lose height due to the curvatures on the top and back panels and lose length when you radius the block to fit the side curvatures. If you use the dimensions given, you should always be slightly large and can trim down to size.
Richardl wrote:
Sun Jun 17, 2018 5:18 pm
The plan seems to indicate a 30 mm thickness while the book requires 35 mm. Is this thickness actually critical as long as there is 12-15 mm of wood in the platform the neck bolts to? If it really needs to be 35 mm, I will have to laminate some. I have some 32 mm thick sapele that would do otherwise.
If you make the head plate thinner (no real problem with that, provided you don't go too thin) you may have to change the length of the screws that hold down the fretboard extension (30mm to 25mm). No problem with that either, provided you remember to do it. If you don't remember, you could split the fretboard away as you tighten the bolts.
Richardl wrote:
Sun Jun 17, 2018 5:18 pm
2 Jumping ahead to the neck joint, I've been hunting down a mortiser. The only one I have come across in NZ (at a reasonable price) is the Carbatec one which is a drill attachment. https://www.carbatec.co.nz/product/1098 ... cl-chisels
Is this likely to be any good for a small numeber of guitars or should I take the neck to a pro who might have a commercial mortise machine?
I use one I bought from Carbatec years ago, and it's still going strong and I've never had a problem with it. Others (Martin?) have not been so lucky, and consider them a piece of junk. Maybe the quality changed somewhere down the line. I've bought plenty of tools from McJing and I've found their stuff to be pretty good quality, though I've never had cause to look at their mortiser.
Richardl wrote:
Sun Jun 17, 2018 5:18 pm
3 Following the instructions I was very particular about the RH when gluing the front and back bracing...
What Col said. (Thanks, Col). When you return things to the target RH, mostly they return to their correct shape. If they remain out of shape for a long while, they may set a bit. It's always best to finish the rim assembly first, then you don't have the top and back hanging around for long periods in uncontrolled humidity .

Richardl
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Joined: Sat Oct 27, 2007 4:09 pm
Location: NZ (Palmerston North)

Re: Further J45 questions

Post by Richardl » Mon Jun 18, 2018 11:10 am

Many thanks Trevor and Col. That really helps. I'll remember about the bolt length or put a washer in to account for the slight difference. Yes, I got the order of making wrong - I thought I could borrow a bending iron but ended up buying one that took a while to arrive (but worth the wait). Hopefully they will end up back to their original shape. Otherwise, I suppose applying bit of extra pressure when gluing might work. Thanks for the mortise kit tip. I'll see if they post to NZ.

Cheers
Richard

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