Further J45 questions

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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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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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Re: Further J45 questions

Post by Richardl » Fri Jul 27, 2018 4:56 pm

Hi again. I've been looking at options for routing the bindings but since I'm following the book religiously, figure I'll adopt the method described with the modification that I have an old linear track I can use as the raising and lowering bearing. One thing puzzles me though. The book indicates routing the binding then the purfling. If you use a ball bearing to dictate the depth and you do it that way around what does the bearing reference when cutting the purfling? Don't you run the risk of it falling into the binding rebate? Isn't it safer to cut the prurfling (plus a bit of the binding) first then cut the rest of the binding with the bigger bearing after?

Cheers
Richard

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Re: Further J45 questions

Post by Richardl » Fri Jul 27, 2018 6:04 pm

I suppose, if you use a spacer to increase the gap between the cutter and bearing, that'd work but it is a very specific cutter. I guess the point of doing the binding first is there is possibly less possiblity of tearout of the soundboard...is that right?

Cheers
Richard

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kiwigeo
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Re: Further J45 questions

Post by kiwigeo » Fri Jul 27, 2018 10:41 pm

When I use the Stewmac bearing/rebate cutter setup I cut the purfling channel first and then do the binding. With the Luthiertools jig I more commonly use it doesnt matter as the jig registers off the side of the guitar well below bottom of the binding channel.

A few things I do to reduce tear out:

1) I use a new spiral downcut cutter or one that hasn't done too many jobs. For the Stewmac bearing/rebate cutter I dress the cutter with a diamond card sharpener.
2) I shellac top around periphery to stiffen up the wood fibres.
2) Direction of cuts is as per diagram in the Stewmac catalogue.
4) I do a preliminary cut with a Schneider gramil prior to cutting the purfling channel
condino mandolin binding channel.jpg
Martin

Richardl
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Re: Further J45 questions

Post by Richardl » Sat Jul 28, 2018 6:18 am

Hi Martin

thanks for the tips - maybe cutting the purfling first is the way to go then. I've just ordered a Stumac bit so it better be good for the price!! I've also decided to make a modified version of the GG system in the end as I have found a track that slides up and down freely that I can attach a router to and should work well keeping the cutter firmly held in the correct orientation. I'm just a bit nervous about the hand held approach. The shellac flakes I have are quite brown (golden I think sounds better :)) so would stain the top a little. Would you recommend blonde shellac or will the colour sand out easily? I havent really decided how I'm going to finish this guitar - I used True Oil last time and it is holding up OK. I understand that'd take OK over shellac, infact it seems to be a common approach - sealing with shellac and then applying Tru Oil.

Cheers
Richard

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Re: Further J45 questions

Post by kiwigeo » Sun Jul 29, 2018 4:14 pm

Hi Richard,

For stiffening up the soundboard where I'm going to route the channel(s) I generally use whats lying around my shop. I had a bottle of Rushton's sanding sealer which is basically shellac which did the job. The sort of shellac really doesn't matter as its going to be sanded off during the final finish sanding process.

Richardl wrote:
Sat Jul 28, 2018 6:18 am
Hi Martin

thanks for the tips - maybe cutting the purfling first is the way to go then. I've just ordered a Stumac bit so it better be good for the price!! I've also decided to make a modified version of the GG system in the end as I have found a track that slides up and down freely that I can attach a router to and should work well keeping the cutter firmly held in the correct orientation. I'm just a bit nervous about the hand held approach. The shellac flakes I have are quite brown (golden I think sounds better :)) so would stain the top a little. Would you recommend blonde shellac or will the colour sand out easily? I havent really decided how I'm going to finish this guitar - I used True Oil last time and it is holding up OK. I understand that'd take OK over shellac, infact it seems to be a common approach - sealing with shellac and then applying Tru Oil.

Cheers
Richard
Martin

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Trevor Gore
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Re: Further J45 questions

Post by Trevor Gore » Sun Jul 29, 2018 8:39 pm

Richardl wrote:
Fri Jul 27, 2018 4:56 pm
One thing puzzles me though. The book indicates routing the binding then the purfling. If you use a ball bearing to dictate the depth and you do it that way around what does the bearing reference when cutting the purfling?
I'm using the LMII router cutter rather than the Stewmac one. Originally, only the LMII one was (sort of) downshear, whereas the Stewmac cutter was straight. Now they are both "downshear". There may be some differences in the spacing between the bearing and the bottom of the cutting edges, too. Bottom of cutter to top of bearing is 5mm on the LMII cutter. The bearings aren't interchangeable between brands, so most people commit to one or the other.

Anyway, there are a couple of reasons for doing the binding channel first. The first is that you get to check the quality of the top cut (into the spruce panel) and can decide whether it is good enough (or whether some sharpening is in order, or a new cutter). The "downshear" cutters can be sharpened on a diamond hone. I use the blue and green DMT "stones" as pictured in the book. However, the main reason for doing the binding rebate first is that doing the purling first (especially on wide purflings) you cut away the surface which the "doughnut" rides on. Depending on the geometry of the doughnut, if it ends up with the rounded/angled part riding part on and part off the top, you get an uneven depth of cut for the binding. With the LMII cutter, the bearing is far enough below the cutter that there is never a risk of it falling into the binding rebate. At least with the geometry of my set-up. The bearings on the LMII cutter are 5mm deep. So you need a 10mm differential between the vertical depth of purfling and the vertical depth of binding before the bearing falls into the rebate. Max is typically 6mm, so 4mm of bearing is still on the side.

Regarding the router/laminate trimmer, these days I use the Makita one. Never a problem with power for a full binding cut in one hit. I use a climb cut all the way round. The Makita is variable speed, which is arguably more important than soft start, as any resonances can be dialed out so reducing the propensity to chatter. I counterbalance the router these days, as the routers I use have got bigger and heavier, and seal the spruce (or cedar) with shellac prior. The shellac is required anyway to prevent grain tear-out when removing the filament tape that I use for taping on the bindings.

Dave M
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Re: Further J45 questions

Post by Dave M » Mon Jul 30, 2018 3:07 am

Well I wish I'd read this a few days ago - assuming it had been written. I think that must have been what happened to me. My bindings came out less tall than the should have been. I thought I had sized them right so it could indeed have been the donut problem you mention. Bit difficult to see by inspection I'll have to do a test some time.

Fortunately they were only slightly out and the roundover has pretty much dealt with it, but I shall know next time.
------------------
Dave

Richardl
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Re: Further J45 questions

Post by Richardl » Wed Aug 01, 2018 4:29 pm

Great explanation Trevor, thanks very much. When the Stumac bit arrives, I'll check the depth with the collar on (didnt know about the other brand). I hadn’t thought about the 'doughnut' Several folk have mentioned shellac. I have golden shellac flakes but I've used bullseye (I think) shellac on a harp in the past. Is that a better bet for preventing tear out as it won’t colour the spruce? ....I guess the question is how much will ordinary shellac colour the wood if its going to be sanded afterwards? Anyway, I have made a router set-up based on your design with a bit of a mod https://www.flickr.com/photos/143232438 ... ed-public/. Hope that works OK. I'll make the cradle next weekend. Man, there is a lot to learn in this luthier business!

Cheers
Richard

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Trevor Gore
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Re: Further J45 questions

Post by Trevor Gore » Thu Aug 02, 2018 1:10 pm

Richardl wrote:
Wed Aug 01, 2018 4:29 pm
... I have golden shellac flakes but I've used bullseye (I think) shellac on a harp in the past. Is that a better bet for preventing tear out as it won’t colour the spruce?...
I use either blonde or Platina, as those are the only two types of shellac I use. Neither of those colours the wood, but I don't put it on very thick, either. I wouldn't want to speculate about other colours.

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