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  #46  
Old 05-09-2017, 08:12 AM
emmsone emmsone is offline
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So after listening to you guys tell me my bracing was waaay to big and clearly a disaster, I decided to carve them smaller and ended up with this...
Untitled by David Emm, on Flickr

I then got distracted by the fact my replacement sides arrived so I did some more bending....
Untitled by David Emm, on Flickr

Untitled by David Emm, on Flickr

I then redid my top bracing completely and ended up with this.... (minus some finishing scalloping on the 2 large transverse braces)
Untitled by David Emm, on Flickr

Then this morning I cut the sides to profile, and glued the rim together to get this. I don't know how you guys manage do the profiling after the sides are already bent without going crazy, its a very annoying process. its SO much easier to cut the profile first, just don't make a mistake in the bending process.
Untitled by David Emm, on Flickr

I ran out of cable ties before I could finish the cutaway section, but here's my Michael Greenfield inspired "even pressure soundboard clamping system version 1" device. It should work fine, but if not there are improvements to be made. I was thinking I could put a tube on the other side too to clamp the back, but with a guitar back that is much thicker at the tail block end compared to the neck end, it might have to much curve to work like that.
Untitled by David Emm, on Flickr

I'm hoping to get at least the top linings glued in place when I go back for 2 hours more this evening.
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  #47  
Old 05-09-2017, 10:02 AM
charles Tauber charles Tauber is offline
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Top bracing is looking much more appropriately sized.

I'd consider making neck and end blocks smaller: they don't need to be that heavy. I usually make end blocks from a laminate of spruce top off-cuts that end up being about 1/2" thick. I find that works well for both steel string and classical guitars.

I like the idea of using plastic tubing as the clamping interface. I've used upholstery foam to accomplish the same thing. A video of the process can be seen here: https://www.youtube.com/watch?v=KSXmP_eD8c4

As far as contouring the sides after bending, it is pretty easy. If you already have some plan you are following, you can easily trace it or draw in onto common poster board to make a functional, flexible template. Using a sharp knife, cutout the template. Then wrap the paper template against the bent side and use a pencil to mark the outline on the side. Then using a chisel, plane or coping saw, remove the excess to the line.

If you are using radiused dishes, just lay the bent sides in the outside mold on the dish and use a pencil in a divider of compass to mark the contour of the dish onto the sides. Remove excess, as above.

Alternatively, if you don't have a template, and don't use a dish - I don't - suspend the braced back above the bend sides in the outside mold. With the back bent to the appropriate shape - braces side-to-side and an appropriate curvature end to end induced - use a pencil in a divider or compass to mark the contour of the back onto the sides. Ditto for top. If that isn't clear, I probably have pictures that I can post of the process. Remove excess, as above.

Last edited by charles Tauber; 05-09-2017 at 10:12 AM.
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  #48  
Old 05-10-2017, 09:04 AM
emmsone emmsone is offline
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Quote:
Originally Posted by charles Tauber View Post
Top bracing is looking much more appropriately sized.
Excellent. thats good to know.

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Originally Posted by charles Tauber View Post
I'd consider making neck and end blocks smaller: they don't need to be that heavy. I usually make end blocks from a laminate of spruce top off-cuts that end up being about 1/2" thick. I find that works well for both steel string and classical guitars.
Actually I've left that end block slightly on the large size because my walnut/maple neck isn't the lightest so i'm hoping that small amount of extra weight in the spruce block at the back end might help balance it out slightly.

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Originally Posted by charles Tauber View Post
I like the idea of using plastic tubing as the clamping interface. I've used upholstery foam to accomplish the same thing.
I had another look at the video where I saw Michael Greenfields jig, he uses much bigger tubing then I did. I found the larger diameter tubing to be very stiff, i'm still slightly concerned my current tubing is on the stiff side, even though it does just about squish when I put a lot of weight on it.

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Originally Posted by charles Tauber View Post
As far as contouring the sides after bending, it is pretty easy. If you already have some plan you are following, you can easily trace it or draw in onto common poster board to make a functional, flexible template. Using a sharp knife, cutout the template. Then wrap the paper template against the bent side and use a pencil to mark the outline on the side. Then using a chisel, plane or coping saw, remove the excess to the line.

If you are using radiused dishes, just lay the bent sides in the outside mold on the dish and use a pencil in a divider of compass to mark the contour of the dish onto the sides. Remove excess, as above.

Alternatively, if you don't have a template, and don't use a dish - I don't - suspend the braced back above the bend sides in the outside mold. With the back bent to the appropriate shape - braces side-to-side and an appropriate curvature end to end induced - use a pencil in a divider or compass to mark the contour of the back onto the sides. Ditto for top. If that isn't clear, I probably have pictures that I can post of the process. Remove excess, as above.
This is pretty much what I did. Traced my template onto the side and then followed the line with a coping saw. I found it very difficult to cut when the side wasnt under tension or either held / clamped against something. In the end borrowing 3 extra hands to hold it while it was being cut seemed to do the trick. That option is probably not always going to be available, I think its 100% easier to cut it before bending

I did manage to get the top lining glued on though
Untitled by David Emm, on Flickr
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  #49  
Old 05-16-2017, 04:42 PM
emmsone emmsone is offline
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I've managed to get a reasonable amount done since I last posted.
I glued the top on, and am almost at the stage to glue the back on and close the box.

One thing I still haven't decided yet is whether or not to implement a floating back brace. The last guitar I built, and now i'm seeing it again with this one both have a similar issue, the back does not hold its dished shape, I have a feeling this is another reason my sides weren't that flat on the previous guitar because the back naturally flattening itself out may have pushed the sides out of square alignmentwise.
I'm not really sure how a floating back brace will affect the guitars sound, but i am quite positive about what it will do for the guitar structurally so i'm leaning towards doing it.

Here are the pictures

clamped and glued my top on using my new super duper tube clamp system. Its so easy and it just works.
Untitled by David Emm, on Flickr

The fact that so few clamps are needed is a huge bonus, the 2 side clamps weren't really required, but they helped balance the pressure and made it less likely for it to somehow slip off.
Untitled by David Emm, on Flickr

With the top trimmed flush to the sides, it actually looks like a guitar now.
Untitled by David Emm, on Flickr

The guitar is now not leaving the mould until the back is glued on. Despite being in the mould while the top was glued on which has made the whole thing much more rigid, it barely fits in the mould now, its weird, its like the mould changed shape.
Untitled by David Emm, on Flickr

Speaking of the back, I glued the bracing on using a heavy table as a makeshift go bar deck. Having never used one before I was impressed with how handy it is, but less impressed by the fact that even though I made sure the glue seemed to have 'tacked' up before applying the pressure to stop the braces moving, when I came back to check it several hours later, all 4 braces ended up not in the position I had originally placed them.
Untitled by David Emm, on Flickr

The traditional way of attaching the centre strip is to do it before the bracing, but due to an oversight of not having a long enough strip to do it that way, attaching the braces first allowed me to have just enough length to glue the centre strip on as individual strips in between the braces. Here I have nearly finished carving the braces
Untitled by David Emm, on Flickr

Here you can see my centre strip gluing system with my floating back brace in place as well
Untitled by David Emm, on Flickr
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  #50  
Old 05-17-2017, 09:16 AM
charles Tauber charles Tauber is offline
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Quote:
Originally Posted by emmsone View Post
One thing I still haven't decided yet is whether or not to implement a floating back brace.
Just out of curiosity, what is a "floating back brace"?
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  #51  
Old 05-17-2017, 09:54 AM
emmsone emmsone is offline
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Quote:
Originally Posted by charles Tauber View Post
Just out of curiosity, what is a "floating back brace"?
Its a brace that runs along the length of the back of the guitar, its notched into the regular braces and effectively locks them in position thus holding the curve of the back, its less flexible.

If my explanation doesn't help, hopefully the images from the current Joel Michaud build thread can. He is one of the builders who makes use of this idea.
http://www.acousticguitarforum.com/f...=466546&page=5


I'm still not sure if I should implement it. I think had I wanted to do this I should perhaps have glued the back on first. I should be able to but if I put this in and it doesn't quite fit perfectly, it can't really be undone without ripping the back braces off and redoing them
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  #52  
Old 05-17-2017, 10:10 AM
charles Tauber charles Tauber is offline
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Thanks. Linked here, for continuity:

http://i1374.photobucket.com/albums/...psmhkn22ha.jpg
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  #53  
Old 05-17-2017, 01:57 PM
cobalt60 cobalt60 is offline
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Quote:
Originally Posted by emmsone View Post
Its a brace that runs along the length of the back of the guitar, its notched into the regular braces and effectively locks them in position thus holding the curve of the back, its less flexible.

What is the perceived benefit of this? The curve of the back perpendicular to the standard braces is held by every inch of the sides and side linings, which is actually a huge amount of structure. I'm just unclear why someone would want even more structure in that direction, but I'm sure there's some interesting thinking behind it.

Of course, many classical builders use a "tilted cylinder" back shape, instead of a dome, in which case that extra beam would be flat.
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  #54  
Old 05-17-2017, 02:46 PM
emmsone emmsone is offline
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Originally Posted by cobalt60 View Post
What is the perceived benefit of this? The curve of the back perpendicular to the standard braces is held by every inch of the sides and side linings, which is actually a huge amount of structure. I'm just unclear why someone would want even more structure in that direction, but I'm sure there's some interesting thinking behind it.

Of course, many classical builders use a "tilted cylinder" back shape, instead of a dome, in which case that extra beam would be flat.
I'm not exactly the expert here,
I would be inclined to agree with what you say about the sides having enough structure to do that job, but I am fairly sure that one of the reasons my neck block and the tail block ended up quite a long way out of vertical on my previous build was because the back naturally flattening itself back out pushed the sides out from how they were sitting before the back was attached. I did not have my guitar in its mould when I glued my back on last time, and that could be one mitigating factor (or the fact my linings are made myself), but while the guitar was sitting in 'closed box' form and before I did the bindings, thats when it seemed to get worse.

With the braces curved on their underside and the back glued to it, the back can't naturally flatten out horizontally, but the typical centre reinforcement can't naturally hold the back in its dished shape, utilising this floating back brace is one way to counteract the natural flattening and add a bit of rigidity.

I'm still not decided what i'll do, its probably going to be a gut feeling when I pick the back up tomorrow to glue it on. Unless someone in the know, perhaps one of the custom shop builders (should they happen to be reading this) chimes in with a specific reason why I should or shouldn't add one in the meantime, i'll decide right then on spot what i'm going to do.
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  #55  
Old 05-17-2017, 03:04 PM
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Quote:
Originally Posted by emmsone View Post
With the braces curved on their underside and the back glued to it, the back can't naturally flatten out horizontally, but the typical centre reinforcement can't naturally hold the back in its dished shape, utilising this floating back brace is one way to counteract the natural flattening and add a bit of rigidity.
I don't believe the back "naturally" flattens, unless there is some change in RH. If that's the case, the additional brace may not help.

I'd also recommend using reverse kerfed linings, or solid laminated linings next time, they make the sides so much stiffer you don't need to worry about flexing when you glue on the top and back.
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  #56  
Old 05-17-2017, 05:00 PM
emmsone emmsone is offline
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I don't believe the back "naturally" flattens, unless there is some change in RH. If that's the case, the additional brace may not help.

I'd also recommend using reverse kerfed linings, or solid laminated linings next time, they make the sides so much stiffer you don't need to worry about flexing when you glue on the top and back.
Have I missed a step here? lets go back to before the back is braced. If i sit the raw wood back on the radius dish, it sits flat on the higher edges/points of the dish with an air gap underneath in the centre, sure it has some slight sag, but not enough to conform to the dish, it only conforms to the shape of the dish if I push down in the centre. As soon as I take my pressure away the wood goes back to its natural flat state. If I radius my braces to force the back to conform to that radius, they only hold in one direction. the other direction the wood naturally recoils to its, flatter, state.

EDIT - lightbulb moment, a radiussed x-braced back could perhaps solve this problem. (but would open up more questions than it initially answers to be confident enough to change to this option on this guitar without thinking it through much more thoroughly)

Am I supposed to have 'bent' the back to hold its shape within the dish? Maybe it should be, because otherwise its under constant tension to stay forced to the domed shape, not sat in a fairly relaxed state like a flat top. Thinking aloud, perhaps this is why radiussed tops and flat tops don't sound as alike as I thought. On the other hand i'm pretty sure these radiussed tops aren't pre bent to conform to this radius, they are forced to that by being attached to radiussed bracing.

Because the back is a dish and not a curve, I can't really do that on a bending iron, the bending iron would need to be 4 or 4 times longer to accomodate the width and length of the back, also that extra long bending iron would only allow bending in 1 direction.
Perhaps if I CNC'd an aluminium radius dish and incorporated a heating element that heated the whole dish up, if I wet the back and put pressure on it while it sat in the dish, when the heat is removed perhaps it would naturally then hold that shape. Pretty sure thats both overkill and i haven't ever heard of anyone else doing that. perhaps thats a new luthiers tool I can market?


The linings, In my previous build I originally planned to go with reversed kerfed linings but in my testing i could barely get them to bend half way round the waists, let alone a cutaway, despite how far through i'd cut the slots, either they didn't bend enough so they snapped, or the join was so thin it snapped. This is why with the ones I finally managed to make, I went with every slot alternating between reverse/non reverse style slots. I made enough for several guitars so I made use of them again. I hadn't suspected they may have been the cause of lack of stability.
I do feel that even though both this Tasmanian Blackwood and the Walnut sides of my other build were both 2mm sides, the Tasmanian definitely felt more solid when it was just the sides joined by the neck and tail blocks. Hopefully that will mean my issues here are reduced, and as such my underlying query.
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  #57  
Old 05-18-2017, 12:52 PM
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My misunderstanding, I thought you meant it naturally flattened out AFTER it was glued. You're overthinking this, sanding the rims with the radius dish should provide the longitudinal arch for the back while the braces support the transverse arch. It's not necessary for the back to conform to the domed shape until it is glued into place, and after it's glued the amount of doming will depend on the relative humidity. As RH rises, so does the amount of doming, for both the top and back.

Try solid laminated linings on your next one, use three strips of 0.10" thick oak, it bends really easily at that thickness. You'll be surprised at how much more rigid it makes the rims. I made my own kerfed linings for my first few guitars, the death of 1000 cuts I called it. (BTW, there are about 1000 cuts required for dred linings). They were a pain to install, they broke at all the tight curves, and it was difficult to cleanly inlet the top bracing. I thought it would be easier to get thin solid linings to conform to the tighter curves, I could make each strip thin enough to bend easily, and put on as many as I needed to make up the necessary thickness. I've found that oak does not bend easily at 0.125", and at 0.08" it bends really easily, heat and water are barely necessary, 0.10" is the optimum thickness for oak. YMMV
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Last edited by Rodger Knox; 05-18-2017 at 01:12 PM.
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  #58  
Old 05-18-2017, 04:41 PM
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My misunderstanding, I thought you meant it naturally flattened out AFTER it was glued. You're overthinking this, sanding the rims with the radius dish should provide the longitudinal arch for the back while the braces support the transverse arch.
Actually that is what I was saying, I'm fairly sure that the natural spring in the back was stronger than the rigidity of the walnut sides and linings and thus the flattening moved the structure enough to push it out of square


Quote:
Originally Posted by Rodger Knox View Post
Try solid laminated linings on your next one, use three strips of 0.10" thick oak, it bends really easily at that thickness. You'll be surprised at how much more rigid it makes the rims. I made my own kerfed linings for my first few guitars, the death of 1000 cuts I called it. (BTW, there are about 1000 cuts required for dred linings). They were a pain to install, they broke at all the tight curves, and it was difficult to cleanly inlet the top bracing. I thought it would be easier to get thin solid linings to conform to the tighter curves, I could make each strip thin enough to bend easily, and put on as many as I needed to make up the necessary thickness. I've found that oak does not bend easily at 0.125", and at 0.08" it bends really easily, heat and water are barely necessary, 0.10" is the optimum thickness for oak. YMMV
I guess solid linings are now on my list of things to try on the next one

in the meantime I got the back glued on today. in the few hours after it was taken out the mould, it didn't seem to have shifted or moved or flattened which is a good sign. The whole thing seems noticeable more solid than the previous guitar. At the moment i think thats possibly down to 3 things. A) Tasmanian seems to hold itself better than the walnut. 2) this guitar is better built. D) i've miscalculated somewhere (again) in this build and its all thicker and heavier than it should be.

I also trimmed the neck to shape. I think i'm about 0.5mm, or perhaps slightly more, too thin per side at the 12th fret and its probably enough that its going to ruin my flush fit neck to cutaway join. I'm hoping I can save it, if not its yet another ruined part of the guitar. If I hadn't just bought some more tools I'd probably be considering packing this guitar building in.

I then spent 3 hours trying to glue a bwb purfling to a binding strip (and completely and utterly and miserably failed 4 times using 3 different methods) so I have the purfling strip on the side of the guitar under the binding. There was a separate thread on this and the solution was that this is not the way to do it. Unfortunately it seems thats my only option at the moment and seeing as I have already (or will have) the bwb in several places on the rest of the guitar, if I forgo it in this area, it could look a bit weird.

Here's the back on and after the excess was trimmed away.
Untitled by David Emm, on Flickr

and an alternative view
Untitled by David Emm, on Flickr
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  #59  
Old 06-06-2017, 03:36 PM
emmsone emmsone is offline
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I've been away but today got back to doing some work on the guitar.

It went well.

or not.

My new stew mac binding channel cutter did a superb job for 95% of the guitar Untitled by David Emm, on Flickr

until for no apparent reason literally as I was coming round to the last curve having routed the entire rest of the guitar I ended up with this....
Untitled by David Emm, on Flickr

I can only assume there was a crack, perhaps on the inside of the guitar, or inside the wood, there definitely wasn't one showing on the outside, and if there was at maximum a hairline crack somewhere there, I still can't believe such a huge chunk got ripped out.

I then cleverly decided to carry on and rout the channel for the top purfling. Also a great decision as I forgot the bearing would run right into the newly created hole. Thus I now have this....
Untitled by David Emm, on Flickr

Untitled by David Emm, on Flickr

Its an annoyingly large hole. I'm HOPING i can find a way to triple up my top purfling that will go deep enough into the top to cover that hole, or perhaps i'll have to buy something in the herringbone/flat look style that will do the same job.


For the side hole, I will probably attempt to create a much larger end graft in some kind of weird arty wing/curved shape to cover the blow out. It will probably be a lot of work and it might end up looking terrible, but it can't look worse then it is now, and the option of patching it with another piece of tasmanian doesn't seem like a valid solution as it would be way too visable.
If that fails too, its going in the bin.
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  #60  
Old 06-06-2017, 05:41 PM
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Make an artistic feature in the offending area.

On the flying brace, I seem to recall it is there to reduce the back from flattening out as time goes on. If the back flattens out the back is longer, something has to give. The neck block rotates into the sound hole, time for a neck reset. At least from what I read somewhere. Tim McKnight has used it, he might be able to give added thoughts on it. (Oh is he going to hate me now)
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