honza992 Posted April 4 Author Share Posted April 4 I love building guitars. I hate building jigs. It's a personality defect I know, but I resent having to do it. So I thought I'd show you a couple of my fuuuugly jigs, that seem to work just well enough that probably I'll never upgrade them. First is the top thickness guage. The guage itself was a cheapo from Amazon. A piece of scrap clamped above the table, and a piece of threaded rod going through a hole in my table. A plastic knob thingamy stops the top from getting scratched. I then write in pencil on the top what the thickness is at each point. It's pretty much a consistent 5mm, so I'm going to go back to the drill press and do another series of holes at just over 4mm. Which strangely is what I thought I did last time, but there you go. That's why you measure twice..... I should also say that pretty much everything I'm doing with this build is copied directly from Ken Parker. He's done an incredible series of videos called Archtoppery, which if you are interested and have a spare 30 hours or so, they are amazing. He's hands down my favourite builder, an absolute genius. Here if anyone is interested: https://kenparkerarchtops.com/archtoppery 7 Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 4 Author Share Posted April 4 (edited) Post #2 in my world's uggliest jigs compilation.... I'm planning on thinning the top till it's quite flexible. Holding firmly without cracking it is therefore a problem. I've taken Ken Parker's beautiful work holding platform which takes several hours of video to explain, and made my own version which took about half an hour to make. It's basically a 6mm sheet of MDF, with a 15mm piece of ply with the shape of the guitar cut out. Some more scrap pieces of 4mm MDF on top of that cut to the shape of the top ensure that the top goes back in the same position. Because the top is still slightly oversized it can sit upside down on the rim. The thing is as it get's thinner an more fragile it really needs support from below. Sooooo......I then filled the space with 3.5-5.5mm polystyrene balls - the ones you use to fill bean bags and such like. So far it's worked really well. The balls are soft enough not to scratch or dent the top, but it seems for the moment to provide enough support. We'll see as the top get's thinner how it works out, but so far I love it! Edited April 4 by honza992 3 Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 12 Author Share Posted April 12 (edited) Top carving continues. I've hummed and ha'd long and hard about final thicknesses. Ken parker thins his tops to between 2 and 3mm, he mentions D'Aquisto tops were 2.5mm to 4mm thick. Obviously those were guitars but the string tension is actually very similar. The arch is a bit flatter on mine and the wood is certainly cheaper...so plugging all those variables into the scientific calculator, my finger in the air came back with the following: 4mm around the bridge, 3.5mm around that thinning to 3.2mm at the periphery. I don't know if you can read any of these numbers, but here we are, getting close: Edited April 12 by honza992 7 Quote Link to comment Share on other sites More sharing options...
AndyTravis Posted April 12 Share Posted April 12 Very bluddy clever this lark 1 Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 16 Author Share Posted April 16 Sides are nearly finished. The final kerfing was glued in this afternoon.... 8 Quote Link to comment Share on other sites More sharing options...
Daz39 Posted April 16 Share Posted April 16 12 minutes ago, honza992 said: Sides are nearly finished. The final kerfing was glued in this afternoon.... Now that’s what I call a hollow-bodied guitar! 1 1 Quote Link to comment Share on other sites More sharing options...
Andyjr1515 Posted April 16 Share Posted April 16 1 hour ago, honza992 said: Sides are nearly finished. The final kerfing was glued in this afternoon.... Lovely job! Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 17 Author Share Posted April 17 (edited) I've started on the bracing. The blanks I've got are very oversized, so by cutting some off at the line I can end up with a brace which is almost perfectly quarter sawn: Putting it onto the platform, I use a biro sticking through a Gibson selector switch washer to mark out the shape of the top onto the blank. You can chose either Rhythm or Treble depending on whether you want thundering lows or blistering highs.....It also means you can get a pretty much exact contour. Because the top is arched in both directions I mark both sides of the blank. With a spokeshave I then carve down to the line... ... My makeshift 'go-bar deck' is ugly but very effective. I find myself using it all the time either for gluing or just holding stuff down. Here I'm using it for both. The brace get's held in position on top of a piece of sandpaper (150G). You can adjust the go-bars very quickly so they apply just the right amount of pressure so the brace is held in place but you can still slide the sandpaper back and forth to get good fit. Finally the brace can be glued down in the same way. I use West System epoxy. I use the Ken Parker method (as usual). Which is wet the brace, put it onto the top, then remove it so you have an imprint: The idea is to let the epoxy soak into the wood as much as possible. I've got a silicone brush which I use to go back and add more epoxy to any parts that soaked it up. Finally, clamping in the go bar deck. One of the (many) good things about epoxy is that it needs very little clamping pressure, just enough to stop anything moving. Squeeze out I clean up with a cotton bud soaked in acetone. Tomorrow, brace number 2... Edited April 17 by honza992 6 Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 18 Author Share Posted April 18 Ok this is a bit frightening. The epoxy hasn't completely hardened. It's hard but I can still push my finger nail into it. I've had failures before with epoxy, but never with West Systems and my way of measuring out exact amounts with syringes. Fingers crossed it just needs more time. This is why it's always good practice to keep the mixing pot so you can check it's completely hardened. We'll see how it is in a few more hours. Quote Link to comment Share on other sites More sharing options...
alittlebitrobot Posted April 18 Share Posted April 18 9 hours ago, honza992 said: Ok this is a bit frightening. The epoxy hasn't completely hardened. It's hard but I can still push my finger nail into it. I've had failures before with epoxy, but never with West Systems and my way of measuring out exact amounts with syringes. Fingers crossed it just needs more time. This is why it's always good practice to keep the mixing pot so you can check it's completely hardened. We'll see how it is in a few more hours. Oh no! I'm new to the epoxy game but this has definitely happened me, thanks to my devil-may-care approach to measuring ratios. With this build, why go with epoxy over wood glue? Quote Link to comment Share on other sites More sharing options...
Si600 Posted April 18 Share Posted April 18 Is it particularly damp or cold in Italy at the moment? I don't know how epoxy works or if it's affected by the weather. Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 18 Author Share Posted April 18 (edited) 2 hours ago, alittlebitrobot said: Oh no! I'm new to the epoxy game but this has definitely happened me, thanks to my devil-may-care approach to measuring ratios. With this build, why go with epoxy over wood glue? Yeah, getting the ratios right is key, as is stirring...a lot. Epoxy has got lot's of advantages. It's got a long open time, so you've got lot's of time to set up clamping etc. it's incredibly strong, it doesn't creep, and it gap-fills better than wood glue. Also, it's not water-based meaning that I'm not introducing moisture and possible warping into my very thin piece of wood. The disadvantage is that if it doesn't cure properly....yer buggered. Up until now West Systems has been spot on.... I generally use Titebond for most things. But for critical joints and anything designed to never come apart, epoxy is great. 2 hours ago, Si600 said: Is it particularly damp or cold in Italy at the moment? I don't know how epoxy works or if it's affected by the weather. It was suddenly colder last night, but this is Italy, it's not the arctic....Cold for us is anythng below 15C !! Fingers crossed tomorrow morning it will be rock hard and all my hair pulling will have been for nothing... Edited April 18 by honza992 Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 19 Author Share Posted April 19 This morning the glue is hard. Hurray! That was close to being very annoying. 36 hours to cure is a loooong time though. I'm throwing away the containers, and have ordered more West System. It's a good reminder to measure exactly the two parts of the epoxy mixture, and to stir them together really really well. It's also a reminder to keep the mixing pot so you can check each batch has hardened. I use a paper espresso coffee cup. Phew😅 5 Quote Link to comment Share on other sites More sharing options...
JPJ Posted April 19 Share Posted April 19 Fantastic work, really stunning, but could the problem with the epoxy be a reaction with the acetone you used for clean up? Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 19 Author Share Posted April 19 4 hours ago, JPJ said: Fantastic work, really stunning, but could the problem with the epoxy be a reaction with the acetone you used for clean up? Thanks JPJ, a very good suggestion! But the mixing pot was the same. There's something odd about the hardener. It's got a skin on the top which I've never seen before, despite years of using exactly the same epoxy. Anyway, it's in the bin and new ordered. Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 19 Author Share Posted April 19 (edited) While the glue malarkey kafuffle was ongoing, I cracked on with the sides. First job, trim the kerfing back with a spokeshave. The best job in luthiery. It's like popping bubble wrap but much better The back is dome shaped, with a radius of 12 feet. So that same radius needs to be sanded into the sides & kerfing. Straightforward to do on the radius dish, even if it takes quite a while. Any time I'm doing sanding I try to do it inside my hi-tech sanding cubicle. A quick n easy downdraft table. Or sidedraft I suppose. Works a treat. Next I need to carve channels through the kerfing so that the braces sit nicely inside. I used a dremel, again in my sidedraft cubicle. (I must get that patented, pronto). The idea being that the ends of the braces go into the kerfing, like this: The gaps will get filled with epoxy when the back gets glued onto the sides. And here they are, not glued yet as there's another job to do first......(ooh mysterious!) Edited April 19 by honza992 4 Quote Link to comment Share on other sites More sharing options...
Owen Posted April 19 Share Posted April 19 On 18/04/2024 at 19:32, Si600 said: Is it particularly damp or cold in Italy at the moment? I don't know how epoxy works or if it's affected by the weather. Wait! He can do all this with wood AND he gets to live in Italy? Wow. Lots of good things in one place there. 1 Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 19 Author Share Posted April 19 Just now, Owen said: Wait! He can do all this with wood AND he gets to live in Italy? Wow. Lots of good things in one place there. Yep, I realise it's entirely unjust. Nor deserved. I've led a terrible life being unkind to the young and infirm and listening to progressive rock. Just goes to show that there really is no justice in this world. Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 19 Author Share Posted April 19 (edited) In the short breaks between eating fresh pasta and drinking prosecco, I started on carving the brace(s). There only one glued on for the moment: My plan is to have one jump over the other, rather than an X-brace which is glued together. Having shaped the first brace into a sort of conical shape, the handle of an iwasaki file was the perfect shape for the corresponding hole in the other brace: So they fit together like this: Clearly, that second brace has still got some work that needs to be done. Just a tad oversized.... Those iwasaki file are the nuts by the way. Hands down the best files I've used. Much better than the Dragon files that Stewmac sells. They create shavings rather than dust and leave a ridiculously smooth surface. Even the handles are the perfect shape. Edited April 19 by honza992 5 Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 23 Author Share Posted April 23 (edited) Today I finished the braces. There are huge differences in the heights of braces that other builders use. Benedetto goes from 12mm in the centre to 4mm at the sides. Ken Parker goes from 5.5mm (!!!!) in the middle to virtually nothing at the edges. I've decided to aim for 8mm in the middle, to 1.5mm at the ends. This is really significantly less than most acoustic bass guitars have. But it seems to me that for bass frequencies you need flexibility. I'm flexing it with my hands all through the process, trying to memorise how it feels so that during the next build I've got a comparison already in my muscle memory. Anway, here's my carving station: Here are the braces at their final heights. I found it really usefuly to write the heights every 30mm all along the braces. They ended up being 8mm (16mm for the flyover) in the centre, thinning to 1.3 & 1.6mm at the ends. It's pretty flexible. Will it withstand the downforces of the strings? Ummm.......not sure. Let's hope so! For this bass though, that's as far as I dare go. The top needs a bit of cleaning up, sanding etc but we're pretty much there. I'm excited! Edited April 23 by honza992 6 Quote Link to comment Share on other sites More sharing options...
Si600 Posted April 23 Share Posted April 23 Is that all the bracing it gets? From my recollection of looking in sound holes acoustic guitars are like a boat inside, ribs and frames everywhere. Quote Link to comment Share on other sites More sharing options...
JPJ Posted April 23 Share Posted April 23 2 hours ago, Si600 said: Is that all the bracing it gets? From my recollection of looking in sound holes acoustic guitars are like a boat inside, ribs and frames everywhere. My thoughts exactly - I was expecting a bass bar or similar plus a reinforcement under the bridge? Quote Link to comment Share on other sites More sharing options...
honza992 Posted April 24 Author Share Posted April 24 23 hours ago, Si600 said: Is that all the bracing it gets? From my recollection of looking in sound holes acoustic guitars are like a boat inside, ribs and frames everywhere. 20 hours ago, JPJ said: My thoughts exactly - I was expecting a bass bar or similar plus a reinforcement under the bridge? Don't forget this is an archtop with a tailpiece so most of the string tension is absorbed by the sides. It's only the downward forces which need to be resisted by the top (something like 15% of total string tension). A normal guitar has all the string tension pulling on the bridge itself which is glued to the top. The arching itself also provides strength. Having said that, I shall be sh_tting bricks when the time comes to string it up! My best guess is that it will be fine, but it's hard to know. 1 Quote Link to comment Share on other sites More sharing options...
Richard R Posted April 24 Share Posted April 24 🫣🤞 Quote Link to comment Share on other sites More sharing options...
Andyjr1515 Posted April 24 Share Posted April 24 It will be fine Quote Link to comment Share on other sites More sharing options...
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