2m x 3m!!??
You was lucky. When I were a lad...
2m x 3m!!??
Yep, it was a garden shed. Later i upgraded to a single car garage space which wasnt all that much bigger.
Hi TrevorTrevor Gore wrote: ↑Wed Feb 21, 2018 11:48 pmIt's very easy to over-build a J45. The originals were made with less-than-best wood and retailed for $45 (i.e. cheap) compared to say the J200 which was originally $200. So if you choose good materials it's easy to end up with everything too stiff.
Having just re-read Section 7.1, I can see that it is not the clearest bit of writing! The dimensions given (20 x 10mm) are essentially back brace dimensions and the procedure described is primarily the back brace making procedure. You need to modify the dimensions to the X-braced plan you're using. The plan from the book can use brace blanks starting at ~15 x 7mm so you can finish at ~1/2" high at the X and a width of 1/4" (~13mm x 6.3mm), Section 11.2.2. The better your jigs and shop practices, the closer you can start to the finished brace dimensions, but the same procedure as for making back braces can be used, whilst leaving the un-gabled bit for the X as described in Section 7.1. These are the dimensions we use to get the resonant frequencies in the right target zone without risking undue distortion. Most published plans (usually taken from factory made guitars) are way over-braced when good materials and assembly practices are used.
There is no need to notch finger braces or face braces into the X braces. If you make good joints with fresh surfaces and glue with Titebond, the wood will fail long before the glue (at normal temperatures).
The bridge plate is beveled or rounded on the exposed top and bottom edges (Section 11.2.2.2) and is glued down first and then acts to locate the X-braces accurately when they are glued down. The X-braces are tightly butted up to the bridge plate edges, to which they are glued.
If you follow the procedures and plans, you should be pretty right. A good many people have been pleased with the results. However, if you do find anything else that requires clarification, just ask here.
Using the 4 brace scheme and a random thickness back does not necessarily give a live back, though clearly that happened occasionally with the originals. If you want to be certain about a live back, you have to design and make it that way. If you can't measure the frequency response, you won't know what you have, so the first step would be to set yourself up with Visual Analyser, otherwise the rest is moot.Richardl wrote: ↑Thu Apr 16, 2020 10:36 amI must have read that bit last time and gone with the traditional 4 transverse braces of 6.3 wide on 2.8 mm thick mahogany - which, I hadn't understood, gives a 'live' back after all - a contribution to the sound from back vibration - which I take it is better and richer in complexity as long as (in layman's terms) it doesn't clash with the soundboard. Must say, to my ear it sounds good, but i don't have a means of measuring the frequency response. Have I generally understood that right?
OK, I have just discovered Appendix A in the first book. I'll have to think how I can set this up at home with a microphone and will check out the software suggested.Richardl wrote: ↑Fri Apr 17, 2020 6:36 amHi Trevor
thanks for your reply. Having just had a quick look at 4.4.9 (must admit I haven't picked up the first book in a while) it appears the answer to my question about radial brace dimensions is: it's 10 mm thick and 20 mm high - the "standard solution that has worked well on many guitars".
I understand that if you want to be certain about performance, one might need to invest in ways to analyse the response, as you might in any industrial lab. However, as a weekend self-taught woodworker, I haven't got a frequency analyser at my disposal and am not too sure where to access one. Personally, I'm still grappling with the difficulties of making a decent structurally-sound box (that plays in-tune) with a limited array of hand tools. So, maybe, if a live back can add unwanted embellishment of the sound, a non-live back is the better option for the novice? My rosewood back is still a 2.9 mm thick flat panel, so if I use it as is, from what I understand from this discussion, it will contribute little to the top's frequency response curve, irrespective of the bracing. Is that correct? Alternatively, where would you find a frequency response analyser - outside a physics lab? Cheers
10GPa. Don't go less than that, but stiffer is OK as you can always shave a bit off the tops of the two lower bout braces.
Trevor Gore wrote: ↑Sun Apr 15, 2018 9:24 pmI do all assembly at 45% RH.
The sides can be problematic because they tend to be heat and damp tortured and then ignored. They are often assembled at unknown RH and, mostly, people seem to get away with it. I tend to bend the sides early in the process and give them a week to normalise at 45% before I cut to length and glue in the end blocks, then linings and side stiffeners. The more you move away from "standard" woods (EIR, mahogany, blackwood) toward the less used local woods, the more I'd want to assemble everything at 45% RH, not just the top and back.
I searched for it on wikipedia and found this: Pterocarpus indicus, commonly called Narra (wood database).WilliamDavidReynolds wrote: ↑Mon Dec 12, 2022 6:02 amSection 11.2.2.2 states New Guinea Rosewood for transverse brace, I looked for it on Wood Data base, for the properties, weight/density/ym,, etc, it’s not there. Is there another name for this wood?
GregHolmberg wrote: ↑Mon Dec 12, 2022 8:47 amI searched for it on wikipedia and found this: Pterocarpus indicus, commonly called Narra (wood database).WilliamDavidReynolds wrote: ↑Mon Dec 12, 2022 6:02 amSection 11.2.2.2 states New Guinea Rosewood for transverse brace, I looked for it on Wood Data base, for the properties, weight/density/ym,, etc, it’s not there. Is there another name for this wood?
You can see a summary table of the data from wood-database here: tonewood (wikipedia). From the table, a similar wood might be Sapele or White Ash.
Greg
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