Froggy Bottom P12

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Peter Lynch
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Froggy Bottom P12

Post by Peter Lynch » Thu Nov 25, 2021 7:25 pm

Hi all , I am now building acoustic guitars as a hobby , so far I have built a copy of a Martin 0 and 00 size. The guitars I build are for my playing pleasure any spares will go to the grandchildren who have indicated they would like one .
I have just finished the 00 and am amazed at the difference between the sounds of the 0 versus the OO . I would like to build something in between similar say to the Froggy Bottom P12. I wonder if anyone has a set of plans they could sell me .
Thanks

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Mark McLean
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Re: Froggy Bottom P12

Post by Mark McLean » Wed Dec 01, 2021 10:45 pm

You could use a parlor style plan like the one for a 1918 Martin 1 series which is available at the Guild of American Luthiers website, and the same plan is also sold by LMI. The FroggyBottom P model is marginally longer and wider in the body than the Martin 1, but is very close with similar shape and depth, and 12 fret X-brace. You can just adjust your body size to those that FB provide for their P model on their website. The shorter scale length (24.7”) is also likely to be a contributor to that guitar’s character so you can adopt that as well. Shorter scale length will result in the bridge being a little bit closer to the soundhole than the Martin specs, so you can shift the bracing a bit north also, to keep the same relationship of the bridge to the braces. Just use the plan as a general guide and don’t be afraid to adjust it a bit. Brace lightly and take the top down pretty thin in such a narrow body. It could be quite fun!

Peter Lynch
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Re: Froggy Bottom P12

Post by Peter Lynch » Thu Dec 02, 2021 3:40 pm

Thanks Mark , I have the plans for a Martin 0 vs , I will look at adapting that , would you have an suggestion on how thin I should make the top I have a set of bear claw Sitka or a set of Appalachian Spruce ( red ) to chose between
Cheers
Peter

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Mark McLean
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Re: Froggy Bottom P12

Post by Mark McLean » Thu Dec 02, 2021 10:45 pm

Top thickness is a debatable thing. Factories like Martin or Taylor make guitars to fixed dimensional specifications, and make a fairly good guitar most of the time. For a small body guitar top (steel string) an industry standard would be something like 2.5mm. But when you build your own instrument you have the opportunity to adjust to the characteristics of that individual piece of wood. Stiffness is the main variable to consider. A stiff piece of wood can be taken down thinner and still retain enough strength to hold up to the string tension, but by being lighter it might be more 'responsive' or have more complex harmonic overtones. Many factory built guitars are probably "over-built" with tops too thick or too heavily braced to produce optimum sound. If you leave it too thick it will have lower volume and less harmonic character. But the factories prefer to make something more akin to a 4WD truck than to a Formula 1 racer, because it is not good for their reputation if it falls apart in the owner's hands. Too bad if it doesn't sound great.

Adirondack (red) spruce tends to be about the stiffest soundboard material you will find, followed by sitka, and then other spruce varieties. Cedar, redwood or Australian timbers such as King Billy or Bunya are floppier, so you need to keep them 10-20% thicker. But every piece of wood is a bit different, and you need to hold it in your hands and flex it across the grain and (most important) along the grain to assess it. You can also get technical and measure Young's modulus or do deflection testing to assess an individual piece - but that is only really useful after you have built quite a few guitars and can compare with ones that have turned out well - and just try to do that again. I would suggest taking your spruce top (whatever species) down to about 2.5mm and then see how it feels. If it is still really stiff, thin it a bit more. When it starts to get a bit floppy you should stop, and brace it. Then it will feel really stiff again. So then gradually carve the braces until it starts to become just a little bit flexible again. You can taper the ends of the braces down to nothing just before the linings, and also thin out the edges of the soundboard a bit by sanding or scraping.

Some people target the ideal soundboard thickness by "tap tuning" - knocking on the top as you go and listening to the sound and the sustain of the vibrating top. This is fun, but not well validated. It is hard to know what you are listening for, and anyway it will behave differently after you glue it to the sides. Good luck!

Peter Lynch
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Re: Froggy Bottom P12

Post by Peter Lynch » Fri Dec 03, 2021 9:27 am

Thanks Mark , you have given me a lot of information which is like gold to a novice . I appreciate the time you have spent no doubt other novices are reading your replies as well and learning from them . You mentioned bracing near the linings assuming I use normal Kerfing which is of course in segments can I safely taper the xbraces to end just before the linings or do I need to use a solid Kerfing such as in the Gore / Gilet books ( which I have )
At the moment I taper the x braces down to 2mm and fit them through the sides , when I install the bindings they are then hidden from view. Both my guitars have been loud and responsive but I suspect overbuilt as I used Engelmann Spruce and thinned the tops to 2.9 mm or there abouts , and i can see by your notes tgat I have probably left them a bit thick ( heavier than needed ) my bracing is per the plane’s scolloped and tapered 7mm ( x brace ) tapered to 1mm or less and 6mm scolloped tone bars , I followed the plans but admit adding a 1mm extra on the x brace for security . It’s a fascinating hobby and as I get to play what I make I am as keen as mustard to learn ( I’m 75 now so running short on time )
Cheers and thanks again
Peter

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Mark McLean
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Re: Froggy Bottom P12

Post by Mark McLean » Sat Dec 04, 2021 8:30 am

Peter, you have built two guitars that you are happy with so you are obviously doing it well. But if you make the next one deliberately a bit lighter you might find it could be even better; especially if it is a small body.

Kerfed linings or solid linings both work just fine. Solid linings are stiffer and a little bit heavier. Trevor Gore has done some work showing that increased stiffness or increased mass of the sides changes the acoustic performance of the soundboard. Simplistically, this is because the sides take less energy out of the soundboard. The books have a much more elegant and evidence-based explanation. So there is a theoretical advantage of the non-kerfed linings (made of solid wood or laminated strips). This is an aspect of the build where “ heavier” might enhance sonic performance. But having said that, there are millions of great sounding guitars with kerfed linings so it is not an absolute.

There are lots of discussions about whether to inlet the braces to the linings and the sides, or to terminate them before they reach the sides. Most commercial builders and most published plans will have the braces tapered to about 2 mm and then notched into the sides, and the ends covered by the bindings - exactly as you described. This contributes to the “heavier build” issue, but it is stronger and makes later development of a loose or “popped” brace less likely. It is certainly the better strategy for a manufacturer who is sending an instrument out into the world without knowing how it is going to be handled by the owner, and where they want to minimize the number that come back under warranty with structural issues. On the other hand if you are building for yourself or a custom order and you want a light and responsive top you can taper most of the braces to nothing just inside the perimeter of the soundboard. But that instrument is going to be a somewhat more delicate creature. And you don’t want to do this with the strong upper transverse brace - that one needs to be coupled to the sides. In previous discussions of this at ANZLF I think opinions tended towards terminating and not tucking the braces in the lower half of the soundboard, and that is also what the G&G books favour, but there is no right/wrong here. So many options.......

Spring
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Re: Froggy Bottom P12

Post by Spring » Sun Dec 05, 2021 4:23 am

I'd like to thank you both for this thread, it's perfect for me, and I appreciate Mark summarizing his experience, and years of forum discussions.
I thought I would contribute, but with the caveat that I'm only 5 guitars in myself, and I'm really interested in experimenting and pushing boundaries. Because these guitars won't be marketed, I'm quite comfortable with failures.
I just completed this guitar, in fact it's only been strung up for a few weeks now, and since I finish my necks separately, I'm still working on the final shape.
It is similar in size to the Froggy Bottom guitar, Body length 19 3/8", width 13 3/4", depth 4 1/2". The top, back, and sides are all Douglas Fir.
The neck is Sapele, the bridge is Arbutus. Bridge plate is Rosewood, braces are Engleman spruce, not let in to the linings, , and linings are kerfed Sapele. Scale length 25.4". Top thickness 2.3 mm. It has K&K pure piezos in it and sounds great amplified.
It has a huge balanced voice for its size, which has been getting nothing but better as the weeks tick by.
I have seen videos of guitars like this, and was always impressed with the voice, so I just drafted one up, and built it, deciding that I would keep it very simple.
Here are a couple of photos.
What would I do differently? Well I really miss the 14 fret neck, otherwise not much.
Small Falcate.jpg
Cheers
Attachments
Falcate bracing.jpg

Peter Lynch
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Re: Froggy Bottom P12

Post by Peter Lynch » Sun Dec 05, 2021 6:31 pm

Than you Mark you have given me some very valuable information , you have been very generous with your time . The information you have given me will help me enormously , great stuff thank you 🙏
I am finding membership of the forum very informative and friendly
Once again Thank You

Peter Lynch
Wandoo
Posts: 19
Joined: Mon Sep 17, 2018 10:51 pm

Re: Froggy Bottom P12

Post by Peter Lynch » Sun Dec 05, 2021 6:44 pm

Spring
The guitar looks good , glad you are getting something from these posts I feel we are very lucky that members like Mark are so generous with their knowledge .

I will attempt to post my two efforts , both 12 fret 24.9 “ scale
Blackwood Back and Sides , Engelmann Spruce Soundboard , red spruce braces , Ebony Fingerboard and Bridge . One is an 0 size about a year old and really sings the 00 is only a few weeks old like you mine will never be sold they are for me or the grandchildren to play with

No tried to use the photo button to download the photos but didn’t work

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Mark McLean
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Re: Froggy Bottom P12

Post by Mark McLean » Fri Jan 14, 2022 12:25 pm

Peter, the usual reason that pictures won’t load is that the file size is too big. You can’t upload the pictures straight from your phone or camera at 2mb per photo. There is a separate thread pinned near the top of the index home page which walks you throu how to post pictures. Give it a go - we would love to see what you built.

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kiwigeo
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Re: Froggy Bottom P12

Post by kiwigeo » Fri Jan 14, 2022 2:04 pm

Max size per file is 5Mb.

Here's the tutorial of uploading photos: http://www.anzlf.com/viewtopic.php?f=1&t=8413
Martin

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