16 inch Florentine archtop.

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blackalex1952
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Re: 16 inch Florentine archtop.

Post by blackalex1952 » Wed Jul 15, 2015 3:02 pm

Lovely work! I have a method for using HHG. I had an overhead bathroom fan with heat lamps that the kids were leaving on allyhe time, which sent my power bill into orbit! So I replaced the lamps with incandescants and te deployed the heat lamps to the shed, mounting them in porcelain bases on a bracket that attaches to a boom microphone stand. Aldi have cheap ones on special occaisionally- quite good.I use the heat lamps for both glueing and undoing glued joins for example, undoing the soundboard/fingerboard join during neck removal. I use a surface thermometer and alfoil on wooden cauls to reflect heat from any area that I don't want heated. Monitoring the temp with a surface thermometer allows for accuracy relative to any lacquer. That may be damaged. The main advantage of using radiant heat lamps is the if the lamp is kept a metre or so away there is less surface heating. The heat penetrates- a much better heat gradient than a heat gun! The boom stand allows for quick adjustment in any situation. I position it ove my go bar deck and work underneath it. Great in our southern winters. It also keeps the humidity in the wood down before I return the parts to my underbench low humidity storage. Use the heat gun as well in the ususal way for locally heating just before and after glueing.
"Everything I say on the topic is based solely upon inexperience and assumption!"

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rocket
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Re: 16 inch Florentine archtop.

Post by rocket » Wed Jul 15, 2015 6:21 pm

The carbon fibre on top of the braces looks cleaner than most or all I have seen so far. I have not yet worked with CF but would like to know what's the key to get the strands down so cleanly. What are the things one must and/or must not do in order to not only prevent a mess but also get somewhere near to the cleanliness you have achieved?[/quote]
Thanks Markus, this is only the second time i've used c/f and the first that i've used it both sides of the brace, to tell you the truth i've seen others work in here using c/f that i aspire to, although this part of the instrument isn't readily seen it's nice to have a neat job of it isn't it?
With this build i've even changed the shape of my braces to a continuous arc from one end to the other, i usually had a peak at the intersection,having already applied one layer of 6K tow between the brace and the top and the remaining layer still to be applied i scraped a very slight groove or hollow in the edge of the braces and applied a line of epoxy in it, using a piece of tape i stuck one end of the tow to the soundboard beyond the point where the tow was to finish and jave the tow a twist,, just enough to keep in a neat line, from there i just pushed it down into the epoxy.
I still think i could get it neater and use less epoxy but like everything,,,, practice makes perfect :wink: :wink: :wink:
Cheers,,,


Rod.
Like I said before the crash, " Hit the bloody thing, it won't hit ya back

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charangohabsburg
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Re: 16 inch Florentine archtop.

Post by charangohabsburg » Wed Jul 15, 2015 8:12 pm

Thank you Martin for the list of what not to do, and thank you Rod for the hints what to do. The slight groove on the brace edge, and the idea of how to stretch the strands will surely help a great deal if I'll ever attempt to go the CF - reinforced brace route! 8)
Markus

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blackalex1952
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Re: 16 inch Florentine archtop.

Post by blackalex1952 » Thu Jul 16, 2015 2:23 pm

I have a question. I understand the use of carbon fibre on the top and bottom of a brace to form an I-beam. I have heard that, along with the weight and stiffness advantages of CF, that its use can prevent "cold creep". However, I have never heard a definition of the term and can only
make assumptions as to its meaning. Violin makers build "spring" into bass bars which given time loose their spring. Unlike guitars, violin tops and backs can be easily removed and new sprung bass bars installed. Benedetto does not recommend building spring into braces. However, does Cf on braces prevent this? Hence my cold creep question.
Also. Is anyone interested in discussing how they fine tune CF braces after assembly as the tops cannot be shaved.
"Everything I say on the topic is based solely upon inexperience and assumption!"

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kiwigeo
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Re: 16 inch Florentine archtop.

Post by kiwigeo » Thu Jul 16, 2015 3:05 pm

I more used to hearing of cold creep when talking about adhesives....eg AR glued bridges can creep over time.

CF topped braces are a bit hard to trim once installed. When you build Gore and GIlet style...trimming of top resonance is done by adding mass to the sides.
Martin

blackalex1952
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Re: 16 inch Florentine archtop.

Post by blackalex1952 » Thu Jul 16, 2015 4:06 pm

Thanks Martin. I have the two books. I am interested in comments re HHG, epoxies, and other soundboard processes. I know a CF luthier who implied that he scallops the sides of CF capped braces to fine tune and adjust stiffness post assembly. Has anyone used epoxy to glue CF into a grooved brace then HHG to glue the brace to the soundboard ? My thinking is that the brace could be easily removed and replaced if the deflection measurements post assembly weren't right. That is the kind of discussion I am trying to elicit.
"Everything I say on the topic is based solely upon inexperience and assumption!"

seeaxe
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Re: 16 inch Florentine archtop.

Post by seeaxe » Fri Jul 17, 2015 8:39 am

blackalex1952 wrote:I have a question. I understand the use of carbon fibre on the top and bottom of a brace to form an I-beam. I have heard that, along with the weight and stiffness advantages of CF, that its use can prevent "cold creep". However, I have never heard a definition of the term and can only
make assumptions as to its meaning. Violin makers build "spring" into bass bars which given time loose their spring. Unlike guitars, violin tops and backs can be easily removed and new sprung bass bars installed. Benedetto does not recommend building spring into braces. However, does Cf on braces prevent this? Hence my cold creep question.
......
My two cents worth......

Creep is the increase in strain that happens over time for materials subject to continuous stress. Timber is generally known for creep and it is not unusual in structural timber members to consider creep strain (expressed as deflection) of 300% of the initial strain. (NZS3603)

For carbon fibre a quick google indicates that the increase in strain (e.g. extension of the tensile fibres per unit length) is about 2 percent of the initial strain, so relatively speaking, five-eighths of bugger all. The carefully selected bits of timber we use for braces reduces the problem but its still a lot "creepier" than CF. Hence CF will not only increase strength but also stability.

Because creep only occurs when something is under continuous stress, if something isn't stressed, it wont creep, hence perhaps Mr Benedetto's recommendation not to put in spring (prestress, in my world)

In reality, every part of the guitar is stressed to some degree once the strings are on and as we all know necks and guitar tops are prone to creep (deformation) failures if not adequately designed or if environmental conditions are unfavourable. From my understanding though this hasn't historically been an issue for well made guitars - the other day I was looking a you tube clip of Andrew York playing a Tarrega vintage Torres - 188 years old and it sounded fantastic. I bet he built that lighter than I build mine.

However, if you do want to build "spring" into a piece of timber and you want it to stay sprung then adding CF should help immensely.

By the way, that is an awesome looking guitar Rod, just beautiful. Inspirational stuff. The new owner will be a very, very lucky man.

Cheers
Richard

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rocket
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Re: 16 inch Florentine archtop.

Post by rocket » Sun Oct 18, 2015 8:13 pm

The latest news on this build, i took it to the Melb. guitar fest, not quite finished, couldn't really tell though, still had to hook up the elecs and polish the headstock and pick guard the rest is a satin finish, ended up a very tidy build, deliver next Thursday, hope he likes it.
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Like I said before the crash, " Hit the bloody thing, it won't hit ya back

www.octiganguitars.com

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Steve.Toscano
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Re: 16 inch Florentine archtop.

Post by Steve.Toscano » Sun Oct 18, 2015 8:36 pm

Absolutely beautiful !!

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56nortondomy
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Re: 16 inch Florentine archtop.

Post by 56nortondomy » Sun Oct 18, 2015 9:10 pm

Well done Rod, it's a real work of art, pretty sure the owner will be more then happy. Wayne

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