Just closed falcate classical - with tap spectrum

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Nick
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Re: Just closed falcate classical - with tap spectrum

Post by Nick » Mon Apr 20, 2015 6:04 am

kiwigeo wrote:A glue, epoxy, shellac and beer proof version of the books would be useful....like those kiddies books with the plastic pages so you can easily clean off the baby shit.
Similar to this :D
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Thanks for posting your build John, very interesting and as somebody who has yet to do a falcate build, it's encouraging to hear yet another person having such a noticable improvement with this style of build.
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Re: Just closed falcate classical - with tap spectrum

Post by Trevor Gore » Mon Apr 20, 2015 8:51 am

johnparchem wrote: Last night and this morning I spent some time trying to come up with any gaps in your build volume and I could not really come up with much....
Thanks for taking the time to respond, John. It seems like we got a pass!

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Re: Just closed falcate classical - with tap spectrum

Post by Dave M » Tue Apr 21, 2015 5:17 am

John and everyone.

I may be putting up a hostage to fortune but I overlaid carbon strands on my (classical) top today so I thought I would show the world what I've done and return at some, possibly quite later date, with the resonance measurements and sound evaluation on the completed guitar.

I have based it on the Fleta outline but essentially followed G&G's steel string bracing pattern. Brace height is at 7 mm maximum as near as I can get to it.

Very hard to be clean which I really don't like. I suppose masking off the areas not involved would be the real way to do it.

Trevor I am thinking about the rather huge question you have posed and will reply later. I suppose the initial response is that any gaps are few and small. And of course you and Gerard keep making the point that we should use your info as an aid to our own thinking so we shouldn't, and don't, expect to have our hands held all the way.

It's a good thing that you had the things bound properly. That white book gets an awful lot of usage!

Dave
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Re: Just closed falcate classical - with tap spectrum

Post by johnparchem » Tue Apr 21, 2015 6:34 am

Dave that looks neater than mine! I will be interested in the tap spectrum once you get the box closed and then with strings. I am right behind you with another classical.

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Re: Just closed falcate classical - with tap spectrum

Post by Dave M » Wed May 06, 2015 5:19 am

Right well I said I would follow up with the build... I closed the box yesterday a bit quicker than I expected.

The rosette is commercial. I am concentrating on getting the construction process right before worrying about that aspect yet - though I must say I liked yours John.

The spectrum is taken straight off the box. no thinning, no shellac. The spectrum is a one off but several repeats gave the same results.
The back is tied down with 4 heavy braces so, as intended, doesn't seem to show in the top spectrum.

I did some thinning round the edge but was pretty wimpish about the amount of material I removed so this didn't change the resonance peaks much.

Coupled resonant frequencies were:

Main air 97 Hz
Main top 199/200
Back 291

Subjectively the tap testing on the top was very encouraging. There was quite a lot of volume and the tone was attractive. We'll see if this tells us anything about the final result later. I note that the active area runs up to and around the sound hole which of course figures with the design but is nice to see in practice.

Will continue to report as the build goes on.

Cheers Dave
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Re: Just closed falcate classical - with tap spectrum

Post by johnparchem » Wed May 06, 2015 7:47 am

Thank you Dave! I am a couple of days away from bracing my next top. It looks like you can hit 190 when you get you bridge on and strung up. That is where I was hoping to land on my last one. I may go a tad higher than you as I will have an active back so there will be more coupling between the back and top. I will go back and look through the models in the book to make sure I am thinking of the coupling the correct way. Did you use the tap tones to figure out your thickness and did you use the classical vibrational stiffness number?

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Re: Just closed falcate classical - with tap spectrum

Post by DarwinStrings » Wed May 06, 2015 10:02 am

Dave M wrote:
Very hard to be clean which I really don't like. I suppose masking off the areas not involved would be the real way to do it.
With a bit of practice you can get it tidier without masking Dave, this is my number four and you can see in the close up I now manage to keep most of the epoxy contained within the centre laminate of the braces. I will clean those couple of little bit of spill.
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Re: Just closed falcate classical - with tap spectrum

Post by johnparchem » Wed May 06, 2015 10:17 am

Jim are you applying the with a small brush, it really neat compared to mine.


I been playing around with the 4 degree of freedom model, I changed the model so that it matched my last guitar as best I could. From It does not take that much more stiffness to get my previous 180 to 190, about 8% more top stiffness than I had. Dave your numbers concern me a bit as your 7 mm brace height is what I thought of trying. Your getting numbers close to my target with a non active back. The active back will cost me 4 Hz or so on the top from coupling, at least the is what the model says. I will have to give this more thought.

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Re: Just closed falcate classical - with tap spectrum

Post by DarwinStrings » Wed May 06, 2015 10:47 am

I use size 4 Chinese made cheap brush, the (I think pig) bristles are about 12mm long and I cut that square, down to 6mm giving a very stiff brush and I also use that brush to impregnate the CF tow on a bit of baking paper before applying it. I sort of scratch the epoxy on to the braces using very little in the brush. When I lay that CF on I just let it hang till the end touched my starting point then I just slowly let it drop down onto the brace sometimes pinning the end down with the brush till I have laid about 50mm on then I just keep dropping it down onto the brace and hardly touch it again with the brush except to guide it with the brush into place but I don't let the brush hit the braces again and so it just sits in place looking like a bit of rope that adds about 0.5mm of brace height. My braces are down to 6.4 mm and I am still coming up a bit stiff for my small guitar (with steel 13's on) so now I will be dropping the value of ƒ in the target thickness equations from now on.

Well done on tackling that 4 DOF business John.
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Re: Just closed falcate classical - with tap spectrum

Post by Dave M » Wed May 06, 2015 10:45 pm

John no I couldn't tap test the panels as my supplier had cut the corners off. I considered getting a E by deflection testing but I have had trouble reconciling the results from these two methods.

The top is Sitka with very little runout and I decided 2.3 mm was not going to be far wrong. Yes I will be aiming for 190 Hz. On this build I have included the mass support blocks so should be able to play with things.

For interest the weight of the full braced top was 205g.

As an aside this 'hippy engineering' binding machine is amazingly successful. My router is a bit heavy hence the counterweight.


Dave M
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Re: Just closed falcate classical - with tap spectrum

Post by Dave M » Wed May 06, 2015 10:52 pm

Jim thanks. That is extremely neat work. The thing I was getting wrong was that I needed to rest my wrist/forearm to keep steady and found myself touching the stuff already laid down. As you say practice is the way forward.

It's all a far cry from cutting mortice and tenons that my previous woodworking tended to be!

Dave M
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Re: Just closed falcate classical - with tap spectrum

Post by Trevor Gore » Thu May 07, 2015 9:07 am

Image

Gotta love that pit head binding machine. Looks properly industrial!

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Re: Just closed falcate classical - with tap spectrum

Post by Dave M » Thu May 07, 2015 6:11 pm

Yup must be my South Wales ancestry showing through. D
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Re: Just closed falcate classical - with tap spectrum

Post by Dave M » Sun Jun 14, 2015 6:10 pm

This is an old thread but the building process is for me fairly slow.

I have started spraying so have completed most of the woodwork, but when I came to start fitting the bridge I found the arched top is much flatter than expected. The falcate bracing was glued up in an 8 metre dish. The arching remains as expected round he edge but much less so in the middle

I wondered if others have found this with falcate bracing?
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Re: Just closed falcate classical - with tap spectrum

Post by johnparchem » Mon Jun 15, 2015 12:34 am

I have not noticed that. My guitars held the dome through the build process. I work in a climate controlled shop.

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Re: Just closed falcate classical - with tap spectrum

Post by Dave M » Mon Jun 15, 2015 5:09 am

Sorry I meant to say that my humidity is currently a bit higher than when the top was glued so I would expect the arching to have increased rather than decreased.
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Re: Just closed falcate classical - with tap spectrum

Post by johnparchem » Tue Jun 16, 2015 8:13 am

Before the bridge is put on there is not a lateral brace across the center of the top in the lower bout. So it will flatten. I put a radius on the back of the bridge, so that helps once it is glued on.

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Re: Just closed falcate classical - with tap spectrum

Post by kiwigeo » Tue Jun 16, 2015 8:24 am

Ive never had this problem but I notice some of the falcate braced guitars being built by students at Thomas Lloyd guitar building school have shaped falcate braces.....they get sanded in a radiused dish prior to installation.

This question was raised with Trevor at one stage and he stated he'd never had any issues.
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Re: Just closed falcate classical - with tap spectrum

Post by Woodsy23 » Tue Jun 16, 2015 12:07 pm

I am building my first falcate steel string guitar. After gluing the braces and boxing up the guitar, it has been not been in a humidity controlled environment and the humidity has generally been a lot higher than 45% - more like 60% to 90% - for many weeks. I have observed that there is a dip in the middle of the top at the bridge location. Placing a 10m radius edge across the top through the bridge location, it appears that the outer edges (1/3 of width) have gone into a smaller radius curve (as you would expect with higher humidity and therefore expansion) but there is a dip at the bridge location. It seems that the main falcate braces, which are very stiff because of the CF, are holding the middle down and preventing it from adopting the smaller radius curve in the middle that it wants to.

I have just put the guitar back into the humidity control room at 45% (been there 1 day). I will monitor the curvature of the top and see if goes back to the uniform 10m radius.
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Re: Just closed falcate classical - with tap spectrum

Post by Trevor Gore » Tue Jun 16, 2015 11:11 pm

I've not had any issues with tops "sinking" but neither do I leave guitars around without a bridge for long periods in varying humidity.

Dave, if there is no bridge plate (as per your earlier photos) there is nothing to hold the transverse arch up in the lower bout until you get the bridge on, other than the induced curvature forced by the primary falcates. When the humidity goes up, most guitars will bulge upwards due to the transverse bracing beneath (includes X-bracing) not expanding. A falcate braced guitar only bulges where there is transverse bracing, i.e. in the region of the secondaries and tertiaries, on a finished guitar remaining flatter in the center held by the stiffness of the bridge and its curvature. This is generally a good thing, as the action doesn't change much with the weather. (Smallman moving to a tilt-neck design was due to the humidity pumping and consequential action changes that lattices cause). If the guitar goes through a few humidity cycles with no bridge or bridge plate, even when equilibrated to its build humidity, it is possible that the single, smooth arch might not fully recover. But you'd want to be sure that you weren't looking at the double arch caused by high humidity. This suggests it may be worth "propping" the center of the top if the guitar is to be left for long periods without humidity control. Not sure it will work, because I've never had to do it. Gluing on the normal classical bridge (as per the book, with CF and design bottom curvature) should smooth it all out again.

BTW, if you do the same with a fan braced classical with no bridge plate (i.e. humidity cycle it) it can and will develop corrugations between the fans that will not disappear when returned to design humidity. I've seen cases where these corrugations have been too deep to sand out, necessitating re-topping the guitar.

So the ways I know that avoid this problem are to complete more quickly and maintain humidity control.

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Re: Just closed falcate classical - with tap spectrum

Post by Dave M » Wed Jun 17, 2015 4:13 am

Thanks for the input all.

Trevor what you say makes sense, I am indeed not using a bridge plate.
Just for information I have been keeping a close eye on humidity and having done the gluing at around 50% it has not been above 60% since. You're extremes Woodsy I can imagine leading to pretty high distortion.

Maybe this is an argument for gluing the bridge on before finishing... at least on a falcate build?
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Re: Just closed falcate classical - with tap spectrum

Post by Woodsy23 » Thu Jun 18, 2015 12:22 pm

My falcate SS (without bridge) has now been in the humidity control room (small bathroom with dehumidifier) for nearly three days at 45%. The cross curvature in the outer areas (1/3 of width) of the top appear to have returned to a radius of about 10m. However, a dip remains in the middle 1/3, between the apexes of the minor falcate braces. Placing a 10m radius edge across the top at the bridge location reveals a gap of about 1 to 2mm in the middle.

So Trevor, you are right about the single smooth curvature not recovering after going through varying humidity before returning to 45%.

I think I will try propping the middle up, off the back, while I glue the bridge on. I guess I should aim to set the middle at a level that will give the correct gap below a straight edge placed along the neck - 2.5mm plus the 7mm thickness of the fret board and frets so 9.5mm in total. As I recall, when I did a quick measure of this gap before putting the body in the humidity control rom, it was 10mm. So, as the humidity rose, it appears the middle didn't rise much above the correct level.
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Re: Just closed falcate classical - with tap spectrum

Post by Dave M » Wed Jul 08, 2015 4:29 am

Well I strung my falcate braced classical that I have posted on before. I am seriously chuffed! It is a really nice guitar. It has volume, it has sustain, it seems to have presence. It makes me want to take up playing all over again!

I'll have to learn properly how to damp strings at the end of a note which I didn't really need to do before.

There are a couple of snaps below, also the resonance spectrum which is a single shot but several repeats gave the same results. Changes to frequencies from the closed box with no neck or bridge to complete were:

Top main: from 199 to 195
Main air: from 97 to 102
Back is around 296 but is heavily braced.

That 195 Hz top ought to be giving me trouble with the open G string but I really can't hear it. Maybe it is just far enough away. I have mass addition blocks on the side so once it is settled a bit I will experiment with some weight to see if it improves things.

I repeat that my falcate braces were 7 mm at their maximum, shaped as per directions in the book.
I did manage a low mass bridge. Despite being a traditional design in EIR it weighed 16 g without a saddle.

With reference to a previous post concerning flattening out of the centre I glued the bridge which was shaped to the original curve on the base, with a similar shaped caul and it is now pretty much back to the 8 m curve.

In terms of appearance I haven't buffed it at all, just used micromesh up to 12000 grit. This a wet and dry abrasive available in the UK and no doubt elsewhere.

Thanks to Gerard and Trevor. This has made my day, My year!

Dave
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Re: Just closed falcate classical - with tap spectrum

Post by demonx » Wed Jul 08, 2015 7:53 am

Looks great, you should be happy with that!

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Re: Just closed falcate classical - with tap spectrum

Post by kiwigeo » Wed Jul 08, 2015 8:04 am

Really nice work there Dave....really nice work. Nice work dealing with the top losing its arch too......
Martin

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