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Re topping Hippner 8 string with falcate bracing.
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Author:  johnparchem [ Fri Jul 10, 2015 6:45 pm ]
Post subject:  Re topping Hippner 8 string with falcate bracing.
A player that I know had a very damaged Hippner 8 string guitar. He had two accidents with it and had destroyed the lower bout of the top. He thought it a total loss so I asked him to bring it over.

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I pulled it apart, all and all it looks very nicely made and is in good condition other than the top. The WRC top was amazingly thin at 1.1 mm. It had a spruce lattice bracing. It probably sounded great but it was a little fragile as a gig guitar.
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The top was a total loss. I thought about trying to keep the old bindings\purflings because the linings that support the top were wide enough. I ended up pulling them as my top was a mm thicker than the old. I would have needed to drop the new top in. I have matching koa bindings that I can use as a replacement.

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The insides looks good. I got the fret board off cleanly so I will be able to reuse it. There were some cracks in the sides that were repaired, with the top off I cleaned up those repairs and make them more permanent. I also had to fix a few other side cracks.

I currently have the instrument re-topped and I am in the process of french polishing the top. I did use a falcate pattern, the molds I have for my Hauser guitars worked fine. I also followed tomigv suggestion and used CF under a 1 mm bridge plate.

To add a bit more lateral stiffness I built A new BRW bridge with CF laminated in the block a mm below the top of the bridge.

To match the geometry of the original guitar I built the top in my solera that is dished out for a 25' radius.

Here a few pictures

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Basic brace pattern with bridge plate. (a cut down version of the SS bridge plate form the book.

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Used my solera in a gobar deck

I was able to match the Koa bindings and BW purfling no problem
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Built the bridge in my handy classical bridge making tool. A simplification of the jig in the book. I cut the wings with a razor saw and a band saw and then used a rasp to shape them.

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I still have about .6 mm to remove from the bottom of the bridge so the weight will still come down
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The French Polish is getting close.

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Right now the top is tapping at 194 Hz, a little lower than I hoped at this point.
Author:  meddlingfool [ Fri Jul 10, 2015 7:00 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
That's too bad, as it's impossible to take it upwards, and stringing it up will drop it further. That being said, if you land at 190 when it's done, that could still be a fine number. Perhaps soft in the trebles, but I've never built either a falcate or a nylon string, so keep that in mind.
Author:  giltzow [ Sat Jul 11, 2015 12:08 am ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Beautiful save. Very impressive!
Author:  ernie [ Sat Jul 11, 2015 8:23 am ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Nice work john ,happy for you and the client. the falcate bracing looks excellent ps tomigv is my moniker on delcamp forum tomi is my nickname in hungarian , and ernest or ernie is my formal legal name. I would have made the rosewood patch slightly thicker at abt . 1.5-2mm especially with the 8 strings and the previous WRC top at 1.1mm ,it sounds like your client was an accident waiting to happen. No worries though, the CF patch will add a lot of x grain strength to the top. cheers from KC, PM me sometime, have some observations about falcate bracing you may be interested in. Is that a shedua bridge ???
Author:  johnparchem [ Sun Jul 12, 2015 5:50 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Thanks all for the comments and suggestions

Today I glued on the fret board, sorry I did not take pictures and installed the bridge. I normally use locator pins but I glued some K&K pickups on the bridge plate, and did not want to drill through them with locator pins. So I set the bridge carefully, using scale and compensation measurements and boxed in the location with tape. With the bridge taped down. I traced the profile with a scalpel and cleared out the shellac from the bridge location. Here are some pictures.

I still have finish touch up and surprise, none of my saddle blanks are long enough for an 8 string saddle. But it looks like the re top came out looking ok.

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Author:  johnparchem [ Tue Jul 14, 2015 3:40 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
I did a tap test with the finish and the bridge on, although I know in a classical the extra stiffness can actually raise the resonance of the top I was surprised that it went up.. With this tap test I ended up with 203.6 Hz for T(1,1)2 up from 194Hz; T(1,1)1 = 107Hz and T(1,1)3= 249Hz.

I need to wait a few days for the finish to cure and I have a set of strings on the way. I am excited to hear how it sounds.
Author:  gregorio [ Sat Jul 18, 2015 9:57 am ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
looks great!

Two questions, what is that funky looking rule and does the vacuum pad for the bridge work well / worth the money?

Gregor
Author:  johnparchem [ Sat Jul 18, 2015 10:14 am ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Thanks, The ruler is an ibex fret ruler, besides being a ruler on the backside it has fret and saddle locations for short and long martin scale length and a 650 and 660 classical scale.

I really like using a vacuum clamp for the bridge. The lmi has worked great for me.
Author:  meddlingfool [ Sat Jul 18, 2015 3:07 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
I think you'll pretty much be on the money then, as string tension will drop it down, ~5hz for steel, so maybe a little less difference in nylon?
Author:  Jim Watts [ Sat Jul 18, 2015 4:20 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
John that looks really good, nice work.
A couple of quick questions for you on collecting the spectra.
1) I seem to get more noise in my graphs than you or what Trevor has in the books, if I recall you fought that also, although I could be completely wrong on that. How did you manage to smooth them out? perhaps I'm tapping to hard.
2) This has to do with Gores top thickness formula. When holding the top for the cross grain vibrational mode, is it the same spot as the longitudinal grain, just tapped in a different place? I'm having a hard time telling from the book, I wish it was clearer on that.
Author:  meddlingfool [ Sat Jul 18, 2015 6:17 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Different spot
Author:  Jim Watts [ Sat Jul 18, 2015 6:20 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Where? It looks the same to me in the pictures.
Author:  meddlingfool [ Sat Jul 18, 2015 8:27 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Volume 2 6-7...
Author:  Jim Watts [ Sat Jul 18, 2015 8:49 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Ed, I've got both volumes in front of me, I'm dense ok. The spots appear to the same or very close to the same, at the intersection of the node line for the cross grain mode and the long grain mode, just tapped in a different spot.
I'm asking because I'm getting a frequency outside of the frequencies reference in table 6-1.
Author:  Trevor Gore [ Sat Jul 18, 2015 11:06 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
First sentence under Fig 6-13:

"To help in producing pure tones, the hold point should be chosen to be on the node of the vibration point under test whilst at the same time being in an anti-nodal position of other modes in order to suppress them."

What are you tapping? (Species, panel size, thickness, grain type?). Sometimes one gets combination modes. Check page 1-72 in Design.
Author:  Jim Watts [ Sun Jul 19, 2015 12:57 am ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Trevor, I've made a sketch of where I'm holding the top and tapping. If I move my hold point for the cross grain position I can't get a very clear tap ( I'm trying to find the clearest tap for each position). The top is Carpathian Spruce well cut AAA top, .140 (inches) thick. The long grain mode is at 60.5 Hz and I'm getting the cross grain at 88.5 Hz which seems low to me. I've always had a hard time finding the proper place to hold for the cross grain tap, so I appreciate the help. In you book you state to "make sure your measuring the lowest frequency present" I'm not sure I understand this, won't all of the frequencies be present no matter where I tap, meaning the twisting and long grain modes? I assume holding it in different paces just changes the amplitude of the various components of the spectra making it easier to pick out the various modes.
Do I need to shift my hold point along the node line one way or another? To me looking in the book they could be in the same spot, as each of the sketches has a different perspective.
Thanks,
Jim
Edit: I just played with the top and tried shifting my hold point about 2-2.5 inches towards the left end of my sketch and got a much high tap tone, but this doesn't seem like the right place looking at your illustration, if I shift it right it drops closer to the long grain tone. I should also note that I'm tapping in line with my new hold position each time as shown in my sketch above.
Attachment:
top half panel.JPG
Author:  Trevor Gore [ Sun Jul 19, 2015 2:29 am ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
In theory, the node lines are at 22.4% from the edges (Table 1.6-1). In practice that is normally the case, but the closer you get to the condition stated in the equation at the bottom of page 1-72, the more displaced and curved your node lines are going to be. So to get clean taps on the cross grain, for example, first try at the 22.4% down the width of the panel, which is a line along the length of the panel. You can hold anywhere on that line, but it is best to stay off the node points of other modes. So stay off the centreline (the node for the twist mode) and the 22.4% point long grain (the node for the long grain bar mode) and the other points listed as node positions in Table 1.6-1. If there is any ambiguity, a bit of tapping around at various hold points and tap points using a spectrum analyser should help you identify which modes are which. If all else fails, you can always do a static test (p 1-24) for long and cross grain E and use a generic 1.0 GPa for G with relatively little error (because target thickness is quite insensitive to changes in G).

88.5Hz seems low for cross-grain, as you say, but you may just have a floppy piece. Find another piece of similar thickness and just flex it in you hands and see if your other stuff is similar or much stiffer.
Author:  johnparchem [ Sun Jul 19, 2015 4:06 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
[quote="Jim Watts"]John that looks really good, nice work.
A couple of quick questions for you on collecting the spectra.
1) I seem to get more noise in my graphs than you or what Trevor has in the books, if I recall you fought that also, although I could be completely wrong on that. How did you manage to smooth them out? perhaps I'm tapping to hard.

Thanks Jim

One thing I found while doing FFTs is that if I had the mic gain too high I had all sorts of peaks that did not exist. Other than that I use the VA setup parameters right off of the document Trevor has posted.
Author:  Jim Watts [ Sun Jul 19, 2015 6:04 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Thanks John, that makes sense to me.
I apologize for side tracking your excellent documentation of re-topping the 8 string. Nice work!

Trevor - Thanks, the static test makes perfect sense and I can easily do this. With it I should be able to figure out my issues on holding the top for the cross grain tap.
Author:  johnparchem [ Sun Jul 19, 2015 7:39 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
No problem Jim, I post these builds just for the type of discussion you started. I strung her up and she sounds pretty good. I am using the original nut and saddle unchanged so far. I need to take about a mm off of the saddle, to nail the action. I think my bridge slot was not quite as deep as the original bridge. I also need to take a bit off of the nut slots. I am going to wait a few day to let the top settle in on a tonerite and then finish the setup.

With strings, T(1,1)1 ended up at 101 Hz T(1,1)2 is at 193 Hz and T(1,1)3 is at 243 Hz pretty close to my target.

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Author:  meddlingfool [ Sun Jul 19, 2015 7:51 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Stringing it up only took it down 1hz? Interesting...
Author:  johnparchem [ Sun Jul 19, 2015 7:58 pm ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
meddlingfool wrote:
Stringing it up only took it down 1hz? Interesting...


Strings did bring down the air, top and back down quite a bit. With the bridge and no strings I was around 203 Hz. The strings brought it down just a bit below where the top was before I glued on the bridge.
Author:  Jim Watts [ Mon Jul 20, 2015 12:02 am ]
Post subject:  Re: Re topping Hippner 8 string with falcate bracing.
Well I verified my numbers today by doing a static check, the modulii seem to match up very well with the modulii calculated by the dynamic test. The top is very stiff along the grain and somewhat floppy across the grain. So I guess my original number of 88.5 Hz is correct.
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