Search found 518 matches

by johnparchem
Sun Sep 05, 2021 1:34 am
Forum: Instrument Builders Forum
Topic: Finding the High Points
Replies: 9
Views: 504

Re: Finding the High Points

One other option to chalk is sand paper to mark the high spots on the cheeks. I insert a strip of sandpaper under the cheeks and pull once. The sandpaper will mark the high spots. I use a chisel to remove the high spots. This is not "flossing" as I am not trying to change the neck angle, just mark t...
by johnparchem
Fri Sep 03, 2021 2:31 pm
Forum: Instrument Builders Forum
Topic: Finding the High Points
Replies: 9
Views: 504

Re: Finding the High Points

Yup normal blackboard chalk.
by johnparchem
Thu Aug 19, 2021 2:34 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Collecting 4DOF models
Replies: 26
Views: 2138

Re: Collecting 4DOF models

Just read through the posts. I am not sure it is addressed, does the mass of the top only include the vibrating area of the top not the weight of the top itself. That thought always kept me from weighing the top.
by johnparchem
Sun Aug 01, 2021 11:51 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Soundport and Weight Effects on Frequencies
Replies: 6
Views: 581

Re: Soundport and Weight Effects on Frequencies

Interesting data, I had always planned on playing with the sound port size but never did. My falcate braced classical guitar all have very long sustain relative to my fan braced guitars. I do not use a lower transverse brace on my falcate guitars and I do on fan braced guitars. I am not sure how to ...
by johnparchem
Mon Jul 26, 2021 12:43 am
Forum: Instrument Builders Forum
Topic: My third guitar
Replies: 9
Views: 955

Re: My third guitar

Very nice! I love everything about it.
by johnparchem
Sun Jul 25, 2021 5:07 am
Forum: Instrument Builders Forum
Topic: Beginners question
Replies: 6
Views: 768

Re: Beginners question

... and some seem to end the lower arms of their crossbraces about 10mm from the Kerfing . In this case it seems to me that tension carried by the strings is being held by the glued rim of the soundboard . How does this work ? It’s attractive as I can see that the lower part of the soundboard is fr...
by johnparchem
Tue Jul 06, 2021 11:45 pm
Forum: Instrument Builders Forum
Topic: Falcate Bridge Plate Thickness
Replies: 6
Views: 758

Re: Falcate Bridge Plate Thickness

If I recall there were two options, the thicker one was to be used if the CF fabric under the bridge plate was not used.
by johnparchem
Fri Jul 02, 2021 5:20 am
Forum: Instrument Builders Forum
Topic: Tear out
Replies: 8
Views: 1103

Re: Tear out

I drop fill with gluboost fill and finish. I wait to drop fill until after I have sealed the top, usually shellac for me. I could see drop filling with lacquer if lacquer is going to be used to finish the top. I find any wood fill always shows more. Sometimes even the matching bit of chip out, as th...
by johnparchem
Sat Jun 26, 2021 8:12 am
Forum: Instrument Builders Forum
Topic: Vacuum clamping bridges
Replies: 20
Views: 2298

Re: Vacuum clamping bridges

John, I do normally use a couple of 1/16" pins through the saddle slot. I tried replacing those with tapered wood pins that I think would have plugged the holes, but maybe not. I realize now that I never tried the clamp on the top with the pins in and no bridge. Should have done that.-Bob I specula...
by johnparchem
Thu Jun 24, 2021 8:25 am
Forum: Instrument Builders Forum
Topic: Vacuum clamping bridges
Replies: 20
Views: 2298

Re: Vacuum clamping bridges

John, I do have a reservoir on my system. The unit will quickly pull the air from a bag when I use it to veneer lap steels. When I stuck the LMI clamp on the back of an instrument, it would seal in about 20-30 seconds, shut off, and hold a vacuum. Just was not able to ever get it to shut off when u...
by johnparchem
Thu Jun 24, 2021 2:46 am
Forum: Instrument Builders Forum
Topic: Vacuum clamping bridges
Replies: 20
Views: 2298

Re: Vacuum clamping bridges

Vacuums are powerful things. How do you stop the guitar from imploding? Do you put in violin style sound pegs? The vacuum is not strong enough to rip through the top; it does pull the membrane down to the top. With regards to leaking the vacuum will pull air through the sound hole. If the guitar bo...
by johnparchem
Thu Jun 24, 2021 12:38 am
Forum: Instrument Builders Forum
Topic: Vacuum clamping bridges
Replies: 20
Views: 2298

Re: Vacuum clamping bridges

a sponge gasket on 2.x mm thick wood is not as air tight as a vacuum bag. So sure, the vacuum needs to be continuously applied. Setups with reservoirs will cycle on and off as a lot of the time the vacuum is maintained by the reservoir.
by johnparchem
Sun Jun 20, 2021 12:39 am
Forum: Instrument Builders Forum
Topic: Falcate Bracing question
Replies: 3
Views: 697

Re: Falcate Bracing question

The CF tow for the primary braces passes under the bridge plate. The primary braces are clamped on to the tow during the open time of the epoxy used to glue down the tow.
by johnparchem
Thu Jun 10, 2021 11:54 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Is two better than one?
Replies: 4
Views: 595

Re: Is two better than one?

I do not see a spectrum spike at 216 Hz. I am wondering if your back is pitched a bit below the top and the back is showing at 206 Hz and the top at 230 Hz. You can stick some mass on the top and/or the back (like blue tac) and see how the peaks move in relation to each other.
by johnparchem
Thu Jun 10, 2021 11:04 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Is two better than one?
Replies: 4
Views: 595

Re: Is two better than one?

Is one of the monopoles the back and one the top?
by johnparchem
Wed Jun 09, 2021 6:31 am
Forum: Instrument Builders Forum
Topic: Just completed first Flamenco Negra
Replies: 4
Views: 706

Just completed first Flamenco Negra

I just completed my first Flamenco Negra. It has the flamenco sound, percussive a lot of separation while played, much less sustain than my classical guitars and easy to play very fast. Before starting the project I was not sure I knew what a Flamenco Negra was. I luckily got my hands on a couple of...
by johnparchem
Mon Jun 07, 2021 4:07 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Adjusting T(1,1)1
Replies: 4
Views: 823

Re: Adjusting T(1,1)1

... Maybe a concern would be moving T(1,1)2 to too close to 185 Hz (F#) ? ... If you use the back to move T(1,1)1 you certainly will move the top down. If you wanted to experiment changing the size of the sound hole may be your best bet. If you want to reduce T(1,1)1 you need a smaller sound hole. ...
by johnparchem
Sun Jun 06, 2021 11:45 pm
Forum: Instrument Builders Forum
Topic: Shellac and other finish
Replies: 4
Views: 759

Re: Shellac and other finish

I use Royal Lac, a modified shellac that is much more durable on some of my instrument. Using straight shellac I find that it takes about a month before the finish truly cures. Even longer if the finish is thick. Once cured shellac stands up to normal wear and tear.
by johnparchem
Sun Jun 06, 2021 4:14 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Adjusting T(1,1)1
Replies: 4
Views: 823

Re: Adjusting T(1,1)1

Where are you in the build? My advise is only relevant if the numbers you listed are on a strung up guitar. My first thought is that unless you are chasing a wolf note on G#, you are in the range to just leave it as it is. With regard to the back braces you would have to really lower them before it ...
by johnparchem
Sun Jun 06, 2021 12:49 am
Forum: Instrument Builders Forum
Topic: 2 geets on the go
Replies: 10
Views: 4857

Re: 2 geets on the go

They both look great! Nice finishes.
by johnparchem
Tue May 18, 2021 9:33 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: T(1,1,)3 Double Peak
Replies: 4
Views: 866

Re: T(1,1,)3 Double Peak

One of the double poles may be another top mode like the cross dipole. The first of the double is probably your back.
by johnparchem
Sun May 09, 2021 2:40 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Confused about frequency response in my first TG style falcate
Replies: 20
Views: 3049

Re: Confused about frequency response in my first TG style falcate

... Just adding the mass of the strings can make quite a difference which people often put down to loading the soundboard with string tension, when I usually find that the change can be accounted for by the added mass. ... Interesting, I do test my steel string guitars with pins and saddle both bef...
by johnparchem
Sat May 08, 2021 2:05 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Confused about frequency response in my first TG style falcate
Replies: 20
Views: 3049

Re: Confused about frequency response in my first TG style falcate

Besides lowering the top resonance (T(1,1)2) the side mass increases the size of the monopole, So having a 160 Hz guitar with a large monopole would be a different sound than you ended up with. I would take a 170 Hz guitar with no side mass over a 160 Hz with 600 grams of extra mass.
by johnparchem
Fri May 07, 2021 10:44 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Confused about frequency response in my first TG style falcate
Replies: 20
Views: 3049

Re: Confused about frequency response in my first TG style falcate

Gorgeous guitar! The frequency spectrum looks good with a lot of peaks and the guitar came out very close to target before doing anything. How does it sound now? How is the intonation?
by johnparchem
Thu May 06, 2021 11:35 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Confused about frequency response in my first TG style falcate
Replies: 20
Views: 3049

Re: Confused about frequency response in my first TG style falcate

Stringing up the guitar drops the top resonance T(1,1)2 about 5 Hz and with coupling drops the air and back. Looking at your set of plots I noticed you made changes before stringing the guitar. You looked pretty close with your back low. I would not have made any changes until I had a plot with the ...