Shaping tone bars

[Darren Kern]

Looks like I've ruined one of my tone bars, it's too thin on one end and it still doesn't fit the inside of my top. #There are plenty of posts explaining how to shape them, I just am having a hard time. #Did anyone else ruined a tone bar or two when they were first learning? #The more work I do, the more respect I gain for real luthiers. #Also, where's the best place for me to get new ones? #I don't have any power tools really, so somewhat pre-cut is best for me.

[arbarnhart]

I could cut one for you from generic spruce. Email me and we could work out a time for you to swing by if interested. I could cut it reasonably close on the scroll saw and then you would have to finish shaping it. My plan for shaping is to use sandpaper inside the top in nearly the same manner as fitting bridge feet. My shop is in disarray right now and I haven't been working on mine as much as I would like to. I would take the opportunity to go ahead and cut a few, so I would have mine roughed out also.

But I hope others respond because I don't have the experience to suggest what will keep you from messing up the next one (or keep me from messing mine up).

[thistle3585]

I went through two before I got it right. I used Siminoff's idea on tracing the profile on the bar. When I tried it that way, vs. the way Arbarnhart uses, it went fairly easy. I sanded down to the traced line then lightly sanded to fit. I too can provide you with some tonebar material. It is spruce.

[arbarnhart]

When I said "cut it reasonably close on the scroll saw", what I meant was using a traced profile, but I would probably err a little on the conservative side.

To be even more specific, I would use 3D cutting technique, taping the parts back together and making multiple passes.

[amowry]

I use a pair of dividers to scribe the curve on the bars, then cut close to the line on a bandsaw (you could use a scroll saw, or just carve them completely by hand). I use a spokeshave set very fine for the rest. I lay strips of crabon transfer paper in the tone bar position, rub the bar back and forth on it slightly, and shave away the darkened areas. It's important not to press down much when you rub the bar on the transfer paper, or you will bend the bar and/or the top, and end up with a bar that fits but must be sprung into place. I've tried using sandpaper in a similar way, but didn't have much luck getting a good fit. I know of others who are able to get sandpaper to work, though.

It definitely takes a little practice-- if you are cutting new bars you could leave them a little higher so you have plenty of wood. It's easy to carve way afer they are glued on, and it actually makes shaping them to fit the top easier if they are higher, because they are less likely to flex while you are working on them.

[van]

I am new to building only working on #9 I have learned a lot and I have found out that basic hand tools are really all that you need. A coping saw is cheap and you can cut a new tone bar with that. Traditionally Spruce is the wood for tone bars but you can use any kind of wood that you want and get satisfactory results. I use Aspen or Cedar or whatever is handy and I have had excellent results. Being lazy, I have even cut just a small brace about 3" long and glued it lengthwise under the bridge and it worked fine. I have seen some early Gibson's done like that, with just one brace. I suggest that you buy a coping saw and a 2"X4", you should be able to get both for under $10.00. Don't let the traditionalist methods hinder your creativity. Experimenting might lead to the discovery of something incredible and maybe 100 years from now people will be talking about you like they do Loyd Loar now.
I don't want to step on anybody's toes, following the traditional methods will net excellent results but don't try to be Loyd. There was only one Loyd and he was it.

Van climbs down off the soap box to run and hide.

[testore]

At the violin making school it took 3 days and I think 4 different pieces of wood to fit a violin bar. Granted violin bars are way more difficult to fit because of many reasons but don't let it discourage you. I use chalk to fit my bars. then I use a knife or a flat bottom finger plane to fit my bars. The final fitting I do with a scraper.
Gary

[sunburst]

I fit 'em with chalk.
I start with the band saw, then finger planes, then scrapers. The chalk does the same job as carbon paper, but takes up virtually no space, so it's slightly more accurate.

Practice makes a big difference, so, if you want to, you can fit random wood scraps together just to get better at it.

[testore]

Van,
I bet Lloyd never put one in himself. does anyone have any info to counter that? I wonder how much input he had in the process. Was he only interested in the end result? It would be great to know what makers from the Loar workshop made the most consistantly Loar autographed mandos. I can promise you that there was a trend that was recognized in the workshop. I've posted the question before about the names of the builders in the Gibson factory. Amongst my friends in the violin trade that I know well, I can hear who made what violin without looking at them. Also I have had a great opportunity to play many Old Wave mados. They all sound like Old Waves. The A strings in particular are very distinct. It would be great to line up several pure Loars and play them with the knowledge of who the makers where. Has anyone had that kind of opportunity, and can the Loar experts point out details that can point to a consistant maker,even without knowing his name? Kind of WAY off topic here I know,but I find that kind of stuff very interesting.
gary

[RJinRI]

I had no problem getting a nice tight fit to soundboard, but I'm stumped to know just how much wood to trim off of the tone bars, w/o investing in a stobe tuner. "tapping" on bass bar is definitely a lower pitch than that of the treble bar, but just how far does one go?
rj

[sunburst]

I used to tap and use a strobe tuner and write down the notes, but, I never saw a pattern of any sort. It's almost impossible to tune to specific notes, and maybe even closer to impossible to tune different pieces of wood to consistent notes.

I suppose I'm using "intuition" now. I grab a finger plane and start carving wood off. Suddenly, a "little voice" says "stop!", and I do. Usually, I come back later and shave off a little more, but I don't tap and tune to notes anymore. Sometimes I even forget to see what notes I have and write them down, because I don't think I've gained anything from doing that in the past. I weigh the top before and after the tonebars, and usually come out within about 5 grams of the same weight. I want to start checking the stiffness somehow other than just feel. Something like what Don McCrostie is doing.

You just have to build a few instruments to get a feel for how big the tonebars should be.

[arbarnhart]

[...]
Being lazy, I have even cut just a small brace about 3" long and glued it lengthwise under the bridge and it worked fine. I have seen some early Gibson's done like that, with just one brace.
[...]
Yep, a lot of the old oval As have that and sound great. My modern oval A has a single bracing bar that runs from the tailpiece to the hole. Freaked me out when I stuck a mirror in there; because its dimensions are so close to the old As, I expected to find a brace like the one they had. My mando sounds great, so I got over it. Some radically different approaches seem to yield good results. But tone bars and F holes seem to go hand in hand. I don't know why that's so, but it seems to be. I am going to do that also.

[RJinRI]

Ok, 'guess i'll stop fretting over it and just go glue the back on, plow forward & hope for best. BTW, its the IV kit i'm building before getting too serious into #1 scratch, f-style.
John...thanks for the experienced words of wisdom.
RJ

[Dale Ludewig]

I'm with John on this one. Intuition. It's good, I think, if the bass side raps a little lower in tone that the treble side, which goes against (at least to my mind) all intuition in that more would would ring higher. Maybe I just don't understand. I stop like John said when my mind says stop. Actually my ears say stop. And then there is the stiffness issue, nothing to be taken lightly! I think to get the best sound you're frequently on the "edge". If it's your first, stop sooner than later. It'll be fine. I've made mandos that I can't get the tops to resonate at the same frequency no matter what I do and I know I'm at the edge. So you adjust with the tone bars (braces in my mind) and go for it. You can't tell the difference. Remember, it's the completed instrument that counts- all made of little pieces. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

[Antlurz]

I'm with John on this one. Intuition. It's good, I think, if the bass side raps a little lower in tone that the treble side, which goes against (at least to my mind) all intuition in that more would would ring higher.
What limited experience I have, the treble bar rings lower than the bass bar.

Ron

[Stephen Perry]

At the violin making school it took 3 days and I think 4 different pieces of wood to fit a violin bar.
Wow, that's amazing. I started with 10 rough pieces of wood and fit 3 bars today in left handed violins. Have 7 more thicknessed bars now, which I like having. Also sold a couple of mandolins and a violin outfit and researched moving up to the Shenandoah Valley. Probably takes me 40 minutes to fit a bar tightly. Maybe just practice to do it fast. I think I wrecked a couple for my first violin.

One can also use carbon paper for finding high spots. I fit a rectanglar tall bar. Run a tuning fork along the top before gluing while holding it in place to find dead spots (gaps). Trim the bar to near final height, but leave the top straight. Apply relatively thick glue to the bar and press in place to leave glue on the top. Let that set and settle a bit. Then apply hot water briefly to bar & top, set in place. It sucks right down. Then put top in fixture that lets a central weight (a plane) press the bar into the top. Makes for a strong, nice fit. I use bandsaw, planes, scraper.

Then I shape the bar to my specs by measuring through the top. Cut with chisel & planes. I cut a little over final size, then use my own tuning technique on the bar. This works well.

[peter.coombe]

Although I do use Chladni plate measurements, I do not place much emphasis at all on the absolute note the tops are tuned to. Usually what I do is to carve to dimensions that get me to a stiffness and sound, when the top is tapped, that I know from experience is in the ball park. Stiffness I measure by flexing with my hands. Then I measure and note the measurements. The braces are then glued and shaved down to dimensions I know will work (from experience). I use my own form of X bracing that has been developed by trial and error ofer the years. Then I measure and note the measurements. The back is then carved and measured closely as it is carved until I get the measurements spot on, or as close as practical, that I know from experience will work well. I believe that matching the top and back is far more important than tuning the top to specific notes. There is a lot of experience involved, and a lot of compromises because of the highly variable nature of wood. The more you make the more you learn what works and how to be consistent with a highly variable material. It is a complete waste of time to try to tune to specific notes because wood is such a variable material it is very often impossible to reach specific notes. Tune to specific notes and you are likely to end up with some of your tops collapsing.

Getting the bracing to tightly fit the top is not so easy, but it comes with practice. Try out different techniques, and there have been a number outlined above, until you find something that works for you. Buy more wood than you need. Expect to waste wood on your first few instruments, you will not get it right the first time.

[P Josey]

I want to start checking the stiffness somehow other than just feel. Something like what Don McCrostie is doing.


What is it that Don McCrostie is doing?

[sunburst]

Don is "deflection tuning".
He has a jig that applies a known force to the mandolin plates, and he measures their responce with dial indicators. He carves and graduates until the plates are within a range of stiffness and weight that gives him consistent results.

[Dale Ludewig]

Ron, what I meant was that I'm not tapping on the tone bars themselves but on the outside of the top in the area of where the feet of the bridge come down. I think this would give you a different result than tapping the tone bar itself and I would think that it would have a good deal to do with placement as well as mass. Then again, maybe I'm losing it. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

[peter.coombe]

Dale, it really does not matter whether you tap on the outside of the top, or tap on the tone bar itself. What you are hearing as the "tap tones" are the eigenmodes of the top. "Tap tones" and eigenmodes are exactly the same thing. The frequencies of the modes do not change no matter where you tap or hold the top, but the relative amplitudes will change depending on where you hold and where you tap. Thus it will sound different if you tap on one place of the top compared to another because in one case you are exciting one mode more than the others. The frequencies of the eigenmodes are a function of stiffness and mass which gives you almost an infinite number of possibilites because you are dealing with stuffness and mass effectively in 3 dimensions (3rd dimension is height of the arch). Maybe intuition is the best way of dealing with all this complexity, but personally I prefer to measure and try to use the measurements to improve consistency.

Don McCrostie measures stiffness by measuring deflection of the plate when subjected to a known force. Personally I believe this is only half the story because it ignores mass. It is fine if the wood is reasonably consistent (e.g. same tree), but wood is notoriously inconsistent. A top that is light in weight, but of the same stiffness of a heavy top when carved to the the same thickness will almost certainly sound different in the finished instrument.

[sunburst]

Don does weigh his tops and backs. Any that are too light, or too heavy at his "correct" stiffness get discarded.

Actually, those that are heavy are usually too stiff, and would be too thin if carved to his "correct" stiffness. So, he uses a range of stiffness, thickness, and mass. If it's not in the range, he doesn't use the plate.

[Dale Ludewig]

Peter- thank you. That explains many of the things I've noticed. As you stated, it does sound different based on where I hold the top when I tap on it. Back to my books on acoustics. I appreciate your sharing and wish I knew more of the science involved. But this type of input just makes me want to get on it that much more. It isn't that I don't have enough reference books. It's that I haven't taken the time to get through them. Wish I could put them under my pillow and have osmosis learning. Thanks again.

John- at what point does Don weight his tops and backs? Are they all cut to the same size/ volume? Or does he rough carve them to a certain point and then weigh?

[french guy]

I don't know if I'm in the right direction , but I do that , and it works for me .
http://perso.wanadoo.fr/jl-mand....rs.html (http://perso.wanadoo.fr/jl-mando/construction/tonebars/us_tonebars.html)

[sunburst]

Dale, Don carves to a starting point on CNC. He does his deflection measurements, then he has a program that selectively carves certain areas to lesson the stiffness of those plates that are too stiff.

That's all I know for sure.
I assume that that is the point where he starts to measure and weigh, and that he probably does it occasionally during the process, but, I also assume it really doesn't matter when you take your measurements.

[thistle3585]

I am curious how Collings does it, because I keep hearing that the Collings mandos are the most consistent in sound. Any ideas?

[Mario Proulx]

how Collings does it

CNC

[Dale Ludewig]

Yes, as far as I know: Collings: CNC

[oldwave maker]

Just talked to Les Hassle of the tonebar dept at old wave heavy industries, he claims they always cut the tonebars first, then get the robots to carve the insides of the tops to match. Dont much believe him, since he also told me routers and drill presses turn counter-clockwise south of the equator.....
ones with my actual signature on the label have the compass, carbon paper, chalk, supersharp chisel, sandpaper, and scrapers before mating with fresh hot hide glue.

[sunburst]

A friend of mine, who worked at Collings, told me there is a guy there who twists and flexes the tops and backs after they come off the CNC, and does the final graduations by hand.

[Stephen Perry]

For final contour in violins, once glued in, I make a first cut by the numbers, in this case, numbers provided by Michael Darnton and derived from the Hill and Wurlitzer practice. Then I round the bar in the typical manner because people make funny comments if I don't. No need to, really. Then I tune the bar by tapping along it, lightly carving down the spots that ping at a higher pitch. With the plate damped against some sheepskin. Post assembly, I continue tuning the bar with small scrapers through the F hole to eliminate irregular response from dead spots and so on. This system seems to work very well for me. Were I making mandolins I would do the same thing. The profile I use puts more strength in the area of the F holes, then drops off as the cross arch becomes complete and can take up the stress.

My experience is that the fine tuning has more effective on the details of tone production than the gross shape. Perhaps there's an interference process going on, where things come in and out of phase. I don't know.

I also fine tune the ribs, the top and back before finishing, etc. Not in a gross sense, but in looking for ways to get the whole instrument working as a unit rather than conflicting parts. Like tuning a piano. Lots of fine adjustments with a particular overall effect in mind. And certain standards.

Steve

[Dennis Russell]

Hello: I have been reading these post on top plates and tone bars, I am not a proffesional to all this, I just finished putting strings on my latest mandolin that I built from scratch, it doesnt sound the way I would like it to sound. I am loking for that rich long lasting sustain that some of the gibsons have. I couldnt afford buying one of those fine playing mandolins so I set out a few years ago to make my own. this last one is #no 7 and one mandola. books I used were Roger Siminoff and the videos by Don Mc Rostie, but the carving and tunning the top plate is a mystery to me, I dont have all the exspensive equipment to check it out . If I had the funds then I wouldnt waste my time on the equipment I would seek out a fine mandolin somewhere, buy it and play the dickens out of it. I bought a exspensive strobe tuner two years ago I am still trying to learn how to use it on sound plates, I still cant get the science of tap tunning. all I can say OH well another mandolin, to hang on the wall to collect dust, start getting material together to build another. I will continue untill I get one that I like thesound, but then I would say all that effort, migh as well build a few more. I have some articles from the GAL about mandolins that have "X" bracing for tone bars, has anyone got good results from this. Dennis In Arizona

[Antlurz]

he also told me routers and drill presses turn counter-clockwise south of the equator.....
....that's cause the sine wave on the alternating current is upside down, down there.

Simple Geriatrics.

Ron

[ShaneJ]

Dennis, you sound like me. Sometimes I'll spend a quarter to save a nickel. I was thinking back just the other day on the amount of money I've spent on tools, wood, hardware, books, videos, glue, sandpaper, etc.... And that's just on #1 - which I havn't finished yet (still need to buy some shellac & stuff). I could have bought a very nice mandolin. I'm sure by the time I'm working on #7, I'll have spent enough to buy another very nice mandolin.

I have just as much fun trying to build something as I do picking though, so that's fine with me. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

[del]

Hi,

"Grease-Free" chalk has been mentioned.

Is it OK to use blue construction chalk (for chalk lines)?

If not who sells the proper chalk to use?

Thanks,

[sunburst]

I've used the blue chalk, and it worked fine, but it's hard to clean off of the wood when you're done fitting.

(For those who don't know, the blue construction chalk is for temporary chalk lines, and will clean off pretty well. The red construction chalk is for "permanent" lines, and I wouldn't recomment using it to chalk fit wood.)

I just (like, 15 minutes ago) finished fitting and glueing a pair of tone bars with white black board chalk made by Crayola.
Dustless chalk is the type that has grease, oil, or something in it to help keep it from putting dust into the air, on your clothes, etc. If you can find blackboard chalk that is not dustless, it should be OK.
White is a little hard to see on the nearly-white spruce, so I have to hold the bars at an angle to the light, and it took a little practice to learn what a thin layer of it looks like, but now that I've learned to use it, I prefer the white because it doesn't leave bits of color in the pores of the wood.

While we're back on the subject of tone bars, I'll mention this:
I posted earlier that I no longer try to tune the bars to notes, but sometimes record what they are. Well, I tapped the bars in a top I just "braced" the other day, and they were C + 25 cents, and C# + 25 cents. Not specific notes, but exactly one half step apart. Happened just by accident.

[del]

Thanks John,

Just my luck, my lady is a school teacher. #I'll get her to sneak a few chalk sticks out of class today. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif

Gerry

[Bill Halsey]

I’ve used white Nupastel for decades to fit bars, washed it off before gluing & have never had a problem. Talcum powder works too -- it's easier to clean up.

When fitting a bar, I glue in three little spruce studs as guides, perhaps only 3 or 4 mm square; two along the layout line (along the inside edge of the bar) about 25% from each end, and the third at one end of the bar as a stop. Just press them in place with a tiny bit of hot hide glue, they’ll grab in an instant and will be plenty firm by the time you get the bar roughed out with a paring chisel. These make fitting the bar much quicker and easier (15 – 25 min. for a perfect fit w/no spring, using chisel, small plane & scraper), and are also an aid while gluing it in quickly, before the glue gels.

Warm the top & bar, butter up the bar, pass it over the alcohol lamp a few times, more hot glue (not too thick) and slap it in. After the clamps are on, the little studs lift right off after cleaning up with hot water. Then, give it a few more passes with the alcohol lamp.

[Yonkle]

I use the pencil cut in half method, or a compass works good. #Once I got the fit to the sound plate close then I use my "secret method" #Tape some fine sandpaper over the area the tonebar will be and rub the tone bar on the sandpaper (the same method you use to flush a bridge to the body) works great and makes a perfect fit in minutes.
Once glued in then I shape with the same stuff mentioned above. For a flush fit this works perfect.

[RJinRI]

Ok, 'guess i'll stop fretting over it and just go glue the back on, plow forward & hope for best. BTW, its the IV kit i'm building before getting too serious into #1 scratch, f-style.
John...thanks for the experienced words of wisdom.
RJ

'on #7 scratch-build and i must be getting dumber, cause i still dont know when to stop or keep removing tonebar wood :)