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| String Pressure and String Clearance http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=53080 |
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| Author: | Ken Nagy [ Tue Apr 07, 2020 5:55 pm ] |
| Post subject: | String Pressure and String Clearance |
I don't know much about the finer points of guitar building. I'm making a new bridge for my arch top, because the G has to be angled with the b and e, and not with the E. A and D. It is like 3-4 mm too short. I checked the clearance that I had so that I could get the new one close, and dial it in. I don't have the convenience of the height adjusting screws. Then I wondered if the string clearance would be the same if I just had the strings tuned down; still straight, but not stretched with tension, It would be easier to do if you don't have to keep tuning them down. I checked, and it seemed that they were about .5 mm closer to the frets with no tension. What causes that? Is it a combination of things? An observation: Making a bridge for an archtop is FAR MORE DIFFICULT than making one for a violin. It should look cool, but it is a lot of work. |
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| Author: | johnparchem [ Tue Apr 07, 2020 6:28 pm ] |
| Post subject: | Re: String Pressure and String Clearance |
The guitar bends under load. The more the load the more it bends. If you are doing any setup the guitar needs to be tuned to pitch. |
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| Author: | Freeman [ Tue Apr 07, 2020 6:51 pm ] |
| Post subject: | Re: String Pressure and String Clearance |
My understanding is that the top of an archtop is slightly depressed under load - I remember reading an article about a mandolin builder measuring that deflection. Liutaio Mottola has a little discussion about the downforce, its basically two times the sine of the break over angle times the string tension. https://www.liutaiomottola.com/formulae/downforce.htm He also has a great little wizard for calculating the amount of compensation needed for different string compositions - I've compared to doing with at tuner and its pretty darn close. https://www.liutaiomottola.com/formulae ... sation.htm |
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| Author: | Ken Nagy [ Wed Apr 08, 2020 7:41 am ] |
| Post subject: | Re: String Pressure and String Clearance |
I used that calculator to figure out string pressures on the belly and the neck when I was designing the archtop. Like a big dummy, I didn't write it all down on a page in my notebook and label it. Bowed instruments have a greater percentage of pressure going into the top, and less on the neck than a guitar. I didn't look at the compensation one before. I don't know what I was thinking. It would be impossible to say that the strings will pull the nut up 2 mm, and 1 mm shorter; and the bridge will sink 1 mm, but the compression on the body lengthwise will raise the bridge 1 mm. All of those things could happen, but unless you are making the same model of the same woods, and test the pieces with quantitative deflection tests; each instrument will be different. Thinking about it; something I did when I designed it, but didn't do yesterday; I guess I have something about what I just said, but I have no idea about the actual numbers. But having movement is good. Tension, to a point, will bring out more sound. I do have a violin with a very heavy, strong, flamed birch back with a very light, .28 sg Engelmann top. With medium Dominant strings it sounded choked. I put on lights, and it is the easiest to play violin I've made. Just about 12% less tension. I set the bridge somewhat yesterday; still WAY too massive; but playing it, the treble seemed stronger. On one piece especially, an alteration between paired notes on the e and b could not contend with the thumb on the open D. They sounded stronger, I usually had to really push them. Maybe the D is just not booming. I won't know until it is finished. I have to finish it, I miss playing and hearing it. |
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