Finally some time to continue

posted 19 Mar 2017, 08:17 by Peter Grankulla

It has been a month and a half since I have been able to be in my workshop and I realize how relaxing it is. Purfling and some rough shaping with fingerplane. Frequencies ok.

Stressing the backplate

posted 29 Jan 2017, 07:43 by Peter Grankulla   [ updated 29 Jan 2017, 07:51 ]

To answer a question on Maestronet: Janito's bench about stressing the backplate, the following is in principal on how it's done. This I have done on some violins and it prevents some deformation after the violin is ready and has been used 1-2 years. The images below demonstrates the task. However it is no quick process, but takes up to 2-3 months for it to be successful as maple is very stubborn and wants to go back to its original state. The cork is formed to fit a small area in the middle (more on the soundpost side). The process must be started at high humidity (and EMC in the wood), then it is cycled a couple of times between 65%-10% humidity (again slow process). The stress is successful when the backplate's frequency stays the same for a month or so at the same humidity. The holes in the board are for even MC% distribution. 

This example 175/357 Hz at 10-15% (january 2017). Caution! Don't use hard objects like wood under the plate, or it might crack. The retraction is VERY strong when MC% drops. Cork is preferable, but a folded cloth to fit is also doable. If you start with a high M5 frequency you might end up with a 380-390 Hz M5. I start with 340 Hz at 6% MC

Extrados tuning as it should be

posted 11 Dec 2016, 23:05 by Peter Grankulla   [ updated 11 Dec 2016, 23:08 ]

I should have known with the previous one that it was defect, because the new one reacts as it use to and I can maneuver the modes (M0/M5) how I want. Removed 100 g of wood and measured every 5 g and documented where I removed wood, now I understand this better. Removing wood at certain areas either lower or increased a mode while the other one remained stable according to the modes pattern's. It's easy to keep them 100 Hz apart. Their shape's switched patterns where the lines cross. 

Making a new top

posted 10 Dec 2016, 10:05 by Peter Grankulla

This piece of wood has some dark stripes and spots, but I think it could be a good one. On the other hand so did I think about the the first top too. It's Finnish spruce cut 1999 and is nicely yellow right through. Heat treated 2014 the usual way I do it. Maybe how the wood feels under the plane and the shavings has something to tell? That's completely different from the other one. The shavings are strong and curls nicely.

Top wood useless

posted 7 Dec 2016, 12:15 by Peter Grankulla

Completely useless wood! No clear extrados M5 freqeuncy pattern and a lot of other frequencies that where stronger and had odd patterns. Impossible to keep up any frequency, even with 2,9 mm in upper and lower channels and 3,5 mm in c-bouts and 17,5 mm high. Hollowing out the inside to confirm the same. 105 g and M2 210 Hz, M5 387 Hz. The wood was kind of brittle a little fat and short/splitting fibers when using a gouge cross grains. Lesson learned, I'll save it for future comparison.

Top quick progress

posted 27 Nov 2016, 10:09 by Peter Grankulla   [ updated 27 Nov 2016, 10:10 ]

Weekend workshop, working quite fast. Did the purfling today and checked that there are no unacceptable gaps.

Back ready

posted 20 Nov 2016, 04:17 by Peter Grankulla   [ updated 20 Nov 2016, 04:19 ]

Some small correction and final adjustments (350 -> 353 over night), thicknesses and modes are the same as in previous post. Final tuning is done when the soundbox is closed. No sandpaper used at any stage.

Back graduation & tuning

posted 19 Nov 2016, 09:12 by Peter Grankulla

Back arching & tuning

posted 15 Nov 2016, 10:21 by Peter Grankulla   [ updated 15 Nov 2016, 10:27 ]

This one was suppose to be a challenge as the wood is on the lowest end in speed of sound. Maybe I'm learning because it was straight forward and it turned out quite beautiful with elegant curves. 17,5 mm high with a shorter lengthwise arch. Hollowed out the inside to 171 g (474 Hz), 155 g (438 Hz), 143 g (417 Hz) to check M5 and thicknesses.


posted 10 Nov 2016, 11:41 by Peter Grankulla

Almost a month since I have done something but today I got the purfling done on the back plate, channel 3,5 mm at this point.

21-30 of 190