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Thread: Martin OM Style Acoustic Guitar

  1. #16
    Join Date
    Jul 2012
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    I've been working on bending the sides. I'm not a happy camper. This Stew Mac bending iron takes forever to heat up. Over an hour to get above 200 degrees!

    The first piece was too thick. That's on me. The second piece I brought down to .085". I managed to get the waist bent in about 20 minutes. Then I moved to the lower bout. Fifteen minutes of trying to get it to bend and nothing! So I checked the temp of the iron and it was between 120-130 degrees. 30 minutes ago I walked away to let the iron heat back up. I just checked it and it's at 165. This is nuts! Maybe I need the 480V version.

    I just emailed Watlow for a price on their heating blankets...
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

    Diapers and Politicians need to be changed often... Usually for the same reason.

  2. #17
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    The second test piece went better


    Until I let sunlight rake across it


    So I scraped and sanded


    And shot it with some nitro


    Not too bad
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

    Diapers and Politicians need to be changed often... Usually for the same reason.

  3. #18
    Julie - that looks much better. I cannot imagine the learning curve...it must be very steep. I applaud your effort.

  4. #19
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    Quote Originally Posted by John Redford View Post
    Julie - that looks much better. I cannot imagine the learning curve...it must be very steep. I applaud your effort.
    Actually John, I think I made it sound worse than it really is. I spent a lot of time fretting over the rippling wood and failed to go back to the books I have to see what I may have been doing wrong. But looking back, I think the most important step is getting to know how the wood responds to heat and moisture. I've read some luthiers soak the wood in a trough. If you did that with sipo, you'd ruin it. I've found sipo to be very sensitive to moisture.

    Yesterday I bent two book-matched sides successfully and I'm ready to move forward. I referred to the Cumpiano book, Guitarmaking, and picked up a tip to spritz the wood only on the side facing the iron. On another forum, some were suggesting to spritz it on both sides and that didn't work for me.

    By the second half I developed a technique:

    1. Use a wet rag on the iron to bend the waist. The waist is the tightest bend and the only part of the bending where the good wood faces the iron so the rag both helps keep the wood wet and prevents the iron from scorching the wood. As the water evaporates, move the rag to keep steaming the wood.
    2. Spritz the inside of the piece and begin bending the upper bout. As the steaming stops, spritz again. As you progress, check the progress against a template.
    3. Repeat #2 on the lower bout.
    4. Once the piece is properly bent, put it in a form and let it sit, under pressure, overnight.

    The first half I did yesterday took me a little over an hour, mostly because I was stingy with spritzing. The second half took about 20 minutes. I didn't notice any rippling.


    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

    Diapers and Politicians need to be changed often... Usually for the same reason.

  5. #20
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    I glued in the head and tail blocks and the kerfing and notched the kerfing to accept the X-braces. Then I fine tuned both the notches and braces so the top fit in snugly and there was no movement. Out of curiosity, I fitted the top in place, flipped it over and placed a template on the bottom to see how the sides telegraphed without the internal forms in place.

    Not perfect bends but it will do.

    Before gluing on the top, I checked to see there were no gaps. Along the way, I stumbled onto the idea of threading mini clamps through existing holes in the form. It worked so well, I drilled more holes in the form to make a total of 16 locations for the mini clamps.

    For glue up, I added cauls and flat stock around the perimeter then added more clamps until there was no more room to fit any more.

    Next was forming the bottom of the sides and fine tuning the braces to fit snugly between the sides.

    Keep moving along. No straight lines to see here folks!
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

    Diapers and Politicians need to be changed often... Usually for the same reason.

  6. #21
    Join Date
    Mar 2003
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    SE PA - Central Bucks County
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    Great idea with the clamps through the cauls. Something you could do to help spread the clamping further is to cut out a piece of plywood that mirrors the edge contour so that the clamps are engaging that rather than directly to the top. That not only protects the top more (it's not super hard wood in most cases), but it also acts as another caul for the clamping pressure on the edge of the top.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  7. #22
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    Your suggestion is spot on, Jim. But for some reason I'm in this phase where I'm trying to cut corners. I think that's in part because working in a split shop (half inside the house and half in the garage) acts as a deterrent. Or maybe it's just a factor of aging. I rough cut the neck last week and when I went to shape the tenon, I opted to do so with hand tools because I didn't want to work in the garage. I ended up fine tuning the tenon in the garage....

    Anyway, here's where I am now:


    The headstock has 1/8" curly cherry glued to the neck wood. Still haven't decided on the final shape.


    The truss rod was cut to a depth leaving the bottom of the truss rod about 1/8" higher than the finished bottom of the neck. The truss rod is from Stew Mac and is supposed to be what Martin uses. After I purchased the truss rod, I read in Guitarmaking it's best to use a double action truss rod (but not the Hot Rod version). Maybe next time.

    The top of the truss rod falls about 3/32" below the top of the neck wood so I had to make up a filler insert.


    Using a Stew Mac fret template that measures a 25.34 fret scale, the fret slots are cut by hand


    Next is to shape the fretboard to a 16" radius


    It's starting to look like I know what I'm doing. (Still trying to figure that out!)
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

    Diapers and Politicians need to be changed often... Usually for the same reason.

  8. #23
    Join Date
    Mar 2003
    Location
    SE PA - Central Bucks County
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    Definite progress...and that's going to be a beautiful instrument!
    --

    The most expensive tool is the one you buy "cheaply" and often...

  9. #24
    Join Date
    Mar 2018
    Location
    Orwell, NY
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    169
    It looks good. I use a propane torch with the tip stuck inside a piece of copper pipe to bend sides. It gets hot in under a minute, and I have had to learn to regulate the flame size for the temperature I want, but with a bit of experimentation it's not hard, and very cheap compared to anything electrical. I make it a bit hotter for guitar and mandolin sides and a bit less hot for violin ribs which are a bit thinner. I personally like the Hot Rod quite well and have installed about 100 of them over the last several years, but if you're making a neck with a very shallow profile they would be too close to the back of the neck since they're 7/16" deep. The welded double action rods use a shallower trench, but I had one that the weld broke after the customer got the banjo neck and was adjusting it, and I ended up making a whole new neck since that was easier than taking off the fretboard and replacing the rod.
    Zach

  10. #25
    Looking good Julie.

  11. #26
    Nice to see you posting this over here. I caught your Thread on the OLF; imagine me delight to see it here as well.
    Looking good!

  12. #27
    Join Date
    Jul 2012
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    Punta Gorda, FL
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    Thank you, Mike & John.

    I took a few days off because I had to get the workshop working. Finally finished the power & lighting. No more temp wiring!

    Did the side radius sanding on the back. Next was the kerfing. I'm using mahogany kerf lining.


    After the kerfing was done, I made up some sitka spruce braces for the sides


    Another look


    I'll do some final tuning on the soundboard before gluing on the back.
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

    Diapers and Politicians need to be changed often... Usually for the same reason.

  13. #28
    Lovely. Nice clean work.
    Mine will not be that clean, I don't think.

  14. #29
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    Thanks again, Mike!

    Got the back glued on and started sanding the sides. I picked up some dowels and wrapped them with 80, 120 & 180 PSA sandpaper to do the curves.


    Then I decided to give a shot at the tail insert. Since I didn't have a template, I had to freehand cut with the Dremel.


    I played around with plastic binding strips and this looked okay. I'm just not sure the BWB plastic looks right.
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

    Diapers and Politicians need to be changed often... Usually for the same reason.

  15. #30
    I think that looks great with the bwb. Love that quilt in the maple.

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