Karl Borum - Borum Acoustics
Forum Replies Created
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I just finished a dreadnaught with the lower X braces feathered to zero and it has a very distinct and pleasing voice. I can’t speak from any real engineering or scientific perspective about it- but it feels and “sounds” very different. It’s only the 4th guitar I have built (all dreads) and its Black Walnut back and sides, so I can’t speak for what element had what effect, but I love its voice, tone and resonance. I’m building an OM and will do the same thing- feather the X braces to zero. It definitely didn’t have a negative effect (more resonance, cleaner bottom end). I measure my resonance modes with FFT but I could not see an appreciable difference in the FFT plot of #4 vs the previous three.
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Great video and discussion- The OP asked specifically about a bound fingerboard with sideways frets. It didn’t seem these answers addressed a bound and sideways fretted board.
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I first used the Tolex spot refinish kit (Eagle Abrasives) and LOVED it and use it all the time. I bought a MIRKA Deros to use with the Super Assilex but ended up doing it by hand with the Assilex flat blocks. Super AssiLex is way faster and better than wet sanding.
I may use the DEROS in the future, simply for “dust” control but the hand method is so easy. I started with the yellow and worked thru the grits. They created a LOT of fine particulates so I did a ton of interim vacuuming. Didn’t use the Buffex, it didn’t seem necessary and turned out great (EM-6000 water based lacquer).
Some users write that using a silicon carbide paper for the first step gives better results than starting with Assilex. I didn’t so I guess I have a baseline…
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I switched from Nitro Cellulose Lacquer to Target Coating’s EM-6000 last build. It was essentially equivalent to nitro without the long cure times or toxicity. And finish-sanded dry before buffing.
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If I could find a source for the clam shell hinges (the offset ones on the plywood acoustic cases), I would do case repair in a heart-beat. I’ve probably spent 100s of hours searching and inquiring. Anyone have a source for the OFFSET hinges? I’ve exhausted every avenue (except that I won’t buy from the Chinese Broker sites like ALIBABA or TEMU). I expect replies that direct me to google luggage repair…. that’s been a dead end for several years.
There must be a source, they sell many thousands of cases with the offset hinges…..
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@Chris Frederick Guitar Recovery LLC I tried some “Lemon Oil” over the already dyed bridge and it actually set the color, thanks for sharing that. I don’t know why that worked, but it did. I’ll finish it up with Howards Feed N Wax and steel wool.
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Thanks for the replies. Surprisingly, both of the Fiebling’s dyes I used, on a EI Rosewood bridge blank, were water soluble: the color wiped away from the surface with plain water- like a moistened Q-Tip or paper towel. I didn’t put it in the original post but I also tested Higgins Black India Ink
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BUG REPORT
22 Aug 2025
MS Edge Version 139.0.3405.102 (Official build) (64-bit)
Nothing in the [Profile] environment (Profile, Account, TimeLine ect.) is working: It links but there is nothing in the landing page other than the page header/ format. This occurs after multiple logout/ logins across multiple days. Also, no profiles are available, even in the [LOOTHS] tab.
KB
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An ‘island” on wheels with integral drawers is better than just a table. I have a mobile computer station table thing- it takes up “cubic space,” from the top, down to the floor, that could be used to store tons of essentials like sandpaper, sanding blocks, wood cutoffs, vacuum accessories, finishing accessories and consumables etc. I’m finding that I need MUCH more drawer space for storage than bench top- because the bench top ends up as storage when there is nowhere else to store things. I was in the process of building out storage drawers every winter, until Baltic birch tripled in price!
I’ve built two chests-of-drawers, one is a double set of drawers (6 in total) that tucks under my woodworking bench, the other is 5 drawers on wheels under my wall bench, and they are full. This may give you a heads up on what you may end up needing to store, and the only reason I’ve detailed it:
Drawer 1: Specialty Measuring tools and gauges, 1x2x3 blocks, brass and aluminum gauge blocks and gauges, dial indicators
Drawer 2: Sharpening equipment, stones, hones, honing guides, strop compound, card scraper sharpening holder tools, cheese graters and card scrapers
Drawer 3: Dremel, fixed base, plunge base, rosette base, all bits and bearings for binding, box of pearl blanks, and everything else related to precision routing.
Drawer 4: Smaller jigs, templates, headstock clamps, Hanger 9 heaters, some specialty tools that I don’t use often.
Drawer 5: Three Sanding beams, various wood spacers and reusable wood shims, templates and flat wooden sanding blocks, platforms, waist spreaders.
Drawer 6: Sandpaper rolls, sanding sticks and belts, steel wool, larger foam contour sanding block, sanding block material.
The working chest; 4 drawers:
Drawer 1: Smallest drawer: Twist drill index 1/64″, Brad Point index, Metric Twist Index, Forsner Bit Box, all drilling realted bits and short drill chuck.
Drawer 2: Three set of calipers w/ boxes, best Irwin Chisel box, Japan Chisels, chisel hoop setter,
Drawer 3: Porter Cable Battery Drill 1, Tuner Battery Drill, Battery flashlight, Tap set, DIe Set, Luthier;s Friend Sand station
Drawer 4: Largest drawer; Hook and Look Sandpaper: about 30 boxes total of 5″ diameter oxide, abranet, Buflex, all grades of synthetic scotchbrite. This is in addition to the 8 rolls of PSA paper on the pegboard above the bench.
I need another one or two of these chests- 10 more drawers might do it. I bought a tool chest from Harbor Freight (awesome chest) but it was a behemoth huge monster that would not fit in my small shop, so I donated it to my wife’s studio.
I wrote this up to give you an idea of all the things you may need to be storing as your skills, and craft progress- it’s a lot. So, for me, the drawers for storage are just as important as the horizontal surfaces. If you use a table, have drawers under it, and make it somewhat mobile. WHen choosing casters, USE DUAL LOCKING CASTERS THAT LOCK THE WHEEL AND THE STEM….. thats all I got
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I had a Mexican martin where the nut on the end of the truss rod was simply missing- it had come off. I didn’t know that until I removed the fingerboard and the truss rod. Truss rod was the square tube with threaded rod. It appeared like the end had snapped off….
I bought a regulation threaded end, on amazon.com of all places
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I’m diggin it
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Great method of work, very crisp production…. thanks for documenting!
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Double sided adhesive sheets:
a.co
Amazon.com: Gizmo Dorks 3M 468MP Double Sided Adhesive Transfer Tape Sheets 8" x 8" (5-Pack) : Industrial & Scientific
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I’ve tested quite a few pore fillers. The ones I’ve landed on:
Rockler Water Based WunderFill
StewMac ColorTone Water Based Black Grain Filler ( they don’t sell the black anymore)
SilverTip Epoxy (Michael Bashkin did a video demonstration on it) I did 2 coats on Walnut and it needed three : (
I used Aqua Coat Water-Based once– it turned white in the pores of the neck after 3 coats of NC lacquer. I stripped the neck to bare wood and picked the filler out of the open grain/ pores with the ragged edge of a ScotchBrite pad. I could never replicate the cause and the mfg didn’t know why either; I don’t want to do that again. I have a hunch that did a grain raising before applying the Aqua Coat without letting the wood dry completely, and the filler slowly turned white- but I haven’t revisited that product to test that theory.
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Black grain filler on mahogany, with Silver Tip Epoxy Grain Filler and EM6000 Top Coat:
What worked best, and what I went with:
1. Sliver Tip grain fill over bare wood.
2. Black StewMac water based grain filler; 2x
3. Final seal with another coat of Silver Tip Epoxy
4. Scuff sand 320 and topcoat with EM6000.
With all the methods, the black color in the grain filler did not bleed, which was a main part of the test panels. I do not like how much the EM1000 sealer raised the grain. Perhaps there is a work around but this case is closed, for now,
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Opps…that thing was the 21st, today, and we missed it
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I’ve built three dreads with torrefied Sitka tops, two of them with torrefied bracewood. I like it a lot, but it’s very brittle, and it’s a bit hydrophobic so TB and hide glue tend to bead up on it. I did some bench tests for glue and found two things regarding the glue beading up :
1. Lighty dampen the gluing surface a minute or two before applying glue (like raising grain).
2. Briskly brush the glue onto the gluing surface- it helps it “wet” onto/ into the wood surface.
You might do a little glue up on scrap to see what I mean.
Be very careful if you flex the top without braces, I broke a top like that- its that brittle. When carving braces, be sure the domed top is supported- like on a bed of towels or in a radius dish.
I love the tone and voice of torrefied spruce while building, you can hear the difference as you work it. I also believe (I could measure with FFT but I havn’t) it makes a more responsive/ sensitive instrument. There is an interactive Looth session on torrefication coming up on the 31st of May with Dana Bourgeois Acoustic Guitar Builders Club: Wood Torrefication, with Dana Burgeois – The Looth Group
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I get the majority of my pearl from https://www.ebay.com/usr/jnnpearlinlay , and get headstock overlay designs from DePaule Supply. J&N pearl is very well packaged and clearly marked for everything you need to know later (thickness, diameter, Inches, mm, radius color, stock number ect.). Everything I’ve purchased from J&N is top shelf and the way they package it is very professional. It comes from overseas so it it takes 3-4 weeks to receive it. Thier shipping cost went ionospheric when US tarriffs were announced, but I just placed a $120 order and shipping is now around $6.
ebay.com
Welcome to J&N Pearl store!We are a manufacturer, and specialize in Mother of Pearl, Abalone inlays for musical instruments, Banjo pegheads and fingerboards, Guitar pegheads and fingerboards, Knife handle scales,slabs,blanks, and custom logos and so on. Genuinely solid mother of … Continue reading
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I use raw pickguard sheet material, apply 3M 468MP Double Sided Adhesive Transfer adhesive sheet and trim to rough size with scissors or blades, depending on the pickguard material. I then attach to a Baltic-ply template with Scotch brand double sided tape. Then I cut the pickguard (with 3M adhesive attached), with a flush cut bearing router bit and bevel by hand with sandpapers. It goes pretty fast if you have a template.
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<div>Buy one and see, trim to fit:</div>Guitar Parts: Pick Guards | Martin Guitar
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The first repeatable FFT plots I’ve been able to get. Used REW and the MiniDSP Umik-1 from Giuliano’s book. This was quite the rabbit hole to get proper, repeatable FFT plots, but the pre-work is done. Figuring out the data implications will be another, like the double humps at 290hz.
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Bump
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My most accurate hygrometer is the little analogue humidor one from amazon. I have a swing psychrometer to check them against. THis one even has an adjustment slot on the back (under the PSA mounting foam). https://a.co/d/igY4qbA
a.co
Buy Cigar Oasis Analog Hygrometer and Humidity Sensor - High Precision Humidity Monitor for Reliable Cigar Humidor Care and Maintenance on Amazon.com ✓ FREE SHIPPING on qualified orders
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I used the rubber waffle weave anti-slip mats until I noticed they left residue on bare wood and marked up lacquer. I used felt for a while but its splinter loving so nix that. Currently I’m using the SM pad with super cheap bath towels on top. The bath towels are cheap enough (buy them in sets on closeout) to rip into “grease rags” after a build or two. I’ll even lay the towels on the radius dish when carving braces over the dish.
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I have various problems with sections not working correctly. Logging out then back in has corrected it and sometimes a restart of Windows 11 (Edge) fixes it……
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Problem solved by logging out of loothgroup then logging back in through Patrion…
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Yes EDGE is the Microsoft Windows 11 browser
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James Huntley, I had the same: AquaCoat turned white, on mahogany,,,,
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Some really nice brown-er celluloid material I’ve used a lot of (shipping is very reasonable too):
Dark Tortoiseshell Celluloid Sheet – Rothko and Frost
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Brad, congrats on nearing the end. It’s a good practice to put a straight edge on the part of the top under the FB extension to verify that the top is flat in the fingerboard plane. I learned from Robbie Obrien/ Jeff Jewitt to put a 2.5-3.0mm spacer at the future position of the bridge saddle and use a long-ish, flat standing stick to flat-sand the top on the neck block end, flat in the same plane as the neck angle (the non-sanding end of the stick sits on the spacer). If you do this BEFORE cutting your binding channels, you won’t have funky bindings (shorter in height from flat sanding).
Before I learned this, I had done it once just before finishing, during the final check of the neck fitment, if there was a slight gap where the FB meets the top. It will likely affect your neck fit set slightly, and could make your binding ever-so-slightly shorter in that area. Choose your weevil.
