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Same here, 6 X 89 all the way. I also pretty much shaped the braces in cross section. The BRW laminations were left flat for the same reason Brad gave...

Brad, I use a jig with a router table and have never had the wave issue. So I think something could be improved with your setup. I use a router with a 1/2" diameter shank which is much more stable than 1/4" shanks. The wave could also be caused by runout in the router or collet. You can check runout with a straight steel rod chucked up and a dial caliper. If you have runout you might need a new collet or even a router.

In my opinion a routed surface more closely approaches an ideal jointed or planed surface than sanding does, and so theoretically this should provide a stronger joint. But this is not saying that a sanded brace is inadequate.

Thanks, Barry. I am indeed using a 1/4" bit. The router is a Bosch 1617EVS that came with the table from Rockler. https://www.rockler.com/bosch-2-1-4-hp-vs-router

I will try a new collet and a 1/2" bit.

Terrence mentioned a climb cut. So far, I've been feeding into the bit. I guess I could take the majority off feeding into the bit and then climb cut just the small amount remaining. I'm always worried about a climb cut on the router table and creating a missile that puts a hole in the wall.

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When I use radiused top and back, I profile braces the same way I do sides in my motorized dish. Assemble the x-brace and hold it in the center of the dish, and the same form all other braces.
I mount the dish on a lazy-susan bearing, then mount the bearing on plywood, then mount it on the drill press table. I use a roller blade wheel mounted on a shaft to turn it.


Works well and speed is adjustable.

Bob[/quote]

I tried the 1/2” shank bit and the climb cut. The brace right off the router was much better.

Also, I ordered the brace jig Woodie recommended, so I may add that to the mix.

The results right off the router are pretty good though I think.





Thanks for all the input. It’s nice to see all the different approaches.

Brad


Sent from my iPhone using Tapatalk

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Most loose bracing (IMO) is due to cross grain expansion and contraction. Mostly see it on old guitars that have been poorly taken care of. As HHG penetrates rather deeply as it dries, I would rather have a rougher surface than an almost polished surface. Backs are sanded (for the most part) anyway.
I've never had a loose brace (that I know of) in close to 30 years of building...

I did a little reading a while back on surface energy and wettability. This article confirms what you are saying, Haans (at least from a improving the glue bond standpoint): https://www.sciencedirect.com/science/a ... 3204004805

In this article it looks like the planed surface was not touched up just before gluing, only the sanded samples were touched up just before gluing. I wonder if the effect would have been the same if the surface was planed just before gluing? I'll dig around a little bit, there was a better article that talked about this. Interesting stuff!

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I would guess that the only thing sanding would do is create a glued layer of fuzz and not penetrate any better. Interested to hear what the scientists have to say on this subject.

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Hutch

Get the heck off the couch and go build a guitar!!!!

There is an early research project around WWII where they studied glue joints on wooden airplane propeller blades to see what they could do to keep them from flying apart. Freshly planed surfaces gave the strongest joints. I believe that others have confirmed these results but I don't have any data or references to validate this.

And then Haans shot a pretty big hole in my argument with the realization that backs (and tops) are usually sanded surfaces. Oh well, I think I will keep using my router jig because it seems to work well.

I'm not about to plane my kerfed linings but I do like to plane my glued surfaces when it's feasible. I don't think we need to concerned until someone buys our guitars and tries to turn them into propellers. Of course the wind pressure is greater on the box side so...

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Hutch

Get the heck off the couch and go build a guitar!!!!

The place where a planed joint does make a difference is the top and back center joint. This narrow and high stressed joint needs all the strength it can get.

That's a good point. I've seen (and used in the past) stickit on a leveling beam to clean up the joint but most folks agree that a planed joint is the right approach. I use a shooting board these days.

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You know, I never gave much of a ____ what scientists had to say, I just kept building. Good fit, no matter if it is sanded to 120, planed, routed, whatever, is best before gluing. Titebond "experts" claim that glass smooth is best, but I stopped using Titebond a long time ago.
I never took much of a scientific path in my building and laminated bracing pretty much displaced a lot of that path. Never spent a lot of time "pondering". Not saying my way is the best or correct way, just that's how I did it.

Done here...

Jeez Haans, lighten up. I was just poking a little fun that you were able to shot a hole in my theory. I wasn't trying to offend you.

Not quite done...
Barry, not aimed at you at all, just poking a bit of my own twisted fun at all the "overthinkers". No one ever goes much for the simple hand done way anymore, always clouded in a "scientific fog" of numbers/magic sparkles/CNC, the latest. I also thought I'd better get some things straightened out before I got a barrage of posts about how much better it is HHG-ing glass to glass.
Just seems to me that a lot of you folk spend more time "thinking" than building and folks are always out-jigging each other or "measuring" clarity and tonal balance instead of just learning how to build by repetition and feel.
Some also have a bad case of "Which pick do I use", "What do I do next?" Coming from someone that had to learn everything without forums like this, books or anything, seems as though some of you just can't think for yourselves (no offence)...maybe it's just a sign of the times in which case, I'm glad I'm almost ready to step out of the canoe...
I realize all of you want to build your 2nd guitar in perfection, but most of us that have built 20-30 instruments know that it takes that long to even decide what you want to do unless you just want to build AGF Martins...
Barry, to be sure, this was NOT about you. Your comment was positive and constructive.

Rant over.

I don’t read any rant in your comments. I agree!

This is how i do mine -

https://www.youtube.com/watch?v=jpLoDviJZAA

G.

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We all have or will have that moment when we find ourselves yelling at the neighborhood kids to get the heck off our grass...I prefer to think of it not so much as a rant, but more just evidence of an overabundance of maturity.

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I will second haans/s comment totally agree. There are many many ways to do the same job , be it power tools or hand tools.. I use a very sharp jack , or number 6 on a angled shooting board made from scrap.

Haans, my apologies if I offended you. If you thought I was pushing back on your advice, I wasn't. I was enjoying the conversation.

For sure, I'm in the overthinker and overjigging category. It's my nature as a software engineer to try to wrap well defined processes around activities that are to be repeated. Coincidentally, my "build system" I've been working on is a direct result of advice from folks such as yourself who recommend to "make an instrument, play it, make another and make only 1 change, repeat". In my mind (admittedly a scary place) this means, control as many variables as possible in my builds so that I can truly achieve just one change. Leave it to me to figure out a way to take advice and then mess it up.

As far as the forums go, I'm sensitive to the fact that there are professionals, hobbyists and total newbies here. I try to take in responses with that in mind. For me, this is all for sport. Not just the forum, all of it. Building and repairing instruments is fun but I'm not relying on it to put mac and cheese in my kids lunchbox. I do try to be aware of the professionals who took their passion and made it a career. It deserves a ton of respect. You also deserve a ton of respect, and that is just what I've seen here in pictures. I'm sure folks playing your instruments would take it to another level.


Any of the OLF folks I've met in real life will tell you that I'm probably the most agreeable person you'd meet. So if I ever comment and it looks like I'm pushing back or discounting the advice, it's probably because I was distracted by the day job and trying to answer at the same time.


Brad

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Never yelled at kids on the lawn and never talked to an empty chair for an hour.
Brad, never meant to direct any of my ranting at you either. If you enjoy process thinking, that's fine too. Just trying to defend what some might call an inferior process: sanded glue joints. I can say with certainty that a closely sanded and cleaned joint is very strong for braces. I've glued braces that I decided were wrong and later tried to chisel off. Several times I have split the braces and had to run the back or top through the sander again to remove remnants of the bracing. Just running a braced top or back through the sander is enough to convince me that the joint is strong enough...
So, once again, if "I" have offended anyone, wasn't my intention. Taken in context, I was just making the observation of how complex folks can make the simplest of tasks.

First let me say that my joints are either about 150 sandpaper or a planed/scraped surface and I have never had any trouble, so I am not looking to change anything for myself - Haans is right about overthinking.

Buuuut - out of curiosity I poked around and came up with perhaps 8 papers written between 1930 and 2006 that mentioned surface prep. It seems that a freshly planed (within 24 hours) surface is the best, and that the blades have to be sharp so as not to burnish the surface which closes off the various size pores (some papers talk about nano-pores!). There are also sizable differences in hard/soft woods and heart/sap woods. This one is the most recent and mirrors all of the other conclusions:

http://www.woodworkslibrary.com/repository/wood_adhesion_and_adhesives.pdf

look on pages 225-229

However, I found one written in 1999 that says that machine (planer) marks are OK as long as there are more than 24 per inch. Then they say:

"The adhesive industry typically recommends 60 - 80 grit sanding as acceptable for wood bonding as this equates to 24 to 30 knife marks per inch when planing. Generally, anything above 200 grit fuzzes the wood surface and is not recommended."

So it is possible to over sand a surface by committing "fuzzing" against it?

Back to your regularly scheduled programming

Ed
Half the people you meet will be below average

One thing I like about these discussions is you get to see the many different ways to do the same task. A way that might be difficult for one person might be the bee's knees for another. And versa vise .

So more a case of different thinking than over or under-thinking?

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Just throwing this into the ring
https://www.popularwoodworking.com/techniques/best-wood-glue-surface-smooth-or-rough/
Made me up the grade I used, previously 180, now 240.
I have had to remove braces glued to a back which were freshly sanded to 120, and they were well stuck on.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.