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IMO...this tool is an accident waiting to happen...both to wood and flesh. I can think of much safer ways to accomplish the same mission.

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JJ
Napa, CA
http://www.DonohueGuitars.com

EDIT (sigh)

I can see tearout, kickback and blood in someone's future!

I hope I'm wrong but be very careful with this one!

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JJ
Napa, CA
http://www.DonohueGuitars.com

It will work fine I have seen it in action. It is held in a verticle alignment. I will probably build a flieshman style holder for it. I may also out a router speed controller on it.

It is just a nice way to do a task repeatably and reasonably quickly

Thanks for the help with the bit.

BYW, this is my first post to the forum from my blackberry.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

jj, having used the bits in a die grinder i don't share your grievous safety concerns, given the normal sort of safety provisos applying to the use of such power tools.

granted, a router bit with a similar profile would be better due to its better chip removal, etc. but a lot of folks have used them in wood carving, luthiery, etc., and i've not heard of any unusual accident statistics related to their usage..

however i do see where an instant of inattention or ineptitude could irrepairable damage a brace, and perhaps the top as well.

hence my suggestion above regarding the use of the binding jig as a possible safe alternative to freehand use. a priori, i can't see any reason it wouldn't work. a riser platform would be required to get the plate up to a suitable working height, but it seems to me that the two dimensional free movement of the trimmer in the binding jig would suit this application very well whilst entailing only minimal time tradeoff.

Michael, I think that using a binding jig like the W/F would be an excellent idea for this and would certainly bring down the risk factor.

This would be, and most likely is a great way to remove material in a short period of time also to a pre-determined shape.

Brock et all ES students, just teasing you. We all have copied most likely all our building tactics and ideas from someone else, I certainly know there is nothing in my shop which I haven't "borrowed"

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"There's really no wrong way, as long as the results are what's desired." Charles Fox

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Is there a logical reason why you wouldn't shape the profile of the brace prior to installing it? I'm wondering if Ervin does something different that would make that impractical.
I had a router bit made that is the profile of my braces. When I cut brace stock, I just zip it through the router table and it's totally set.

...of course, my comments were based solely on the picture of the tool in the first post. I have no "statistics" on the frequency of accidents...but I do have an instinct for a dangerous operation and I consider this deserving of more than the normal amount of care to maintain safety for the user and reliability of its intended use.

Naturally, if it is modified to improve its reliability, stability and safety then you "increase the waiting period for an accident to happen." Yours as well as Brock's intended modifications may reduce those risk factors...I sure hope so.

There are a lot of "new kids" coming here who have no concept of power tool safety as well as how to shape wood. I was one of those "new kids" just a few years ago. Having a healthy fear and instinct for danger so far has kept me in possession of my limbs and digits. Hopefully, we can inspire a healthy respect for those hand-held high speed spinning bits.

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JJ
Napa, CA
http://www.DonohueGuitars.com

i had the same thought when i first looked at the bit/indexing foot setup. but after thinking about the geometry and the process, i can easily see why trying to impart the concave profile to the side of the brace prior to its attachment to the plate would be problematic.

for instance , if you put the concave profile in before radiusing the the brace, the width of the gluing surface could end up varied when the radius is cut, or else the depth of the unprofiled segment of the brace adjacent to the plate would be varied. if you radius the brace first, then try to put the concave profile into the side of the brace, you would be trying to control a rocking, unstable piece of stock against the bit. neither is likely to give the desired result.

[QUOTE=Brock Poling]
BYW, this is my first post to the forum from my blackberry.
[/QUOTE]

Nerd alert!

Also, I'll mention that I'm at least a little jealous...

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

[QUOTE=SteveS] I think I found it.
McMaster Carr Carbide Burr. Item #43035A65 has a 1/4 shank and a 1/4" tall cutter $33.29.

[/QUOTE]

The listing for that number looks like a 3/4"x1" cutter to me, if I'm reading the page correctly. That seems a little on the big size for this job. I was thinking more along the lines of a #43035A61, 3/8" dia with a 3/4" length of cut. My braces are only 1/4" thick and you only want to take about a third of that, split between the two sides. If you want to remove more than that you'll probably want to switch to sandpaper for fine adjustments. It does look like an intriguing idea and should fall right into the realm of the Willians/Flieshman style router base if it's built relatively tight.

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Tickle your guitar daily, and it'll tickle you back.

There are any number of ways to preshape braces that way, straight or radiused.  Here's one for straight ones.  Cutting the second side, you need to put a spacer under the cut side to keep it flat ont he table.  For cutting a radiused brace, radius it first, then use a radiused fence to match.

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http://www.chassonguitars.com

 

The triangle brace deflected .065" and weighed 11.0g.

The parabolic brace deflected .040" and weighed 16.7g.

The inverted T deflected .037" and weighed 13.6g.

 

I  then trimmed the height of the two stiffer braces till all the braces deflected .065" (within .002").

The triangle stayed the same at 1/4" x 5/8" and 11.0g.

The parabola was reduced to 1/4" x 33/64" and 13.5g

The inverted T came in at an even 1/4" x 1/2" and 11.4g

 

I kept the widths at 1/4" because I like to have at least that much gluing surface for larger braces and I also think it's needed for lateral stability.

 

As a side note, the parabola feels stiffest by far in torsion and the triangle the most flexible.

 

The results show that the parabolic brace is inferior on a stiffness to weight basis.  I would say that if a triangle brace of 1/4" x 5/8" is stiff enough for your purpose, it shows excellent stiffness for its weight.  But that cross section feels like the limit, if not a bit beyond, of the height to width ratio I would consider for a triangle brace.  It feels pretty flimsy torsionally.  The T brace comes out looking pretty good to me for taller braces.  For anything shorter than 3/8" though, I go more triangular.

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http://www.chassonguitars.com

Brock,

    That is a tree shaped fluted burr for use in soft materials like wood or
plastics. The typical carbide burrs for use in metal have much more
frequent burr edges tht are cut at intervals of 1/32" or less. They are
intended for use at much lower speeds than we use for wood so the
edges can be much more frequent since they will clear and cool.

    The sparse burr edges on this piece are a clear indication of its
intended application. I haven;t found a source for them, but I think I know
of a shop that uses very similar cutters and will try to reach them for their
source.

    I used the alot of them while working as a modeler and toolmaker for
several machine and CNC design shops back in the day.

    I'll let you know if I find anything out.

Regards,
Kevin Gallagher/Omega Guitars

[QUOTE=Kevin Gallagher]    The sparse burr edges on this piece are a clear indication of its
intended application. I haven;t found a source for them, but I think I know
of a shop that uses very similar cutters and will try to reach them for their
source.[/QUOTE]

Cool Kevin, Thanks!!

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

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http://www.chassonguitars.com

yes, as i said before, you can put the side profile in like this before the brace is radiused, but then when you radius the brace, either the gluing surface width will change as the material is removed, or the width of the small vertical unmilled side of the brace will change. granted, these changes will be small, but they will be visible. whether they would be structurally significant is problematic.

cutting the side profile after the brace is glued in position eliminates the problem.

Michael, you can put this profile on a radiused brace without the problems you mentioned.  I've done it a couple of different ways.  Here's the last one.  The brace is radiused first.  My radius template is used as a fence.  The stuff clamped and taped to the table are just hold-downs.

I've also used a pretty simple jig with a hand held router and the same bit but I don't have a picture of it.

The big benefit of pre-shaping is that, as someone stated, you are limited with how close you can get to the rims and other braces if you do it after they are installed.  Lots of hand work to clean up.  Both certainly work in the end though.

 

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http://www.chassonguitars.com

i see how you are getting your desired profile on the radiused brace, but must admit i wouldn't want to be the one manually working stock past an unshielded bit that size.

but that doesn't solve the instant problem, as your router bit, and none other that i know of off the shelf, would yield the desired profile. a custom bit is always a possibility.

as for your worries about the rim and other braces; i can't see any problems with the rim as it would not even be in the picture, and there would seem to be plenty of room around the brace intersections for that little foot and the bit to do their work.

The diffrences in weight between a tirangle, T and parabolic brace profile is rather small if they are shaped to carry the same load compared to the total weight of the soundboard. Is there a tonal benefit to shaping the brace with concave sides?

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Rian Gitar og Mandolin

[QUOTE=ToddStock]
Adopting tools based on instructor's preferences is nothing new...I used Cumpiano's patternmaker's paring chisels until I figured out they were way more work than what I do now. Also used homemade wood planes for years as a homage to Krenov, although the MD humidity shifts made that an exercise in semi-annual tuning and sole flattening (metal for me now, although I still love the feel of wood-soled planes). Most recommendations are keepers, though, and it looks like ES's stuff might work.[/QUOTE]

True Todd...in the furniture building days I took a dovetail workshop with Mario Rodriguez...the first day was taking a Home Depot variety "dovetail" saw and filing half the teeth away, jointing, and re-sharpening it to be a straight-cutting, thin kerfed, rip saw...and then how to grind a chisel down to not mar the tight corners of dovetail tails...with that done, the dovetails themselves were almost a no-brainer! I still have a couple of those saws and my fear of modifying tools is all gone!

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http://www.presnallguitars.com