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  #46  
Old 08-11-2017, 07:06 PM
redir redir is offline
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Yeah that sure is odd how they show that one cross section brace right in front of the bridge like it's a ladder brace. Maybe one of the Martin experts like John A. will chime in on this thread.

I remember reading that Martin would have a few different bridge thicknesses readily available to match the plus and minus error in their factory set neck angles. But 5/16th seems awfully low.
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  #47  
Old 08-12-2017, 11:24 AM
Howard Klepper Howard Klepper is offline
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That low bridge is consistent with what I noticed earlier about the plan appearing to have zero neck angle. I couldn't see the bridge close-up then, but from what you have shown, it is a poor design. It is too low. The pin holes are countersunk down to the top, which would be a big mistake. The bridge plate is too wide. This is not the plan for any vintage Martin.

I would say there is good reason to mistrust these plans. You might think that by the time a plan is marketed it has been properly vetted, but I have seen this not to be the case, and more than once.
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Last edited by Howard Klepper; 08-12-2017 at 11:43 AM.
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  #48  
Old 08-12-2017, 12:55 PM
CabinetMan CabinetMan is offline
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Howard,
Thanks for posting. So what do you suggest for the bridge plate size?

I guess I just need to go ahead and glue in the neck block and move on from that.
I will keep the neck angle in mind and adjust that as necessary when I get to that point. Thanks again for all the advice everyone has given, much appreciated.
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  #49  
Old 08-12-2017, 02:18 PM
Howard Klepper Howard Klepper is offline
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I like to make the bridge plate extend 1/8" beyond the front and rear of the bridge, and a little more than that in the middle of the edge that goes on an angle from the central portion of the plate to the X in the rear (see photo--braces not yet shaped). Some builders try not to extend it beyond the bridge, but IMO that concentrates stress at the edge of the bridge, which the plate can relieve by extending a bit beyond. I bevel the edges of the plate, except for the ones that butt to the X.

I suggest getting a look at some other plans, at the photos that builders post during construction in Custom Shop, at the insides of some good guitars (especially Martins and their progeny like Collings and Santa Cruz, etc.) and then trusting yourself to figure out what you think will work, because there will be a lot of inconsistencies among the different builders. You will never go wrong by copying vintage Martins. You don't have to do everything the way Martin did, but they set the standard for steel string guitar construction for a long time, and when you depart from their designs, you should know why. Have a good look around at vintagemartin.com. And hang around the tech forum on UMGF.org.

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Last edited by Howard Klepper; 08-12-2017 at 02:27 PM.
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  #50  
Old 08-12-2017, 07:18 PM
CabinetMan CabinetMan is offline
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Thanks Howard, I'll take your advice. I'll post more as I continue to work on the build. As always, if you all see anywhere that I'm making a mistake or that I can improve on feel free to let me know.
Thanks again.
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  #51  
Old 08-13-2017, 11:21 AM
redir redir is offline
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I used to make the bridge patch as small as possible. That was 1/8th inch larger than the bridge at it's widest points and it was a rectangle. Since I started building lighter and lighter I've noticed that corners are not good. My tops telegraph after a while and you can see what edges to to the distortion of the top. So I now round off the back of the bridge plate much like Howard shows above. That way when the top distorts it gives it a softer distortion - if you will.

I kind of think of the top bracing as a webbing like in a rope hammock. If you place a bowling ball on a rope hammock it will distort it's shape in a spherical dimension. If you put a cinder block on it then it will distort in an angular dimension.

The sphere is the strongest most resistant shape in nature
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  #52  
Old 08-15-2017, 04:44 AM
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murrmac123 murrmac123 is offline
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Quote:
Originally Posted by redir View Post
The sphere is the strongest most resistant shape in nature
Hmm...I'm not sure about that, redir.

An egg isn't spherical, and the "design" of the egg is such that it can withstand a far greater degree of compression (applied endwise) than it ever could if it were perfectly spherical.
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  #53  
Old 08-15-2017, 09:40 AM
redir redir is offline
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Quote:
Originally Posted by murrmac123 View Post
Hmm...I'm not sure about that, redir.

An egg isn't spherical, and the "design" of the egg is such that it can withstand a far greater degree of compression (applied endwise) than it ever could if it were perfectly spherical.
I should probably have said spheroidal. In a former life I was a Geologist(so this is how I still think), the common response in defense of weathering of rock for example is to round off. That's why pebbles that bounce their way down stream from the mountain tops that flow all the way to the ocean end up as round rocks deposited as sand. Not necessarily a sphere per se but rounded.

But anyway, an arch is also spheroidal and a very strong construct for similar reasons. Points erode away first and become round in the response to what ever force is eroding it. It's a defense mechanism if you will. Likewise points are areas of increased stress.
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  #54  
Old 08-15-2017, 09:47 AM
charles Tauber charles Tauber is offline
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Howard,

Is that carbon fiber on the top of your transverse brace? If so, do you have any quantitative results on what it adds to the build? Just curious. Trevor Gore espouses the use of carbon fiber, but provides no quantitative justification for its use. My "educated guess" is that it does very little, particularly if the adhesive used allows it to creep, but I'd like to be wrong.
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  #55  
Old 08-15-2017, 06:47 PM
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Used to be into RC aircraft, they use carbon fiber to add stiffness to wings using CA or epoxy.
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  #56  
Old 08-15-2017, 07:35 PM
CabinetMan CabinetMan is offline
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Ok guys, so I have gotten a little more done since my last post. Glued up my rosette out of some wormy chestnut go it routed out then routed the top and glued it in. Didn't get a perfect fit but not bad for the first time. Cut out the sound hole and Laid out the bracing on the back of the top. Glued the neck block in and trimmed the excess side material from the mortise.

BUT, I now have a problem. After the glue set, I noticed that if you are facing the top of the guitar and the neck is in the mortise, the neck is angled towards the right side of the guitar instead of being centered with the end block. Even when its in the mold. I still haven't figured out what's causing this.

Never got to work on the guitar any today. Started to work on my Real Job today then had machinery problems. Had to get a new miter saw. After 20 years of using my Dewalt almost everyday it finally gave out. The armature is completely worn out. Go Figure. ANYWAY;

When I made the mold, Every lamination was routed from the same pattern. I also used the pattern as part of the mold.
When I made the neck block I made sure all surfaces were square.

If any of you have had this sort of problem how is the best way of correcting it?

And Thanks for all the post on the bridge patch.

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  #57  
Old 08-15-2017, 07:46 PM
Neil K Walk Neil K Walk is online now
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You took the sides out of the mold to do a test fit of the mortise only, correct? Without the top and back glued to the sides they will flex and the blocks will therefore move in relation to one another. Don't attempt to set the neck angle until the box is closed.
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  #58  
Old 08-15-2017, 07:53 PM
charles Tauber charles Tauber is offline
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Quote:
Originally Posted by CabinetMan View Post
When I made the neck block I made sure all surfaces were square.
Without seeing it, I'd guess that the cheeks of the mortise/tenon are angled.

Quote:
If any of you have had this sort of problem how is the best way of correcting it?
Sure, I've had that problem.

There are two ways that I have used to correct the problem. One is to shave/plane one side of the tenon until there is enough "slop" to allow the neck to be centered correctly, then shim the joint to be snug in that position.

The second, if you've allowed sufficient excess width in your neck blank - I leave the neck blank not trimmed/shaped to final width until after the fingerboard is glued on and until the neck is shaped - you can slightly angle where the fingerboard goes so as to have it pointed correctly at the centerline of the top at the bridge position. A small change in position at the nut can produce a large change at the saddle.

Somogyi, purposely offsets his bridge a few mm from the centerline. Unless the neck position is out by a lot, it might be fine just as you have it.
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  #59  
Old 08-15-2017, 08:00 PM
CabinetMan CabinetMan is offline
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Quote:
Originally Posted by Neil K Walk View Post
You took the sides out of the mold to do a test fit of the mortise only, correct? Without the top and back glued to the sides they will flex and the blocks will therefore move in relation to one another. Don't attempt to set the neck angle until the box is closed.
Yes it was to test the mortise only and to see how it looked together. I just couldn't resist.
But even when they are in the mold it is still angled towards the right of the end block. By more than I would assume that is acceptable.

I guess that I just need to proceed forward and that I should correct it with taking the necessary amount off of correct side of the neck where it meets the body when I get to that point. Correct?
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  #60  
Old 08-15-2017, 08:19 PM
CabinetMan CabinetMan is offline
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Quote:
Originally Posted by charles Tauber View Post
Without seeing it, I'd guess that the cheeks of the mortise/tenon are angled.



Sure, I've had that problem.

There are two ways that I have used to correct the problem. One is to shave/plane one side of the tenon until there is enough "slop" to allow the neck to be centered correctly, then shim the joint to be snug in that position.

The second, if you've allowed sufficient excess width in your neck blank - I leave the neck blank not trimmed/shaped to final width until after the fingerboard is glued on and until the neck is shaped - you can slightly angle where the fingerboard goes so as to have it pointed correctly at the centerline of the top at the bridge position. A small change in position at the nut can produce a large change at the saddle.

Somogyi, purposely offsets his bridge a few mm from the centerline. Unless the neck position is out by a lot, it might be fine just as you have it.
Thanks for the reply. I see what you are saying

I know at the time I cut all the mortise and tenon that all was square and not angled. I checked it with my Starret square to be sure. It sat for a few days before I glued it in. I will admit that I didn't recheck it before I glued it in. Now that I think about it , I did notice that when I went back in the shop to work on the guitar that the neck block was sitting on my miter saw table and the sun was shining through the window on it. I guess its possible that it could have shifted some from the sunlight hitting it.
I used Titebond to glue it in. Any recommendation on how to get it loose from the side material to shave it some if necessary?

Yes the neck is wide enough to adjust there some if necessary also.
But even doing that I will always have it in the back of my mind that I could have done better getting that block right.
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