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PostPosted: Thu Nov 08, 2018 11:17 am 
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Woodie G wrote:
Fascinating stuff!
(e.g., Mr. De Rocher's three same-direction plies)


Just to keep things accurate, the three layers in the tenon I make are not same-direction plies. The tenon is a crossgrain laminate as I said in my post above. The grain orientation alternates by 90 degrees in each layer.


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PostPosted: Thu Nov 08, 2018 11:44 am 
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I've had a tenon-related question rolling around in the back of my mind for a while and I'm wondering what you all think the answer would be. Which grain orientation in the diagram below would be more resistant to failure from tension on the barrel nuts. This is assuming a non-laminated tenon.

Then what's the answer when you make a laminated tenon with alternating grain orientation?

I've been wondering because I could be making my three-layer tenons with the grain of the outside two layers vertical and the middle layer horizontal (parallel with the neck grain), or I could do the opposite. I'm wondering which one, if either, would be stronger with respect to the pull on the barrel nuts.

Attachment:
Grain orientation in tenon.jpg


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PostPosted: Thu Nov 08, 2018 12:01 pm 
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I think the grain orientation in the first picture would resist the barrel nut splitting out much more ans it has more wood to split along the grain in order to fail. I'm not sure about a laminate but my gut says that having the outer laminates oriented like the first picture would be better. The laminate in the middle will have much of it's wood taken away by the bolt hole.

I could be way off the mark here.

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These users thanked the author Bryan Bear for the post: J De Rocher (Thu Nov 08, 2018 12:07 pm)
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PostPosted: Thu Nov 08, 2018 12:41 pm 
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The second diagram has the grain running the same direction as the neck. When folks just use a regular cut tenon with barrel nuts, they worry about whether the front of the nut will act as a froe and split the wood along grain lines. Some folks combat that fear by adding strips to the outside of the tenon, with the strips having a grain orientation like the first diagram. I think that decision is driven by a perception that the grain orientation in the first diagram is more resistant to a split (as caused by a barrel nut) than the grain orientation in the second diagram. My impression is that they are right. So, I think the first diagram is more resistant to a split caused by tension on the barrel nuts.

These are just impressions. If someone has done destructive testing, I defer to that data.



These users thanked the author doncaparker for the post: J De Rocher (Thu Nov 08, 2018 1:03 pm)
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PostPosted: Thu Nov 08, 2018 5:11 pm 
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Could be a high-quality birch plywood would make a good floating tenon? I've used barrel nuts but I have to agree with Gerard Gilet on this - that they can act as a "blunt wedge." By not being glued in, they can exert a lot of pressure on the tenon. The floating tenon idea really appeals to me after reading this thread, as does screwing straight into it.

So many ways of doing the same thing...

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PostPosted: Thu Nov 08, 2018 7:56 pm 
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The second configuration is the strongest. The first one is prone to splitting of the laminates.


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PostPosted: Thu Nov 08, 2018 10:40 pm 
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I use two maple strips laminated cross-grain just on either side of the truss rod slot. Easy to do if you make the maple the same thickness as the saw blade kerf. The one in the photo was a laminated neck hence the maple veneer in the center.

Attachment:
DSCF0171-1.JPG


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PostPosted: Thu Nov 08, 2018 10:55 pm 
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nkforster wrote:
jfmckenna wrote:
I do the same thing as you do Jay. Then when I am done flossing the whole of the heal is flush to the head block/sides. I've always thought that it would be important for sustain and tone to have a nice flush mount. But that's probably not true. Kind of goes back to the old bolt on VS dovetail joint but none the less it's one of those things that I don't give up on and it's good for the marketing department :D



The best sounding guitar I've ever played and owned was my 1890s How Orme. And If you've ever seen a Howe Orme neck joint, you'll understand that the solidity of the connection between neck and body is not as important as people imagine.

But you're right - from a marketing point of view the closer your views to your customers, the better. Even if they are wrong.

The Howe Orme neck joint doesn't need much flossing.


Those are very cool guitars, must be a pleasure to own one.

Yeah I had this idea in my head for a while. When I started building I built classical guitars and I built them with a Spanish foot till one day I decided to experiment with bolt on. In the classical guitar world, at least in the 90's, that was blasphemous. But I did manage to convince one very good player who wanted one of my guitars that it was 'just as good' becasue it was flush and made contact at all points. I guess since I half believed it too the nit was not a con job :D


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PostPosted: Fri Nov 09, 2018 8:43 am 
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SteveSmith

What are the little brass dowels in that neck for? They look almost like dowel centers.

Ed


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PostPosted: Fri Nov 09, 2018 9:00 am 
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First, to Mr. De Rocher, my apologies for misstating your tenon configuration. Second, this has been a fascinating discussion, and after asking the two engineers in the shop for some further explanation, here's what I got back this morning from boss and Mr. Morelli:

Quote:
Same (ed: stuff) we talked about with you and Jon WBL. No best practice just stuff to avoid + trades to be made. Cumpiano works fine until whacked and tenon shears on the grain lines (see the sketch). The fix is cross-grain reinforcement, but that can cause problems or useless if done wrong.

Attachment:
TenonFailureSketchesV01a.jpg


Re: Q1: Three ply lam your bud is using is fine. Material behind the barrel nut is not doing anything useful and reduces tenon tensile strength, but even with bolt cutout, still effective. Moving the reinforcement outside the bolt access prob helps, but the joint is over-strength already. Lams support each other, so splitting of crossgrain not that big a deal, but could see compressive fail. Loose tenon is fine - just has to be long enough insertion into heel to avoid a glue line fail in shear or fail of outer layer of tenon. Plywood just more lams, so reduces tensile strength and has same issue as any laminate w/ reinforcement not being very efficient. Also heavier, but prob not issue (grams)

Prob need to label these and edit. Gen Y's won't get hardware store, so just footnote with Cump web site link. Shot of Jon's neck in stuff I sent last week. Section thru tenon screen cap off Fusion...you can label

Re: Q2...no - FPL handbook no xgrain shear number because compression failure/other fail before the stress gets close to what's needed. Read text - all there

Attachment:
Tenon Section v1.jpg


Re: Q3..any insert not full length causes stress riser at edges...prob not issue because of how o/s system is. Could taper, but PITA to make


Attachment:
Tenon Inserts.jpg


Mr. Morelli sent the following by way of addressing my questions:

Quote:

Attachment:
meme.jpg



Nice to be appreciated ;)


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PostPosted: Fri Nov 09, 2018 9:54 am 
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Looks like my 'aha' moment about using a loose tenon has been thoroughly explored before I came to the party. Nice to know it wasn't something tried and rejected, anyway.

Back to the hangar bolt theme, I am attracted to them by their virtue of accepting nuts for fastening as opposed to screws. I find nuts a whole lot easier to start in blind applications, like neck attachments. There's a reason that a whole lot of stuff in confined spaces is installed with studs and nuts instead of bolts and screws if the materials will allow it.

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PostPosted: Fri Nov 09, 2018 11:59 am 
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One of the reasons I like the furniture screw (KD) and insert over the hanger bolt and KD nut is that I like to use a countersunk hole in the heel block. With the nut you need 2 steps in the countersink, one for the flat part of the nut and one for the threaded part. Using those, I had to countersink the block before I closed the box. that wasn't a big deal but it made lining up where to drill the holes in the neck a bit more annoying.

With the screws, I can measure for and drill the holes with the body completed and neck angle cut on the neck heel. I recently bought a reverse countersink form Elevate Lutherie so I can do the countersink after.

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PostPosted: Fri Nov 09, 2018 12:21 pm 
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I use the reinforced barrel nut tenon for everything but for a standard flat top neck angle the hanger bolts are fine. Where the barrel nuts really shine is with higher neck angles like an archtop or some weird flattop designs where the bolts can self align.

My holes in the headblock are 5/16 and the tenon is slightly loose in the mortise so as to simplify minor fine tuning. That has never posed a problem.

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PostPosted: Fri Nov 09, 2018 12:22 pm 
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Woodie - Thanks a lot for your post above with the diagrams. Very good information there.


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PostPosted: Fri Nov 09, 2018 12:52 pm 
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Bryan Bear wrote:
One of the reasons I like the furniture screw (KD) and insert over the hanger bolt and KD nut is that I like to use a countersunk hole in the heel block. With the nut you need 2 steps in the countersink, one for the flat part of the nut and one for the threaded part. Using those, I had to countersink the block before I closed the box. that wasn't a big deal but it made lining up where to drill the holes in the neck a bit more annoying.

With the screws, I can measure for and drill the holes with the body completed and neck angle cut on the neck heel. I recently bought a reverse countersink form Elevate Lutherie so I can do the countersink after.


I've been leaning towards the hanger bolt method for my current builds, especially after this discussion. I do like the 'self-aligning" aspect mentioned above, and have puzzled about the counter sinking issue. I usually drill the holes through the neck block when using the barrel nut approach once I've cut my mortise. That way I get them positioned perfectly in the center of the mortise. With the flat head of the bolt against the neck block, I never felt I wanted or needed a counter sink for the head. I guess it's not really necessary with the hanger bolt approach, but I do like the finished look of a countersunk bolt head.

There was a recent discussion on mylespaul.com (http://www.mylespaul.com/threads/proble ... ng.417130/) where the heel block was too thick to accept a pickup jack, thus needing a way to countersink the inside of the block. Some interesting methods came up, but using a reverse spot facing bit from the inside was a simple solution. Someone even suggested modifying a spade bit to have a square shoulder, and then using that as a reverse spot facing bit.

Gets my synapses firing.

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PostPosted: Fri Nov 09, 2018 1:09 pm 
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This is what I bought. I haven't used it yet but it is exactly what I had been looking for. when I saw that Chris was offering them for such a reasonable price, I stopped looking. I needed something like this to fix a problem with the heel block in my last one. I thought about reshaping a spade bit but I was worried that the thin shaft would cause me problems Nd I would get an ugly cut.

https://elevatelutherie.com/product/nec ... unterbore/

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PostPosted: Fri Nov 09, 2018 1:38 pm 
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Bryan Bear wrote:
This is what I bought. I haven't used it yet but it is exactly what I had been looking for. when I saw that Chris was offering them for such a reasonable price, I stopped looking. I needed something like this to fix a problem with the heel block in my last one. I thought about reshaping a spade bit but I was worried that the thin shaft would cause me problems Nd I would get an ugly cut.

https://elevatelutherie.com/product/nec ... unterbore/


That's a good price for the spot facer + the pilot.

If other spot facer or pilot hole dimensions are needed, MSC Industrial has a good selection although at a steeper price. https://www.mscdirect.com/browse/tn/Holemaking/Reverse-Counterbores-(Spot-Facers)?searchterm=spot+facer&navid=4287922913



These users thanked the author J De Rocher for the post: Bryan Bear (Fri Nov 09, 2018 1:51 pm)
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PostPosted: Fri Nov 09, 2018 1:52 pm 
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Spot facer! I knew what I wanted the tool to look like and do but I couln't find exactly what I wanted. It helps to know the name!

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PostPosted: Fri Nov 09, 2018 3:33 pm 
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Bryan Bear wrote:
This is what I bought. I haven't used it yet but it is exactly what I had been looking for. when I saw that Chris was offering them for such a reasonable price, I stopped looking. I needed something like this to fix a problem with the heel block in my last one. I thought about reshaping a spade bit but I was worried that the thin shaft would cause me problems Nd I would get an ugly cut.

https://elevatelutherie.com/product/nec ... unterbore/


That's a great deal! Thanks for sharing it!

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PostPosted: Fri Nov 09, 2018 3:39 pm 
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Ruby50 wrote:
SteveSmith

What are the little brass dowels in that neck for? They look almost like dowel centers.

Ed


Hi Ed, the brass dowels are bearing points for set screws used to adjust the neck side to side (yaw). That one was a Doolin type adjustable neck he showed in American Lutherie #86. The neck has worked well for 10+ years although the inside adjustment is a minor PITA.

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PostPosted: Fri Nov 09, 2018 7:03 pm 
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Lee Valley sells a similar tool, in the pen turning section.
http://www.leevalley.com/en/Wood/page.a ... 48523&ap=1
Easy enough to fab your own if you have a couple pieces of 3/4 and 1/4 inch rod and a 1/2 hour
to spare. Easier to buy tho.:D
One of the quickest things I've ever made and works as intended. Not as pretty as store bought but...


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PostPosted: Sat Nov 10, 2018 4:28 pm 
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If this is hi-jacking, let me know and I will start a new thread

Has anyone done just machine threads into the neck without an insert? According to testing, it would require the vertical dowel in the heel to provide side grain, but I have done these in other furniture applications without a problem - although nothing under extreme stress.

I could not find the technical paper that really dug into it, but I did find one from the magazine "Woodcuts". It is a pdf and I don't know how to attach it. It says that for most bolt vs screw sizes, the tapped hole in wood is stronger than a wood screw, provided a proper sized pilot hole is drilled. One of the main advantages of this is easy removal without damage. It also said that the machine bolts don't work well in end grain,hence the dowel in the neck. The original paper that I can't find also said that an application of thin CA glue, then a re-tapping increased the durability.

Here is a short article from The Wood Whisperer:

https://www.thewoodwhisperer.com/videos/tapping-threads/

They say it is easier to use a power drill to tap than to use a handle. And here is Lee Valley's offering:

http://www.leevalley.com/US/wood/page.aspx?p=40057&cat=1,43455,61994

Just a thought. Anyone know how to attach a pdf?

Ed


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