Official Luthiers Forum!

Question from an inexperienced builder (what should I do?)

I have my backpieces cut and I have the decorative backstrip. The backstrip is as thick, if not thicker, than the backpieces. In putting the back together, would it be smarter to 1.) glue the 2 backpieces directly together and afterwards inlay the decorative backpiece over the seam, or, 2.) sandwich the backstrip in between the 2 backpieces.

It seems reasonable either way, but seems there would be a large amount of scraping down the backstrip if it were inlaid. I think I've heard/seen it done both ways. I knew you all would know.

Thanks in advance,

Shane.

I glue it between, but there is a good case for inlaying it, in that seam becomes stronger because of the added gluing surface created by the 3 sided trough that you will inlay your strip into.LanceK38744.5785648148

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Lance@LuthiersForum.com

Inlay the back strip. thickness sand the back strip before inlayin just proud of the finish thickness and scrap flush after.

Thanks for your help. Looks like a matter of personal preference and either way would be fine.

Shane.

Shane, I'm with Lance and Michael. Either way will work, and Martin sandwiches their backstrips between halves, but the joint will be much stronger if you glue up the back first, then inlay the strip.

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

I'm in the inlay camp. For the main reason that if you use someting pre-made (harringbone or the like) you are relyin g on the factory glue to hold your back together. You don't know what it was glued with or when or under what conditions. Inlaying is much safer.

I'm with Paul on that too! Inlaying would definately offer a stronger joint, specially if you are using a wider strip.

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Peter M.
Cornerstone Guitars
http://www.cornerstoneukes.com

With a backgraft covering your hiney, I see no problem just dropping her in as part of the back.

That is of course you do a good job making the joint and get a great glue up on the graft, and that the head block and tailblock hold and the inside braces don't peel off......

Does it really matter?

Shane,

    On my latest rosewood back I inlayed the backstrip and at least half the D-28 style strip was proud of the surface after gluing. I carefully used a small low angle block plane and then a scraper to bring it down level again. It was quick and easy to do and turned out perfect.

For me, the tedious part was routing the shallow slot for the strip (and setting up for the cut). I routed to a depth of 1/2 the thickness of the back, right down the center of the glue joint.

I have done it both ways & both work fine. I have found that when you inlay the strip, you can end up with a deformation along the centre line caused by the glue shrinking as it dries.
Its a really good idea to wait until the joint has fully dried before leveling the strip. If you do it too soon you can end up with a distinct dip along the length of the strip.
If I sandwich the strips in, I use a wider graft on the inside. Those fibre purflings we use are little more than strips of paper & have very little strength.

I'm with Bruce on this one, the center strip on the inside should keep the seam nice and tight. I think there is less set up to just sandwich it. You could even just super glue it and keep going if you were in a hurry. I knew a builder who superglued this joint for years and never had a failure. With the inside seam glued with wood glue, I can't imagine this joint going anywhere.
Tracy

Just a thought from a non-built-Yet wannabe, but if there's enough on the thicknes of the strip, could you inlay it and then skim off the half that's proud and maybe use it for another build?

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DES - Shepherd, MI

I know people do it both ways, and I don't suppose that it REALLY makes that big of a difference.

However, I think inlaying it makes the most sense... and here is why I think so.

Once the back is joined you are going to cover it with the back inside center seam piece -- more strength from that.

And if you route a channel down the back and inlay this piece you are getting yet more total glued surface area from the center seam and the inlay strip.

I don't KNOW that thinking is rational, but it appears to me that would make a stronger bond. Brock Poling38744.769375

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

Brock,
I think there is no question you are correct about the joint being stronger with the inlay method. The question is really how much stronger is it than just the sandwich method. If time is your enemy, then I'd think the sandwich method with super glue will do the trick. You could have the back joined and braced in less than 2 hours with this method.
Tracy

I don't disagree.       Having it sandwiched between may be plenty good enough.

I don't do it that way... but that certainly doesn't mean the other way isn't a fine method.

I was just sharing my rationale for inlaying it.

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

Having just completed my first two back center seams, I have a question that I hope the answer to which is not too obvious:

If I join the back plates together, and then route a channel and inlay a strip of material whose grain runs parallel to the length of the back, how and I strengthening the back? It is fairly well established (or so I thought) that a well done glue joint is stronger than the wood itself so where is the real advantage? The thickness is the same as no center strip.

The only possible advantage I can see from my inexperienced eye ( ) is the half height glue joint from a wood species that may be stronger than that of the center seam.

Thanks, Steve

PS Oh, and of course, MY glue joints are always perfect! sfbrown38744.951099537

Well again.. this is just going on a hunch.. not any sort of empirical testing...

but.

When you route a channel and glue a strip in the back you are gluing a reinforcement across the joint and the surface area of your glue is substantially larger than just gluing the center seam together.

Couple this with the inside reinforcement strip and I think the resulting plate MUST be noticably stronger....

but again. This is just my hunch.

I glue lots of back plates together with no center strip. So I am not advocating the use of one over not using one.

My point is that ** IF ** you use one, this seems like the way to get the strongest bond.

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

Lance addressed the strength question back in post #2.
You've got--in effect--a "T" shaped join. That's a lot more glue area than just a straight "I", as in a sandwich glue-up. And Paul as well as Daniel bring up good points about the glue used in the seam decoration as well as the material itself. Fiber? Strong?? Not when the shrinkage forces are pulling against it. I know the reinforcing seam is doing a lot of work inside, but why not give yourself every advantage?
All that said, I have used the sandwich method when I just had to have the extra width. (Back piece too narrow otherwise.)

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

I always inlay them ... But... if I had a back set that was just a little too narrow for a particular model, I would not hesitate to sandwich a strip to add a little width. Of close there would be a closer inspection of the back strip to be used. I haven't had to do it yet, but I sure the day will come.

for the reasons stated above, i.e. greater strength and doubts about bought in laminates of unknown strucural integrity i have usually gone the inlay route.

and i have fudged and used the sandwich when i needed a tad more width.

although i do my own center strips these days, so i should know how well they are glued, i still prefer to inlay.

Has anybody here ever heard of a failure on this joint? I know MANY classical builders who just use the CA method and wick it between the sandwiched sides and I have never heard of a failure here ever. Think about it, there is almost no stress at all put on this joint, then you add a center re-enforcement strip. I think either method is fine, it's just a matter of preference. I will say however I think it's easier to get more consistent results with the sandwich method.

Cheers!

JohnJohn Elshaw38745.4419791667

And there you have it folks--

More than one way to skin a cat!

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

I only ever use a backstrip when the bookmatch on my back plates isn't very good and I'm trying to disguise the fact as I always have this nagging worry about differential expansion! This would infact argue for a sandwiched joint, but I have always inlaid them. Go figure.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.