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I'm looking for ideas for routing a chanel for the backstrip. I will not join the back sets with the backstrip in between anymore. To risky. I'm thinking of usings my wells-Karol jig with an improvised guide to do successive cuts. Sound good?

Mike

Mike,

I've done this a few times with my dremel tool & StewMac dremel router base and a simple straight edge clamped at both ends.

Sure worked easy for me after making the obviously needed adjustments for alignment.

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P A U L B U R N E R
Burner Guitars

Paul, did u use an undersized bit and make several passes?

Small router, micro-adjustable fence, under-size bit, straight edge stuck down with double-sided tape. Works immediately after the plates are joined or after the guitar is boxed; whichever you find most convenient.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I clamp a steel ruler and then I do a few cuts with a flat back veneer knife. Then start chiseling (with one narrower than the needed width, and vertical sides, like a mortise chisel). You can cut in the normal way and alternate with vertical scraping. When I get some depth I clamp the ruler on the other side and repeat. For a faster clean bottom a router plane works great.

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Build log

Wonder why you think it's risky to include during glue up.....?
Tom

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A person who has never made a mistake has never made anything!!!

I just clamped 2 Aluminium bars (straight edge), set the depth and then route

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Sen CL Goh
http://senguitar.blogspot.com

Here's my rig. I do it on the joining table and use go bars to hold the strip in place during glue up. One pass.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

It's not structurally sound. It's only happened once to me, but I had a back set split along the backstrip.

Some of you appear to be using a single cut. I don't have router bits that match my backstrip dimensions.

Thanks, these ideas fall into line with my thoughts.

Mike

The reason I now do inlaid:

I did a few with sandwiched strips. Even if I did my best to fit them well with no gaps and clamp them tight, on a couple guitars I noticed some shellac activity between the rosewood and purfling. It wasn't a split but a sign of wood movement. Then I switched to inlaid strips (about 1.2mm final thickness) and the shellac looks perfect. I noticed the same when changing from full depth perimeter purfling to 1/2-2/3 depth. I imagine with thinner purfling the different wood movement is lower in strength and unable to affect the delicate shellac finish.

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Build log

I had a inlay strip pull away from a yellow cedar back glued 3 mo . ago.. WE have had an unusually dry summer 35-40% humidity. Next time I will use a 1/4in carbide cutter with a accura fence and router table.Have ordered the L/nelson left and rt dado rabett planes to finess the joint, and like alex mentioned abt 1.2mm strip inlaid with HHG. Allegedly inlaying is supposed to create a stronger joint??

I doubt it is stronger, my offcuts fail very easily (rough 3.5mm Indian rosewood back, 10mm wide strip, 1.5mm deep, maple black maple rosewood)
I actually think the sandwiched backs held better to breaking, but I noticed the story above.

When using mosaic or herringbone, it must be even weaker; whatever type of strip, the internal patch really is mandatory. But I guess I wouldn't bother with that on a stripe-less back if there weren't visual expectations involved.

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Build log

I must be lucky. Have done quite a few backs by sandwiching the strip and have never had a problem. After thicknessing I do soak the joint on both sides with CA glue.
Tom

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A person who has never made a mistake has never made anything!!!

I still just join my backs with the strip included - haven't seen any movement issues yet that would send me in another direction.

Regarding the internal reinforcement - I'm looking at my 1994 Larrivee L-9 right now, which is a superglued joint in EIR with no
internal reinforcement, and I still wouldn't be able to see that joint if I didn't know it was there. Nevertheless, I'm still wondering what possessed them (or possesses them still? I don't know) to send guitars out without something as simple as a back reinforcing strip.

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Jim Kirby
kirby@udel.edu

Tom - do you use CA for the initial sandwich glue-up? If not, is there any concern for having multiple glues in the same joint?

If the main wood for the back is a rosewood, I just butt everything together and soak the joint with thin CA.

I'm growing fond of Spanish Cypress, though, and you can't let CA anywhere near Cypress - it makes Spruce staining look nearly invisible in comparison. No CA on anything on a flamenca blanca. Too bad - I really like CA.

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Jim Kirby
kirby@udel.edu

Charlie: My main concern is with any delamination in the back strip it's self. The initial joining is not done with CA. If I just use a solid single back strip I don't use the CA after thining. To be honest I have never considered the fact that there may be two glues coming together. Guess I may be double lucky.
Tom

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A person who has never made a mistake has never made anything!!!

Perhaps ,the reason your sandwiched backs held together was better glue ,and higher humidity swelling up the sandwiched joint, From what I remember Nova scotia and delaware are much more humid in summer than KC, this is the 1st time mine came undone.But we/ve had a bone dry summer for 3 long months ??

Thanks Tom. Now that I think about it, it probably shouldn't matter if whatever glue is used in the initial glue up is fully cured and solid when the CA is applied.

Yeah, Delaware is humid - all my builds are sitting in the basement with two dehumidifiers cranking full time. I get a one week grace period in the fall before the humidifier needs to be turned on.

But, I've never been particularly protective of my finished guitars around the house, and I've never had a back joint (with internal back reinforcement) move or fail. Ask me again in ten years.

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Jim Kirby
kirby@udel.edu

I dunno. It just makes more sense to me. Inlaying the backstrip after joining means the backstrip is glued on three sides. It's the same effect we count on for binding, though that only uses two sides, but sides at 90 deg to each other. I will never sandwich backstrip and backs again.

Mike

It was a minor pain setting up a jig to do the routing, and I did end up using the wells-karol jig as an adjustable fence. Worked great. Hardest part was finding the glue joint.

Mike

I use my Bosch colt palm router for this. It just handles the job better then a Dremel router....Mike

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Another day, another dollar.

I sandwich the strip between the back halves because it is faster, and the fit should be as good or better that an inlaid strip (clamped plates with jointed edges facing the strip vs. an inlay). The cross grain reinforcement is what gives the joint its strength, I don't believe the minimal amount of long grain wood under the strip does much for the joint one way or the other.

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Rian Gitar og Mandolin

(selective quote again)

I think, like alot of things the execution is more important than the actual method. I usually sandwich, but had one client who decided he wanted a back strip after I had joined the back. I clamped down a straight edge to guide my router.

For back (and top) joints poor joinery usually results in a crack, right next to the glue joint, not along the joint, at least that's they way most center seams cracks I've seen were. If it comes apart at the actual joint I suspect it was a gluing problem. I use HHG. It's hard to get a sandwiched joint together before the glue jels, at least for me. I just apply glue, assemble and clamp, even if it's already jelled, then heat it with a heat gun to reactivate the glue.

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I didn't mean to say it, but I meant what I said.
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