Author Topic: "Z" splices  (Read 3637 times)

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Offline PatM

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Re: "Z" splices
« Reply #15 on: March 06, 2017, 04:58:30 pm »
I always make my joints as tight as I can, I use chalk to check for high spots and cascamite is my weapon of choice, but two part epoxy is different.  Two part epoxy has little or no penetration into wood fibres. Boat builders will butter a plywood joint with epoxy before applying the laminating layer of epoxy. This joint is only lightly clamped, enough to hold the laminates together, and very specifically not enough to squeeze out the epoxy, as the glue does not penetrate the fibres it relies on the fillet for its strength. In point of fact the epoxy can even be thickened with wood flour for gap filling and certain construction methods use a fillet of epoxy on the surface to strengthen a joint. I guess it reply all depends on your adhesive

 Epoxy soaks in more than that. If you butter up laminates and let them sit, "dry" spots will emerge and need to be topped up before assembly.

 Also end grain soaks up more volume and that's the part you are putting it on when splicing.

Offline stuckinthemud

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Re: "Z" splices
« Reply #16 on: March 06, 2017, 05:13:35 pm »
Agreed, I am given to sweeping statements, the buttering is mostly used, I believe, for open-pore woods (I did say plywood)and does soak in, needing topping up for the laminating.  So, doesn't that confirm the importance of a (thin) fillet? The laminating coat is needed because the joint has gone dry as the butter coat soaks into the fibres? Bow-woods tend to be dense, not porous, but in the end grain of a z-splice the extra glue would be more important. wouldn't it?  Like Mike said, different adhesives will need slightly different approaches so, for pva, cascamite and resourcinol, really good, tight joints, tightly clamped, are important, but, with two part epoxy,while a good tight joint is also really important, a loose clamp and a thin film might be necessary. For instance, the West 105 system directions specifically state the builder must avoid starving the joint by "wetting out first...and  then must ensure they apply sufficient epoxy to ensure the joint is not starved...squeezing out a small amount by clamping with the force of a firm hand-grip"
« Last Edit: March 06, 2017, 05:48:10 pm by stuckinthemud »

Offline DC

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Re: "Z" splices
« Reply #17 on: March 07, 2017, 08:10:56 pm »
Just one more thing. When you are test fitting to you just use hand pressure or maybe tap the end on the floor a bit?

Offline PatM

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Re: "Z" splices
« Reply #18 on: March 07, 2017, 09:23:29 pm »
You run the chance of splitting if you do that. I've had snug splices split by hand pressure. Depends on the wood too of course.

Offline DC

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Re: "Z" splices
« Reply #19 on: March 07, 2017, 09:31:16 pm »
That's true, I have split Yew that way, OS not so much. I am working OS at the moment so that slipped my mind. I've got a pretty slippery mind sometimes. Sometimes a feeler gauge will go in on one side of the tang but not on the other. You know a little tap will just fix that right up. Thanks Pat

Offline vinemaplebows

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Re: "Z" splices
« Reply #20 on: March 07, 2017, 10:05:28 pm »
I always make my joints as tight as I can, I use chalk to check for high spots and cascamite is my weapon of choice, but two part epoxy is different.  Two part epoxy has little or no penetration into wood fibres. Boat builders will butter a plywood joint with epoxy before applying the laminating layer of epoxy. This joint is only lightly clamped, enough to hold the laminates together, and very specifically not enough to squeeze out the epoxy, as the glue does not penetrate the fibres it relies on the fillet for its strength. In point of fact the epoxy can even be thickened with wood flour for gap filling and certain construction methods use a fillet of epoxy on the surface to strengthen a joint. I guess it reply all depends on your adhesive

Have you read the bowyers bible on glues?
Debating is an intellectual exchange of differing views...with no winners.

Offline LittleBen

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Re: "Z" splices
« Reply #21 on: March 07, 2017, 10:10:45 pm »
One word .... epoxy.

I've never had a splice that didn't fit like crap .... I've also never had one fail .... I use smooth-on EA40

Offline vinemaplebows

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Re: "Z" splices
« Reply #22 on: March 07, 2017, 11:06:42 pm »
I use, and have for many yrs devcon 2-ton slow set, never had a failure that I know of. I only use this for splices.
Debating is an intellectual exchange of differing views...with no winners.

Offline stuckinthemud

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Re: "Z" splices
« Reply #23 on: March 08, 2017, 07:29:12 am »
I always make my joints as tight as I can, I use chalk to check for high spots and cascamite is my weapon of choice, but two part epoxy is different.  Two part epoxy has little or no penetration into wood fibres. Boat builders will butter a plywood joint with epoxy before applying the laminating layer of epoxy. This joint is only lightly clamped, enough to hold the laminates together, and very specifically not enough to squeeze out the epoxy, as the glue does not penetrate the fibres it relies on the fillet for its strength. In point of fact the epoxy can even be thickened with wood flour for gap filling and certain construction methods use a fillet of epoxy on the surface to strengthen a joint. I guess it reply all depends on your adhesive

Have you read the bowyers bible on glues?

Nope, shamed to say I haven't, :-[ worked in boat building for a while, 20 years in wood-working.  ;) Always learning, always happy to be taught ;D: is Cascamite a bad choice (for non-bending) splices? Just in case, I would add that depending on what I am gluing, I also use 2-part epoxy, cyano, foaming poly glue, hide glue, PVA (white or yellow) or even varnish, it all depends. >:D

My second post on two-part epoxy, I hope, clarified and evidenced my statement -speaking personally, I think you should always consider what you are sticking, what you are sticking it with and what the manufacturer's guidelines say about the suitability of the adhesive and the proper way to apply it  :laugh: