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Thread: Best Gluing Practice with Shop Sawn Veneer?

  1. #16
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    John, I also don't glue the seams. I don't see the point as I can always see glue having been pulled through the seam after taking the panel out of the press.
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  2. #17
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    Brain, what glue are you using?

  3. #18
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    John, using titebond II currently.
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  4. #19
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    Thanks Brian. That's interesting how it sucked up into the seam yet PRG doesn't.

    John

  5. #20
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    Here are some photos I took of maple veneer glued with PRG onto the composite core substrate. I think this was from 1 lb/40 sq. ft coverage but can't remember for sure.

    Here's the panel after I peeled off the veneer near the seam, but before opening it.



    After opening the right side.



    On about 90% of the area the glue pulled up the particle board; just a small area near the bottom where the glue let go from the veneer. On the area where the hardwood edging was the glue split cleanly not taking any of the veneer or edging with it.

    Looking closely at the edge at the seam.



    No glue. The other side is the same. I guess I know how to make tight seams. But you can see that the veneer was bonded to the particle board at the seam. Looking at both sides is shown below.



    Most of the seam openings I've seen are where the veneer is curling away from the substrate. In that case, either the veneer was not bonded well to the substrate or the veneer was bonded but the substrate is delaminating. I can't look under any of them yet so it's hard to say which is the case.

    I certainly do not like the poor bond at the hardwood edge. That might be reason enough to switch glues.

    Comments welcome.

    John

  6. #21
    John, I saw your mention of the low pressure with vacuum bag. That makes me think you will have to
    put glue on both sides, that is actually less messy and more dependable than one heavy coat. Or go to a different glue. I've posted two or three times about how well PRG works with glue on both surfaces ,material covered with plastic to
    prevent adhesion to caul ,spring clamps around perimeter, weight in middle. That glue has a strong
    atraction to itself. I've seen failures on bent laminations where one heavy coat was used on each layer
    and none where glue was applied to both ( or all).

  7. #22
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    Thanks Mel. I know you mean well but I take it you've never put waterbased glue on veneer. You can't believe how quickly it will curl and become unmanageable. If putting glue on the veneer is required I would switch to epoxy.

    John

  8. #23
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    I generally go by instinct on the time in the bag. I spoke with the Titebond guys some years ago when I had a tricky project to do to discuss how long parts should be kept in the bag, and they were pretty un-helpful in that regard. So for flat work I generally leave it in the bag under pressure for two hours, or sometimes more if I have the time. For curved work I go longer based on how much tension there is on the parts. As a really rough example.... if I can hold the parts to the form with little force, then 2 - 3 hours is fine. If it's something that requires some exertion to make the parts comply I'll shoot for 6+ hours to be safe. With TB 1 or 2 there will be a bit of spring-back on curved parts. Not a lot, but you do have to account for it.

    As far as bleed through goes.... if your using shop sawn veneers roughly 1/16" thick, bleed through should not be an issue unless its some really tricky burl type stuff or??? With paper backed veneers same situation, no bleed though worries. I usually order my veneer paper backed for just this reason. It's only non-backed veneers that the bleed through can be an issue. I've done them on occasion with older veneers I've had in the rack for a while and have been pretty lucky, though I know some stuff can be problematic.

    I use a variety of materials for the cores. On large flat pieces I really like mdf, or if it needs to be more structural then a veneer core with hardboard faces, ie Pluma ply. On small parts for furniture I'll do solid cores glued up from stable hardwoods.

    good luck,
    JeffD

  9. #24
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    Thanks very much Jeff. One more follow up question or maybe two. What spread rate are you using? And how long do you let the panels sit after coming out of the bag before further processing? The water in TB glues can't evaporate while in the bag, only migrate into the substrate. Thanks.

    John

  10. Quote Originally Posted by Kevin Jenness View Post
    Joe, Titebond cold press is a PVA with crushed walnut shells added to prevent bleedthrough when pressing thin sliced commercial veneer. The additive is unnecessary with thick veneer, and the greater movement potential indicates a more rigid glue than PVA.

    I generally use epoxy with thick veneer for a rigid glueline and long assembly time. One advantage is that epoxy will be sucked up into the joints between leaves in a vacuum press, bonding them together.

    A point that is sometimes overlooked is that epoxy bonds best to rough surfaces, sawn or sanded at 80#, especially when gluing dense woods.
    Thanks for this, learned something valuable.

  11. #26
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    Jeff, you mean this stuff? https://www.dropbox.com/s/memn43f39v...50102.pdf?dl=0 I was looking at that only a week or so ago. Looks like a very good substrate for veneering plus the structural aspect. But it looks like it's only made in 3/4"; I need 5/8".

    As an experiment I took some 3/4" poplar plywood and drum sanded off the outer plies on both sides to get to 5/8" then veneered it with my shop sawn veneer in the standard cross banded way. It will be interesting to see how that performs compared to the composite core the rest of it has been made with.

    John

  12. #27
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    Yup, thats the stuff. It comes in a whole lot of sizes though I can't say if 5/8" is one of them, that's an odd size. I've used 1/2", 3/4", 1", and I even used 1-1/2" for a custom desk I built last year. The stuff is also pretty flat, almost comparable to mdf in the thicker sizes. Almost all my paint grade work is done with Pluma now as the finish on that substrate is excellent.

    I use a pink roller cover I think is made for contact cement to roll the glue on, that way I get a good even spread. One side only, if I did both it would certainly be too much glue. Once the parts come out of the bag I usually let them sit overnight. As far as the "evaporation" aspect I don't think its much of an issue. If you think about it glue doesn't easily evaporate through solid wood parts even when not in a vacuum bag, so..... probably not a huge difference there?

    Anyway I hope this helps a little, I should say I'm no expert when it comes to veneer work. Though I get by and haven't had too much trouble so far
    JeffD
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  13. #28
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    Thanks very much for the follow up Jeff. Love the clean lines and gorgeous wood of that office space.

    John

  14. #29
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    Quote Originally Posted by Jeff Duncan View Post
    Yup, thats the stuff. It comes in a whole lot of sizes though I can't say if 5/8" is one of them, that's an odd size. I've used 1/2", 3/4", 1", and I even used 1-1/2" for a custom desk I built last year. The stuff is also pretty flat, almost comparable to mdf in the thicker sizes. Almost all my paint grade work is done with Pluma now as the finish on that substrate is excellent.

    I use a pink roller cover I think is made for contact cement to roll the glue on, that way I get a good even spread. One side only, if I did both it would certainly be too much glue. Once the parts come out of the bag I usually let them sit overnight. As far as the "evaporation" aspect I don't think its much of an issue. If you think about it glue doesn't easily evaporate through solid wood parts even when not in a vacuum bag, so..... probably not a huge difference there?

    Anyway I hope this helps a little, I should say I'm no expert when it comes to veneer work. Though I get by and haven't had too much trouble so far
    JeffD
    Wow Jeff, beautiful work! What's the wood species and finish?
    Last edited by Andrew Joiner; 03-08-2019 at 10:13 AM.
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  15. #30
    Quote Originally Posted by John TenEyck View Post
    Jeff, you mean this stuff? https://www.dropbox.com/s/memn43f39v...50102.pdf?dl=0 I was looking at that only a week or so ago. Looks like a very good substrate for veneering plus the structural aspect. But it looks like it's only made in 3/4"; I need 5/8".

    As an experiment I took some 3/4" poplar plywood and drum sanded off the outer plies on both sides to get to 5/8" then veneered it with my shop sawn veneer in the standard cross banded way. It will be interesting to see how that performs compared to the composite core the rest of it has been made with.

    John
    The site says 3/8" - 2".
    Best, Metod

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