Replies

1. 
   Tao | Apr 29, 2004 07:08pm | #1

   I think you are wasting your time.  Unless you have over a hundred to do, I'd just rip the appropriate bevel, lay the wood down face up with the pieces tight together, and tape the joint tightly along its whole length.  Then I'd turn it over, brush glue in the groove, and then close the groove. 

   I did a some 14 foot tall faceted columns for a fireplace surround a few years ago, and this technique worked great. The joints were tight, and it saved a lot of complicated veneering.

   Michael R. 

1. 
   MBL | Apr 29, 2004 07:41pm | #2

   Thanks Woodwiz.

   Total cut has been done as you suggest. It takes two cuts, one to separate the p.w. and a second cut at the bevel angle.

   Since this is only 1/2" thick p.w., line-up is not as simple to keep, and the slightest clean-up takes veneer off and wants to show core, which takes more effort to finish.

   If a one step cut could be done, it'd be nice. The plan is to make a few, that's why a better way is being sought, if it is practical.

   Would like to hear if hand-powered a dado-plane has been used for such a thing. For a powered tool, the angle is too sharp and would probably be short-lived, unless it were of costly material and making.

   Thanks, again.

   -mbl-

1. 
   Tao | Apr 29, 2004 08:39pm | #3

   Try the taped joint.  It works amazingly well if you get the joint lined up tightly to start with.  I use 2" blue masking tape the whole length of the joint.  As you close the joint, the tape has to stretch a little, and this pulls the joint good and tight as well as lining it up.  The only cleanup that should be needed is one light pass with some 220 to break the sharp edge.  Believe me, If it worked on 14 foot columns, it will work for you.

   V groove jointing works best on vinyl or paper clad sheet stock.  In my experience, veneers, especially as thin as those on plywood, tend to splinter, regardless of whether the joint is with or across the grain.

   In my experience, there is no practical way to do the joint the way you are suggesting.  If there were, the results would be pretty ugly because of the tendency of the veneers to splinter.   If you were using "wrapped" MDF or particle board, it would be another matter.

   Additionally, doing such a process by hand would be a LOT slower than pushing material through a table saw.  You just need to rough cut your pieces slightly oversize, then rip at a bevel to final dimension.  Even ten sheets of plywood shouldn't take more than a couple of hours, if you have a good cabinets saw.  The setups will almost take more time than the actual cutting.  Just make sure you use a good blade, well sharpened so you get super clean cuts.

   And do samples on scrap until you have the technique down.

   It might be best to use a gap filling glue such as epoxy when edge jointing plywood.  I would also use triangular glue blocks the whole length of the joint.  Biscuits would help with strength, but would make it very hard to get really good joint alignment, plus there is a very good chance they would telegraph.

   If I were going to do a lot of these, I would use an MDF core because it would give me a much better glue joint.  It's a lot heavier I know, and nastier to work, but in this case it's a little more suitable for what you are doing.

   Michael R

   Edited 4/29/2004 1:47 pm ET by Woodwiz

1. 
   MBL | Apr 30, 2004 01:34am | #4

   Thank you Woodwiz,

   Made an experiment with a specially sharpened chissel mounted sideways on a woodblock, and although it would be possible to cut as thought, it looks like it'd take some good effort to complete such a cut, even though it's only about 15" long and less than 1/2" deep. That'd be due to p.w. not so easy to cut as solid wood with a hand tool as intended.

   Another possible solution that is fast to do, so far, is to cut with a regular sawblade, which cuts a small rectangular groove, and then fold the plywood. However, the glueing would have to be glued with epoxy or another gap-filler wood. The joint has to be strong too.

   What alternatives are there on gap-filling glues, brand names, and aprox cost or relative costs? What curing times?

   Thanks for any replies.

   -mbl-

1. 
   eddiefromAustralia | Apr 30, 2004 05:56am | #5

   mbl,

   Normally, these grooves are table saw cuts - set the blade height about 3mm short of the surface and run the grooves/kerfs.

   A common way of bending ply - the more kerfs, the tighter the bend.

   If you want strength, there are several ways to get it - could you give a bit more detail on what you're doing with the piece - is the inside visible or hidden?

   Cheers,

   eddie

2. 
   Tao | Apr 30, 2004 06:12am | #6

   Kerfing works fine for radius bends as you describe.  I got the impression he wanted a sharp, but shallow, corner.

   MBL - I cant be much help on epoxy brands.  The ones I use are proprietary and not available to the general public. You don't need anything special here.  About 1/2 hour pot life should be plenty, and a regular bodied glue should work fine -- nothing real thin or thick.

   Honestly I think you are trying to reinvent the wheel here.  A taped joint for a sharp corner, kerfing for a radiused corner (or kerfboard) are pretty well tried and proven techniques.  They are simple and quick, and don't require any special equipment.  It's good to always be looking for a better way, though.  It's just my experience tells me your ideas will give a less satisfctory result with a lot more effort.  If I didn't have a decent table saw, I'd still use the same technique with a circular saw and guide.  Wouldn't be as clean, but better than any other way I could think of, other than making the joint, cleaning it up, and veneering over it.

   Michael R

3. 
   MBL | Apr 30, 2004 07:42am | #7

   Friends,

   What's required is quite simple. It's only a small slope of about 15 degrees on a small piece of plywood that assembles into another structure.

   Woodwiz, have already done it exactly as you suggest, a few finished pieces had been done, prior to asking the question. The way you describe is fine, it is not being disregarded. However, observation says that there's got to be a simpler way, and it is getting close.

   Did a partial cut on the table saw with an even thinner kerf blade and this is pretty much what's wanted, except now have to get a glue that has some degree of gap-filling. Even yellow glue almost works, but it's not quite up to the job. The kerf cut is less than 1/8" and even getting the glue inside is not that easy, have to use a putty knife to push it inside and then clean-off the excess before assembly.

   Have been looking at glues that are available for average woodworking, and if it's not Dap plastic resin, probably Gorilla would do it. The Dap is not available at Grainger, nor at Lowes, nor at Home Base here, at least as per the web-sites. But will check with more specialists tomorrow.

   It is not easy to describe the details of everything a person is trying to do. The slope part is simple, but it assembles into the rest of the structure via dadoes, and must edge glue AND dado at the same time, so if the p.w. is in one piece, it'd be much simpler to integrate.

   The hope was that perhaps someone had done something like this: Partial cut and fold but at a very minute angle. Folding at 90 degrees and making boxes with V-grooves is somewhat conventional for there are bits to do that.

   Have found a thread on glue and have asked about the Dap Plastic Resin too. In the mean time, will try to get some and test it.

   Thanks for the suggestions to this rather peculiar, but not that significaive issue.

   -mbl-

4. 
   eddiefromAustralia | Apr 30, 2004 08:39am | #8

   mbl.

   Thanks for the clarification.

   Here's two options that may work.

   1 - kerf as you have, use the epoxy glue (it'll be plenty strong enough, and epoxy needs a minimum glue line thickness of 20 thou (0.5mm) to successfully bond.  You've got this in this instance.

   2 - rip the boards to the correct angle - use a biscuit jointer to cut slots so that the outside corner of the ply is aligned/pinned correctly - this assumes that you have an adjustable fence on the biscuit cutter - in your case the cuts are 7.5 degrees and the biscuit slots would be cut with the fence referenced at 97.5 degrees.

   You may want to cut a couple of support pieces to fit under the plywood side to ensure that things stay where you want them to as they dry - stiffening braces are a more permanent solution

   Cheers,

   eddie

5. 
   MBL | Apr 30, 2004 08:50am | #9

   Hi, Eddie.

   Thanks for the suggestions.

   Buiscuits are not for this one due to the thickness of the p.w. is only 0.5". It's not too difficult to actually make the joint by first total cutting and then beveling and then gluing together as said already, it's that am looking for the simplest way to do it with one cut, not two cuts and try to keep it as one piece.

   Some simple glue-up that fills just a small amount of gap will be OK. It's just that have not used the gap-filler glues before. Have had no real need for them. Have used some epoxy to repair small voids, but not as a joint-glue. Have not needed to do so.

   Thanks a lot to all.

   -mbl-

   Edited 4/30/2004 1:51 am ET by mbl

6. 
   Tao | Apr 30, 2004 06:42pm | #10

   Upon further reflection:

   A single saw kerf and NO glue might do the job if both halves are restrained by dados.  The kerf is wide enough to allow the bend you want withiout splintering.  a triangular glue block to line the inside of the joint would give good reinforcement and a finished appearence.

   Epoxy would be the glue of choice in the joint.  UF (plastic resin) glue would probably work, but harder to use.

   Gorilla glue foams and loses most of its strength in gaps.

   Titebond would work fine on glue blocks.

   You could modify the knives on one of those table saw molder heads to give the cut you want, but I'd still worry about splintering on a sharp bend, as opposed to a saw kerf.

   If it were me, I'd still cut and tape.  If I had a lot of pieces to do, I'd make a fixture to hold the pieces as the glue set.  I would preassemble the panels, before doing the overall assembly.

   Kerf and bend as Eddie recommends would be a viable second choice, but I'd seriously consider not using any glue in the kerf, and applying a fitted glue block the length of the joint for reinforcement and a nice finished look.

   Good luck.

   Michael R