07-23-2010 07:05 PM
I have been working on the Celtic Knot project from the last issue of Wood Magazine. I put the laminated veneer for the Celtic Knot in a 36" long piece of cherry to be tuned for a walking cane. I used Titebond III wood glue to glue the laminated veneer pieces into the 45 degree kerf cuts. I cut one kerf each day and clamped and glued the laminated veneer and let it cure. As I was turning the piece, the knot was coming out perfect but as I neared completion the glue joint failed. There was no adhesion between the veneer and the cherry. The veneer has a face grain and the 45 degree cut in the cherry is almost like an end grain cut which makes a poor bonding surface. The article suggested using 5 minute epoxy but I thought that was just to speed up the gluing process. My question is -- would the epoxy work better( stronger joint) or any other glue work better. Or any other suggestions?
07-23-2010 07:29 PM
Epoxy would be stronger for sure but not as strong as you think. You could also make it stronger by wetting the joint with diluted yellow glue. Let it sit for a minute or so and then rewet with full strength yellow glue and put the parts together and let them dry.
I think your asking a lot to do this on a walking stick. Even with epoxy an end grain glue joint is surprisingly weak. The reasons the pens hold up is the brass insert put in them before they are turned. You might think about making a short segment with the celtic knot. Then drill out the middle and insert a metal rod that sticks out about an inch on each side. Drill the walking stick top and bottom and use epoxy to glue the 3 sections together. Then turn the whole thing. The metal will strengthen the joint. You could even put a piece of veneer between this joint to dress it up.
07-24-2010 06:32 AM
Another thing to consider is that regular glue does not have any strength if the joint is not tight. If there are gaps, the glue won't fill it. In other woodworking glue is applied then the joint is clamped. With the Celtic knot the only clamping is how tight the insert fits into the kerf. If it is not tight the glue will not fill the gap and will fail.
Epoxy is the choice in a application like this. Not for speed of glue up but for gap filling. You want the insert to fit as tight as possible and the epoxy will do the rest.
I agree also that the end grain to face grain joint may not be strong enough for a cane. Pictures are required when you finish.
07-24-2010 08:50 AM
I agree with having a tight fit. That was a concern as when I would slide in the laminated veneer it would seem to scrape the glue off. I didn't want it too tight or too loose. It would seem that I have some trial and error left to do. I am actually trying to make the walking stick for display of the Celtic Knot and not actually using it but I need to make it as strong as possible. Thanks for your assistance.
07-24-2010 04:27 PM
Just an after thought on my part, but are you using older glue by chance? There is a shelf life to most all wood glues. There is also an expiration date, but you have to break the code depending on your glue brand. If not, forget what I said. LOL
07-24-2010 07:27 PM
It could be old glue. I've had problems with that, especially CA glue. The test I ran on end grain gluing was to glue 3/4" square by 5" long piece together. I tried all the glues I had. On the yellow and white glues I did an initial soaking with diluted glue followed by regular glue. This is because it tends to soak into the end grain.
To test them I clamped one end in a vice and then put a 5lb weight on the joint. I slid the weight out until the joint poped. Polyeurethane and CA glue were so weak I just barely move the weight before the joint broke. Yellow and white glues only slightly better by about 1/4 to 1/2". The epoxy didn't break until the weight was almost at the end of the 5" piece.
That told me 2 things. #1 if you need strength on end grain use epoxy. Possibly because it is gap filling andm may have filled the pores to make a stonger joint. #2 If you can get any long grain glueing by overlapping long grain joints over the end grain then you are better. That's part of why I recommend the metal.