Thread: 10 years ago
1st Aug 2019, 10:00 AM #16
Wongo, I can't remember if it was in that thread or another that I related my story of demonstrating glue-strength to the members of a woodies club. I prepared several examples of side to side & straight end-to end joints from the same wood using 4 different glues, and let them cure thoroughly. So I fronted up on the night & proceeded to demonstrate the relative strengths by ripping them apart. The side to side joints all failed under similar (extreme) loads with 80% plus wood failure. The end-to end joints were easy, just a sharp rap on the bench & they popped apart cleanly. That is, until I came to the epoxy example. I picked it up saying "and even epoxy won't work in this situation...." as I whacked it on the bench. The joint remained intact. I gave it as hard a whack as I could - still nothing! The other blokes reckoned the look on my face was worth a year's subscription & were still chuckling about it years later. I put it in a vise & whacked it with a mallet and it gave up & broke - very cleanly across the glue-line.
So in some situations, with some woods, it seems you can indeed get a pretty strong end to end joint with epoxy glues. In a non load-bearing situation an epoxy joint may be as durable as needed, but my lifetime's experience has been that just about any glue fails, eventually, so any joint relying on glue alone, whatever the glue, is probably not a good idea & better avoided if possible.
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1st Aug 2019, 10:30 AM #17
Thanks for the story Ian and I agree with you entirely.
1st Aug 2019, 12:15 PM #18GOLD MEMBER
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- Jun 2005
When are you going to test it, thousands are waiting to see what happens.
1st Aug 2019, 12:28 PM #19
In the next day or 2 I promise
1st Aug 2019, 01:08 PM #20SENIOR MEMBER
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- May 2013
- Auckland, New Zealand
10 years ago this month I started my solo bicycle tour from Beijing to Istanbul via the Stans and Iran!
photo taken at Bukhara, Uzbekistan. near Turkmenistan
just a little more interesting than some glue/timber joint lolMachines: Masterwood OMB1V, SCM 5 RCS1100, Danfoss VT2882, Griggio Unica 400, Felder AD951, Casadei FV110, Holytek DC006, SICAR Top6, Chicago Pneumatics CPRS10500, Ceccato CDX12
Power tools: Festool DF700, DF500, HK55, CT36, LEX 3, OF1010, OF2200, VAC SYS, Starmix 1635
1st Aug 2019, 02:34 PM #21
Tin ears already!!
1st Aug 2019, 06:42 PM #22GOLD MEMBER
- Join Date
- Aug 2016
10 years ago my shed was mostly just used to store junk. Half of it belonging to other people.
Now it's completely different.
Now I can hardly squeeze myself in there. ... oh wait.My YouTube channel: https://youtu.be/2_KPRN6I9SE
2nd Aug 2019, 10:48 PM #23
I glued a piece of wood 35cm long on either side. Placed a 9kg weight in the middle.
Next I put a piece of Spotted gum (160cm X 20cm X 5 cm). It is probably 25 to 30 kg.
Finally I tried to stand on it. It broke with just one foot on it and it broke easily.
Once again I am not trying to prove that it is a strong joint because it is not. In fact it is very weak which we all know. What I am proving is without any load it won't just fall apart, not after 10 years anyway.
3rd Aug 2019, 11:20 AM #24
I'm reviewing my opinion of modern glues. In 2004 I made a pair of stools from Tas. myrtle. The glue used was supposedly good quality PVA. One of these stools is used every day; the other, less often.
Kitchen stools - Tasmanian myrtle 1.jpg
Recently I noticed that the back supports, rear legs and the front-to rear stretcher have become loose. When I say loose, I mean the joints move slightly: the glue has failed, but I cannot pull them apart.
The back supports to legs joints are finger joints which were a gentle fit to each other and to the seat. They have plenty of edge-to-edge surface area and no large gaps. The stretcher joint is a short double tenon - not as much surface area, but it should not have as much load, either.
I can't think of any obvious reason for the glue to fail. It wasn't old, and the temperature was > 20C. Although there is more load on the back supports, the joint should have been strong enough.
3rd Aug 2019, 06:12 PM #25
Coupla quick points Alex: 1), as I said above, you should build expecting all glues will eventually fail, and with chairs it tends to be sooner rather than later, given the sorts of stresses they are commonly put under.
2). PVA glues are not good choices for chairs, they tend to remain at least slightly plastic, and moreso at high ambient temperatures, so creep & letting-go are always on the cards.
3). When I use 'stretchers' on chairs, they are used for stretching, i.e., pushing the legs apart, and really don't need glueing. It often takes a lot of effort & some very carefully-planned assembly steps to get the chair together (& even more to get it apart if something goes wrong!), & if I do use glue on these joints, it's more for lubricating the bits so they slide together more easily..
3rd Aug 2019, 10:27 PM #26
9th Aug 2019, 08:20 PM #27Novice
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- Aug 2019
- Palmerston North
I admit it’s a little more interesting than Auckland / North Harbour derbies, but it’s much more interesting .to you than are glue joints, to me.
Ten years on a bike - where did you get? See, kinda interested, but data on wood joints will hold my attention longer.
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