butt gluing up oak planks together

Sean Farrell

I got 2 pieces of oak that i want to butt join together...i was thinking od biscuit joining them. But from my knowledge, if i use ordinary glue on the joinery the chemical reaction with the natural oils and resins of the oak will cause an unsightly black mark along the join.Is there a poly glue or epoxy glue that anyone can recommend that will do the job seemlessly?
Also what is the best way to glue and clamp up the two pieces together.i.e the positioning of the clamps ,where pressure is uniform by placing the clamp heads on opposite sides(see attached). And how do u prevent bowing or cupping...cause i noticed even thou i'm not putting too much pressure on the clamps that the piece when clamped together is not flat......maybe the sides of each oak piece is not square perhaps and need to be planed....ohhh for a planer/thicknesser!

Calahonda52

re the bowing, the cramps are the issue here in the main as even in pic 1 the back of some of the cramps are bowed due to the lever arm effect. They are just not strong enough and they are too deep, even if u put them flat on the work piece the rotational effect will be much reduced
This can also be helped by cramping from both sides and key an eye on the surface with a long try square or straight edge

recipio

Sean, its worth getting a nice 'invisible' glue line first. You will never force small hairline gaps together, tempting as it is.
Looks like you didn't get the planer going yet ? You can get a good edge straight off the table saw if you have a good blade and the saw is running true.
Best to alternate the growth rings one up , one down to minimize wood movement. I would use Titebond glue which dries a golden yellow colour or plain white PVA which dries to a translucent colour. They will not stain the oak unless you let them ooze all over the clamps which can cause black staining due to the tannic acid in oak. Use plastic tape on the clamp. ( Other glues like Epoxy are far too thick ) Trying to keep the surfaces level with each other is tricky. You can use a biscuit or two in the middle using the fence of the joiner. I prefer to clamp them flat but I have long reach clamps. Try and get some scrap polyethylene ( plastic ) off ebay as you can use them under the clamps and they won't stick to the glue that will ooze out.

cheers.

Sean Farrell

"Trying to keep the surfaces level with each other is tricky. You can use a biscuit or two in the middle using the fence of the joiner."
well i know u were expecting this reply from me ....at least i have a use for the Scheppach. .....thanks for the advice.

recipio

Sean Farrell wrote: »

"Trying to keep the surfaces level with each other is tricky. You can use a biscuit or two in the middle using the fence of the joiner."
well i know u were expecting this reply from me ....at least i have a use for the Scheppach. .....thanks for the advice.

I mean the fence of the biscuit joiner !! If you use the base of the biscuit joiner as a reference you will be inaccurate as the board always has a very slight curvature. Even a mm out in the level will feel like a step to the fingertips.

Sean Farrell

Well it took a while to return to this thread...my apologies. So i got a nice piece of beech that i wanted to butt join. So here is my set up. I made some cauls to keep everything even. My clamping set up is ok I think....i dont need to tighten them up too much. This is a dry run...I am going to use ordinary wood glue for the beech. The cauls are not concave or convex....I forgot what is the best shape for the caul to work best ...any ideas anyone.

woodturner

You will only get the black staining where a metal clamp touches the glue and oak.

Calahonda52

the three cramps in this position will tend to cause a bow upward due to the offset/law of lever/etc.
Do u have a fourth cramp?
At least switch the middle one to on top

Sean Farrell

At least switch the middle one to on top.

Thanks for the advice but I'm a little confused on that one Calahonda. what do u mean switch the middle to on top?......i cant get a mental image of that.

Calahonda52

u have 3 cramps all with the bar on the bottom which means when u tighten up the fact that the force is offset from the Centre of the board it means there is a tendency for the boards to bend up in the middle as the bar on the cramps, while strong, will bow down a bit at each end.

So by putting the middle cramp with the bar on top, u have two bending up and one bending down

if u had four the same then two and two

recipio

Sean Farrell wrote: »

Thanks for the advice but I'm a little confused on that one Calahonda. what do u mean switch the middle to on top?......i cant get a mental image of that.

Nice bit of spalted beech Sean.
He means turning the middle sash clamp upside down so the bar runs across the top - it will counteract the tendency of the other two clamps to force a concave shape to the boards.
Traditionally the cauls should be convex pointing down but I don't think you will get enough pressure on them with butterfly nuts. You could try regular bolts and nuts or invest in some long reach clamps to reach the centre.
Put some plastic tape on the cauls or they will stick to the squeezout and the same for the sash clamps where they cross the joint line.
With a bit of practice you will find it easy to align the boards and just give them a gentle 'nip up' .If you have to squeeze the daylights out of the clamps you have probably not machined the board edges well enough.

Sean Farrell

i got the beech from Woodworkers and Hobbies in Harolds Cross. Nice guys. They machined a 9ft rough plank down to 15mm par at a good price...25 euro in fact. Thanks for the tips and advice...sorry for the confusion earlier...the photos i put up earlier did'nt show very clearly .there were 4 clamps in all. thats what got me confused. Anyways, i changed the clamping setup so that they are inverted ie one clamp under then another over to avoid the bowing. I also got some packing tape to put on the caul faces to avoid glue sticking. so now after so many dry runs i can actually start gluing up for real...!Thanks for the advice again.

recipio

That ought to do it. I see you have found PVA glue that is a lot cheaper than Evo- Stick !

Sean Farrell

Yea ..i'm trying to remember where i got the cheapo glue either McQuillans or Woodwork and Hobbies...cant come to mind atm. I saw this article ,see attached , about cauls so i went the whole hog I'm now in the process of varnishing my cauls! I'll wax them next...then i will do what recipio suggested with the tape over the face sides. I dont know about epoxy the coach bolts...seems unnecessary tp me...it was on the shopping list...but i have it for future use. Recipio , u got me worried now....i'm fretting over using the cheapo glue , it might not be up to scratch,and it might ruin the job after getting this far with the project. Also I'm going to pm u recipio if thats ok.

recipio

The glue is fine. I buy German made stuff which is about 1/3 rd the price of Evo -Stick