Cabinet top-grain

[Yian]

Hello boys
Could I please ask for some help ? I need to glue two pieces of dressed Tazy Oak 30ml thick ,each 240ml wide, and 2.4meters long. Both are very slightly "bowed " looking from the ends. Q . Do I domino / glue them so that from ends they look (exaggerated) like a " uu" or like a wave " un" ? All faces look pretty good. I gather there is a wood movement issue here.

Thanks so much
Yian (new boy)

[artme]

G'day Yian and welcome to the cubby!!

Usual mehod is to glue with the end grain facing in opposite directions - in your case that will make a "wave".
You will then have to run the board through a belt sander or thicknesser to flatten the resulting single sheet. Of course you will lose some of the 30mm. thickness.

Best joined with biscuits or domino and glue.

[Yian]

Thanks ARTME . Will check. Yian

[munruben]

I agree with Arthur (artme) Biscuits make for a good join.

[derekcohen]

If you are able, joint the boards flat and thickness before glueing them together. That way you will avoid any conflicting stresses in the joined boards.

Further, all you need is glue - domino or dowels or biscuits are quite unnecessary when creating a table top. No extra strength is needed and, in fact, they can make it more difficult to align.

Edit to add: make sure that your grain runs in the same direction. Whether you handplane to finish or later use a thicknesser to flatten the joined boards, opposing grain will cause you trouble (tearout). If the "bow" that you speak of is just a board bent under its own weight, then joint the edges as is and glue, then finish. If the "bow" reflects cupped boards, flatten and thickness first before glueing.

Regards from Perth

Derek

[rod1949]

Yian,

Never under estimate what timber will do, if it wants to move (and is usually after) it will. If you can clamp the boards together without any undue stress then by all means proceed that way.

The barest minimum you should be trying to achive is that the two edges of the joint are as straight as possible and when placed together (without any pressure) should be touching without any gaps thus ensuring a perfect joint.

In most cases a glued joint will not break on the glue line, it usually breaks out the timber either side of the glue.

The use of dowells/biscuts etc do and will strenghten the glued joint by providing a greater gluing surface area. If set out and cut correctly dowells/biscuts etc will greatly assist in the alignment of the boards when gluing up.

After the glue joint has dried it is then you proceed to thickness to the desired thickness.

[Yian]

Thank you to each of you. I'm now on it. Rather than clean up the faces with a plane.,as usual, I'm making use (carefully) of my rather new router. Another little gem , I picked up from the yard, is to clamp both sides to prevent bowing . Pretty obvious eh ? Yian

[old pete]

Hi Yian,

Rod 1949 has got it correct IMO. I assume the distortion you describe is in the straightness of the boards along the edges and that the boards are still flat along their length and also flat across their wide face.

240mm x 30 mm Tassie hardwood is a very big set of boards to force straight if there is any level of bow beyond say 1 to 2 mm total in terms of the stress you will inevitably build into the joint in the process. I would go for re-straightening the boards on the buzzer followed by a single shaving off the joining edges with a No.7. That's how I do things and I don't seem to have any problems with edge joining. It's not reasonable IMO to expect to buy timber straight and square enough on the edges to go straight to edge joining.

If you have boards that are bowed, sprung and perhaps no longer flat across their wide faces you nave a serious moisture content problem or a moisture content gradient problem or built in drying stresses. You couldn't hope to get a good outcome for a high grade application like a table top from material like that. Send it back!!

I won't enter the debate about whether you need biscuits or dominos to assist the joining process. I use dominoes with one set back 50 mm from the finished ends and the intermediates at about 200 to 250 mm intervals. If you use straight and flat stock to start with and cut the domino mortices with care you can start sanding the panel with 150 grit. I'm pretty sure I can't do that with edge joining without any means of accurate registration but then it's many years since I last did that. I guess we all do what works for us and I respect that in others

Old Pete

[rod1949]

Yian, you mention your new router. Did you know that you can straighten the edges of the timber using the router thus making the near perfect joint?

[Christos]

Welcome to the forum.

[jredburn]

Yian
You cannot build good furniture with boards that are cupped, twisted, curved, warped or anything other that straight and square. Been there, done that.
Run the rough stock through a shaper (or joiner as I know them) to flatten one side. Cut the rough stock to length plus a little bit first. Then put the board on the joiner so the edges touch and the middle is raised. Run it through until this side is flat, turn 90 degrees and cut the edge flat. Put it on the table saw and cut the raw edge. Run it through the planer until the top is flat. You must do to the opposite side what you do to the first side or it will twist and you will have wasted time and material.
Once you have the stock ready, glue it up, clamp it and weight it down.
Biscuits are used primarely for alignment and positioning. Proper gluing will give you a stronger joint than the wood so additional strength is wasted.
An old cabinet maker.
Regards
Joe