Help needed mitre joint 45mm thick spotted gum

Hi, just picked up some beautiful 240mm x 45mm pieces of spotted gum. Looking to build a coffee table 1200mm long x ~700mm wide x 350mm high. I am looking to join three boards together and cut a top and two sides to build a coffee table with waterfall sides, with the sides and top mitre joined together (Hope this makes sense, effectively an upside down U shape). What would be the best way to strengthen this joint sufficiently given weight of timber and likelihood of kids sitting on it! Would biscuits be sufficient here, or perhaps blind spline mitre joint? Or something else? Any help with this would be greatly appreciated for this forum newbie. Thanks!

Hi, given the fact that the timber is quite thick and the table quite low I would say either method would be strong enough.

You could use a double row of biscuits or splines if you want extra strength.
You are probably aware but the splines need to be cross grain or they add no strength to the joints.

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Originally Posted by mark david

Hi, given the fact that the timber is quite thick and the table quite low I would say either method would be strong enough.

You could use a double row of biscuits or splines if you want extra strength.
You are probably aware but the splines need to be cross grain or they add no strength to the joints.

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Hi Mark,

Thanks for the help, much appreciated. I wasn't aware of the need for cross grain, so will remember that for when I do one. Might go with double biscuits this time around. Cheers,

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Originally Posted by Sxkg

Hi, just picked up some beautiful 240mm x 45mm pieces of spotted gum.

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Sounds like you might have been at the timber auction at Woodend last weekend.

Hi , Yes Biscuits or the spline way are good for this .

But the main question is, how well its prepared with the cutting and jointing prep , and then how are you intending to clamp it together ?

Guys with fancy panel saws can make quick cutting of these sort of mitres , and they may even come up so clean that no planing is necessary possibly ? I don't have a panel saw, so I don't know .
At the other extreme a hand saw, a circular saw, or a table saw or radial arm saw and a razor sharp no 6 or 7 could do the same job . How are you doing this ?


The clamping is very important . I'd love to know your intentions on how your wanting to do this part.

Clamps running parallel to the top with other ones parallel with the sides doing one end at a time ( or two , even worse) and with the weight of the clamps having an effect as well , what a nightmare ! You can try it this way and give it a dry run but then when the glue is added it lubricates the joint and it does not react the same as it did in the test run. It works but is not much fun at all IMHO.

Clamping pleasure is obtained by gluing temporary clamping blocks that have surfaces parallel to the join and are set at 90 degrees off the middle of the join along the top and the leg of each end .
Are you thinking of doing it this way? Or how do you want to do it ?

You can chip them and plane them off later when finished. Use pine or a cheaper softer wood.
Your test runs will be simple and you can check for square and adjust by shaving, and when you re test the pressure angles are the same as the first dry test run. Setting up to clamp this way will make the job good fun . I get a kick out of doing it this way .

Rob

Personally, because I don't have a biscuit jointer, I would drill holes for dowels so that they are not seen then mitre the joints.

Insert the dowels, do a dry fit up and if everything aligns, do the glue up.

Auscab has given excellent advice. The only thing I'd add is that with spotty, clean both faces of the join with plenty of acetone immediately before gluing up. I've had a sad experience with it when I didn't clean it.

Make you construction method simple, a spline is the best method but stop it before the end. Unless the timber is below 12% the mitre will most probably move and maybe open. You should consider butt joins instead. If you decide to mitre the join, forget clamps use duct tape, yes duct tape. When you have mitred the joins layout the side-top-side (mitres down) and duct tape them together along their length. Turn over, insert spline and glue, lift up sides and use extra tape to hold together. This method only works if the join is spot on.
I was taught this method when I was at trade school and have used it ever since.

Good luck

+1 for the panel saw (we should all be so lucky)
+1 for the tape-and-fold method; I was shown that at work, but with many strips going across the join rather than one along it (you get more area being held that way)

Make sure you use polyurethane glue and NOT PVA. It's much stronger and PVA doesn't like waxy timbers like spotted gum. Don't know about the acetone wipe; I keep hearing it, but we've never done it at work and we've never had a polyurethane join come apart.

Thanks for all the advice from everyone, this forum is awesome.

So basically going to go with a combo of advice. I have used tape in my glue ups before but not for something this big, so am kind of interested to see how the duct tape will work, so will give it a try, with acetone prior to glue up and go with the polyurethane glue. Fingers crossed (or perhaps duct taped) should all go well!

Thanks again.