Jointing reclaimed timber boards - best method?

[NightShadow1991]

Evening all. Quick question. I use reclaimed 9x2 joists, dry stored, plane them up on all sides to 220mm X 40mm or so and they make excellent table tops. I prefer using kiln dried oak, but some customers prefer reclaimed. I always biscuit joint and use spacers on my metalwork to aid any expansion or shrinkage, but on the whole they're pretty dry with 10-14% moisture content. However, I'm thinking of also using worktop connector bolts as well as biscuits, which is what you'd normally do I guess, but I've never bothered. I wanted to to ask, when it comes to biscuit jointing, are strips of ply better than individual biscuits? I just use my Axminster biscuit cutter and do two levels of biscuits - often very time consuming - and go from there. However, I have a router bit for full length rips, I guess these are better as they're the whole length of the boards? However, does standard ply work as well as beech biscuits? I think they're beech? Just trying to work out what timber expands and forms a better 'grip'. Also, if ply, hardwood ply or softwood? I guess softwood is more prone to expansion so better? I'd be inclined to do two strips of 6mm ply if so - as the router bit is doubled and the boards are 40mm thick, so will form a stronger bind, then maybe some connector bolts as well, 3 connectors, 4 board top, so 9 bolts. Probably overkill. Just wanted to ensure no issues with shrinkage down the line. Only really had issues with scaffolds before as they're hemlock and warp and twist like nothing I've ever seen. These methods twinned with my metal frames with expansion slots milled out should work a treat. People have such hot homes these days, just want to ensure minimal movement where possible. I'm not a carpenter/joiner by trade, a welder, so excuse any lack of knowledge above.

Thanks all!

 

[Doug71]

In theory you should be able to rely on just the glue, a few biscuits will help keep things aligned during the glue up but at 40mm thick you have a good area for glue so nothing else should be needed to add strength.

As long as the top is floating so it can shrink or expand as needed the whole top can move as one so there should be no problems

 

[Inspector]

If you are making clean light tight joints when you put the pieces together you only need glue. Biscuits, splines (plywood) etc do not add strength to long grain to long grain joints. They only aid in alignment. Biscuits are great for joining mitres or replacing dado, housings I think you guys call them, when making cabinets or other end to long grain joints. With wood you can't force it to not move. You need to allow for the movement as it takes on/looses moisture in the same way you need to allow metal to move with thermal expansion/contraction. You are trying to do the equivalent of riveting, bolting and welding two pieces together.
Doug just beat me to it but I'll still throw my 2 bits worth in.

Pete

 

[Cabinetman]

Exactly what they said!

 

[NightShadow1991]

Thanks all. Stupidly I never really thought of it that way. I mean biscuits always help line up the boards to keep the top flush, but always thought they were doing most the work, more so the glue I guess. Thanks all.

 

[pils]

Forgive my naivety* but are there any visual samples you'd care to point to that show (somehow) shrinkage/expansion and how one deals with it in various circumstances. I'm highly interested and way, way, out of my depth.

I'd happily embarrass myself (further) by making this a full post if required.

*I'm being unusually polite to myself. The more I read the posts/comments on this site the more I realise I know nothing and am, at times, dumbfounded by the complexity of working with wood.

 

[recipio]

Thanks all. Stupidly I never really thought of it that way. I mean biscuits always help line up the boards to keep the top flush, but always thought they were doing most the work, more so the glue I guess. Thanks all.

Exactly. Biscuits have only one function in edge joining, they align the boards when cramping up and prevent slippage. However always use the fence of the joiner rather than the base. If there is a slight bow in the wood, using the base will throw the biscuits out of alignment. Getting a clean join at right angles to the face calls for good technique. I use my table saw with a good blade which I think is easier than edge planing.

 

[Doug71]

Forgive my naivety* but are there any visual samples you'd care to point to that show (somehow) shrinkage/expansion and how one deals with it in various circumstances. I'm highly interested and way, way, out of my depth.

I'd happily embarrass myself (further) by making this a full post if required.

*I'm being unusually polite to myself. The more I read the posts/comments on this site the more I realise I know nothing and am, at times, dumbfounded by the complexity of working with wood.

Not a great photo but this is the underside of a large rustic table I made for a friend (the top is in two halves, you can just see the worktop connector bolt cut out in the shadow where the two halves will join). You can see the holes for the screws are slotted so the top can expand or shrink. If you don't allow for movement the top would probably bend as it expanded if it took on moisture or crack if it dries out and shrinks. The slots allow the top to "float" so hopefully there will be no problems.

 

[Droogs]

To the OP, do a search for the thread by "Custard" of this parish on how to edge joint. it is clear and concise with pictures and is written by one of the most experienced, qualified and talented woodworkers I know of. He is an ex Barnsley workshop apprentice, you may not be aware of this workshops standing in the world of furniture but it is held in the highest regard by the master craftsmen the world over.

 

[Jacob]

Yes to all the above.
There is an interesting technique of inserting a loose tenon between two boards and draw boring to pull them together. More for industrial environments perhaps but mouseman Thompson uses it on some of his table tops. Hasn't worked too well in this example but it's not been done well either.
Better to have both dowels close to the join line or 3 dowels on each side in a shallow triangle close to the line. Little repeat patterns of 6 dowels
Glue to join the boards but no glue in the mortice and tenon.

 

[Lazurus]

How To Edge Joint | UKworkshop.co.uk

 

[pils]

Not a great photo but this is the underside of a large rustic table I made for a friend (the top is in two halves, you can just see the worktop connector bolt cut out in the shadow where the two halves will join). You can see the holes for the screws are slotted so the top can expand or shrink. If you don't allow for movement the top would probably bend as it expanded if it took on moisture or crack if it dries out and shrinks. The slots allow the top to "float" so hopefully there will be no problems.

View attachment 121585

Really. I didn't know.

 

[Nelly111s]

I use ply to aid alignment when making solid (olive) wood worktops and bar tops. A 6mm strip of marine ply fits perfectly in a 6mm routed groove (on 25mm thick boards in my case). If you're gluing up over a long length they make things easier. I use marine ply because "normal" play is about 5.2/5.3mm thick and marine is 6.0mm you can glue them in place, or not. I do, but I doubt it adds much.