Do I use a coarse or fine threaded screw to fasten an 3/4" oak table top?
Can I allow for expansion/contraction by making the hole in the fastening cleat larger than the screw, using a washer and leaving the screw somewhat loose ?
Thanks
Barry
I would believe that the accepted rule would be course threads for softwood and fine threads for hardwood.
Don't know if you're a purest but...I've been using pocket hole screws for this application for a few years with excellent results (no flames please, this works for me.) With a =BE" top, I'd use a #8 like
I would slightly oversize the hole by creating an oval shape that's parallel with the wood movement. I'd drill a properly sized pilot hole in the top, a washer (flat) and tighten the screw snug by hand.
It's good you're thinking about the wood movement.
Don't know if you're a purest but...I've been using pocket hole screws for this application for a few years with excellent results (no flames please, this works for me.) With a ¾" top, I'd use a #8 like
I would slightly oversize the hole by creating an oval shape that's parallel with the wood movement. I'd drill a properly sized pilot hole in the top, a washer (flat) and tighten the screw snug by hand.
It's good you're thinking about the wood movement.
Two things - oak is coarse-grained, and would be better, in my opinion, with coarse threads.
Second, I'd get stainless.
Usually 'fine' threaded screws are used in hardwoods.
Slightly slotting an oversize hole in the direction of movement on the the exit side is a time honored method.
Another convenient method, one that makes the top more secure when moving the table around by the top and still allows for wood movement, is a figure
8 fastener (often called a "desk top fastener"). There are also other mechanical fasteners that use a slot in the apron, as well as similar ones that can be made easily in the shop.
Barry:
I've put a sketch up on ABPW showing what I use to fasten tops of the kind I believe you are talking about.
These can be easily made and you can make enough for the whole top by sizing the wood, forming the rabbet, and drilling the holes - then ripping out the individual pieces.
The quarter inch tongue fits into a quarter inch groove in the rail and the single #8 or #10 Wood Screw allows the fastener to pivot with wood movement.
If you make the top of your rail groove just slightly lower than where the top of the tongue would hit if it was flat, you will get a nice tension on the top.
HTH
Regards,
Tom Watson
tjwatson1ATcomcastDOTnet (real email)
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