Woodchick
26th April 2004, 04:47 PM
I am making a dining table. The top is a NSW rosewood slab with a 100 mm Victorian Ash border (total size 2300mm by 1000 mm) The legs are a pedestal type assembly with a piece of Tassie Oak 40 mm thick along either side. I need advice on the type of screws to use to attach up through the Tassie Oak into the bottom of the slab. I've been told that in order to allow for expansion of the table top across the grain there should be either slots or over size channels in the lower pieces. Can anyone offer suggestions?
leighd
26th April 2004, 05:03 PM
i dont really understand what u mean by the slots or channels? are u making a slot for the pedestal to fit in the screw it? if u are maybe u can use coach screws with a washer and contersink it about 20mm
echnidna
26th April 2004, 05:11 PM
There are a few different ways to fix the base to the table top so I expect you will get a number of replies to your post.
Probably the easiest way is the slots.
Put one screw in the middle of each under rail, it shouldnt be slotted as it will then keep the legs centred to the top.
Mark out the location of the other screwholes and drill extra holes that you then make into slots. This lets the top expand and contract due the atmospheric moisture variations.
I usually allow 4mm each side of each screw per each 300mm width of of the top.
The slots can be bevelled along the inside to suit the shape of the screw head so that countersunk screw heads wont be visible.
Woodchick
26th April 2004, 05:43 PM
Thanks foe your reply, Bob.
Perhaps describing the legs as pedestal was a bit misleading. I have attached a picture of them (upside down). As you can see, the Tassie Oak rails run along the length of the table. Should I still do one on each side without a slot, or will that not allow any expansion at that point?
Bob Willson
26th April 2004, 06:34 PM
Timber expands across its width far more than along the grain, so make sure that the slots are correctly oriented.
The long rails should not have a fixed point but the end rails should each have one in the middle.
echnidna
26th April 2004, 07:03 PM
For all practical purposes timber doesnt expand or contract length ways but it does move across its width (and thickness)
Your leg frames won't move but the top will.
So fixing the centre of each end of your leg frames locates the top.
On the outsides of your leg frames its necessary to have slots (at right angles to the table top grain) so the top width can vary.
Given the type of table you are building and that the tas oak is relatively thick you could use a alternative approach to slots.
Drill a shallow counterbore through your long tas oak members so a large automotive body washer will fit neatly in the hole. Then drill the centre of the hole in the tas oak out completely with a 3/4" (19mm) spade bit. The Screws then go through the washer and centre of the clearance hole that you have just made so the top will have room to expand and contract.
BTW Thats a very nice table - congratulations on a nice job.