tinkerman wrote:Hey all, when "Streatching'' plywood another good router method is to use along mortice and tenon joint or a deep tounge and groove.
WIth a double fluted bit cut a rabet on both sides of one end of a sheet on the other a slot cutter bit is used doing t or more passes to make the tongue fit. PL the snot out of the joint and pipe clamp till the glue cures.
Want a smooth joint, wipe away all excess PL using a putty knife. if your joint is visible and you want it to look seamless use bondo as afantastic filler. It is sandable and paintable.
this can also be done with just the one slot cutting bit if that's all you have. you have to cut the slot first on one piece then adjust the cutter to rebate the second piece from both faces leaving a tongue.
it's best to get the bit as close to centred on your stock as you can and run the slot twice, once from each face of the first piece. this will guarantee a centred slot.
then rebate the second piece from both faces starting with the bit set to cut the rebate a little shallower than you need. then with a couple of more adjustments and passes you can creep up to the perfect fit..
perfect fit does not mean tight fit...
as with all interlocking joints you have to have enough slop to allow you to apply the adhesive and bring the joint together without splitting the slotted half. this fit will depend on the type of adhesive you use. remember it's the adhesive that gives the joint it's strength not the interlock. that is for reenforcement and alignment.
a good rule of thumb is to be able to fold a piece of writing paper or a dollar bill over the tongue and still be able to insert in in the slot.