How to cut regular rabets on a table saw

The problem was that I'd little experience with cross cutting on the table saw. The theory is fine, but I learn by doing. After about 40 cuts I eventually arrived at what I consider a safe and effective way of achieving an accurate castellation.

The starting point is the sketch of how they should look. Fully dimensioned, worked out on paper. Each cut as it will appear on the finished piece.

Each end (of course it's supported isn't it? No pocket relying on the side for support? OK. Check the sum of the dimensions. I pick an arbitrary point in the middle and calculate it from both ends. If the sums don't work, start again. First check done.

Next, review how that sketch will transfer to the wood. Two points to bear in mind. Firstly will the marks, when transferred to the wood, be on the edge facing the saw blade ? They should be. Next, is the wood the 'correct' (read appropriate) side down, towards the table? That's the side which the saw will take the cut from, so it wants to be the right one. I'd cut a whole set of six rabets in oak when I realised I was 90 degrees out. Drat, or some such expression. Next (OK, 3), is there sufficient timber to one side of the area being cut for you to hold against the mitre fence? Sure? Your fingers are worth more than the wood. Honest. I'm in favour of exceeding this by a couple of inches for safety. Even better, run two sets of rabets from the same piece of timber, then you can use one piece as the support for the other, then simply saw each to length after the rabets are cut. Finally, just check that you've left enough scrap each end, yes each end, for your needs. Easy to cut it off, less easy to glue it back on!

Now draw it up to scale, or mark lengths on your rough sketch (see the figure above, the dimensions are enough to draw the rod below it). Either way, you need enough lengths shown to be able to draw up a full scale 'rod' (on paper, not timber) from your sketch.

Next, draw down from the sketch if it is to scale, or start to measure if not, picking one side of the cut out as a reference. When you cut against the right hand side of a rebate of the castellation the mark needs to be against the right side of the blade, and vice versa. This establishes a baseline and removes error options later. I chose the right hand side, implying that my reference was the right hand side of the blade, its extremity in that direction, when cutting, not when still if your blade doesn't run true. What I mean is, drop a line down from your chosen side of the saw cut, to some point on the paper which will be the line that you use to transfer to the wood. Choose a reference end of the wood from which to start. Again I picked the right hand side. Mark a zero reference and ensure you know where it is relative to that end of the finished piece. Draw a horizontal line from that, long enough to stretch to the other end (i.e. make sure your paper is long enough. I drew my 'rod' directly beneath the sketch, so I could relate on to the other. Beware, the rod looks nothing like the sketch!) Now continue dropping lines down at each point a reference saw cut is required, i.e. one at each end of the cut-out. Yes, you'll need to nibble bits out in between, but the crucial ones are the two end cuts. Now the clever bit. Not really, just that once you've made the mistake of forgetting the kerf width, it seems clever, or we're stupid for not thinking of it. As I said, this is the clever bit. Taking my example of the right hand side of the blade as the reference. The right hand side of the rebate will be directly below that point on the sketch, yes? The left hand end of the rebate will be the width of the kerf less than that from the required width of the rebate. Example. I was cutting a 14mm rebate. My saw blade leaves a kerf 3mm wide. So from the right hand side, I needed to move over 11mm to find the next alignment point for the right hand edge of the blade... since the blade width takes up the remaining 3mm. See? clever isn't it! No, I know, just account for it then. Continue like this until you have dropped marks down from each cut point from one end to the middle. Now start at the other end and mark the other half out. The two halves should produce evenly marked points along the accurately marked rod. These are measured, not guessed or sketched. If they don't, check them. If they do, it's probably worth checking them anyway unless you have plenty of spare timber.

Now, lightly, pencil in, on the rod, the actual rebates that will be removed from the timber. This makes it easy... easier, when it comes to nibbling out the parts between the reference cuts. Next...

Tape the paper 'rod' on top of your actual timber. Checks are that the timber, when faced to the saw blade, presents the right face. That the cuts, when made, are in the right face of the timber and that the reference end is towards the right.. or was it left.. that you decided minutes ago. Now go back and check them again (yes, I got this one wrong too).

Next, go borrow a sharp point. My sons compass was ideal. Holding the paper steady, prick through onto the wood at each reference mark (the right hand side of the saw blade remember?) Before removing the paper, lift one end and make sure the pin pricks are visible. I needed a magnifying glass and good light. Get a (small) square, and mark down to the edge which will slide along the saw table. Make it square and not too thick if you're dealing in small dimensions. Again copy over the 'cut this piece out' marks so that you dont nibble out what should be raised! I just hatched them roughly (see the photo above), avoiding the reference marks. Now we can approach the table saw, remembering all the safety hints you've been told and read in the manual. If you're feeling blasé, think of Jeff, he's two fingers missing from the middle joint through playing with a table saw whilst not thinking safety first? I never forget his example. I'm assuming by now you've run a cross cut in scrap to find out the kerf width. Power to the saw off, set a straight edge along the blade and mark a point on the table (on top of masking tape if you don't want to mark the table) which is well clear of the blade and in line with the reference edge (rhs in my case). . This is used to align the wood prior to sliding the mitre (and wood) up to the blade. It needs to be well clear of the spinning blade, yet visible such that the wood can be slid along the mitre and aligned with the transferred markes from the rod.

Now cut the reference marks. Since we know they are aligned to the rhs of the blade, from which mark on the table is taken, each cut is repetitive. Align with the mark, hold firmly against the mitre slide and run it up to the blade. When all the cuts are done, start again and nibble out the hatched area between the reference cuts. If you are unsure, stop the saw, go back to your sketch, the extended 'rod' marks and the marks on the wood to check.

That's it. Easy isn't it!