This is how I make my ZCI for table saws. I like ½” MDF because it is stable (won’t warp or shrink). It usually will fit most contractor or cabinet table saws without any thickness planing. To view images, just click on them and use the “back” button on your browser to returm/ Sorry for the hassle.
First I trace the outline of the original insert on the MDF. (Just be sure not to trace it smaller than the insert! Don’t worry about being too precise. This will be taken care of with a trim router.)
Next, measure two finger holes to assist in installing and removing of insert.
Drill all holes. (I used a forstner bit, but you can use a spade hole bit or a regular drill bit.) Use jig saw or band saw to trim wood. Keep outside of lines, as the final trimming will be done with flush trimming bit in router.
Now, we stick carpet tape to the original insert and fasten the new ZCI insert to it, keeping the mounting holes and tabs aligned.
Use a flush-trim bit in router to trim insert to match original insert. You can see my outdoor project in background. Red picket fence.
Fine tune new ZCI to fit using file or rasp.
Install new ZCI on table saw and hold down with fence.
If your blade does not have enough clearance, like my Ridgid, then stick some carpet tape on original insert and stick new ZCI on top of that. Then install original insert with new ZCI on top.
Then crank blade up until it is fully up. This will cut a slot that is uniquely fitted to that blade.
I then write on back of insert the saw and brand of blade it is suited for. This blade is for my Ridgid with Oldham 40-tooth blade.
I hope this helps!
-- Saving barnwood from the scrapyards