Motor Club of America Online: ZCI Inserts #1: MDF and Garolite

https://lh3.googleusercontent.com/xVXoAzLaTQk4hOjkAdN1jvRZ9koQltA1TSNyIYBUp94=w168-h222-p-no

Thought I’d post a few pics of the latest incarnation of ZCI that I made for my Craftsman 113 series table saw. These saws are a little frustrating for someone looking to make his own ZCIs, since it is necessary to rabbet a very thin lip (3/32”) around the outside of the insert for it to rest flush against the table. This is in contrast to most saws nowadays, which use inserts that are simply like extrusions of a basic 2-D shape, easily duplicated with a straight router bit and guide bearing.

I at first tried using plywood for the insert, but I did not have a piece whose flatness could rival that of the steel table of the saw. Perhaps if I’d gotten some baltic birch I would have had an easier time of it.

I then considered making the whole thing out of MDF, but the thought of having such a thin lip made only out of MDF worried me for structural reasons.

Eventually I bought some garolite (phenolic) and used that as the top part to form the thin lip, while using the MDF for the underside of the insert to provide stiffness. I tried gluing and screwing, but it turns out that glue alone (3M spray adhesive) is plenty strong enough to hold the materials together.

I used epoxy underneath to form “shims” in place that would keep the garolite level with the table saw surface.

These inserts worked very well, until the humidity changed and the MDF shrank a bit, causing the insert to bow upwards in the middle. It was enough that I could feel a bit of rocking while cutting small pieces on the saw, since small pieces are mostly registered against the insert and not the table.

The other issue I ran into is that when the insert flexed a bit, it introduced a tiny bit of mismatch between the insert and the table at the ends, so that workpieces (especially small ones) would catch a bit as they transitioned on or off. This did not feel safe like a safe condition.

My next plan is to try making some one-piece versions out of 1/2” thick, UHMW polyethylene. I will post to let everyone know how it goes.