Work(shop) in Progress #3: Bosch 4100 TS - Zero-Clearance Inserts

I got a few questions about the zero-clearance inserts I made for my bosch table saw, so I figured I’d post the procedure here as to how I made those.

The basic Idea is to take the factory inserts and use that as a template for the router. but alas, the factory insert is just too thin at some points to be able to follow it with a trim router bit, so to tackle this issue I made an initial template out of 1/2” plywood. This first template took a bit more patience and care so that it matches the original shape perfectly. Once I got this 1/2” ply template I am set for as long as I need to make inserts as I can always use that template easily with a trim-bit.

Notice how the bottom face of the template has a groove in to allow the blade to fit in – this is merely done so that I could push the template in and check for precise sizing (the blade was slightly in the way):

Next I ripped some 1/2” MDF (I am not a big fan of working with MDF – health wise, but I do have some, and will rarely use it for jigs) to closely match the width of the ply-pattern, and cut it to length.

If you want, you can use a jigsaw and cut the MDF square to the insert size as close as you can to relieve the extra work from the router (next step).

I glued the ply-pattern on top of the MDF block, and with a trim-bit in my router table shaped the MDF to the exact insert size and shape.

Next, I used a straight-cut bit and trimmed the bottom face of the insert by 1/8” – this may vary depending on your saw,and your insert material (the saw lip – where the insert is being held – is 3/8” deep, and I was using 1/2” material). I found that raising the bit up, and holding the insert upright against the fence and protruding the bit 1/8” from the fence gave me cleaner more controlled cut (and also enabled me a deeper cut) as opposed to laying the insert flat on the table and having the bit extend 1/8” above the table.

Last step I cut a 3/4” hole in the front right side (away from the blade) to use as a finger hole to be able to pull the insert up and out of the saw (I drilled mine at a slight angle, but a straight hole would do just fine). I then placed the insert into the saw. moved the fence over the right side of the insert and locked it down. took a long board, and placed it over the left side of the insert (to the left of where the blade is) and clamped it down on both edges of the table. This will hold the insert in place. I then started the saw,and slowly raised the blade up through the insert. and Voila! – Zero-clearance inserts at almost $0 cost.

I made 3 at the same time – might as well. and labeled the bottom of the insert with the ANGLE and BLADE MODEL so that I’ll know to which setting it was made for.

hope this helps…

-- When in doubt - There is no doubt - Go the safer route.