What is a zero clearance insert and why you should use one

Zero clearance table saw insert

When it comes to your table saw, accessories need to improve performance or increase safety. One add-on that does both is the zero-clearance insert.

It improves table saw cuts by reducing the nasty edges on some cuts. You will also decrease the potential for material jams or kickbacks. The following information provides you with all you need to know about zero-clearance table saw inserts, including how to make your own!

What Is A Zero Clearance Insert?

A zero-clearance insert is a replacement for the throat plate that came with your table saw. The insert provides a smaller opening for the table saw blade. Eliminating the space around the saw blade prevents material from falling into the table saw and adds support to the workpiece.

Why Use A Zero Clearance Insert?

The throat plate that comes with a table saw provides space for you to use saw blades with various kerf widths. It also gives plenty of clearance for those blades to operate at angles other than 90-degrees.

A zero-clearance insert matches a specific kerf width. That eliminates the gaps on the sides of a blade that loose materials can fall in. The lack of a gap between the saw blade and insert also provides extra support that reduces chipping as you make crosscuts.

What Are The Limitations Of Zero Clearance Inserts?

First off, a zero-clearance insert has an opening that matches a specific saw blade kerf. That will limit it to use with that blade width only. You will need several inserts if you use multiple saw blades in your table saw.

Secondly, the lack of clearance on these inserts means that they will wear out over time. The saw blade opening will widen over time, eventually needing replacement.

Thirdly, a zero clearance insert is only suitable to be used at a one blade angle. If you want to make a cut a 45 degree bevel cut, you will only be able to use a zero clearance insert that was made to fit the blade at a 45 degree angle.

How To Make A DIY Zero Clearance Insert

You can buy prefabricated zero clearance inserts from various manufacturers. Making your own zero clearance inserts is a fun DIY project, and the process includes these steps:

  1. Select materials
  2. Gather tools
  3. Zero clearance insert layout
  4. Rip cut to width
  5. Crosscut to length
  6. Mitered cuts
  7. Sand the blank
  8. Test fit
  9. Clamp insert down and cut
  10. Drill finger hole
  11. Test your insert

One: Select materials

Like most DIY shop accessories or jigs, you will want to use a stable material for the insert. Plywood is a smart choice since it does not move with seasonal changes due to the multiple layers. Birch plywood is hard and would make a suitable zero clearance insert.

Some woodworkers like to use hardboard, laminate or phenolic sheets to make inserts. In this case, you can use two hardboard sheets glued together. Attach laminate sheets on both sides of the hardboard to complete your blank.

No matter which materials you plan to use, keep the overall thickness slightly less than the throat insert that comes with your table saw. That will put it in the range of between 1/4 and 1/2-inch thick. Use blanks an extra inch or two in length and more width than the final insert dimensions.

Two: Gather tools

You should need only a handful of tools to build a zero clearance insert, including:

  • Table saw – Used for all cuts
  • Calipers or combination square – Measures length, width, and thickness
  • Sander or sanding block – To shape the insert and smooth rough areas
  • Drill/driver and spade bits – For drilling out holes
  • Pencil and marking knife – Marks for layout
  • Ear and eye protection – Keeps you safe while working

Three: Zero clearance insert layout

You will start by removing the throat plate on your table saw. Use your calipers and combination square to get the dimensions of the throat plate. The measurements that you will need include the length, width, and thickness.

Next, turn the throat plate over and place it on your blank. Trace around the exterior of the throat plate. You now have an outline of the zero clearance insert on your blank material.

Four: Rip cut to width

Adjust the fence on your table saw to the width for the insert. If you placed one edge of the throat plate along the edge of your blank, you only need to make one cut here (if the blank was previously squared).

You must make sure the fence is accurate, as the cut needs to match the opening on your table saw that holds the insert.

Five: Crosscut to length

You can use your miter gauge to hold the blank perpendicular to the blade as you cut it to length. Keep a bit of extra wood beyond the outline. The sander or sanding block will remove the material later.

Just make sure that your miter gauge is at a 0-degree angle before making your cuts.

Six: Mitered cuts

Adjust the miter gauge to 45-degrees to cut two of the corners off of the blank. That will take away most of the waste and leave only a small portion of the wood to sand later.

Reposition the gauge (or set a 45-degree angle in the opposite direction) to cut off the remaining corners.

Seven: Sand the blank

You can now sand the ends of your insert blank, taking the excess material down to your tracing line. A sanding station, or an upside-down belt sander, excels at this task. You can use an orbital sander or sanding block as well.

Avoid heavy grit sheets. Using anything from 150 to 220 grit should work fine. Do not sand beyond your outline marks. You can smooth any rough edges by hand with fine sandpaper.

Eight: Test fit

Place your zero clearance insert into the throat plate hole. You are looking for a snug fit here. Use hand sanding to knock off any points that stand proud.

Do not over-sand. The insert needs to fit snuggly.

Nine: Clamp insert down and cut

Retract the saw blade down completely. Place the insert blank and cover it with a piece of lumber that you can sacrifice (framing lumber 2 x 4 is a good choice). Clamp the sacrificial lumber down on both ends so that it will not move.

Next, start the table saw and slowly raise the blade through the insert and the lumber holding it in place. Slowly retract the saw blade and turn it off. Remove the clamp and lumber so that you can inspect the cut through your zero clearance insert.

Ten: Drill finger hole

Use your throat insert to locate the placement of the finger hole. Insert a spade bit and drill out a finger hole (3/4-inch is accessible for most fingers). Smooth the edges by hand with fine sandpaper.

Eleven: Test your insert

Finish the process by installing the zero clearance insert. Make a shallow, medium, and maximum depth test cut to make sure it is working safely. You now have a zero clearance insert to use on upcoming projects!

Zero Clearance Means Better Performance

Put down the zero-clearance insert as a must-do for your next project. The results will be a cleaner cut and a safer workshop. That will make all of your table saw work more enjoyable!

About the author

Arthur Kudriavcev

Arthur Kudriavcev

I was introduced to woodworking by my grandfather when I was 11 years old. I spend most of my free time working on woodworking projects and writing for this blog. Apart from that, I also enjoy weightlifting and chess.

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