What is Square-Ground Filing and How Do You Do It?

Overview

The term “square-ground filing” refers to the process of using a file to sharpen square-ground chain by hand. Square-ground filing can be much more difficult than round filing and requires different techniques. Because square-ground chain is less forgiving of errors, it is important that the corner alignment and filing angles be precise.

Learning the proper method for square-ground filing can take time. In fact, most people don’t get it right on their first try. So, don’t get discouraged if your chain doesn’t perform the way that you expect it to on the first attempt.

Topics

When Should You Perform Square-Ground Filing?

Things to Keep in Mind the First Time You File Square-Ground Chain

Three Rules for Sharpening Square-Ground Chain

Where to Position the Square File

What Direction Should the Square-Ground Chain be Filed? 

Sharpening with a Square-Ground File

Gullet Filing

When Should You Perform Square-Ground Filing?

Since square-ground chain is not very common, most chain saw operators will never have an occasion to perform filing with a square file. Square-ground chain is only used in conjunction with longer guide bars designed to cut larger trees. However, the performance advantages of cutting timber with square-ground chain can outweigh the fact the square-ground filing can be more difficult and affords less room for error.

Things to Keep in Mind the First Time You File Square-Ground Chain

While square-ground filing can be done out in the field, a shop with a light and a work bench is an ideal learning space. It’s easiest to file in a setting where your cutters are stable and there’s lots of light.

The first square-ground chain you sharpen should be a square-ground chisel chain that still has its factory grind. Do not use an old chain – especially one that has been previously filed. A chain that has already been resharpened may still have gullet material attached that needs to be removed.

Tip: A second, new square-ground chisel chain on hand can be a handy reference point for square-ground chain sharpening. You can look at the cutter teeth on the second chain to see what the cutter teeth should look like.

Three Rules for Sharpening Square-Ground Chain

1. Keep the corner of the file aligned with the cutter’s tooth
2. Maintain the angles of the cutter’s tooth
3. Repeat the same angles on every tooth; all cutters need to be the same.

Where to Position the Square File

A square file sharpens the top-plate and the side plate, simultaneously.

This creates a line, (A), where the top-plate cutting angle meets the side-plate angle. For best results, file so that the line intersects the cutting corner (B).

To properly sharpen the cutter, use the correct filing position, as shown here from three different points of view: 

Before you begin filing, place you square file next to the fact of a cutter tooth. Decide on the corner of the file you will align with the corner of the cutter tooth. When the corner is aligned, reposition the file on its other axis so the other surfaces match up. Reference the above graphics so you know what the right filing position looks like. 

What Direction Should the Square-Ground Chain be Filed?

Once your file is positioned, it’s time to sharpen. But what direction should you use?

Square saw chain should be filed from the outside in (in a downward direction). This leaves a better edge on the chromed cutting surfaces and makes it easier to keep the file’s position, and the resulting cutting edges, in correct alignment as shown in the preceding File Positioning section. However, filing from the outside in will wear out your file faster.

Some square saw chain users may prefer to file from the inside out (in an upward direction). You should be aware that inside-out filing is much more difficult.

Whichever direction you choose, be sure your file and your cutting edges stay positioned as shown in the preceding section. File all cutters on one side of the saw chain, then reverse the saw chain and repeat the process. Use the same file positions for cutters on the opposite side of the saw chain.

Sharpening with a Square File

To start sharpening after you’ve gotten your angles lined up, take a file strokes with the file, then remove the remove and take a look at the cutter tooth. There will be some marks where the file has removed some steel. Adjust the file based on what you see. Continue sharpening until the tooth looks as sharp as the one of the reference chain.

After producing the first sharp cutter tooth, it’s time to move on and make the rest of the teeth look the same. The best way to do this is to look at the chain. Counting the number of strokes is only provides a rough estimate, since not all stokes remove the same amount of material.

Each tooth needs to be the same, because this will help ensure a consistent cut. If one tooth is bigger or smaller the others, it will cut off different-sized chunks of wood, causing the chain to chatter and vibrate. This inaccuracy can also make it so the chain cuts crookedly.

What Kind of Square File Should You Use?

Only use files specially designed for square-ground chisel cutters, available from your chain saw dealer. There are three different types of square files: hexagon, double bevel, and “goofy”.

The most popular file type is the hexagon shape, also known as “triangular chisel file”. True to its name, a hexagonal file has six sides, plus three corners which act as the filing edge. Out of the three file types, the hexagonal file is the smallest in size and usually fits well into 3/8” pitch chain.

The other two file types – double bevel and “goofy” have two corners for sharpening and also allow people to lower depth gauges with surfaces on the top and bottom of the file.

Gullet Filing

Correct Gullet Filing (Right)

Clearance is maintained between the working corner and the gullet’s outer edge.

• Some square-ground chain users may prefer to file from the inside out (in an upward direction).
• Inside-out filing is much more difficult.
• Whichever direction you choose, be sure your file and your cutting edges stay positioned as previously shown.
• File all cutters on one side of the chain, then reverse the chain and repeat the process.

Correct: Clearance is maintained between the working corner and the gullet’s outer edge.

Incorrect Gullet Filing (Wrong)

Incorrect: Little or no clearance between the working corner and the gullet’s outer edge.