This guide compiles the usage and selection of rulers specifically for circular saws, as used by Japanese carpenters. There’s a wide array of guides for circular saws, including speed squares (right-angle rulers), rip fences (parallel rulers), bevel gauges, aluminum rulers, and homemade rulers.
Given the potential hazards of using a circular saw, employing these guides correctly is essential to prevent accidents. Mastering these tools can significantly enhance the efficiency of carpentry work, enabling quick and precise operations. To create exquisite woodworking pieces, utilize Japanese skills!
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日本語版の記事（丸ノコ定規の使い方まとめ【プロ用】エルアングルやスライド定規）はコチラ
List of Contents
Article Author
Kentarou Fukata
A Kyoto, Japan native born in 1985, I am a seasoned carpenter boasting five national qualifications in housing-related disciplines in Japan. Committed to the dissemination of carpentry expertise, I actively contribute to professional development within the field through instructional content on YouTube.
Introduction Video
Complementing the guide is an informative video designed to augment comprehension.
If you wish to utilize features like subtitles, please reopen the video on YouTube. You can access the subtitles through the ‘CC’ button on the playback screen or in the settings.
About Circular Saw Rulers
The Allure of Circular Saw Rulers
Craftsmanship fundamentally pursues the goal of achieving a desired finish in any creation. Throughout this process, the method of making is continuously refined. The more efficient the process, the faster, more beautiful, and safer the work becomes. One way to enhance such efficiency, as we introduce here, is through the use of rulers.
The tools in use today originate fundamentally from someone’s ingenuity and handmade efforts, making the use and creation of rulers an essential aspect of making things.
Points on Utilizing Commercially Available Rulers
When using commercially available rulers, the goal is to fully harness the design intent and maximize the product’s potential. This requires a deep understanding of the ruler, including its intended use and capabilities.
The value of a ruler is measured by how much it can speed up the process, beautify the outcome, and ensure safety. To appreciate this value, it’s also necessary to consider the efficiency of work without the use of a ruler.
In this article, we will introduce methods discovered by Japanese craftsmen who have spent a long time experimenting and refining their use of rulers.
The Hazards of Circular Saw Rulers
Among the tools used in carpentry, the circular saw stands out as the most frequently used and efficient. However, it also has a dangerous aspect, being one of the tools most associated with accidents during work. Circular saw rulers are used in conjunction with this hazardous tool. Therefore, it is crucial to have a thorough understanding of the characteristics of the circular saw and the properties of wood when using them.
Dangers Inherent to Circular Saws
The nature of the circular saw involves a rotating blade that moves through wood like a wheel, exerting a strong force. The direction of this movement is determined by the rotation of the saw, running opposite to the direction of the saw’s advancement. This phenomenon, known as kickback, is extremely dangerous and constitutes a significant portion of circular saw accidents. Absolute caution is necessary when using a circular saw ruler to ensure that accidents are prevented.
Risks Associated with Wood Properties
Wood has a tendency to warp, and warping can occur simultaneously with cutting. While there are general patterns to how wood warps, it does not always bend predictably. Unexpected warping can increase the risk of accidents.
Dangers of Using Circular Saw Rulers
When cutting with a circular saw using a ruler, you are likely to be holding the ruler with one hand and operating the saw with the other. Although using a ruler may seem to allow for smoother and seemingly safer cuts than freehand cuts, the concentration and force applied are divided between the tools, increasing the danger. When using a ruler, it is imperative to be more focused than when cutting freehand.
Tool Malfunctions and Loose Adjustment Screws
Always ensure that the circular saw’s adjustment screws are securely tightened before use. For example, a loosened or malfunctioning screw adjusting the blade’s cutting depth is extremely dangerous as the blade can protrude unexpectedly. Such malfunctions can occur at any time, unpredictably. It is vital always to be mindful of the possibility of malfunctions to prevent accidents.
Situations for Using Circular Saw Guides
The decision to use a circular saw guide involves weighing its dangers against its efficiency. Circular saw guides are not a one-size-fits-all solution, so here we introduce criteria to help you decide when to use them.
When It’s Better to Use a Guide
Advantages in Terms of Work Speed
Employing a circular saw guide can stabilize the saw blade, leading to smoother cuts and increased cutting speed. It can also eliminate the need for marking cut lines, thereby reducing the time spent on marking. This is particularly effective when producing multiple pieces of the same shape, as the efficiency gains multiply with the number of pieces.
Advantages in Terms of Precision
Using a guide can easily ensure precision. Accurate cuts improve joint quality during assembly and result in higher strength.
Examples Where Not Using a Guide is Preferable
In renovation work, it’s more common to cut without using a guide. The reason for this is that guides also have their disadvantages. Here, we introduce some drawbacks of using guides.
Dissipation of Focus and Force
When using a guide, one hand operates the circular saw while the other holds the guide, leading to a dissipation of focus and force that increases the risk of accidents. Therefore, the use of circular saw guides is limited to situations where concentration on the tool can be maintained with both hands, such as on a workbench. For example, when cutting already installed materials, it is safer to operate the circular saw with both hands to apply adequate force, hence not using a guide.
Potential for Reduced Accuracy
In cases like cutting through multiple layers of plywood or thick materials, the saw’s base adjustment or blade sharpness may prevent cutting precisely along the set guide.
Sometimes, cutting freehand along the marked line can result in higher accuracy.
Considering Efficiency
In renovations, operations like fitting flooring against curved walls are frequent. Cutting out irregularly shaped materials without a guide, by visually aligning and following the cut line, can reduce the need for post-cut trimming, resulting in a quicker finish.
It’s overwhelmingly faster to make minor adjustments and shape with a circular saw than to trim with hand tools. Therefore, the use of circular saw guides becomes less frequent in renovation projects.
Preparing for Using a Ruler
Essentials for Safe, Quick, and Accurate Processing
Securing a Workspace
In fabrication tasks, materials are placed within a room for processing. Sometimes, positioning these materials can be challenging. However, the success of processing tasks heavily relies on securing a workspace, as it significantly impacts workability and safety. Thus, it is crucial to meticulously plan in advance, including the arrangement of the workbench, management of leftover and waste materials, and the placement of easily accessible rulers and similar tools.
Working Height
When processing with a ruler, the height at which you work is critically important. To achieve a clean and quick construction, it’s essential to adjust the stand to the appropriate height to ensure safety and a powerful, proper posture.
A key consideration is that the optimal stand height varies depending on the type of ruler used. For instance, when using a speed square type ruler, it’s necessary to press down from the top, which cannot be done if the stand is too high. In contrast, cuts can be made at shoulder height when using a rip fence.
Another factor to consider is the height of the material stack. As the stack decreases with use, maintaining the correct cutting height becomes challenging, increasing the risk of injury. Therefore, the height of the stand under the material should be carefully considered. Of course, the best height varies according to the worker’s height and personal habits during processing, making it a matter of trial and error.
Tips for Setting Up a Ruler
To facilitate the setting of a ruler for a circular saw, mark the blade width on the front part of the saw table. Setting it using the mark on the front part of the table is quicker than checking and adjusting the blade itself.
For precise setting using this method, it’s necessary to make an accurate mark. One way to do this is by using a speed square to make a partial cut in the material, stop the circular saw while the ruler is fixed, and then pull back the saw. This reveals a cutting line on the front part of the saw table, which you then transfer to the front part of the table as your mark.
This mark can be used for setting all types of rulers and offers high precision. However, slight deviations may occur with rip fences due to their structure. These deviations are consistent, so remembering this pattern allows for quick and accurate settings even with rip fences.
*For cutting precision within 0.2mm, mark the cutting line at the start position of the material for accurate alignment.
Features and Usage of Circular Saw Rules for Right-Angle Cutting
The Speed Square Type
Basic Usage
The Speed Square is a ruler specifically designed for making right-angle cuts in materials such as plywood. In Japan, Shinwa’s “L-Angle” has gained particular popularity and has become synonymous with the tool itself.
The Speed Square is held with the left hand, allowing cuts to be made to the right of the ruler. However, there is a limit to the size of the piece left on the left that can be cut accurately; it cannot be less than 40cm in width. *With a special technique, it is possible to leave as small as 30cm.
The “L-Angle” features a handle, which is designed to be firmly pressed downwards during use. Modifying the ruler by slightly bending it towards a concave (forward-leaning) direction makes it easier to stabilize with one hand (the left hand), and enhances its grip, even on thin materials, reducing slippage.
*This is a common mistake with the use of the Speed Square. Many try to fix the ruler in place by pressing the guide part against the material, but if not pressed downward, the versatility of the ruler for fine adjustments becomes unusable.
The “L-Angle” includes features such as fine adjustment and setting guide functions, but these can lead to divided attention and unnecessary snags, increasing the risk of injury, so they are not recommended.
Advanced Applications
Right-Angle Parallel Cuts
The Speed Square isn’t limited to just right-angle cuts. By pressing the front part of the circular saw base against the Speed Square and cutting, you can easily make parallel cuts at a right angle. Furthermore, with the Speed Square and the circular saw base fixed in place, sliding the Speed Square along the side of the material allows for parallel cutting in the direction of the angle.
Fine-Tuning Right Angles
When cutting materials like plywood at a right angle with the Speed Square, there may be times you want to adjust the angle by a few millimeters. Although there are rulers specifically for this purpose, they can be bulky, inconvenient, and expensive. Hence, acquiring the skill to adjust using a single ruler becomes essential.
The method involves adjusting the ruler, securing it, and making the corrected cut by utilizing the characteristics of the circular saw base. Despite the distance between the ruler contact point and the cut line, focusing on the ruler and adjusting its angle will also correct the cut line’s angle.
For such adjustments, a method of securing the ruler without relying on the material’s side guide is necessary.
Gradient Cuts
In tasks like creating materials with a consistent slope, such as roof slopes, you might wish for a gradient ruler. However, the “L-Angle” can actually be used as a gradient ruler by inserting a slope packing between the material and the guide touching the material, allowing for cuts at the desired angle.
For making improvised slope packings, please refer to the method of cutting any slope introduced in the aluminum ruler section.
Planning the Order of Cuts
Due to its design, the Speed Square has limitations on the size of the piece left on the left side. While narrow materials can be processed with a rip fence, using the Speed Square is far more efficient.
When working with multiple materials that need to be processed in the perpendicular direction, planning to cut narrower materials on the right side maximizes the efficiency of the Speed Square.
Rip Fence
The rip fence is an indispensable ruler for new construction work, designed for making parallel cuts from the side of the material.
Characteristics of the Rip Fence (Parallel Ruler)
The rip fence is a more challenging tool to use compared to the Speed Square. However, for parallel cutting of materials like plywood with anything other than a circular saw, large machinery would be required. Enhancing your skills with the rip fence, a handy tool that allows for processing with a circular saw, expands the possibilities of what can be created even in DIY projects.
How to Use the Rip Fence
The difficulty in using a rip fence lies in the fine adjustment of the ruler’s width setting and maintaining the linearity of the cut section. Moreover, there are several points to consider, such as the angle being prone to tilting.
The basic use of the rip fence involves inserting it from the motor side of the circular saw and making cuts parallel to the right side of the material. Due to the structure of the rip fence, the cut may tend to curve at the beginning and the end of the cut, so care must be taken to ensure the circular saw progresses accurately.
How to Choose the Rip Fence
When choosing a rip fence, it is recommended to select one that can be set to overlap with the circular saw base, even for cutting small widths, and one that allows for adjustment of the ruler surface up and down depending on the thickness of the material. The part that is inserted should be made of a firm material with good sliding properties for better workability. *As sliding properties deteriorate with use, it is recommended to replace it when it becomes difficult to use.
Tips for Making Tenons and Mortises with a Rip Fence
A rip fence is typically used by inserting it from the side of the circular saw’s motor. However, when making incremental cuts such as tenons and mortises in the direction of the wood’s grain using a circular saw, it is advised to insert the rip fence from the opposite side of the motor.
The specific method involves positioning the material so that the tenon will be vertical and standing on the end to be processed. Then, perform the cut with the circular saw in a “backhand” manner.
*Backhand cutting refers to holding the circular saw in the opposite direction for use, utilizing it in a reverse rotation.
During this procedure, while pressing the circular saw table against the end grain of the material, ensure that the ruler placed on the blade side (opposite the motor) on the material’s left side makes contact by pushing it towards the back right. Then, cut from the top down.
Adjustable Square (Incline Ruler)
Features of the Adjustable Square
An adjustable square, essential for carpentry work, is a ruler used for setting and cutting slopes with a circular saw. However, despite its infrequent use, this type of ruler tends to be bulky and inconvenient to store on job sites, often getting in the way. Its construction includes movable parts that are not very durable, making it prone to breakage. Additionally, due to its high cost, replacing it is not always an option, leading to work plans that avoid its use as much as possible.
Usage of the Adjustable Square
In terms of usage, it’s typically applied against the front side face of the material, but using it against the back side face can make it easier to secure, which is recommended for ease of use.
Although the adjustable square can be set to a right angle for cutting perpendicular slopes, constantly setting it to a right angle can be cumbersome. Therefore, it’s advisable to have a separate ruler (like a small speed square) specifically for right angles.
Bevel Gauge (Incline Ruler)
Features of the Japanese Bevel Gauge
This ruler is not exclusively designed for circular saws but can be utilized for cuts with one. Similar to the adjustable square in its use for measuring inclines, the Japanese bevel gauge offers more robust incline fixation due to its triangular shape that locks the angle securely. Additionally, it is more affordable, and its foldable design into a rod shape enhances its storability.
Points of Caution with the Japanese Bevel Gauge
Compared to the adjustable square, this ruler, being rod-shaped, presents a challenge in securing it to the material with just one hand.
Moreover, the absence of a protruding guide at the incline end means there is no guide when starting a cut with a circular saw, requiring familiarity for use as a saw guide. Also, it cannot be flipped over to use at the same angle, which users must be mindful of.
Where the Bevel Gauge Shines
In Japan, carpentry work often utilizes the bevel gauge, especially for marking during staircase construction, measuring and marking inclines for sloped ceilings, and other precise measurements. It is employed in situations where a relatively large marking surface is available and high accuracy is required.
Aluminum Ruler (Simple Straight Edge)
Features of the Aluminum Ruler
The aluminum ruler is originally designed for use with a utility knife as a cutting ruler. It’s a must-have in any workshop, and when used correctly, it allows for precise arbitrary incline cuts with a circular saw.
Using an Aluminum Ruler for Circular Saw Cuts
Using an aluminum ruler for circular saw cuts is not the standard method. Set the ruler 30mm away from the cutting line, and cut with the circular saw using a “backhand” technique.
The reason for backhand cutting is that using the circular saw in a pushing manner positions the motor to pass over the left hand holding down the ruler. Moving the hand that’s holding the ruler as the motor passes can cause the ruler to shift, leading to circular saw blade binding and kickback. Never place your hand near the saw blade in a manner that risks injury.
When cutting with a circular saw using an aluminum ruler, always use backhand cutting, secure the ruler with your foot or another method to completely fix it in place, and pay careful attention to kickback. Although this method comes with risks, it significantly expands the range of techniques available and is worth trying as your circular saw skills improve.
Handmade Plywood Ruler
Features of the Plywood Ruler
The plywood ruler is crafted by laminating plywood, designed to serve both as a guide for running a circular saw and as a ruler to mark the cutting line. This type of ruler is especially useful in renovation work, where irregularly shaped cuts are common.
Points of Caution with the Plywood Ruler
While the plywood ruler can be quite convenient when used correctly, it has a tendency for its accuracy to degrade over time, necessitating its disposal after some use. Furthermore, due to its larger size compared to other rulers, it can become cumbersome to handle.
Moreover, this ruler has its dangers. Despite often being presented on platforms like YouTube as a safe option for beginners, professionals who frequently use circular saws do not share this view. The handmade nature of the ruler means it’s more prone to breaking than commercially available rulers. As mentioned, a malfunction during use can lead to severe injuries. The failure of a circular saw ruler, which requires placing hands near the saw, is particularly hazardous. Therefore, it’s advised to create a plywood ruler only when you have a thorough understanding of the circular saw’s behavior, including during malfunctions.
How to Use the Plywood Ruler
To use the plywood ruler, align the side of the ruler that displays the cutting line with the desired location of the cut. Since the circular saw’s base will pass over the ruler marking the cutting line, adjust the saw’s depth to account for the thickness of the ruler.
The plywood ruler is not limited to straight cuts. Personally, I use it when creating rounded bevels. By making multiple straight cuts along the rounded line, the ruler helps improve the precision of the cuts, enabling the creation of rounded edges with a precision akin to machine-made work.
Conclusion
Have you managed to find valuable insights regarding circular saw guides?
While composing this article, I embarked on my first exploration of circular saw guides beyond Japan and was enlightened about the regional uniqueness embedded in such tools. Circular saws are not only tools of frequent use but mastering their application can immensely broaden the possibilities in carpentry. Nonetheless, given the inherent risks associated with circular saws, I advocate for maintaining vigilance and approaching your work patiently.