When you walk into your home workshop, you likely find a bin of various sized nuts and bolts, several drawers filled with washers and screws, and perhaps a handful of miscellaneous hardware from past projects. At first glance, your hardware collection may look impressive; however, until you actually try to get something to stay in one place, you quickly realize your “impressive” hardware collection is completely useless. The table saw fence will slide during your cut. The drill press table will not lock at the desired angle. Handmade jigs that should provide solid support will slowly move, providing just enough movement to mess up the piece. Although the issue is not necessarily your technique or your ability to tighten, the real problem is that you are stocking the wrong fasteners for the application.
While standard threaded fasteners are excellent for joining two items together, and while they excel at clamping items together, they are poorly suited for preventing the rotation of an item, locking an adjustment in place, or keeping an item positioned on a shaft or rod. While you can achieve these functions by torquing a bolt or screw down extremely tightly, doing so can result in damaged threads, stripped holes, and does not guarantee that the items will remain in the desired location.
Fasteners Used In Professional Shops
Professional fabrication and machine shops stock a wide variety of fasteners specifically for certain mechanical problems. However, most of the fasteners stocked in these professional shops are simply standard threaded fasteners designed to solve different mechanical problems. The biggest category of fasteners that is commonly absent from home workshops is internal fasteners. Internal fasteners provide mechanical advantage from the inside of an assembly rather than clamping from the outside.
When you need to lock a collar on a shaft, keep a pulley from spinning, or prevent a knob from rotating independently of its post, external threading provides very little assistance. Therefore, the need for internal fasteners arises. Internal fasteners like Bolts Set Screws provide friction and mechanical resistance to the fastened items without requiring any visible external hardware. Think of all of the adjustable aspects of your woodworking tools: the fence on a router table, the depth stop on a drill press, the miter gauge angle lock. All of these use some form of internal pressure fastening to maintain the adjusted position once you have completed the adjustment. Once these start to move or shift, it is typically due to the internal fastener wearing out, backing off, or being the wrong type in the first place.
A Frustrating Problem That Few People Discuss
Many of us experience frustration in our workshops when parts we have placed in an exact location suddenly shift during the course of a project. We adjust the cut, lock everything in place, and then halfway through the project the adjustment slips or moves. It is infuriating because it appears to be random; however, it is not. The vast majority of the time, it is due to a mismatch in fastening.
Machine screws thread into the threaded holes of both items they join. That is their primary function. However, when you thread a screw all the way through into another threaded hole, you create a connection between the two items that still permits some degree of rotational movement. There is inherent clearance built into the threads. As the applied load increases (such as from leverage, vibration, or repeated adjustments), the slight degree of play in the threads becomes a significant amount of play.
This is when many people reach for the “fix.” The typical response to this problem is to tighten the screw more. Tightening the screw causes the threads to strip, the parts to deform, or the screw to break. Many people then spend hours attempting to drill out broken screws, retap holes, or replace entire components. The correct solution requires spending a few dollars for internal fasteners that are designed to apply pressure without engaging the threads on both sides of the assembly.
Understanding Pressure Points And Contact Methods
Internal fasteners are better suited for positioning and anti-rotation applications than standard bolts and screws because of how they make contact. Bolts create clamping force by pulling two surfaces together. Internal fasteners create holding force by applying pressure to a surface from the inside of the assembly.
Internal fasteners vary in the point style based upon the type of surface they are pressed against. Flat points are useful for the majority of applications. Conical points provide additional gripping force in softer materials such as mild steel, aluminum, etc., where a small indentation does not present a problem. Cup points create a small depression that maintains the centering of the fastener. Oval points are beneficial when working with curved surfaces. The variety of points is needed because the different materials and applications require different contact methods.
In terms of home workshop applications, flat-tipped and conical-pointed fasteners are the most versatile. Flat-tipped fasteners are best suited for use on hardened surfaces and will not damage the precision-ground shafts of many woodworking tools. Conical-pointed fasteners provide a better grip on soft materials including mild steel, aluminum, and other materials where a small indentation presents no problem. These fasteners are well-suited for applications such as securing collars on shafts for lathe projects, creating custom tool handles, and fabricating adjustable work-holding devices.
Where These Fasteners Are Needed In A Home Workshop
These fasteners are found in numerous applications throughout a home workshop. Anytime a shaft is involved, with a component attached to the shaft, the potential for the component to rotate independently of the shaft is a problem that internal fasteners address. Drill press cranks, lathe handwheels, and router collet wrenches are examples of components that benefit from internal fasteners to prevent unwanted rotation. Knobs on handmade jigs and fixtures also benefit from internal fasteners as well as numerous other components that require repeated adjustments.
Custom workholding is another area where internal fasteners are frequently required. The custom builders create ingenious clamps, stops, and positioning tools. However, the adjustable portions of these tools often drift or slip because the internal fasteners are either missing, worn-out, or the incorrect type for the intended application.
Pulleys and belts are also an application for internal fasteners. Homemade drum sanders, DIY lathes, shop-built bandsaws, etc. All of these machines use pulleys that need to be secured to motor shafts and drive shafts. Using bolts that pass through the pulley hubs are cumbersome and create stress points. Internally mounting fasteners in the pulley hubs is a cleaner and more effective method of distributing the applied forces.
However, many people do not recognize the need for internal fasteners in their applications. They design and build a project, test it with minimal loads, and everything appears to be functioning properly. However, when they finally start using the project, the parts begin to slip. At that point, they are faced with the option of either redesigning the project or retro-fitting the proper fasteners, which would involve partially disassembling the project and possibly re-drilling holes. Avoiding this situation in the future means designing your project with how forces will act on the assembly under real-world conditions.
Material Grades And Their Significance
All fasteners are not created equal. Even within the same type of fastener, the quality of the material used affects the strength of the fastener, as well as its hardness, which is important for many applications. Low-grade fasteners are generally acceptable for light-duty workshop applications. Examples of low-grade fasteners include securing knobs, locking adjustment screws, and maintaining the orientation of components in positioning assemblies.
However, low-grade fasteners are unacceptable for applications involving high levels of torque and vibration. The deformation of the fastener under the applied load will render the fastener ineffective. The mushrooming of the tip of the fastener, stretching of the threads, and damage to the fastener head are all possible outcomes of excessive load on low-grade fasteners. These problems occur frequently in the case of custom-built tools that are subject to high usage.
High-grade alloy steel fasteners offer greater strength and durability than low-grade fasteners, although they cost more. High-grade alloy steel fasteners are suitable for applications involving high levels of torque and vibration. Motor mounts, high-stress pivot points, and other components subjected to continuous vibrations fall into this category. Spending the extra money