I thought I’d spend a little time looking at the fundamentals behind the drag on our reels. Yep, you got it; the stuff beneath the drag star on your bait caster or the knob on your spinning rig. Along the way we’ll look at friction, what causes it, and how it relates to fishing and reels. I’ll also touch on a few things not related to drags; primarily to provide a little broader perspective on friction — we put a lot of effort into reducing friction, …but it’s not always bad!
In many ways the information will establish a foundation that I’ll build on later, when I get into actual drag hardware, maintenance, modding and other topics. But for now, think of it as Drag 101 if you like.
Unlike my previous blogs, I won’t get into specific hardware in this one. So, you won’t find many pictures of reels or components, junk box cast-offs, testimonials, etc. Instead, I’ll have some diagrams and graphics that help in discussing the theory and basics underlying a reel drag.
A Blog Note: I’ll take the liberty of generalizing and simplifying some of the theory and principles, so we don’t get too bogged down in details or things that aren’t related to fishing. I know that theory isn’t necessarily everyone’s bag, so I’ll start off slowly and keep things simple, while also limiting the length of this blog. However, one of the risks in doing this is that it can introduce some inaccuracy – but it should be fine for our purposes.
Now there’s no way you can discuss reel drags, unless you cover friction. Think of the next few sections as a refresher on the basics!
Friction
Everyone on the planet has been exposed to friction; we studied it in school, deal with it every day and probably don’t always recognize it, might even take it for granted, or simply not care. But just like “the force” in the Star Wars movies… it surrounds us. An Aside: Sometimes I wonder, how many can still explain what it is and what causes it, and how it relates to our reels or even fishing; based on comments I’ve read on some forums over the years.
Friction is a force that opposes the motion of an object, and it is commonly referred to as a resistive force in physics or mechanics. Friction occurs to some degree in just about all situations that involve physical objects. In many cases it hinders a process, like when casting a lure or walking in water while wading. But friction can also be useful – the spool tension control on your reel, pulling your boat out of the water at the ramp, backlash control on a friction braked reel, and the blade rotation from a favorite spinner bait wouldn’t be possible without it.
Friction helps convert one form of motion into another. For example, the friction between a rotating propeller and the water is converted into motion of your boat; and when the propeller is no longer turning, the friction between the hull and the water allows the boat to stop. Without friction, the line guide on your reel would not travel smoothly across the face of a spool while cranking, and the line would not rest evenly on top of itself.
While friction allows for the conversion of one motion to another, it also converts some energy into heat, vibration and wear. Losing energy to these effects might not only create undesirable conditions, it will also reduce the efficiency of a process and equipment. For example:
- Level wind components will gradually wear due to friction, and may eventually need to be replaced.
- The contact of a line with itself while tying a knot may create sufficient localized friction to alter the chemical and physical properties of the line, and it can weaken and fail later. The movement of line through a line guide on your rod can make a distinct audible noise while casting or cranking a reel; and I suppose some would describe the vibration as soothing, while others just call it irritating!
- Friction resulting from dry or dirty spool bearings can result in reduced casting distance; it is often accompanied by increased noise and vibration during the cast, and accelerated wear of internal bearing components.
- Excess frictional heat can damage a boat engine without sufficient coolant flow. In addition, the efficiency of the engine in converting the energy from the fuel to mechanical motion is directly related to frictional affects on components.
However, the heat, wear, vibration, etc. produced by friction is useful for some aspects of our hobby. For example, if you’ve sharpened your hooks or polished a few components while super-tuning your reel, you’ve used sliding friction to remove material and alter the surface. Your favorite crank bait wouldn’t dive, wobble and vibrate as it is being pulled through the water without fluid friction. I’m sure we’ve all rubbed our hands together to warm them – the dynamic friction with our skin provides temporary relief while fishing “the opener.”
The 3 most common types of friction we encounter while fishing are sliding friction, rolling friction and fluid friction. I’ll spend most of my effort on sliding friction, since this blog is primarily about drags, and will just touch on the other two. A Note: There are other types of friction that I won’t get into in this blog.
Sliding Friction
There are two general forms of friction:
- Static friction is the friction acting on an object when not in motion, but when a force is still applied upon it. The frame screws in your reel are a good example of static friction; the force applied on the threads securely fastens other components.
- Kinetic friction is the friction acting on an object when it is moving. It is frequently referred to as dynamic friction. Energy is always lost with kinetic friction, which is not the case with static friction.
A Note: The state between static friction and dynamic friction is an important condition, and is called limiting friction. Limiting friction is the friction on an object just before it starts moving; and the force required to get it moving is often called the break-away or start-up force. [If you are taking about rotational force, it will be called break-away or start-up torque. Many will casually refer to the state itself as “start-up” or “shear”, essentially describing the transition from a static to dynamic condition.] I’ll have more about this later in the blog; it can be important in the performance of a drag.
Dynamic sliding friction is probably the most common type of friction encountered in our reels. It occurs when the surfaces of two objects are forced together, and they slide against each other (e.g. there is a relative motion between them). Spool drag, tension and friction backlash braking wouldn’t work without the proper amount of sliding friction. It even occurs between level wind components and gears. Unfortunately, dynamic sliding friction is a double-edged sword – it’s responsible for wear of reel components!
The amount of sliding friction that occurs between two objects is a result of two important factors – the nature of the surfaces in contact and the amount of force that holds them together:
1. Simply put, the nature of a surface is influenced by the material it is made from, chemical and molecular properties, and its surface finish.
2. The force that pushes the surfaces together can be caused by gravity; but in a reel it typically is a result of an adjustment control, the design configuration of the reel itself, and/or conditions that occur during use. An Aside: The force is actually called Normal Force; and for friction, is the force perpendicular to the plane of contact.
In the case of a reel drag, the compression provided by an adjustable drag star will vary the force between metal discs and friction washers in the drive gear. Loosen the drag star and you have less force between the sliding surfaces, so the force required to pull line from the spool is less. Tighten the star and the opposite occurs. A Teaser: Unfortunately, a lot can happen in either case when it comes to our reels, and the actual results you get might not always be what you want or expect. I’ll have more on this in a future blog, when I get into drag troubleshooting, maintenance and the hardware itself.
Friction occurs in part because surfaces tend to catch on one another as they slide. Even surfaces that appear extremely smooth will be rough at a microscopic level, like in the previous picture. Notice the ridges, grooves, gouges and pits still on the polished surface; some may have even been caused by the polishing process itself! As the blemishes on one surface contact with those on the other, it creates a type of bond between them.
The diagram shows two surfaces in contact. Sliding
friction partly occurs due to the surface finish.
Two surfaces in contact will attract and interact with one another at a molecular level, forming different types of chemical or electromagnetic bonds in the process. Without getting into any of the details; let’s just say that the bonds can prevent one surface from moving across another, even when a force is applied. Furthermore, if one of the surfaces is in motion the bonds will repetitively form and release; and energy will be lost in the process. [A Note: Yes, I used the words 'chemical or molecular bonds,' …and maybe you thought some lubricant manufacturers were making this stuff up? The specifics get a lot of attention in Tribology, which is the specialized study of friction, lubrication and wear. You can Google 'Tribology' for more information if you don't believe it! However, I will admit that the marketing hype is getting excessive, and just about everyone is now 'touting' what has been an accepted principle for many years! But I guess it sells stuff....]
The mechanical and chemical properties of a material determines how you can finish its surface, how it behaves under compression and sliding force, how strong the molecular forces are on the surface, etc. So, the material that the surfaces are made from will have an influence on sliding friction. A Note: Maybe you’ve wondered why Teflon or Dulron is often used in place of bearings or even for gears which don’t carry much load? Both don’t produce hardly any friction when in contact with another material; because of their surface, mechanical and chemical properties.
Plot of Friction vs. Force for two surfaces in contact. No movement occurs until sufficient force is applied to overcome static friction.
When two materials are in contact with each other under a constant force, you can plot the applied force it takes to get them to move relative to each other. When you do this, you’ll typically get a plot similar to the one shown in the previous picture. Notice the region of static friction on the plot; there is no motion until the applied force finally increases to the point that it overcomes the frictional force, and movement occurs. But once you overcome the frictional force, the amount of force it takes to continue movement drops to a lower value, like in the region of kinetic friction.
A Big Note: By the way, the peak between the two regions is where the limiting friction occurs. This is typical for most cases involving sliding friction; the kinetic friction is usually smaller than the limiting friction. Some anglers will measure or judge the effectiveness of a reel drag, by comparing the limiting force to the running force, required to pull line under drag. They might even call it “drag start-up” or “break-away drag.”
You can describe this situation a number of different ways, but a few ways you may have heard before include:
• Start-up force is usually higher than the running force with sliding friction,
• It will usually take more force to get two surfaces to break-away [shear] and slide against each other, than it does to keep them sliding, or
• Drag start-up pull will be higher than running pull, due to the sliding friction.
Another Note: Limiting friction can also occur with rolling or fluid friction, but sometimes another type of friction might actually be involved or occur first. Confused? A Hint: The bearings in your reel are a good example of the later case, where the balls may initially slide on a race before they actually begin to roll! The design of the bearing and how it is lubricated are just two factors that can influence this; but load the bearing carries and roundness of the balls are also important.
If you divide the frictional force between two surfaces by the applied force acting on one of them to cause it to move, you’ll get a number that can be useful in comparing the sliding friction of one material pair to another. The number is called the Coefficient of Friction (COF) for the two materials, and there are two values; one for the static region of friction and the other for the kinetic region. (If the surfaces are lightly greased (wet), there will even be two more values, again one for each region. I’ll get into this more when I talk about wet drag systems and drag lubricants in a future blog.)
COF will generally range in value from .02 to 1 for most common material pairs. For instance, the COF for rubber sliding on concrete is .8 (a relatively high value), while the value for Teflon sliding on steel is .04 (a very low value). I suppose that’s why tires aren’t coated with Teflon and roads aren’t made from steel plate, eh?! Today, most material pairs used in bait cast drags have COFs that typically range from .1 to .6 or so, but can be significantly different in other parts of our reel.
For example, some approximate dry COFs for other material pairs can be found in the following table.
Sliding Coefficients of Friction (COF) for common configurations found in a bait caster. Values are only shown for comparison.
The previous Coefficient of Friction Table is for illustration only, since exact values for sliding friction will depend on many different factors. Note 1. Notice the values for aluminum and aluminum, the kinetic COF is actually greater than 1, and is higher than its static COF. Aluminum oxide on the surface of the material can have a significant affect on kinetic friction; the surfaces will quickly oxidize and affect sliding surfaces. This can result in accelerated wear if not controlled; but if the force of compression gets extremely high the materials will eventually fuse together. By comparison, the greased COF (wet) for aluminum and aluminum is .3 static and .25 kinetic, the surface oxides are not much of a factor in this case! A big reason for keeping your level wind components lubricated, eh? It’s also why some manufacturers are now anodizing aluminum level wind components! Note 2. The COF for dry woven graphite and steel will vary across a range, dependent on the weave and fill density of the woven graphite, when all other things are considered. Note 3. The COF for dry cork and steel will also vary across a range (similar to leather and other materials), dependant on the quality, fill and density of the cork. These materials can also significantly compress, which can affect COF.
Rolling Friction
Rolling friction occurs when one object rolls on the surface of another. The Coefficient of Friction between the surfaces plays heavily in the energy lost to friction, and in some ways it’s similar to sliding friction, just usually much-much less. But compression and distortion of the surface(s) also needs to be considered, since both can have a big influence on things. For instance, if you’ve ever driven your vehicle in the sand on the beach you know what I’m talking about; it’s totally different when compared to a hard roadway!
The miniature rolling ball bearings in our reels experience both rolling and sliding friction – although you might think that only rolling friction would be involved. The difference between the circumference of the inner and outer races causes the balls to periodically slide on them (slip), as they roll inside the bearing!
Trivia: One might think that the COF is very low on a Teflon bushing that supports a stainless steel shaft; it’s on the order of .o4 (as shown in the previous table). However, the equivalent frictional coefficient for a properly lubricated bearing will be at least 10 times lower than that (<.004)!!! No wonder many anglers upgrade the bushings in their reel to bearings, eh?
Fluid Friction
Objects moving in a fluid or gas experience fluid friction, and it is called drag. (Drag is also referred to as air resistance when it acts between an object and gas, and fluid resistance when it acts between an object and fluid, to hinder motion.) Some good examples related to fishing include the flight of your lure in the air while making a cast and the way water affects your lure during a retrieve. That should give you something to think about the next time you’re hammering a hot shoreline with your favorite crank!
Drag is much more difficult to calculate, when compared to many other types of friction. The amount of drag that occurs is influenced by things like: the viscosity of the fluid; adhesion; turbulence; and shape, speed and material of the object in the fluid.
Viscosity is a measure of a fluid’s resistance to flow, and it results from the friction that occurs between the fluid’s molecules. The viscosity of a fluid can change significantly with temperature, and many reel oils (and greases), are classic examples where this can occur:
- As temperatures increase, viscosity will decrease, and the less affect it has on fluid friction.
- As temperatures fall, viscosity will increase and the more affect it has.
Looking Forward
Although I’ll eventually get into the drag system on a Daiwa low profile in future blogs, the general configuration is similar to other bass reels. (The arrangement is straight-forward, but you should review your schematic for details.) A drag star attached to the drive shaft controls the compression between metal discs and one or more friction washers that set in the drive gear. Since the drive gear is not directly connected to its shaft, it will turn backwards when line is pulled from the spool, and the force required to pull the line is directly related to the sliding friction between the discs and washer(s). Line will even pull from the spool while you crank the reel (like while fighting a fish), since the amount of friction between the gear and shaft is dependant on the compression from the drag star. By the way, an arrangement of this type is technically referred to as a drag friction brake or clutch; anglers simply call it a drag.
-dModder
Tags: bait casters, cleaning, Daiwa, Drag, Maintenance, modifications, spinning reels
