Resistance from a drag washer, re: average diameter regardless of surface area

[jurelometer]

Yeah.  A good discussion.  I appreciate all the contributions too.

I don't want us to overlook that this this discussion has been primarily focused on dry CF drags, but the majority of us grease the drags, which means that we are most likely diving into a partial fluid film situation of some sort that is going to be more complex and variable with heat and rpm changes.  I am already over my head in tribology here, so I am not going to touch this one.

I also don't want us to overlook Boon's point that if something appears to work, it could be a worth a try.  Messing with reel drag is a low stakes game compared to something like aircraft engine design.  But I would just suggest that if something appeared to help one one aspect of drag, it still might hurt others, and we shouldn't be too confident that we know why it worked. This makes it a bit harder to judge the outcome...


-J

[jurelometer]

To broaden the topic as Joe and Jason has suggested,  I think we need to look at drag design as a series of tradeoffs.  I see lots of discussion on more or better drag without any definition of what it means.  Here is a stab at some starters:

1. Coefficient of friction.

A pair of materials has a unit-less  relative smoothness number called the coefficient of friction (CoF).  The higher the CoF, the less clamping load you will need from the drag tension knob/star to achieve the same amount of drag. Less clamping load is desirable because it takes less force to tighten the drag, is more tolerant of less than perfect planar surfaces, requires less axial load on the drag system, and probably some other stuff too. 

These surface pairs will have different static (from a dead stop) and kinetic (already moving)  CoF numbers.  The closer the numbers, the more close the startup to ongoing drag will be.

Some material pairs can have a certain amount of elasticity, sort of stretching as it eases into slipping into static friction.  I don't know if this technically falls under CoF, but this a related  valuble trait in a reel drag.

2.  ID and OD of drag disks-

We discussed this one already, but to recap, more of the drag happening father from the center results in more braking work per revolution for the same clamping load.  But a larger diameter and lower surface area (especially combined) will magnify drag surface alignment issues (uneven drag) and affect heat conduction and convection.

3. Stacking.

Putting more surface pairs into play allows us to achieve more combined friction for the same clamping load, but it also traps heat, and at least in practice, the load doesn't appear to transfer fully down the stack, especially with eared drags. Too much stacking, especially if you have to make the washers thinner to achieve it,  can lead to shearing and unreliable drag performance.

4. Durability/Reliability/Maintenance.

The ideal drag design lasts for a long time with the same behavior, is not sensitive to environmental issues like heat/cold, wetness, corrosion, etc.  I think that this is primarily a material choice.  Some designs do try to address this by sealing the drag chambers, but this also seals in heat, and whatever water that leaks in as the seals degrade quickly or slowly over time.

5. Other stuff.

There are a bunch of things to consider that can matter to varying degrees like affect on design simplicity, volume, manufacturing and material costs, and so on.

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So lets look at a hypothetical situation starting with material choice:

Let's chose Delrin on stainless steel.  Delrin has very close static and kinetic CoFs, and is relatively impervious to  water and most chemicals- making it very low maintenance.  It will accept reasonably high surface speeds and reasonably high clamping loads.  It is also inexpensive.

But the overall CoF for Delrin is low, meaning more clamping load is required for the same drag relative to other materials.  And Delrin starts getting squishy at a pretty low temperature.  So Delrin would be a good material for an inexpensive low maintenance reel used in situations where longer runs at higher drag is not required.  bumping up the drag diameters can help a bit, but that will require better alignment, and more accuracy costs more to manufacture.Stacking may not be too good of an idea with it's low heat tolerance.

Rulon is sort of in the same camp as Delrin, except that it has extremely high hear resistance, albeit at a much  higher price point.  So Rulon can be a good target for a smooth reliable drag that can handle longer runs, but is still is going to struggle at some point when the clamping load requirements gets too high unless you are willing to accept a large volume drag area. Rulon could be an ideal choice for a higher end fly reel drag, but would be less than ideal for a large lever drag  conventional.

And so on.

Delrin, Rulon, Cork, Carbon fiber all have their place IMHO.  So does stacking and not stacking drag surface pairs. And so does large and small ID/OD drag washers.  The system has to be looked at from multiple perspectives.

No free lunch.  No absolutes.  Only tradeoffs.  I like designing stuff, and am continuously humbled by all the tradeoffs that I missed after I reckoned that I must have thought of nearly everything this time... 

-J

[boon]

I would first like to point out a for the record that while I am getting nicked on this thread for oversimplification (rightfully, I might add), I am getting nicked on the thread that spawned this one for potentially scaring folks off for being too technical. On the exact same topic.  Can't win

Ha! You can never please 'em all 

There is a time and a place for a "deep dive". This felt like one of them. I always appreciate your considered thoughts, and that you take the time to articulate them.

[Gobi King]

Wow, I need to reread this entire thread,
Just a few comments from an over eight single dad of 2 very mouthy girls:
1. Grease your drags -
2. Asking light gear to do big tasks - lube parts often to prevent premature failure

[jurelometer]

1. Grease your drags -

This is a good example of tradeoffs.

Greasing a carbon fiber drag decreases the overall coefficient of friction (bad), and introduces more heat and velocity related variability in drag (bad).

But it decreases the difference between static and kinetic  COF especially once there is any contamination (good). It also reduces the risk of galvanic corrosion, especially if the CF comes in contact with aluminum (very good).

At the factory, the clean dry CF wins out when testing.  Meanwhile in the real world, most of us actual users are willing to require a little more clamping force to get more smoothness, durability and reliability in return.  And we don't notice the drag load variability since the effective spool diameter change and line on water friction already introduce a ton of variability as well. 

This is probably why  reel manufacturers were reluctant to grease drags until after it became popular as a maintenance technique in the field.

[

Ha! You can never please 'em all 

There is a time and a place for a "deep dive".

Not all the time? Now you tell me.  I have a whole wedding toast that I need to rewrite now.

-J

[Gfish]

We oughta come with an adjective for Dave's description; "the closer the numbers, the more close the start-up to ongoing drag will be". This, I assume, means the CoF of the 2-surfaces works as drag  better under the condition of the 2-CoF's being close to one another. People talk about "start-up", as less is better, but not how to get it and maybe maintain it.(post 31 near the top).

[jurelometer]

We oughta come with an adjective for Dave's description; "the closer the numbers, the more close the start-up to ongoing drag will be". This, I assume, means the CoF of the 2-surfaces works as drag  better under the condition of the 2-CoF's being close to one another. People talk about "start-up", as less is better, but not how to get it and maybe maintain it.(post 31 near the top).

I am a bit confused by your statement (or is it a question?).But I think that Igot the gist of it.  Check out the sentence before the one you quoted:

These surface pairs will have different static (from a dead stop) and kinetic (already moving)  CoF numbers. 

The closer the static and kinetic coefficient numbers are, the closer start-up to ongoing drag will be. This is beneficial.

Lower overall CoF is not generally  beneficial for a reel drag for the reasons that were discussed.

Generally speaking, the options to changing the coefficient of friction for the same surface pair are limited to polishing and lubricating. This  can lower the both CoFs, but can bring them closer. Often a worthwhile tradeoff for most of us.

Regarding adjectives:  I can suggest an adjective for you:  "free"

You are welcome for the free overview on drag design.

-J

[Gfish]

Yes, yes. Thank you Dave, Jason, boon and everyone else for a great discussion on drag washer resistance. Research and organized writing is work, hopefully it was fun work. I definitely benefited from it. "The best things in life are free!".
The adjective comment was real, not trying to make fun of that part of it. I thought it might be fun to try and come a name for measuring that condition.

[boon]

The adjective comment was real, not trying to make fun of that part of it. I thought it might be fun to try and come a name for measuring that condition.

I'd probably go for "consistency" or one of its synonyms like "steadiness". Actually the more I roll "steadiness" around my brain the more it feels like it fits.

[jurelometer]

First, my apologies to Gfish. I misunderstood his intent on on the "adjective" comment.

Getting back to the question, here is my take:  the word you are looking for is a noun, and it is difference. I am using this definition: "A degree or amount by which things differ"

In our case: "the difference between the static and kinetic coefficient of friction". Since the static CoF will be larger than the kinetic, we can experience an instant of  higher amount of drag to start the spool turning.  This is a one shot deal for every run. Until the spool stops turning, you wont experience that static CoF again.

What we experience as an ongoing sticky drag requires something to be out of whack, like the surfaces not being well aligned and causing the clamping load to change during rotation.  There can also be differences in surface finish, corrosion and/or contamination that can temporarily increase the CoF when pairs of "bad" spots happen to to be in contact.

If the drag is sticky enough, I guess you could get into micro stops and restarts, and bring the static CoF back into play.

A drag material that has relatively high and not very different static and kinetic COFs is valuable, but the most important thing is probably a stack that maintains alignment of the surfaces under drag load.

-J