Polishing Washers

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toocool006
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Polishing Washers

#1

Post by toocool006 »

I've read quite a few posts here and elsewhere about folks polishing up PB washers for slicker action. What tools are typically used to do the polishing? It would make me nervous to remove material from the washers given the exacting tolerances at play. Thanks for any input y'all can provide!
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abbazaba
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Re: Polishing Washers

#2

Post by abbazaba »

I've used 1500 grit and 3000 grit automotive sand paper with success many many times. Lay the sand paper on a flat surface and polish each side by moving the washer small circles with light pressure as evenly as possible with your finger until all of the tarnish has been removed. This is when any dishing or raised edge of the washer will be exposed in the tarnish.

Then just clean with alcohol and put a dab of nano lube during reassembly. This is also a good time to inspect the inside of the knife for burrs and uneven wear marks that can sometimes benefit from some light sanding.

In my experience you'd have to really go crazy to screw it up. Washers are cheap if you do somehow ruin one. There is probably a video or two out there as well.
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Re: Polishing Washers

#3

Post by anycal »

I rub mine on ultra-fine tri-angle stone (or any fine stone), index finger on top of washer, rotating it once in a while. Not too long, not too much pressure. I can see spots where the washer took a polish.
Last edited by anycal on Tue Jan 22, 2019 9:50 pm, edited 1 time in total.
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Re: Polishing Washers

#4

Post by toocool006 »

abbazaba wrote:
Tue Jan 22, 2019 9:40 pm
I've used 1500 grit and 3000 grit automotive sand paper with success many many times. Lay the sand paper on a flat surface and polish each side by moving the washer small circles with light pressure as evenly as possible with your finger until all of the tarnish has been removed. This is when any dishing or raised edge of the washer will be exposed in the tarnish.

Then just clean with alcohol and put a dab of nano lube during reassembly. This is also a good time to inspect the inside of the knife for burrs and uneven wear marks that can sometimes benefit from some light sanding.

In my experience you'd have to really go crazy to screw it up. Washers are cheap if you do somehow ruin one. There is probably a video or two out there as well.
Thanks for the pointers, Ian!
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Re: Polishing Washers

#5

Post by toocool006 »

anycal wrote:
Tue Jan 22, 2019 9:48 pm
I rub mine on ultra-fine tri-angle stone (or any fine stone), index finger on top of washer, rotating it once in a while. Not too long, not too much pressure. I can see spots where the washer took a polish.
This sounds like a great method too, thanks Peter!
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Re: Polishing Washers

#6

Post by toxophilus »

I use a partially cracked Chosera 10,000 grit stone from my Edge Pro, a few drops of oil and use a circular motion till it's nice & shiny; remember you're 'polishing', not removing metal... sorta like polishing the finish on a car :spyder:
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Re: Polishing Washers

#7

Post by Bloke »

toxophilus wrote:
Tue Jan 22, 2019 9:57 pm
... sorta like polishing the finish on a car :spyder:
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Re: Polishing Washers

#8

Post by crazywednesday »

anycal wrote:
Tue Jan 22, 2019 9:48 pm
I rub mine on ultra-fine tri-angle stone (or any fine stone), index finger on top of washer, rotating it once in a while. Not too long, not too much pressure. I can see spots where the washer took a polish.
Exactly how I do it.
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Re: Polishing Washers

#9

Post by JacksonKnives »

One thing to remember with lapping bearing surfaces: once you knock down any obvious ridges or bumps, fit and thickness/flatness are far more important than smoothness. Binding/slop matters, finish doesn't. A polished surface and a marred surface have the same coefficient of friction, since the same amount of weight is borne per square inch of rubbing material either way. [edit: this is a bit of an inaccurate way to phrase the problem. See my clarification below.]

The holes or grooves you find in some washers/bushings will allow you to "store" grease/oil for longer-term dispersal, but the amount of friction is the same until you change the material or put in bearings.
Last edited by JacksonKnives on Wed Jan 23, 2019 12:44 pm, edited 1 time in total.
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Re: Polishing Washers

#10

Post by Daveho »

The tolerances arnt that tight here given that the pivot can simply be adjusted.
I have a dragons tongue stone I occasionally smooth a washer on but not all that often
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Re: Polishing Washers

#11

Post by Pelagic »

I use my wood strops loaded with compound plus diamond powder. Fast and easy.
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Re: Polishing Washers

#12

Post by ChrisinHove »

Rigid strop and blue compound for the washers. Cloth and compound for the mating surfaces.
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Re: Polishing Washers

#13

Post by freebird610 »

leather strop with green compound occasionally.
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Re: Polishing Washers

#14

Post by toxophilus »

Bloke wrote:
Tue Jan 22, 2019 11:11 pm
toxophilus wrote:
Tue Jan 22, 2019 9:57 pm
... sorta like polishing the finish on a car :spyder:
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ROFLMFAO!!!
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Re: Polishing Washers

#15

Post by toocool006 »

JacksonKnives wrote:
Wed Jan 23, 2019 12:01 am
One thing to remember with lapping bearing surfaces: fit and thickness/flatness are far more important than smoothness. Binding/slop matters, finish doesn't. A polished surface and a marred surface have the same coefficient of friction, since the same amount of weight is borne per square inch of rubbing material either way.
The holes or grooves you find in some washers/bushings will allow you to "store" grease/oil for longer-term dispersal, but the amount of friction is the same until you change the material or put in bearings.
This is really interesting. Is it possible that lapping (if done accurately) would bring some microscopic increase to the flatness of the surfaces in question?

I'm finding it hard to follow the argument that a marred surface has the same coefficient of friction - my sens is that there would be some amount of mico-binding vs a polished surface. Why isn't that so?
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Re: Polishing Washers

#16

Post by JacksonKnives »

toocool006 wrote:
Wed Jan 23, 2019 11:13 am

This is really interesting. Is it possible that lapping (if done accurately) would bring some microscopic increase to the flatness of the surfaces in question?

I'm finding it hard to follow the argument that a marred surface has the same coefficient of friction - my sens is that there would be some amount of mico-binding vs a polished surface. Why isn't that so?
If you can make two surfaces truly flat to a molecular level, they actually stick together. Gauge blocks machinists use are actually pretty hard to get apart if you "ring" them together.

No doubt I'm forgetting something about the way friction and surface finish work out, but if you read the textbooks and other reference material they all have the same note.

*edit* I misspoke. I'm remembering something I read about perforated washers after investigating the advantages of CRK's design in the Sebenza

It's not accurate to say that "surface finish doesn't matter." Obviously, a badly-machined surface is going to cause more friction. But why?
Evenness is important. You don't want to machine in a way that will leave ridges that can interlock, but if nothing is binding then you're just left with the friction properties of the material.

So long as the peak, load-bearing surfaces are even and spread the same load over the same area, the amount of load per area over the surface of the washer is the same no matter what you try to do. If you cut holes in your washer, or add ribs, or do anything to reduce the contact surface, you're increasing the amount of force borne by those contact points and your design feature is cancelled.

Dirt and uneven ridges or bumps will obviously change the dynamics of the washer when it's moving, but once you get the washer flat it's hard to increase its efficiency. Once the surface has an even finish and there are no unusually high peaks on either side, you're just getting more and more microscopic peaks to bear the weight, which means more and more surface area rubbing.

Contrast polishing a slightly-uneven washer (with one point that's thicker than the rest of the washer) with compound to sanding that same slightly-uneven washer with 400-grit paper to get an even thickness. Making the surface area even means you're actually changing the contact area that rubs when you tighten the pivot. Polishing the washer can only very slightly improve the characteristics of the contact patch that's already rubbing.

In my actual experience with knives, the washers are rarely cupped or un-polished. They are, fairly often, bent enough to make two "sides" (e.g. 3 o'clock and 9 o'clock if you think of the washer as a clock face) bear more load on one side (and of course the opposite pattern on the other side.) The surface finish is almost always rougher on the knife blade, but the fact that the finishing lines are parallel on the knife (or, better yet, stonewashed) means it doesn't cause many problems. I feel that the knife is smoother if I can flatten the washer, but I know I'm almost always getting the same result with a good cleaning.

Also note that if you use any kind of lubrication, the effect of surface finish is basically nil. The residue left when your lube dries out is far more important than surface finish in that case.
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Re: Polishing Washers

#17

Post by JacksonKnives »

Daveho wrote:
Wed Jan 23, 2019 1:28 am
The tolerances arnt that tight here given that the pivot can simply be adjusted.
I have a dragons tongue stone I occasionally smooth a washer on but not all that often
I actually agree with this, in principle, given that the washers as they come from the factory are pretty good. But many of us are chasing smoothness with zero blade play, so we try weird things to see what happens. :)

A precise fit of perfectly-even washers with perfectly-even mating surfaces on the blade means that you can adjust the amount of tension on the pivot screw until you hit the effective friction coefficient of the material. That should be, in theory, the best pivot smoothness you can achieve without bearings.

In my experience, though, the tension of handle screws (and sizing of spacers/standoffs and the holes they sit in) has almost as much influence on blade play and smoothness. You can't just assume that the scales/liners are mathematically flat parallel planes and blame all the binding on unpolished washers.

So, the tolerances aren't "tight" in terms of what we can achieve with lapping of washers, but the tolerances that influence how much blade play/friction we can perceive are *very* small.
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Re: Polishing Washers

#18

Post by toocool006 »

JacksonKnives wrote:
Wed Jan 23, 2019 11:57 am
toocool006 wrote:
Wed Jan 23, 2019 11:13 am

This is really interesting. Is it possible that lapping (if done accurately) would bring some microscopic increase to the flatness of the surfaces in question?

I'm finding it hard to follow the argument that a marred surface has the same coefficient of friction - my sens is that there would be some amount of mico-binding vs a polished surface. Why isn't that so?
If you can make two surfaces truly flat to a molecular level, they actually stick together. Gauge blocks machinists use are actually pretty hard to get apart if you "ring" them together.

No doubt I'm forgetting something about the way friction and surface finish work out, but if you read the textbooks and other reference material they all have the same note.

*edit* I misspoke. I'm remembering something I read about perforated washers after investigating the advantages of CRK's design in the Sebenza

It's not accurate to say that "surface finish doesn't matter." Obviously, a badly-machined surface is going to cause more friction. But why?
Evenness is important. You don't want to machine in a way that will leave ridges that can interlock, but if nothing is binding then you're just left with the friction properties of the material.

So long as the peak, load-bearing surfaces are even and spread the same load over the same area, the amount of load per area over the surface of the washer is the same no matter what you try to do. If you cut holes in your washer, or add ribs, or do anything to reduce the contact surface, you're increasing the amount of force borne by those contact points and your design feature is cancelled.

Dirt and uneven ridges or bumps will obviously change the dynamics of the washer when it's moving, but once you get the washer flat it's hard to increase its efficiency. Once the surface has an even finish and there are no unusually high peaks on either side, you're just getting more and more microscopic peaks to bear the weight, which means more and more surface area rubbing.

Contrast polishing a slightly-uneven washer (with one point that's thicker than the rest of the washer) with compound to sanding that same slightly-uneven washer with 400-grit paper to get an even thickness. Making the surface area even means you're actually changing the contact area that rubs when you tighten the pivot. Polishing the washer can only very slightly improve the characteristics of the contact patch that's already rubbing.

In my actual experience with knives, the washers are rarely cupped or un-polished. They are, fairly often, bent enough to make two "sides" (e.g. 3 o'clock and 9 o'clock if you think of the washer as a clock face) bear more load on one side (and of course the opposite pattern on the other side.) The surface finish is almost always rougher on the knife blade, but the fact that the finishing lines are parallel on the knife (or, better yet, stonewashed) means it doesn't cause many problems. I feel that the knife is smoother if I can flatten the washer, but I know I'm almost always getting the same result with a good cleaning.
Thanks for taking the time, this is very well explained and giving me a greater appreciation for and understanding of the levels of machining involved.

I googled Gauge Blocks (of which I was previously completely ignorant) to see the see the sticking together you described - https://youtu.be/2lOOl3VxOtE - wow physics is so cool. What an amazing world we live in!
~andrew
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Re: Polishing Washers

#19

Post by Evil D »

All the washers I've seen are fairly smooth, I'd look more into polishing the grind lines off the tang and polish the liners that contact the washers. Seems like that would yield better results.
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Re: Polishing Washers

#20

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