Polished edge

[flava]

Yesterday I took my brand new Dremel Pro tool and "refurbished" the blade of the old Buck Oddyssey I have. I use this folder quite a lot and the blade was full of scratches. While bringing it to a mirror finish (or close to it) I had no other choice but buff the edge too. I was thinking it will probably dull the knife but didn't care much. The result was quite unexpected. The edge has the same angle but it's high polished and I can tell you it cuts WAY better since! The knife was tested on cardboard and performed very well. I used to sharpen the knife on medium Arkansas plus fine ceramic but I never got an edge that cuts so well (on this knife at least). How come such a small difference in the polish makes a lot of difference in cutting?

 

[Cliff Stamp]

A higher polished edge will generate less friction along the edge bevels and thus you would expect it to cut with less drag. This effect has been studied in detail in the woodworking industry and found to be insignificant as long as the grind lines are running into the edge, parallel with the direction of motion of the blade. This is why you should never sharpen with circular motions. I have also looked at this for knives and could not see any significant difference between knives ran with a high polish on the flats vs a coarse one when the edges were at the same level of aggression, .1 mm deep microbevel. To be specific, going from a 1000 to 4000 polish on the flats produced significant gain in cutting performance.

It could simply be that the greater polish of the Dremel gave an edge that was formed with a smaller depth of microteeth, as polishes can go up to 0.5 micron and even the finest hones (8000 grit waterstone) are twice as coarse. If this is the case then the edge would push cut through material with greater ease. It is also possible that the buffing gave a cleaner edge. I have found that with finishing edges that they are cleaner after a light stropping. Checking the edge under magnification you can see debris in the form of abrasive and metal on the edge after honing, this is particularly true with diamond rods. This is why I have taken to giving the edges a few passes on canvas loaded with wax after honing. It is not abrasive enough to remove any amount of material, it just cleans up the blade.

Of course it could also just be that you simply put a better edge on the blade with the Dremel in terms of alignment and consistency of grind. I have found in the past that I can often achieve better results with poorer materials simply because I am more familiar with them.

-Cliff

 

[matthew rapaport]

This effect has been studied in detail in the woodworking industry and found to be insignificant as long as the grind lines are running into the edge, parallel with the direction of motion of the blade.

Now that's interesting. Makes intuitive sense too. For a push cut, the grind lines would end up perpendicular to the edge. What about in a slice? There is still a downward component, but also a front-to-back. I would guess that perpendicular microteeth would still be more effective even when the knife saws back and forth. I had to saw (with a straight edge) through really thick cardboard (push would not do it) just recently and reported on it just yesterday over here: <a href="http://www.bladeforums.com/forums/showthread.php?s=&threadid=185970" target="_blank">over here</a>. Even more interesting, my DMT alignment kit instructions recommend making one last sweep with the stone along the arc of an edge from back to front, on both sides! I always thought that this was to smooth out any points hit slightly unevenly due to the need to move a fixed width stone from point to point along the edge for the whole of the sharpening process. I hadn't thought of what a difference that might make on a pure push-cutting test like shaving, or sawing thick cardboard, but I'll give it a try.

This is why I have taken to giving the edges a few passes on canvas loaded with wax after honing. It is not abrasive enough to remove any amount of material, it just cleans up the blade.

Is this better than a rinse in water and wipe with a dry towel?

 

[Cliff Stamp]

Matthew :

What about in a slice? There is still a downward component, but also a front-to-back.

Yes, and this motion does grate directly across the grind lines, however the force exerted against the sides of the edge of a blade in a slice is far less than in a push cut, so it would make sense to optomize for the latter in regards to drag. When you slice into material, you haul a little bit of it along with the blade and thus reduce the binding. When you push cut, you just mash it down, compressing the material which greatly increases the binding.

[canvas]

Is this better than a rinse in water and wipe with a dry towel?

I would avoid water mainly because of the corrosive aspects. The wax on the canvas will also act as a mild lubricant and corrosion inhibitor, plus it will act to lightly align the edge. But you could make do with any clean material and just use a stropping motion.

-Cliff

 

[Jameson]

Cliff S.,

What do you mean avoid water for corrosive reasons. Sure if you are in the field maybe and water is precious, or all at hand is saltwater (rare but possible). But this guy is obvioulsy talking aobut his home, how would rinsing the blade under FRESH tap water (Poland Spring if your so inclined) and wiping it w/ a paper towel be exposing the blade/edge to ANY corrosive aspects? Does the flouride or trace amts of chlorine in tap water really make it corrosive?

JC

 

[Cliff Stamp]

Jameson :

how would rinsing the blade under FRESH tap water (Poland Spring if your so inclined) and wiping it w/ a paper towel be exposing the blade/edge to ANY corrosive aspects?

A few days ago I was reworking the edge on an A2 blade on a belt sander, using tap water to cool the blade after each pass. After I finished the last pass I went upstairs to check the edge under magnification. Less than five minutes after the last pass, I noticed the whole side of the edge bevel had visibly rusted. This is a worse case senario for corrosion as the temperature is high, and the finish was low (100 grit cheap AO belt).

That being said, the blades obviously do come into contact with water from time to time, both fresh as well as salt water and even worse like acidic foods etc. . It is not like the edge will instantly be destroyed if you rinse it off, and if corrosion was the only aspect I would not go out of my way to use the canvas. However as noted in the above there are more reasons to use the rough side of the strop. In addition to what I mentioned previously, it also improves the edge, by alignment and a small amount of abrasion.


-Cliff

 

[Jerry Hossom]

Flava, in my judgement you did a couple things that made that edge "better". Polishing certainly made it cut smoother, with less drag, but you also created a convex edge in the process, rounding over the shoulder of the bevel that is created by using a fixed angle sharpener, reducing drag even further. The more that shoulder is rounded, the less drag through a cut. It makes a huge difference in most cutting tasks, including chopping. Further, the more it's polished the more corrosion resistant the edge is, avoiding the problem Cliff cited. Corrosion can be an important component of dulling as can microchipping, both of which are reduced by polishing. SO you made your blade cut better and likely made it cut better longer in the same process.

 

[wolfmann601]

I am just learning. I am using a digital Dremel to try to put a nice Polish on a CRKT. Being the NEWBIE, I am getting serious swirls and cannot seem to get that "sheen" and "smoothness" to the blade as I thought I could. Right now I am sticking with jeweler's rouge, white Polish and just felt wheels. I run at about 9,000 RPM with very light pressure, with the blade secured in a vice. No can do!!!! Since the topic of a DREMEL was mentioned, what the heck I am doing RIGHT??? [I know I am doing everything wrong, hence the CRKT as the Guinea pig]

Thanks for the help...........wolf

 

[Jeff Clark]

One reason that the polish helps is due to the high-drag nature of cardboard. Cardboard has a moderately high friction coefficient and is wide and elastic enough to bind on the side of the blade. You may see greater benefit to a polished blade in carboard than in many other materials. A narrow and thin blade will work even better.

 

[Cliff Stamp]

Wolfman, the problem with a Dremel is that the contact area is low and thus you tend to polish very unevenly. As well, if you are going to do this, you really want a better buffing compound. Jewlers Rouge is meant for very soft materials like Brass.

Jerry :

[convex edge]

rounding over the shoulder of the bevel that is created by using a fixed angle sharpener, reducing drag even further.

This is certainly true in general, however I doubt that the Dremel removed enough metal to really make this significant in this case.

It is an interesting aspect of performance though, as in theory you don't lose much in the way of cross section, and you should see an increase in both cutting ability and durability. I would be curious however as to the extent of the increase, assuming of course that the shoulder was just modified to take out the sharp transition, not actually lowered enough to modify the edge profile as a whole.

I might look at this on the weekend, as I have some cutting to do with a freshly v-ground blade so I can compare its ability with the same edge profile with and without the sharp transition.

-Cliff

 

[johnniet]

OK dammit, I want a Dremel! What kind and accessories should I get? I want to be able to do whatever Flava did, as well as general modifications, maybe use it for other things around the house also.

 

[wolfmann601]

Cliff:
What do you suggest that I use for a polishing compound. Also what is a good "rpm" to work at? I kind of enjoy using the dremel as I just do not have the manual detexirity to run power tools of ANY kind without Trauma
I use a Digital Rotary and have bought just about every attachment. Now I need help finding what compounds I should use to take a blade and put a "Brend-like" finish on it..........Thanks...............Ira

 

[Cougar Allen]

I've had the same experience as Cliff wet-sanding an edge -- it'll rust literally in minutes -- even when highly polished. The wet-sanding takes off all the oil and naked steel with no oil or grease or even dirt on it is so susceptible to rusting that just plain tap water eats into it like acid. Just set it down wet while you answer the phone and by the time you come back it's rusty -- not just a little rusty, either; rusty enough to ruin the edge.

That little bit of oil that is nearly always on steel makes a big difference. If you thoroughly degrease a piece of bright polished steel with solvent and set a coin on it and breathe on it and then lay it aside a few minutes, when you come back you'll see the round unrusted area where the coin protected it from the moisture that condensed from your breath -- all the area around that circle will be rusty. Try it....

 

[wolfmann601]

but now I am somewhat confused (what else is new)OK, when using stones, they should be dry, even if they are oil or "wet stones"??? Yes or no.

To take a stain finish and remove the fine scratches and restore the finish to a mirror, I need to NOT rely on Jeweler's rouge but need a little more abrasive compound???What?

To Strop, It's best to use the UNFINISHED side of a belt. Load it with Jeweler's rouge???? Now I am lost.... I finally nailed down the corect "way" to sharpen. I also seem to come out with a nice polished edge, which I prefer over the "toothy edge" I was getting. But am I using my tools CORRECTLY?

And as far as the Dremel to restore that fine morror finish that I like, I REALLY enjoy the Dremel. I just cannot figure out how to NOT end up with those damn swirls.

and then to finish, I use a Mil-tec/Rem-oil combo and a blow-dryer. I then Tuff-coth my knives regularily.

What am I doing RIGHT and WRONG....Please help me!!!(LOL)
Thanks.....Ira

 

[Cougar Allen]

but now I am somewhat confused (what else is new)OK, when using stones, they should be dry, even if they are oil or "wet stones"??? Yes or no.

Most of us don't use oil even on oilstones -- we either use them dry or use water.

Don't let my post above scare you away from using water -- just wipe the knife off and oil it when you're done -- and if the phone rings wipe it off before you answer the phone.

To take a stain finish and remove the fine scratches and restore the finish to a mirror, I need to NOT rely on Jeweler's rouge but need a little more abrasive compound???What?

Rouge is for finishing; it would take years to polish out a deep scratch with it. There are a lot of faster-cutting polishes around; in fact just about everything cuts faster than rouge.

I personally don't like rouge even for finishing -- it does work; it's been used for thousands of years to polish metals, glass, and gemstones -- but it has a nasty tendency for the particles to clump together and make sleeks. You're almost to a perfect mirror finish and then the damn stuff makes a sleek and you have to polish that out, and while you're doing that it makes another sleek ... I hate the stuff. Some people like it, though; YMMV.

I usually finish with tripoli compound on leather. If I want a finer polish than that I use Raybrite A, a submicron aluminum oxide that's available from rockshops. We all have our own pet methods, though; and most of them work -- my way is not the only way.

To Strop, It's best to use the UNFINISHED side of a belt.

That is an endless argument -- people have been arguing whether the smooth side or the rough side of the leather is better since the neolithic revolution and I expect they will still be arguing when the sun expands into a red giant 6,000,000,000 years from now. There's no reason they should ever stop arguing about it because it makes no difference.

If you're using an old belt that's painted on the smooth side don't use the painted side, though -- unless you remove the paint.

Load it with Jeweler's rouge????

Whatever polish you use you don't need much of it. When you first load the strop with polish and start stropping the polish gets rubbed into the pores of the leather and the excess falls away and then you're all set for a long time to come. It may look like there's no polish left on your strop but there is, and if you put more on it won't work any better.

And as far as the Dremel to restore that fine morror finish that I like, I REALLY enjoy the Dremel. I just cannot figure out how to NOT end up with those damn swirls.

Finish stropping by hand. Or do it all by hand in the first place ... Dremel tools are really not labor-saving devices.

 

[flava]

Originally posted by wolfmann601
I am just learning. I am using a digital Dremel to try to put a nice Polish on a CRKT. Being the NEWBIE, I am getting serious swirls and cannot seem to get that "sheen" and "smoothness" to the blade as I thought I could. Right now I am sticking with jeweler's rouge, white Polish and just felt wheels. I run at about 9,000 RPM with very light pressure, with the blade secured in a vice. No can do!!!! Since the topic of a DREMEL was mentioned, what the heck I am doing RIGHT??? [I know I am doing everything wrong, hence the CRKT as the Guinea pig]

Thanks for the help...........wolf

Wolfman,

I'm no Dremel expert but I'll describe how I polish a blade, using the red compound and small felt wheels.
I get a bunch of compound on the wheel running at 5000, then work on the blade at 12000 apllying a moderate pressure and avoiding to stay too much time one a spot. I do short sessions like 1 minute or so, clean&check the blade then start again. When the blade starts to look kinda cool, I go down at 8000 and lighter pressure and run the wheel all along the blade faster than at 12000. After a few sessions like that I go to 5000 with very light pressure and uniforme moves.
This works OK if the blade has very shallow scratches only, the deep one will still be there. To get rid of deeper (but not deep) scratches I start with the stainless brush at 12000-14000 and if it works too slow I use a fine sanding wheel. If you go for the sanding wheel, be exremly carefull since it eats metal faster than you would think and you could ruin the blade. Let's say you didn't ruin it, you have a blade free of deep scratches but buttugly and uneven, here is where you forget the Dremel and get some sandpaper, 280 should work fine. You handrubb the heck out of it then you switch to 360 or 400 and kepp sanding until you have a fine uniform finish with extemly shallow and uniform scartches, or until you get tired of it. When you achieve this you switch to the Dremel with the felt wheel and polish it. If the polish doesn't get as good as you expect, you can always put a handrubbed finish back in no time.
Hope I make sense and that it helps.

 

[flava]

Originally posted by johnniet
OK dammit, I want a Dremel! What kind and accessories should I get? I want to be able to do whatever Flava did, as well as general modifications, maybe use it for other things around the house also.

Get them all.
The basic kit would be grind wheels, sanding rolls, felt wheels, polish compound, maybe brushes. But you'll end up buying them all anyway.

 

[Duck]

LiL OT but ....Cant toothpaste also be used as a fine polish..IIRC I read a artical wayyyyyyyyyy back about using toothpaste to smooth out the action on a revolver..

 

[Jerry Hossom]

Revolver parts are not hardened steel.

 

[Mutant]

Duck,

Read the same thing about using toothpaste to smooth out the gears in a fishing reel. I've used it for polishing brass when I had nothing else. It gets sticky messy but it works.