Stropping Angles

[Mark76]

When bodies are in sliding motion across each other and they are of similar hardness, there will be adhesive based wear which will include things such as fracture, welding, burnishing, etc. . If they are of very similar materials then this can be very high due to localized bonding. This is why you don’t want to use D2 to try to stamp 420J1 for example as there is too much chromium to chromium bonding and it produces high adhesive based wear.

A leather strop loaded with paste which is used on a knife will develop almost immediately metal particles on the surface, this when used again generates metal on metal contact and you get all the large mish-mash of non-abrasive interactions as you just have two pieces of the same metal grating against each other. Now it isn’t the only effect. This is complicated by the fact that you have at the same time the abrasion from the paste still happening as well.

Wow… I think you hit the nail on the head. From what I remember reading this theory has not been proposed as of yet and it makes a LOT of sense (more than any of the others I’ve seen).
[/quote]

I agree. This sounds like the first plausible theory of what is actually happening when stropping, next to abrasion! :cheer: :cheer:

Many thanks, Cliff!

A nice thing about this theory is that it is actually falsifiable. By stropping the same edge (first cleaned) with a clean unloaded leather strop we should not (or hardly) see any of the results of adhesive based wear.

Molecule Polishing: my blog about sharpening with the Wicked Edge

[wickededge]

Mark,

You’re right – I used plain cow leather with 14um diamond paste. I will try to rig up a scale under the sharpener to measure the force I’m using. I was pushing fairly hard, not hard enough to lift up the base.

-Clay

[Mark76]

Oh well, once you’re used to the WE pastes, the phrase “almost enough to lift up the base” gives a good indication of the force. I never realized it could have such an effect… :cheer:

Molecule Polishing: my blog about sharpening with the Wicked Edge

[Zamfir]

Enough pressure to almost lift the base? I had not come anywhere close to that kind of pressure. Had no idea that much was needed. I am starting to get the suction feel and I just press enough to feel that and drag the strop.

It will be interesting to see the difference when you play with different pressures. And Balsa vs cow. This is super helpful Clay! Thank you much for doing it.

[wickededge]

Enough pressure to almost lift the base? I had not come anywhere close to that kind of pressure. Had no idea that much was needed. I am starting to get the suction feel and I just press enough to feel that and drag the strop.

I don’t normally use that kind of pressure, just when I want to get a super polish. I normally use very light pressure stropping. Even so, there is definitely edge rounding that occurs unless you lower the angle.

-Clay

[wickededge]

Here’s the latest round, stropping at 19 dps. First I reset the bevel to 15 dps with the 1000# stones, then added back the 20 dps micro-bevel. Then I stropped with the 14um diamond on cow leather strops with moderate to heavy pressure at 19 dps.

20 dps with 1000# diamonds

19 dps with 14um diamond on cow leather strops

I didn’t do quite as good a job sharpening with the 1000# stones on this round, averaging a score of 268 (I must have used a little too much pressure with my final strokes.) Even so, there was a sharpness decline after using the strops at 19 dps with an average score of 308.

Attachments:

• 19dps14um.jpg
• AtAngled.jpg.jpg

-Clay

[wickededge]

I also photographed the bevels straight down onto the edge:

20 dps with 1000# diamonds

19 dps with 14um diamond and cow leather strops

Attachments:

• 20dps1000edgeon.jpg
• 19dps14umedgeon.jpg

-Clay

[wickededge]

I redid the study, again restoring the 20 dps bevel with the 1000# diamonds:

20 dps with 1000# diamond plates

and then stropped the edge with moderate to heavy pressure at 18 dps:

18 dps with diamond and cow leather strops

It seems to have added about 1 degree per side.

I tested the sharpness after restoring the 20 dps bevel: 294
and then again after stropping at 18 dps: 250

So, it looks like I could even drop the angle by one more degree to minimize rounding but I did get a pretty nice bump in edge sharpness stropping at -2 degrees.

Attachments:

• AtAnglee.jpg
• 18dps14um.jpg

-Clay

[Cliff Stamp]

Is the sharpness on a draw being affected either way? That machine does a push cut correct?

[wickededge]

Here are a couple of shots of the 18 dps stropped blade shown edge on:

The bottom one is shown with a human hair for reference.

Attachments:

• 18dps14umedgeona.jpg
• 18dps14umedgeonb.jpg

-Clay

[Josh]

that is too awesome!! Yeah I think it depends on how much pressure you use… if you are using lighter pressure, 2 dps lower is good. if you use heavier pressure, 3 dps lower is better. Can you increase by a few degrees (say 25 dps) and strop lightly to see what happens? This is great =)

[wickededge]

Is the sharpness on a draw being affected either way? That machine does a push cut correct?

I believe I can make some modifications the way the machine (Dan’s design) works so that it can do a draw cut. I’ve got it set up now with a compound table so I can put a piece of rope in the jig, apply a fixed amount of weight and then use one of the axis to draw the knife under the loaded rope. I’ll try to get a picture to explain what I mean.

Edit: uploading a video now of the idea I have for measuring draw cutting sharpness. I’ll post when the upload is complete.

Here is the video: http://youtu.be/XHFDYY4G3ok

-Clay

[wickededge]

Can you increase by a few degrees (say 25 dps) and strop lightly to see what happens?

I’ll work on this next… 🙂

-Clay

[Mark76]

Now we’re doing requests… I’d be really interested what happened if you stropped a clean edge with a plain, unloaded, strop.

Molecule Polishing: my blog about sharpening with the Wicked Edge

[wickededge]

Now we’re doing requests… I’d be really interested what happened if you stropped a clean edge with a plain, unloaded, strop.

I’ve done something like that before. It didn’t do much of anything. I also got some of the paste without any of the abrasive from our supplier. It also doesn’t do much of anything on its own.

-Clay

[Author]

Posts