Power Stropping - Ever Consider Trying It?
I used to post about this a lot years ago but got away from encouraging people to try this out themselves because it's probably not wise for everyone to go there. I do think that there's a benefit (or two) for some folks who might want to play with some different tools/equipment and maybe up their sharpening game. So here I am to start a discussion on power stropping where I'll share some of what I've learned that will hopefully keep you from making some of the same mistakes and help you to get some success for your efforts.
Since this is something that's done using power equipment I felt that this post is best put in the Shop Talk forum vs the Kitchen Knife forum where sharpening is usually discussed. Yes, this is sort of specialized for someone who has some shop space and is comfortable with being around machines with spinning parts and such.
So, what is power stropping?
Un-technically correct answer: To remove a burr, to identify and remove a wire edge, and to refine an edge to the level of proper aggressiveness for use within an intended task through the application of a powered medium (substrate) such as a belt or wheel.
What types of belts and wheels are we talking about?
Leather/cork/felt belts used on a belt grinder/sander, leather clad and buffing wheels used on buffing machines/bench grinders.
Do these belts/wheels get used as is or would be appropriate to use a compound of some sort with them?
It's rare, but not unheard of, to use belts/wheels plain or "as is", most everyone uses some sort of compound with wax based bars being the most common.
Is there a specific combination that works best?
Ask 100 sharpeners and knifemakers that question and you'll likely receive as many varying answers. You could have asked me this question every 6 months for the last 7 yrs and received a different answer each time. Part of the fun, and yeah - frustration, is the experiments you can conduct by playing with the variables.
I currently use leather belts with a combination of green rouge & diamond spray for 85% of Japanese knives, for German knives I use a slotted paper wheel with white rouge, and for axes/meat cleavers/etc I use super hard buffing wheels with black & white rouge.
Some things to consider is that some compounds can reduce a wire while others raise a burr so what you use and when you use it factors in. For instance, if I use white compound on a leather belt I will very quickly remove burrs from a Japanese knife but make too many passes on this combo and quickly a burr will form again and that's just because most white compounds cut steel pretty aggressively. Now flip this to using a buffing wheel with white compound and you'll quickly see that you'll get a slick (very burr free edge) and that's because buffing wheels tend to round edges and the white compound cuts fast. Change the compound used in both of those scenarios to say green and you'll get completely different results and that's because green often contains chromium oxide which is spherical in shape thus cutting different than the sharper edged (white) aluminum oxide particles. Also, it should be noted that each and every compound found is different meaning that white isn't just white - there's lots of differences between each manufacturer and even within their lines. You will see some bars that are dry and other super greasy, more experimentation for you.
The same thing can be said of diamond and CBN compounds, just so many variations to play with. You have sprays, powders, pastes, slurry, suspensions & even solids to contend with. This could be it's own thread subject so I won't go into details here, it just needs to be known that there's many options for you to try if you're so inclined.
How the heck do you use (or apply) these compounds to the belts or wheels?
Compounds that come in bar form are directly applied to the rotating substrate.
Compounds that are in paste form are best applied by hand while the substrate is not in motion, well unless you want to paint your shop a pretty color. Even still pastes are going to want to leave the belt/wheel on start up so beware. I don't use pastes anymore but when I did I would rub "just enough" into the surface and put up a back splash to catch the waste.
As I mentioned above I do use diamond spray on a leather belt and yeah this is messy but I continue with it because of unequaled results I achieve. I spray while the belt is in motion and find that enough remains on the surface to work effectively, it's somewhat wasteful though. If you're fortunate enough to have speed control then I would suggest turning the RPM's down and keep more compound on the substrate.
What size leather/cork/felt belts are available?
It's important to realize what availability of belts you have before purchasing a grinder/sander. The most common sizes are (in order), 2x72, 2x48, 1x42, 1x30, 4x36
If you have a machine outside of those sizes you're likely screwed here and even the 4x36 size won't be easy to find belts for. I use a 2x48 and find it challanging to acquire belts.
Are there different types of leather belts available?
Yes and no....yes in that you can find a couple of different makers but no in that they're pretty much all the same. The most common leather belts found are the 5/6oz Surgi-Sharp belts. These are OK but they stretch something fierce but they have solid glue joints.
I've tried to have custom leather belts made by many leather workers over the years and everyone has failed in one way or the other. They either use leather with too much give, leather that's too stiff and won't flex around the wheels, waxy leather that won't hold compounds, leather that insta-stretches, or most commonly comes apart way too easily at the seem. For a brief time I was constructing my own leather belts and had enough mixed (mostly not so great) results that I scrapped the project. Now I've just come to realize that I will order leather belts at 2 a month forever and like it.
What type and size of leather wheels are available?
There's a company who makes solid leather wheels in small sizes, they're OK but difficult to use because the machine housing gets in the way. There's also an 8" (I think) wood wheel with leather cladding but my preference for a leather wheel set up is the synthetic leather Tormek wheel mounted to a Baldor buffer. I like using a buffer because the motor housing is low profile providing proper blade clearance in use. Leather wheels are longer lasting than leather belts because they don't stretch but it's MUCH easier to round an edge with a wheel than with a belt.
What kind of results could I expect from power stropping?
Well, even if I gave you the exact recipe that I use and trained you personally you may have problems. Like everything in life there's a learning curve. Poke around the internet and search for people's opinions on power stropping and you'll find most hate it and speak badly of it. I think that these folks are correct but also I think that they gave up before the got the hang of it. Again, it's experimentation here folks.
What type of machine would you recommend for someone who just wants to try this out?
The cheapest most easiest set up I can think of is the Harbor Freight 1x30 mini belt sander and Surgi-Sharp leather belt. This machine isn't at all a good machine but it's cheap enough for a try, probably like $40 (ish?).
My first belt sander was one of these HF 1x30's (seen directly above with a crap waxy leather belt) that I flipped over onto it's back to present me with a horizontal belt running away from me. You can get crazy and make a frame or just simply re-mount the base plate on the back side and then clamp it to a table - shazam!
So what's the deal with testing for a wire edge?
Not to get too complicated here....when using a leather belt to de-burr you will first see the burr fly off the edge but if you continue to make passes (under pressure) you may (and hopefully not) see what appears to be another burr popping up along the edge. Yes this could be a burr coming from too many passes or the wrong compound being used (as explained above) but if you keep going and see this fly away or disappear then you've just seen a wire edge leaving your knife. If it keeps coming back then you're creating a burr. This is a neat test to see how tough you're making your edges, most people's sharpening work fail this test miserably or if they pass the edge is seen as way too slick. I've personally fought with all these issues over the years but because of all my experimentation I now know how to get a tough edge that still has bite - to me that's what is the best.
You didn't really cover buffing wheels, why?
Because they're dangerous. I use them myself but I'm not going to recommend them. If you do go there please be careful - buffing wheels like to grab edges and pull knives from hands.
Got any tips for using leather belts and wheels?
Yeah....most importantly - don't leave a leather belt on a machine under tension while not in use, they like to stretch. To clean the leather use a light oil on a rag. To refresh (or smooth) use sandpaper. Hone on the platen - never in the slack section - using the slack section will round even a thick convex edge (like found on a meat cleaver) and when working on thin Japanese knives the slack section will destroy all your sharpening work straight away.
So there you have my thoughts on power stropping. If you have any questions please ask away here and if you give it a shot please share your results, I'd love to see what you get into.
Dave, Great write up. Thanks for sharing a bit of your expertise.
Used to do this in the met lab on diamond wheels and alumina wheels but that was 20 years ago, before I knew what I was doing. We used flat platens .
Great and comprehensive write-up.
I started doing this a couple of years ago on a Kalamazoo 1x42 (Surgi-Sharp leather and chrome oxide), and I have no desire to go back to manual stropping.
Good write up Dave. Thanks! I recently got myself a Kalamazoo 1 x 42. It's awesome and fun too.
What diamond spray sre you getting your good results with?
looks like i'm shipping these things over to my country =D
I hope to see some pics of your set ups.
Used to do this with cheaper knives on leather and felt wheels. Still do every now and again but prefer hand stropping with anything decent as never felt as controllable on a wheel. Stropping belts appear to be unobtainable in the UK so have ummed and ahd about importing a few times, but shipping and tax is the killer. Is on the list for next time I'm in the states for sure.
Getting there, kind of.