Thinning knives with powered tools instead of elbow grease

[Chasingsharpness]

So each time I thin a knife by hand on stones my dodgy elbow tendons start protesting about 30-45mins in. Also even with the coarsest fastest stones, it feels like it takes too long to remove a significant amount of material.

I was wondering what are my options for thinning knives with something other than elbow grease? I'd also like to avoid ruining the heat treatment of the blade if possible. Are belts with water dipping the best option? I've seen a few rotating stones. They seem ideal but hard to find.

 

[HumbleHomeCook]

I've used a 1" vertical belt sander with no adverse HT affects. Quality, fresh belts is key. I also kept a bin of water next to the sander and would dunk after every pass. Passes were somewhat light, steady, full end-to-end and a "medium" pace. When I had a trouble spot I would still do a full pass but just apply a slight bit more pressure in that spot and repeat until satisfied.

No gloves and don't let it get hot to the touch.

Now, that was on a Wok Shop cleaver that I had absolutely no aesthetic concerns about. Just like with manual thinning, effective material removal is done with coarse abrasives. That means deep scratches and in the case of power tools, that can mean very deep scratches very quickly.

I would practice before trying on something nice.

 

[blokey]

Thinning with grinder should be fine, the heat will only affect a very shallow layer on the surface, but avoid using it for the edge. Can’t speak on the evenness tho.
https://knifesteelnerds.com/2019/04/08/does-sharpening-with-a-grinder-ruin-your-edge/

 

[Chasingsharpness]

Many thanks for the info. I'll have a look at some options for belts, if anyone has any recommendations that would be appreciated. I don't have much space or a ventilated workshop and I assume there will be dust, so I'll try and find something I can set up outdoors in the garden when needed.

Thank you I'll check out that knifesteelnerds article. I only intend to touch the side of the knife and not the edge on the belt, I wasn't sure if the heat would transfer down deeper into the knife into what will be the edge. I'm not too bothered about scratch patterns or anything cosmetic.

 

[deltaplex]

You can do a lot with a 3"x21" (76mmx533mm) belt sander and a dunk tank next to it for cooling. I have a well ventilated area and I still use a half mask respirator when I'm operating mine.

 

[NickMinton]

Check out videos by district cutlery on YouTube, they do high volume thinning and reprofiling via belt sanders with great success, including usage of an ice bath after each pass. Ryan (guy in the videos) is highly highly regarded here

District cutlery

 

[coxhaus]

Check out videos by district cutlery on YouTube, they do high volume thinning and reprofiling via belt sanders with great success, including usage of an ice bath after each pass. Ryan (guy in the videos) is highly highly regarded here

District cutlery

That looks good to me. It is what I try to do. I don't have room for those big machines, so I use a Worksharp Ken Onion outside on my picnic table.
I am still using leather, but I will look for a felt belt next time.

If I don't let my knives get too dull, I can resharpen using just my leather belt that removes less steel than starting from scratch every time.

 

[Chasingsharpness]

That looks good to me. It is what I try to do. I don't have room for those big machines, so I use a Worksharp Ken Onion outside on my picnic table.
I am still using leather, but I will look for a felt belt next time.

Do you use the worksharp for sharpening or can it work for thinning?

 

[coxhaus]

Do you use the worksharp for sharpening or can it work for thinning?

I do what he was doing.

I probably go to higher belts on the initial sharpening.

 

[user 37848]

You can do a lot with a 3"x21" (76mmx533mm) belt sander and a dunk tank next to it for cooling. I have a well ventilated area and I still use a half mask respirator when I'm operating mine.

This is the way. It's like a motorized stone

 

[HumbleHomeCook]

Check out videos by district cutlery on YouTube, they do high volume thinning and reprofiling via belt sanders with great success, including usage of an ice bath after each pass. Ryan (guy in the videos) is highly highly regarded here

District cutlery

He's just sharpening there. Thinning will be much more aggressive.

 

[NickMinton]

He's just sharpening there. Thinning will be much more aggressive.

Yeah, I hear ya. I’ll try to find the video where he does some thinning but I meant it as a general showing of
Using a belt grinder and water bath

 

[TB_London]

Vari speed is your friend. Belt grinders are good for material removal but need practice to get good consistent grinds. Disc grinders are easier to keep stuff flat and even on - I tend to use after a belt to even it all out.

A big horizontal stone is the dream.

In a pinch anything that moves abrasive can work- even a random orbital sander can be used for a nice satin finish if you want to mask errant scratches from thinning attempts.

 

[coxhaus]

Using power makes sharpening fast for knives. You are done in a minute or 2. I have 30 active knives, so I don't want to spend a lot of time sharpening by hand.

 

[Genghis_F]

Andrew Bishop has this video


I have not tried it but some people I’ve talked with have had good results
Despite the dodgy setup

 

[HumbleHomeCook]

Using power makes sharpening fast for knives. You are done in a minute or 2. I have 30 active knives, so I don't want to spend a lot of time sharpening by hand.

This is about thinning the knives not sharpening the edge.

 

[mike59]

Belt suggestions .... I've tried a handful of belts and these are both noticeably cooler running, quicker working, and longer lasting.

3M Cubitron at the coarse grits
3M Trizact for anything you can't get in Cubitron


I've never thinned a knife with belts but have sharpened enough to get decent at it. Very light, fairly quick moving, not stopping in one place and I don't have heating problems but I'm also using a Kalamzoo 1x42 that runs at around 1725 rpms / 1800 belt speed (the important number). That's much slower than many 1x30 3650 rpm belt sanders. A bucket of water nearby is a good thing and doesn't hurt to use so use it if any warmth is even felt.

I'd also recommend a belt cleaning/eraser stick - kind of like a big eraser that can be used to clean your belts. Get's all the abrasives/loading out of the belt and keeps them cutting cooler and longer.

Definitely get a cheap knife to practice with before using on anything you really care about. In my experience it took 5-10 tries to get to the point of having a good, smooth moving passes with consistent and light pressure that fixed the inconsistencies from the previous tries.

I prefer to sharpen with stones but for decent size chips, broken tips, grinding down heavy choils, ... etc I'm definitely not afraid to use the belt sander to do the heavy work and then off to the stones.

Just my experience - hope it helps and good luck.

 

[Pie]

Andrew Bishop has this video


I have not tried it but some people I’ve talked with have had good results
Despite the dodgy setup

I can vouch for his grinds, I took a look at some of the stuff he was working on earlier this year at his place and the convexes are pretty perfect.

 

[Genghis_F]

Thinking about using my harbor freight 1x42 belt grinder to thin (not sharpen), the platen it comes in is short and flat, should I modify if? Give it some radius?
Plan on using 80-120 grit
Anyone use one of these for thinning?
Got a bit of tendinitis so trying to give them a rest

 

[deltaplex]

Thinking about using my harbor freight 1x42 belt grinder to thin (not sharpen), the platen it comes in is short and flat, should I modify if? Give it some radius?
Plan on using 80-120 grit
Anyone use one of these for thinning?
Got a bit of tendinitis so trying to give them a rest

It'll be slow going, and I find grinders made for 1" wide belts have a platten that's more narrow than I care to use. I have to think too much about making sure the blade is sitting on the platten right instead of being able to focus on placement and pressure of my fingers that are determining how the stock is coming off. That said, it still a good amount faster than using course stones, especially if your hands/arms/joints are not 100%. Just have a big bucket of water to dunk the blade in, don't remove material in a way that you're forming a burr on the cutting edge, and don't let it get warmer than is comfortable to touch. It should be a faster stand in for most of what you'd be doing on a 320 grit or more course stone, but there's more potential for an error that's a bear to correct.

 

[HumbleHomeCook]

Thinking about using my harbor freight 1x42 belt grinder to thin (not sharpen), the platen it comes in is short and flat, should I modify if? Give it some radius?
Plan on using 80-120 grit
Anyone use one of these for thinning?
Got a bit of tendinitis so trying to give them a rest

I have more or less the same thing and have done this twice. @deltaplex gives good advice.

BE CAREFUL!!! That narrow, fast spinning belt will dig in real quick if you're not paying attention. Especially the edges. The narrow belt also means the work is more concentrated on a small spot so be mindful of that as well.

I personally wouldn't mess with the platen as they are too small to really get anything out of. I recommend making fairly quick, low pressure passes. The fresh low grits can grab and the knife will want to snap downward so a light touch against the belt but a good grip on the knife is important. Dunk the blade with every pass. I also let it sit after a couple minutes.

A marker is still a good tool here. You have a lot to focus on so the marker just helps you know where you're hitting. At least to get you started. As said, stay away from the blade edge. This is more bulk removal and then that stuff you do by hand.

Some calipers and a notepad can help you know how you're doing too. Measure various spots on the blade and record them.

It is easy to mess up and I wouldn't recommend jumping in on a nicer blade that you care about the aesthetics to start. But, after I've done it a couple times, I'm less intimidated by it now than before I started. It does make a huge difference if you're trying to remove a lot of material. Especially with my messed up hands. But leave everything proud and then finish by hand.

 

[JustAnotherJoe]

I'm still pretty new to the world of thinning and polishimg, but I recently picked up and inexpensive nakiri that required a lot of thining, which might serve as inspiration for you.
Barrowed a bit of time on a friends tormek and made a silly guide out of paper clips, as I had never taken a knife to a powered grinder be for. This tormek has a diamond wheel for it, so I just worked on the flat side as one might on a belt grinder. Here is a WIP photo.
It worked great! There is still a lot of work I'll be doing by hand, but powered grinding saved this knife from being perpetual rubbish.
Good luck!

 

[Chasingsharpness]

That's really interesting using the tormek for thinning. Did you find it removed metal significantly faster than coarse stones? Did you have any difficulties or run into any issues?

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