Jump to content
Maestronet Forums

Can't get my knife sharp enough


Adrian Lopez
 Share

Recommended Posts

2 hours ago, Mike_Danielson said:

Do not believe that you can sharpen using this wheel without much heat.  The boron nitride is a very thin coating on the wheel surface, and it will soon load up with ground particles from your tool.  Now it is tool steel grinding on your tool.  Heat will result.

How do you clean this wheel so that there is a fresh grinding surface?  This is easy to do with a traditional ceramic wheel either by fast wear or by the ability to renew the surface with a diamond shaper.   

HSS is a special tools steel that can take higher temperatures than traditional carbon steel.  It was developed for lathe cutting tools; not wood cutting tools.  These grinder wheels were developed for HSS.

This sounds like another great idea that falls flat on it face.

Mike D

 

I've heard many many....many rave reviews of CBN wheels from woodworkers not necessarily turners.

Link to comment
Share on other sites

  • Replies 127
  • Created
  • Last Reply

Top Posters In This Topic

I needed to be taught how to sharpen tools when I started violin making. I use a dremel to grind the hollow edge as it is more hollow and I have better control, not to mention storage. I wouldn’t bother with the angle guides, just feel the bevel against the stone and keep it there. I only sharpen one side, leaving the other flat

Link to comment
Share on other sites

12 hours ago, Adrian Lopez said:

Anyway, here's what the knife looks like after grinding away on the 1500 stone. Only some of the edge looks like this (there are high spots along the length of the bevel so I'm not always touching the edge), but I think it's getting better.

20190727_214824.jpg

Positioning the knife blade nearly perpendicular to your thumb nail, does the edge of the blade "stick" when you touch it to your thumb nail or slide?  If it sticks you're good to go.

-Jim

Link to comment
Share on other sites

After final sharpening on an 8000 grit stone and stropping on a piece of leather I have managed to get the knife to cut newsprint and shave hairs, but it's not very effective at cutting wood. I'm giving up for now -- I've spent hours on this -- and look forward to receiving the knife I ordered from John (violins88).

Link to comment
Share on other sites

Hi Adrian, just a tip, at 1500 grit you should be able to get it to cut hairs. It sounds to me like you might not have apexed the cutting angle.

Work one side till you get a burr then work the other. If your unsure make a bigger burr. Practice is about the only thing that will get that angle straight.

Link to comment
Share on other sites

21 minutes ago, David Hart said:

Hi Adrian, just a tip, at 1500 grit you should be able to get it to cut hairs. It sounds to me like you might not have apexed the cutting angle.

Work one side till you get a burr then work the other. If your unsure make a bigger burr. Practice is about the only thing that will get that angle straight.

Went through 200, 1500, 8000, and leather impregnated with 0.5 micron diamond suspension. I did get a burr on the 200 and 1500 stones, and finished on the 8000 and the leather strop.

Link to comment
Share on other sites

24 minutes ago, David Hart said:

Could be right Jackson. Could also be that the burr wasn't worked off. Basically I'd treat it like a blunted knife and start sharpening again. 

Hi All - the last step I do before checking the edge, is to clean off the burr by dragging  the edge of the blade through a piece of scrap spruce.

Adrian - your edge has improved greatly since your first pics - well done. Further improvement and consistency only come with practice - and you have a lifetime of that ahead of you. ;-)

cheers edi

Link to comment
Share on other sites

10 hours ago, Adrian Lopez said:

Went through 200, 1500, 8000, and leather impregnated with 0.5 micron diamond suspension. I did get a burr on the 200 and 1500 stones, and finished on the 8000 and the leather strop.

Each grit needs to go all the way to edge and past.  Should be somenburr in each case.    Almost to the edge, or mostly to the edge if still uneven simply won't work, even in the last stages.  Infact, especially at the last stages.

Think of it like a light switch, each grit needs to reache the edge fully, or no good at all.

It's ok to go extra and get a heavier burr, but to stop short is no good at all.

To not do this in the last final grits means a blunt final edge.  To not do this in the coarse early grits means wasted work and an unclean approach to rhe edge.

The last fine grit edge should bite on the fingernails crisply.  If it doesn't, then back up a grit or more. Fully to the edge on each step, feeling a burr all along.

If a grit level is going too slowly without getting fully to the edge, then backup to a coarser faster curting grit.  Don't go passed that until fully reaching or exceeding reaching the full edge without compromise.

When it's time to strop, be very careful not to round your edge.

 

How did the blade cut after that last picture?  

 

Link to comment
Share on other sites

On 7/27/2019 at 9:35 PM, Melvin Goldsmith said:

I just bought two CBN wheels 200mm x 35mm 80 grit and 180 grit  to run on a Axminster 'Trade' rated grinder at 3000rpm after reading this thread. I like the sound of them and will report back with my experience. Anything that speeds up the lost downtime of sharpening is a bonus. I recently changed to DMT diamond stones for honing with no regrets although I must admit I do the final finish on a china white Arkansas oilstone still.

OK I used my CBN wheels today. As Mike Danielson speculated they will heat a very fine edge like the tip of a bridge cutting knife and I would reserve final shaping and sharpening of fine tipped knives for a Tormek. On the other hand they will grind a primary bevel on a plane blade or chisel VERY fast with no bluing or sigh of heat problems. The chisel will become warm but not too hot to touch. It does the job much faster than a Tormek. I was able to rough grind to near shape some small bridge cutting knives in HSS steel and WS steel as well as a Hock blank but these had to have the final grinding on the Tormek but a lot of time was saved as a wear on the tormek stone. The CBN wheel does not clog or retain any metal particals but will clog if used to grind unhardened steel of softer metals so would not be suitalbe for Japanese laminated blades.  These wheels are way better , faster and cooler cutting than a conventional grinding wheel...I am very pleased to have these in my workshop. Mainly I will use for re grinding and primary grinding and not for final sharpening....My experience is only with 80 and 180 grit...maybe finer grits will cut cooler but I am happy to do secondary bevels etc on a Tormek on bench stones

Link to comment
Share on other sites

  • 2 months later...

I have a 3600 rpm grinder and a 60 grit 8 inch dia cbn wheel. For me, 3600 is uncomfortably scary. I fear burning the steel in blades. But I have found that pulsing on/off works because the wheel has a large momentum. I will install a foot switch to do the pulsing. I suppose a dimmer switch would also work.

Link to comment
Share on other sites

5 hours ago, violins88 said:

I have a 3600 rpm grinder and a 60 grit 8 inch dia cbn wheel. For me, 3600 is uncomfortably scary. I fear burning the steel in blades. But I have found that pulsing on/off works because the wheel has a large momentum. I will install a foot switch to do the pulsing. I suppose a dimmer switch would also work.

If it's an AC induction motor, the dimmer won't work. The dimmer can work though, if it's using a brush-type, universal series wound motor.

Link to comment
Share on other sites

1 hour ago, David Burgess said:

I bet I can get a cutting edge sharper, in less time, without even using my feet. :)

My point (or kissaki, in this case) is that if someone in Japan (whose work I greatly respect) can produce a geometrically perfect 2 1/2 foot razor blade like this:

 

image.png.dc991a59a69d95ecdede35c3b2a8c00d.png

From something like that:

image.png.a06ef15c14531cb241eda12df1bd8491.png

Mostly doing little besides manually rubbing the blank across a series of whetstones:

image.png.f20cd2240329fc94387dbb8f4f954471.png

......then using modern abrasives and power tools to sharpen an inch or so of edge on gouges, chisels and knives (without regard to texture, either) is purely a matter of convenience, not necessity.   :P  :lol:

Let the art of sword polishing be an inspiration to those here who don't have the latest, greatest, most expensive power sharpeners and abrasive media available in their shops.  With technique and persistence, your bridge knife can be as sharp as anyone's.  :)

Link to comment
Share on other sites

On 10/28/2019 at 9:02 PM, BassClef said:

What camera and lens are you using to get these excellent closeups? Thanks for sharing your experience. How much money and how many hours do you estimate you have spent trying to sharpen the original knife to your satisfaction?

It's a little USB microscope that I use with my phone. I'm not sure how much time I spent trying to sharpen that knife, but I think 8 hours would be in the ballpark. I spent ~ $150 (USD) on the sharpening stones, but I've given up on that method for lack of skill.

I ended up buying a Tormek. It's very nice (and expensive), though I find sharpening curved blades has something of a learning curve because you need to position the knife just right in the jig to get a uniform edge from heel to tip. I actually managed to get the knife pretty sharp the first time around, but I mucked it up when I repositioned it looking to get a more uniform edge.

I'm going to use the Pfeil knife to master sharpening with the Tormek before I try it on any of my good tools (one of which is really great knife I bought from violins88).

Here's my Tormek on top of a cheap ($50) Ikea chest (which I think makes a good stand):

20191030_033648.thumb.jpg.5563273a6a2c08d14b44bc68fbdc0552.jpg

 

Link to comment
Share on other sites

Here's the edge of my sacrificial knife after sharpening with a Tormek.

20191104_234759.thumb.jpg.97974ed7cee98fdc839783e18c68b00b.jpg

A much better edge, I think, though after so many failed attempts at sharpening the blade is now badly worn. The edge is still not perfect along the entire blade (not shown), but at least I can see the goal. No idea how long it might have taken me to master sharpening with water stones.

Link to comment
Share on other sites

11 hours ago, Bill Yacey said:

Power tools can be a double edged sword ( no pun intended); they can quickly bring a blade to a sharp working edge quickly, but they can also destroy a blade equally as quick in the wrong hands.

I think you'd have to be trying really hard to do irreparable damage to a blade with a Tormek.

Link to comment
Share on other sites

11 hours ago, Bill Yacey said:

Power tools can be a double edged sword ( no pun intended); they can quickly bring a blade to a sharp working edge quickly, but they can also destroy a blade equally as quick in the wrong hands.

Indeed, though in this case much of the wear happened while grinding on the 220 grit water stone. The Tormek can take off material much more quickly than a water stone, but it isn't nearly as likely to destroy a blade as, say, a high-speed grinder.

This is what it looks like now:

58857416_20191105_141342(small).thumb.jpg.82eb3927da12b846c48a6778a47cdadf.jpg

It needs another go on the wheel (dressed for fine grinding) as the bevel is still a bit wonky in spots.

Link to comment
Share on other sites

18 hours ago, Adrian Lopez said:

Here's the edge of my sacrificial knife after sharpening with a Tormek.

20191104_234759.thumb.jpg.97974ed7cee98fdc839783e18c68b00b.jpg

A much better edge, I think, though after so many failed attempts at sharpening the blade is now badly worn. The edge is still not perfect along the entire blade (not shown), but at least I can see the goal. No idea how long it might have taken me to master sharpening with water stones.

No reflections from the edge, the bevel is now set.  Take your sacrificial knife to the very fine stones and see how sharp you can actually get it.  It won't require much time to get an excellent edge.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

  • Recently Browsing   0 members

    No registered users viewing this page.




×
×
  • Create New...