Carbide cutters

[Dave Jain]

Do the carbide cutters that are much more expensive cut better or last longer than the cheap Amazon or eBay ones.

[David Walser]

Maybe. There are different grades of carbide. Carbide has a crystalline structure. The smaller the size of those crystals, the finer the cutting edge. Also, the smaller the crystals, the more densely they can be packed into a given area -- allowing the edge to be more durable.

Also, there are different types of carbide cutters. Most used for woodturning, have a simple flat top with a sharpened bevel along the edge. These are scrapers. Recently, Easy Wood Tools introduced negative rake carbide cutters. These, in addition to the bevel along the edge, have a slight bevel on the top of the cutters, too. These, too, are scrapers. But, having a negative rake, they tend to be less aggressive and, with some types of materials, produce a cleaner surface. They are particularly well suited for turning plastics, end grain, and denser woods. Finally, Mike Hunter sells a line of carbide tools. His cutters have a micro flute on the top of the tool. That is, they are designed to work like a spindle gouge, using a bevel supported cut. Used in this manner, they produce an exceptionally clean surface. The Hunter tools can also be used as scrapers.

If you find carbide cutters on the web that are made from the same grade of carbide and have the same shape (bevel and/or flute) as the original cutters, they should cut just as well as the originals. EWT claims to have patented their negative rake cutters, so you might not be able to find ones that are identical to theirs. But, the others are not too difficult to find.

Also, you can sharpen carbide cutters using a diamond stone and some lapping fluid. If you're using the flat cutters, simply lay the top of the cutter flat on the stone and swirl it around in small circles using your index finger. Light pressure and 10 - 15 seconds should do it. Each sharpening will reduce the size (diameter or length/width) of the cutter slightly. After a few sharpenings, the cutter will no longer fit properly and will need to be replaced. Still, with a few sharpenings, you should get a few year's heavy use out of each cutter. Given that, why go to all the hassle of trying to save a few dollars on replacement cutters? YMMV.

[Dan Gaylin]

In my experience there are substantial differences in carbide cutter quality. And the more expensive ones from reputable brands generally cut significantly better. Also as others have reported, while you can resharpen carbide cutters they don’t perform as well once resharpened, in part because you are really just sharpening one plane of the two sided wedge that makes the cutter.

[roger wiegand]

in part because you are really just sharpening one plane of the two sided wedge that makes the cutter.

Wondering how that is different from sharpening planes or chisels where, once you know the back is flat, you never touch again aside from possibly polishing off a burr.

Or on carbide scrapers are you actually cutting with the burr raised by sharpening the bevel edge, as in a conventional scraper? I have a couple of Mike Hunter's tools for hollowing and I have to say I'm surprised and pleased how well they work. I also have carbide and steel scraper bits for my hollowing rig and have noticed that they are (briefly) much more effective when sharpened on the bevel than just on the top, flat side, leading me to suspect it might be the burr doing the work, at least right after sharpening.

To the OP, there are huge differences in carbide quality-- seen most readily in router bits and saw blades where the edge sees a lot more wood. I'm sure some of the ebay ones are just fine, and some may well come from the same factories as the "brand name" product, but without a degree in metallurgy or a lot of experimentation, how do you tell? For as long as the cutters last it's not worth it for me.

[David Walser]

Wondering how that is different from sharpening planes or chisels where, once you know the back is flat, you never touch again aside from possibly polishing off a burr.

...

My belief is the primary reason a hand sharpened carbide cutter isn't as sharp as the factory version is because, in our shops, we don't use as fine a grit as the factory did. I state that as a belief because I have no way of proving it -- without knowing what everyone else is using to sharpen their cutters.

However, unless the bevel has been damaged, there should be no reason to sharpen it. We do just the opposite with a spindle gouge. When sharpening gouges, we sharpen the bevel and (except for a light honing to remove the burr) we don't touch the inside of the flute. Unless the flute has been damaged, there's no reason to try to sharpen it. And, as Roger suggests, this is the same principle that applies to plane irons and chisels.

Another reason hand sharpened carbide cutters aren't quite as sharp as from the factory is because few of us properly clean the cutter. Sharpening the top of the bevel will remove any gunk, but the bevel may still be coated with thin coat of resin that builds up as the tool is used. Often, this film is hard to see with the naked eye. Remove the film with a good solvent -- kerosene, simply green, lacquer thinner -- and a tooth brush. (Be sure to rinse your wife's tooth brush before putting it back.)

[Kyle Iwamoto]

(Be sure to rinse your wife's tooth brush before putting it back.)

To reduce the embarrassment of living outside in the dog cage for 3 days, I say use and old toothbrush, or buy a new one....

[Peter Blair]

I bought some of the cheaper 'off shore' ones but found that they were not a sharp as the more expensive ones. Typically I now only use cupped and negative rake cutters. I get my cutters from Ron Campbell in the US and the NR ones (for plastic etc.) from Easy Woodwork. Both are pricy but both also last a long time. I'm certain the cup ones can't be sharpened successfully but I would guess (never tried) that the NR ones could be with the provisions listed by others above.