Sharpening a carbide disc cutter, et al.

[Rob Miller]

I've just got a carbide disc type cutter I'm using with my home grown articulated rig. I've only hollowed two forms with it and I'm getting tearout and chattering. i'm presenting it basically right at the center line and in a horizontal or nearly horizontal orientation. I'm working dry mesquite. the blade seems quite dull already but it seems to me carbide should have stayed sharp longer. What are your thoughts on this? Can I sharpen this thing? I'm assuming I can just lay it flat on a diamond sharpener and move it around with a fingertip?

[John Keeton]

Rob, I don't use carbide cutters, but it is my understanding that their primary purpose is machining. For that, they need to be hard and tough, but not necessarily super sharp. You also might get a better cut by setting the height just above center. You will probably find the the quality of the cut will improve with a smaller cutting edge - at least until you are ready for a light finishing cut.

I use HSS cutters for hollowing and find that keeping them sharp is essential to a good cut.

[Bruce Pratt]

Rob,

To your proposed method of sharpening, if the cutter is not working now, what have you got to lose? Before you sharpen, you might check out a couple things; check the tightness of all the linkages, if they are loose, you will get chatter in the head. Second, check out the performance with a different piece of wood which is not mesquite, it may be just the piece you are working on is giving you problems.

[Paul Gilbert]

There are a couple of videos on YouTube showing how to sharpen these cutters:
https://www.youtube.com/watch?v=mCX4lMssxcU (about 10 min. into video)
https://www.youtube.com/watch?v=JcB5edQuOXQ

[Dave Mueller]

Rob,
You don't mention if the cutters are flat like EWT type or cupped like Hunter type. If they are flat, your idea of sharpening on a diamond hone by laying it upside down flat on the hone and moving it with your finger is dead on. I use this method all the time. Sharpen often before the cutting edge gets rounded requiring you to remove more carbide to produce a good edge. You can help by lubricating the hone with oil, water or WD40. I also clean my diamond hones regularly with WD40. I would not sharpen it as shown in the videos because you will likely put a bevel on the cutter's edge, making it more difficult to sharpen it the next time.

[Dennis Nagle]

It is my understanding and experience that when the cutter is horizontal you will get tearout and chatter. It should be set at a 30 degree angle.

[Jamie Donaldson]

It is my understanding and experience that when the cutter is horizontal you will get tearout and chatter. It should be set at a 30 degree angle.

Dennis has noted the problem you're encountering, because you're using a scraper rather than a cutter. Scraping will always leave a less desirable surface than a cutter that slices rather than scraping the wood fibers. That is the difference between the cupped Hunter carbide bits that are honed for slicing through the fibers, and the flat top scraper bits that scrape the fibers.

[Grant Wilkinson]

In addition to the advice so far, don't forget that, when one part of the cutter is dull, the rest of it is not. Loosen the screw, turn the cutter a quarter turn or so and you have a new cutting edge.

I use Hunter-style cutters and they give a much better surface when I angle them to the surface about 30 degrees, as Dennis suggested.

[Roger Chandler]

+1 on the advice Dennis gave you above........if it is a cupped carbide cutter.......a 30-35 degree angle works best......otherwise it can be very grabby and you will also get tearout! A carbide cutter is for smoothing cuts, so you need a shear angle of attack!

[Rob Miller]

Thanks, all! To clarify, I am using a flat-topped disc-type scraper rather than the cupped type. I can't imaging why this thing would cut at all at a 30 degree negative angle, especially if there's no burr. I am assuming you are talking about angling the cutter down rather than up, right?

[Michael Gibson]

This is a better video and far simpler. http://youtu.be/kLQk4U5ihz4 Michael

[Scott Conners]

Thanks, all! To clarify, I am using a flat-topped disc-type scraper rather than the cupped type. I can't imaging why this thing would cut at all at a 30 degree negative angle, especially if there's no burr. I am assuming you are talking about angling the cutter down rather than up, right?

They are talking about rotating the cutter along the axis of the tool shaft, so that it shear cuts instead of scraping. The cutting edge of the tool tip should be 30 degrees off axis from the top of the tool rest. Check out the pics here on the Hunter site (http://www.hunterwoodturningtool.com/pages/product_taper_01.html) and you can see the how to swan neck tool has the twist pre-built into it.