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Trying to sharpen Hunter carbide tips

I recently posted about a Hunter Hercules tool I am using on the abrasive materials that I often work with. The manufacturer says the tips last a very long time. This may well be true when using ordinary wood, but not for me. I roughed out a number of items in mdf and some unusually abrasive hardwood, and the initial sharpness was soon lost. The tip kept on cutting while in my ball cutting jig in scraping mode, but was leaving a poorer surface. I am satisfied with the Hunter as a roughing tool until something better comes on the market. But the edge is now so blunt that the tool is hard to use freehand. The cutting edge feels quite rough, like a miniature hole saw.

The maker says the tips are disposable and cannot be sharpened. Sharpening Hunter carbide tips would be a useful option. It seems to me that if they were sharpened at the factory, it should be possible to sharpen them again. My first attempt involved honing the bevel. I put a bit of wood in a chuck and turned the end of it to a short dowel, just under the diameter of the tip, and faced off the end. I pinned the Hunter tip against the end of the dowel with the revolving tail centre. Then, with the lathe running slowly, I used a diamond hone to touch up the bevel. I found that a narrow hone was easier to keep in contact. A coarse hone took off visible carbide dust, then I polished it with a fine one. The bevel looked fine after this treatment.

I found that this had improved the cutting action somewhat, but on close inspection with a lens I saw that the edge was still quite badly chipped and uneven. More honing would eventually reduce the diameter enough to remove these chips, but the next thing I tried was to re-grind the inner bevel.

I used a very small ball-ended diamond cutter in my Dremel tool. This would not enter the groove in the tip because the tail centre was in the way. I drilled a small hole in the end of the dowel and used the Hunter fixing screw to mount the tip on the end of the dowel. It easily cut its own thread in the wood. As I write this, it occurs to me that I could just have turned the dowel thinner, reversed the tip, and worked from the other side. Anyway, with the tip on the dowel and the tail centre out of the way, I used the diamond cutter, with the lathe running slowly, to open out the groove a bit. Again, visible carbide dust was coming off.

I put the tip back on the shaft and tried a cut. The tip was certainly better than before. But not sharp. The lens revealed that the inner groove that when new had a mirror finish was now like a ploughed field. The diamond grit on the cutter I have is too coarse. The chips on the edge were smaller, but still there.

I shall use the tip for a bit longer, then try honing the top flat and putting it on a different shaft, one with a horizontal presentation.

My conclusion is that the manufacturer may be right. Unless you have a fine ball-end diamond grinder point to follow a coarse one (this would presumably leave the inner bevel as good as the outer), it is going to be difficult to bring the tip back to ‘as new’. I think I have prolonged the life of the cutting tip, but it is only good for rough work now. Perhaps I left it too long before attempting to sharpen. I may have to bite the bullet and replace the tip! Most turners would be happy with the edge life, and the cost of an occasional replacement would not be high, but the stuff I use them on will make disposable tips expensive.

Update – I have sharpened the tips now, but not back to new condition.

 

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