I turn quite a lot of mdf and gritty reclaimed hardwood, both very abrasive and hard on the tools. The mdf turns quite well with HSS or even carbon steel scrapers, but they soon blunt. The gritty timber sometimes strikes sparks from the edge of a steel scraper, and knocks the edge off a gouge after just seconds of cutting. So I have been looking out for a tool that would hold up better. One day I shall try diamond tips – you can get diamond router bits, so perhaps they are available for fitting to woodturning tools, or perhaps a router bit could be adapted. I’ve tried various tungsten carbide scraper tips (though so far not the well-known Easywood tips), but found them to blunt quickly and not cut as well as HSS even when new.
The other day I purchased a Hunter Hercules tool. This has a little round cupped carbide tip set at a forward angle on a very robust, heavy steel shaft with a substantial handle. The tips are silvery-bright polished carbide and when new will catch on your thumbnail as sharp tools should.
It has three modes of operation. Used with the tool shaft horizontal and flat on the rest, perpendicular to the surface and cutting on the very tip, it gives a semi scraping cut that is quite aggressive. If the handle is twisted and the side of the tip used, it shear scrapes and can give a good finish. It can be used for a bevel rubbing slicing cut that also gives a good finish.
I tried the tool on some edge-grain mdf. In semi scraping mode, it cut freely for a while before the edge lost its initial keenness. But it kept going. The small tip penetrates easily and whether semi scraping or slicing it keeps on taking off the waste. Even on the mdf face-grain, which with normal scrapers produces shavings, the waste was very dusty indeed. The finish produced was not brilliant, but adequate after a little sanding, and I shall normally make the final cuts with HSS tools anyway. I made several complete components with the tip still going strong.
I found the tool quite catchy when going into a spindle cove in semi scraping mode. To avoid problems, the tool has to be swiveled and the cut kept on the front third of the tip’s circumference, say between 10 and 2 o’clock. The inclined edge at 9 and 3 tends to catch on the sides of the cove and run back. I found it can catch and run in this mode on a flat surface or a hollow on faceplate work too. The best way to prevent runs when semi scraping is to push rather than pull the tool. The small diameter of the tip means that it is not so easy to get a sweeping, regular curve – the tip penetrates easily so any additional pressure makes a dip in the surface.
It is easy to ride the bevel in a straight line or round a curve. This gives a controllable cut and clean surface just like a gouge, but only light cuts can be taken as the tip is small.
Shear scraping with the Hunter is similar to with a normal scraper, but the small diameter tip makes it a little harder to get an even sweep.
Replacement tips are not cheap, though they may last a long time on easy timber. The maker hopes they will be considered disposable, but I hope it will prove possible to sharpen them. Flat carbide tips can be sharpened on their upper surface with a diamond hone, but this would flatten the top of these cupped tips. I intend to try three alternative methods – hone the top and afterwards use the tip as a normal flat tip scraper; mount the tip on the end of a rod like a dop stick (or just pin it on the end of a rod using the tail centre) and hone the bevel while it spins in the lathe; and hone the groove in the top using a very small diamond ball point in a Dremel, also while spinning the tip. I doubt if any of these will equal the original grind, but shall report the results in due course.
So I am pleased with the tool so far. Quite impressed.
If it cuts mdf, I’m sure it will cut ordinary wood. I tried roughing down a small oak spindle blank in semi scraping mode and it worked well, though it did leave small feathery shavings not completely severed if traversed too fast, due to the small tip diameter. I have not yet tried it on the gritty stuff but shall update in due course. I have however roughed out a number of boxes in some unknown but hard and very abrasive wood. I have not yet changed or sharpened the cutter, though I have turned it through 180 degrees to a fresh edge, and it is still cutting quite well – HSS would have needed many sharpenings in this time.
It will not replace my gouges and scrapers. I shall use it on difficult materials as a roughing tool, and be grateful for the long edge life. When really blunt, the edge becomes badly chipped and eroded, and then will not give a good finish. No doubt others will use it on more tractable timber and get nice polished surfaces straight off the tool, but for me it is too slow-cutting for routine use – I get on better with normal gouges and scrapers that are more free-cutting.