There has been considerable advertising in the last decade for woodturning tools with replaceable tungsten-carbide-tips in the American and British woodturning media. In this article I’ll discuss and give my personal opinions on these tools.
These tools are not new. Mark F. Palma in an article “Carbide Tools? Fad or Future?” in the August 2020 Woodturning FUNdamentals revealed that carbide-tipped tools were promoted in an article “Turn with Carbide Tools” in the February 1948 Popular Mechanics. However commercial production of these what I’ll call carbide tools didn’t start until 2005.
Turning exclusively with these tools has been promoted as an alternative to conventional turning techniques in which the sharpening angles of the tools are typically ground to about 30°. For example in August 2012 the company Carbide Wood Turning Tools stated: “From roughing out blanks to hollowing bowls our turning tools cut down turning times by at least 50% to 75% with far less strain on the turner. Our carbide inserts and bits are 25 to 100 times more wear resistant than high speed steel”. Also in 2012 the book Turning Wood with Carbide Tools written by John English of South Dakota was published. It included the statement “If a trip to the grinder takes ten minutes” thus adding support to the promotional thrust that carbide tools eliminate “the drudgery of sharpening”. Whether Mr English “takes ten minutes” to regrind is unclear, but someone who has taken the trouble to learn to regrind efficiently typically takes about a minute.
There is, however, another promotional thrust, elimination of the need to learn a skill. Thus the current Ultra.Shear Woodturning Tools website includes: “All the joys of turning without the complicated learning curve involved in traditional tools or the expensive and complicated sharpening equipment, either. The cutting edge is an industry-leading nano-grain carbide insert that rivals high speed steel for edge quality, but outperforms high speed steel for edge quality by 20 to 30 times”.
What is noticeable is that over the years the promotions have lost some of their fervour, and that conventional turning tools continue to be produced, promoted, and purchased. Where does to the truth lie?
Let me admit that for more than forty years I have used “conventional” turning techniques, and only used scrapers on those infrequent occasions when I judged them the appropriate tool type to use. I therefore cannot be certain that the trials I report below are free from subjective bias.
The three carbide tools called a rougher, a finisher and a detailer that I used for the trials were manufactured by Easy Wood Tools in Kentucky, and supplied by Timbecom. They’re shown in Photos, 1, 2 and 3. Easy Wood make tools with similar shaped tips in four different lengths, they also make a range of other carbide tools.
A couple of days ago a limb broke off a river peppermint (Eucalyptus elata) tree. The wood was unseasoned, and fairly hard. I turned the two bowls shown in Photos 4 and 5, a shallow one with gouges and a deep one with a carbide tools. I have no hesitation in stating that using the carbide tool was somewhat quicker, that the deep shape presented no problems, and that the surface was less rippled and exhibited no greater tear out than I could have achieved with gouges. There was a slight fuzziness, but that would have been readily dealt with during sanding. So, if you’re only going to turn bowls and vessels with little turned ornament in harder woods, carbide scrapers (and no sharpening equipment) is an entirely sound choice.
Bowls and vessels don’t have to be turned from harder woods. I turned a bowl from seasoned radiata pine, and turned the twelve distinct surfaces using gouges and carbide tools. The gouge-turned surfaces were distinctly better on all except the side-and parallel grain surfaces. This strongly suggests that unless you love sanding, you should avoid turning bowls and vessels in softer woods using carbide tools.
Despite the impression given by much of the woodturning media, by far the majority of turnings produced annually are spindle turnings. Photos 8 and 9 show two similar spindle turnings in seasoned radiata pine produced using conventional techniques and carbide tools. Clearly the unsanded surfaces produced using carbide tools shown in Photo 9 would need excessive sanding. Also the arises are furry, and the pommel end is severely damaged.
Trials 1 and 2 suggest that perhaps carbide tools should mainly be used to turn spindles in harder woods. I tried the same spindle turning in seasoned European ash (Fraxinus excelsior). The overall tear-out was less than with the softer pine, but it seems impossible to avoid breaking off the corners of pommels.
Carbon-tool-steel scrapers and shear scrapers have been in use for centuries; high-speed-steel versions since the 1970s. Carbide tools don’t do anything that the earlier scraping tools couldn’t do. In fact they do slightly less because their edges don’t have a burr which lessens the tear-out with softer woods. Carbide tools do however have very keen edges when new, and they retain that keenness for much longer, although whether 20 times or the 120 times stated by English or some other ratio I cannot say.
The softer the wood, the more extensive and the deeper the tear-out with carbide tools. However softer woods do sand at a faster rate.
Pommel ends cannot be satisfactorily cut with carbide tools. Nor usually can sharp arrises, cusps or quirks be achieved.
Some of the advertising for carbide tools extols the benefits of shear scraping, scraping with side rake with the edge skewed to the velocity of the oncoming wood. The shafts of the Easy Wood tools are square which doesn’t facilitate shear scraping, and anyway shear scraping is limited in its applications. Because the sharpening angle of scrapers is typically between 60° and 80°, in shear scraping the edge must be dragged: it can’t be pushed. Therefore the steep sides of coves and beads in spindles, where tear-out is typically greater with scrapers, can only be shear-scraped outwards, towards the turner, which is “against the grain” and is therefore likely to increase the tear-out.