Fe at u r eCarbideCuttersAre Here to StayLyle JamiesonJohn English wrote about themanufacturers that producecarbide cutters in the December2010 issue of American Woodturner(vol 25, no 6). Many woodturnersuse their own shopmade versions.This article will move the discussionof carbide cutters to another level todiscuss how we use themfor woodturning.During my lifetime of workingwith wood, I've acquired informationfrom others—reading books, attending demonstrations, and one-on-oneconversations—as well as from personal experience. I had a learningcurve to go through with carbidecutters, and this time much of myresearch came from the Internet, aswell as from my own experience.There are conflicting viewpointsexpressed on the Internet, but thereis consensus enough to supportmy conclusions.HistoryA few years ago, Mike Hunter askedme to consider using carbide cutterson my boring-bar system. In spiteof my initial comment, “No thanks,carbide does not get sharp enough forturning,” Mike began my education.He described the new technology ofwoodturner.orgnanograin carbide. “Okay,” I said,“prove it.” And he did—my assumption was wrong.Carbide cutters have been in usefor decades: metal machining, military, sports, plastics, wood-production duplicators, and in flat woodworking for tablesaw-blade tips. Theearliest mention I found for carbidewas in the 1860s, but the woodturning tool market did not acceptcarbide until recently.The first commercially produceduse of carbide for turning that I knowof was when Dennis Stewart put acarbide tip on his slicer tool, sometime in the early 1990s. It was theprecursor of the coring systems usedtoday. While it had wear resistancebetter than HSS or carbon steel, itwould not get as sharp. For the useDennis intended, however, it wasperfect. Then why didn’t other usesof carbide take off with Dennis’sexample? The answer is: That carbidedid not get as sharp as high-speed steel,and a diamond hone was required tosharpen it.MetallurgyThere are many different carbides andgrades of carbide. Carbide is not justcarbide. The quality of the manufacturing varies greatly, and the particlesthat make up the carbides are different sizes. A microscope is needed tosee the difference. Let’s break downcarbide cutters into two categories.First is tungsten carbide. It is formulated from a gray powder and theresult is three times stiffer than steel.The second category is the newnanograin tungsten carbide, sometimesreferred to as micro-grain carbide. Thenanograin, as you might guess, ismade of much smaller particulatethan for tungsten carbide—the difference in grain size is that of BBs tobeach balls. Nanograin carbide grainsare cemented with another metal,usually cobalt (Figure 1). Generally,there is 6% to 12% binder in thecarbide. With optimum grade selection, submicron-grain-size particles oftungsten carbide are manufactured tohave a razor edge. What does this haveto do with us in the turning world?21
Figure 1. Magnification of carbide: Illustration of (gray) carbide cemented with (red)cobalt under high magnification.Start with a sharp edgeIn woodturning, we begin with asharp edge on our tools, and theinstant we start turning, the sharpness of the edge degrades. Let’s dosome math. Take a 10"-diameterbowl and calculate the circumference: 10 3.14 30 ". Thirty inchesof wood are passing the cutter everyrotation. Let’s say we are turning at1,000 rpm. In one minute we havejust cut 30,000" of wood—almostone-half mile or 500" per second.Will any tool retain its sharp edgevery long?After the initial sharpened edgeis gone, the structure of the basematerial the cutter is made from isleft. This remaining cutting edge iscalled the land. With carbide, thebase material is very wear resistantand the tool will cut reasonably wellfor a long time on the land beforethe edge deteriorates enough tobecome unusable.With nanograin carbide, the finerparticulate will allow the edge tobe even sharper to begin with thanwith the old carbides—manufacturers are able to produce a razor-sharpedge. The land edgeleft after the initialnanograin razorsharp factory edgehas been used tocut wood will stillbe sharp becausethe fine grainstructure is resistantto wear.How can you tell ifyour tools are made fromthe old-style carbide orthe new nanograin carbide?The nanograin carbide is manufactured under high heat and highpressure. The surface ends up witha mirror or glossy finish. The oldcarbide will have a dull, flat-grayappearance. To confuse the distinction, some carbide manufacturersapply coatings to enhance sharpness. These coatings are usuallyyellow or gold in color and theyare intended to mask the dull gray.The coating wears off quickly andthe tool is now cutting with theland made of the same basemetal structure.nanograin carbide will begin withand hold a sharper edge than theold carbide and stay sharper longerthan HSS. This is demonstratedto me in daily use of the Hunternanograin carbide tools on myboring-bar system.With HSS tools, the sharpenededge will degrade rapidly, but wecan go quickly to the grinder andconstantly renew the sharp edgeto optimal performance. Thesharpened edge of HSS tools willbe sharper than the old-stylecarbide ever gets. You also canuse a burr on HSS tools that isnot present on carbide. Othersteels like stainless and composites have the same trade-off. Theknife industry has been strugglingwith this issue for centuries. Theold carbon-steel knives wouldget sharper and last reasonablywell for culinary needs, but theyrust and their appearance was aproblem. Flat woodworkers havebeen arguing forever about thebest tool steel for router bits andcarving tools.Grain sizes and sharpnessWhy use carbide?I spoke with Tom Walz, President ofCarbide Processors Inc. in Tacoma,WA, to compare nanograin carbideto HSS. He said, “Consider thatthe sharpness level of HSS is in therange of 1 to 20, with 1 being thesharpest possible for HSS starting out. Nanograin carbide, onthe other hand, starts out at 2 or3 sharpness. Turning with bothfor the same amount of time, HSSis dull and has reached a 20 whilenanograin carbide is still sharp at a4 or 5 in the 1 to 20 range.” My conclusion is that the finer structure ofNanograin carbide tools cannotbe resharpened to their originalrazor-sharp factory edge; they aredesigned to be disposable. Theyare, however, economical becausethey last so long. I believe theywill wear up to 100 times longerthan HSS.Nanograin carbide cutters leavea much better surface on thewood than the old carbide. Why?Because it begins and remainssharper, and we can use a slicingcut that leaves a cleaner surface onthe wood.22American Woodturner December 2011
Fe at u r eHow woodturners usecarbide toolsThere are two types of cuts we canmake while turning wood: a scraping cut or a slicing cut. It does notmatter whether the tool is HSS or acarbide. The rule for scraping is thecutting edge must touch the woodat a 90 angle or less. Cutting at thecenterline with the scraper heldflat on the toolrest, the 90 angleis achieved by having the handleslightly up from horizontal (nose ofthe tool pointing slightly down). Asthe wood passes by the cutting edge,it scrapes some wood off. If we touchthe wood with any sharp edge atmore than a 90 angle, handle downwith a scraper, the tool will dig in,starting a catch.The rule for a slicing cut is the bevelbehind the cutting edge must be supported against the wood. If you areslicing on an angle without bevelsupport, the cutting edge will grab,dig in, and skate across the wood’ssurface until you get a catch. This isa critical concept to understand andwhen you understand it, tool catcheswill become a thing of the past (seeFigure 2).The two different carbides areused for different cuts for differentreasons. The old carbide is used inthe scraping mode. Carbide cuttersare especially useful for beginners.Learning to use a scraper is easy, andthey can scrape for hours and theirtool will still be sharp enough.Old-style carbide cutters are alsogreat for what they were originallymade for—roughing out. The turnerjust presents the tool to the wood in ascraping mode and just pushes it intothe spinning wood and scrapes away,keeping the handle slightly up, never 12violating the 90 -angle rule. The oldcarbide cutters are wear resistant,so going through dirty bark andmiles and miles of waste wood, theywill hold their edge for a long time,longer than HSS scrapers. The tradeoff is that the old carbide cutters arenot as sharp as HSS scrapers or bowlgouges, which is okay—we are usingthem as roughing tools.The new nanograin carbide canbe used for either a scraping cut ora slicing cut. Professional turnerMike Jackofsky has set up thenanograin cutters to workonly in the scraping mode witha tip angle dedicated to scrapingacross the bottom, inside a hollowform. Mike Hunter developed hisnew Hercules tool to scrape inthis manner, which works betterthan the old carbide because itis sharper.39Negative-rakescraping1 (Above) Carbide cutter clock positionsfor a nanograin cutter on 3 16" (5 mm)square shaft to be used with swivelinghead boring bar.Bevel-supported cutWill not cutFigure 2. Nanograin carbide cutter in threepositions tilted to cut wood (or not).woodturner.org(Right) The carbide cutter is showncutting under the shoulder of a vessel.The cutting motion can be in bothdirections, as indicated by the arrow.Notice the swivel has positioned thecutter to allow scraping at the 9:00position. This means the carbide cutteris cutting at the 9:00 position and isdirected toward the tailstock whencutting under the rim of the vessel. Notethe obstacle created by leaving the wastewood behind the cutter, which couldeasily become a problem later.223
3The direction of cut is to the left whenthe carbide-cutter insert is angled tothe left. The ring visible in the photoshows the transition shoulder betweenthe surface of the wood just cut andthe wood ahead of the cutter. Noticethe large thickness of the shaving. Thecutting motion is slightly pulling awayfrom the tip, on a taper, across thebottom of this vessel. This hogging-offcut is aggressive and removes largequantities of wood quickly.4This bevel-supported cut in the bottomof the vessel is made with the cutter atthe 12:00 position, angled to the left,and the direction of the cut is to theleft. Note the fine shavings as a light cutis taken. 5A light cut, riding the bevel, and slicingpart way up the side of the hollow formproduces a smooth surface. The cutteris cutting at the 12:00 position and thecut is to the left.6This is the correct way to undercuta shoulder by removing the wastewood from behind the cutter beforeworking on the underside of theshoulder. The cutter is at the 12:00position, riding the bevel, and slicingup the side wall to the left.24Mike Hunter, Trent Bosch,Eliminator, or Jamieson toolshave set up the nanograin carbideinserts so the bevel can be used ina slicing action to get a smoother,cleaner surface on the wood. Itacts as a hook tool or ring tool toslice through the endgrain fibersof a hollow form or lidded box.Mike Hunter has great tutorials onusing nanograin carbide forslicing and scraping in bowls andhollow forms on his website,hunterwoodturningtool.com.Nanograin carbide:Three cuts possibleThe new carbide tool is onecomplex little workhorse. The 3 16"(5 mm) nanograin carbide cutter isefficient and in this case, smalleris better. Larger cutters stress thewood and the chucking method.Using this small cutter, it is easierto hollow deeper vessels withoutvibration. The turner takes manysmaller cuts quickly rather thanslowly grinding away with a largercutter bit.If you set it up as I do in my captured boring-bar system, there arethree different cuts possible.Let’s envision the cutter assemblylocked in a boring-bar swivel assembly and positioned straight forward.Looking toward the headstock anddown on the cutter, imagine a clockface (Photo 1). When presenting the8:30 to 9:30 section of the cutterto the wood, the cutting actionmimics that of a negative-rakescraper (Photo 2). The arrow indicates we can cut in both directionswhile scraping.The second type of cut is to usethe cutter from the 10:00 to 12:00section. The result is an angledslicing action that is efficient andeasy to cut with (Photo 3). In fact,this is the workhorse section ofthe cutter that gets most of the useAmerican Woodturner December 2011
Fe at u r eand abuse; wood can be hoggedoff. There is no bevel support forthis cut or for the scraping cut.Note the arrow in Photo 3: Onlycut to the left.At the 12:00 position of thecutter, a bevel-supported cut isthe result. It is a slicing action andleaves a smooth and clean surfacebehind. This cut is intended forremoving only a small-shavingslice to clean up tool marks andprepare to sand, if needed (Photo4). To make a bevel-supportedcut, you must swing the handle tokeep the bevel on the surface ofthe wood to make a curved shapeinside a hollow vessel. As indicatedby the arrow, the cutting action isto the left.Even if the entry hole is small,the swivel will allow the 12:00position to be used in any quadrant of the vessel, bottom, side, ortop. This will require working instages as you move the swivel oftento position the cutter to use thebevel at the 12:00 position. Theinside contour achieved from thismethod is really sweet because it iseasy to pick up the line from a previous stage and carry it through thenext stage (Photo 5). With a littlepractice, the line that the bevel andcutter follow will be superior toscraping cuts. (A laser-measuringdevice will help monitor the transition from stage to stage and keep auniform wall thickness.)The cutter will not cut in the12:00 to 3:00 position. If youpresent this quadrant to thewood, it will just rub the shaftand the bottom edge of the cutter,and may even result in somechatter and/or vibration.Learning curveHSS cutters attached to the endof boring bars can be directedleft, right, in, or out to producewoodturner.orga cut. With a nanograin carbidecutter, however, there is a bit ofa learning curve. For example,the cutting action of the carbidecutter will always be to the left ifit is angled or facing to the left.the tailstock. Photo 2 shows thenegative-rake scraping cut used toundercut the shoulder area.The shearing/slicing cut of thenanograin carbide cutter producesa shaving. A scraping cut wouldOne caution to keep in mind:Do not combine the ride-the-bevel and the hogging-off cuts—that combinationremoves too much wood, too fast, and starts some vibration going. Doing both cutssimultaneously stresses the chucking method, stresses the wood, and stresses theboring bar. The trick to hogging off fast and easy is to cut with a slight sweeping orscooping motion to pull away from the bevel slightly as you cut. This will create aslight curve to the inside surface of the vessel (see Photo 3).The direction the cutter is facingdictates the direction of the cut. Itwill try to “climb” if you try to cutin the opposite direction. Goingthe wrong way will not usuallyproduce a catch, but it will causethe cutter to skate.When hollowing under a highshoulder, make sure to get thewaste wood out of the middlebehind the shoulder of the vessel(Photo 6). Photo 2 shows the incorrect way to hollow by leaving thewaste wood in the way behindthe cut. Removing the wastewood will prevent an inadvertentskate should you bump the woodbehind the cut with the back sideof the tool.Photo 4 shows the correct direction for cutting the endgrain onthe bottom of a hollow form. Photo6 shows the correct direction of acut coming up the side of a hollowform vessel. The cutter needs to cutpulling toward the shoulder of thevessel when the cutter is swiveledto the left. And in Photo 6, “left”is actually pulling the cut towardproduce sawdust. Try one of theselittle cutters on the nastiest woodyou can find and you will be abeliever. These nanograin carbidecutters excel in wet wood, drywood, hard wood, and soft wood.There is no sharpening and theyare economical. I find them to beeasy and fast for hollowing, andI like it that there is less sandingrequired. It takes making a fewvessels to master the cuts, but it isworth the effort.Photos by David SpeckmanPhotography.Lyle Jamieson is a full-time woodturningsculptor and instructor from TraverseCity, MI. He is President of theNorthwest Michigan Woodturners(tcturners.org). Lyle is known forhis figurative sculptures and forthe Jamieson boring bar and lasermeasuring system. He will be afeatured demonstrator at the San Josésymposium, 2012. For more about Lyle,visit his website, lylejamieson.com.25
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