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Grinding Custom Shaper Knives

Learning to make your own tools is a step up for the serious woodworking carpenter

Most of my work is at the high-end of the New England custom home market. For the jobs I do, in Boston brownstones that even today sell for several million dollars, there are no off-the-shelf parts—everything is completely custom, or an exact reproduction of work done in the 18th or 19th centuries.

I’m often called in to replace or repair an existing stair; to create a fanciful one-of-a-kind design; or to satisfy a client and architect who know exactly what they want, even though they often don’t know what that is until I draw it, and turn or carve samples (in some cases repeatedly).

Early in my career, I learned how to grind the shaper knives for my big old Yates-American cast iron shaper, and I’m glad I did. That skill has saved me from having to order custom knives for almost every job I do. There are many good companies that will supply custom cutters from a sample or a CAD drawing, but by grinding my own I can save a little money, and make the moldings the day I decide I need them. I can also modify the cutters if the molding doesn’t look quite the way I want. Not only that, but in our shop we take great pleasure and pride in being able to build architectural millwork and furniture from scratch. Sometimes we have to, or want to, use 19th-century techniques to get results that are as good as the old carpenters’ we learned from—they’ve been dead for 100 years, but we get to look at their work every week.

Mike milling 12/4 mahogany rail stock

We are all carpenters because making things is in our hearts more than making money, and I’m not going to buy something if I can make it as well, or better, myself. Learning to make your own tools is a step up for the serious woodworking carpenter.

In the time it takes Mike Kennedy, who works with me in my shop, to rip, join, and plane the railing stock (see photo, left), I can cut and grind the shaper knives. I think we’ve made over 40 different handrails over the years. And I’ve got a couple of sets to make next week.

Before I get into the actual process of knife cutter grinding, I want to say a few words about design.

Moldings aren’t just random squiggly lines cut into wood. Both the shapes and proportions of moldings have a long history. Moldings are meant not just to connect different levels with graceful curves, but also to create interesting lines of light and shadow. We don’t have to reinvent the wheel every time we design a molding or handrail. Almost every traditional and modern molding has its origin in the Classical Architecture of the ancient Greeks and Romans more than 2000 years ago, or in the Cathedrals, castles and manor houses of the Middle Ages—the Gothic period. 18th and 19th century builders studied this stuff, and you can, too. There are many inexpensive reprints of books about classical architecture with actual molding patterns in them, as well as reproductions of old millwork catalogues. (* See end of article for a selection of book recommendations.)

Of course, looking at the exteriors of traditional buildings is free, and the details can be scaled down for residential interiors. Churches and temples often have beautiful woodwork. Helen, my wife, and I are at that age when a lot of our friends’ kids are getting married; we went to three weddings this fall. I wonder if she’d notice if I brought my sketchbook to the next one.

Handrail also has to meet strict requirements of building codes. To see a good explanation of the required profiles, download this great IRC Stair Code Visual Interpretation from the Stairway Manufacturers Association.

Getting Started

Cutting knife stock on my retired Makita chopsaw

I cut the steel stock for the knives from a bar of shaper steel with a 10-in. x 1/8-in. fiber-reinforced cut-off wheel mounted in an antique no-tilt no-slide Makita chopsaw.

Shaper steel is available in many sizes and types. I have both lock-edge and corrugated-back heads for my shaper. I also grind knives for my Williams and Hussey machine, which uses special bar with bolt hoses drilled on 1-in. centers.

I buy my shaper steel over the phone from Charles Schmidt Co. in Montvale NJ. I almost always use 1/4”-in. thick XLW-type steel in 25-in. bars of various widths. I always make two identical knives for each molding—they go together in the shaper head, and balance each other. I try to make them as close to identical as possible, so that they each cut the same amount.

I start with a full-size paper printout from a CAD or freehand drawing of the railing or molding profile.

I glue the paper drawing to a piece of 1/8-in. acrylic or plastic laminate, like Plexiglas or Formica,
then cut out the shape of the railing profile using a scroll saw with a fine blade.

If I am copying an original molding, I cut the sample off at a 15-degree angle (about the angle that the cutter will hit the wood) and trace that section onto the plastic. I spray the knife blanks with black stove paint, and, using the plastic template and a needle-sharp awl, I score the profile on the face of each knife.

Scribing the pattern on the knife blank

Remember that the shape of the knife is the negative of the shape of the finished railing. It’s a good idea to mark the knife on the side that will do the cutting, and to mark the side that you want up when the knife is in the machine. Don’t ask me how I learned these last few tips.

Now comes the dirty part.

Grinding knives by hand is dangerous business

This technique isn’t for everyone. It’s dangerous—like a lot of the things a carpenter or woodworker does. If my hand slips while I’m grinding, I can get a nasty abrasion from the wheel, and the knives are very sharp—they can cut you even without being in the shaper and running. Grinding wheels can shatter, and the pieces can cause serious injury. The dust from grinding is dangerous to breathe, and steel filings, sparks and silica from the wheel are eye hazards. It can be a fire hazard, too: the steel can become hot enough to burn.

I use a dust mask and eye protection. I also work looking through an illuminated magnifier with a plastic lens, which gives an additional layer of eye protection, as well as improving my accuracy. I use a spray mister which cools the work, keeps the grinding wheel sharp longer, and helps to control dust. I set the tool rest very close to the wheel so the work or my finger can’t slip between.

I hold the steel with a very firm grip. I mount and check the grinding wheel according to the manufacturers instructions. Before I put the wheels on the machine, I hold them with my finger through the center hole and tap them with the plastic end of a screw driver—they should ring like a bell, not make a dull thud, which indicates cracks. Good lighting is very important, as well as a comfortable posture—I usually grind sitting on a stool with both feet on the floor.

 

Most important, I always pay very close attention to what I’m doing. I don’t recommend this technique for everyone. But I’ve never had an accident at the grinder, except for an occasional scraped knuckle, and I’ve ground hundreds of shaper knives. Whenever I’m working with power tools or hand tools, whether I’m sharpening, sawing, turning, carving, or cutting miters on the chopsaw, I try to stay focused on the task. I know that any machine that will cut wood or steel can also cut me. There is no smart way to hurt yourself woodworking, but there are a million stupid ways. (THISisSafety)

A note on my equipment:

I use a 10-in. diameter pedestal-mounted grinder that is bolted to the floor. Mine is Dayton Brand, which I bought new from Grainger’s 20+ years ago. I believe they still carry it.

Attached to the grinder is a mister/cooler, from MSC, powered by my compressor. You can get one for about $140.

Both of these companies also carry illuminated magnifiers.

Rough out

Blocking out the knife with a fiber-reinforced cut-off wheel; notice the coolant spray

I start grinding with a 1/8-in. fiber-reinforced 10-in. cut-off wheel to rough out the knives. I set the tool rest level at the height of the center of the wheel so it makes a square cut. I turn the grinder on, start the mister, and dress the edge of the wheel with my diamond dresser to clean and center the wheel. Then, with a series of cuts from different angles, I remove as much of the excess steel as possible.

[Note: For a look at Jed's grinding technique, see the video at the end of this article.]

Curved profiles

Next, I use a 1/4-in. x 10-in. 36-grit aluminum oxide wheel to rough out the molding profiles. The wheels I use are Norton brand and come from Charles Schmidt Company, the same place I usually buy shaper steel. They are very friable, that is: crumbly, which is a good thing, because it makes them fast-cutting, and they don’t clog up with metal from the knives.

First, I reset the tool rest to 45 degrees. The angle doesn’t have to be as acute as a plane blade (30 degrees); it just has to be steep enough so the heel of the bevel doesn’t hit the wood when it’s in the shaper.

The first pass I make is to bevel the knife; I’m just removing stock from the underside of the knife blank. Then I start grinding away at the profile.

Roughing out with a 1/4-in. aluminum oxide 36-grit wheel; you gotta lean into the knife, but carefully!

I start by dressing the wheel with my diamond dresser to a half-round shape. (See photo, left) Then I work from right to left, taking the material off in repeated passes. The closer I get to the scratched line, the slower and more carefully I go. I re-dress the wheel whenever it starts to cut slower and hotter from being clogged with steel, or whenever it begins to lose the shape I want. I finish this step by carefully cutting up to the lines on all the concave shapes. (Concave on the knife, I mean. On the molding, these shapes will be convex.)Then I dress the wheel square. (Or better yet, I use a similar size—but harder and finer grit—wheel mounted on the other end of the grinder. Then I can go back to the half-round wheel and touch up the concaves, if needed, without re-dressing.)

Dressing a harder wheel square to cut inside corners. A diamond dresser can last for years, but eventually the steel around the diamond gets worn away - then the diamond is gone.

Cutting inside corners

With the square wheel, I cut up to the line on the straight parts of the knife, and on any convex shapes.

Finally, I put a very slight bevel on the square wheel, making sure that the corner is sharp—not rounded—and dress the inside corners of the knife (which will be the outside corners of the molding) nice and sharp.

Often, I’ll clean up the knife, turn off the spray for better visibility, and make one last, very light pass with both wheels for accuracy. This is sparking-off—a cut so fine that it just barely makes a spark.
Before leaving the grinder, I weigh the knives. They must be balanced, or the cutter head will vibrate. They should be within 1/10 of gram. It shouldn’t be too hard to figure out where to remove the stock from the heavier knife.

Finally, I hone the knives razor-sharp with a hand-held stone. Gesswein is a good company for stones and stone oil.

I make a test cut,
then check the profile against the drawing.
Sometimes the fit is perfect, but if I need to make adjustments, it’s easy—just remember that the more you grind off the steel, the more wood remains on the molding. It’s just a matter of grinding a little more here and there until the molding fits the drawing perfectly. (Don’t forget to check the knives for balance.)

We make both straight, large, and tight radius level-turn rails with these knives—completely custom. A shaper is one of the most versatile tools in a woodworking shop, and also one of the most dangerous. So, know what you’re doing, and pay attention.

•••

. . .

THISisSafety

Please don’t try anything you see in THISisCarpentry, or anywhere else for that matter, unless you’re completely certain that you can do it safely.

. . .

Selected resources:

Asher Benjamin, The American Builders Companion — an influential book written for Federal era  (c. 1810) builders

Edward Whitehead and Frank Chouteau Brown, Early Homes of Massachusetts and other reprinted titles of the White Pine Series — contains beautiful detail drawings of Colonial-era millwork, exterior and interior

William Ware, The American Vignola — a good collection of classical revival designs

Tunstall Small and Christopher Woodbridge, Mouldings and Turned Woodwork of the 16th 17th and 18th Centuries

C. Howard Walker, Theory of Mouldings — just what it says, originally published 1926

 

Roberts’ Illustrated Millwork Catalogue — and several other reprinted millwork catalogues from the late 1800s…Victorian!

Comments/Discussion

18 Responses to “Grinding Custom Shaper Knives”

  1. David Collins

    Jed!
    Thank you so much for that article. It was great to see you even if only in a video. You are a natural teacher, you always broaden our horizons with your instructions and it’s fun to see you working in your own environment.

    Happy Thanksgiving

    Reply
  2. Dixon Peer

    How can one “balance” two knives by hand? The preferred method is to use a machine designed specifically to handle the grinding of two knives while mounted in a “head”, whether corrugated or lock edge, that insures that each knife, when engaging the grinding wheel is at the same distance radially from the grinding edge of that wheel. Am I making sense here, or missing something? I know these grinders cost a lot of money, but they are the only way I know to achieve the most balanced set up.

    Reply
  3. Jesse wright

    Jed
    You are without a doubt one of the best carpenters I have ever seen! Thank you for sharing your tricks and techniques with all of us

    Reply
  4. Mike Pelletier

    Very good arcticle, might add Schmidt has some very good books on the subject of knife-grinding and tool making.

    Years back my first head was a two-pin head from weaver that used thin (I think 4mm) stock pretty easy to grind, but too thin to cut very deep profiles.

    All my tooling now is corrugated back and I have found getting the two knives exactly the same too time challenging for me, plus the5/16 thickness requires removing a lot of material. Part of it is I learned I was using the wrong cutting wheels. How deep a profile knife do you think is safe from 1/4 inch knife stock?

    I have a couple of shops I deal with that grind their knives exactly the way you do, and enjoy the independence of being self-sufficient. I presently depend on Schmidt or Dino-saw for knife-making, and still find myself wishing I wasn’t waiting for knives to arrive.

    How much time do you think you have in grinding an average pair of three inch knives. And is the 10 inch wheel diameter necessary or do you think a smaller wheel works?

    Reply
    • Jed Dixon

      In reply to Mike Pelletier’s comments:
      I make 1/4″ knives 3″ high that cut to the center of a 2-3/4″ handrail. A pair of handrail knives might take 2-1/2 hours to grind, and I can grind a 1-1/2″ base-cap or panel molding for my little Willliams and Hussey machine in about an hour. A 10″ wheel cuts much faster than a smaller wheel even though it doesn’t stay 10″ for long- it gets smaller as you dress it. The coolant spray also speeds the process up a lot. Usually I use corrugated back knives in a 4″ head to make wider shallower moldings , and lock edge knives to make shorter and deeper cuts for handrails.

      In reply to Dixon Peer’s comments:
      Hand-made cutters can be balanced in weight very accurately with an inexpensive beam balance like the one I use. It’s also useful for measuring dye powder for making stains, and, of course, for weighing hops for home-brew. Knives made on a pantographic knife grinding machine (or with a CNC machine) will always be faster and more accurate. I worked in a big shop where we used one to make molder knives, and they definitely will achieve the most balanced set up. Hand-made knives will invariably cut a little unevenly; that is, one knife will remove a little more than the other from certain parts of the molding. However, with some care, the moldings they make are just about indistinguishable, and I believe that, all other things being equal, they are just as safe.

      Really, the important thing is not how the knife is made, but what the molding looks like. I’d bet that a lot more ugly, and historically incorrect molding knives are made on expensive machines then are ground by hand; but I could be wrong.

      Thank you very much for your comments. I learn a lot from the experienced and interested woodworkers and carpenters who read my articles.

      Reply
    • Larry

      There are guides for how much a knife can stick out based on its thickness. I had a 1/4″ knife snap off once. I knew @ the time I was “pushing” it, dumb! Luckily was running a powrfeed.

      Reply
  5. Dan

    It’s good to see the creative end of carpentry. Much of the carpentry now days has become assembly, and cheap labor. We have lost many masters of the trade and turned the creative end over to large corporations. I am glad to see proof of how talented carpenters are, and that we need them to continue to inspire others into the trade.

    Reply
  6. Johan

    Jed,
    Thanks for the concise lesson. I have a fair knowledge of metals and grinding, and now more confidence in making my own knives.

    Reply
  7. Sebastian Eggert

    Thanks for showing us how you grind your knives. You are a natural teacher and writer. Thanks also for carrying on the tradition of doing quality work amid the proliferation of extruded plastic.

    How do you transfer the CAD or freehand drawing to the slightly different shape of the knives at the 15 degree angle?

    I’m fortunate that I use an older Weinig profile grinder that makes it much easier, but I did have to pay dearly for it. The greatest advantage is that if a knife gets knicked it can be resharpened in about fifteen minutes. That’s not so easy with handmade knives!

    Sebastian Eggert

    Reply
  8. Evan

    Mr. Jed,
    I want to say thanks for a great article too. I have ground my own knives a couple of times with a pneumatic sheet metal cutter while holding the knife in a vise. The sheet metal cutter runs at a high speed and cuts fast while keeping the metal a little cooler with the exhaust air. A light touch with my hand braced on the vise gets me really close. Then I would finish by touching them up with a combination of the Tormek and a mini die grinder. They were not perfect but for a few feet of custom trim I can get the job done for a reasonable price. Now I know a far better way to do it if I have to again. Thanks!
    Evan Meister

    Reply
  9. Matt Follett

    Hey Jed

    Stellar as always. Was wondering if you make custom handrail scrapers in a similar fashion? I have done a little custom fabrication of my own handrail parts but struggle with the refining. I’m usually copying a stock product but stock scrapers never seem to do the trick.Perhaps that is another subject or article in the works but was just curious. BTW, the ‘roots of rail’ shot at the top, I stared at it for nearly 10 minutes before I could continue reading.

    Matt Follett

    Reply
    • Jed Dixon

      Sebastian, Evan, and Matt, I don’t have to help you guys much; you’re already making custom cutters! Sebastian already has a Weinig grinder, I bet it’s a nice one. My brother has a Foley/belsaw grinder in his shop, that’s the one I’m used to, they seem to go for about $5000.00 on ebay.

      It’s possible on Autocad to stretch out a molding profile to cut true at 15 degrees, but to be honest, I don’t bother. The length of the knife only increases something like 3.5% , I just grind the deep part of the cutter a little deeper by eye, it’s only about 1/16″ per inch. Only when my moldings have to mitre to the same moldings made by another sub am I extra careful.
      Evan, I like your attitude, as you can probably tell, I’m a believer in designing and making things myself, and making the tools to make them if I have to. That’s what you’re doing with your system for grinding cutters. My system is a combination of time honored techniques handed down from other craftspeople- no need to always reinvent the wheel- and things I worked out myself in my ignorance. I hope I’ve made it easier for you.

      Matt, No shaper work on the roots of rail, I layed it out, and it was hand -carved by MIke Kennedy: angle grinder, die grinder and sharp chisels. The staircase winds upward with a continuous handrail for three stories, most of it is hand-carved with a few level turns and one or two pieces of straight rail made on the shaper.

      We do use the same technique to grind pattern hand scrapers for handrailing and also pattern scraper chisels for faceplate turning on the lathe. The lathe tools can be made from flea market files, or oil-hard tool steel bars, and the hand scrapers can be made from cabinet scrapers or, better yet, pieces of yard sale hand saw blades. These are very guick to grind because they are thin. I usually grind them at 45 degrees or more, and leave a burr on the edge to cut a fine shaving. Be sure to keep the tool rest very close to the wheel, other wise the thin steel can flex or bend downward.

      Reply
      • Matt Follett

        Ah good. All those old handsaws that my father in law gave me will come in handy. Time to get scrapin’. BTW, if you ever have a class on hand carved volutes, send me an email. I’d love to add another facet to me repetiour.
        Thanx

        Reply
  10. D.Mason

    I already have a 4in diameter schmidt head for corregated profiles; but I’m more interested in deep profiles–so what size lockedge head would you reccomend (I have a 1 1/4 bore)? It seems a 3 x 3 head is all I would need for lockedge?

    Reply
  11. Larry

    Grinding Custom Shaper Knives
    by Jed Dixon on November 26, 2010 Thisiscarpentry.com
    I also started grinding shaper knives early in my woodworking career. It was one of the most profitable things I did. When I started I used lockedge. I had two heads, one had a bearing for template work. I bought a SAC TS80 shaper & 4 wheel feed, new, sometime in the early ’70′s. The feed was always used for straight moldings. I later got some used molder heads so I could use corrugated steel. With the lockedge I only ground one knife to pattern then sorted through my pile until I found a near balance. I didn’t turn the spindle at high speed and would check for vibration @ startup. I bought my steel from the same place as you. The one thing I have to take issue with is the comment below “so that they each cut the same amount” Nice thought but not going to happen.
    “I buy my shaper steel over the phone from Charles Schmidt Co. in Montvale NJ. I almost always use 1/4”-in. thick XLW-type steel in 25-in. bars of various widths. I always make two identical knives for each molding—they go together in the shaper head, and balance each other. I try to make them as close to identical as possible, so that they each cut the same amount.”
    “Often, I’ll clean up the knife, turn off the spray for better visibility, and make one last, very light pass with both wheels for accuracy. This is sparking-off—a cut so fine that it just barely makes a spark.”
    We also take a last pass with the Weinig profile grinder but set to a slightly different angle. This also makes the knives more nearly identical since there is almost no wheel loss with the very little material being removed. No honing is required as the last pass is done with a very high wheel speed.
    Over the years I’ve changed the processes. Most of our moldings are now made on our 5 head Weinig, nice machine. Knife grinding often starts as a CAD drawing, template is cut from plastic on the CNC router, knives are balanced, set up in molder head(s), ground on the Weinig profile grinder, measured on a digital readout stand, put on the molder using the digital readouts on the spindles. Even with this level of technology it is assumed that we are single knife cutting and the feed speed is set to acknowledge that. Only high quality jointed molders will cut with all knives.
    We now have 9 shapers, several left setup for commonly run items, saves setup time & errors. Most have power feeds. One is a Gomad tilt used for curved crown moldings. A heavy monster @ 985kg. One is a Stegherr horizontal spindle used for curved casing and the like. It automatically traces whatever shape the wood is. We also have an R8 pin router that still gets used, the tilt table is nice. For some off the wall 3D shapes we use the Komo CNC router.
    “A shaper is one of the most versatile tools in a woodworking shop, and also one of the most dangerous.”
    I couldn’t agree more! I’ve seen the quote below several times and have it posted on the bulletin board with slightly different wording. You might want to change the photo/video of the bench grinder W/O side cover!

    “There is no smart way to hurt yourself woodworking, but there are a million stupid ways.”
    Larry Schweitzer, web page: http://www.lks-inc.com
    PS, I really like your vine newel.

    Reply
    • Jed Dixon

      Hi Larry,
      I admire you for building your business into a big modern millwork shop with up-to-date equipment, while sticking with custom work. The article, of course, is aimed at the small shop guy who shouldn’t have to be content with stock parts and moldings. You make two very good points: (at least!) First, A close examination of the moldings I make definitely shows that hand-ground knives, no matter how skillfully made, do not cut equally. Typically one knife does most of the work on one part of the profile, and the other on another part of the profile. Sometimes I take advantage of this with moldings that need very crisp edges with one knife cutting the vertical part of a filet, and the other the horozontal. I do try to set the knives out equally so they both cut, although many people let one knife do all the work, and the other is there for balance. A slower rate of feed is definitely necessary for good results when the knives are not exactly the same. Second, a power feeder is a must-have for making moldings on a shaper, for both quality and safety.
      Thanks for your comments!

      Reply

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