piercer, table bit, etc.

the other night I saw a post by Chris Schwarz about some weirdo wooden pins securing joints… (many will have seen it, but here it is just in case http://blog.woodworking-magazine.com/blog/An+Unusual+Shape+For+Wooden+Nails.aspx  and immediately recognized what was happening there. Turns out to be a long-time favorite topic of Jennie Alexander’s – the use of spoon-type bits, variously called “peircer bits” “table bits” “shell bits” etc., for boring the peg/pin holes in mortise-and-tenon joinery.

two piercer bits

Alexander taught me a lot about these bits, we have used them for years in the joinery work we do. They make a very distictive hole, with torn grain resulting when the bit comes around from the “long” grain to the end grain of the stock. Here’s one from a 17th century joined chest front that was attached to board sides with square wooden pins. Alexander calls the torn grain disturbance “sprucks” – a case of onomatopeia says Jennie…the bit makes that sound. I haven’t heard it myself, but I see it all the time.

So I wrote to Chris and told him there was no mystery tool to fashion those weirdo-shaped pins; it’s the bit that makes a funny hole, then the pin is shaped by the bit. Mike Seimsen clocked it as well, but he uses gimlets according to Chris’ note:   http://blog.woodworking-magazine.com/blog/Weird+Wooden+Nail+Its+The+Bit.aspx

The bits are often found in two different configurations; one of which might result from sharpening the other over time….

side view of piercer bits

One way to think of it, says Alexander, is that the one in the top of this view will hold water, the bottom one will not. But over time, the top one evolves into the bottom type here…sort of.

Like any tool, you can hear a lot of different ways to sharpen these. inside, outside, files, stones. I say inside only, I have worked them with burnishers, files and stones. these days I mostly do it with a burnisher. Mark Atchison, the blacksmith I work with, has a nice method of getting these things really sharp. He takes a worn-0ut round file, and grinds the end of it square and uses it as a burnisher run down the inside of the piercer. Needs various sized burnishers to fit different sized piercer bits.

sharpen piercer with the end of a file

To get back to Schwarz’ original post, I tried to replicate the exaggerated shape of the sprucks and pins in his example, I took a quick swipe at it – note that the example Chris had was in softwood, I assume some European Pine; so I used white pine in my shop. (Sorry for the garish light, Thanksgiving season is no time in my shop for experiments & photos)

sample holes etc

Here is one in oak, a photo Alexander shot years ago. Note that these disturbances (sprucks) happen more dramatically in the tangential plane of oak, as here in this 17th-century joined stool.

pin in joined stool

(that’s a photo of a photo, sorry for the glare)

In the black & white shot above, it appears that the boring was counterclockwise, based on the direction of the torn fibers. For many years I thought that, but now I think it’s an exit hole. that photo is of a rabbet joint, fixed with wooden pins. I have found the easiest way to eyeball the placement of pin holes in rabbet joints is to bore them from the inside.

boring pin holes in rabbet joint

Someone asked over on Chris’ blog, where do you get these bits – they aren’t terribly old, I assume, but not made these days. Typically nowadays I get them in box lots in auctions, it’s a grab-bag but not too pricey. Otherwise, digging thru antique dealers’ odds & ends…


5 thoughts on “piercer, table bit, etc.

  1. Peter:
    Thanks for your description. Just a bit more on the 17th Century joiner’s bit. They called it the “piercer”. Moxon and Inventories use the term. The two telltale disturbances of the grain are one of the first tests to determine if a joined work is period or not. Moxon unfortunately comments that the office of the piercer is so well known that no discussion is necessary! Sprucks? Remove the wax from your ears and shut off the Grateful Dead, you will hear the sprucks. While the piercer bit does indeed pierce wood, the term is a bit misleading. The tool is really a parallel-sided reamer. Though also a reamer, the spoon bit is a different tool. It is the principal “boring” tool of the traditional chair maker. Notice that the spoon bit has a circular or almost circular leading edge. This allows the spoon bit to bore a hole through chair parts that almost bores all the way through the part yet does not weaken it. It is rare to find a spoon bit that is as narrow as a piercer. There is no need to sharpen both edges of the piercer or the spoon bit for that matter. Most are sharpened on just the leading edge and rotated clockwise when in use. I find the best way to sharpen is to run a ticketer, any sharp edged toll steel, down the inside of the reaming edge. The piercer is a wonderful tool and does its job faithfully. Old tool sources are best places find piercers. Some gimlets may be modified to act as piercers. If they have a screw thread point, grind it off.

  2. Whoops! I forgot to mention what happens to a pin when it is driven into a pierced hole. The pin is usually four or eight sided, slightly tapered and dry. It is driven into the hole until quite tight. The pin is under substantial pressure and no matter how one holds it during assembly, the pin rotates until one of its arrises (sharp corners) seats itself in one of the sprucks. The pin is so compresses that it deforms so that the other spruck is also filled with the pin. We end up with a double bladed pin wheel cross section. Peter and I diverge in pin making practice. He, an active joiner on a daily basis, quickly whittles his somewhat approximate pins with a chisel and mallet. I fastidiously shape mine with shaving horse and drawknife. I am a certified overcautious joint freak. I haven’t heard of Peter’s joints failing. The piercer’s sprucks are fully filled in either case and the pin is securely locked by the sprucks. The sprucks also prevent pin rotation. The next time you pass period joinery look for the sprucks. The piercer, the sprucks it makes and the dry oak pin combine to make an amazing fastening. Listen up. If I get my chores done, perhaps I’ll have time to ruminate about why pins on drawbored joints have slightly mushroomed heads and stand slightly proud of the surface of the piece. Perhaps Peter could find time to put up some slides and diagrams on this subject and get me revved up. It is a good day when one carefully examines a drawbored joint pin that has been in place and functioned for three and a half centuries.

  3. They still have value today. To remove a snapped off screw, a spoon bit can be started around the broken screw, worked down until the ‘plug’ will break out. Cleaned up with a twist drill the hole can be doweled and re-used.


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