Make ‘Pinch Rods’ With Home Center Materials

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There are lots of ways to confirm that a carcase or sub-assembly is square, but my favorite method is to use so-called “pinch rods.”

Pinch rods are simply two pieces of wood that have pointy end bits. You put the pointy ends into two diagonal corners of your carcase. If that measurement matches the measurement of the other diagonal, your case is square.

There are lots of ways to hold these two sticks together, from splines to blue tape to a commercial product from Veritas. The best way, in my opinion, is to make a metal and wood assembly yourself. I first saw this sort of arrangement at Roy Underhill’s “The Woodwright’s School.” I was so enamored with them, that I decided to make some for myself and friends today while taking a break from an editing project.

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I went to the home center and bought some 3/4” steel square tube (with 1/16”-thick walls) and some 1/4” x 20 thumbscrews. For about $12, I got enough metal supplies to build a dozen sets of these jigs.

Here’s how a friend and I made them:

Cut the steel tube to 7/8” lengths – you’ll need two of these bits to make a single jig. Deburr and dress all the raw edges. Drill a pilot hole in one of the pieces and tap it for 1/4 x 20 hardware (a very common tap size).

Mill up some wood. You’ll need something stable with straight grain. I used old heart pine flooring I had sitting in the racks. The interior dimension of the channel is 5/8” x 5/8”, so I milled up two sticks that were 5/16” x 5/8” x 30”. Two 30”-long sticks will handle most assemblies, but your mileage may vary.

Point the ends of the sticks and you are ready to assemble.

Some of the hardware I bought was covered in zinc, so I stripped that off with a citric acid solution. This greatly improves the appearance of the metal bits.

That’s about it. Sleeve the two metal bits onto the wood and engage the thumbscrew (make sure the screw is pressing into the face grain of one of the sticks instead of pressing into the seam between two sticks). You are done.

You can finish the sticks if you like, but heart pine makes its own resinous finish.

In my opinion, pinch rods trump all the other systems I’ve used for checking the squareness of an assembly, from measuring diagonally with a tape to using oversized try squares.

— Christopher Schwarz

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19 Responses to Make ‘Pinch Rods’ With Home Center Materials

  1. joemcglynn says:

    Neat idea. You can fancy it up with brass spade head thumbscrews (mcmaster.com # 92427A537). Maybe even some brass/bronze square tube.

  2. John Switzer says:

    Have you thought about some form of clamp pad betweenn the screw and the wood? seems like it won’t take to long to leave the wood strip full of holes.

  3. fitz says:

    binder clips and two sticks works, too (for those 2 a.m. glue-ups when the big box store is closed).

    • Patrick says:

      Darnit. I was going to sent that into “Tricks of the Trade.”

    • Fred Freitag says:

      I think binder clips are the best option – not because they are really cheap and readily available but because you can use standard 3/4″ material PLUS they allow you to “move” the wooden strips to make an accurate measurement.while holding them together. The second binder clip then holds them together to make your measurement OR you can use a spring clamp to make sure the wooden strips don’t move for certain. A spring clamp is to much pressure to allow easy movement of the strips of wood to make the measurement – although it’s good to use for the final clamp to keep the wooden strips from moving. I have 3 binder clamps along with a cheapy spring clamp that I routinely use for a “pinch” or “bar” gauge. However 2 binder clamps are usually enough to satisfy me that I haven’t moved a wooden strip accidentally before I measure them.

  4. Dave says:

    Glue ups at 2 a.m., ( around the Christmas Holiday ) I thought I was the only one?
    FYI; A number 7 drill bit makes the correct size hole for a 1/4-20 tap.

  5. markhochstein says:

    Chris, What are you using to cut the steel tubing? That’s been my limitation when it comes to using steel. Got a quick and dirty way?

    • lostartpress says:

      A hacksaw makes short order of mild steel. If you have a table saw you can (with care) use an old carbide blade to cut mild steel. Or a metal-cutting band saw blade. Or have them do it for you at the hardware store for a minimal charge.

    • William Duffield says:

      I use a hacksaw blade in my bowsaw, made from Bugbear’s plans. I have the hacksaw blade in it a lot more often than the turning blade.

  6. Jonathan says:

    I love reading Charles Hayward’s How to Make Woodwork Tools but never could understand his diagonal strip tool on page 43. I understood what it was meant to do but just couldn’t understand it’s usage perhaps because the picture is showing the tool upside down. Anyhow, finally today after re-reading it again after being prompted by your post I think I get it. As soon as I flipped it around in my mind I could see how it would work well because it would be resting on top of the far diagonal and the pointed end could be positioned in the same plane as well (sticking out above the face.)

    I doubt anyone else has struggled with probably his most simplistic tool in the book but just thought I’d post this anyhow.

  7. tsstahl says:

    Can’t get too many threads on 1/16″ steel. Fortunately holding a stick doesn’t require too much force. I love inexpensively crafting effective solutions. Kudos.

  8. GregM says:

    Tap a finish nail into each stick, snip off the heads, file to a point and you immediately have an adjustable trammel. Choose your sticks with care, and you can add “winding sticks” and “straight edges” to your arsenal as well. This (IMHO) is one of the very few actually useful combo hand tools – after the Nicholson chisel/rasp, of course!

  9. Barron says:

    You can also get metal cutting blades for a jig saw.

  10. Richard says:

    Sorry, I am a bit slow…and confused.
    How does the second sleeve stay in place? Is it just friction fit and left to slide freely? Or is it held i place with a screw?
    Sorry, must be this head cold…..damn long airplane rides….

    Hoss

  11. J. Pierce says:

    I got one of these in a toolbox buy once. (Where all my saws came from) Whoever made ’em just bent some brass plate. Almost as great (and unfortunately, almost as useful) as the saw-handle cane that came in the same box.

  12. Tony Z. says:

    Borg has nylon 1/4-20 wing nuts. Won’t leave indents in the wood, but will provide tension. The LV model has one of the sleeves attached by a flat head screw into one side of the wood, though one could use two wing nuts.

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