Tapping Wrench & Tap Guide
By Allan Cusworth
A great addition to our toolbox for threading wooden faceplates of anything else needed to fit the lathe’s headstock spindle is a tap with the same thread configuration as the spindle. My Nova DVRxp spindle is 1¼”-8 tpi. A good source for these taps is Beall Tool Company in Texas (www.bealltool.com). When we use this tap we need to find a way to turn the tap with the spindle locked. You can use an open-end wrench, or a set of vise grips but both have limitations. The wrench falls off easily, and the vise grips chew up the square end of the tap.
I recently made a tapping wrench that eliminate both challenges. I read about it in Doc (Clarence) Green’s book, Fixtures and Chucks for Woodturning.
I also bought a spring-loaded Tap Guide on the internet that applies constant pressure on the tap when threading so the chance of the threads being torn away is reduced.
Both the wrench I made, and the tap guide are shown in the picture with this article.
I turned a 3” diameter MDF disk and drilled three ½” diameter holes equally spaced around the outside edge surface. Three pieces of ½” dowel I bought at a Dollar Store were glued into the holes for handles. I drilled a ½” diameter hole in the centre of the disk and chiselled it square to match the square end of the tap. I drizzled thin CA glue into the square hole to make it a little stronger.
To use the device, the piece to be threaded is mounted in the scroll chuck on the headstock with a 1 1/8” diameter hole drilled through it. A small chamfer is cut on the edge of the hole to guide the start of the threading procedure. A Jacobs Chuck is placed in the tailstock quill and the tap guide is mounted in it. The tapping wrench is placed on the square end of the tap and the assembly is placed against the hole to be threaded, the tailstock with the tap guide is brought up to touch the dimple in the end of the tap and the tailstock is tightened securely. The headstock spindle is locked and the tailstock handwheel is tightened to compress the spring in the tap guide.
Now the fun begins. Gently start turning the tap with the tapping wrench while maintaining the pressure on the tap guide with the tailstock handwheel. With a little practice a clean thread can be obtained.
If you do not have a tap guide; you can use a small cone point on a live centre placed in the dimple in the tap. However, you must be more careful when applying the tailstock handwheel pressure.
I also made a tapping wrench with a 7/16” diameter square hole to match the tap I use to thread fixtures to fit my OneWay Live centre which has ¾”-10tpi threads.