Making pipe jaws were a challenge in the beginning. I wanted to support the old vises by making these jaws since you can’t find any new ones very easily. My first issue was how the heck do you measure them. I wanted to build these as close to originals as possible since some customers want to replace only one.
Back in my mold making days I had to figure out how to measure shapes that were curved and needed it very accurate. I did this with a microscope attached to my CNC. I like the Skoal scope shown in my picture, which is very affordable.
I used the readout on my CNC to create points at every intersection. On this drawing of a Starrett 326 Pipe Jaw, I added small circles at every intersection where it is easy to connect the dots.
After squaring up the A2 Tool Steel blocks, I rough in the large and small V section where the teeth go, as with this CO Wilton Pipe Jaw. I do this so when I cut the teeth so I am not removing too much material. It keeps the cutters corners sharp.
After carefully looking at the geometry created taken with the microscope, it became clear the teeth were rotated at 14 degrees and the teeth are cut at 90 degrees. The vise companies had special cutters made to cut the teeth at one swoop but I cannot afford to have a cutter of this size made or have room for a machine to handle this horizontal cut. Instead I made a special set of jaws to hold the pipe jaw at 14 degrees and use the corner of a 3/8 end mill and step down each cut.
Before I could do that, I needed the geometry and depth numbers so I could program my CNC. Here is a drawing I used for a American Scale Pipe Jaws. Looks more complicated than it really is.
As you can see in the drawing above, I color coded the geometry to help me in programming. After that, I pick up the pipe jaw noted here. When rotating blocks at a angle it becomes more difficult to locate the block. It is helpful to use a 1/2 inch gauge pin held on with a flat magnet and sweep in the pin center with a test indicator. I rotate the indicator 180 degrees then drop the indicator to hit the high point of the pin and rotate the indicator to find the high spot, set the dial to zero and do the same 180 degrees on the other side of the pin till I have reached a zero reading finding the pin center. You could use a edge finder but I choose an indicator.
I also set the end mill to the top of the pin and that would be my Z-zero. All the numbers on the drawing are taken from the pin center line in the X axis (left to right) and the depth of the cut (Z-axis) is taken from the top of the pin.
After programming my CNC, the rest is easy. Using a sharp carbide end mill I cut a roughing cut leaving .005 on the X-axis and .005 on the Z-axis, and then do a finish cut.
De-burr the entire jaw. Send to heat treating and harden to 54/56 Rockwell. Done.