Tuesday, January 5, 2016

Pipe-End Grinding Jig




This season of the show I'm trying to focus more on workshop skills, and one of the most basic workshop skills is designing and building jigs and fixtures. In a small shop you almost never have specialized machines to do particular jobs. But as long as you have a few basic power tools, and some ingenuity, you can usually build jigs to do any job you need. For example, the other day I was building something out of metal, and I had a problem. I needed to socket a piece of pipe into a hole, but the end of the pipe was bigger than my biggest drill bit. I could have ground the end of the pipe down by hand, but this was a precision job and it would have been tough to keep everything straight and circular. I would have had the same problem if I tried to file out the hole bigger. Instead, I spent about 20 minutes and created what was essentially a new power tool to do the job, a grinder that produces tendons on the ends of pipe or round stock.

You may never have the same problem, but I thought it would be a good example of a jig with moving parts that might give you some useful ideas.

Step by Step

  1. Find a piece of pipe that has approximately the same inside diameter as the outside diameter you need to grind. If you don't have a pipe vice, grind some flats on the end of the pipe so a regular machinist's vice will grip it securely.
  2. Use a hand ream to smooth the bore of the pipe and enlarge it to a couple thousandths of an inch bigger than the finished diameter of the tendon you need to cut. The ream I use is made for bicycle seat tubes but I use if for all sorts of jobs. Be sure to use plenty of cutting oil and take many light cuts.
  3. Find a piece of steel strap to hold the pipe. I broke this one off the back of an electrical box.
  4. Use a table saw to cut the v-shaped notch where the jig hits the pipe.
  5. Use a table saw to round the corners on the upper piece of wood and to rough out the hinge. You could do all of this with a hand saw, the table saw is just faster.
  6. Use bench chisels to clean up the hinge.
  7. Drill a hole and insert a hinge bolt.
  8. Put a couple screws through the wood to reinforce it at likely splitting points (not shown in video).
  9. Attach the pipe, using screws to hold on the strap.
  10. Attach the grinder to the jig with some 12-gauge electrical wire. You can also run a screw through the wood to engage one of the holes in the grinder (not shown in video).
  11. Build and install the cut depth adjustment screw. If you decide to make a wing-screw, follow these steps:
    1. Find a wing-nut with an inside diameter slightly smaller than the outside diameter of the screw head.
    2. Turn the screw head to the thread-crest diameter of the threads on the wing-nut. If you don't have a lathe you can chuck the screw in a drill and turn it with a file.
    3. Use a die to thread the screw head then screw on the wing-nut.
    4. Solder the two pieces together.


    Another method, which doesn't require threading, is to clip a dime in half and solder one of the halves into the screwdriver slot on (flat-head) pan head screw.
  12. Blunt the end of the cut-depth adjustment screw and add another screw where it contacts the upper piece of wood. This will keep it from digging into the wood.
  13. Clamp the jig in your vice.

Using the Jig

Slowly rotate the pipe you're grinding against the grinding wheel as you slide it into the other pipe. You get smoother action if you grease the inside of the larger pipe. PRO TIP: Set up a "junk yard" for all your old one-off jigs. When you build a new jig it's often faster to cannibalize old ones for parts than to start from scratch.

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