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tap extension

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  • tap extension

    Material is 3" thick, 4 ea. 5/16-18 bolts broke off on back side with no way of getting to them without disassembling machine. The holes are drilled and tapped all the way through. Bolts were loctited with "Red Loctite". Sprocket tap not available. Drilled through with tap drill size. Ground shank of tap down in spin jig to .220. What is the best method for attaching round stock extension to tap? I have tried several methods over the years with mixed results. Any one have any method that works most of the time?
    Kevin Middleton
    Rome Georgia

  • #2
    Cut a groove in the end of the extention rod to match the tap flats, silver solder to the HSS tap.

    Never tried it, but it sounds like a good idea.


    • #3
      They're called Extension Taps and/or Extented Taps. McMasters has them. Or just do as JCD suggests.


      • #4
        KBC Tools sells a nut tap which is 5.5 inches long for $25cdn/$15us, pn 1-369-0201.


        [This message has been edited by coles-webb (edited 01-01-2006).]


        • #5
          I would probably grind a blunt v on the end of the tap, then grind the matching v shape slot in the end of the rod. More surface area to take silver solder.
          You ground the tap down to .220- that leaves room for a piece of 1/4 inch od brass or stainless tubing to be used to help align the tap with the extension rod, which I would make from drill rod or music wire. Grind a hole in the side of the tubing where the solder can be introduced to the join. Flux the ends, insert into the tubing with the hole positioned so the gap where the v's meet is visible. This is where you introduce the silver solder.
          I would take a scrap of metal, tap that size hole in it, and clamp it in a vice. Screw the tap into that hole, and use a nut also as a locknut to make it snug. This will prevent the heat from affecting the tap, if that would happen with your tap material. Fasten this with the hole in the brass tubing upwards, and lay a chunk of silver solder in the hole, with some flux. Heat from the other side until the solder flows, then apply more solder until the join is saturated. Grind the tubing down only until it's an easy fit into the threaded hole.
          It almost takes longer to explain this than to do it. I've done this with brass tubing from a hobby shop, but I suspect stainless tubing would add a touch more strength to the join. Hopefully you could lay your hands on some thin wall stuff that would be suitable.

          FWIW, my application was to thread a hole through both sides of some channel, which was 3 or 4 inches wide, don't recall exactly now. The tapped holes had to have the threads aligned so a threaded rod could pass through both holes without binding. I tapped the first hole, then took a piece of the threaded rod and ground a divot out of one side at one end. I used this to mark the threads in the opposite hole, so I could then insert the lengthened tap and start it on the marks. Though the threaded rod was soft, it left enough of a mark that I was able to follow them with the tap. Worked ok.

          [This message has been edited by darryl (edited 01-02-2006).]
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


          • #6
            Remember you will always have problems with trying to tap through existing threads especially if lock tight has been used on old threads.

            I would opt for buying a long tap. You will eventually have a need for a long tap again so it won't be a waste of money.

            McMaster Carr, MSC, and just about all tooling companies have them in stock.
            Living By the Square and On the Level


            • #7
              This is a technique by my mentor in Indianapolis, Bob Bienke.

              Grind the end the tap and extension to the same diameter, then grind both to a shallow angle (20-30 degrees). Prepare a sleeve with an ID to match tap and extension and with any available OD. The width of the sleeve should be a minimum of .37". Place the tap in a brass heatsink. Flux the ground surfaces and the sleeve and slide slide together. Silver solder, then grind off the sleeve. More than one sleeve can be used if alignment proves difficult. We used this technique to make bent taps for automatic screw machines.


              • #8
                I made an extended 1/8" NPT tap a couple weeks ago. I ground the tap shank down using a Spin Index and surface grinder. I drilled & reamed one end of some drill rod for a press fit on the tap and put four flats and a center drilled hole on the other end. On the tap I left about a 1/4" of the ground down section oversize so when pressed together there would be a gap for welding. I MIG welded them together after pressing together. I welded small beads on opposite sides and then let it cool and then repeated.

                Jon Bohlander
                My PM Blog