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Making Taps for 1/2 inch and 3/8 inch Acme precision rods

Discussion in 'Other Builds' started by Giarc, Jun 29, 2016.

  1. Giarc

    Giarc Master
    Builder

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    A while back, someone asked me on one of the threads here how I made my taps for my 1/2 inch 5 start and 3/8 inch 4 start Acme rods. I finally had time to write it up. I would not have gone through the trouble if the the nuts I needed were readily available like the 8mm nuts in the OB store. I had thought about ordering from DumpsterCNC, but it would have cost me over $100 for the number of nuts I needed. A 6" X 6" X 3/4" block of white Delrin was $18 at McMaster Carr, and I can make a lot of them from that one block, so I figured I would give it a shot. Most importantly, I also figured it would be fun. Another criteria was I needed them to be compatible with the Cbeam. The DumpsterCNC nuts weren't if I remember correctly. It has worked out very well and I have all three axes working with them. I will use the 1/2 inch nuts for this build log. This is it in a nut shell:

    1) I found a piece of suitable length wood that was 1 1/4" X 2 1/4" X about 24" in the scrap pile and routed (or one could use a dado blade) a 1/2 inch wide grove in the wood and slightly less than 1/4" deep.
    [​IMG]
    2) Cut a grove with the saw blade (the table saw made this easy) approximately 6 inches long. I widened the grove to a little over 1/4" by making multiple passes with the saw blade.

    Drill pilot holes in the grooved piece for screwing the two pieces together.
    [​IMG]
    3) If you have a drill with a chuck big enough, stick your threaded rod in the drill and taper the end you intend to be the cutting end on a bench grinder by spinning it while grinding it. If you don't have a chuck big enough (I didn't for the 1/2 inch) spin it as best as you can by hand.

    4) Insert the threaded rod and screw the two halves together. In the first photo you can see the halves don't go together easily.
    [​IMG]
    But once screwed together the rod is held firmly.

    [​IMG]
    5) I had a metal cutting chop saw with an abrasive blade available to me so I clamped my piece to the saw table grooved side up and slightly to the right of center to under cut the cutting edge of the "teeth" of the tap. My original plan was to use my table saw with an abrasive blade, but I was using that as my build platform for my CNC. If I had used the table saw, I would have put it slightly left of center since I would have been cutting from underneath.

    Once clamped, I cut down through the pre-cut groove in the wood into the rod with the saw blade. The cut was made all the way down through the threads. You can see by the burn marks on the wood in the previous pictures how hot the rod got.

    6) After the first cut, I drew a line on the block and I loosened the two halves. Then, I rotated the rod 90 degrees. I marked the rod end in 4 places to try to be as accurate as possible prior to rotating it.

    7) Repeat step 5 and 6 until you have your 4 grooves cut in the rod. The rod got really hot when I was doing this so I would dunk it in water between cuts.
    [​IMG]
    8) using the grinder again, make the non-cutting end square so a wrench or vise grip can grab it to help with tapping of the delrin nuts.
    [​IMG]

    Here is a finished anti-backlash nut. Can you tell where I got my inspiration?
    [​IMG]

    I had done all of these steps prior to taking photos which is why there was only one opened beer in the build log. This was definitely a 2 beer project. :thumbsup:
     
    Moag and Kyo like this.
  2. Kyo

    Kyo Master
    Staff Member Resident Builder Builder

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    Nicely done! This will come in handy for those who have been looking for larger screws compatible with OB parts.
     
  3. Giarc

    Giarc Master
    Builder

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    I like the 1/2 inch 5 start rods. Mine span 1500 mm and I had my CNC router doing up to 5000 mm/ minute with no whipping. It would be much easier to get inexpensive components if it was 12 mm though. I had a friend turn mine down to 12 mm and the 3/8 down to 8 mm. The metric shaft couplers and bearings I used are so much cheaper.
     

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