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IndustryArena Forum > GENERAL MANUFACTURING PROCESSES > DRILLING > Best practice question for drilling holes for metal dowel pins
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  1. #1
    Join Date
    May 2013

    Best practice question for drilling holes for metal dowel pins

    I'm using 1/4" metal dowel pins for alignment pins on two aluminum plates ( Molds for lead fish lures )

    I need the holes on one of the plates to be a tight fit so the pins stay in place.

    The matching hole will be a loose fit so the plate can easily be split apart.

    What would be my best approach to get a consistent result?

    A: Drill a pilot hole and finish it up by boring out the hole to the correct size with an end mill

    B: Don't do a pilot hole and just do the hole operation with an end mill boring tool path

    C: Don't use an end mill and do the hole operation with drill bits.

    On another project I've been using a drilled pilot hole followed by boring out with an end mill and I've noticed my holes are not always perfectly round...

    Thanks much for any suggestions..


  2. #2
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013

    Re: Best practice question for drilling holes for metal dowel pins

    Drill and ream. Normally you want a tight fit on side and loose in the other. So drill with a 0.234'' (15/64'') and ream with a 0.2495'' or 0.250'' reamer. For the loose side, drill with the same drill and ream with a 0.251'' or 0.252'' reamer. It's best to clamp the die halves together and drill and ream both in one setup, that way you are sure they are in perfect alignment. You will want to drill all the way through so you are able to punch the dowel pin out if needed.

    And another hint: make sure the hole locations are not symmetrical. If you locate one 1/4 inch from the edge, then locate the other at 5/16'' or 3/8'' from the edge, that way it's impossible to put the die halves together incorrectly.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
    Join Date
    May 2011

    Re: Best practice question for drilling holes for metal dowel pins

    What Jim said, and also...

    On the side where you want the pin to stay put, you take a center punch and hammer a good divit on the inside of the hole. When you hammer the pin in it will most likely stay put.

    You probably can't do this to the pin because it's hardened steel, so you do it to the aluminum. Also works on mild steel. I have used this technique, but it wasn't for a casting mold.

    There's probably a more professional approach to doing this, like using some special loctite compound, but unfortunately I haven't been able to try that.

  4. #4
    Join Date
    May 2013

    Re: Best practice question for drilling holes for metal dowel pins

    Thank You Very much for the suggestions...

    I followed your suggestions... and that did the trick. ( Perfect Fit )

    I didn't have a reamer bit for this test.... so I used a 3/16" 4 flute end mill that was choked way up so there wasn't any deflection and that seemed to work fine.... but I will probably still order the reamer bits.

    Honestly I think that was my problem... I was using an 1/8" end mill for the cleanup pass before, and it wasn't choked up in the tool holder... so I think it had plenty of deflection verses the thicker 3/16" end mill.

    Thanks again for your help...


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