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Lathe hole drilling off center, Why?

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  • J Tiers
    It can happen if you force the drill too much. Usually you want to go easy, the easier the better if you want the hole to stay centered.

    It can happen if the drill is deflected by differences in hardness inside the part.

    Using a regular jobbers drill is typically more of a problem. they are quite flexible, and can wander more easily. I like to use a drill with more solid shank, and a shorter fluted section, as a starting drill. They go straighter, and following drills usually do not wander off of an existing hole.

    A jobber drill that has unequal lips is bad, because it starts off with a tendency to be off- line. Chances are it may wander off at some point and stay off-center because the flexibility means it does not tend to cut straight as much as a short flute drill

    If the drill is stiff, it tends to cut toward center, because the stiffness pushes it that way.
    Last edited by J Tiers; 07-31-2017, 01:19 AM. Reason: Spelling

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  • chipmaker4130
    How'd the chip look coming out of the hole? Even (approximately) from both flutes? You purged chips regularly, but how hard did you push the drill otherwise? What was the drilling speed? Factory grinds are usually great on US or other major brands, not necessarily on chinese imports. What did the drill point look like after the hole was drilled?

    The #1 suspect so far is still the point grind.

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  • Mr Fixit
    started a topic Lathe hole drilling off center, Why?

    Lathe hole drilling off center, Why?

    Hi Group,

    I have a Southbend 9A lathe that I was drilling some .75" CR round stock that was 2.75" long. I used a center drill in a fixed holder in the tail stock to start a hole.
    Then I used a 25/64 drill that was new (manufacturer sharpen) and my Jacobs MT2 mounted drill chuck, then I drilled with frequent cleaning of the chips and cutting oil. The start end is on center but the finish end is off center and I'm trying to figure out why.
    This was not a NASA piece but, It was off enough that I could see it without measuring, which bothers me. It will work for the need, but I want to solve the problem if I can to prevent future problems.


    Mr fixit for the family