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Getting A Straight Hole With Drill Press?

Discussion in 'QUESTIONS & ANSWERS (Get Help Fast Here!)' started by dontrinko, Jan 1, 2017.

  1. dontrinko

    dontrinko United States Active Member Active Member

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    Sometimes when I drill a hole using my drill press the hole is not perfectly straight? i have checked with a square and the platform is perpendicular to the drill chuck. My drill vice has a "V" in it to hold round stock straight. i have checked this also. What am I doing wrong? Thanks; don

    P.S. when I need a perfectly straight precise hole i use a lathe but i would think The drill press would be straight also
     
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  2. tweinke

    tweinke United States Active User H-M Supporter-Premium

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    I have had pretty poor luck with hole sureness with a drill press, mill is a lot better. both are better then a hand drill for me.
     
  3. Uglydog

    Uglydog United States Active User H-M Supporter-Premium

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    The table on my DP tilts relative to the column slopes down from the middle toward the front and back about an 3/16 of an inch.
    Make sure your quill is 90degee to the table.
    If the table is 90degrees, does the vise hold things square to the column & quill?

    Note: I cobbled this table together from 36inch tall I beams (legs) from a torn down bridge and left over 12" channel (top) from the same demolition.
    All was twisted, bent and free. Works well for putting holes in stuff. Not so well if you want precision.
    Come spring this table is being reassigned as an outside welding table and I bringing in a barn find gang table.
    The reason I'm elaborating is that we don't necessarily need to spend huge money to make things work.
    Question becomes what is the application and what are the tolerances.
    What are the reconciliation options?

    Having a good time in the shop and doing good work doesn't necessarily mandate spending huge $.

    Daryl
    MN
     
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  4. kd4gij

    kd4gij United States Active User Active Member

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    First what model drill press? Second most drill presses aren't precision machines. And I said most.
     
  5. Uglydog

    Uglydog United States Active User H-M Supporter-Premium

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    How did you check square?
    Consider chucking a drill rod, or other known straight rod.
    Then check square.

    How far is it off?

    Daryl
    MN
     
  6. dontrinko

    dontrinko United States Active Member Active Member

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    i did check and it is suare, don
     
  7. Chuck K

    Chuck K United States Active User H-M Supporter-Premium

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    Your problem could be more about the grind on your drill bit than the machine itself. Drills aren't real precise under the best of circumstances but if the bit isn't perfect it's pretty tough to get a straight hole that's on size. You might try pecking at it.
     
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  8. dulltool17

    dulltool17 United States Active User Active Member

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    You might also try a center drill or spot drill to establish a better start to the hole. If your holes still wander as your drill deeper, then, as has bee suggested, look at the grinding of the point.
     
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  9. hman

    hman Active User H-M Supporter-Premium

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    +1 to all the above.

    Another possible cause of crooked holes is trying to use too much downward force on the drill bit. This is most likely with smaller diameter bits. They can flex if pushed too hard. It's also natural to bear down harder if a dull drill bit isn't cutting as fast as you think it should (don't ask how I know). So be sure your drill bit is sharp, and use cutting oil.
     
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  10. coffmajt

    coffmajt H-M Supporter - Premium Content H-M Supporter-Premium

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    are you talking about keeping a hole straight when drilled into a round piece of stock? If that is the issue, then it could be your drill bit tip is walking as it tries to start the hole. For these situations I use a hardened drill bushing as a guide to keep the drill bit running true. You can make some pretty simple jigs to hold different size drill bushings == Jack
     
  11. silence dogood

    silence dogood United States Active User H-M Supporter-Premium

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    One problem with a drill press is the way the table is supported. The table is cantilevered from the column. The cast iron table will actually flex from both the weight of what you are machining and the pressure from the drill bit. You can actually see it by using a dial indicator and watch it go out of square(if it was square in the first place). One way that I got around it was to block up the front part of the table. Did not do it very often since it was a hassle. Now I have a milling machine that I use that for precision drilling. Also, watch Tubalcain's tip #92.
     
  12. bosephus

    bosephus United States Active Member Active Member

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    something i have found that makes holes wander is chip load , even more so if one flute is cutting more then the other ... using cutting oil and constantly clearing chips can help some .
    deep drilling with a small bit and you should be clearing chips at least once per dia of the drill in depth .
     
  13. mikey

    mikey Active User H-M Supporter-Premium

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    A drill press can potentially drill pretty accurately but there are a lot of variables, as folks have pointed out. Assuming your machine is in good shape - bearings good, quill adjusted, chuck installed straight - then it usually comes down to the drill and technique. If your drill is sharpened properly such that the geometry at the tip is symmetrical and you spot the hole first, the drill should drill a reasonably straight hole.

    I've found that there are a few things to watch:
    • Use enough feed pressure so the drill cuts continuously. Not only is this a more accurate and efficient way to drill, it keeps cutting temperatures down. I usually go one step down on speed and increase feed and it works better for me.
    • Pilot drilling is fine and we all use it but if I have a hole that I need to be straight I go straight to an on-size drill. Pilot drills are typically only large enough to span the web of the on-size drill and these smaller drills often will bend and drift, causing the pilot hole to be inaccurate. Your on-size drill then follows this inaccurate hole and you get an inaccurate result. When using an on-size drill you have to increase pressure to get it to cut but it will usually drill more accurately. This is especially useful if you plan to ream the hole; spot the hole and then go straight to the drill you need just before reaming. That hole will be more accurate and the reamer will do a better job.
    • Pay attention to your tip geometry. If the chips flow differently from the flutes then your geometry is off and your hole will be off; one side of the drill is cutting and the other is not. Time to re-grind your drill.
     
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  14. 12bolts

    12bolts Global Moderator Staff Member Active Member

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    Don,
    Maybe its flexing under load. Try preloading your table with a few pounds and then check it for squareness and perpendicularity, (is that really a word??)

    Cheers Phil
     
  15. British Steel

    British Steel United Kingdom Active User Active Member

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    It's really a word!

    I have a cheap benchtop drill press which flexes at the table/column joint, a wooden block and a scissor jack go under the table to support it when I'm looking for precision...

    A dial indicator on the table, base on the column while you apply "firm pressure" through a piece of bar in the chuck is quite revealing, quite apalling in the case of my drill press!

    Dave H. (the other one)
     
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  16. brino

    brino Active User H-M Supporter-Premium

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    Lots of good info above.
    One thing I did NOT see mentioned above is to lock the drill-press table height clamp on the column.
    It is surprising the amount the front of the table droops when it's loosened and rises when it's tightened.

    I consider most drill-press work to be "close enough" tolerances ie., not for precision work.

    However, if you need the best you can from it then use a dial indicator on a swing arm in the chuck (with the machine unplugged!) Just like you would on a vertical mill. Set it at a radius that allows it to read flat against the table in four spots (left, right, front, back) and not in a t-nut or thru slot. With the table height column lock tight, adjust the table tilt (left/right), and nod (front/back) to ensure it is square. My drill press has a bolt to adjust table nod, depending on your machine you may need to add shims.

    For interest, measure the table nod/droop that occurs just from loosening the table lock.
    You will likely be surprised.

    -brino
     
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  17. dontrinko

    dontrinko United States Active Member Active Member

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    Thanks everyone for the tips. There are at least 3 or 4 things that I was not aware of. The hole in question was in aluminum in a coupling that had a 5 mm hole that I needed to make bigger.
    In hind site I should have either turned down the part that went into it or drilled the hole on a lathe. Thanks; Don
     
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  18. dontrinko

    dontrinko United States Active Member Active Member

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    I did some more testing. It is a cheap HF table top drill press. I think the press is Ok. With a transfer punch in the chuck and a machinist square on the table I get a gap of about .003" 4" up from the table for/aft. Right/Left is OK.
    when I get a bad hole it is much worse than that.
    I think it is a combination of flex and technique. Next time I will try not pressing so hard and "pecking". Don
     
  19. dave2176

    dave2176 United States Active User Active Member

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    I think you mentioned your solution. I've read in several sources that when you want a straight hose you rotate the work and the drill bit is stationary. This is how a gun drill works. When you want precision, use your lathe. A good bit is required as well of course.
    Dave
     
  20. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Drill bits do not drill holes the size listed on the drill or measured across the drill O.D. Drills do not make round holes. Drills do not make holes in the correct position. Drills are to remove material, nothing more. On some, maybe most work, that is fine, if you want a precision hole you must not use a drill for a finished hole. A boring bar can move a hole to where you want it. A reamer can make the hole the size you want and make it round. A drill press does not produce a hole square to the table unless perhaps if it is a very high end machine in correct adjustment. Drilling with a milling machine has all the same issues, just far less, better with more machine rigidity. Making good holes using only a drill bit is always something that includes luck.
     
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  21. mikey

    mikey Active User H-M Supporter-Premium

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    +1 on the luck!
     
  22. dave_r_1

    dave_r_1 Canada Active Member Active Member

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    Somebody out there must be getting their drill press to put the holes in exactly the right spot, every single time, just to balance out my inability to get holes where I would like them to be.
     
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  23. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    I know just what you mean. Dave. If I am just punching a hole for some simple, quick and dirty jig or fixture, and bang it out, it usually turns out beautiful. If it is on something that absolutely. must. be. right. then everything is guaranteed to go wrong... 8^)
     
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