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IndustryArena Forum > MetalWorking Machines > Tormach Personal CNC Mill > Lost drill hole size accuracy in drilling operations
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  1. #1
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    Lost drill hole size accuracy in drilling operations

    Hello everyone,

    Some months ago I've been drilling pin holes (6mm) with very tight accuracy.
    The pins were just sliding into the holes smoothly.

    But on the last job I've lost that tight size tolerance and now the drill holes are way looser than before.
    Even with new drill bit (from the same brand).
    Now I need to use 6.2mm pin in order to fit nicely in a hole drilled with 6mm twist drill.
    It wasn't the case before when I was using 6mm pins for a holes drilled with 6mm drill and the fit was almost perfect.

    I've tried drilling with a drill chuck holder and also with a TTS ER collet holder, the result was the same.
    Not even close to the tolerances from few weeks ago.

    Here is a link to some videos that I've made measuring the run out of the tools.
    https://drive.google.com/folderview?...BkV4RzQDa6q3gm
    Please let me know if you have any problems viewing the videos.
    The scale on the indicator is in mm, 0.01mm

    Could you please advice what would be the reason for loosing that accuracy.
    What should I do to fix it.

    Machine is Tormach PCNC 1100 and we're working mainly with steel and aluminum.

    Thanks a lot!

  2. #2
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    Re: Lost drill hole size accuracy in drilling operations

    drilled holes are not very accurate, I would put in another op and ream to 6mm.

    drilled holes depend on how the end is ground, a bit off center and it will drill oversize.
    mike sr

  3. #3
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    Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by popspipes View Post
    drilled holes are not very accurate, I would put in another op and ream to 6mm.

    drilled holes depend on how the end is ground, a bit off center and it will drill oversize.
    Thank you for the reply.
    I do understand that, it was accurate enough for my purpose and now the holes are way oversized.
    I've also tried to drill with 5.7mm and then use 6mm reamer. That didn't produce better result. Still too oversized for 6mm pins.
    Can't figure out what is different now unless there is some tool holder run out, as I mention even with 6mm drill only the tolerance was good for my purpose.

  4. #4
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    Re: Lost drill hole size accuracy in drilling operations

    What material are you drilling? What are your feeds and speeds? What is your peck depth? Did you change the brand of drill you are using?
    You can buy GOOD PARTS or you can buy CHEAP PARTS, but you can't buy GOOD CHEAP PARTS.

  5. #5
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    Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by venta7 View Post
    Thank you for the reply.
    I do understand that, it was accurate enough for my purpose and now the holes are way oversized.
    I've also tried to drill with 5.7mm and then use 6mm reamer. That didn't produce better result. Still too oversized for 6mm pins.
    Can't figure out what is different now unless there is some tool holder run out, as I mention even with 6mm drill only the tolerance was good for my purpose.
    Well it used to work fine and now you have some runout or something going on. I would put a dial indicator on your chuck and with the drill bit in the chuck. Try to move the the bit with your fingers or something while the dial indicator present. Rotate by hand with the dial indicator on the bit and etc. Has your drill bit got run out or is it the chuck or perhaps the machine has some wear on the axis?
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router

  6. #6
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    Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by venta7 View Post
    Thank you for the reply.
    I do understand that, it was accurate enough for my purpose and now the holes are way oversized.
    I've also tried to drill with 5.7mm and then use 6mm reamer. That didn't produce better result. Still too oversized for 6mm pins.
    Can't figure out what is different now unless there is some tool holder run out, as I mention even with 6mm drill only the tolerance was good for my purpose.
    Another thing is I always spot drill first, takes a bit more time but keeps drill "wander" to a minumim when starting the hole.

    An old mentor showed me a trick to make a drill drill an onsize hole, he just touched the outer edge of the cutting lip with a stone dulling it slightly, this forces the drill to hunt center and makes it drill a tighter hole. I wouldnt have believed it but I was shown and it does work in a pinch.
    mike sr

  7. #7
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    Re: Lost drill hole size accuracy in drilling operations

    For locating pin holes I first drill then single point bore and then using this floating reamer holder I built using a 3/8" TTS holder ream to size.

    Don

    Attachment 422444

  8. #8
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    Re: Lost drill hole size accuracy in drilling operations

    Folks he's using a CNC machine, he does not need to spot drill and it all worked fine before.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router

  9. #9
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    Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by wmgeorge View Post
    Folks he's using a CNC machine, he does not need to spot drill and it all worked fine before.
    If the surface is dead flat, and using a web thinned drill, or preferably a screw machine drill no need to spot drill.
    mike sr

  10. #10
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    Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by Don Clement View Post
    For locating pin holes I first drill then single point bore and then using this floating reamer holder I built using a 3/8" TTS holder ream to size.

    Don








    I like your floating reamer holder!, may try to make one for myself......
    I also like your indicator holder that fits in the spindle with a dovetail assembly at 90 degrees, I have looked on ebay etc but havent found one like yours, very good idea Don
    mike sr

  11. #11
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    Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by wmgeorge View Post
    Folks he's using a CNC machine, he does not need to spot drill and it all worked fine before.
    It does not matter what the machine is CNC or a manual Drill Press a Spot drill is always needed unless the Drill bit is designed to be used without a Spot Drill, there are some quality Drills that are ground so a Spot Drill is not needed, I would say he got lucky with his hole sizes before, a drill Bit unless you know how to grind it can make any size hole you want, over size or on size

    Using the Drill Chuck that he has is never going to be very accurate, these drills are some of the best there are if he wants a quality drill Wedevag that will drill on size if his spindle and holder runout is very low and he would need to be using a Screw Machine Drill

    North Bay Cutting Tools

    Or Ebay https://www.ebay.com/itm/3906-25-64-...ss!37179!US!-1
    Mactec54

  12. #12

    Re: Lost drill hole size accuracy in drilling operations

    "got lucky"

    That's my assessment too. I think OP got above average results and is now getting the results we all would have expected.

    In a pinch I've milled/bored pockets with an end mill using a helical path then hit them with a drill as sort of a make shift reamer. This generally is only useful for deep holes where an end mill would't be practical or if you don't have a spot drill. It does provide nice results. The added benefit is it greatly reduces the amount of chip evacuation during drilling and the surface finish can be quite nice as a result.

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