Enlarging a hole in aluminum on the drill press
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  1. #1
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    Default Enlarging a hole in aluminum on the drill press

    Hi folks,
    I have what I am sure is a rookie question so I appreciate your understanding. We often need to enlarge holes that are either 10mm or threaded M10 but need to be 12mm. Often this happens one part at a time but more common is 6-10 pieces. I get good results using a stub length drill in the Bridgeport with vise stops and all the associated settings to make the drill run concentric with the existing hole. I need our technicians to be able to do this efficiently and need a nicely finished hole since the part is very “customer forward”. I have been screwing around with the drill press and get a good result with an undersized hole followed by a reamer when I changed to a better chuck than is shown. The problem with that is there are too many steps in preparation for doing the multiple operations. I was getting ready to order a 12mm taper shank drill and just close my eyes…. Accuracy isn’t as important as just a nice looking professional hole. I remember having used a drill designed for such a purpose (a core drill or “dreamer”?) but searching McMaster-Carr hasn’t turned up such a tool.

    I attached a photo of the setup I am trying to use which is a light duty drill press with a floating vise. The chuck pictured is what is normally mounted but runs out too much causing some chatter starting the hole. I hope my question makes sense. Telling me I am dumb won’t be insulting since I know I’m not experienced in this kind of thing. I appreciate any guidance from you folks!
    Rick564992ec-19b5-419b-90dc-d5a455906f45.jpg

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    Quote Originally Posted by NC Rick View Post
    I need our technicians to be able to do this efficiently and need a nicely finished hole since the part is very “customer forward”. I have been screwing around with the drill press and get a good result with an undersized hole followed by a reamer when I changed to a better chuck than is shown. The problem with that is there are too many steps in preparation for doing the multiple operations.
    Dreamer Tools

    Since it sounds like your guys are not very experienced, just make sure to emphasize that the drill press is the ost dangerous tool in the shop. Do NOT attempt to get by with just holding the work by hand.

    Dab a little lube on the hole will make it look prettier, too. Anchorlube is nice, not messy and non-staining.

    Anchor Lubricants LLC

    Comes in convenient little squeeze bottles.

    Or just use WD-40 like a lot of people

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    One thing you can do to get better looking holes is to send your drills out to a cutter grinding shop rather than sharpening by hand.

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    How about a 12mm step drill like this one?

    uxcell Step Drill Bit HSS 4241 4mm to 12mm 5 SizesTitanium Coated Straight Flutes Hex Shank for Metal Wood Plastic: Amazon.com: Industrial & Scientific

    It should pick up on the existing holes easily and the single point is less prone to grabbing than a twist drill. For thicker work it would be necessary to stop the press and switch to a stub drill but it will make it easier to find the center.

    Other option is to have pilots ground on standard bits by a company that does custom sharpening.

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    I would try it in the Bridgport with a 3 flute drill grab it with a collet instead of the drill chuck. 3 flute drills don't care so much if you don't get them perfectly lined up with a pre existing hole.

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    I think what you need is a 12 mm drill with the appropriate pilot section in front, either a 10 mm or M10 tap drill sized pilot. You probably want to run this drill a bit slower than you are now. Chatter on starting is a sign things are a bit fast. Also a drill bushing centered on the existing hole (think fixture to clamp to the part, with the bushing installed in the correct spot) will do wonders for the chatter problem.

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    +1 for the drill bushing idea. Can you make a fixture that mounts to the vise so that you can line up your 12mm drill to the bushing part of the fixture, clamp the vise to the table, then just load/clamp/run parts without moving anything?

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    just get a 12mm cbore with a 10mm pilot and go all the way through

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    You could use a standard 12mm drill, with the work clamped and put a small piece of Emery tape between the drill and component with the abrasive side to the job. Prevents the drill grabbing and chattering when only taking a small amount of a slightly smaller hole.

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    Man, I love these ideas! The mill or any kind of precision alignment is out as it needs to be done in the drill press by a non-machinist. I worked at a place as a teenager in the early 70s using multi head drill presses and fixtures and I never thought of a fixture and drill bushing! That’s awesome. I really need to try the counter bore option too. I’ll look if I have one in that size and if not do a test with what I have. If the step drill works I could get the outside de-burr done to but setting a depth stop isn’t practical. I need a solution where I don’t have to be involved. Thanks for the comments on safety. I like to remind the guys with something a friend told me about something bending in the drill press and the operator watching in amazement as his intestines wind up on the chuck…. Clamped down makes precision alignment necessary but a drill bushing or pilot would be the deal! The last batch we did at about 320 rpm to not end up with a triangular hole. I have never considered drilling a through hole with a c-bore. Thank you all for the great ideas! I don’t get a lot of practice but these kind of “problems” are really quite fun. We are not a machine shop but we do some machining to get customs and low volume stuff out the door. Hi volume stuff goes to a CNC shop. One-offs I do and the in-between stuff is a challenge for us. Been doing this same stuff for 20 years as of this coming 2022 and I love learning new stuff. This site and it’s members have been a constant source on people who really know what they are doing and have always been willing to help me. Thanks! Really.

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    A countrbore will need a vaccuum to remove the chips if it goes deep. A piloted counterbore in a countersink cage would work well
    Bill D

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    For a few parts, what I often do is to use a 10mm drill blank to align workpiece to drill press spindle center, clamp workpiece to drill press table, remove drill blank and install a 12mm drill bit, and go to town.

    Use alcohol or kerosene to lubricate the cut. If the drill tends to grab too much, dub the cutting edges.
    Last edited by Joe Gwinn; 11-30-2021 at 10:11 AM. Reason: Fix typo.

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    Best bet is a step drill.

    The design makes it a controlled cut and it is self guiding.

    Only critical thing is GO SLOW so it lasts.

    If material is thick there are either step drills with long steps or piloted drills that have a smaller bit to make a starter hole.

    If you need a lot a custom drill could be made from existing one but that could be expensive.

    We use step drills for many If not all cases where we already have a hole that just needs to be larger, quick and easy with hand held drill motor.

    Sent from my SM-G781V using Tapatalk

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    There are tools called "Dreamers" combination drill and ream. A step drill of sorts. There may be one available in a configuration that suits your needs.

    If not, a step drill will be a good choice, or a custom sharpened piloted reamer (Sharpened so the cutting edges are more "drill like".

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    Locate work, then clamp vice. No floating non-machinist tampering. Three-flutes drill, one pass. Heavier vice, if possible

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    Use the existing size drill in the hole to line the existing hole up straight to the machine spindle when you clamp the part.

    You might try a 12mm spiral flute/ or straight flute if sucking is a problem reamer spun down to under 10mm circle grind pilot with having 10 degrees end clearance... run with coolant so as not to load up with sticking aluminum.

    Easy grind for a cutter grind shop.. also a 12mm drill can be ground to have a (under) 10mm pilot

    Solid Chucking Reamers - Standard - -

    Yes shown is the wrong size/not 12 mm

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    c6629cc8-3b5a-4983-bc81-d87a8fdd5e00.jpgI have drill bushings and a couple of those “unibit” drills off Amazon ordered. I’m hunting counterbores or step drills with the correct dimensions. Not much luck around here. I tried to make a step drill but my skill and equipment limited the results yet the shop made drill worked better than anything else I have tried. I ended up with a “dubbed” point because I couldn’t really do a reasonable job providing clearance on the narrow cutting margin. I plan to check into getting some customs made if not too pricey. 3 to 5 of them would last for ever.

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    I cannot tell what kind of drill press that is, but the better the drill press the better the hole

    I don't have a drill press in the joint that isn't on the slowest speed, and better drill presses tend to go slower.

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    Didn't read all of the comments,but a 3 flute drill and a reamer is what I'd try.


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