best drill bit for hand drilling larger holes and enlarging existing holes
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    Default best drill bit for hand drilling larger holes and enlarging existing holes

    Hey guys,

    Here at our plant we have some silver deming bits - made in the USA cobalt bits. We don't use them a lot - but today was one of the times we needed them.

    One of our employees had to enlarge some 3/8" holes to 7/8" holes. The material was about 3/16" carbon steel. He did this by stepping up bit sizes one at a time. He said all our bits were dull and no good. I look at the bits and all seem sharp - each had a minor damage to the very outside tip of the cutting edge - so maybe that will kill the effectiveness of the bit.

    I have read on here that some people say stepping is not necessary and deming bits will not step good - then other people say they have been doing it for 30 years with no issue

    Later I tried drilling one of the holes personally going from the 3/8" straight to the 7/8" size. We were using a heavy duty Milwaukee cordless drill. It worked pretty good until we got about half way to three quarters through the thickness and then it slowed down big time. We made it through but it took another 3-4 minutes to make it the rest of the way.

    Is there a better way to enlarge holes like this? maybe a different type of bit? still needs done with a hand drill though if possible since we can't use our mag drill on everything - like in this case

    Thanks! Eric

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    Quote Originally Posted by ericfox View Post


    Later I tried drilling one of the holes personally going from the 3/8" straight to the 7/8" size. We were using a heavy duty Milwaukee cordless drill. It worked pretty good until we got about half way to three quarters through the thickness and then it slowed down big time. We made it through but it took another 3-4 minutes to make it the rest of the way.
    This is in 3/16" thick steel? You shouldn't have any issues other than personal strength opening up a 3/8 hole to 7/8 in that thin of steel plate with a hand drill.
    If your drill can't do it, then it's most likely not sharpened correctly.
    With a properly sharpened drill, this should take 30 seconds to a minute tops with a cordless drill.

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    Quote Originally Posted by ericfox View Post
    Hey guys,

    Here at our plant we have some silver deming bits - made in the USA cobalt bits. We don't use them a lot - but today was one of the times we needed them.

    One of our employees had to enlarge some 3/8" holes to 7/8" holes. The material was about 3/16" carbon steel. He did this by stepping up bit sizes one at a time. He said all our bits were dull and no good. I look at the bits and all seem sharp - each had a minor damage to the very outside tip of the cutting edge - so maybe that will kill the effectiveness of the bit.

    I have read on here that some people say stepping is not necessary and deming bits will not step good - then other people say they have been doing it for 30 years with no issue

    Later I tried drilling one of the holes personally going from the 3/8" straight to the 7/8" size. We were using a heavy duty Milwaukee cordless drill. It worked pretty good until we got about half way to three quarters through the thickness and then it slowed down big time. We made it through but it took another 3-4 minutes to make it the rest of the way.

    Is there a better way to enlarge holes like this? maybe a different type of bit? still needs done with a hand drill though if possible since we can't use our mag drill on everything - like in this case

    Thanks! Eric
    I routinely use step drill bits in a portable drill to enlarge holes in thinner materials. The trick is to buy only the quality ones (not from Horror Fright) and use a good cutting oil while avoiding excessive speed. I've seen more drill bits ruined by spinning too fast and using without lube during a long career in industry. Too many boneheads think it doesn't matter and just lay on the trigger and push hard.

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    Stepping up will almost certainly kill the outside edge of the drill. Especially in a heavy duty cordless drill. Fundamentally its a question of stability. when stepping up only the very end of the cutting edge cutting so ther is nothing to keep the drill stable in the hole so it will bounce around a bit. How mcuch it bounces depends on how strong the guy holding the drill is but bounce it will. Just another version of the crappy finish you get at the bottom of a hole before the drill gets deep enough to cut on full diameter. Or the not round hole you get when drilling thin material with a large drill.

    Several things you could try.

    With ordinary drills in such thin material I tend to reach for an old fashioned "gut buster" hand drill with bell/chest pad to lean on. Reasonable pressure and steady turning of the handle in low speed range goes through surprisingly quickly. With a sharp drill the main issue is stopping it cutting too thick a chip. Obviously need space to get at things but it does work well on the right jobs.

    In 3/16 its worth trying a hole saw if suitable diameter can be got. Low speed in the battery drill, don't force it and pull back a couple or three times to clear the chips. A squirt of lubrication helps. I have some plain parallel pins to use in place of the standard centre drill as this is more stable when you already have a hole or when the starter hole is too large. Starrett make a device that carries two concentric hole saws specifically for such enlarging duties but the ineer one has to be small enough to go on the simple screw mount and the outer one large enough to go on the pin drive mount. One day I shall use mine.

    If the sizes are right and ordinary flat bottom piloted counterbore works fine. I think you can get counterbore sets with interchangeable pilots to suit different size holes but these are probably very spendy.

    Dunno if they can still be got but there was / is a counterbore system usinf lat rectangular blades with hollow ground cutting edge on the end. Blades and pilot slot into a carrier shank. Presumably many permutations of blade length and pilot size although we only had a few.

    Clive

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    My guess would be and I see this quite a bit is when you use drills to step drill holes a lot and aren't particularly careful you get a dead spot at the sizes you step to.

    It is barely noticeable visually but when you get the hole to that diameter it just slows down or nearly stops. Then you press harder and it takes longer and that one little area then gets worse.

    Pretty soon you have a useless twist drill because of that spot. Take the drills throw a quick sharpen on them and you should be good to go.

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    Thanks guys!

    I have a few Milwaukee 7/8" to 1-1/8" step drill in my cart on Amazon. Also a new set of Viking deming bits to get us back to good condition drill bits again.

    Also we will try to use our mag drill whenever possible from now on to avoid damaging the edges of the drill bits which seems to have happened on each bit.

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    Step drill is the best in this case.

    Drilling by hand allows for EVERYTHING to move and it trashes both tools and hole if using normal bits.

    Step drills have built in bushing to keep bit centered as well as a controlled cut.

    If drilling thicker material than steps are long then use step drill to open hole to proper size then use drills matching steps in material to guide the drill.

    Do NOT over-drill meaning drill bit must fit an already drilled area so that acts as a drill guide.

    Sent from my SAMSUNG-SM-G930A using Tapatalk

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    Quote Originally Posted by Tony Quiring View Post
    Step drill is the best in this case.

    Drilling by hand allows for EVERYTHING to move and it trashes both tools and hole if using normal bits.

    Step drills have built in bushing to keep bit centered as well as a controlled cut.

    If drilling thicker material than steps are long then use step drill to open hole to proper size then use drills matching steps in material to guide the drill.

    Do NOT over-drill meaning drill bit must fit an already drilled area so that acts as a drill guide.

    Sent from my SAMSUNG-SM-G930A using Tapatalk
    Thank you for the advice!

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    Step drills are my favorite when doing this kind of thing, lot easier on the wrists than a grabby S&D drill too. Keeping the speed down and run a cutting fluid helps a lot too, if you burn the tips up, and you will if your step drilling them with multiple bits, stop and regrind the drill.

    I also will only run a corded drill as a last resort, the clutches on cordless tools are great. At a prior job I had some hilti corded hammer drills with safety clutches, I liked those, but don't have any here.

    If it allows though, I use my mag drill now, but it doesn't always fit everywhere.

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    A plasma cutter and a washer for a template ?

    Never goes dull
    Never kicks back

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    Best drill for a new hole: Probably your Silver and Deming bits. A long time ago I tried drilling large holes in steps. It did not work well because the bits tended to grab because of the small contact area at the outer edges. Now I drill a pilot hole that's about the size of the web on the final bit and then go directly to that final bit. This goes a lot faster than changing the bit several times and the final bit does not grab. Do use a good cutting fluid and make smoke. Lighten off on the pressure as you approach the break-through point.

    Best way to enlarge an existing hole: This is what reamers are made for. But you will need to make several steps. The steps are OK here as the reamers are made for cutting only on their outer edges.

    Step drills would be good in either case, but you will need one that can handle the 3/16" thickness or you may have to drill the final step size from both sides. BTW, you will notice that step drills have a zero degree rake angle.

    If you insist on step drilling with drill bits or enlarging existing holes with them, I would suggest decreasing the rake angle as you would do when drilling a soft metal like copper. That will decrease the tendency to grab and will result in a more durable cutting edge that will wear slower. This is done by grinding a flat at the forward side of the cutting edge inside the flute. A Dremel tool is good for this.

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    Quote Originally Posted by EPAIII;3426070...
    Best way to enlarge an existing hole: This is what reamers are made for. But you will need to make several steps. The steps are OK here as the reamers are made for cutting only on their outer edges.
    Did you just suggest enlarging a 3/8 hole to 7/8 using reamers?

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    Step drill in hand drill would be no problem. Norseman is a great value. Milwaukee is readily available.

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    First thing I would go for is a reamer. A tapered reamer commonly called bridge or car reamers. (meaning railroad car) These are used in structural ironwork to align bolt holes that do not match up.

    McMaster-Carr

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    Try one of those 'sheet metal' drills with stepped diameters. For 3/16" should work fine.

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    I suspect the problem is not initially the drill. It is most likely the driller. The operator must be skilled and smooth. he must use a sharp bit, steady pressure and slow speed. Miss any one of the above and you can start again with a new, sharp bit and more skill.

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    Use a Blair Bit With a custom made pilot to fit your existing hole, or a external hole guide clamped to your work.

    They make razor clean holes with minimal effort and last for years when used and lubed properly.

    https://www.blairequipment.com/rotabroach-cutters[

    d347a5_e9f4416936fb4eb5802c12f03105fa83-mv2.jpg

    Blair Holcutters - for large diameter holes


    d347a5_7ebdceaf110d499f9b855b243663f8cd-mv2.jpg

    Hougen Annular Cutters for Mag Drills, Sheet Metal, Machining and Industrial Applications

    12134-shadow.jpg

    photo-vi.jpg

    SAF Ω

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    Quote Originally Posted by Hazzert View Post
    Did you just suggest enlarging a 3/8 hole to 7/8 using reamers?
    Bridge, car or construction reamers. Can easily take off 1/8" on diameter, more if you've got a good rigid drilling setup (which is not how they are normally used).

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    I've used annular cutters to "enlarge" electrical knockouts on heavy sheet to a larger size. The existing hole was much too large to pilot on directly, and I wanted the new hole to be tangent to, not centered on, the old hole. The simple wood jig SAF showed works well when you can secure it. Because of bends in the housing, I could not use that technique. I ended up making a simple jig that clamped into the hole itself, with an offset pilot hole sized for the annular cutter pilot. Cutter trimmed off a bit of the flange of the jig at the same time it cut the hole. Jig was two pieces. One piece of 1/4" steel scrap turned to fit ID and slightly less than thickness of existing hole, with remainder of scrap thickness turned as a clamping flange. Other piece was used on inside of hole as clamp. The two pieces were slip-doweled together with a drilled/tapped hole for clamping, and offset pilot hole drilled through.

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    The OP was talking about enlarging it with a succession of steps with drill bits. I don't know about you, but I would rather do it with reamers which won't give me the grabbing problems that drill bits almost certainly would. Of course, you would need a proper selection of reamers.

    I also suggested other ways.



    Quote Originally Posted by Hazzert View Post
    Did you just suggest enlarging a 3/8 hole to 7/8 using reamers?

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