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Thread: Problem drilling mild steel flat bar

  1. #51
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    Re: Problem drilling mild steel flat bar

    Slow and lots of pressure and some oil.
    You just finally wore your bit out and then spun it without making chips.

    If ever you are not making chips you must stop quickly or you will do what happened.

    If that bit spins on the work with pressure applied but not cutting it will as mentioned already will work harden the metal right under the bit. A new fresh bit will usually get you back through with extra pressure and a slow speed until that hardened layer has been cut out then it will drill like normal again.

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  3. #52
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    Re: Problem drilling mild steel flat bar

    So much to learn about something I took for granted and never even thought about.

    My first grinding attempt was almost close, not hand grenade close, but at least I can see what I did.

    I found my chisel angle was close to 90 degrees and not the 135 they recommend which means the relief behind the cutting edge was too shallow. I should have held the bit higher on the curve of the wheel and not low and straight into the grinding wheel center.

    Good PDF listing all the bit parts and angles. Thanks again for leading me in the right direction.

    http://www.neme-s.org/2005%20May%20Meeting/drills.pdf
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  5. #53
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    Re: Problem drilling mild steel flat bar

    Ideally the cutting lips of the drill bit should be the same length. As close to exactly the same length as possible. Again ideally, it should be forming a shaving from both lips. If they are not the drill may drill oversize except for a short distance as it breaks though the bottom side of the plate. Some unscrupulous machinists may have used this phenomenon to drill oversized holes for relief for fasteners because they did not have the proper sized drill so they would only have to file out a thin section at the bottom of the hole to let bolts go in easily. This are examples of a devise to check angle and length of the lips.
    https://www.amazon.com/Drill-Gage-De...%2C201&sr=8-10
    https://www.amazon.com/PURPOSE-Protr...s%2C201&sr=8-9
    ---Meltedmetal

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  7. #54
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    Re: Problem drilling mild steel flat bar

    Quote Originally Posted by Flyer58 View Post
    So much to learn about something I took for granted and never even thought about.

    My first grinding attempt was almost close, not hand grenade close, but at least I can see what I did.

    I found my chisel angle was close to 90 degrees and not the 135 they recommend which means the relief behind the cutting edge was too shallow. I should have held the bit higher on the curve of the wheel and not low and straight into the grinding wheel center.

    Good PDF listing all the bit parts and angles. Thanks again for leading me in the right direction.

    http://www.neme-s.org/2005%20May%20Meeting/drills.pdf
    A stationary belt grinder works well also. It will grind way cooler but I would still quench the drill bit to cool.

    A cheap unit typically designed for woodworking would most likely work as well as an expensive unit.
    :

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  9. #55
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    Re: Problem drilling mild steel flat bar

    My belt sander has the disc on the side that I have used for small bits as well, but mostly I just use the finest grit on the grinder wheels. Coarse grits leave a rough surface, cut the metal away very quickly and heat the bit up, I prefer fine grits and very quick light applications of the bit. If you are seeing color change in the metal you are heating up the cutting edge too much.
    The harder you fall, the higher you bounce...

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  11. #56
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    Problem drilling mild steel flat bar

    i've had this for 55 years ...





    it works really well for those lacking good hand to eye coordination

    the plan is to mount it permanently on a small fine grit belt sand for quick touch ups.
    Last edited by Lis2323; 08-06-2022 at 01:40 PM.
    :

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  13. #57
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    Re: Problem drilling mild steel flat bar

    I've got one like that too... that's what taught me what angles to hold them at...
    The harder you fall, the higher you bounce...

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  15. #58
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    Re: Problem drilling mild steel flat bar

    I have wonder if worked
    Thank you for clearing that up.

    Even today I just use 6" grinder and off hand down to 1/16" and upto 2 ˝,"

    Dave

    Quote Originally Posted by Lis2323 View Post
    i've had this for 55 years ...





    it works really well for those lacking good hand to eye coordination

    the plan is to mount it permanently on a small fine grit belt sand for quick touch ups.

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  17. #59
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    Re: Problem drilling mild steel flat bar

    Quote Originally Posted by smithdoor View Post
    I have wonder if worked
    Thank you for clearing that up.

    Even today I just use 6" grinder and off hand down to 1/16" and upto 2 ˝,"

    Dave
    anything 3/16” and under I throw away.

    not only am I not skilled enough to hand sharpen the smaller sizes but it’s just cheaper and more efficient to buy extras and have them on hand.






    doesn’t make sense to spend $2-3 of shop time to sharpen a $1 bit (unless of course it’s the only one you have )
    :

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  19. #60
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    Re: Problem drilling mild steel flat bar

    I to probably would throw away but big number of bits. Today a drill bit last a long time ⌛ as I am only using the drill bit.

    Dave

    Quote Originally Posted by Lis2323 View Post
    anything 3/16” and under I throw away.

    not only am I not skilled enough to hand sharpen the smaller sizes but it’s just cheaper and more efficient to buy extras and have them on hand.






    doesn’t make sense to spend $2-3 of shop time to sharpen a $1 bit (unless of course it’s the only one you have )

  20. #61
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    Re: Problem drilling mild steel flat bar

    The camera doesn't lie. Here's my second attempt and I may have the chisel angle close and the cutting edges are equal length but looks like they're not straight and a rough cut based on the scoring. I'll blame the grinding wheel The 118 deg angle is also close. The relief behind the cutting edge - oh well...

    I'm the new guy here so I'm open to all questions, comments and verbal abuse. I have the day off so I'm having fun trying.
    you may want to close your eyes Cheers!


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    Last edited by Flyer58; 08-06-2022 at 04:53 PM.
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  21. #62
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    Re: Problem drilling mild steel flat bar

    I hand sharpen larger bits in pinch. Larger bits are easier to sharpen well enough to get back in service. Hand sharpening is definitely fasted than a drill doctor. I had a drill doctor for years. It will give consistent finish, however. But, It was faster and economical to just buy new smaller bits.

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  23. #63
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    Re: Problem drilling mild steel flat bar

    It does look in even, however a side view will show if the profile is close. It the relief is not correct the the edges will not contact the material… No drilling.

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  25. #64
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    Re: Problem drilling mild steel flat bar

    Quote Originally Posted by tapwelder View Post
    It does look in even, however a side view will show if the profile is close. It the relief is not correct the the edges will not contact the material… No drilling.
    The primary relief looks good. It's my understanding the relief angle is what determines the chisel point angle - looking for the 135deg. I tried adding a secondary and steeper relief a little behind the primary relief. I think the Drill Doctor just rounds it down after the cutting edge.
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  26. #65
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    Re: Problem drilling mild steel flat bar

    It doesn’t look even. Correction

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  28. #66
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    Re: Problem drilling mild steel flat bar

    Quote Originally Posted by tapwelder View Post
    It doesn’t look even. Correction
    There's a lot that still not right but the camera gives me an idea what's happening.
    Better than my eyes.
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  29. #67
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    Re: Problem drilling mild steel flat bar

    I must have unwittingly bought some fine bits or am just lucky. More than 40 yeras ago I bought a set of bits from a hardware store and only replaced those I broke or lost. The index says Hanson. Due to vision problem I have to use a jig to sharpen but despite several sahrpenings the bits still make curled ribbons. If a bit doesn't start cutting right away I stop and regroup. I think most people here have witnessed ho quick an abrasive cut off wheel can work harden and stop cutting. It's the same with drilling,it doesn't have to spin long before bit and work overheat and harden. My grandson thought I was being silly when I told him to dip the bit after every hole he was drilling in a new trailer floor but he was impressed after the same bit drilled all the holes without resharpen.

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  31. #68
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    Re: Problem drilling mild steel flat bar

    I resharpen EVERYTHING. Being able to touch up a 1/16" bit is actually pretty helpful.

    I tend to change tip angles, bevel sizes, etc. Based on material. Only takes a second with a bench grinder.

    I just save up all my dull drills and sharpen them as a batch.

    With a 1/8" or smaller drill, I might "rough in" the point with the grinder, then give it a lick or two with a bench stone. I usually just use the grinder, though...

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  33. #69
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    Re: Problem drilling mild steel flat bar

    Quote Originally Posted by 52 Ford View Post
    I resharpen EVERYTHING.
    But can you sharpen a 3-flute cobalt drill bit with all the relief angles?!?

    1st on WeldingWeb to have a scrolling sig!



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  35. #70
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    Re: Problem drilling mild steel flat bar

    Still too much land behind the cutting edges. You want it to look more like the pic below where you remove the parts circled in red. Then you want more relief on the part farthest away from the edge. Otherwise you have a very hard time making chips as it requires a lot of pressure to get the edge to bite. Not enough relief.

    Myself, I will sharpen down to about 1/4" and then it is too hard to do for me. Fine wheel on an 8" bench grinder. I often find I have to come back and add more relief to the bit, so I am very familiar with that part of it...


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  37. #71
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    Re: Problem drilling mild steel flat bar

    My wife bought me a couple of Chinese drill bit sets years ago, it was obvious out of the gate that they were junk & wouldn't drill anything but soft wood. Closer inspection revealed that they were sharpened backwards, the heel of the bits were higher than the leading edge, after resharpening they were almost halfa$$ed decent, I think I ended up giving them away.

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  39. #72
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    Re: Problem drilling mild steel flat bar

    Quote Originally Posted by Oscar View Post
    But can you sharpen a 3-flute cobalt drill bit with all the relief angles?!?

    You do realize that these kind of bits, with the 3 flutes, were originally designed to widen holes. It's very hard to find them anymore. I'd like to have a decent set of the diameters I work with the most.

    And..........."cobalt" is just a sales gimick to sell HSS. Sorta like Titanium, or other coatings/additives. In the end, it's the sharpened HSS cutting edge that does the work.

    Regular HSS, off the shelf, is plenty hard to drill anything but steel that's harder than HSS. Provided it's kept sharp.

    The relief angle is key to the deal. The sharper the angle, the better it cuts. It will actually suck its way down into the steel. Kind of like a plow. On the flip side, the cutting edge will decay much faster. But if you have a bench grinder, it's not an issue. Takes about 3 minutes to sharpen a bit. I came to this the hard way. I got tired of throwing out bits when they got dull. Found that the drill bit sharpening machines are mostly junk.....................bought a General Hardware drill bit gauge, and never looked back. You can virtually get a lifetime out of most any drill bit, if you learn to sharpen it freehand.

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  41. #73
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    Re: Problem drilling mild steel flat bar

    Does anybody dress their grinding wheel. The nastiest operation in the shop.

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  43. #74
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    Re: Problem drilling mild steel flat bar

    Quote Originally Posted by farmersammm View Post
    You do realize that these kind of bits, with the 3 flutes, were originally designed to widen holes. It's very hard to find them anymore. I'd like to have a decent set of the diameters I work with the most.

    And..........."cobalt" is just a sales gimick to sell HSS. Sorta like Titanium, or other coatings/additives. In the end, it's the sharpened HSS cutting edge that does the work.

    Regular HSS, off the shelf, is plenty hard to drill anything but steel that's harder than HSS. Provided it's kept sharp.

    The relief angle is key to the deal. The sharper the angle, the better it cuts. It will actually suck its way down into the steel. Kind of like a plow. On the flip side, the cutting edge will decay much faster. But if you have a bench grinder, it's not an issue. Takes about 3 minutes to sharpen a bit. I came to this the hard way. I got tired of throwing out bits when they got dull. Found that the drill bit sharpening machines are mostly junk.....................bought a General Hardware drill bit gauge, and never looked back. You can virtually get a lifetime out of most any drill bit, if you learn to sharpen it freehand.
    Ehhhh... that's not entirely true. Titanium nitride, aluminum titanium nitride, and other coatings like that can make a huge difference in a production environment. Especially on a CNC machine.

    They let you run high feeds and speeds.

    With a hand held drill or a drill press, it'd not really worth it.

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  45. #75
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    Re: Problem drilling mild steel flat bar

    Quote Originally Posted by Oscar View Post
    But can you sharpen a 3-flute cobalt drill bit with all the relief angles?!?

    Well... guess there's one way to find out! You go ahead and buy me a set of them, I'll use them till they're dull, then try and sharpen em.

    I prolly could touch one up if I was in a pinch. I've turned regular drills into split points with a sharp corner on a bench grinder and a set if diamond files.

    Look up "hyper step" drills. It's a twist drill, but the point is ground in steps (like a normal step drill). They're supposed to be pretty great.

    Actually, here's a link to some. Apparently "hyper step" is just a sorts generic term for them.
    https://www.amazon.com/Norseman-2290...77678630&psc=1

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    Last edited by 52 Ford; 08-07-2022 at 12:28 AM.

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