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Twist Drill Angle with Center Drills vs Spotting Drills

Discussion in 'A BEGINNER'S FORUM (Learn How To Machine Here!)' started by wildo, Mar 15, 2017.

  1. Randall Marx

    Randall Marx United States H-M Supporter - Premium Content H-M Supporter-Premium

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    This long and interesting discussion has piqued a question: how well or how poorly would a 118 degree drill center in a hole spotted with a 140 degree spotting drill? I ask because I do not own any spotting drills. I've used just the tip on center drills to locate holes for 118 degree drills. That worked very well. I now have 135 degree cobalt split-point drills AND 118 degree drills. I'm considering getting some 140 degree spotting drills to use with the cobalt drills and wonder if I can safely and effectively use the same spotting drills for my 118 degree drills. If not, I might get some 120 degree spotting drills to use with the 118 degree drills and keep the spotting drills with their respective drills in the indexes (120 with 118's and 140 with 135's). If the 140's will work as well with the 118 degree drills, that is less to buy and track.
    Thanks!
     
  2. Bob Korves

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

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    I have not tried it, but I expect that the 140 degree starter drill followed by a 118 degree main drill would work just fine, probably no different than following a 120 degree starter drill. As long as the main drill has a smaller angle than the starter drill, the drill should center in the cone. I love the 135 degree split point cobalt drills, especially the machine screw (stub) length. If you are square to a smooth surface with them, you can pretty much forget about starter drills if you are using a drill press or a mill. I also have some of the jobber length ones as well, and they work almost, but not quite as well without a starter drill.
     
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  3. Scruffy

    Scruffy Active User H-M Supporter-Premium

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    I quit using center drills for spotting when I broke the tip off one and spent an hour getting the broken piece out! I have bought sets of lettered, numbered and fractional in stub length and love them.
    Posted from the osu heart center in Columbus Ohio. My 84 year old father had a bad episode Friday morning. This is night numer 2 for me , got one and a half hours sleep last night sure hope tonight is better.
    Thanks scruffy
    Update my father just asked me if I had a pocket knife? His iv line had got tangled and he wanted me to cut it. Gonna be a long night.
     
    Last edited: Apr 1, 2017
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  4. EmilioG

    EmilioG United States Active User H-M Supporter-Premium

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    The 140° to 150° spot drills will work for (me), on any drill below those included angles; 118, 135. With my 8mm Guhring 142 carbide spot drill, I can make the spot shallow or wider/deeper, depending on the drill size up to about 5/16". For small holes, I'll use a 1/4" spot drill. If the holes I need are not deep, I mostly use stub length drills.

    Tom Griffin told me that he doesn't even bother with spots, he just pecks a spot with the final drill and goes.
    I use spot drills most of the time, especially with smaller size drill bits or on round parts. I may start using a sharp conical point to find my punch marks.
    I have used a Starrett wiggler and the conical point on a Starrett double end edge finder with some success. Hitting a target hole on center w/o a DRO is a challenge.
    But I like a good challenge, so I keep drilling. I just have to take my time, I don't want to ruin the parts I'm working on.
     
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  5. Randall Marx

    Randall Marx United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Thanks for the input everyone. Sounds like the consensus is that it should work for me to use one set of wide-angle spot drills for all of my drills. I plan to order some with my next tooling order. If anyone has a GOOD reason not to use the 140 degree spotters with 118 degree drills, please speak up. Otherwise, I'll get some.
    Thanks again.
     
  6. EmilioG

    EmilioG United States Active User H-M Supporter-Premium

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    The 140° will work with all drills under 140, but I would also test the matched examples, 120 spot with 118, 140 spot with 135.
     
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  7. Ken from ontario

    Ken from ontario Canada Active Member Active Member

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  8. darkzero

    darkzero Global Moderator Staff Member H-M Supporter-Premium

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  9. Mutt

    Mutt United States Active Member Active Member

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    the 140º spot drills are near impossible to find, but 135º drill bits are EVERYWHERE. Companies act like it is a major job to grind the spot drill to 140º instead of 120º ??????????????????????????? Seems to me, if I were in the drill bit making business, I would be offering the 140º spot drill before a 120º as both 118 and 135 drills would work using it, but not visa-versa. Besides, what happened to companies making what people want, instead of making what they think customers need?????????

    After reading an article on this and buying a couple of spot drills, the concentricity of the holes being drilled on my lathe have improved immensely
     
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  10. mikey

    mikey Active User H-M Supporter-Premium

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    Yup, 140 degree spotting drills are harder to find but they have a bunch on ebay and Amazon usually has some. They sort of last forever; I'm still using a 120 degree spotter that is old, not sure how old, but its still sharp. I have maybe 5 more as a backup but haven't had to pull one out. I buy cobalt spotters, not carbide, because if I drop it then it is more likely to survive the drop.
     
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  11. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    Sometimes traditions were developed before technology interfered. The stubby screw machine drills took a long time to migrate to machinist's tool boxes.
     
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  12. David S

    David S Canada Active User H-M Supporter-Premium

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    Well all I can say is that I would vote this "tip of the year". I have noticed improvements in the past few weeks since I started using them.

    David
     
    Last edited: Apr 29, 2017
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  13. Jimsehr

    Jimsehr United States Active User Active Member

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    If the angle is not what you want grab a protractor and hit the grinding wheel.
    Jimsehr
     
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  14. EmilioG

    EmilioG United States Active User H-M Supporter-Premium

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    I have a Guhring 142° spot drill. I have a few Guhring 140° drills carbide, so I needed one. Guhring recommends using 90° spot drills with non carbide drills.
    The 90 degree spot used looks like a size to just fit the chisel point of the follow drill. Guhring now makes spot drills in cobalt bright. Msc has a pretty good selection, even 145°.
    see>> http://www.guhring.com/Documents/Catalog/Drills/NCSpotDrills.pdf
     
  15. Splat

    Splat Active User H-M Supporter-Premium

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    FWIW, McMaster-Carr has all different angled, including 140º, spotting drills.
     
  16. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

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    Unless you are in a production environment any method of spotting a hole is valid, there is no right or wrong way there is only a faster or slower way.

    Let us use a bit, no pun intended, of reason, lathe centers are typically 60 degrees so a Center drill is 60 degrees with a pilot diameter that ensures that the sharp point of the center does not reach the bottom of the hole. When spotting a drill location the pilot diameter is not in any way useful. A center drill is used to create work holding features.
    Why do many taps have centers in each end? They are not there to make your life easier, they are there because this is how the manufacturer holds them, small taps are often sharply pointed ends where the point is held with an external center when being ground.

    Spotting drills are often 90 degrees included angle which will create a 45 Degree chamfer on the hole entrance which will require no deburring afterwards, this in itself is an advantage.
    They are less easily broken then center drills.
    The angles are better when followed by a twist drill, this may help answer your original question. As a hobbyist are you drilling 10 holes per day or 1000 holes per day?
    If only several holes per project use whatever method works for you and your equipment as this is what is the "right" method. Ignore most of the "How To Do This Correctly" web advice, for many people the exercise of thinking about a process is more important then actually doing it.
     
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