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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Twist Drill Angle with Center Drills vs Spotting Drills
- Thread starter wildo
- Start date
Sometimes traditions were developed before technology interfered. The stubby screw machine drills took a long time to migrate to machinist's tool boxes.
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
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
FWIW, McMaster-Carr has all different angled, including 140º, spotting drills.
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.
I did find spot drills smaller than .250" Msc has Keo and MA Ford spot drills in 140° and 142° bright, solid carbide, not expensive, down to 1/8"
The Guhring spot drills are very expensive. I have one that was sent to me as a sample. MA Ford also has spot drills in their Hi Roc line for hard steels in 145°, down to 3mm.
These spot drills are very short and rigid. I prefer cobalt, but these carbide spotters should work nicely.
The Guhring spot drills are very expensive. I have one that was sent to me as a sample. MA Ford also has spot drills in their Hi Roc line for hard steels in 145°, down to 3mm.
These spot drills are very short and rigid. I prefer cobalt, but these carbide spotters should work nicely.
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And money.
You use a 90 degree spot drill when you want to put a 45 degree chamfer on the part and also use drill as a starter.