Twist Drill Angle with Center Drills vs Spotting Drills

Bob Korves said:
I recently bought some USA made cobalt, 135 degree, split point, screw machine (stub) length drills. Got a dozen each of 1/4 and 3/8" diameters, new and in the original sealed packaging, for less than $1 each, free shipping on eBay.
Click to expand...

Bob, would you have a link to that supplier?
Thanks,
-brino
Of course, not likely free shipping to Canada.....
 
brino said:
I guess I shoulda asked in a PM! :cautious:

Nah, I hope you fellow H-M'ers enjoy them in good health! :encourage:

-brino
Click to expand...
I probably should have PM'd you, Brino. :( PM me your address and I will send you a few...
 
been using stub drills in medium and small mills for a while now and it works amazingly well. Saves time and makes a better hole. Good advice all around.
 
Very interesting thread. Like darkzero, I found some conflicting information when I looked into this as well. I just remembered where: www.guhring.com/documents/catalog/drills/ncspotdrills.pdf
Guhring specifically states that with HSS the spotting point angle should be less that the drill angle. But, as Bob suggests I'm going to buy a 120 degree spotter and compare with the 90 degree that I bought
before. I wonder if Guhring's advice assumes a CNC environment, where rigidity and accuracy is a given. Probably not aimed at folks with floppy old drill presses. :)
 
Last edited:
Bob Korves said:
I probably should have PM'd you, Brino. :( PM me your address and I will send you a few...
Click to expand...

No worries Bob, I'll keep an eye out at my local used tool shop and I'm sure I can find some.
Thanks for the considerate offer!

-brino
 
Nogoingback said:
Very interesting thread. Like darkzero, I found some conflicting information when I looked into this as well. I just remembered where: www.guhring.com/documents/catalog/drills/ncspotdrills.pdf
Guhring specifically states that with HSS the spotting point angle should be less that the drill angle. But, as Bob suggests I'm going to buy a 120 degree spotter and compare with the 90 degree that I bought
before. I wonder if Guhring's advice assumes a CNC environment, where rigidity and accuracy is a given. Probably not aimed at folks with floppy old drill presses. :)
Click to expand...

Back when I tested these drills (can't even remember how long ago that was), I used a 1/8" drill bit. I tested them because I noticed that my smaller drills were not drilling where I wanted them to when I spotted with the 90 degree spotter. I also noted that a freshly sharpened drill was not outputting equal-sized chips, which suggested to me that the edges were being dulled or damaged somehow. At the time, I didn't even know that there were other angles available in spotting drills but when I looked, I saw that a 120 degree drill was available so I ordered one and all the issues went away.

Were it not for the fact that I was trying to fit a part to another part that required the holes to line up precisely (I was building a precision square) I may never have stumbled upon the difference between these spotting drills.

My point is that when using larger non-carbide drills with greater inherent stiffness and less fragile edges, a 90 degree spotting drill may be fine. For myself, I prefer a 120 but admit that I are a bit anal about it.
 
You must log in or register to reply here.
Back
Top