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spot drill 135+ deg

P

PeterT

Ultra Member
Premium Member
Has anyone come across a (lower cost) supplier of spotting drills with included angle of 135-deg or more? I've been hunting the usual catalogs. The ones made in USA are very spendy. For example USA KEO 142-deg, 3/16" shank is about ~35CAD. The Euro ones cost even more. I see lots of 120-deg in many flavors - carbide, coated, various flutes. But strangely larger angles 135+ seem to be much less prevalent, which is odd because I would have thought they are used often for CNC spotting for screw machine (stub drills) which are predominantly 135-deg.
 
I think a lot of CNC operators are skipping the ”spotting” step and go right to the pilot drill size with a stubby HSS drill or a carbide one - saves a tool change.
 
I think you're probably right. CNC machines have the rigidity & rpm control (and budget). From what I can tell 80% of the screw length drills are 135-deg. Varying geometry & tip profiles & coatings but you don't see many stub drills in 118-deg. 120-deg spot drills are available in abundance so probably for conventional jobbers. Precision Twist makes a few sets of stubby 118-deg. I like the drills but they are now 2-3X house brands which I've been perfectly happy with.
 
So I've got a few spotting drills (Aliexpress) and they are 90 degrees. I thought I've read a few places that 90 degrees was the best angle for spotting?
 
The best spotting angle is equal to or slightly greater than the drill point angle. So 120-deg is favored for typical 118-deg drills. Seems like if you ever want to start a bar fight of machinists spanning a few generations of age difference, this is the topic to get things kicked off LoL. I don't have links handy but this subject is quite well documented among the drill gurus as to why. I'm not sure if Stefan has a video dedicated to it but I know he has mentioned it & the underlying rationale. Once you see it, makes perfect sense. Coincidentally Joe Pi did an instructional video on deep hole drilling. After some good intro on flute angles & other info, he proceeded to spot with the classic 60-deg double cone we all used in high school. You could actually see his drill start to do the hunting wobble as he cautiously pecked his way in. Not a good way to start a straight hole IMO.
 
PeterT said:
The best spotting angle is equal to or slightly greater than the drill point angle. So 120-deg is favored for typical 118-deg drills. Seems like if you ever want to start a bar fight of machinists spanning a few generations of age difference, this is the topic to get things kicked off LoL. I don't have links handy but this subject is quite well documented among the drill gurus as to why. I'm not sure if Stefan has a video dedicated to it but I know he has mentioned it & the underlying rationale. Once you see it, makes perfect sense. Coincidentally Joe Pi did an instructional video on deep hole drilling. After some good intro on flute angles & other info, he proceeded to spot with the classic 60-deg double cone we all used in high school. You could actually see his drill start to do the hunting wobble as he cautiously pecked his way in. Not a good way to start a straight hole IMO.
Click to expand...
Yes, I think I arrived at the decision to buy 90 degree spotting bits based on my own half assed research and incomplete comprehension of the problem. Stefan does have a good video explaining it all
as does Winky
 
Thanks for the video reminders. Making my own D-bit style like Stefan shows is on my to-do list.
 
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