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spot drill 135+ deg

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.
 

RobinHood

Ultra Member
Premium Member
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.
 

PeterT

Ultra Member
Premium Member
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.
 

DPittman

Ultra Member
Premium Member
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?
 

PeterT

Ultra Member
Premium Member
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.
 

DPittman

Ultra Member
Premium Member
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.
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
 

PeterT

Ultra Member
Premium Member
Thanks for the video reminders. Making my own D-bit style like Stefan shows is on my to-do list.
 
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