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The Ultimate Guide to Drill Bits 8 The right drill bit tip style is determined mainly by your work material. This is an important choice for a clean job without walking, slipping, or other common drill bit shenanigans. Conventional Conventional Drill Points are the most common tip style for general purpose drills, and usually have a tip angle ...
See any of the drill maker sites for suggested drill angles on various materials. I always grind the tip rake for brass, but unless I'm doing a lot of holes in one kind of material, I'll generally go with the general 118 or 135 degrees and not grind the optimum angle for that material.
The angle near the drill center is handled one of two ways. One, the drill may have a split point. The "split point drill" if done correctly has a sharp point ground at precisely the drills center for starting the hole on location and machining it on size. It also has a varying clearance angle increasing near the drill center for easy penetration.
The angle formed by the hypotenuse of the paper triangle should match the relief angle at the circumference of the drill . In reality , the clearence at the tip should be slightly more . ( at least this is how they checked hand ground drill back in shop class 40+ yrs ago ) Thanks for the photo of the Oliver drill indicator .
Formula for finding 118 Deg. drill tip length. Yes sir the General rule for finding tip of drill tip length is: Dia. of drill bit X .300 = point length. Example: on a 118 Degree 1/4" drill is: .250 x .300 = .075 I have been Machinist for 40 years and this formula has worked every time. What I do on a metric drill is I convert the MM to English.
Always to the tip. We use a lot of carbide drills that have 140°, 150° and 130° point angles and to get the correct allowance I use a simple as follows Allowance = TAN (180-drill point angle/2)* hole Ø/2 so a 140° point on a 10mm Ø drill would be: Tan (180-drill point angle/2 = Tan 20° = 0.36397 Multiplied by 10/2 = 0.36397 * 5 = 1 ...
I have my eyes on a 140 degree spot drill because if I'm not misunderstanding, that will be the most versatile? I've read on here "For 118 degree drills use a 120 degree spot drill. For 135 degree drill use a 140 degree spot drill", and don't see why 140 wouldn't work for both. We stock McMaster-Carr drills which seem to vary in angle too.
The long tip (118') provides clearance for the tip of the center, then the taper (60') provides an correct angle for your center to engage in. If you don't take a Centre Drill to the point that it would engage the 60' angle, it would be fine, but just don't get into the shallower taper.
A drill bit with 180 degrees point angle is an endmill to me. Sort of Guidance by a pilot hole is usually done with a 120 degrees two-flute drill followed by a 118 degrees coil drill. That way the full-coil drill is first captured and centered at the web center if not pushed forward too fast.
Agreed, same or larger angle for a spot. Allows the tip of the drill to contact first and start the hole straight. If a shallower angle is used to spot the outside of the drill contact's first and will cause the drill to walk. Found this out the hard way.