Spotting Drills

[rwm]

Hmmm...seems to me that if you use the 90 deg and drill larger than the final hole you may as well just use a center drill and do the same thing. I think I have a lot of 135 deg drills so I may need the 140 deg spotting-hard to find.
I am also noticing this: the cobalt steel drills (what I like to use) almost always come as a 130 or 135 deg tip. I never noticed that before. Apparently there is more science to this than I was aware.
This is from McMasterCarr:
"135° Point Angle—Perform better than 118° point angle bits on hard materials and produce smaller chips to prevent clogging. They also have a split point that keeps the bit centered without a pilot hole and meet NAS 907 Type B aerospace specifications, unless noted.

118° Point Angle—Metric-size 118° point angle bits are made to DIN length specifications"
R

 

[Bob Korves]

Spotting drills will not help much or at all if you do not have the fundamentals right. The work needs to be firmly and rigidly held. The drill needs to be sharp and ground correctly. The drill press, milling machine, or whatever setup you are using must turn the drill at an appropriate speed and with very little runout. The drill must be fed at the proper feed rate.

If you are having problems with starting holes, check the drill for a sharp grind and equal length, angle, and relief cutting edges. Check a hole drilled with the drill. The drill should fit fairly snug in the drilled hole. If not, grind the drill correctly or replace it with a quality replacement.

When drilling there should be an approximately equal chip coming from each flute. If not, the grind is bad and needs to be reground.

Get and use a drill point gauge. This one will work fine for 118 degree drills:
http://www.harborfreight.com/multi-use-rule-gauge-65339.html
This one is nicer but does the same thing: 8^)
http://www.amazon.com/Starrett-22C-degree-Graduations-Length/dp/B0006J4CT0

If you can see runout in the drill bit, stop and fix it before proceeding. The drill might be bent, the chuck or arbor may be introducing the runout, or the spindle or bearings may be out of tolerance. Or some combination. You will have grief drilling holes until you address the problems.

Make sure your setup is not flexing and changing the angle of the hole as you press the drill into the work. A sharp, properly ground drill will take much less pressure to cut.

I have drilled some really awful holes in my time, always by not paying attention to the fundamentals...

 

[Dan_S]

This is the only direct reference I could find online, but the manufactures recommend a shallower angle for hss & cobalt bits, and a larger angle for carbide bits.
http://www.guhring.com/documents/catalog/drills/ncspotdrills.pdf

 

[Wreck™Wreck]

Once again I shall have to point out that tool manufacturers such as Guhring make products intended for use by shops that need to drill hundreds if not thousands of holes per day through multiple shifts 5-6 days per week in nearly ideal conditions. The advantage of optimized tooling is tool life at target production rates. If on the other hand one is a hobbyist drilling 10 holes per week with little or no time constraints where general purpose tooling will work fine there is no reason to not to do so.
If Guhring's target was homeowners and hobbyists they would have a tool display in every Home Depot and Ace Hardware outlet across the land.

 

[rwm]

This is the only direct reference I could find online, but the manufactures recommend a shallower angle for hss & cobalt bits, and a larger angle for carbide bits.
http://www.guhring.com/documents/catalog/drills/ncspotdrills.pdf

OK, that's weird. They make it look like you can use a 90 deg spotting drill and be undersized for a HHS drill with a larger angle? (if I am reading it right) That contradicts the earlier advice.
R

 

[Bill Gruby]

Contradiction is everywhere, When working with Automatic Screw Machines we ground the Spot Drills at 100 not 90 or 120. They didn't work as hard at 100 so changes and regrinds were way less.

"Billy G"

 

[rwm]

It's decided then. I'm going to get a 90 deg spotting drill and fool around with it. I will post my experience here after I drill a few (off center) holes.

Oh yeah...that video by Tom is really nice. I like that Hardinge.
Robert

 

[Dan_S]

It's decided then. I'm going to get a 90 deg spotting drill and fool around with it. I will post my experience here after I drill a few (off center) holes.
Robert

if you have an Amozon prime account you can get Keo brand pretty cheaply with free shipping.

 

[rwm]

I'm getting it for Christmas. Really cheap and no shipping!
R

 

[kingmt01]

I might stick to my center drills & cutting to sharp of an angle on my drills so far it has been working.