Spotting Drills

[rwm]

I am new to spotting drills. I have always used center drills (incorrect I know) to start holes and now I want to do it right. I am confused about the point angles. I see spotting drills that come with 3 different angles: 90, 120, and 140 deg. I have read that the 90 can be used with any drill angle if the spotting hole is larger than the final hole. Is this good practice? Which angle do I want to use with standard drills? I think my twist drills have both 118 and 135 deg angles?
Any other thoughts on spotting drills or hole starting are welcome on this thread.
Robert

 

[davidh]

Spotting drills- Function? i think this post for 2011 pretty much sums it up. i must look into it. now i use center drills after a good smack with a center punch, or just go right to the stub drill. . it seems stub drills have a hard time to wobble also.

 

[rwm]

I did a search and read that post. It really only addresses the 90 deg drill use. I am hoping someone can enlighten me on the best practice and which angle I should buy.
R

 

[kingmt01]

Watching with interest since I use center drills also.

 

[Bob Korves]

This can get into a pissing contest disagreement, but here is how I see it. The spotting drill needs to have a larger included angle "cone" than the drill that will follow if it is to be a centering aid. If you are using a standard 118 degree drill then you should use a 120 degree spotting drill, if using a 135 degree drill, then use a 140 degree spotting drill. Make the starting hole a little larger than the chisel point of the drill. That way the drill is actually centered by the larger angle starting cone. If you use a spotting drill with a smaller angle, the drill's cutting edges will catch on the corners of the cone and the drill will walk. If you drill the spotting hole larger than the drill bit, then the outside edges of the drill will kinda wanta center in the smaller angle cone, but the outer cutting edges will still tend to grab and the drill will still tend to walk in the smaller angle hole.

Now, if you check out the sale catalogs of Enco, MSC, Travers, etc., you will find that about all they put on sale are 90 degree spotting drills. Is everyone using drills with angles less than 90 degrees? I don't think so. 120 and 140 degree spotting drills are certainly available, but they are much harder to find, and you probably won't find any on sale.

Me? All I have on hand are a few 90 degree spotting drills, so I do not walk my talk. Instead, I just use the 90 degree spotter, drill slightly larger than the chisel point of the following drill, and start the second drill gently and carefully. That seems to usually work OK. More and more, I just use a stub length drill bit with a split point and just drill the damn hole, starting gently to get it established on the mark. That works well. The stub drills are stiff, and the split point drills do not walk, those drills require less pressure to cut, and it eliminates changing out drills constantly. With a stub length, split point drill you do not even need a center punch mark for drilling with a drill press or on the mill if the work is flat and perpendicular to the drill. Just start the hole by pecking gently.

There are arguments for other approaches as well, listen carefully, think about it, and decide for yourself.

 

[Ed ke6bnl]

Check out Toms video he says it all.

 

[Ebel440]

I use 90 for aluminum and other soft metals. 120 for steel etc. the 120 lasts longer in steel.

 

[Wreck™Wreck]

I did a search and read that post. It really only addresses the 90 deg drill use. I am hoping someone can enlighten me on the best practice and which angle I should buy.
R

A 90° spotting drill can serve 2 purposes at once, spotting the hole position and if larger than the finished hole deburring the entrance saving one a second operation. As to the question of "best practice" use what ever works best for you in a particular application, keeping in mind that a tool may be used for things other then it's intended purpose. If you need to drill several thousand holes per day, every day, then certain angles may provide a longer tool life of the finish drill, if a hobbyist doing several holes per week ignore the point angle debates.

For instance a 90° spotting drill may be used as a countersink for flathead screws of the same angle, in non-critical applications it will also do fine for 82° ASME screw heads as it is only a 4° per side difference.
Exactly how accurate do you think a countersink or screw marked 82° bought from Enco, Harbour Freight, Home Depot or anywhere else actually is?

 

[Bill C.]

I am new to spotting drills. I have always used center drills (incorrect I know) to start holes and now I want to do it right. I am confused about the point angles. I see spotting drills that come with 3 different angles: 90, 120, and 140 deg. I have read that the 90 can be used with any drill angle if the spotting hole is larger than the final hole. Is this good practice? Which angle do I want to use with standard drills? I think my twist drills have both 118 and 135 deg angles?
Any other thoughts on spotting drills or hole starting are welcome on this thread.
Robert

I always used center drills, depends how you are trained and are comfortable with. Don't recall using spot drills, sounds interesting.

 

[Bill C.]

I did a short Google search. I can see advantage using spotting drills since you are not dealing with that small pilot drill, I had a few to snap off because I didn't increase enough RPM. From what I could find the spotting drills were made popular with CNC machining. That's what I like about this site always learning.

Hope all have a Great Weekend