Spotting Drills

I use center drills. When they dull, I save them and sharpen them as usual, but grind off that nub. They work perfect.
 
I may be one of the few who say it, but I don't see using center drills as opposed to spotting drills as "incorrect". Over half my career was spent working in a machine shop. The company I worked for preferred we use center drills. It may have been partially an economic issue in that center drills were needed for most lathe work. One set of drills could do multiple duties so they didn't have to supply everyone with both types of drills. We did have spotting drills in the supply cabinets, but they were rarely used by comparison.

Another reason the center drills may have been more popular is that they were close at hand as opposed to having to walk a hundred yards to the supply room to get them. Everyone had an assortment of center drills either in their tool box or at their machine. To this day I still use a center drill far more often than a spotting. To me it's a personal preference. I've never seen a situation where a center drill didn't produce the desired results. There are however situations where a spotting drill isn't appropriate. It's tough to use lathe center with a locating hole made with a spotting drill.
 
I have always used center drills in every shop I have worked in, supplied by the shop, and I've worked in quite a few.

It is also what we use here at the school.
 
The big thing is that spotting drills are only a slight improvement over center drills. How much of that improvement you actually see, will depend greatly on the material your working with and the machine your working on. If your working close to your machines maximum capability you will probably see the difference, if you are bellow that you probably won't.

for example. with my little 8" lathe, if I use a center drill I will get chatter in harder material, or with larger drill sizes. If I use a spotting drill, I either get no chatter or significantly less than I would get with the center drill.
 
I too will continue using center drill. no spotting drill can be as ridged as a 1/4" center drill. And I have a fair supply of standard "jobbers length" drills.
 
T Bredehoft said:
no spotting drill can be as ridged as a 1/4" center drill.
Click to expand...

I have to disagree with this as a general statement. If you are referring to the long reach spotting drills, then yes, but a standard length spotting drill is the same length/stiffness as a regular center drill.
 
"a spotting drill is the same length/stiffness as a regular center drill."

My error. I spoke from ignorance of spotting drills. I will continue using the drills I have on hand, uses my money for other tooling.
 
I'd suggest keeping your eyes open too for a set of stub/ screw or mechanic length drill bits - they're alot stiffer for the same size than jobber length (stub>mechanics>jobber) although it's a good idea to keep the jobber bits around for those deeper or awkward to reach holes. I managed to drill a 1/8 hole about 3 1/2in through a cast iron tailstock with only a degree or two deviation. Stub length, then jobber length (didn't have my mechanics length drills at the time), then aircraft length. The hole was accurate enough that a 1/8 crossed drilled hole at the start and at the end both hit it easily.
 
I don't think my chuck is true enough to matter. I usually use collets to drill with unless I'm just punching out a hole & changing drills often that doesn't matter much. I took as I could see with my eye but I'm sure that isn't perfect. I just use the center drill to keep my drill from taking off across the piece & cutting at an angle.
 
I've used them all just try them and see what difference it makes.
I have a Guhring 140° carbide spot drill and 60, 90, 120. Spot and center.
What I've read is that the spot should be smaller or larger than the included angle of the drill.
I think the trick is to make them shallow. Too deep and the lips edges start to chatter.
I've had to then use a countersink to fix the problem. Now I go shallow with the spot.
 
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