Well, I reread the initial post after seeing some of the comments about using them in a mill and such. I also noticed this time through he mentioned holding it in a collet and power feed as well as the vertical spindle comment. I know that in theory you sometimes center drill something in the mill or drill press for mounting on the lathe, but I don't recall ever having done so (not that I've been doing this for long...).
That extra drill tip is for clearance when using a center. For dead centers, it's an oil reservoir to help prevent galling. For a live center, it just provides clearance to make sure you’re not riding on the sharp point. But in either case, it is purely for mounting a center, hence the name “Center Drill”. And it is not a design flaw at the transition from small to large, it is a requirement to minimize that transition in order to retain maximum bearing surface in the cone riding on the center.
Because they are short and rigid, they are often also used as spot drills, particularly by us HSM types since we tend to minimize and multi-use our tools as much as possible. But they are FAR more fragile than center drills, and if your breaking a lot of them as you suggest, then your sure not saving money by multi-use. If you are in fact using them this way, may I suggest getting an actual spot drill? I don’t think you’ll ever have any luck running a small center drill in a drill press, particularly an inexpensive drill press. Drill presses often have at least a few thou of run out in the spindle, and that is too much for a small center drill tip. A mill would be better and should have less run out, but still not under power feed, and you need HIGH rpms which may not be available depending on mill. Again, using an actual spot drill will fix all these problems, lasts MUCH longer, easier to sharpen, and does the job just fine without the hassle.
And the regrind is a good plan to salvage some broken center drills as spot drills. Just make sure you also thin the web sufficiently.
Small Center Drill Blues
I must be doing something weird because I have only broken about two center drills in the past 15 yrs. I do not find them at all fragile. I use them in the mill and drill press to pilot a hole that has to be right on as well as for drilling centers for the lathe. I even have some of the #1s, never broken one yet. Not saying I am superman here, but I have never had the trouble posted originally, EVER.
It sounds to me like you have the runout problems mentioned, the chuck is crooked on the arbor, or you are just running too slow with too much feed. Typical error is too slow a speed and too much feed when drilling. The smaller bits, as pointed out, are much less likely to be burned up running too fast than wrung off due to low speed and feeding hard. I run the spindle as fast as possible and feed very gingerly by hand.
It sounds to me like you have the runout problems mentioned, the chuck is crooked on the arbor, or you are just running too slow with too much feed. Typical error is too slow a speed and too much feed when drilling. The smaller bits, as pointed out, are much less likely to be burned up running too fast than wrung off due to low speed and feeding hard. I run the spindle as fast as possible and feed very gingerly by hand.
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dirty old man
- Posts: 44
- Joined: Tue Nov 15, 2005 6:49 pm
- Location: Griffin, GA
I earned a living as a machinist for 38 years till I retired and have my own shop now. And like Mike C. I've used center drills in drill presses, mills, and lathes all that time, and have broken very few, not over 2 or 3. I also never saw anyone using a spotting drill till I saw them in use on CNC machines, so until recently, I thought they were developed for CNC machines.
Recently I've read a bit on spotting drills and I can see where they would be more durable and forgiving than a center drill when used as a spotting drill. And the next time I see a sale on them in a good brand, I'm gonna order a few.
Dave
Recently I've read a bit on spotting drills and I can see where they would be more durable and forgiving than a center drill when used as a spotting drill. And the next time I see a sale on them in a good brand, I'm gonna order a few.
Dave
I've got to go with Jim's #6...Use a spot drill when ever you can. It's just the way I was taught 30+ years ago at Giddings & Lewis...use a spot drill for "spotting" holes (going a little deeper will chamfer the hole at the same time)...center drill is for making a hole for a lathe center. In their tests at that time the most accurate hole location was achieved using a spot drill with the same point angle as the drill (usually 118*).
All good advice.
I also use the "flutes vertical" technique when drilling in the lathe; it seems to help a bit, especially if your machine has been around for a while (my lathe was built in 1942 so its almost as old as I am). The tailstock spindle in my South Bend has a little play which actually seems to help a bit in this application; as Harold says, when you start the center drill, you can see it wander just a little at the beginning & then it will settle down on a true center. When doing this I also make sure the spindle lock is quite loose to aid in the "float."
Like the rest of you, I've also found that sometimes when you start drilling with a regular drill in the lathe, it will wander a bit even when the hole was initially true. When that happens, I bring the tool over to the drill & force the point off center to stop the wobble. After its running true, I back off the tool as I feed the drill in & that way it runs true again.
At least part of Don's problem is because the Millrite milling machine he has is one that doesn't have a lever operated downfeed on the quill. Instead it has a screw/nut arrangement that is turned by a handwheel. That means for small drills, he has no "feel" for the load he's putting on the drill, so that coupled with a rotational speed that's on the slow side is probably the cause of the breakage. Yes, the transition between the straight part & the cone of the drill is also a "stress raiser" which doesn't help either. As well, any table movement, and you are sure to break the drill because it has no "give," but then that's why you use it in this application. I don't break too many, but you definitely do have to treat them with more care.
I guess my own personal dislikes are small tapped blind holes (5-40 & amaller, down to 0-80) and drilling small deep holes. There are probably more, but those are the ones that come to mind at the moment.
Again, I'm glad that so many people are willing to take the time to add their knowledge & experience to this forum. Believe me, it all helps.
Richard Trounce.
I also use the "flutes vertical" technique when drilling in the lathe; it seems to help a bit, especially if your machine has been around for a while (my lathe was built in 1942 so its almost as old as I am). The tailstock spindle in my South Bend has a little play which actually seems to help a bit in this application; as Harold says, when you start the center drill, you can see it wander just a little at the beginning & then it will settle down on a true center. When doing this I also make sure the spindle lock is quite loose to aid in the "float."
Like the rest of you, I've also found that sometimes when you start drilling with a regular drill in the lathe, it will wander a bit even when the hole was initially true. When that happens, I bring the tool over to the drill & force the point off center to stop the wobble. After its running true, I back off the tool as I feed the drill in & that way it runs true again.
At least part of Don's problem is because the Millrite milling machine he has is one that doesn't have a lever operated downfeed on the quill. Instead it has a screw/nut arrangement that is turned by a handwheel. That means for small drills, he has no "feel" for the load he's putting on the drill, so that coupled with a rotational speed that's on the slow side is probably the cause of the breakage. Yes, the transition between the straight part & the cone of the drill is also a "stress raiser" which doesn't help either. As well, any table movement, and you are sure to break the drill because it has no "give," but then that's why you use it in this application. I don't break too many, but you definitely do have to treat them with more care.
I guess my own personal dislikes are small tapped blind holes (5-40 & amaller, down to 0-80) and drilling small deep holes. There are probably more, but those are the ones that come to mind at the moment.
Again, I'm glad that so many people are willing to take the time to add their knowledge & experience to this forum. Believe me, it all helps.
Richard Trounce.
That be the case, I'm surprised he has any luck at all. The "feel" of a quill is all important. When I was actively machining, it was common practice to stop what I was doing and wash the quill of my Bridgeport with a chemical cleaner, then wipe it down well and re-oil to restore the feel. It was generally sensitive enough to be able to feel drills smaller than #60. One uses only a finger on the lever, never a hand.RET wrote:At least part of Don's problem is because the Millrite milling machine he has is one that doesn't have a lever operated downfeed on the quill. Instead it has a screw/nut arrangement that is turned by a handwheel.
In Don's case, he should address the quality of his chuck, too. It's very important that the center drill run true, or chucking it short as I advised for lathe use should become common practice.
Harold