- Joined
- Feb 17, 2013
- Messages
- 4,407
I nearly always use a center drill (aka combination drill & countersink) when making holes with my lathe or mini-mill. All too frequently on the mill, I've been notice an irritating "chatter" when using them, especially the larger sizes. Not really so much of a chatter, but they tend to make the head shake when they're drilling into a part.
First off, I checked the runout of the drill chuck ... 0.003" TIR or a bit less. Shouldn't have caused as much shaking as I'd been seeing in some cases.
So a couple nights ago I gathered together all 12 of my size 2 thru 5 center drills and tested both ends of each. I was drilling into a piece of steel and holding the center drills held in the appropriate collets (measured 0.001" TIR or less). Lo and behold, all of them caused head shaking to some extent on at least one of their ends! I measured for relative motion between the table and head a couple times, and in at least one case, they were moving what looked like 0.009" with respect to each other.
I know this would be much less of a problem with a more rigid mill, which might well overcome the out-of-centerness, but the mini is all I have for now. And even so, I don't think it's right for a center drill to be off center to the extent most of mine are.
Is it that the drills were no good to start with ... or is there some failure mode or bad practice that causes these drills to go off-center?????
Does anybody have a suggestion for where to get decent, reasonably priced center drills? What I've seen so far is cheap sets of 5 for around $10-15 and singles for under $3, then what looks like a pretty big gap, and then singles in the $10-20 range. I'm a firm believer in "you get what you pay for," and I've previously been going low-ball (though from some relatively good suppliers). But the high-end ones seem overpriced to me.
Thanks!
First off, I checked the runout of the drill chuck ... 0.003" TIR or a bit less. Shouldn't have caused as much shaking as I'd been seeing in some cases.
So a couple nights ago I gathered together all 12 of my size 2 thru 5 center drills and tested both ends of each. I was drilling into a piece of steel and holding the center drills held in the appropriate collets (measured 0.001" TIR or less). Lo and behold, all of them caused head shaking to some extent on at least one of their ends! I measured for relative motion between the table and head a couple times, and in at least one case, they were moving what looked like 0.009" with respect to each other.
I know this would be much less of a problem with a more rigid mill, which might well overcome the out-of-centerness, but the mini is all I have for now. And even so, I don't think it's right for a center drill to be off center to the extent most of mine are.
Is it that the drills were no good to start with ... or is there some failure mode or bad practice that causes these drills to go off-center?????
Does anybody have a suggestion for where to get decent, reasonably priced center drills? What I've seen so far is cheap sets of 5 for around $10-15 and singles for under $3, then what looks like a pretty big gap, and then singles in the $10-20 range. I'm a firm believer in "you get what you pay for," and I've previously been going low-ball (though from some relatively good suppliers). But the high-end ones seem overpriced to me.
Thanks!