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drilling holes with lathe
- Thread starter Deny1950
- Start date
A centering bit is always preferred because they flex less.
Any bit will find the center of rotation -which is not necessarily the center of the shaft. If your jaws are not aligned and/or if the piece is not otherwise centered, the hole will not be exactly in the center of the shaft. It will indeed be a straight hole though, relative to the axis of rotation at the time the hole was made. This is why people spin shafts between centers. First, using a chuck, you drill holes as close to center as possible in both ends of the shaft. Next, you put a center in the headstock and tailstock. The tailstock must be perfectly aligned with the center in the headstock. This establishes a new line of rotation from which you lathe off the outside of the shaft and make it perfectly uniform in diameter. If the tailstock is not aligned, the shaft will have a taper. Often times, you make the first pass down the shaft, measure for taper and adjust the headstock accordingly -unless of course you are intentionally trying to make a taper -as that is how you would go about it.
Ray
Any bit will find the center of rotation -which is not necessarily the center of the shaft. If your jaws are not aligned and/or if the piece is not otherwise centered, the hole will not be exactly in the center of the shaft. It will indeed be a straight hole though, relative to the axis of rotation at the time the hole was made. This is why people spin shafts between centers. First, using a chuck, you drill holes as close to center as possible in both ends of the shaft. Next, you put a center in the headstock and tailstock. The tailstock must be perfectly aligned with the center in the headstock. This establishes a new line of rotation from which you lathe off the outside of the shaft and make it perfectly uniform in diameter. If the tailstock is not aligned, the shaft will have a taper. Often times, you make the first pass down the shaft, measure for taper and adjust the headstock accordingly -unless of course you are intentionally trying to make a taper -as that is how you would go about it.
Ray
The short answer is no. There are variables involved. If you take a shaft (length unknown), and chuck it in a 4 jaw or good 3 jaw, or a collet, and face it square, chances are pretty good that, provided there is no nib in the center to push it around, a center or spotting drill is rigid enough to get close to center. Then the drill intended to make the hole will generally follow the start given by the center or spotting drill. Exactly on center? No. To get a drilled hole to be exact (relative term in machine work), you should center drill, drill undersized a depth of around 3x the diameter of the finished hole, then set up a boring bar and open the hole to about 0.001 over the desired drill size. Boring the hole will true it up to the center of rotation of the chuck or collet. Then the drill will follow the bored hole closely. So it starts with how accurately you are holding the shaft to begin with. The hole can be true to the spindle axis rotation and still be out or true with the part.
Now consider this: The drill will drift, no matter what you do. Sometimes not a lot, but sometimes quite a bit. So even if you get it to run pretty true at the starting face, chances are more than good that on the exit end (assuming you are drilling the entire length) it will not be on center. If the part you are making requires an accurate ID/OD TIR, then you should start with an over-sized piece of stock, drill it, then finish turn it between centers. If you aren't drilling all the way through, there are other ways to get there, but since you didn't provide all the details, we'll leave that out of the discussion for now.
If the shaft is long, but not so long you can't drill the entire length from one end, yet can't swallow it in the spindle, then you'll need to use a steady rest, and with the same care, get the shaft running true, and face it square and proceed as above.
Now consider this: The drill will drift, no matter what you do. Sometimes not a lot, but sometimes quite a bit. So even if you get it to run pretty true at the starting face, chances are more than good that on the exit end (assuming you are drilling the entire length) it will not be on center. If the part you are making requires an accurate ID/OD TIR, then you should start with an over-sized piece of stock, drill it, then finish turn it between centers. If you aren't drilling all the way through, there are other ways to get there, but since you didn't provide all the details, we'll leave that out of the discussion for now.
If the shaft is long, but not so long you can't drill the entire length from one end, yet can't swallow it in the spindle, then you'll need to use a steady rest, and with the same care, get the shaft running true, and face it square and proceed as above.