Hi guys, I am fitting a BXA toolpost to my new lathe and tomorrow's job is to drill and ream a 12mm hole about 40mm deep in the centre of the 16mm bolt I bought today. I've already drilled an 8.5mm hole right through the piece (as an 10 thread is required as well) and have a set of unused chucking reamers to do the job with.
I just wanted to check the hole size to use. From what I have read, it seems that an 11.5mm hole is the right size to go for. That is 0.5mm or 0.002" undersize.
It just sounds too easy to use a standard sized drill. Should I be using a fractional drill? I do have a set of imperial Letter and Number drills that I can use for fractional sizes if required.
Anyway, I just wanted to check this before diving in and breaking something.
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Reamers are quite simple things, but they're a little bit persnickety. It's not like a drill bit even though it kind of is.... But before I scare you off.... It's not that bad either. They feed a little slower than you'd think (But KEEP THEM FEEDING, don't let them dwell. A drill press with a hand operated quill, a tailstock chuck with a screw operated feed, powerfeed if you could figure out how to arrange that... All will work fine.
Whatever speed you have the best success drilling the hole at, you're going to want to be at half of that or less. Not the speed chart speed for that sized drill, but half of the actual speed where you have good success. Which it's self is (probably) well less than the published "speed limit". Half or a little less of YOUR most successful speed.
Of course, that speed will (probably) depend what machine you're using.....
Do NOT stop the reamer to back it out. Run it in and out while it's rotating. Lots of oil (or whatever cutting lubricant you're using), modest speeds, modest feed pressure/feed rate, and you're not describing a very deep hole... Conservative speeds, conservative speeds, constant CONFIDENT smooth motions on all the above, like you just know it's gonna be fine.... You'll be fine. These are one of those tools that can smell fear. Hesitation, "too slow" of a feed, and generally being "too careful" can make them act up just as much as heavy handeness can.. Don't hesitate, don't stop, just keep it moving confidently at those modest speeds and feeds, get it in and then get it out out, you'll be fine.
As far as the setup, it really doesn't make much difference which one you spin, whatever way it's easiest to set up would arguably be the best way. I would suggest that drilling the hole and then reaming it in the same setup would be the best orientation, whichever way you chose to accomplish that would be fine. If that setup is lost already, I wouldn't loose any sleep, but the more concentricity you can maintain, the more on size that hole is going to come out. Even if you're not perfect in your technique, the hole is gonna be pretty darned accurate. Even a "badly" reamed hole is still WAY more accurately sized and better finished than a drilled hole.
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