Tool post drilling in a small lathe

benmychree said:
For me at least, it is definitely faster, and easy to set up, I set my QC tool holder by setting up a tool holder up facing the chuck, moving it against the chuck and tightening the block down to the compound, once the height is set, and the adjustment locknut tightened, all that remains to be done is to find the horizontal center, which is easily done with a smallish center drill; drilling in the lathe is not a highly precision operation, a few thousandths off center is no big thing in most cases. Where time is saved for the most part is in backing out of the hole to clear chips and returning to drill deeper, I have done this since my apprenticeship back in the mid '60s, and it beats the hell out of dragging a tailstock back and forth to say nothing of loosening the clamp bolts and retightening them repeatedly. The strain on the cross slide and compound need be no more than a heavy cut in turning a diameter.
Click to expand...

I've been lining up the chuck on the QCTP by putting a piece of drill rod each in the lathe chuck/collet and the QCTP chuck/collet (depending on what's set up) and lining them up by feel. I've successfully drilled 20:1 holes this way — 32mm deep with a 1/16" drill bit (it's generally a metric project but I have a lot of 1/16" drill bits handy) didn't wander measurably. (Before I found that alignment trick, a 12:1 7/16" hole wandered slightly when I was carriage drilling over 5" deep.)

For that 1/16" hole, I was drilling 0.05"/peck. I did that once with the tailstock and it sorely tried my patience. With the carriage, it was easier to feel the work due to the reduced mechanical advantage of the pinion vs. a script, as well as faster to clear chips.

I'm also using this setup for rotary broaching. While learning with my first few broaches using the tailstock, I ran them too quickly through steel and damaged them. Using carriage feed, I can set an appropriate rate easily (I use .02mm/rev and haven't experimented with pushing harder).

(Incidentally, the 20:1 holes have been in the broaches themselves, as pressure relief when broaching holes cut undersized.)
 
mcdanlj said:
I've been lining up the chuck on the QCTP by putting a piece of drill rod each in the lathe chuck/collet and the QCTP chuck/collet (depending on what's set up) and lining them up by feel. I've successfully drilled 20:1 holes this way — 32mm deep with a 1/16" drill bit (it's generally a metric project but I have a lot of 1/16" drill bits handy) didn't wander measurably. (Before I found that alignment trick, a 12:1 7/16" hole wandered slightly when I was carriage drilling over 5" deep.)

For that 1/16" hole, I was drilling 0.05"/peck. I did that once with the tailstock and it sorely tried my patience. With the carriage, it was easier to feel the work due to the reduced mechanical advantage of the pinion vs. a script, as well as faster to clear chips.

I'm also using this setup for rotary broaching. While learning with my first few broaches using the tailstock, I ran them too quickly through steel and damaged them. Using carriage feed, I can set an appropriate rate easily (I use .02mm/rev and haven't experimented with pushing harder).

(Incidentally, the 20:1 holes have been in the broaches themselves, as pressure relief when broaching holes cut undersized.)
Click to expand...
Please explain what 20:1 means. Is it .020 to 1 revolution?
 
1/16" is almost 1.6mm, 20*1.6mm = 32mm

Sorry, mixed units obscured the point.
 
mcdanlj said:
I've been lining up the chuck on the QCTP by putting a piece of drill rod each in the lathe chuck/collet and the QCTP chuck/collet (depending on what's set up) and lining them up by feel. I've successfully drilled 20:1 holes this way — 32mm deep with a 1/16" drill bit (it's generally a metric project but I have a lot of 1/16" drill bits handy) didn't wander measurably. (Before I found that alignment trick, a 12:1 7/16" hole wandered slightly when I was carriage drilling over 5" deep.)
Click to expand...
I use the same approach. I align the rods to be parallel by backing the cross slide out so I can overlap the two rods, then adjust the angle so they're in even contact the entire length of overlap. I faced the two rods to make it easy to feel when the two ends are exactly in-line.

If I'm concerned about the cross slide drifting while I'm starting to drill I will install a cross slide clamp I made. It installs in mounting holes intended for a travelling rest. A horizontally drilled/tapped hole with a screw in it bears against the cross slide -- well, not exactly. I have a short length of aluminum rod between the screw and cross slide to keep the screw from marring the slide. But most of the time I don' bother with that.
 
I was thinking about cross slide clamps and hadn't thought of that approach. I like it and will put it on my mental project pile! Thank you! ☺

I hadn't thought about that approach to parallelism. I'm just using the same approach for squaring the toolpost as I use for parting off. (I do have a thrust washer in my toolpost clamp nut to avoid spinning the toolpost; that might make it more effective.) I'm just using two pieces of drill rod and butting them together to get them aligned coaxially by feel.
 
homebrewed said:
I use the same approach. I align the rods to be parallel by backing the cross slide out so I can overlap the two rods, then adjust the angle so they're in even contact the entire length of overlap. I faced the two rods to make it easy to feel when the two ends are exactly in-line.

If I'm concerned about the cross slide drifting while I'm starting to drill I will install a cross slide clamp I made. It installs in mounting holes intended for a travelling rest. A horizontally drilled/tapped hole with a screw in it bears against the cross slide -- well, not exactly. I have a short length of aluminum rod between the screw and cross slide to keep the screw from marring the slide. But most of the time I don' bother with that.
Click to expand...
You guys are way more complicated than I am. I use a 123 block against the chuck to square the mt2 holder and then a center to find center. Once that's done I want the backlash loose so the drill can slightly self center. Over constraint is no virtue. I've drilled very accurate holes this way.
 
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