Is it normal for lathe tailstock drill to lift up when contacting work?

strantor

strantor

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As a machining hobbyist and a not-retired person who works long hours often out of town, I think it is safe to admit that I spend more time watching machining videos on YouTube than I do actually machining. Most often in bed when I'm supposed to be sleeping but the ol cranial flywheel can't be stopped.

One thing I notice in (most?) Of these videos is when people bring a drill bit into the work, it lifts up. If I'm not mistaken this means the tailstock is not on center (worn ways?) and the hole will not be straight. But they don't seem to care or ever acknowledge it happening.

I've noticed other things, what I consider to be an odd side effect of the internet: "Trends" in videos I assume are caused by Youtube-educated youtube-instructors perpetuating oddities. Like how so many people refuse to run a bead of weld. Everything is a series of zap-zap-zap like they they're applying concepts from auto body repair to 1/2" plate.

I'm wondering if that's what this drill-lifting thing is, or if it really doesn't matter, and that's why so many people post videos unabashedly showing close-up footage of it happening over and over and over.
 
strantor said:
As a machining hobbyist and a not-retired person who works long hours often out of town, I think it is safe to admit that I spend more time watching machining videos on YouTube than I do actually machining. Most often in bed when I'm supposed to be sleeping but the ol cranial flywheel can't be stopped.

One thing I notice in (most?) Of these videos is when people bring a drill bit into the work, it lifts up. If I'm not mistaken this means the tailstock is not on center (worn ways?) and the hole will not be straight. But they don't seem to care or ever acknowledge it happening.

I've noticed other things, what I consider to be an odd side effect of the internet: "Trends" in videos I assume are caused by Youtube-educated youtube-instructors perpetuating oddities. Like how so many people refuse to run a bead of weld. Everything is a series of zap-zap-zap like they they're applying concepts from auto body repair to 1/2" plate.

I'm wondering if that's what this drill-lifting thing is, or if it really doesn't matter, and that's why so many people post videos unabashedly showing close-up footage of it happening over and over and over.
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Movement is normal and expected. Even when center drilled. A drilled hole itself, is not very accurate. That's why it's followed with a ream or bore. With practice, holes end up right where they should be.
 
Probably the lift is due to looseness overall in the tailstock fit to the bed and the quill itself- a drill will tend to "self-center" somewhat
when drilling the end of a rotating workpiece so it's not a big issue

I know that sometimes with welding it's better to run several short beads instead of one long one to minimize warping
and often a couple short well-placed beads are plenty strong enough- no need to go overboard and waste rod
 
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Lathes get worn. Tailstocks get worn. Drill bits aren't as straight as we'd like to think they are. Drill chucks aren't as accurate as we like to think they are. Morse tapers, Morse tapers aren't as accurate as we'd like to think they are. Drill chuck adapters aren't as accurate as we like to think they are. Gravity sucks. Wear is (almost) exclusively in the "low" direction. Those two are the biggest contributors to why it seems the drill bit "always" lifts up.

In practice, if you feed in just so, the drill bit will actually self center to some degree. What you're seeing is real, and in practice, (and with practice), if you tease the drill point into the work kinda gently but not too gently, within reason it will find it's center (ish). At least plausibly close to center for most applications, and very much close enough to follow up with a boring bar to final dimensions. (Drilled holes don't qualify as precision diameters no matter how good your drills, your machines, and your skills are. They're good, plenty good for most tasks, but they're not precise.

Add to that, the close up shots magnify stuff that might be happening right in front of you, on your own machine, but are not so easy to see as when it's on a video. So it usually looks ten times worse than it really is.
 
It indicates the centerdrill is below the spindle centerline. It is likely due to wear on the front edge of the tailstock base or wear on the bore the tailstock quill rides in. Chuck up an indicator and sweep the OD of the centerdrill. That will show how much the centerdrill is below center. Minimize the effects of tailstock wear by using a centerdrill driver instead of a chuck to hold the centerdrill.
 
A toolpost mounted chuck sidesteps tailstock issues. But the slide plates have to be well adjusted otherwise the drilling force will lift the carriage up. I discovered this on my 7x12 lathe. I hadn't noticed the problem until I used the toolpost mounted chuck because the forces are different compared to normal turning.
 
Center drills are not the best tool to start drills with, as the pilot drill frequently breaks, especially in the smaller sizes and to 60 degree angle on the body diameter is not ideal to start a normal drill point angle on. As has been said several times on this forum, spotting drills are a much better choice, as there is no pilot to break off and the angle better matches the drill point angle. Again, the proper tool for the job.
 
homebrewed said:
A toolpost mounted chuck sidesteps tailstock issues. But the slide plates have to be well adjusted otherwise the drilling force will lift the carriage up. I discovered this on my 7x12 lathe. I hadn't noticed the problem until I used the toolpost mounted chuck because the forces are different compared to normal turning.
Click to expand...
And forcing the carriage up invites getting dirt and chips under the carriage, causing galling and wear. This should not be done on small hobby type lathes, OK for industrial type machines, I.E. I have a 19" swing Regal Leblond lathe with a 4MT Aloris tool holder that I routinely use for drilling.
 
I have chuck adaptors for my QCTPs on 2 lathes. I do not use them because they cause the entire tool post to rotate under drilling forces.
 
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