drill bit jump

[dryfarmer]

why does the drill bit jump up when you first start to drill a hole on the lathe?

[Magicniner]

A Centre Drill will self centre on the rotating material but I wouldn't call it a jump.

[KiddZimaHater]

because the drill is drooping a bit in the tailstock.
When it makes contact with the rotating part, it will self-center, or "jump" a little.

[3 Phase Lightbulb]

Make sure the ejector is backed off and the chuck is fully seated in the MT. You're probably just seeing the chuck fully seat itself in the MT once you apply pressure to it. if it happens a lot you probably need to clean out the MT in your tailstock and make sure the tool tapers are also clean.

[ahidley]

Because your not using a split point drill bit. If you look close at the very top of the bit the two tiny little flats at the point DON'T drill. Drill bits are all ground mostly the same so tinny ones are the same, puportimatly, as large ones. But look at a large bit for more clarity in what I describe. Split points don't have that little flat. That's the only differance.thats why they drill location more accuratly

[CCWKen]

Get a set of center drills or a couple in the sizes you use most.




I've seen some videos on YT where I don't know how some of these guys don't break bits. Or how they even do anything. The chuck and tailstock looks like they're flopping around. But I guess it's better than a bit brace...A little.

[MattiJ]

Get a set of center drills or a couple in the sizes you use most.




I've seen some videos on YT where I don't know how some of these guys don't break bits. Or how they even do anything. The chuck and tailstock looks like they're flopping around. But I guess it's better than a bit brace...A little.

Very short drill bit that is only 1/4" or 1/2" out of the chuck works equally well and you can save the center drills for actually drilling centers.
Pop rivet drills are cheap and short. Some of them I have cut in half to make two extra short starting drills for lathe work.

[Willy]

I use machine length 135° split point drills for pilot holes and make sure that I don't have a pip protruding on previously faced work, never had the problem of a drill bit jumping. This and good sharp center drills.
I could certainly see the issue arising when using a long drill in a loose tail-stock. This and what ahidley referred to in reference to the chisel edge portion of a drill bit, no self-centering function in that portion of a drill.

[BCRider]

why does the drill bit jump up when you first start to drill a hole on the lathe?

Perhaps a better description of what you mean by "jump up" would be helpful. I can imagine a few different options. At least one of them being that the tail stock ram isn't accurately aligned with the head stock spindle axis. So it's pointing the drill bit downwards below center by a little. Or do you just mean the tendency for the drill to catch and flex upwards and start running around a little off center when trying to drill without a starting recess?

[dryfarmer]

I use centering drills, it is when I then start to drill the pilot hole with a drill bit that the drill moves up. I will try to get a video and then try to post the video to better explain what I am seeing.

[BCRider]

No need, got it now.

OK, just for giggles try turning the drill bit in the chuck. See if it's just as bad or "pulls" in a different direction. It's not common but in cheap drill bits I've found some that are bent. Or if the shank was burred badly sometimes the jaw will sit on a burr and shift the drill around. Next up is to unseat, rotate and re-set the chuck arbor in the tail stock at a different angle. Again see if the "aim" is off the same or rotates around with the chuck. If all that is for nought then it's time to rig up the dial gauge and check for vertical alignment of the ram and see if it's sitting level and coaxial to the spindle.

With the ram extended about half way "lock" it and see if the dial gauge shows it lifting up some amount. You might simply have some wear in the ram and tail stock body so the fit is loose enough to allow the ram to sag a little. And finally with the ram fully extended and locked to center the end run the tail stock back and forth under the gauge to see if the ram is angled down towards the head stock side.

This can be "fixed" if you find that it's out in some manner or two but at least if you find an issue it'll explain what you're seeing for now. If it's simply that you're getting a little sag of the ram when it's not locked into the tail stock then it may well be that it's not hurting you any. The ram is simply lifting up within the "play" to center itself. If it's something critical and the ram lock does lift the ram up neatly perhaps just use a light locking force to center up the ram for the critical holes. Or if it's really bad and bothers you then it may be time to line bore the tail stock and make up a new slightly larger diameter ram? Or to bore out and fit an end bushing in the tail stock body to better center the worn ram's current diameter?

As part of my new "solid" lathe pedestals and alignment I performed all these and a few other checks. Ended up shimming between the tail stock upper and lower castings along the split line that is used to allow offsetting the tailstock for taper turning. It was a few thou low and now MOST of the time the drills enter the holes neatly centered. And when they don't the entry "kick" seems to be far less and far more random for direction. So that's just the cheap drill bits I'm using.

[Illinoyance]

If you look at a conventional drill bit there is a flat chisel edge. Because of that chisel edge the drill tends to walk around until the flutes start cutting deep enough to center the bit. Split point drills don't have that problem. 4 facet grinds are also self centering.

[brian Rupnow]

I always use a center drill like the picture posted earlier in this thread, both in the lathe and the mill, before using a drill. My most commonly used drills are all between 0.100" and 1/2". I have had too many bad experiences with "drill walk" to ever totally trust any kind of drill to start where I actually want it to. Another issue is that my lathe has a very wide saddle, so the drills have to be fairly long to reach the part held in the chuck to be drilled, or I have to have the tailstock extended over 2".