Center drilling (More basic questions)

[EOsteam]

What is the proper way to center drill with the lathe tailstock? The last time I did this it seemed like the center drill was wandering all over the place trying to find it's center on the bar.

Thanks again!

HJ

[spro]

The face at the end of the bar must be perpendicular to the axis of rotation. Let's say the bar is perfect round and the chuck locates it on center. The end where it was cut may not be perfect flat in the center area and that would be the same as if the bar was bent. That area must be lightly faced to the center of rotation. This does happen with long stock as things get bent but are still useful.

[SteveM]

That may indicate that your tailstock setover (front to back) or your tailstock height (up/down) is off.

If you have a center for each the headstock and tailstock, put them in and bring them together and see if they line up. I use a magnifying glass and a sheet of white paper on the other side to see the lineup.

If they don't adjust side to side, there are adjustment screws to take care of that. Adjust until they are together.

If it is off up/down, you might have to shim the tailstock.

Note that all this is when the tailstock is close to the headstock. If your lathe is not in alignment (i.e. the bed is twisted), then it might line up at the headstock and not further out.

Steve

[EOsteam]

The lathe is leveled and the tailstock has been checked. The end had a facing cut taken. I will try a different center drill.

[jcfx]

I'd check to see if the tailstock quill doesn't have any play when you tug on it to and fro,
meaning towards you and away, that can make your center drill wobble as it tries to find center.

[Harold_V]

Center drills will seek center if you allow them to do so. Grip the center drill by only a short amount of its length, and don't over tighten the chuck, so it can move about when you approach the spinning material. If it's not dead aligned, it will try to scribe a circle on the face of the part (which must run true, so ensure that it has been faced). Unless misalignment is excessive, the circle formed will help guide the center drill towards center as you feed slowly. Once centered, drill to the desired depth, using lubrication.

This process works for even small center drills (#1 or smaller), which are VERY easy to break if you aren't on center. In such a case, hand tighten the chuck, so the center drill is held just snug, so it can seek center all the easier. Because very little pressure is required to drill small centers, hand tightening should be adequate. Not so for larger center drills.

Harold

[liveaboard]

I thought I knew how to do something as simple as drill a center hole; I did ok when my center drill bit was new and sharp, but when it's just slightly imperfect I got "orbiting".

And now I do it as Harold wrote; and I'm on center again.
Thanks Harold.

[Harold_V]

And now I do it as Harold wrote; and I'm on center again.
Thanks Harold.

Welcome!
Of note, I spent five years in precision grinding. We did all the finishing grinding for the test and launch sets for the missile, which included no end of small diameter stainless steel shafts. Amazingly, rarely was a center concentric with the exterior. Not off a lot (a thou or two), mind you, but it was obvious that the center drill wandered.

It should be noted that the center was not used for turning the pieces involved, as they were typically short enough to be turned without tailstock support. The centers were provided strictly for the grinding operation.

If a center MUST be on location, it is best machined by boring.

Harold

[liveaboard]

My work is generally pretty crude stuff; I just want starter hole somewhere in the vicinity of center for further drilling.
But even for my lumpy needs, drilled holes are too irregular. It's just to get material out of the way before single point boring to the final dimension.

[earlgo]

When I need a center on center, I routinely use a little sharp tool bit to "bore" a tiny dimple in the stock, then following up with a center drill held as Harold has suggested gives a center pocket as close as I can get to true position.
Just another way.

--earlgo

[Mr Ron]

I can't recall where I read it, but it said; "lock the tailstock spindle and by hand, push the entire tailstock toward the headstock until a dimple is produced. Then clamp the tailstock down , release the spindle clamp and finish the center hole with the handle." The reason supposedly was to eliminate play in the unclamped spindle. Has anyone heard of this?

[ctwo]

I think the tailstock has a quill instead of the spindle.

I read that the quill (center drill) should be allowed to float so it can find center, and that the stock could be moved closer to the head stock chuck for more precise centering.