Proper Use of Center Drill

[Leagle]

I have another newbie question. After cutting a center with a center drill, I have turned down several rods with the rod in a three jaw chuck at the headstock end and centered with a live center at the tailstock end. They do not turn out right. I just finished one today and discovered that there was 0.015 runout. The only thing that I can come up with is that I am not properly cutting the center with a center drill. Any thoughts or suggestions would be appreciated.

 

[jamie76x]

Did you indicate the work piece in? If the chuck is not holding the stock on center, the hole will not be on center.

 

[British Steel]

Hi Leagle,
You call 'em "rods" - are you turning down long skinny workpieces? If so, it's best to centre drill with the.minimum possible projecting.from the chuck, no more than 2 it 3 times the diameter, then pull the stock out from the.chuck and support with the tailstock centre. You.may find it necessary to use a traveling steady (travel rest) as well, if the workpiece is slender - this attaches to the lathe carriage and supports the work opposite the cutting tool to prevent deflection. A slender workpiece will.deflect away from the tool due to cutting forces, leaving a barrel-shaped (or.random) part instead of cylindrical.

Hope this.makes sense, I'm "in my cups" tonight

 

[TOOLMASTER]

make a centering jig

 

[Bill Gruby]

As said already chuck the workpiece as close as you can in the chuck. Center drill it then extend it to the tailstock and live center.

"Billy G"

 

[stevecmo]

Leagle,

Have you aligned your tailstock with the headstock? Can you describe what you measured when you got .015" of "runout"? Are you saying that the diameter of the rod is .015" different from one end to the other? If so, that would indicate you are turning a taper and your tailstock is probably not aligned correctly.

We need a little better description of what you did before we can diagnose the problem. Pictures are always welcome and helpful.

Steve

 

[Ray C]

If it is a taper as Steve pointed-out, let us know which end (headstock or tailstock) is less in diameter then, we can tell you which direction to adjust the tailstock.

Ray

Leagle,

Have you aligned your tailstock with the headstock? Can you describe what you measured when you got .015" of "runout"? Are you saying that the diameter of the rod is .015" different from one end to the other? If so, that would indicate you are turning a taper and your tailstock is probably not aligned correctly.

We need a little better description of what you did before we can diagnose the problem. Pictures are always welcome and helpful.

Steve

 

[fastback]

I agree, start with the tailstock alignment.

 

[Tom Griffin]

Are you talking about runout or taper? And if you think you have runout relative to the center hole, how do you know? Haw are you measuring it?

Runout at the tailstock end then can be caused by either the center itself having runout, or by the fact it is not tight in the center hole when you turn the part. It's possible you are drilling the hole too deep and creating a counter bore effect on the center hole which will quickly wear off and leave the center loose. The center hole should be drilled approximately 2/3 the depth of the tapered section of the center drill.

Taper on the other hand, occurs if the tailstock is not aligned with the headstock when you turn the part. You can check that by measuring each end of the part and adjusting the tailstock until the taper is eliminated. Moving the tailstock toward you makes the part smaller and moving it away. makes it larger.

Tom

 

[cazclocker]

You can make yourself one of these things - among clock repair people they're called the "Magic Center Finder". You can't see it in the picture but the brass slide has been coned with a female taper at the end near the 3-sided drill point. You can use hardened drill rod or music wire for the drill point. As mentioned before, index your workpiece so it's centered in your chuck at the headstock end. Then use a low to medium speed to turn your piece. You have to start by withdrawing the 3-sided point into the slide so it doesn't protrude at all. With the lathe turning, gently rest the female taper over the circumference of the workpiece's end so you know it's touching but not pressing - then gently press the wooden handle to drive the drill point into the end of your workpiece. You won't end up with a dimple large enough to support a center, but it will be PERFECTLY centered and you can follow the Magic Center Finder with a center drill.
EDIT: You don't have to use brass for the slide (steel works well), but the slide obviously has to be larger diameter than your workpiece. It helps to put a dab of grease into the female taper before using because you can easily get circular score marks in there. It works best if you face off the "tailstock end" of your workpiece so it presents a perfect circle to the female taper. Geometry is your friend!