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View Full Version : Jacob's chuck and center drill: the drill press farce continues....



jgourlay
06-19-2012, 11:33 AM
All,

With your help, I got my Delta DP 'within spec'. 'Spec' being .007" TIR 1" below the chuck (whoopity doo)...

Part of the fix was putting on a new jacobs keyless chuck. Worked spanky until this weekend, when I put a center drill in. It's a typical 'two ended' half inch shank tool.

TIR with this thing is about .25". No kidding. Put a 6" long half inch drill bit in, and I can see the runout if I stare at it briefly. Put the center drill, and I have to duck out of the way as the end of the drill comes swinging at my head.

The drill isn't warped. Chucked it up in my lathe, and it's fine. What it is, is that for some reason this chuck won't grip on a center drill. Of any size.

ALL MY OTHER CHUCKS do just, including 'mr cheap chinese wobbly chuck' that I replaced with the jacobs.

Sometimes, I just can't win....

bborr01
06-19-2012, 12:46 PM
Some drill chucks will not allow a center drill to enter far enough to seat right in the jaws. Try cutting the center drill in half and see if it chucks better that way.

Brian

PaulT
06-19-2012, 12:58 PM
I'd switch to a spot drill, they work better than center drills for making pilot holes and they chuck up easier.

The US made Keo brand ones work really well and last a long time and are often on sale at Enco.

Even on my lathe I mostly use spot drills now, the only time I use a center drill is for actually drilling for using a live center. That's what center drills are actually intended for, spot drills work better for making pilot holes.

Paul T.
www.power-t.com

Paul Alciatore
06-19-2012, 01:34 PM
I have at least ten different drill chucks for lathe, mill/drill, and drill press: 1/4" to 5/8" sizes. This does not count those on hand drills where measuring run out would be more difficult. Some are name brands like Jacobs and others are imports. None of them have more than 3 thousandths run out or perhaps 5 thousandths for the older, import, large size ones.

You need to check the run out in a systematic way. First check the spindle. While the spindle is exposed, run a finger into it to check for irregularities. Then put the adapter (MT to JT) in without the chuck and check run out on it. Then check the run out of the chuck body. And finally, chuck a piece of ground, drill rod and check it. Remove the drill rod and chuck it again and check it a second time for consistency. Somewhere in this chain of checks you will see where the real problem is.

I have never seen a Jacobs brand chuck that would not properly grip a center drill, not even going to extremes like a 3/16 diameter center drill in a 1/2" chuck. The jaws of the chucks are guided by holes in the chucks and have very little room to get out of alignment.

Do properly clean out the chuck. Blow it out with compressed air to be sure there are no chips inside it that interfere with proper centering. Run the jaws all the way in and swish it around in a parts washer or container with some mineral spirits to get smaller stuff. Run the jaws partially out and swish it again. Re-oil it to prevent rust. Check the gripping surfaces of the chuck jaws for burrs or other irregularities. Check the OD of the center drill for burrs. Use a new drill (to be sure it is straight) and chuck it with different depths of insertion in the chuck and see if the run out is consistent. Mark the side of the chuck it leans toward in each chucking and see if they are the same or different.

All or some of the above should help to pinpoint where the problem is.

DR
06-20-2012, 12:32 AM
All,

.................................................. ......................................

TIR with this thing is about .25". No kidding. .................................................. ....................................

....


And you seriously expect us to believe this...???????

Astronowanabe
06-20-2012, 04:37 AM
All,

With your help, I got my Delta DP 'within spec'. 'Spec' being .007" TIR 1" below the chuck (whoopity doo)...

Part of the fix was putting on a new jacobs keyless chuck. Worked spanky until this weekend, when I put a center drill in. It's a typical 'two ended' half inch shank tool.

TIR with this thing is about .25". No kidding. Put a 6" long half inch drill bit in, and I can see the runout if I stare at it briefly. Put the center drill, and I have to duck out of the way as the end of the drill comes swinging at my head.

The drill isn't warped. Chucked it up in my lathe, and it's fine. What it is, is that for some reason this chuck won't grip on a center drill. Of any size.

ALL MY OTHER CHUCKS do just, including 'mr cheap chinese wobbly chuck' that I replaced with the jacobs.

Sometimes, I just can't win....


Could you be holding the drill with only two of the three jaws?
Or maybe seating one or more of the jaws in the relief gullies?

coalsmok
06-20-2012, 06:14 AM
You are getting the chuck jaws down inside the flutes on the center drill. It happens to me with my glacern keyless chuck if I am not careful.

Carld
06-20-2012, 09:18 AM
.25", that's 1/4", surely you meant .025". If it's 1/4" run out it's between two jaws instead of all three.

Jaakko Fagerlund
06-20-2012, 12:50 PM
As have been said, the reason it is wobbling is that one or more chuck jaw enters the flutes of the center drill. I have two or three keyless chucks that do that very easily, if I'm not careful in the positioning of the bit.

Cut the bit in half or buy an NC drill (aka spotting drill). Most chucks usually dull the other end of the bit if you bottom them out in the chuck and tighten the chuck, as the bottom part is moving outwards when tightening. This ruins your bit quite quickly, especially if the bit slides in the jaws from pressure.

And yes, 1/4" wobble is nothing new in that situation.

Arthur.Marks
06-20-2012, 01:27 PM
I blame a lot of the often-referenced, older machining texts for the prevalent use of center drills in lieu of a spot drill for anything but drilling a true lathe center socket. They all seem to tell you to do it. I wonder why that is... ?

As referenced, though not really part of this current issue, don't ever bottom any tool in a keyless chuck. It will either damage the tool, the chuck, or mess up the grip/centering of the jaws.

Mcgyver
06-20-2012, 09:38 PM
I blame a lot of the often-referenced, older machining texts for the prevalent use of center drills in lieu of a spot drill for anything but drilling a true lathe center socket. They all seem to tell you to do it. I wonder why that is... ?
.

a low point in the progress of the species no doubt. Must be the same people who believe in alien abductions and ghosts :D

seriously though you are right on. based on what ends up in a guy's tool box, centre drill sales must have outnumbered spotting drills 100:1 ....and bet there's at least 100 holes spotted for every lathe centre hole drilled

JoeLee
06-20-2012, 10:59 PM
About the only way you could be off .250 is to have grabbed the bit with two jaws. I've done it before my self by being in a hurry and failing to close the chuck up to the approximate dia. of the bit.

JL.............

gcude
06-20-2012, 11:07 PM
I blame a lot of the often-referenced, older machining texts for the prevalent use of center drills in lieu of a spot drill for anything but drilling a true lathe center socket. They all seem to tell you to do it. I wonder why that is... ?

They probably never read a newer more enlightened article like the following about spot drills vs. center drills:

http://blog.cnccookbook.com/2012/05/15/when-to-use-a-spot-drill/

Paul Alciatore
06-21-2012, 11:04 PM
I blame a lot of the often-referenced, older machining texts for the prevalent use of center drills in lieu of a spot drill for anything but drilling a true lathe center socket. They all seem to tell you to do it. I wonder why that is... ?

<snip>.

I can offer some insight into why a center drill may be suggested instead of a spot drill. First, I am not referring to CNC work or even to work on a mill-drill or lathe where the work is precisely positioned for the start of the drilling. I am talking about holes that are drilled manually as in a good, old-fashioned, drill press; after being located with scribed lines and a center punch. So, please don't tell how what I am saying does not apply to CNC work or work in the mill-drill or other such machines.

Normally drilled holes have two, primary properties or specifications, diameter and location. Depth may or may not be a third one with many holes simply being through holes. When drilling a hole using manual means, the diameter is very closely determined by the drill's size so the one that the machinist is most concerned with is the location. It is my observation that most people, not just machinists, but people can locate a hole in a manner such that the error in that location is within a small fraction of the drill's diameter. Perhaps 20% or less. So a 0.125" hole (1/8") will probably be no more off center than 0.024" or so. This is just human nature. So a machinist will try to accurately locate the center punch and then he or she will try to accurately place the tip of the drill in that center punch. Now, two things happen here. First, a smaller drill will probably be located more accurately than a larger one and two, a smaller drill will have a smaller tip which is more likely to FIT INSIDE that center punch than a larger one would. Consider the width of the chisel point of a 1" drill. It will be 1/8" or larger wide and would completely span over any center punch mark I have ever made. All centering action would be completely lost in such a situation. So, a small drill makes a much more accurate start than a larger one would.

Once an accurate start has been made with a small drill, a larger diameter drill will follow that start because it is far easier for the chisel tip to follow a hole than for it to make one. And the two cutting edges of the drill will self center on that hole if it is big enough for them to come in contact with.

When I drill holes manually with punched marks to start them, I use a small diameter drill first and then a larger one to finish it. If the hole is large, a third drill can be used to enlarge the original hole to the size of the web of the final sized drill. Small drill for accurate location; followed by web sized drill; finally followed by full sized drill. In this manner I can locate small holes withing two or three thousandths and larger ones within five thousandths or less. An almost universal choice for the first drill in this sequence would be 1/16" or 3/32".

Now why a center drill instead of a spot drill? Well, spot drills are designed to do two things. First they are designed to accurately locate the hole through their rigidity. This rigidity is mostly due to their short length: you are drilling at a fraction of an inch from the support offered by the chuck jaws. But secondly, they are also designed to eliminate the extra step of de-burring or countersinking the final hole. Thus, they MUST be of a larger diameter than the final, hole sized drill to be used. If it is used to countersink then it is more than twice the diameter of the basic hole. I am not saying that you always use that large of a drill, I am just saying that they are designed that way. Have you ever tried to buy a spotting drill less than 3/16" in diameter? I have and they are not very common. I actually made a 1/16" spotting drill from a broken jobbers length drill. So the locational accuracy of these large diameter drills is going to be less than that of a smaller one. It will have a large web and a large chisel "point". It is more likely to start outside of the center punch mark than a smaller drill would. Actually a smaller (1/16") jobbers length drill which is quite flexible, is more likely to be centered in the punch mark and therefore produces a more accurately located starter hole. The small tip of a center drill is not as flexible as a jobbers drill, but it is smaller and it's tip will fit in the center punch mark. It will therefore be almost perfectly centered in that punch mark and the holes that follow it will also be well centered.

One thing I do when manually drilling with cross hairs and a punch mark is I take a light peck at first contact with the center drill or small diameter (spotting) drill. I then observe the location of the small divot in the metal and see if it is well centered on the cross hairs (scribed location lines). If not, a light sideways pressure while pecking a second time can often correct the location. Then, when I am satisfied with the location, I drill to a depth that is at least 150% of the diameter of the final, hole sized drill or of the second drill if three drills will be used.

So I do feel that a center drill will have a significant advantage over a spotting drill in many situations. I look at the spotting drill as more of an advantage in CNC and other situations when the machine will determine the hole location. And if you want to save a de-burring or countersinking step after drilling the full sized hole.

Arthur.Marks
06-22-2012, 01:29 AM
Paul, I like the argument you put forth. It makes a lot of sense. There are many ways to approach location with a drill press, and yours is practical. My technique is similar. If I have a location based on a prick punch from scribed lines, I chuck up a piece of tool steel which has a precise, 60-degree point turned on one end. I bring the drill press quill down until this point lines up initially by view. Then I carefully bring the quill down until the tool steel point positively aligns in the punch mark. While I do this, the work is free to float position. Once this is done, I clamp the work to the table. Then I follow with a spot drill; then my twist drill. What I read in your response is that your use of a center drill has similar advantages to my method: a short length tool, rigidity, and the comparative increase in accuracy of aligning smaller diameters. While a spotting drill has a superior cutting angle for a twist drill to follow accurately, its locating ability is limited in comparison to a center drill. I would tend to agree it is useful in this instance as long as the depth of the hole is limited with regard to the 60-deg. portion of the center drill. Too deep and the small, central locating pip created by the center drill is outweighed by too acute an angle for the twist drill to follow. -Arthur