Seeking tips to drilling an absolutely dead-center hole w/drill press

Have you tried using brad point or forstner bits? You could also chuck a centering bit to line up and clamp your workpiece.

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Without a spotting pip, you'll never, never get your hole dead center that way. A drill press will be too loose for it and the drill will always skate. Some of the guys will recommend using a spotting drill to start with. You can get within a couple of thousandths using one of the optical center punches where you line up the mark in the crosshairs and then substitute the marking punch. That would probably be the best method for what you've described, if it's a one-off. Using stub drills will help, too. Get name brands, cheapy chink ones will do you absolutely no good at all.

There's other methods, but if all you've got on hand is a drill press, suggesting use of a vertical mill is kind of useless. Guy Lautard details a poor-man's jig borer for drill press use in one of his later Bedside Reader series but you aren't going to make that up with just a drill press on hand, either.

Stan

Get a center finder- used to use them in machining all the time-- simply a 1/4" rod with a 30 degree cone machined on one end. Helps to center punch the center of the hole on the workpiece first, as the indentation will provide an easy physical reference for the end of the finder. Chuck it in the drill press Find the center of your drill hole- you may want to lock the quill at this point Clamp the work to the table-- unlock the quill Change out the center finder with the bit you will use Drill

The usual way is to use a centerpunch. Most of the time I use an automatic centerpunch to start, then deepen it with a "manual" centerpunch and hammer. Auto-centerpunches are available at most any hardware outlet, less than $10 USD.

Ken Grunke

First tip: use an awl or center punch (depending on whether it's wood or metal you're drilling) to mark the precise location of the hole first. Even with a brad point bit, it's difficult to prevent drills from wandering off the target when they enter the material. The smaller the gauge of the bit, the worse the problem is.

Second tip: depending on the nature of the work involved, you may be able to use a cross-slide vise for fine positioning of the work relative to the bit. They only work on stock that can fit inside the jaws, but they are quite useful to have when precision matters.

Something like this:

Now, whether you have one of those handy gizmos or not, position the work (with the hole locations pre-punched), then pull down the quill with the motor off. Listen for a plinking sound, and watch with hawk eyes for the slightest bit deflection. If the bit is deflecting to enter the dimple, your hole won't come out right.

I find it helpful to rotate the chuck by hand to position the flutes or other cutting edges in a way that allows a clear view of the very tip of the point in relation to the dimple. Repeat the process of making fine adjustments to the X and Y axes and then checking with the quill until the bit enters straight and true, then drill the hole.

This process is tedious and time consuming, but if there's a better way to ensure a hole as close to perfectly placed as possible with a drill press, I haven't discovered it.

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Turn a sharp point on a bit of thin bar in the lathe and use that in your drill chuck to centre on your graph paper. Ideally make it with a collet chuck or 4 jaw chuck to get it dead concentric. Then use a centre drill to start the hole before drilling right through.

Your pointy bar will also come in handy for setting tool heights exactly on centre on the lathe. I have a couple of them in various sizes made out of old engine valve stems and bits of ground silver steel.

First of all, forget "absolutely dead center" -- that term is incompatible with a drill press. A drill press is a tool for rapidly putting holes within a reasonable tolerance of where you want them. That being said, this problem breaks down as:

1) making the hole start directly under the spindle axis (i.e. preventing drill bit wander) which is done by centerpunching and also by using very rigid drill bits known as "center drills" which you can get at 2) putting your centerpunch mark exactly where you want it which is easy to do within ten thousandths but very hard to do closer than two thousandths. This is done for high precision by the use of an optical center punch.

Holes that have to be very precisely located aren't drilled, they are bored. The machine that does this is a jig borer.

Most woodworking tolerances are on the order of .010" so you can probably get away with learning to do layout and centerpunching. Once you have a centerpunched mark, then it's also tricky to get it lined up exactly under the machine's axis.

All of this supposes that your drill press table is at precisely right angle to the spindle axis, and that your drill chuck has zero runout, neither of which is likely true, especially if you're using something you bought at Home Depot.

GWE

Doc wrote:

Switch to a brad-point? And stick the center point where you need it?

I use both center drills as well as punch, depending on whichever is easier. Works out okay.

i

You got to drill a center punched mark with a very small drill. Then drill the hole larger with the next size or two up. Recheck the locantion and if it is off, hit the top edge of the hole with a punch on the side of the hole you want the hole to move to.

You could also drill the hole a 32th under size and then go through it with the proper size end mill if your drillpress quill is stiff enough, or drill another block with the finishe size and clamp that block in place and use that to hold the endmill on center useing it as a guide bushing.

John

The problem is not so much your alignment, as the fact that unless the end of the drill is perfectly symetrical and equally sharp on both cutting edges, it has a tendency to wander off.

You don't say how big the hole is. If it's small, a full length drill is very hard to control because there's so much flex in the shaft. Instead use a center drill like these to start the hole:

If the hole is larger than 1/4 inch, use a spotting drill like one of these: stocky drills like that don't wander around when their cutting tips meet the work.

"Doc" wrote in message news:1ajDd.2352$% snipped-for-privacy@newsread2.news.atl.earthlink.net... | Looking for any tips/tricks for drilling a hole w/a drill press that's as | close to dead-center to a specified point as possible. | | Here's what I've been doing - I have the position marked with graph paper | that's taped to the workpiece. With the help of a magnifying glass, I | painstakingly move the piece until the tip of the bit is aligned with the | conjoining lines. By aligning with the tip I mean I view the tip both from | the narrow or "pointy" persepective within the channel of the bit and then | turn it 90 deg and look at the the wider perspective, and view it from the | side and front to make sure I have it aligned with both the X and Y axis. | When I finally get it so the tip is as centered as I can make it whichever | way the bit is turned and in relation to both axis, I clamp the piece to the | plate of the drill press and drill the hole. However, on examination, the | hole comes out obviously not dead center in relation to the graph paper | lines. | | I've also tried aliging it with the drill running, going visually by where | the "point" appears to be when the bit is spinning. I get somewhat better | results this way but wonder if there's a more precise and dependable way of | achieving a centered hole. | | Thanks for any input.

Finding one of the optical center punches is the best way to locate the center punch hole. After that, find the smallest drill bit your press will handle and drill the hole with that, or at least a quarter of an inch or so. The next thing is hardware you have to go look for. Double margin drill bits. You work your way up using the previous hole size as the first margin, or pilot bit. Not sure where to some, industrial supply, ebay, aviation supply, or similar places. I've also used what we call "core drills" which are special drill bits made by turning down the first quarter of an inch or so of the drill bit to the pilot hole you're working with, but obviously not too small. You still have to sharpen the remaining edge of the bit. In doing this, I've started with a center punch mark and worked my way up to a 0.3125" +/- .002" which is even harder without the right tools. By the way, double margin drill bits are awesome for drilling stainless! I bought a bunch at Boeing surplus near Seattle and absolutely love using them.

My ears are burning....

"Absolute" DOES NOT work in machining. There is _always_ a tolerance. Sorry for being obnoxious but when you start to get paid to do this work, tolerances are not a factor - they are life.

What is your application? Do you need your hole to be straight as well?

Others have given good advice. Do you have a combination square with a "center head"? These are specifically used to draw a line on the flat face of a cylinder which intersects the center of that cylinder (the line is a "diameter"). Drawing two such lines (three may be better if your stock is uneven about its diameter) will give you the center of your part.

Simply center punch (you may want to use a prick punch first), center-drill, pilot drill (if final diameter exceeds roughly 1/4"), drill, then ream if necessary.

While this will give you the location of the *top* of your hole, anything below the surface is a crap shoot and is severely dependant upon your knowledge and skill of setting up your part correctly, using appropriate tools and using good technique for drilling.

HTH.

Regards,

Robin

I was surprised at the number of replies I got in such a short time. It occurred to me that I never said that I'm drilling into wood. I included the metalworking forum to see if there overlapping skills. I suppose I could clamp a piece of sheet metal over the spot and drill through it if that would help.

Let me amend that, plexi that's been glued over wood.

Easy to make these. Next time you are in a machine shop supply get some metal dowel pins. (They are cheap, a good hardware store might have them also.) Chuck them up in your hand drill and spin them when you grind the point, being sure to have a little cup of water to cool the point as you are grinding.

The op didn't say what material he was trying to drill but in some instances you can get close to the center punched point and let the work float into position under the spinning drill bit. If he is drilling wood, a brad point is in order.

Another way would be to position a piece of Plexiglas that has a guide bushing centered on a set of cross hairs. Then you can extend the reference lines on the graph paper and the center will then be right over the target.

First off you cannot drill anything with the degree of precision you mention in your topic - namely "absolutely." Don't even bother trying to do that. Instead take the time to think about the tolerance for the positional accuracy of the hole, based on how it is supposed to function. Then put a *number* on that tolerance. In other words, "the center of the hole has to be located within 1/64 of an inch."

Or, "the center needs to be true +/- 0.001 inch."

That sort of thing.

You should be aware that one can put a very accurate hole in place this way, and get it within five thousanths or so:

Scribe the position using layout dye and the appropriate measuring tools.

Use a sharp scriber to indent the workpiece at the intersection of the two lines. A magnifier helps here.

Pick up the indent with a center punch, and punch it.

*Inspect* the newly formed center punch with the magnifier. It will not be at the exact center of the crossed lines.

Drift the center so it *is* at the center to the best of your optics.

Place the workpiece in a drill press and use a small drill to start the hole. 1/16 or so is about right for most cases. The drill will _PICK_UP_ the center even if the spindle of the machine is not perfectly aligned with the centerpunch. It does not need to be.

Drill through with the small drill. (I do NOT use a center drill or rigid spotting drill for the technique. I *want* the smaller drill to be somewhat flexible so it picks up the center on its own)

Drill up with the correct final size, and the larger drill will follow the smaller hole.

Basically you cannot count on drilled holes to be round to better than a few thou. So by the same token don't try to spot them better than than that: +/- 0.003 or so.

Any design requiring sub-thousandth precision on drilled holes is doomed from the outset. If this is the case, change the design _now_.

Jim

The procedure Jim Rozen describes appeals to me because it uses the kind of shop tools I have, rather than special drills, laser guided center punch, and so on. Here's another technique I have found to work for me, but I don't pretend it will produce "absolute" accuracy.

I scribe two lines at right angles through the center I want, and center punch at that location. I then start drilling to a size smaller than the finished hole size. Chances are the hole will start a little off-center, for the reasons cited by others, earlier. I chuck a drill bit in a hand drill, and drill at an angle until the pit I am making looks visually centered on the scribe lines, and then continue with the drill press. I can't put a number on it, but your eye is pretty good at judging the centering of a small round dimple.

A great tool for dead-centering is available from Micro-Mark. It is a laser guide which is gripped in the chuck and projects a red dot onto the workpiece:

Of course, you will still need to centerpunch and/or use a center drill as outlined in the other responses. The laser guide just assures that the drill is aimed EXACTLY where it should be!