PDA

View Full Version : Locating & accurately drilling holes



berol
09-04-2010, 11:39 AM
What sequence is best to locate and drill a cross scribed mark for a hole? I don't have a DRO or an edge finder (1) Punch then use a center drill (2) Spotting drill (3) Brad point 135 degree drill bit (4) any other recommended options

danlb
09-04-2010, 12:59 PM
I use a wiggler for that when I need to.

Scribe, punch, wiggler, spotting drill, drill.

Dan

Lodsb
09-04-2010, 01:30 PM
4. Forgo the center punch and try a $15 "wiggler" followed by a center or spotting drill. These contraptions come with several points, one of them being a needle point that you steady and then line up to the scribed marks (spindle running, point not contacting the work). Another is offset for a test indicator to center on an existing hole or pin.

One other point is a ball end that is used like an edge finder. Touch the ball with something (anything) as it flies around until it steadies and then soot it up with a flame (match, candle). Approach the edge of your workpiece until a bright line appears on the ball, stop the spindle, swing the ball away and then move the work 1/2 the ball diameter (usually .125") and there's your edge. Not too bad for $15. You can buy a good one for $50.

4.1 I don't see why a guy couldn't chuck up a piece of brazing rod, turn the spindle on, file to a point, and with the spindle on watch it navigate around your punch mark.. Along these lines, drill one size under and make a poor-man's reamer by carefully rounding the outer tips of a properly sized drill.

danlb
09-04-2010, 02:00 PM
Thin brazing rod will work, but you generally need to keep it short enough to work without moving the head (assuming a drill press). Too short and it will not flex as it finds the crossed scribe lines.

Someone will bring up the point that drill presses, drill chucks and drills are nut usually considered "accurate". A run of the mill drill chuck will have several thousandths in run-out. Uneven flutes will cause a drill to cut unevenly, etc.

Dan

Carld
09-04-2010, 02:48 PM
berol, since you say you don't have a DRO I will assume your using a mill of some type. Use cross scribed lines to mark the spot you want the hole then use a wiggler to center on the crossed lines. Lock the table and switch a stub drill or center drill or spotting drill to make a starting hole and finish to required size.

Using a center punch mark to align on is not very accurate.

You could also use an edge finder to locate to sides and set the handwheels to "0" and move the table the required distance to locate the hole and drill as described above.

MuellerNick
09-04-2010, 02:54 PM
Scribe, center punch, drill (POS drill).
Correct, bore bigger, correct again, bore even bigger. This way, you can get well below 1/10 mm accuracy.

When you lower the drill into the center punch's hole, look close. You can see how it bends into the hole. Look from two sides and correct so that the drill is not bent.


Nick

rohart
09-04-2010, 03:27 PM
MuellerNick's way, when working on a mill or a drill press. But it's important to make sure the punch hole is a good one.

Mark roughly (meaning gently but approximately) with a fine punch. Use a magnifying glass and a rule to adjust the point, still with the fine punch.

When you're close, use a heavier punch, moving the hole if necessary by punching at an angle.

When you've got the punch mark dead on, file the top of the messy punch crater away and check again. When you're happy you have a clean strong punch mark in the right place, go for it with a small (1/8th) drill.

Just kiss it to start the drill at first. Then, lower and raise the drill several times looking for the drill bending as it seats itself in the hole. Keep adjusting the work till the drill hits the hole straight and doesn't bend.

If you're going to get heavy - 1/2" or up, anchor the work.

QSIMDO
09-04-2010, 04:10 PM
Does anyone use those centering scopes that fit in the spindle?
They look interesting but the prices have always put me off.

http://www.use-enco.com/ProductImages/0653933-11.jpg

berol
09-04-2010, 04:47 PM
Scribe, center punch, drill (POS drill).
Correct, bore bigger, correct again, bore even bigger. This way, you can get well below 1/10 mm accuracy.

When you lower the drill into the center punch's hole, look close. You can see how it bends into the hole. Look from two sides and correct so that the drill is not bent.


Nick
Do these brad point bits locate accuratly onto cross scribed lines or are you better off with a spotting drillor center drill and a conventional 118 degree drill bit. Thanks, Berol

Paul Alciatore
09-04-2010, 06:00 PM
Up to now, I have worked a lot without DROs. Actually, I am installing some today.

When working in the mill I try to scribe the locations of the holes first, but I do not punch. I locate the part with an edge finder and then zero the dials. From there on, I just go to the locations of each hole, always keeping the motion in the same direction as when found the edges and set the zeros to prevent backlash. A spotting drill is best to start a hole, but I will use a small center drill if the hole is small (under 1/8" or so). Then I go to full size, preferably with a screw machine length drill. Holes located this way will not always be spot on the cross hairs formed by the scribed lines. I have trusted the dial readings and so far all my parts have been OK. This is one good reason why I do not punch the locations. This method is usually good for +/- 0.001" or better. This would be worse if the lead screws are badly worn in an uneven manner.

When I am making the drawings, I imagine the machining process and try to use dimensions that are located by two sides. If possible these two will be at the upper left as the part will be located on the milling table. This helps with using the dials as you are then turning CW to get to the hole locations. If I am using someone else's drawing I may take a few minutes to re-dimension it this way.

Many times the part I am making has only a few holes and they are not that critical. Perhaps +/- 0.003" or even worse will be perfectly OK. Here I can scribe, use a magnifier to punch lightly, check with a 10X magnifier or better, correct as needed, then punch deeper. If I am going to use the punch mark for centering the drill, I figure that the web thickness of the drill determines the maximum error that you will have. The web of your first drill needs to be smaller than the diameter of the punch mark or it can wander. Again spotting drills are great for larger holes, but for smaller ones it will be difficult to find a spotting drill that has a small enough web. I have made a 1/16" spotting drill from a broken 1/16" jobber's drill for this kind of work, but even this has a larger web than a small center drill.

I mentioned magnifiers. I keep an assortment of them in the shop, some in my pockets at all times. My favorite is a 10X Hastings triplet. This is an excellent, color corrected, low distortion lens that has been described as the king of magnifiers. You can get these in a brass, tear drop shaped holder with a key ring hole. I carry the 10X and a 20X at all times. I have 2X, 5X, 10X, a couple of magnifying visors, and a low power, zoom microscope (10X to 30X) with a graticule in the shop. Each of these has it's uses and I consider them essential for accurate shop work.

oldtiffie
09-04-2010, 07:24 PM
The title of the OP is: "Locating & accurately drilling holes".

The text is:

What sequence is best to locate and drill a cross scribed mark for a hole? I don't have a DRO or an edge finder (1) Punch then use a center drill (2) Spotting drill (3) Brad point 135 degree drill bit (4) any other recommended options

As the title "Locating & accurately drilling holes" addresses both "location" and "accuracy", I presume he means both the location of the job with respect to the intersection of the "cross scribed" lines as well as drill size accuracy.

I notice a lot of posts here have part of the question/problem in the title and the rest in the body of the text which seems to cause some to only address the matter in text - as seems to be the case here.

MuellerNick
09-05-2010, 05:25 AM
Do these brad point bits locate accuratly onto cross scribed lines or are you better off with a spotting drillor center drill and a conventional 118 degree drill bit.

Things are made a bit different here and there.
Here (Germany) we use a sharp center punch and only one kind of. It has a 60 cone. If it is sharp, you can feel when you are on the scribed line. A light tab with the hammer and then have a close look how much you are off. Correct if necessary and a "normal" hit with the hammer. No filing or whatever. Then you start with a say 2mm drill. No special drill, no special tip.
Check for proper location.
To correct, you need a small needle file. If you are off say by 0.1 mm in direction X, file the hole oval to be 0.2 mm wider (2 times the error) in exactly that direction. Drill with a bigger drill.
You need a special caliper to measure. One with very acute tips to reach into the hole. Looks like one of these (http://www.messmittelonline.de/images/big/werkstattmessschieber_digital.jpg).


Nick

oldtiffie
09-05-2010, 06:55 AM
I agree with Nick generally except that I've always used two punches if and as required.

The first is a HSS 60* cone - called a "prick punch" - same as Nick's - and a ~100*+ point called a centre-punch. Most times I use a 90* punch but if I am "fussy" I will use the prick punch as Nick says to.

If I am "off" I use a centre or prick punch tilted toward centre and just on the edge of the "off" pricked "dimple" or the started hole and tap the punch which will cause a burr which will "draw" the drill. Traditionally on larger "draws" a diamond-ended or half-round chisel was used.

Here is a "wiggler" "point" in pieces:
http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Centring6.jpg

and here it is picking up a curved line on a centre-punched job:
http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Centring5.jpg

Rich Carlstedt
09-05-2010, 06:13 PM
Some good thoughts put forth above

The question first is:
Where do you want to drill holes, in a mill or a drill press ?

Usually in a drill press, the work is not clamped, therefore all layout holes should be centerpunched to assist the drill in finding the location.
For a milling machine, it is a totally different story.

Here is a method I use that does not use edge finders or wigglers.
I have both, but they make the setups needlessly long
I shot some pics in the shop for you to follow

This is all you need, Your square, a few spotting/ starting drills , and a piece of modeling clay ( Newbies, notice how short and sturdy the spotting drills are !)
http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20tales/P9050024.jpg


Now your square has a nice scriber built right into it.
Pick it up and place it in the center of the clay ball.
( If your clay is hard, ypou need to warm it in your hands. For old clay, mix in some Kerosene or Mineral spirits)
http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20tales/P9050025.jpg


Wrap the ball around your drill bit and roughly center the scribe....It does not have to be accurate, in fact, I put mine in at an angle !
http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20tales/P9050026.jpg



Start up the spindle. you will note the tip of the scribe is nowhere near straight. Now with your finger, gently nudge the scribe to the center point where you see no runout. PAY attention to the tip ONLY. It does not matter if the rest of the scribe is angled. The tip needs to be at the center of rotation
http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20tales/P9050028.jpg


To be continued

Rich Carlstedt
09-05-2010, 06:15 PM
now move the table until you are inline with the witness marks or spot.
You can see in the photo, that by having the scribe offcenter in the clay ball, the spinning scribe becomes invisible BUT the point is very visible for allignment ( no distraction from the stem)
http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20tales/P9050030.jpg


And finally you start your drill
http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20tales/P9050031.jpg

You will find this works extremely fast. Having soft clay is important as it allows considerable movement of the clay without dislodging the scribe.
As you try this, you will get better..

As with any shop equipment, wear good safety glasses

What you have here is double duty of a scribe
It is both for scoring AND finding center
Have fun
Rich