Drilling holes Correcting mistakes in hole locations

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The right method is an endmill in a milling machine. Bet you ain't got that.

Drill a 1/4" hole in a fairly thick piece of scrap stock. Clamp it to the piece you want an offest hole in. Use the scrap stock as a drill bushing guide to hold the drill on the new center. Feed slow this is hard on drill bits.

Karl

"Fred" wrote in news:8O2dneyn38vL0M snipped-for-privacy@comcast.com:

A rattail file and a vice.

A bridgeport and a small 1/4 inch end mill.

Either that or you need some of those bolts with the built-in offset. :^)

If you are really, really desperate and need to do this with a drill press, you can take another small piece of steel plate, and drill a quarter inch hole somewhere in it. Then clamp that existing plate and over where you want your correct hole location to be in your workpiece. Thus forming a crude drill jig.

Drill down through the jig and *slowly* nibble into the side of the 'bad location' hole. The upper plate will take the side load.

To prevent the problem from happening again, centerpunch your hole locations in the original plate. Then pick up the punch marks with a pilot drill and start each one.

Now's the time to go and inspect to see that the started hole is DNO the cross hairs of your marks. If not, it's a lot easier to 'drift' the hole at this point. Only when your're satisfied do you drill up to the finish size.

Jim

You don't say how much you missed by. A tapered rotary file can probably fix your problem. A good sharp drill bit in the drill press will deflect, but will usually let you gain a little.

Typical disclaimer: You know you're not supposed to side load the drill press chuck, it is not a mill. Some of us who do not own mills have been known to do so.

(top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

They are expensive but a small carbide burr on the Dremel will last for many holes. We often do this for holes punched in plate slightly off location. The burr we use has a 1/4 shank and half inch diameter body. Randy

All replies suggested methods of moving the hole over to the proper location. Of them, the drill jig was best. However, the OP stated he had already drilled the hole through in the wrong location. So, any attempts to "move" the hole over, even slightly, will enlarge the hole. That may or may not be critical to the finished product.

A method that works well is this: Drill out the mislocated hole to the next size machine screw tap drill diameter. Drill the tap drill hole for a tightly fitted machine screw, say 75% threads or so. Run a bolt in the hole and cut it off on both sides so that it stands "a fraction" proud of the hole. Using an anvil and ball peen hammer, upset the bolt on both sides such that it expands and locks itself well into the threads in the hole. Now, go back and accurately lay out the center pop mark for redrilling the hole in the right location. You don't want to repeat this procedure, do you?

Bob Swinney

"Robert Swinney" wrote: (clip) cut it off on both sides so that it stands "a fraction" proud of the hole. Using an anvil and ball peen hammer, upset the bolt on both sides such that it expands and locks itself well into the threads in the hole. (clip) ^^^^^^^^^^^^^^^^^^^ I've never actually done this*, but it seems to me that it would be helpful to countersink both sides also--this would give the excess metal room to expand and form a "head" on each end. ____________________

• "Cause I never make mistrakes.

This sounds like the approach I'd take if I didn't have a mill. Just be sure the screw is mild steel and not stainless.

I've watched a real machinist handle this problem in AL tooling plate. He bored a much larger hole, perhaps 3/4" on the center of the correct hole, but large enough to completely cover the area of the wrong hole. He then made a plug of the same material a couple thou over and pressed it in the big hole. Then he drilled and tapped the correct hole in the center of the plug.

As close to a perfect fix that you could get.

I second that -- it's slow, but it's much more controlled.

Next time verify the correct hole location as you drill. You should be able to get to within 10 thou on a drillpress if you take your time marking and center punching. You can even get a light centerpunch off center and ease it over by careful double-punching or angled punching. This is a skill I'm only now developing, after years of making slots to correct poorly drilled holes.

If I have already finished drilling the hole, I either use a round file or decide I really could use holes that are one size larger. Sometimes I do both. Use a round file and then drill with the next large size drill.

To avoid getting the holes in the wrong place: First center punch where you want the hole. If you are a little off slant the center punch and punch some more to move the depression to the right spot.

Next start to drill the hole with a small drill the thickness of the web of the drill for the right size. If that is off, use the file and drill with a somewhat bigger drill untill you get the hole centered.

If you are making the holes to mount something, try using a transfer punch to get the locations right.

For thicker material there are a few more things you can do.

Dan

When you are drilling holes that you intend to match other holes, one of the best things you can do to help yourself is not use a center punch. Even with a drill press, if you clamp your work and use a wiggler to locate the cross hairs from your carefully scribed locations, you should be able to work to less than .005" consistently, avoiding those flyers.

For what it's worth, and many will choose to argue------a center punch has no place in the tool box of one that is considered a precision machinist-----not unless they work with hand tools. There are other methods that insure proper location and reduce unacceptable results-----although at the cost of speed. Still, applying such methods are faster than doing a project twice----or more.

I'm sure it comes as no surprise to any of us when mention is made of the fact that drills are circular ground and relieved to minimize the amount of metal in contact with the hole. The circular grind acts as a guide in the hole, but lacking proper relief for side cutting, they are not well suited for such cuts.

Harold

When I just have to move a hole a 'lil bit I grab the nearest size "Saw Drill" from this set of three I bought from Harbor Freight:

Search for 42804 at:

They say they're for softer metals only, but I've used 'em more than once on mild steel and they still seem to be ok.

You just have to remember to "push" the work against them about 90 degrees from the direction you want to move the hole.

Before someone jumps me to mention "hand grenading" drill press chucks, my 40+ year old Craftsman floor model's chuck is held on the spindle with a threaded collar, and the bearings still feel good after all the sideways hand loading I've given them so far. Sears made power tools "right" back then, so there!

Jeff

If what you have in the way of tools is Dremel-ish, try a carbide burr in the smallest size you can lay your hands upon; no bigger than 1/8". Your grinding stone was probably too large relative to the hole, resulting in far too much contact area around its diameter --> CRUNCH!

With the small burr, you might try a piece of steel scrap (perhaps even sheet metal) with a 1/4" hole in it above and aligned with where you want the hole to be. This will help you keep the @#$#$^)(&*()!@ burr where you want it.

Leo sez: ". . . I've never actually done this*, but it seems to me that it would be helpful

Countersinking would drill away metal in the center that could be better expanded to the outside. IMO, it is better to begin striking the center area(s) first with the ball peen, thus forcing that metal to the edges.

Bob Swinney

uh Bob,

I think that Leo was referring to the hole what was to be filled, not the plug material. In fact it would be a good idea, but too often the material is so thin anyway that countersinking would be difficult to do without opening the hole beyond all help.

As for drilling the plug material, it does make it easier to expand but weakens the plug for exactly the reason you state.

George Vigneron

That's my machine shop. :)

Jon

Bob Swinney

I had a need to 'move' by about 3/16" a few dozen 9/16" holes through 4-inch structural steel channel (about 1/4" thick). I made a jig of oak that wedged tightly in the channel using woodworking clamps and fitted it with a couple of standard, hardened drill bushings from MSC (next day delivery). Using a little lubricating oil, it was no problem at all to cut out those segments using a 12-inch benchtop drill press. The holes, of course, were left oversize but that was not a problem for the application in question.

The drill bushings protect the spindle bearings from excessive side loads, assuming the work is rigidly clamped. Their extreme hardness minimized wear on the drill and friction and galling that might occur with softer bushing material.

David Merrill