Accurately Drilling Holes.



Can you accurately drill 5 holes in a row? I can't - at least not using a ruler and center punch. What is needed is an accurate method of repetition, which is possible with the INCRA-brand track system I use. The key is the sawtooth racks on the track system which position your work instantly and automatically in EXACT 1/32" steps with true machine shop precision without measuring. It's also micro adjustable for 1/1000" precision. And, it can be instantly set (or reset) to any position with machine shop accuracy and ZERO repeatability error.

If you want your own precision system, or an in-depth discussion on the track system, review my project on constructing a Precision Drill Press Table.

The easiest way to describe how the system works is to provide an example of a complex drilling job on a recent project I did.

This switch panel required 48 holes of different sizes drilled into a 1/2 thick piece of Corian, all of which were of a repetitive nature - which was a natural for the INCRA system. I think you can imagine how bad this project would have looked if the holes were not perfeftly aligned.

The first requirement is the work piece must be exactly square; with opposing edges perfectly parallel. The INCRA fence must then be aligned to the first hole. Once the exact location of the first hole is determined, the fence is adjusted forward or rearward so that the workpiece rests solidly on the fence. Then the Shop Stop is fitted to the precision tooth rack and tightned down. Finally the stop edge of the Shop Stop is positioned so that it touches the side edge of the work piece. At this point, hold the piece with pressure to the right and rear so that the work piece is secure on those two surfaces. This is also now a good time establish the zero reference, by moving the measuring tape on the top of the INCRA fence so that "0" is at the edge of the Shop Stop.

 

 

Setup the piece as shown above. As shown, the Track and Shop Stop teeth are meshed. Once the location of the first hole is double-checked, and checked again, the first hole may be drilled.

To drill the second hole, without disturbing the fence alignment or Shop Stop settings, loosen the Shop Stop and move it one inch to the right, using the ruler as a guide. There is a bit of technique here, but you can feel when the teeth re-mesh in the new position. When this is completed, tighten the Shop Stop down again. It will be exactly one inch from the prevous position. A reminder to blow or brush away any drill chips before each step as they can affect the accuracy if they become trapped between the workpiece and fence or stop. Next, hold the piece with pressure to the right and rear and drill the second hole.

Continue with the remainder of the holes for the row by moving the Shop Stop the prescribed distance and drilling the next hole.

When the first row is completed, rotate the workpiece 90° counter-clockwise as shown, then re-align both INCRA fence and Shop Stop to the first hole you drilled. You can take advantage of the micro adjustment capabilities of the Shop Stop here. Hopefully if you have a straight drill bit, you can get the drill centered exactly over the hole. This time, run the left side ruler to the zero mark on the Shop Stop.

Once you are satisfied the drill bit is aligned (you don't need to re-drill the first hole), move the piece 1" (or whatever is required) to the left, and lock down the Shop Stop as before. Drill the second hole, which will be the next column. Now its simply a matter of repetition. Continue by drilling the remainder of the columns, then flip the piece back 90° clockwise, re-align the drill bit to the second column, then drill the second role... and so on.

If you are careful and have some patience, you will be able to accurately drill the required pattern. Remember to blow the chips out after each hole drilled, and take your time. In this example, many of the holes will be larger, but its easier to drill smaller pilot holes first, then go back and enlarge the holes to the proper size. When you do this, you can use the pilot hole for the alignment, and you will not need to rely on the INCRA track system.

Another advantage of using small diameter pilot holes is for counterboring operations as shown here. This is the backside of the switch panel, and unfortunately the toggle switches came up a bit short when mounting through the 1/2" material. So the solution was to counterbore the switch positions from the back with a Forstner bit. You can usually center a forstner bit on a 1/8" dia pilot hole, but if you drill the hole to size first, this is almost impossible.

It should also be noted that I rounded the corners of the workpiece to be asthetically pleasing. This should only be done AFTER the drilling process as the rounded corners may affect the accuracy of the Shop Stop.

 


Reader Comments

Home            Return