Drill centering jigs are certainly nothing new. However, finding one off the shelf for an odd size drill bit can be quite a challenge. We needed one specifically for a large metric drill bit that had to be dead straight and dead center for our return air filter grille frames. It had to be substantial enough to endure drilling 25 – 50 holes per day and we needed to be able to see the point of the bit enter the wood due to where the markings are located on the material. The one thing we had going for us was that it would almost always be used in conjunction with a drill press. Additionally, we had to be able to account for slight variances in the thickness of the material since the holes were drilled prior to the finish milling stage. This is what rendered our previous jigs and stops ineffective at maintaining the level of accuracy we needed.
The design we settled on was simple to build and has worked exceptionally well. Since the entire jig is only 7” long, we use nothing but scraps that were lying around so you could certainly use different materials or sizes based on your needs or what you have available. We needed to drill 14mm holes 22mm deep into ¾” frame stock.
The key to the jig was the top piece that serves as the drill guide itself. I used a 3/8” thick x ¾” piece of aluminum bar stock cut to 7”. I used a press mill, but a drill press vice or a simple stop held down with a C-clamp would due. The precise center was determined by placing the tip of the bit on the metal, spinning it by hand just enough to make a mark, then rotating the bar stock 180° and making another mark with the tip of the bit until they matched exactly. (Fig. 1) Once the 14mm hole was cut, I used a countersink bit to flair the hole so it would be easier to insert the bit when the jig went to work.
The process was repeated for the ¼” holes placed 1” from either end of the aluminum bar stock for the pivot bolts. (Fig. 2) I repeated the process again for the 2 clamping members made from 3/4” square aluminum box channel using the top drill guide bar stock as the template for the hole spacing. (Fig 3) Using the same method, a center hole was cut along with 2 outer holes 3/8” from either end of 2 pieces of ½” square box channel which was cut to a length of 2 ¾”. (Fig 4)
Now that all the components were ready, it was time to modify the hardware and assemble the jig. (Fig. 5) I could have tapped the ½” box channel, but I wasn’t confident that it would be strong enough for long term repeated use. Therefore, the 2 opposite surfaces of a pair of hex nuts were filed down to fit in the box channel. (Figs. 6 & 7) Placing washers between all of the pivot points, a pair of ¾” long ¼” hex bolts were used to connect the top drill guide to the center hole in the ½” steel pivot sections with the hex nuts previously inserted. Four 2” long ¼” hex bolts were used to connect the clamping members to the pivot sections, again using washers at the pivot points. Two ¼” hex nuts torqued against each other on each bold secure the apparatus together allowing it to pivot without becoming loose. (Fig. 8) Nylon insert lock nuts would work just as well or better, but again, I was using what we happened to have around.
Finally, a piece of ½” x 1/8” steel bar stock was bent around a 5/8” bolt to create a finger hook to easily pull the jig tight to the work piece. (Fig. 9) It was secured with some self –tapping screws.
The jig has held up well with several hundred holes drilled so far. It has produced a notable quality improvement due to the jig compensating for variances in the thickness of the wood. (Fig. 10) The jigs production speed is equal or better than other jigs we have used, particularly when you factor in making adjustments for the inaccuracy of the former methods.
Rod Gunter is General Manager at Gunter Building Solutions and has over 20 years of experience in the homebuilding and cabinetry industries. Rod has been responsible for building over 200 homes above the $500,000 price point. Rod has trained large groups including all the major home centers on selling skills, construction techniques and sustainable natural wood products. Rod resides with his family in Holly Springs, North Carolina. Gunter Building Solutions owns WoodAirGrille.com, a leading manufacturer of wood return air filter grilles and wood return air vents.