Newsletter Article - Designing and Building Jigs
Designing and Building Jigs
Building jigs and inventing devices are almost one in the same. To make simple, accurate, and time saving jigs there is a process to follow; here is how I do it.
1. Dale Nish’s Wood Hinge. I am going to walk through how I invented my Wood-hinge Drill Jig that solved the problem of drilling a centered 1/16" hole in the end of a 1/4" dowel. First, a bit of the back story, I was introduced to the wood-hinge back in 1983 by Dr. Dale Nish at Brigham Young University (BYU).
I was taking a crafts class the first time I saw this hinge and I was gobsmacked! It was, and I still think it is, the coolest way to hinge a box. Since 1983 I have made hundreds, if not thousands of these boxes and obviously I solved the main challenge in making the hinge; drilling a dowel precisely on center.
For this hinge to work properly you must drill a 1/16" hole, 3/16" deep, in the center of several segments of a 1/4" wood dowel. The smooth opening and closing of the hinge are dependent on drilling the dowel segments perfectly on center. This is the critical concern in making the hinge. Other concerns such as matching the grain of the wood dowel to that of the box are all secondary to drilling on center.
If you have never tried to drill a centered hole in the end of a dowel, let me tell you it’s a difficult task. My first instinct was to hold the dowel steady and drill it with a drill press – a terrible idea. It’s almost impossible to hold the dowel stable enough for such a precise task. I tried other methods with equally miserable results. Obviously, this task required some type of jig that could achieve the precision required.
2. The Jig Challenges. My first step in making this or any jig is to clearly understand the task and the problems, so I can envision a jig that will solve the problems. I made a list of the challenges I encountered in attempting to drill the precise center of a dowel, here they are;
- 1/16" drill bits are very flexible due to their size and the stresses on a bit as it cuts.
- Drilling into the end-grain of any wood is problematic since the spring wood (fast growth) and the summer wood (slow growth) in most trees have different densities due to growth rates; drills tend to follow the path of least resistance flowing with the softer wood.
- The dowel must be held parallel, stable, and centered with the drill bit.
- This wood-hinge works by several pieces of dowel pivoting around a 1/16" by ¼” metal rod that fits into the end of each segment of dowel approximately 1/8". Once all the dowel segments are assembled (odd number works best) the dowel segments are glued alternately to the lid and the body of the box. If the holes for the metal rod are not drilled precisely on center, raising the lid will break the hinge.
There are three tools I could use to turn a drill bit: a hand drill (eggbeater type), a cordless drill, or a drill press. Of the three, the drill press is the most accurate. In operation, the drill press’ quill extends and retracts while the drill bit is spinning keeping the drill bit in the same vertical plane throughout the process. Neither a hand or cordless drill could achieve this level of precision, so I decided to make a jig that works with a drill press.
4. My First Attempt at Making the Jig. To solve the problem of a thin drill bit flexing in use, I keep as much of the drill bit in the drill chuck as possible with just enough exposed to drill the required 3/16 “ deep hole in the dowel pieces.
The next task was to figure out how to hold the ¼” dowel in a fixed position, in the same vertical plane as the drill bit and positioned so the drill bit will engage the exact center of the dowel. From Dale Nish, I got the idea to clamp a piece of wood to the drill press table. I then drilled a ¼ “ hole in the wood to hold a dowel segment, I then change the ¼” bit to a 1/16” bit and both dowel and drill bit would be aligned for a perfect center hole.
This idea worked but it was clumsy. The main problem was the inconsistency of the dowel thickness. Often the dowel would be too tight in the wood block and I had to use pliers to remove it. This left scarring on the dowel. Other times the dowel was too loose in the hole and it would either spin instead of getting drilled or it would not line up on center.
Another issue I kept running into was dealing with soft and hard grain in the wood. Maple, Birch, Cherry and Mahogany have an even consistency of spring and summer wood, so the drill bit tends to stay on its intended path. Oak, Walnut, Ash, and Hickory have inconsistent spring and summer growth rings and the drill bit will wander if it happens to cross the rings. I avoid this problem by sticking with Maple, Birch, Cherry, and Mahogany species whenever possible.
This “hole-in-a -piece-of-wood” jig solution worked most of the time, but it was slow and there is a small but definite failure rate. Since I also wanted a wood-hinge that matches the grain of the box and therefore becomes almost “invisible”, one poorly drilled hole means scrapping the hinge and starting over. This method was not the solution I wanted for fast, consistent, and accurate dowel drilling so I had to go back to the drawing board. Not a failure but I had just discovered one way I did not want to drill the dowels. I wanted a way that would be faster than having to change bits and set up a drill press so time to take stock, carry forward what was good about the first attempt and leave behind what wasn't good. Round 2!
5. My second Attempt to make the Jig. To speed up the process I had to leave the drill press behind and figure out how to make a jig for a cordless drill. The primary challenge remained how to keep the dowel on the same axis as the drill bit. This is where all focus comes to bear on one task. Some like to doodle on paper, I tend to keep running ideas over in my head until one makes sense and shows promise. After pondering the problem, I envisioned a jig that spun in with the cordless drill, and allowed me to move the dowel segment into the spinning drill bit through a ¼” hole in the other end of the jig.
I had a machinist friend fabricate a jig out of a piece of metal 1-1/2" long and 1" in diameter. One end of the metal piece was turned down to ⅜” and ¾” long. This end could be held in the cordless drill chuck. The other end he bored a 1/4" diameter hole 5/8" inch deep. In the end of the ⅜” section he used a center boring tool to drill an ⅛’ hole to within ⅛” of the bottom of the ¼” hole. The last eighth was drilled with a 1/16" bit and came out in the center of the 1/4" hole. Next he drilled and tapped two holes through the 3/8" shaft that were perpendicular to the 1/8" hole and in 1/2" from the end of the metal rod. Now with a set screw on either side, the 1/16" drill bit could be held in place and centered in the 1/8" hole while protruding into the 1/4" hole about 3/16".
Now I could chuck the 3/8" stub in a cordless drill, 1/16" drill bit locked in place with the set screws and while spinning the device, guide a piece of 1/4" dowel in the open end till it engaged the small drill bit. With a bit of a push you would have a perfectly centered hole in the end of your dowel. This worked great and was faster except for the inconvenience of having to remove the dowel several times to clear the sawdust that had accumulated in the bottom. To solve this, he drilled a 3/16" exit hole on opposite sides of the jig. The holes were perpendicular to the 1/4"guiding hole and positioned at the bottom of the 14” guiding hole. Centrifugal force would clear the wood chips while the jig was in use. We finally had the jig working flawlessly, it was fast, accurate and produced centered holes every time. In the jig where the hinge dowel end met the 1/16" drill bit, both were tightly controlled so neither could move off center, the works like a charm!
6. How You Can Use this Process to Make Jigs for Your Shop. Now I know that tackling such a complicated jig as the one I have just described may be beyond what most hobby woodworkers are willing to do; however, the steps and process I went through for this complicated jig are the same steps you need to go through for simpler jigs that are more common in the shop.
The good news is that for common shop jigs you can typically find dozens of jig plans online or in books where someone else has already gone through the mental gymnastics of figuring out how to solve a particular problem. Your issue will typically be deciding which jig plan to use. This is where you can apply my process of jig making.
Remember this rule – make your jig simple, accurate, and time saving. There are numerous jig plans out there that are so complicated or full of whistles and bells that I would never make or use them. Go simple. Then build for accuracy.
A jig typically holds a piece of wood securely in a predetermined position to safely do a specific and repeatable cut. Take one of the simplest, but most important jigs – a crosscut sled for a table saw. This simple jig is a beautiful tool if made correctly and accurately.
Take your time building the jig to get it right. If your first attempt is not good enough do what I did on my first attempt with the Woodhinge jig – learn from it, set it aside, and try again. By the way, here is a picture of Luther's crosscut sled. Its made of Baltic Birch plywood and a 2x6 piece of lumber. The fence is dead square to the saw blade. No attachments or other whistles and bells.
Study your jig plans and determine what the critical features are. For example, with a crosscut sled you should be able to figure out that the critical feature is making a perfect 90 degree crosscut with your table saw – every time you use the jig. So, what's important about the jig? Getting the jig’s fence 90 degrees to the saw blade and making sure the sled’s runners fit perfectly (no slop) into the tablesaw’s miter slots. Focus on these two critical items just like I focused on keeping the dowel and the drill bit in the same vertical plane. By the way, a great technique to ensure your crosscut fence is square to your table saw blade is the “5 cut square method” (Look it up on the internet). Once you achieve a square fence and tight runners you will have a crosscut sled that does you proud.
7. Final Thoughts on Jigs. There are some other things you can do to make a good jig. Use premium, stable materials. I recommend either ¾ inch or thicker MDF or Baltic Birch plywood. These two materials don't move with humidity changes like solid wood and will remain flat. Please don’t skimp on the jig and build it from a piece of scrap construction plywood that will curl like a potato chip after a couple of weeks and ruin all the precision you put into making the jig.
Another hard lesson I learned is from not labeling my jigs (Picture of one of Rob’s jigs with a label on it), especially if you have a lot of them. It’s a terrible invent and make a jig, not use it for a while then pick it up one day and say, “What does this jig do?”
I hope this has inspired you to make simple, accurate, and time-saving jigs. Good luck!
P.S. Send me some pictures of your jigs and tell me what you learned from building them.