I employ several techniques when drilling a hole longer than your bit on the lathe. But, before I get into the drilling part, be sure your lathe is in top operating condition. Specifically— the tailstock should be well maintained and tuned-up. Read my blog or watch my video, Maintain Your Lathe’s Tailstock to Drill Accurate Holes. Or, you’ll suffer through the drilling operation and the resulting hole will be off-center if your tailstock is not tuned right.
How to Extend the Drilling Depth
- Reverse Chucking
- Commercial Drill Bit Extensions
- Custom-Made Extensions
- Extending the Shank 1/2″
- Break-Down a Project
- Splitting a Blank in Half
- Using a Combination of Techniques
The easiest way to extend the drilling depth on the lathe is to drill from both sides of your wood blank by reverse chucking your blank. I reverse chuck all the time when boring my traditional peppermills. Even short bits can give you double the depth-range when drilling from both sides. Primarily, I use Forstner bits. Forstner bits provide the cleanest holes, and it’s a pleasure to work with a good set of carbide Forstner bits. I drill lots of holes when making my signature peppermills, and the Forstner bit is the first bit I turn to when drilling out peppermill bodies.
The overall length of a standard Forstner bit is 3-½ inches. Of course, the 1-1/8 inch long x 3/8 inch shank is chucked in a jacobs chuck and subtracted from the total length leaving you about 2-3/8 inches of useable drilling depth. A Forstner bit that measures 2-3/8 inches can bore a hole, completely through, measuring 4-3/4 inches. Technically, you can drill another one inch with the same bit just by extending the shank a half-inch out of the jacobs chuck after boring to full depth (fig 6). Go slow, though. Don’t try doing this until you’ve finished boring to the maximum depth, or the shank of the Forstner will spin in the chuck. (This will score up the round shank if you go too fast. Try using Forstner bits that feature hex shanks if slippage is an issue.) You will also invite vibration, chatter, and you won’t drill accurately.
A beneficial side effect of reverse chucking is that any discrepancy from off-center drilling is hidden inside your project. For small jobs like an eight-inch peppermill, the reverse chucking method works fine. For a project requiring deeper holes, try using extensions.
Use Extensions to Add Drilling Depth
Extensions are a great way to add depth to a previously drilled hole. Extensions come in all shapes and sizes. (See photos below) There are several different varieties available on the market for different styles of bits. Forstner bits have a standard-sized shank of 3/8 inch making them convenient for manufacturers to fit them with an extension. As long as the diameter of the hole you’re drilling is larger than the diameter of the extension, you should have no problem getting to your required depth. But, don’t begin drilling with the added extension. Start with a Forstner bit fully inserted and chucked in your jacobs chuck (fig. 5). You want to start with the shortest, stoutest bit to ensure trueness. Then you can add the extension to reach your depth.
The extension in fig. 7 should reach about 6½ inches deep when mounting a standard 2¼ inches long Forstner bit. If you need a bit more depth you can always add another extension to the extension. But that can lead to vibration and off-center drilling. So, it’s best to reverse chuck.
You can achieve more depth by making custom extensions on a metal lathe. (fig. 10) Make them stout to ward off vibration. If you’re careful, you can even make an extension on your wood lathe (but that’s another article.) I fabricated an extension on my metal lathe. I drilled out a 3/8 inch hole at one end of one-inch round steel stock and then cut a 9/16 inch shank on the opposite end. I drilled and tapped two holes for set-screws and now have a beefy extension, which easily allows me to drill out bodies for 18-inch peppermills. The heft in the main body of the extension absorbs the vibration. This allows me to bore accurately. Order one at your local machine shop.
Breaking Down a Project into Manageable Pieces
Another way to drill deep holes on the lathe is to break the project down into smaller pieces, drill out the individual parts, and then glue them up as a whole. I recently completed a set of lamps for my wife, Debra.
Lamps are a fun project to complete and make terrific gifts. I turned this lamp for my wife as a Christmas present. It was a big hit! We remodeled our bedroom last year and purchased a new bedroom set sans lamps. She did not like anything she saw commercially, so I offered to make her a cherry burl set with contrasting ebonized parts.
I knew I could drill a long, accurate 3/8 inch deep hole through the entire body of a 14-inch tall lamp. The hole is necessary to run the electrical cord from the lamp hardware through the lamp and out the base. I employed two of these three deep boring methods. Making three separate pieces that measure 1-5/8 inch, 4-1/2 inch and 8-5/8 inch simplified the drilling process a lot! (See prototype photos below) For strength, when gluing, I added a mortise and tenon on two of the parts. That’s why the individual parts add up to over 14 inches. This made the central burl part of the lamp longer, but I had a plan of action. Of course, I did not have an eight-inch long drill bit but I did have a five-inch brad-point bit with a useable 4 inches of depth. This easily drilled through the 8-5/8 inch blank by incorporating the reverse chucking method and then sneaking the shank out a bit for the last boring pass. Combining methods can add additional depth to boring deep holes.
Not All Long Bits Can Drill Accurate Holes
I also own a twelve-inch length set of brad point drill bits from 1/8 inch to ½ inch. (fig. 17) I believe they are used to drill a hole through a wall for running different types of wiring for telephone or cable TV. They are not the most accurate of bits, and if you start a hole on the lathe with one, you will wobble your way out the other side and find you’re off by an inch or two from the center, provided you don’t break the bit off inside. That being said, they can still be of help in certain circumstances. If you start with an accurately drilled hole using a top-quality standard-sized brad-point bit you can continue drilling deeper by following it with the twelve-inch long brad point drill bit. Just like a dowel jig (fig. 18) starts and keeps your bit on-center and provides support while drilling, the accurate hole you start with, will act just like a dowel jig and keep your bit on track for quite a while to gain more depth.
Drill Accurate Holes on the Lathe
The most important part of drilling an accurate hole is the first one inch of depth. That first one inch, if it’s straight and true, will stabilize the bit further down the hole. Do all you can to stabilize the bit on the entrance. Start with a pilot hole. (fig. 20) Using the point of a skew chisel laid on its side does the trick. It cuts a pilot hole that is dead center. I also usually vary the speed on different sized bits. Smaller bits (in general) require more speed. For example, if I’m drilling the cap of a peppermill for the shaft to pass through, I would drill a 17/64 inch hole. I would set lathe speed to about 1000 rpm. While supporting the tip of the bit with my left hand, SLOWLY crank the tailstock quill out to try and eliminate any vibration. I might slow down the speed of the lathe if I’m working with spalted maple. When working punky wood, slow everything down. Use sharp bits. It also helps to stabilize the entrance hole of punky wood with CA glue if possible. If working on the end grain, let the CA glue soak in deep. The dried CA glue shell acts just like the dowel jig support (fig. 19). It provides support to your bit and keeps it on track.
Larger bits like Forstner bits require a slower speed. How fast should you be drilling? That depends on the wood and the size of the bit. If in doubt, slow it down. If the wood is smoking and you know your bit is sharp, slow it down. Let experience be your guide.
Another tip to drilling accurate holes is to keep the bit clean. Sawdust build-up in the flutes can clog and jam a bit quickly. You’ll regret not withdrawing the bit often after getting your first bit stuck in your project. They are not easy to remove, so pull the bit out often during the drilling operation. I usually drill on the lathe by turning the tailstock handle five turns and then I withdraw the bit. Then I clean the flutes on the bit and continue the operation till I’m at the correct depth or I drill through.
Also note, If the travel on the quill in your tailstock is 2-1/2 inches, don’t start drilling at the beginning or end of that travel. I usually drill in the half-inch to one-inch travel range. That will provide the most support from your quill, and if you should clog the flutes with sawdust, you will still have the extra 1/2-inch of travel to help withdraw the bit; otherwise, you might eject your Jacobs chuck with the bit stuck in the spinning blank. This will score both the male and female morse taper of the chuck and quill, respectively.
While you can use spade bits or speedbore bits to drill holes, their small shank isn’t stable enough for accurate deep boring on the lathe. Extensions are available for spade bits, but I tend to shy away from them because of vibration. Chances are you won’t drill an accurate hole. They might get you an extra inch or two in a pinch, however; they are not something I would rely on in a production turning environment.
Remember, if your turning project is long, and you need to bore a deep hole with a Forstner bit, use a steady rest. It will significantly support your work and help you keep things in-line when drilling.
Before drilling any deep hole on your lathe, think through the process and make sure it feels, looks, and sounds safe before proceeding. Bad things happen quickly on a lathe, especially with long and slender items mounted onto the headstock, so take all safety precautions into account because safety is no accident!
If none of these methods help you out, you can always cut the blank in half lengthwise on your band saw. Then cut out a dado lengthwise using a table saw or a router. Keep the channel you cut square, so you can run it on-center when mounted back in the lathe. Then glue the blank back up. The hole may not be round but if it’s a lamp, no one will be the wiser.
Using one, or a combination of these techniques, to drill deep holes on the lathe will aid you in completing projects thought to be unattainable. Peppermills, salt mills, lamps, flutes, scoops, vases, and hollow forms are just a few of the items that come to mind when needing to drill deep holes. No need to put them off any longer. It’s time to get into the shop and make something!