Turning a twisted peppermill

Transcription

1 Turning a twisted peppermill By Brian Horais (AAW 50641) This tutorial is intended to accompany my tutorial presentation on multi-axis turning. A thorough understanding of 3-point off-axis turning is a necessary first step. You should practice making sample twisted columns before tackling the twisted peppermill. Once you have achieved success with your twisted columns, they should look something like this: and the finished peppermill should look like this: What better device to have a twisted shape than a peppermill? You can certainly see the similarities in the basic and finished twisted shapes. Getting to the final peppermill shape requires some preparatory work on the insides of the cylinder before turning the twist and finishing the ends. Step One turning the cylinder Choose your favorite block of wood. It should be approximately 9 inches long and over three inches in diameter. You can trim the edges as shown below before turning a cylindrical shape. The wood I am using here is spalted black gum. It is actually a little shorter than my normal peppermills, but it was a nice (and available) block of wood. Once you have turned a cylinder (approx. 3 inches in 1

2 diameter), turn a tenon on each end (approx. 2.5 inches in diameter) just wide enough to be able to hold the block with a 4-jaw clamp throughout various stages of the fabrication process. Your block of wood should look like this with the tenons. Step Two, parting the cylinder This next step is an important procedure to establish the internal tenon for the peppermill. This must be done before turning the twist to ensure that a clean parting line is established. Trying to make a clean parting line in the twisted shape is not advised. You should pick a stretch of straight grain that is about ½ inch wide and mark it to begin the parting process. I like to use a narrow parting tool to establish the two edges and then I use a wider bedan tool to clean out the wood to establish the tenon diameter. Here s what it should look like with the tenon established. I use an internal peppermill mechanism with a ceramic grinder. It can be tailored to various lengths and has a grind adjustment dial on its base. This allows the peppermill to have a clean look on the top without a visible adjustor. The peppermill mechanism I use is the Penn State Industries (PSI) PKGRINDTL model. You can find it on the PSI website ( I use a tenon diameter of 1 ¾ inches to make sure there is sufficient material to bore out the hole in the top for the knob mechanism. These dimensions work for the PSI hardware but can be modified to fit other internal peppermill 2

3 hardware. Note the two horizontal lines I have made to provide a guide for aligning the grain when reassembling the basic cylinder. Once the tenon is established, with clean edges, it is time to part the top and bottom sections of the cylinder. A clean top and bottom edge, perpendicular to the cylinder centerline, is essential to ensure a good fit of the peppermill top and bottom. I use a narrow parting tool to part the tenon on the bottom of the peppermill head (left edge of the gap shown here). Here is how the base should look after parting. Notice that the cylinder is being held in a 4-jaw clamp. Make sure not to disturb the cylinder in this clamp so that you do not lose center as you begin to bore out a hole for the tenon. Step Three boring the hole for the tenon Bore out a hole in the top of the mounted cylinder that is approximately 1/8 inch deeper than the length of the tenon. You can also begin to bore out part of the center hole to give you a guide for later steps. Here is how the tenon and hole should look after completing the boring (actually very exciting) process. Be sure to have a snug fit between the tenon and the hole. You can always remove material later to make the fit smoother. 3

4 Step Four stabilizing the top and bottom cylinder pieces When conducting the off-center turning steps, there is a lot of torque placed on the wood. Because of this, using a method to stabilize (immobilize) the top and bottom pieces of the cylinder is essential to maintain grain and twist alignment throughout the twisted turning process. I have developed a method of using three small finishing nails with the heads cut off. These small pins are about 1.25 inches in length and are used to pin the top and bottom sections of the cylinder together. Drill out three holes just smaller than the nail diameter in the inner diameter of the tenon, within 1/8 inch of the tenon edge, to mount the three pins with their pointed ends up. The height of the exposed pins should be a little less than the depth of the hole in the cylinder base so that you can align the tenon to the hole when inserting it. Also, you need to use the horizontal alignment marks, made previously, to ensure grain alignment when inserting the tenon with pins. Here is how the tenon should look with pins inserted. Check the fit and if the pins are too long, take them out and drill the holes a little deeper in the tenon. Insert the tenon and align the grain marks. Lightly tap it into position and then use the tail stock to press it into place and align it on center. With it fully inserted, you should have good grain alignment and no separation between the top and bottom sections of the cylinder. Below are two in-process pictures of the tenon insertion. 4

5 The cylinder is now ready to perform the three-point off-axis turning of the twist. Note the horizontal line drawn on the cylinder to provide an alignment guide for the top and bottom off-axis mounting points. Step Five turning the twist This is an abbreviated discussion of the off-axis turning process. It assumes you have carefully studied the preliminary tutorial and have practiced off-axis turning on waste blocks to refine your technique. It also assumes that if you are at this point, the wood you are using for the peppermill is not the type you want to waste. The three off-axis points are measured and marked with a center punch and then numbered to make sure the proper sequence is used. The marked end of the cylinder should look like the image below. The in-process off-axis turning should look like the later image. Note in the second process image that I have attached another piece of wood to the base of the cylinder. This occurred during turning the twist when the soft material of the spalted wood tore out due to the torque of the off-center drive. I use a small (5/8 inch), 4-blade drive bit and even this smaller bit tears out the softer wood sometimes. Being able to recover from a setback like this can save a nice piece of wood. 5

6 You can mount the twisted shape on center after turning the basic twist and use sandpaper to achieve the desired surface quality. Once you are happy with the surfaces, it is time to take the two sections apart and complete the internal and external fabrication. Step Six finishing the internals and externals The images below show the completed twisted shape before and after separating the two pieces. Notice the pins are still in place (and did their job of immobilizing the two pieces). Now you can choose to first complete either the top or bottom of the peppermill. I choose to finish the top first, using the tenon that was originally cut in the top of the cylinder. With the top mounted in the 4-jaw chuck, bore the desired hole size and depth to mount the knob mechanism. Once the hole is completed, turn the top piece over and use the tenon on the bottom to hold it for finishing the top surface. To make sure you don t scar this tenon, I use a small piece of rubber tube material to cushion it in the clamp. Here are images of the hole boring and top finishing steps. 6

7 Now for the bottom part of the peppermill. I like to partially bore the center hole in the top section by mounting the part on the base tenon. Because I had an additional piece mounted on the base, I drilled a small center hole to maintain center and then parted the base so that I still had sufficient tenon to hold the part in the clamp. Drill out about half the length of the center hole according to the peppermill hardware layout details. After drilling out the top section, flip the part over and use a center jaw (expansion clamp) to complete the fabrication of the base holes. Before boring out the base holes, make sure the part is on center by aligning it with the tailstock. Here s how it should look. Final finishing is up to your individual desires. I use two coats of Watco Danish Oil and then polish with the Beall System. It s always fun to see the grain appear when the oil finish is applied. Here s a view of my finished product. Enjoy the process. 7

8 Brian Horais - Knoxville, TN 8