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This mask helps you easily reverse your work for basic rotation.
P.the bowls finished to perfection never reveal how the turner assembled them. However, traditional methods of inverting a bowl to turn the base involve a lot of confusion and annoyance. Cole Jaws, for example, requires you to start at least 48 hex screws for each use (not to mention the aggravation of having to scribble chips for fallen screws).
Leslie Longworth must have been irritated too, because she did something about it. Two decades ago, he conceived an ingenious sliding self-centering chuck that does the reversal work quickly and elegantly. Unfortunately it has aroused little interest, perhaps because it appears complicated. His instructions were incomplete, because he was only able to write the first of two planned articles on its construction before he died.
However, with a little imagination, the first article contains enough information not only to make its spindle, but to develop it further.
The spindle is just a pair of counter-rotating discs. Their maximum radius is slightly less than the distance between the lathe head and the bed. Outboard tippers may size the spindles to accommodate even larger jobs, but they should consider increasing the thickness of the materials. An additional external consideration is that the routed arcs must be cut in the opposite direction to those described below if the head is not reversed such that the workpiece rotates counterclockwise.
Some preliminary comments before starting to build:
1. Longworth’s design shows only four jaws which are not suitable for handling lateral pressure. I have found that it is just as easy to make a six-jaw chuck.
2. It is essential that you perform the following steps in order. Trust me.
3. Rotating jaws and wing nuts can hurt. A lot.
Start by cutting the corresponding discs of 3⁄4“MDF for the back e 1⁄4”Baltic birch for the front. Other materials might work, but I know these stay flat.
The next step is to choose how to mount the spindle on the lathe. You could rotate a wooden flange to fit the mandrel jaws, glue it and screw it to the MDF disc. However, a self-assembling chuck is a convenience, so adding a small faceplate works well. It also binds an expensive component, because removing and replacing the faceplate would soon lead to screw holes in the MDF. An alternative is a nut with the same thread as the head of the lathe. (See “Making the Headstock” on page 55).
Whatever you decide, secure the front disc to the back with four small finishing nails 1⁄2“From the edge. Mount the assembly on the lathe, align the circle and round the edges.
Now for the most crucial step: use a mandrel in the tailstock to drill a 1⁄16“Hole through the exact center of both discs. This hole will ensure that the spindle functions properly after final assembly.
Remove the spindle from the lathe and secure it in a vice. Draw three circles. The smaller the diameter of the faceplate or nut, plus about one inch; the largest is the diameter of the disc less than about one inch; the central circle is centered between the other two.
At this point, if you are making a chuck larger than about 14 “, you need to decide how many jaws you want. I have done both and while four are adequate, I recommend six. The photo at the bottom of the page shows the layouts for a chuck four-jaw and one six-jaw chuck. For four jaws, draw two perpendicular lines through the center of the 1⁄16“Hole you drilled earlier. For six jaws, draw three lines at 60 ° angles. I used drawing triangles.
Dimple the intersections of the diameter lines with the center ring, then use the dimples to draw arcs from the outer ring to the tangent of the inner ring. (Drawing these arcs helps to avoid mistakes on the way.) Keep the compass set for the router template.
I made a circular base (pic on next page) for my router out 1⁄4“Baltic birch. The hole is 3” in diameter for good viewing, because all start and end points are by eye. With a 1⁄4In a router, place the compass pin against the edge of the tip closest to the wing on the base of the router and draw a short arc over the wing. Drill a 1⁄16“Hole through that arch and insert a nail as a pivot pin. Push it through so that about 1⁄2“It protrudes and places it in a dimple on the disc. Push the jig flat and hammer at least the nail 1⁄8“To ensure that the mask cannot slide out of position.
Drawing arches is so easy that you can get a little complacent and make a fatal mistake. Take your time. Begin a cut by partially dipping the tip into the work about 1 ″ away from an external starting point, bring it back to that point – cautiously; this is an uphill cut and then pull forward to the end point. A solid carbide tip required only two delicate passes to go through both discs. Repeat until all arches have been cut. The result will be similar to the photo above right.
Now make some finger holes (approx 3⁄4”Diameter) around the perimeter of the sandwich disc; drill four for a small spindle and six for a large one. These provide the means to counter-rotate the discs to set the jaws.
A # 10 x 1 ″ round head wood screw with an unthreaded shoulder acts as the axis, then widens the center hole in the front disc just enough for a snug fit on the screw shoulder. Enlarge the center hole in the rear disc to the inside diameter of the screw thread.
Sand both faces of both discs to smooth, taking special care to remove any fluff on the edges of the routed arcs. Apply a pair of well-polished coats of paste wax to the face of the MDF disc and the face of the Baltic birch disc that has the design on it. This will facilitate rotation. Now flip the front disc over and place it against the back disc so that the addressed arcs cross over. Insert the axle screw and unscrew it just enough to allow the front disc to rotate. This completes the spindle body.
Now for the jaws. The photos on show the buttons on the front of a 10 “four-jaw chuck and the wing nuts on the back of a 15” six-jaw chuck.
The jaws are made from rubber leg tips available at hardware and home stores. (Do not purchase the vinyl versions. They do not take.) The 5⁄8”The sleeve type is ideal for large spindles and also provides increased reach. However, I have found that the screw button type is the best choice for smaller models.
The tips of the sleeves require wood inserts for fastening, so turn a dowel up 5⁄8”Diameter and lengths of cut to fit inside each sleeve. drill 1⁄4”Holes lengthwise through the top of the rubber tip and the gusset. With 1⁄4“X 21⁄2Machine screws inserted through the dowels and arches, wing nuts and washers on the back of the rear disc allow for quick and easy adjustment.
The buttons that hold the tips of the sleeves require washers (smaller in diameter than the buttons) under the screw heads to compress the buttons against the workpiece.
Rotate the discs until the outer ends of the arcs overlap. Insert the jaws and place the washers and wing nuts loosely on the rear side. Rotate the front disc again and see how it perfectly synchronizes all four or six jaws as they move in and out. Place a bowl upside down against the face of the disc, rotate the jaws until they press against the outer or inner edge of the bowl, tighten the wing nuts and the whole unit is secure.
Now, take out Cole’s jaws and jammed mandrels.
Create the palette
Smaller lathe heads generally use standard pipe threads and nuts are readily available. Unfortunately, for those with 1 1⁄4”Palette, the standard 1 1⁄4“The pipe thread is seven teeth per inch (TPI), so you’ll need to go to a specialist supplier for 1 1⁄4“X 8 TPI nuts. I bought several and used them to make a variety of faceplates. To mount them, I drill and countersink three holes through the face of the nut – the metal is soft – and use wood screws to secure it. holes so that the screws fit snugly.) A small nut has an added advantage as the diameter of the nut / faceplate sets the limit for the inward travel of the buttons.
However, manufacturers don’t need to make sure the faces are perfectly coplanar. All of mine have been out just a little bit, inducing wobble in the spindle. The solution is not difficult. You can put the nut on the headstock and use a sanding disc in the tailstock to address it. Alternatively, mount the nut on the MDF disc centering it as best as possible. While this placement is not critical, I twisted a cap that will just squeeze through the nut and inserted a small finishing nail into its center. By ruffling the center of the disc, the nail will ensure that the nut is centered. Tapping the three screws with a hammer marks the pilot holes.
If your nut induces wobble, you can reduce it to near zero by shimming one side of the nut with a single business card. Eliminate the rest by facing the rear disc.
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