At the guts of woodturning is the way to maintain a workpiece on the lathe. For a newbie, this could be a sophisticated, complicated query. A latest woodturning catalog supplied 205 completely different holding units. What makes it much more complicated is that there are a number of methods to carry a workpiece for a similar operation, and lots of tasks require a sequence of completely different holding strategies. Yet one other supply of confusion comes from the evolution of holding strategies; consulting older woodturning books will lead to completely different solutions than present day practices.
To discover your approach via this maze, it’s good to know the fundamental ideas of workholding on the lathe. I believe of holding strategies in phrases of 4 classes—squeeze it, broaden in it, push on it, and screw it — which embody all holding strategies. For any given workpiece, take into consideration every of the 4 classes and whether or not a holding machine, or technique, is a secure approach to maintain your clean.
I discover it useful to jot down out the steps once I know I’ll want a number of holding strategies for a mission. When figuring out the sequence, begin with the holding technique for the final process and work via methods to get there. For instance, to hole the within of a bowl mounted in a scroll chuck, a tenon or recess is required to carry the clean with the chuck. How are you able to mount the clean to create that tenon or recess? There are a number of attainable solutions, however the level is to begin on the ultimate holding technique and work backwards. Thinking in phrases of squeezing, increasing, pushing, or screwing will allow you to visualize the choices.
The scroll chuck, or 4-jaw chuck, is essentially the most generally used machine within the squeeze class. When utilized in compression mode, the chuck jaws squeeze down on a tenon to carry the workpiece. Chuck our bodies come in numerous sizes, with all kinds of jaw sizes and kinds Some chuck jaws are serrated and straight-sided, and others are clean and angled for a dovetailed tenon. Generally, jaws are interchangeable on chucks made by the identical producer.
Different chuck jaws are designed for various makes use of. For instance, massive, 4″- (10cm-) diameter jaws excel at holding massive blanks for coring as a result of the bigger diameter of the tenon offers extra energy. Smaller jaws are appropriate for extra delicate work. Jumbo jaws are made to carry a bowl by the rim so the underside, or foot, will be accomplished.
The measurement of your chuck also needs to be a operate of the dimensions of your lathe. The mass of a big chuck on a small lathe means the motor will likely be strained at startup. You can run a small chuck on a big lathe, however a big chuck on a small lathe is a foul mixture.
New turners steadily permit their chuck jaw measurement to find out the dimensions of the finished kind’s base. But this observe usually dictates proportions that aren’t superb; it may end up in items which can be squat and backside-heavy.
One approach to keep away from this design flaw is to make use of a tenon measurement and jaws which can be smaller than the supposed base. The pictures present the identical bowl clean on the identical chuck, one with 4″ jaws and one with 2″ (5cm) jaws. For every case, are you able to visualize how you’ll full the underside?
The largest of the holding units within the squeeze class is a chuck outfitted with jumbo jaws. These jaws are designed to carry a bowl so its backside will be accomplished. As the chuck is tightened, rubber bumpers compress and maintain the skin of the rim, although it is usually attainable for the bumpers to broaden contained in the rim, relying on the bowl’s form. There is a larger fly-off danger with this sort of mounting; it’s best to deliver up the tailstock for added help and switch at a gradual lathe velocity.
A collet is one other “squeezing” kind of chuck. It exerts a clamping pressure on the workpiece when it’s tightened by means of a tapered outer collar. Collet chucks excel at holding small-diameter blanks or tenons.
Collets supply restricted adjustment of capability. That is why usually they’re offered in units, relatively than individually. However, collets have two benefits for holding small-diameter blanks: they supply a powerful maintain on the workpiece and won’t mar the wooden. A variation of a collet chuck is the devoted collet with drawbar. In this case, the drawbar runs via the headstock spindle and pulls the tapered collet tight. The taper causes the jaws to contract, holding the workpiece firmly. This holding technique is used steadily when making bottle stoppers.
Drill chucks are one other instance of holding units within the “squeeze” class. A drill chuck has a bonus over a devoted collet in its wider capability.
An obstacle of drill chucks is that they go away compression marks on the wooden. Like collet chucks, drill chucks needs to be used just for small workpieces.
Expand in It
Scroll chucks can be utilized in growth mode, which suggests the jaws broaden inside a recess within the workpiece. Expansion mode has the benefit of larger repeatability; a chunk will be chucked, faraway from the jaws, after which re-chucked and can often nonetheless run true. This not often occurs when utilizing a scroll chuck in compression mode.
A second benefit of growth mode is that it makes use of much less wooden. The recess wanted for chucking finally turns into half of the bottom, so no wooden is wasted. When a chuck is utilized in compression mode, the tenon being held within the chuck usually turns into waste if it isn’t to be included within the base/foot design. Losing 1/2″ (13mm) of wooden from a chunk of 2″ inventory is critical. Push on it
A standard approach of holding wooden on the lathe is between facilities. The work is pinned between the headstock and tailstock, with strain exerted from the tailstock finish. The headstock and tailstock factors have advanced to at this time’s improved drive and stay facilities. Drive facilities are inserted into the headstock and transmit rotational pressure to the clean.
Live facilities are inserted into the tailstock. Ball bearings within the stay heart permit it to rotate freely. The mixture of the 2 facilities permits a clean to be held securely on the lathe and but rotate.
Drive facilities range in measurement and sort. When turning massive, inexperienced blanks, a drive with a bigger crosssection offers extra “bite” within the wooden. This minimizes the issue of a drive heart “drilling” a gap into the wooden and spinning freely. A two-prong drive heart permits larger adjustment of the clean and nonetheless produces a great chunk into the wooden. Drive facilities with a small cross part excel at multiaxis work.
Live facilities additionally can be found in all kinds of configurations. The selection of turning varieties has given rise to specialised configurations of stay facilities. Live facilities can come as a equipment that provides specialised factors for various sorts of work. Some stay facilities have the choice of an adapter that permits a scroll chuck to be threaded onto the tailstock. The stay heart permits the chuck to rotate freely, which will be helpful when reverse-mounting a kind. Mounting the piece on the tailstock whereas nonetheless within the chuck ensures concentricity is maintained.
The “push on it” class additionally consists of jam chucks. The pictures present how a shopmade jam chuck can be utilized to reverse-mount a bowl to permit the underside to be accomplished. The foam-lined disk is threaded onto the headstock, the bowl is centered on the froth disk, and the stay heart within the tailstock is introduced as much as push the bowl in opposition to the froth disk.
The foam protects the rim of the bowl from injury. This technique is a substitute for the use of jumbo jaws, although right here the tailstock should stay in place throughout all the course of, leaving a nub that may be carved away after turning. Turning needs to be performed at gradual speeds with this sort of mounting.
A quite common kind of jam chucking is the use of a wasteblock customized-turned to just accept the work at hand. Very typically, turners will form a spigot so a mission will be friction-match for reverse-mounting. This works properly for small vases and endgrain bins. Another variation, with out friction-becoming, is for a bowl to be positioned over an appropriately formed wasteblock and held in place with tailstock strain, permitting entry to show the bottom.
Another kind of jam chuck is beneficial for mounting tasks that contain a via-gap. In this software, a block of wooden has been threaded and screwed onto the headstock spindle, and a second piece of wooden has been threaded and mounted on a stay heart adapter. Each jam block is formed to match the opening within the center of this small pepper mill. The tailstock is superior to use the wanted pressure to each maintain and switch the pepper mill clean. Using wood jam blocks signifies that if my instrument goes off the clean, it would contact wooden, not metallic.
Another kind of jam chucking is vacuum chucking. A pump is used to attract air via the lathe spindle to create a vacuum that holds the workpiece in opposition to a specialised chuck. The measurement of the vacuum chuck determines the quantity of holding energy. As the diameter of the chuck will increase, the holding energy of the vacuum additionally will increase.
Vacuum pumps are categorized in line with the quantity of vacuum they’ll create and the amount of air they’ll transfer. The quantity of vacuum is denoted by what number of inches of mercury the pump will carry (inHG), and move is measured in cubic toes per minute (CFM).
Vacuum pumps utilized in woodturning will not be in a position to obtain an ideal vacuum, so the move price of your pump is essential. Wood is porous, so some air will cross via it. Regardless of the extent of the vacuum, if the move price of the pump is simply too low, air transferring via the wooden will hold the vacuum beneath the extent wanted to show safely. Be certain to check move price in addition to inches of vacuum when contemplating the acquisition of a vacuum system. Use the tailstock for help so long as attainable throughout turning.
A rule of thumb is that your vacuum gauge ought to register no less than 20 inches for secure workholding. As with all guidelines of thumb, use widespread sense. Airflow via the wooden will be minimized just by rubbing wooden mud over the workpiece. The move of air will draw the mud into open wooden pores, closing the airways and bettering the vacuum. A second approach to cease air from being pulled via the wooden is to place masking tape over the porous areas of the workpiece.
Faceplates are second solely to between facilities within the quantity of safety they provide. They have been the holding technique of alternative earlier than at this time’s scroll chucks and nonetheless retain the benefit of being one essentially the most strong holding strategies accessible.
The holding energy of a faceplate relies on the energy and size of the screws. Common drywall screws are inclined to interrupt and shouldn’t be used. A better option is sheet-metallic screws. The essential aspect is the shear energy of the screw you choose. Use longer, thicker screws for bigger faceplates and workpieces.
When utilizing a faceplate of any kind, be sure that all the floor of the plate is involved with the wooden. Note that when a screw is compelled into wooden, there will likely be a bulge of dislodged wooden across the screw, which might push the faceplate up and trigger a spot, compromising holding energy. Pre-drilling pilot holes will assist cut back this concern.
Screw chucks, or woodworms, are one other holding technique within the “screw it” class. Common sorts of screw chucks will be threaded instantly onto the headstock spindle, inserted within the taper of the spindle, or used along with a scroll chuck. An appropriately sized pilot gap is drilled within the turning clean, which is then threaded onto the screw chuck.
The holding energy of this technique comes from each the screw itself and absolutely mating the clean with the face of the screw chuck. The holding energy will be so nice that it may be tough to take away a clean from the screw chuck when the turning is accomplished. Waxing the threads and/or utilizing a spacer plate diminishes the issue. Large screw chucks excel at holding massive, inexperienced blanks. As all the time, mentioning the tailstock to supply extra help is a beneficial observe.
Developing a psychological library of holding strategies is essential to creating your ability as a woodturner. If the alternatives appear overwhelming, assume in phrases of every of the 4 classes of holding strategies and work via the probabilities.
One ultimate thought on holding strategies: not all items of wooden will be safely mounted and turned. Sometimes, the wisest determination a woodturner makes is the choice to not flip a selected clean. There is all the time extra wooden.
Dennis Belcher retired from a profession of 30+ years within the funding world to his lifelong ardour of working with wooden. A member of the Wilmington Area Woodturners Association (North Carolina), Dennis demonstrates for golf equipment and participates in juried artwork exhibits. For extra, go to his web site, dennisbelcher.com.