Mounting a Work on Lathe Chuck (III)

Special-Purpose Chucks

Centers and faceplates are the two basic ways of holding work on the lathe. They’ll cope with the majority of your turning requirements; indeed, you could turn for a lifetime using nothing more. There are times, however, when other chucking methods can make life easier. Special-purpose chucks can be invaluable for grabbing odd-shaped work, small work, and finished work that requires modification. In production work, a special purpose chuck can often speed things up considerably. Let’s look at the vast array of special-purpose chucks that you can buy or make yourself.

Jam chucks are used primarily to hold small items in the lathe, but bowls can also be jam chucked to allow turning of the base
Jam chucks are used primarily to hold small items in the lathe, but bowls can also be jam chucked to allow turning of the base

With this information, you’ll be able to tackle any turning job safely and confidently.

JAM CHUCKS

One of the simplest and oldest homemade chucks is the jam, or cup, chuck. It’s a sure, simple way to grab small items without leaving marks in the work. I use it to hold anything from knobs and finials to trays and bowls. Until the early 20th century, a turner would typically have a range of jam chucks made from gun metal by a local machinist. They worked splendidly.

The body of a jam chuck should be spindle-turned from a 3-in.-dia. To 4-in.-dia. piece of close-grained hardwood. Maple, ash, and beech all work very well. Since scrap stock of this diameter is hard to come by, I normally glue two pieces of 8/4 stock together. Yellow glue works fine, but be sure to plane both surfaces for a perfect joint, use plenty of glue, and clamp for a full 24 hours.

In the old days, a tap hole was drilled through the center of the billet, and it was threaded to screw directly onto the headstock spindle. Since suitable wood taps are unavailable today and wood threads do not work out well in end grain anyway, it’s easier to screw the billet to a faceplate. (Remember I suggested buying extra faceplates?) Attach a 3-in. to 5-in. section of the billet to the faceplate with I -in. or I 1h-in. sheet-metal screws.

As shown, mount the faceplate in your lathe, and true up the outside diameter of the billet with a roughing-out gouge. Face the end, and drill a 3k-in. hole through the center with a drill bit mounted in the tailstock. The drill hole allows you to use a knockout bar to eject the work from the chuck.

Next, scrape a tapered pocket into the face of the chuck that is the diameter of the work you want to hold. The taper should be about 3° inclusive (the same angle as a Morse taper). To cut the taper, I use a special scraper that can easily be ground from an old file and a long-forgotten auxiliary tool rest, called an arm rest (for more about scrapers and the arm rest,). You’ll quickly find the right taper if it’s too steep or not steep enough, the chuck won’t hold the work.

Most work for jam-chucking is turned between centers or on a faceplate before it’s mounted in the jam chuck. Remember to square the end of the work face that will go into the jam chuck. Insert the work into the chuck by lining it up as square as possible and giving it a solid rap with a hammer. Next, turn the lathe over by hand, watching for eccentricity. Rap the edge opposite the point that is most eccentric and retest, then continue until the work is perfectly centered. Rubbing some blackboard chalk on the walls of the pocket will add greatly to the chuck’s holding power.

To use a jam chuck, you have to be able to turn well enough so that a catch is the exception rather than the rule because a catch can throw the work from the chuck’s embrace-or at least throw it out of kilter. J am chucking is a skill, so the first few times will be an uphill battle; once learned it will become second nature. Your first jam-chucking is best done on small items.

I’ve successfully chucked items as big as boccie balls, and I jam-chuck bowls regularly. If I have the least doubt about using a jam chuck, however, I add security by trapping the work in the chuck with a tailstock. I also keep speeds moderate, often no more than 200 rpm to 300 rpm for bowls. (This is another reason I find variable speed indispensable.)

COLLET CHUCKS

A slightly different version of the jam chuck is to turn it into a collet chuck. To make this chuck, mount a piece of wood on a faceplate with sheet-metal screws. (Be sure to screw into end grain so that the wood is aligned in spindle-turning orientation.) Drill a hole in the very center that is the diameter of the tenon on the knob (or finial) you are going to hold. Next, turn a gentle taper on the outside of the chuck, and split it into fours with a backsaw or bandsaw. Pound a wood or metal ring onto the taper to force the collet closed. (Don’t be tempted to use automotive hose clamps-they don’t have the closing power for this task.)

Often a metal ring of suitable size can be found, but it is little trouble to turn a wood one. It’s best to faceplate-turn the ring, but remember to keep the cross section robust for strength. I like to make the chuck a bit long for several reasons. First, it can be split far enough back to give the jaws plenty of spring. Second, it may be cut back if you hit it with a tool or for subsequent jobs. By tapping the ring in place to where the jaws are held but not compressed, it may be drilled out to larger diameters.

Making and Using a Jam Chuck

TAPE RED MANDRELS

Tapered mandrels, or cone chucks, are essentially j am chucks turned inside out. They’re a good way to hold small items such as napkin rings (or the closing ring for a collet chuck) and a great way to hold hollow spindle turnings between centers. The advantages of tapered mandrels are that the outside of the work can be turned concentric with the bore and that the work can be chucked and unchucked quickly and held safely.

This homemade chuck is no more than a shop-built collet chuck. The outside of the chuck is turned to a gentle taper, and the tip is partially split by bandsawing or backsawing. A ring of suitable diameter is then added. By forcing the ring down over the taper, the chuck is closed.
This homemade chuck is no more than a shop-built collet chuck. The outside of the chuck is turned to a gentle taper, and the tip is partially split by bandsawing or backsawing. A ring of suitable diameter is then added. By forcing the ring down over the taper, the chuck is closed.
You can turn small items like the closing ring for a collet chuck on a tapered mandrel.
You can turn small items like the closing ring for a collet chuck on a tapered mandrel.

To mount an item such as a closing ring for a collet chuck, start with a billet of wood on a faceplate, just as if making a j am chuck. However, to make a tapered mandrel, turn the outside to a gentle 3° taper. Place the bored-out ring over the mandrel, and using a block of wood and a hammer, alternately “adjust” until it runs true. You can now finish-turn and sand the outer surfaces of the ring.

As in the case of this coopered birdhouse, the headstock mandrel can be left on the screw chuck.
As in the case of this coopered birdhouse, the headstock mandrel can be left on the screw chuck.

Depending on the size of the central hole, you can mount hollow spindle turnings on the lathe with tapered plugs or tapered end caps. Tapered plugs are used for cylindrical objects (such as a pepper mill) with a fairly small central bore-anything up to about 1 in. inside diameter. Turn the plugs as a single piece between centers, then saw them apart. Tap the plugs into the ends of the turning, and remount on the lathe on the original center marks. The outside of the object can now be turned concentric with the bore.

Tapered end caps are used with hollow work that has a large central bore. This is often coopered work (glued up out of staves), such as birdhouses, buckets, and columns. An important difference from tapered plugs is that the mandrel for each end is faceplate-turned as a separate item. A good way to hold each end cap is to use a large screw chuck, which allows the tapered step in the mandrel to be turned concentric with a center hole. Leave the headstock mandrel on the screw chuck, then insert the tailstock mandrel into the work. The center hole left by the screw chuck is caught by a 60° live center. The work is now safely trapped between centers on the set of mandrels and can be turned easily. I’ve chucked 1 2-in.-dia. by 8-ft.-Iong coopered columns using this method.

PRESSURE-TURNING CHUCKS

A pressure-turning chuck is great for high-production turning, and it is a dandy way to chuck lightweight, flat, round items such as plates. This improvised chuck may also be used to hold work while scraping a dovetail recess for expanding scroll chucks. The basis of a pressure-turning chuck is a glue block that has been scraped flat, as described previously. Using a drill chuck in the tailstock,

drill a pilot hole slightly smaller than a l0d nail three-quarters of the way through the center of the glue block. Pound a l 0d nail into the hole so that it bottoms out, then cut off the nail about 1/16 in. proud of the face of the block and file it to a point (see the top photo below). The easy way to point the nail is by touching a file to the nail with the lathe running.

To prepare for pressure turning. file the nail protruding from the glue block to a point.
To prepare for pressure turning. file the nail protruding from the glue block to a point.

Traditionally. screw chucks were used for light work and were built on Morse-taper blanks.
Traditionally. screw chucks were used for light work and were built on Morse-taper blanks.

Because rounds are laid out with a compass, there will be a center mark on the workpiece. Align this mark on the nail point, and force the work against the glue block with the tailstock spindle. You can do this either by using a flat live-center point in the tailstock or by interposing a small block of wood between a cup center or 60° point and the work. Gluing I SO-grit sandpaper to the face of the glue block will provide more positive drive to the work.

Using a pressure-turning chuck, you can completely turn flat work on both sides, except for a small nub under the center point. Once the piece is removed from the lathe, you can chisel away this nub and sand it smooth. The only sign of chucking will be a small indent at the center of the plate base.

SCREW CHUCKS

A screw chuck has traditionally been a favorite for holding small items, although it can also hold work as large as a dinner plate. The time-honored design is simplicity itself. A wood screw protrudes from the face of a Morse-taper blank. A small hole, the body diameter of the screw, is drilled in the work to facilitate threading it onto the chuck Since a right-hand thread opposes the rotation direction of the lathe, the work self-tightens on the chuck. You can chuck and unchuck work from a screw chuck with fair consistency. Screw chucks built on Morse tapers are perfect for turning repetitive parts such as chess pieces and drawer pulls. The small screw leaves little visible evidence of turning (and the screw hole is typically concealed on the finished piece anyway).

Recently, a second type of screw chuck has gained popularity. It has a much bigger screw and is built on a faceplate-like body, which allows it to be threaded onto the headstock. The heavy screw has a straight body with a very coarse 45 ° thread profile. The thread looks much like that on a drywall screw and makes for a very positive hold in wood. Depending on the chuck, a 3/8-in. to 7/16-in. hole is required for mounting. The more positive drive of the threaded faceplate like mount, combined with a heavy screw, makes it possible to hold very large work such as bowl blanks.  These chucks are also good for furniture bases, trays, and plates.

In recent years, I have come to use heavy screw chucks a great deal. I look at them as a great chucking bargain for the faceplate (especially bowls) turner because one screw chuck will replace a bunch of faceplates. I can mount a heavy bowl blank on a screw chuck and turn the outside, then I can mount a glue block on the same screw and glue the base of the bowl to the glue block to turn the inside of the bowl. Finally, I can mount a disk of plywood on the screw chuck and scrape a groove the diameter of the rim for reverse chucking to turn the base of the bowl (see Tum a Bowl with Ernie Conover, The Taunton Press).

When I was a boy, I always made my own screw chucks at the lathe. I still think a shop made chuck is superior to commercial models for holding small items such as knobs, finials, and chess pieces. The great advantage of a shop-built screw chuck is that you can turn the face of the chuck to the base diameter of the workpiece, which makes duplication of additional pieces easy. Also, you can match the screw in the chuck to the screw that will install the finished turning, as in the case of knobs.

To make a screw chuck, start with a l-in.- to 1 1/4-in.-thick glue block, and scrape the face of the glue block to the base diameter of the workpiece. Lightly touch the point of a skew to the center of the glue block, then drill a small hole for the screw in the center of the block with a drill bit secured in a chuck in the tailstock. Remove the faceplate from the headstock, and screw a suitable wood or sheet-metal screw into the hole in the back of the glue block. Applying some epoxy or cyanoacrylate glue to the screw thread will prevent it from unscrewing during mounting of the work. The screw should protrude about 3k in. from the face of the block.

VACUUM CHUCKS

The vacuum chuck is a nifty chuck that is particularly useful for high production work but is also very good for one-off items, especially bowls. To build a vacuum chuck, you need a vacuum source. There are several ways to create a vacuum. The best way is a vacuum pump, but a good, new pump is expensive-$300 to $500. It is sometimes possible to find used or surplus vacuum pumps designed for the printing and refrigeration industries for less than $100.

If you own an air compressor, you can buy a venturi unit that will make a vacuum from compressed air (see the photo below). The quality and price of venturi units vary greatly as does the volume of air required to run them. In general, the higher-priced units require a lower volume of air to maintain a vacuum, with the best units running well from a nail-gun compressor (3 cfm or less).

Another option is to use a shop vacuum, but they don’t work very well. First, they are noisy, which disturbs the state of tranquility you are trying to reach by turning. Second, a shop vac does not create sufficient vacuum to have good holding power, and the suction is further diminished by the fact that the vacuum motor will burn up if you completely seal the system. You must leave a small hole for the shop vac to breathe. The result is that you get only 14 in. to 20 in. of mercury from a shop vac (a perfect vacuum is just a tad shy of 30 in. of mercury). With a venturi, you can get 20 in. to 25 in., and a pump will generally give you at least 24 in.

The vacuum chuck is a fairly old idea in turning (shop-built examples date back to the 1950s), but it has really taken off in the last few years. This is mainly due to an inexpensive adapter designed and built by North Ogden, Utah, turner and entrepreneur Clead Christiansen. The problem with vacuum chucks has always been how to get the vacuum through the headstock spindle and into the chuck. A shop-built adapter entailed a lot of work, typically requiring the services of a machine shop. Clead’s E-Z Vacuum Adapter solves the problem so elegantly that you can only think, “Gee, I wish I had thought of that!”

The E-Z Vacuum Adapter sells for about $75 and is composed of three pieces. A hub with a standard quick-connect air-compressor fitting set in a router bearing is placed on the outboard end of the headstock spindle. It has a 60° taper to center it in the spindle. Setting the air-compressor fitting in a router bearing allows the headstock spindle to rotate, while the fitting (and the vacuum hose connected to it) remains stationary. The nose assembly is placed in the spindle nose and has vents to deliver the vacuum to the chuck. It also has a centering point that can be adjusted to any height or removed altogether depending on the needs of the chucking situation.

The beauty of this design is that it will hold the inside and outside of bowls as well as flat objects such as platters.
The beauty of this design is that it will hold the inside and outside of bowls as well as flat objects such as platters.
Oneway makes a nice line of vacuum chucks as well as its own rotary vacuum adapter. It also sells vacuum pumps.
Oneway makes a nice line of vacuum chucks as well as its own rotary vacuum adapter. It also sells vacuum pumps.

Connecting the two parts and carrying the vacuum through the spindle is a piece of standard ½ -in. lamp rod. The beauty of the lamp rod is that it can be hacks awed to any length so it can accommodate any length spindle. (After sawing, it is best to square the cut and lightly chamfer the thread start on the grinder.) A length of lamp rod comes with the chuck, but you can purchase replacement lengths at any hardware store. The vacuum hose is connected to the adapter with a standard air-line quick connector.

The vacuum chuck itself can take almost any form according to the needs of the chucking situation. It is easy to make a custom vacuum chuck for a production situation and discard it later. Vacuum chucks are most popular with bowl turners, and I have made a shop-built chuck that will handle a wide variety of chucking situation. Oneway makes commercial equivalents of this chuck in three sizes, which work very well. It also sells vacuum pumps and its own rotary vacuum spindle adapters. Since you can make essentially the same chuck yourself for the price of a faceplate in less than an hour, it is time well spent.

Closed-cell foam rubber, neoprene rubber, and O-rings form an effective seal between the work and a shop-built vacuum chuck. Closed-cell foam needs to be thin (1/16 in. or less) and resilient, while ) 1/16-in.-thick neoprene works best.
Closed-cell foam rubber, neoprene rubber, and O-rings form an effective seal between the work and a shop-built vacuum chuck. Closed-cell foam needs to be thin (1/16 in. or less) and resilient, while ) 1/16-in.-thick neoprene works best.

Although turning a suitable wood chuck to hold any item is straightforward, getting a working seal between the work and the chuck is problematic. Rubber or neoprene gasket material is required. Most turners find that foam (either rubber or neoprene) works, but it must be thin, resilient closed-cell foam to work. Do not use a thick piece of foam because it allows movement of the workpiece, inviting a catch. Self-adhesive weather stripping (available at any hardware store) also works well for special chucks. I find that 1/16-in.-thick neoprene works best because you can cut it to any size and shape, and it forms to concave and convex chuck surfaces well and is highly resilient. Once cut to shape, the neoprene can be affixed to the chuck with plastic-laminate adhesive or spray adhesive.

Another viable sealing material is a neoprene O-ring. Any bearing supplier and many auto parts stores sell do-it-yourself O-ring kits. Selling for about $25, the kit includes 7 ft. of O-ring material in four sizes (0.1 03 in., 0.139 in., 0.210 in., and 0.275 in.), a splicing jig, and glue to affect the splice. Using this kit, it is easy to scrape an O-ring groove at the contact point between the chuck and the work and to make an O-ring to fit in it. All wood has some porosity, but a couple of coats of shellac will plug any leakage. Paste wax is good to keep the O-ring in the groove and provide further sealing at this point.

Once made, the vacuum chuck is fun to use. Simply place the work in the chuck and turn on the vacuum. As with paper joints, you need sufficient vacuum area in relation to the size and weight of the work. A good rule of thumb is a minimum of 10 sq. in. of area, which would give approximately 135 lb. of pressure at 28 in. of mercury but only 100 lb. at 20 in. of mercury. A 10-sq.-in. area works out to a 35k-in.-dia. circle inside the gasket. A 3 5/8-in. circle may not, however, have sufficient diameter to give a stable hold for work much larger in diameter than the chuck or with a poor vacuum source. Common sense is required here, and keeping the periphery of the chuck to about one-third the diameter of the work is good shop practice. Also keep speeds low to moderate when using these chucks.

JACOBS CHUCKS

Correctly called a “drill chuck,” the Jacobs chuck is an old stalwart that is more often named for its original American manufacturer. The head of this chuck has an outer ring and an inner ring that encloses the jaws. Turning the outer ring with a key causes the jaws to open and close. The drill chuck mounts into the lathe on a Morse-taper shaft, which is actually a separate piece that fits into the back of the chuck on a short Jarno taper. Morse-taper “backs” can be purchased in any combination of Morse and Jarno tapers. If you have a drill chuck that does not fit your lathe, you can buy replacement backs from any machine-tool supplier. Also, smaller tapers can be adapted to larger spindle sockets by using taper-sleeve adapters.

The main use for drill chucks is to hold drill bits in either the headstock or the tailstock, but they can also be used to grip small work such as knobs and miniature turnings. Drill chucks are sold according to the largest diameter they can grip. Common sizes are 3h in. and 1/2 in., with the latter being better for wood turning lathes.

FOUR-JAW SCROLL CHUCKS

Scroll chucks are crossovers from metalworking. A steel body encases four jaws that open or close in unison by the action of a circular scroll plate (see the illustration on the facing page). The jaws grip around the end of the workpiece. In metalworking chucks, the scroll plate is typically actuated by means of a key acting through bevel gears. To save expense, woodturning scroll chucks are often made without the bevel gears, instead using steel levers that fit into holes in the two halves of the chuck body to allow turning the scroll plate directly. The Nova and small Oneway chucks operate this way.

Oneway’s Stronghold and Nova’s Super Nova chucks use a novel approach-a key fits in a hole in the chuck body and in effect becomes a bevel gear. This affords much greater leverage in tightening the chuck.

For woodturning, a four-jaw scroll chuck is much more satisfactory than the three-jaw variety because four jaws will grip squares nicely. Although you may be tempted to use a surplus metal turning chuck, it doesn’t work as well. Even if the metalworking chuck is of the four-jaw variety, the jaws are not designed for holding wood. They’re too small and tend to indent wood without ever centering it. The jaws are real knuckle busters, too.

Scroll chucks made specifically for wood turning have jaws that hold over a much greater surface area. The top half of the jaws can be unscrewed so that a variety of jaws can be used, each holding a range of sizes (grip range). On some scroll chucks, four plates with numerous tapped holes in their face can be mounted in place of the jaws. By screwing rubber posts to the plates at strategic positions, you can hold odd shapes. For example, you can hold a nearly finished bowl by the rim so that the base can be turned. I call these rubber baby bumper jaws.

Regardless of the maker, rubber baby bumper jaws do not hold well. They cannot be used for primary turning and are only of value for turning away the chucking marks on the bottom of an open-shaped bowl. I can typically mount a disk of plywood on a screw chuck and scrape a groove that is a press fit with the rim much faster than I can change the jaws over and arrange the baby bumpers on the correct circle for the hold. (A vacuum chuck works far better for this purpose.)

Scroll chucks are quick and easy to use and leave no screw holes. If used within the grip range of the jaws, they don’t significantly indent the wood. They’re ideal for holding small furniture parts such as knobs and finials. A handy way to turn small parts is to feed a standard-sized dowel through the headstock spindle then through the chuck itself. (The advantage of using a dowel for turning is that it doesn’t have to be trued round first.) As each small piece is finished and cut off, the dowel can be advanced through the chuck, ready for turning the next piece.

Woodturners tend to think of scroll chucks as gripping by compressing around the outside of the work, but the chucks can also be expanded inside a recess in the work, which could be a pedestal, a bowl, or a small tabletop. Woodturning scroll chucks are angled on the outside faces of the jaws. If a dovetailed (undercut) recess is scraped in the work, the chuck can be expanded to hold securely. This is one of the scroll chuck’s most useful features.

All of the chuck makers offer (usually in the standard package) a screw that turns the scroll chuck into a heavy screw chuck. This is one of the handiest accessories for a screw chuck. You can use the screw chuck to grab a bowl blank for the turning of the outside and scraping of a dovetail recess in the foot (base). You can then grab the dovetail recess with a set of jaws of the proper grip range for the turning of the inside of the bowl (see the illustration on the facing page). Now, you can convert back to a screw chuck and grab a disk of plywood to jam-chuck the rim and turn away the dovetail recess. Since you can generally grab the screw without removing the primary jaws, this makes for quick holding.

Safety concerns with scroll chucks are twofold. First, the spinning jaws present an ever-present danger. At best, they’re knuckle-busters; at worst, they can maim. Second, inadvertently extending a jaw beyond the grip of the scroll will cause one or more jaws to go ballistic when you start the lathe. Most scroll chucks have a safety feature that prevents this, but it’s still a good habit never to extend the jaw more than halfway out of the chuck body. I once overextended the jaws of a scroll chuck when using a metal lathe. A 9-lb. jaw ricocheted off the lathe carriage, went through a Thermopane window, and landed 10 ft. from the building. I’ve never disobeyed the halfway rule since.

If you are turning with the jaws outside the chuck, it’s a good idea to wrap the jaw area with duct tape. The tape softens sharp corners and prevents fingers from getting into the recesses between the jaws.

COMMERCIALLY AVAILABLE SCROLL CHUCKS

ManufacturerModelSizeMethod of operation
AxminsterCarlton4 in.Lever
AxminsterPrecision 4-Jaw4 in.Key
Latalex Ltd.Nova (standard)3 ½ inLever
Latalex LtdSuper Nova4 in.Key
Oneway Mfg.Scroll4 in.Lever
Oneway Mfg.Talon3 ½ inKey
Oneway Mfg.Stronghold4 ½ inKey
VicmarcVM 1406 inLever
VicmarcVM 1205 ½ inKey
VicmarcVM 0903 ½ inLever
VicmarcVM 1003 ½ inKey

Manufacturers offer a variety of jaws for their chucks. Right now, Nova is the only chuck that allows the jaws to be switched between the lever and key chucks. All of the Nova lever jaws may be used on the Super Nova, however, there is one new set of jaws for the Super Nova that cannot be used on the lever. For those who already own a lever Nova and want to upgrade, the Super Nova is sold sans jaws at a cheaper price.

You need to look at more than just the price of a chuck. Cost out the basic chuck and all of the jaws you think you will need to get a fair comparison. The jaws run up the price of a chuck rapidly. Finally, don’t think a scroll chuck will be a panacea to your holding problems. I use scroll chucks but not all that much. Learn to use centers, faceplates, and jam chucks before rushing out to buy a scroll chuck.

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Author: Aliva Tripathy

Taking out time from a housewife life and contributing to AxiBook is a passion for me. I love doing this and gets mind filled with huge satisfaction with thoughtful feedbacks from you all. Do love caring for others and love sharing knowledge more than this.

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