Woodturners' Guide To Screw Chuck Drill Size

Woodturning is the craft of using a lathe to shape wood. A screw chuck, also known as a single-screw faceplate, is a useful tool for this process. It is often used for small items and provides a quick and easy way to mount or remove workpieces. However, it is important to ensure that the screw pulls the workpiece firmly against the chuck face to avoid movement and potential breakage. The size of the drill bit used for a screw chuck depends on various factors, including the size of the screw and the type of wood being worked on. For softer woods, it is recommended to use a drill bit one size smaller than the screw. When working with larger blanks, some turners may opt for a fatter screw and a larger drill hole to prevent the workpiece from unscrewing.

Screw chuck vs faceplate

Screw chucks, also known as single-screw faceplates, are a quick and easy way to mount and remove workpieces. They are particularly useful for small items and when the workpiece is not large enough to accommodate the screws of a faceplate. Screw chucks are also useful when the screw holes of a faceplate might penetrate an important feature of the piece.

Faceplates, on the other hand, are more secure and have a greater torque capacity. They are typically used for larger items and provide a stronger hold than screw chucks. Faceplates are also better suited for end-grain workpieces, as screws do not hold very well in end-grain wood.

When using a screw chuck, it is important to ensure that the workpiece is pulled firmly against the outer edge of the chuck face. If this is not achieved, there may be movement, and the screw may break. The chuck face, not the screw itself, supports and drives the workpiece. It is also important to consider the size of the workpiece when using a screw chuck, as a small chuck may not be strong enough to support larger items safely.

In terms of drill bit size, the general consensus is to measure the size of the screw without the threads and drill a hole that size. For softer woods, it is recommended to drill one size smaller. Additionally, when using a faceplate, it is important to use the correct screw size to secure the workpiece. The screws should fit snugly within the faceplate screw holes and protrude approximately seven threads beyond the faceplate.

Screw chuck sizes

Screw chucks, also known as single-screw faceplates, are used to hold workpieces in a lathe. They are popular among production turners when turning platters and small bowls because workpieces can be mounted or removed quickly. They are also useful when the workpiece is not large enough to accommodate the screws of a faceplate or when the screw holes might penetrate an important feature of the piece.

Screw chucks can be purchased that screw onto the headstock spindle, but those available are typically 4” in diameter or smaller. The most popular type is the screw insert that comes with almost every scroll chuck on the market. The screw mounts at the center of the chuck and the front of the jaws act as the bearing surface. The bearing surface is the circular disk that surrounds the screw, and it is important for the workpiece to seat firmly against this surface to ensure the workpiece runs true and to provide a transfer of “power” from the screw chuck to the workpiece. The workpiece should have a flat surface to seat against the bearing surface.

The screw is typically rather large with deep-cut threads, and the end may be pointed or flat. It is assumed that a pilot hole will be provided for the screw, so a point is not essential. The size of the pilot hole will depend on the size of the screw. If the screw is too large, there is a risk of splitting if the wood is small. It can be difficult to screw the blank on and the finished item off the chuck. It is useful to have a smaller screw chuck, or several in different sizes.

One user on the American Association of Woodturners forum recommends measuring the size of the screw without the threads with digital calipers and drilling a hole that size. For softer woods, they recommend drilling one size smaller. Another user recommends eyeballing the drill bit against the screw and matching the minor diameter (the size of the screw without the threads). A third user recommends using a drill bit that is the same size as the shaft of the screw with the threads cut off.

The diameter of the bearing surface should be in line with the size of the workpieces you intend to turn. A diameter of 4” is the norm because the disk will then fit comfortably on a 3” faceplate and will be good for workpieces up to 6” or 8”. If you anticipate turning plates or platters in the range of 12” in diameter, a bearing surface 6” in diameter may be a good choice.

Screw chuck limitations

Screw chucks, also known as single-screw faceplates, are not very well-known but are highly useful for quickly mounting or removing workpieces when turning platters and small bowls. They are also useful when the workpiece is not large enough to accommodate the screws of a faceplate or when the screw holes might penetrate an important feature of the piece.

However, they do have some limitations. Firstly, the bearing surface of the screw chuck, which is the circular disk that surrounds the screw, is relatively small in diameter. This can result in a higher load on the screw, as it needs to pull the workpiece more tightly against the bearing surface to produce the necessary friction force to keep the workpiece spinning.

Secondly, the jaws of the screw chuck are typically slick, which can also increase the load on the screw. This is because a slick surface provides less frictional force than a rougher surface. As a result, the screw needs to work harder to keep the workpiece in place.

Thirdly, screw chucks are not suitable for end-grain workpieces. This is because screws do not hold well in end-grain wood, and with a screw chuck, it is difficult to control how much the screw gets tightened.

Additionally, when using a screw chuck, it is important to ensure that the screw pulls the workpiece firmly against the outer edge of the chuck face. If this is not achieved, there may be movement, and the screw could break.

Finally, screw chucks are not suitable for large or heavy workpieces. They are typically only used for small items and do not have enough holding power for anything other than a very small piece. Therefore, it is always advisable to use tailstock support when using a screw chuck to provide additional stability.

Making your own screw chuck

A screw chuck, also known as a single-screw faceplate, is a very handy and useful item for woodturning. It is often used for turning platters and small bowls because a workpiece can be mounted or removed quickly.

To make your own screw chuck, you will need the following materials:

• A small faceplate or a scroll chuck to attach the screw chuck to the lathe.
• A good grade plywood or hardwood for the disk that forms the bearing surface. MDF can also be used if the screw chuck is mounted on a faceplate.
• A hex head lag screw, preferably 1/4" in diameter and 1.25" long, for the screw.

• Cut a disk with a diameter slightly larger than your desired final dimension for the bearing surface.
• Drill a hole at the center of the disk, 3/4" in diameter and 1/4" deep, to allow the head of the lag screw to rest below the surface.
• Draw a circle, centered on the hole, with the same diameter as the faceplate you will be using. Install the faceplate inside this circle.
• Screw the faceplate onto the headstock spindle. True up the edge of the disk and make a small dimple at the center to help center the drill bit.
• Install a Jacobs chuck in the tailstock and use a 3/16" drill bit to drill a pilot hole for the screw all the way through the disk. Turn the face of the disk to slightly concave.
• Remove the assembly from the lathe. Using a 7/16" socket wrench with an extension, screw the lag screw into the hole until the head seats.
• Check the extension of the screw beyond the bearing surface. It should be about 3/4". Adjust as needed by drilling the hole deeper or adding a washer under the screw head.
• Put the assembly back on the lathe and check for any noticeable runout of the screw tip. If necessary, gently tap the tip with a small hammer to reduce runout.
• Remove the assembly and cover the screw head with epoxy. Allow the epoxy to cure before using your new screw chuck.

For a screw chuck that mounts in a scroll chuck, follow these additional steps:

• Cut out another disk with a diameter slightly larger than the tenon you will need for mounting in the chuck jaws.
• Jam chuck this disk against the chuck jaws and drill holes for reinforcement screws. Attach it to the larger disk with wood glue or epoxy.
• Jam chuck the assembly against a flat plate and true up the smaller disk. Form a tenon on the smaller disk to fit your scroll chuck.
• Drill a 3/4" hole through the tenon side, ensuring the hole penetrates the larger disk by 1/4".
• Mount the piece in your scroll chuck and drill a 3/16" pilot hole through the center. Turn the face of the disk to slightly concave.
• Screw the lag screw into the hole until the head seats, then continue with the final three steps as described above.

Using a four-jaw chuck

A four-jaw chuck is a spectacular tool for any serious bowl turner. It is easy and safe to use, with underlying advantages of stability, strength, and ease of use.

Parts of a Four-Jaw Chuck

The jaws of a four-jaw chuck are attached to the chuck with recessed machine screws, allowing for quick access when changing jaws. The jaws are attached to the jaw slides, which are the moving parts that expand or contract when the internal mechanism of the wood chuck is adjusted. The internal mechanism contains a scroll ring that allows all four jaws to move in unison when adjusted with a tool or key that comes with the chuck.

Selecting the Right Four-Jaw Chuck

The first thing to consider when purchasing a four-jaw chuck for turning wood bowls is the size of the bowls you will be turning. A good rule of thumb is to have a tenon or foot on a turned bowl that is at least 30 to 40% the size of the largest diameter of the bowl. For example, a 10-inch diameter bowl should have a three- to four-inch tenon on the base. In this size range, the four-jaw chuck will perform well and provide ample support and stability.

Most bowls are much shorter than they are wide, but in the process of making a taller bowl or hollow form, the ratio of tenon size to diameter changes. The farther the turned piece moves away from the headstock, the more vibration and instability may occur. However, for wood bowl turning, a 30-40% ratio is a good place to begin.

• Center and mount a wood bowl blank to a faceplate.
• Rough-turn the bottom shape of the bowl.
• Form a tenon to the size of the four-jaw chuck.
• Sand the exterior of the bowl.
• Remove the bowl from the lathe.
• Remove the faceplate.
• Mount the four-jaw chuck to the lathe.
• Mount the bowl tenon to the four-jaw chuck.
• Turn the interior of the bowl.
• Sand the interior of the bowl.
• Remove the bowl from the four-jaw chuck.
• Insert a jam chuck into the four-jaw chuck.
• Mount the bowl reversed to the jam chuck with tailstock support.
• Sand the bowl bottom area.

Mounting Bowl Tenon to Four-Jaw Chuck

Mounting the bowl tenon flush and square to the four-jaw chuck is simple but critically important. With a properly turned tenon, this is not a problem at all. Check for any debris on or around the tenon and also on the jaws, ensuring they are free from any shavings or debris. Expand the jaws wide enough to insert the tenon freely. Never force or push the tenon into the chuck, as this might damage the tenon. Once the tenon is inside the jaws, hold it loosely and slowly tighten the jaws using the chuck key or hex wrench. When the jaws start to make contact, lightly apply pressure to the center of the bowl, seating it squarely on the top of each jaw section. Snug up the jaw grip and, while continuing to apply pressure to the inside of the bowl, rotate the chuck and tighten the opposite chuck adjustment point. Slow opposite tightening will balance tension and prevent the bowl from being too tight on one side. Firm up the chuck until it is tight and the bowl does not move within the chuck. Don't over-tighten, as this might damage the tenon. With green or wet wood, it's a good idea to check frequently and tighten the chuck as needed. Most dry woods will not move once tight, but every wood and each bowl blank is different, so check and snug as needed.

Mounting Bowl Mortise to Wood Chuck

The same process applies if you are attaching a bowl with a mortise to the four-jaw chuck, but in reverse. Before beginning, contract or close the chuck completely, then expand the jaws until they make contact with the recessed mortise. Then snug up the bowl as previously described.

Frequently asked questions