Choosing The Right Screw Size For Mdf: A Comprehensive Guide

Medium-density fibreboard (MDF) is a tricky material to work with, especially when using nails or screws. While wood glue is the simplest method of fastening MDF, it's important to use nails or screws to hold the material in place while the glue dries.

When it comes to selecting the best screw size for MDF, it's crucial to use a coarse-thread screw with a straight shank. The screw length should be at least twice the thickness of the MDF board. For example, if you're working with a 5/8 (16mm) thick MDF sheet, an ideal screw length would be 40-50mm. This ensures that a sufficient number of threads engage with the MDF fibres for a strong hold.

It's also essential to pre-drill pilot holes when working with MDF. The pilot hole should be slightly larger than the screw shank and deeper than the length of the screw. This prevents the MDF from splitting and provides a strong joint.

While special MDF screws, such as SPAX MDF Countersunk Screws, are available, regular wood screws can also be used effectively if the above guidelines are followed.

Screw types: SPAX MDF, drywall, sheet metal, and wood screws can be used

When working with MDF, there are several screw types that can be used, each with its own advantages and applications.

SPAX MDF Screws

SPAX MDF screws are specifically designed for interior finishing applications, especially for use with hardwood trim or medium-density fiberboard (MDF). They feature a T-STAR plus trim head and patented thread technology, which eliminates the need for pre-drilling. SPAX MDF screws offer faster and easier driving than conventional lags and structural lag screws. They are available in two sizes: #6-MDF Trim Head T-Star Plus and #8 MDF Trim Head T-Star Plus.

Drywall Screws

Drywall screws are commonly used for attaching drywall to wood studs. They have a sharp point and coarse threads, making them ideal for gripping and holding the drywall securely in place. Drywall screws typically have a Phillips bugle head or an external hex head and come in various lengths, such as 1-1/4 inch, 1-5/8 inch, and 2 inches.

Sheet Metal Screws

Sheet metal screws are designed for fastening thin metal objects to wood, brass, or steel. They have sharp threads and a sharp point to pierce through the metal and create a tight, secure hold. Sheet metal screws are available with different head styles, such as flat head, hex head, or pan head, and in various lengths and thread sizes to accommodate different material thicknesses.

Wood Screws

Wood screws are designed specifically for connecting wood to wood or other materials. They feature a coarse thread that helps reduce splitting and speeds up installation. Wood screws often have a star drive or a Phillips flat head and come in various lengths, such as 1-1/4 inch, 1-1/2 inch, and 2-1/2 inch. Some wood screws are coated to combat corrosion and add an attractive colour to wooden applications.

Screw size: The screw length should be a minimum of twice the thickness of the MDF board

When selecting a screw for MDF, it is important to consider the length of the screw in relation to the thickness of the board. A general rule of thumb is to choose a screw with a length that is at least twice the thickness of the MDF board you are working with. This ensures that the screw has enough threads to grip the MDF fibres and create a strong joint.

For example, if you are working with a standard 18mm thick MDF board, you would want to select a screw that is at least 35-40mm in length. This will provide ample grip and holding power for your joint. It is also important to note that the screw should have a straight shank and a coarse thread. The coarse thread will help the screw to bite into the MDF and reduce the risk of stripping or slipping.

When working with MDF, it is always recommended to use a pilot hole. The pilot hole should be drilled to a depth that is slightly longer than the length of the screw. This will help to prevent the MDF from splitting as you drive in the screw. Additionally, using a countersink bit can provide relief for the head of the screw, preventing it from forcing the MDF fibres apart.

It is also important to keep the screws at least 3 inches (75mm) away from the ends of the MDF board, as the fibres near the ends tend to be weaker and more prone to splitting. With these tips in mind, you can successfully screw MDF boards together without worrying about splitting or weak joints.

Screw placement: Keep screws 3 in from the ends of the MDF

When screwing into MDF, it's important to keep screws 3 inches (75mm) away from the ends of the board. This is because the fibres of the MDF tend to be weaker near the ends of the board, as they are unsupported. Keeping the screws 3 inches in will drastically reduce the chances of the MDF splitting. This rule also applies to any wood you plan on screwing together. Keeping the screws in from the ends can prevent splitting in real wood and it makes your finished project look better.

MDF is prone to splitting, so it's important to take this precaution, as well as using a pilot hole when screwing into MDF. This will ensure that the screw threads bite and hold into the MDF rather than wedging the fibres apart and causing splitting.

In addition to keeping screws 3 inches from the ends of the MDF, it's also important to follow these other tips when screwing into MDF:

• Use a good-quality MDF with a good density. Cheap MDF with low density will be harder to work with and will split very easily when screwed.
• Always pre-drill with a pilot hole that is the right size.
• Ensure the pilot hole is deeper than the length of the screw.
• Always use a countersink bit.
• Using a clearance hole is recommended.
• Do not overtighten the screws.
• Always drill into the centre of the MDF edge.
• Use a straight-shanked wood screw.

By following these tips, you can successfully screw MDF together without it splitting.

Pilot holes: Drill a pilot hole deeper than the length of the screw

When working with MDF, it is important to remember that it is not the easiest material to fasten with screws. Screws can cause MDF to blow out and churn up. However, if you are using screws, it is recommended to use countersunk screws with a coarse thread. A coarse thread will reduce tearing and churning of the MDF fibres, minimising the chance of splitting.

Pilot holes are an important step when using screws with MDF. They help to guide the screws into place and reduce the force required to insert them. When working with MDF, it is recommended to pre-drill a deep pilot hole that is slightly bigger than usual to help the screws catch and bite into the MDF. The pilot hole should be deeper than the length of the screw. This is because, when you wind the screw into the MDF, excess material will be forced into the bottom of the hole. If the hole is not deep enough, this can weaken your project.

There are several instances when you should drill a pilot hole:

• When screwing through the end grain or near the edge of a piece of MDF, a pilot hole will help to reduce the risk of splitting.
• When screwing through a dense or thick material like MDF, a pilot hole will reduce the force required by removing some of the material.
• When you need to screw in precise locations, a pilot hole will help you to be more accurate.

Drilling a pilot hole is simple. First, choose an appropriate drill bit size. For softwoods like pine, the pilot hole should be slightly smaller than the screw shank diameter, while for hardwoods like MDF, the pilot hole should be slightly larger. If you are unsure, choose a drill bit that is 1/64 inch larger than the diameter of the screw shank. Next, mark the location of the pilot hole on your MDF with a pencil. Then, use an awl to make a small hole to ensure your drill bit begins drilling in the right place. Now, you can drill your pilot hole. After that, insert your screw into the pre-drilled hole and fasten it with a screwdriver or drill.

Glue: Use glue with screws to strengthen MDF

MDF is not the easiest material to fasten, especially with screws. However, you can strengthen MDF by using glue alongside screws.

Firstly, select a good quality, high-density MDF. This type of MDF will be less prone to splitting. Then, when screwing, always pre-drill with a pilot hole that is the right size. This is the most common problem beginners have which usually leads to MDF splitting. Using a pilot hole to suit your screw is the single best thing you can do to ensure success!

Next, use a heavy-duty, multi-purpose, solvent-based wood glue. Nails or brad nails can be used to hold the MDF in position while the glue dries. Once the glue has dried, it will be strong enough to hold the MDF in place.

When selecting the right screws, use straight-shanked wood screws with medium to coarse threads. The length of the screw should be a minimum of twice the thickness of the board being screwed. For example, if you plan on screwing through a piece of MDF that is 5/8″ (16mm) thick, then the ideal screw length would be at least 40-50mm long. The reason is you need as many threads as possible in MDF to ensure a nice stronghold on the fibres.

Finally, do not overtighten the screws. Because MDF is made from pressed wood fibres, it will not be as strong as real wood. Overtightening will result in the screw threads pulling through the MDF and stripping out your screw hole.

Frequently asked questions