Next-Generation Screw GuideComments (0)
This article is from Issue 33 of Woodcraft Magazine.
There’s a whole new twist on the latest fasteners.
Having worked in the fastener industry a dozen years, it’s hard not to get upset when someone says there’s nothing new in screws. On the one hand, they’ve got a point: the basic design remains unchanged. A 15th century craftsman wouldn’t have any problems driving a 21st century screw. On the other hand, the science and technology behind this seemingly simple fastener could fill libraries.
One of the most significant changes centers on the creation of production screws, fasteners manufactured for specific tasks. Considering that the varieties number in the hundreds of thousands, it’s easy to feel overwhelmed. The way to handle the info overload is to face the facts: production screws are made for production, not necessarily small-shop woodworkers. But that doesn’t mean you can’t benefit from a trickle-down technology.
You don’t need a store-sized collection of fasteners or an engineering degree to get the job done right. What you need is the knowledge to pick and choose a manageable screw assortment for handling most woodworking tasks, plus a few specialty fasteners to tackle specific applications.
Drywall Screws: Don’t Screw with 'Em
Want an easy way to reduce slipping, bridging, and breaking? Ditch your drywall screws. The characteristics that make these screws good for hanging gypsum to softwood studs become major liabilities when jointing boards in the workshop.
You’re not the first person to witness a traditional screw slip off the driver or strip out. Manufacturers have searched for a “slotted-head solution” since the 1860s. Slotted screws work well for reproductions and restorations, but newer recesses make driving easier.
Matching the recess(es) to the driver is critical for your screws, driver bits, and work.
Slotted – Prone to slipping and easily strips out. Not suitable for power drivers.
Phillips – More positive engagement than a slot, but still prone to stripping.
Square – Resistant to cam out and helps the screw stay on the driver.
Combination – Use a square-drive bit when you can, a Phillips when you must.
Pozi – Watch for the cross. A Phillips driver will eventually ream out the recess.
Some production screws sport tips and threads designed to reduce the need for pilot holes. In addition to saving time, these tips reduce the amount of torque needed to drive the screw and decrease the chance of splitting the wood.
Although helpful for certain instances, predrilling remains the best choice for fine woodworking. Pilot bits establish a precisely located hole and protect against jacking, splitting, and stripped heads.
Metals and coatings
Platings and other coatings can offer a decorative touch and cheap insurance against stains and/or fastener failure that can happen when building outdoor projects or using acidic woods.
Although they cost more, corrosion-resistant metals offer the best defense, making them a smart investment for projects that need to withstand the elements.
Stainless Steel – The ultimate in corrosion resistance, but at a price. Stainless is expensive and softer than hardened steel screws.
Clear Zinc – Silver color provides some corrosion resistance, but chosen over yellow because color matches common builder hardware.
Yellow Zinc – Provides better defense than clear, but color may not match some hardware. Use with acidic woods, such as oak, when plugging to prevent staining.
Galvanized – Ten times more corrosion resistant than zinc but can cause some staining with acidic woods. Coatings can chip.
Epoxy Coated – Twenty times more corrosion resistant than zinc. Colors blend with wood and composites. Can still cause some staining with acidic woods.
Specialty screws for special situations
You don’t need to blow next year’s tool budget on a catalog’s worth of fasteners. In addition to an assortment of #8 flathead screws, consider a second fastener case stocked with specialists. Having these fasteners on hand will help you overcome some of the most common assembly and installation problems you might face in and out of your workshop.
General Purpose Screws
Woodworkers don’t always admit to tackling projects outside the workshop, but for jig building (and the occasional outside project), it helps to have a few general-purpose screws. The auger tip and self-sinking head can’t compare with a predrilled, countersunk pilot hole, but it works well enough with pine and plywood. Stock up on clear or yellow zinc for interior work and epoxy coated or stainless steel for exterior work. Compared to the total cost of materials, not to mention your time, you’ll find the price difference is inconsequential.
Cabinet Hanging Screws
The big brother of the smaller washer head screws, the cabinet hanger has a large diameter shank to increase holding power and accommodate the shear force of heavy cabinets. The auger point drills through cabinet backs while deep threads and longer shanks resist pullout and ensure maximum engagement in softwood studs. Cabinet hanger heads are typically plated or painted to provide a finished look inside cabinets.
Drawer Front Screws
Oversized washer head screws are designed for use with an oversized clearance hole in order to make adjustments, such as when mounting drawer faces to drawer boxes. The lower head profile reduces the chance of catching on the inside of the box. Ignore the 1:3 screw length rule. Select a length that provides good engagement but doesn't poke through the drawer front.
Another descendent of the washer head, pocket-hole screws have thinner shanks and shorter thread lengths (compared to cabinet hanging screws) to engage the second piece only after clearing the first, minimizing the chance of jacking. The auger tip works like a pilot drill, reducing the likelihood of splitting or raising a chip between the two pieces.
Two basic head designs exist. The larger washer-style head distributes pressure and prevents overdriving. The pan head does the same when joining thinner (½" or less) materials, but the smaller head doesn’t protrude past the pocket.
Trim heads (or finishing screws) work like a finish nail but with a reverse switch. Capable of sinking into oak without a pilot hole, these thin-shanked fasteners attach trim, cabinet backs, even stair treads. You can drive the screws below the surface, like a finish nail. The square drive recess provides the positive bit engagement you can’t get from a Phillips.
Designed for processed wood substrates such as MDF and particleboard, the large diameter shoulder and shank provide extra strength and stiffness while the self-sinking head pulls panels tightly together without pulling through. The thread angle resists withdrawal and allows for reassembly without compromising joint integrity. Use the 7 × 50 mm screws with ¾" materials, and the 5 × 40mm with ½" materials.
Like Confimats, Euros are designed around the poor holding power of processed wood substrates. Used primarily for cabinet hardware, the screws have large shanks and coarse threads to increase holding power and allow removal and reinsertion. They may look similar, but Pozi-Drive recesses resist cam out better than Phillips.
Pilot Holes: Then & Now
Pilot bits defend against bridging, splitting and stripped heads, provided that you select the right pilot and use it correctly.
Traditional woodworking screws require tapered bits to match the root. To minimize splitting without affecting the holding strength, the pilot hole needs to match the screw’s diameter and the penetration depth of the screw.
Drilling pilot holes for production screws isn’t as fussy. Because of the uniform shanks and narrow shafts, you can get by with a straight pilot. Drill a clearance hole through the upper piece to prevent bridging; drill deeper to prevent splitting.
If you’re using modern screws and still have tapered bits, it’s time to make the switch. When used with a straight-root screw, the conical hole can sacrifice holding power.
Traditional Screw/Tapered Pilot
Production Screw/Straight Pilot
About the Author
Before becoming technical director for McFeeley’s, Darin Lawrence was a professional luthier for nine years. He now works as director of product development for Woodcraft.
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