I am building benchwork for my layout and was wondering if there is a chart to tell me what size drill bit I should use when drilling a pilot hole for a screw? I am using deck screws. Should the bit be as long as the screw?
I was taught my my dad to hold the screw up in front of the bit. You want a bit that is slightly smaller than the shank of the screw. If you can see the bit through the threads of the screw, it is too big.
As for the depth of the hole, ideally it is just shorter than the length of the screw so the tip of the screw bites into the wood. The key, depending on the wood type and width, is to have it deep enough to prevent the wood from splitting.
Just get yourself a set of these and don’t worry about. They are sized for the screw #.
In my limited experience, both are correct. I have one of the bits shown in Carl’s post just above, and used it extensively on my second layout that had MDF spline roadbed. I pre-drilled the retainer screws driven down into the middle of the top surface of the roadbed and through into the risers with one of those, and it worked well. On my latest build, I pre-drilled pilot holes in all the spruce 1X2 and 1X4 bench members where I joined two pieces together, but I only used a 3/32" small bit in a drill, somewhat thinner than the shanks of the 1.25" long wood screws. No splits either way.
Hello All,
There are several resources to determine the size of the pilot hole.
Using your favorite search engine type in “Pilot Hole Size.”
Several charts I saw differentiated between soft woods and hard woods.
Hope this helps.
Many deck screws sr self tapping meaning pilot holes are not necessary. But I drill pilot holes any way.
And the combo bits Carl showed are I big time saver.
Hi Maurice
Here is a drill chart:
http://engineershandbook.com/Tables/woodscrewpilotholes.htm
However, I’ll second Carl’s suggestion to get the bits with the counter sinks built in. The drill bits are replaceable if you break one and you can adjust the depth of the hole.
They can be purchased individually if you don’t think you will need the whole set.
Dave
The all in one’s are a great resource. generally, they’re made for drilling holes in wood for wood screws and work well for that.
jj and Roger offer up suggestions to consider. Most of the time we use a drywall screw of some sort on benchwork these days. This is a different screw than a wood screw, but we won’t pursue technical differences, just note that this can sometimes require a different pilot hole size. The hard vs soft wood thing has been mentioned already. But you can also get screw with different threads, fine or coarse, in basically the same screw size. In some cases, you don’t want a supertight fit; in others you do.
With drywall screws, I usually use a bit that is as close in diameter to the body of the screwthreads as is possible. A little bigger hole is OK most of the time, but could make it easier to strip out. Too small and it is a PITA to get in.
For standard wood screws, the charts usually work, but sometimes need a little adjusted for all the reasons I mentioned and some I may have forgot. A chart that has different listings for hard and soft wood is often helpful. If no difference is noted, they often are for softwood and you may need something slightly bigger in hardwood.
I generally bore full depth for the pilot hole. In some case, leaving the last 1/2" or so undrilled in softwood works well and gives a fit more resistant to loosening. Yes, you can skip the pilot hole in softwood, but you’ll find a lot of splintering, depending on what and how you do things. Pilot holes take a little longer, but tend to give more reliable, superior results.
Not directly related to the drill size, but using the square drive head gives you superior control over running the screw in or out. It can give you more grip to let you use a smaller diameter pilot hole, for instance. I use 'em because I have a bad shoulder and rarely drive nails.
Wow, I thought everyone had gone to sheet-rock screws for building now-a-days. No drilling, just screw them right in!
I have done lots of deck construction and have used a pilot bit similar to the one’s Carl pictured. The bit does not need to go to the bottom of the screw when inserted but rather start the whole and cut the cone for the head of the screw. Some of the really cheap counter sink combo’s are so poorly made that they are eccentric and do not do a good job of center boring. I have had good luck with DeWalt countersink sets but not some of the big box store brands made in that big Asian country.
The countersinks that carl shows work and set pilot hole/ counter sink fine for your use. The “flip bit” that has been offered by dewalt, Stanley makita and copied by many others is what I have used proffessionally for over 20 years since thier introduction (what a pain, years ago w/ 2 VSR plug in drills set up w/ the bits needed- cords and more cords and spaggetti). The Quick change kits have made finding them harder lately. But they are still stocked or can be ordered. wnen dealing w/ such softer materials like pine and fir or pine plywood, it is not as critical to select an exact bit. I deal w/ hardwoods (maple, ash, oak) and the pilot, clearance (bit) and proper countersink is immperitive to be more exact in cabinet construction and intallation
This flip bit has the proper sized pilot/ countesink as well as the built in allen to change depth setting of bit. Shown is the #8. Sets are #6,8, and #10 (some w/#12)
If the 'newer" deck screws are robertson (square) or even newer offerings the torque, just change out the phillips bit w/ the one supplied. deck screws are quite robust and actually quite expensive compared to coarse thread DW screws, but your choice. Hint: whatever bit needed to drive screws, get a couple spares.
Well, as mlehman posted above, there is always the chance* of splintering, or even worse spliting. the wood if you don’t use pilot holes, especially when you are fastening near the edge of the board. Away from the edges, yeah you can usually get away with it.
*(or in my experience, the likelihood)
True, softer materials as we generally use will take DW screws w/o any prep, However, depending the wood moisture and eventual drying, the wood can split. Also DW screws tave a tendancy to snap, especially the head, when not pilot/ countersunk. I have been using deck or stainless lately where Reg DW screws used to be the “norm”
I’ve had splitting even with a pilot hole when I didn’t pre-drill the countersink and let the screw head sink itself.
If you don’t want to pre-drill holes, there are newer screws available that actually drill their own pilot hole. The drywall screw kinda squeezes it’s way into the wood. The new ones actually make sawdust as they go in. There are other brands available, but I’ve been using Spax. When I’m near the end of the wood, I pre-drill the countersink only - no pilot hole.
The dryness and grain of the material make the decisions for us. In the case I mentioned, where I was using laminated MDF for splines, I had to countersink the tops of the screws I was using so that they didn’t interfere with the ties overhead. Any screwhead that must be driven sufficiently deep to place its top surface at most flush with the surface into which it is sunk runs the risk of splitting the material, and I did not want that anywhere on my glued and carefully aligned roadbed. I certainly wasn’t going to be happy splitting frame members where the material is already both small in cross-section AND weak…think spruce (think cost).
Thank you for the replies. The chart was just what I was looking for. I did follow the suggestions and stopped at my local big box store to look at their offerings. The guy working the tool department said they don’t carry anything like that but I took a look anyway. Sure enough the Dewalt quick change set was there. The only problem I see with it is that the drill bits have a flat spot on the base for the set screw. My spare drill bits don’t have the flat spot so they might not work if I need to put a longer bit in.
True Carl, wood fasteners that are installed w/o any predrilling, part the grain/fibers of the wood. many soft woods are more forgiving and may not be a problem. The same is true, if you see a carpenter invert a nail and flatten the point. This allows the nail to partly rip its way through the grain rather than parting and creating a potential or eventual split. Did this regularly back before the "age’ of nail guns. Of coarse you didn’t do this to every nail, only where experience tells that fastening trim/ moldings, etc where the nail will be close to the end of a cut or miter, or the old dry piece may split. So thankful for all my Senco, Hitachi and other pieces.
I have found the bottom grade of boards sold at the Big Box stores (frequently called whitewood at Lowes) has a very high tendency to split if you don’t drill a pilot hole regardless of the type of screw used.
I always use a pilot/countersink and woodscrews, usually #8s and #10s. Personally, I think they work better than drywall screws, but I know others have had sucess with drywalls.
Enjoy
Paul