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Longbow
03-16-2009, 01:57 PM
This will probably be the "newbie" question of the month, but when I'm drilling countersunk holes should I be drilling the hole to a depth that matches the length of the screw? Should I drill it less so that the tip bites into the wood or drill it a little deep (longer than the screw)? I'm using the fuller countersink, if that makes any difference. Thanks!

Peerie Maa
03-16-2009, 02:04 PM
This will probably be the "newbie" question of the month, but when I'm drilling countersunk holes should I be drilling the hole to a depth that matches the length of the screw? Should I drill it less so that the tip bites into the wood or drill it a little deep (longer than the screw)? I'm using the fuller countersink, if that makes any difference. Thanks!

I hope that you are talking about the pilot hole, the diameter of the root of the treads. I would not leave it much less than the screw length, especially if you are driving into a decent hard wood.

Tom Jackson
03-16-2009, 02:18 PM
An excellent source of information on the proper use of screws is WoodenBoat magazine, Nos. 54-55, in an article by Ed McClave, "A Close Look at Wood Screws."

Your pilot hole should be the length of the screw or a little more. "Bottoming out" can cause excessive torque on the screw, increasing breakage. The diameter of the pilot hole can depend on what type of wood you are screwing into. Other variations can come into play: If, for example, you are screw-fastening a plank to a frame, the bore through the plank should equal the shank diameter, and the pilot hole in the frame should just about match the root diameter.

Jim Ledger
03-16-2009, 02:27 PM
Fuller tapered bits do a reasonable job of boring, but, in some cases leave something to be desired. The problem is that the portion of the hole in the upper piece of wood, the piece with the countersink, can be too tight, causing binding around the screw shank. This prevents the screw from pulling the two pieces together effectively. Sometimes, a separate drill with a straight bit of the correct diameter can be used torun through the top piece, to loosen up the hole. The hole should be exactly the same size as the screw shank.

Scott Rosen
03-16-2009, 04:24 PM
Jim, that's a good point. I've found the Fuller bits are especially troublesome with very short and very long screws. With the long screws, the root diameter for the threads ends up being too large. If you use a smaller bit, the shank diameter is too small. Ideally, you need three different sized bits -- root, shank and head diameters.

It's especially important with bronze and brass screws to get the root diameter right. If it's too small, then you run the risk of breaking the screw when you try to drive it into a too-small hole. Been there, done that.

larry wave
03-16-2009, 04:51 PM
With the fuller tapered bits, the depth of the pilot hole depends on the wood your dilling into. The harder the wood the the deeper you have to drill. Really hard wood like purple heart, kapur, ipe... will probably require that you drill an 1/8 to3/16 deeper than the length of the screw. Don't forget the bees wax.

Wooden Boat Fittings
03-16-2009, 05:43 PM
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My advice would be to forget about Fuller bits altogether. Drill a pilot hole at root diameter for the full length of the screw, as above, then open it out with a larger-size bit to clearance-hole diameter for the shank (which will mean right through the upper piece of wood and possibly part-way into the lower piece as well,) and then finally use a countersink bit to allow the screw-head to lie flush (or else drill right out if the head's to be plugged.)

Easier if you have three separate drills of course, to save having to keep changing bits. But that way will give you no mistakes.

Oh yes, and if a line of screw-heads is going to be visible when you've finished the job, make sure their slots are all aligned in the same direction -- particularly if they're the old-fashioned single-slotted sort. That tells viewers you're a good workman (even if you're not :) ) whereas when the heads are all the ahoo they're broadcasting the fact that you're a sloppy worker.

Mike

paladin
03-16-2009, 06:32 PM
use nails or staples....

rbgarr
03-16-2009, 06:47 PM
... prevents the screw from pulling the two pieces together effectively.

I was taught that the screw is there to hold pieces already in place, held and/or clamped together, not to pull pieces together by the screwing action of the fastener. McClave's article is the definitive treatise to my mind.

Bill Mercer
03-16-2009, 07:04 PM
.

Oh yes, and if a line of screw-heads is going to be visible when you've finished the job, make sure their slots are all aligned in the same direction -- particularly if they're the old-fashioned single-slotted sort. That tells viewers you're a good workman (even if you're not :) ) whereas when the heads are all the ahoo they're broadcasting the fact that you're a sloppy worker.

Mike

Uh, doesn't that tell people that the way things look is more important than good fastening? I mean, when the screw's in tight the screw's in tight. Giving it another 1/3 turn (or backing off) to get the slots lined up seems sloppy.

carioca1232001
03-16-2009, 07:23 PM
Jim, that's a good point. I've found the Fuller bits are especially troublesome with very short and very long screws. With the long screws, the root diameter for the threads ends up being too large. If you use a smaller bit, the shank diameter is too small. Ideally, you need three different sized bits -- root, shank and head diameters.

It's especially important with bronze and brass screws to get the root diameter right. If it's too small, then you run the risk of breaking the screw when you try to drive it into a too-small hole. Been there, done that.

Second that !

The Fuller tapered-drill-bit and the matching (co-centric) countersink-bit with adjustable collar looked very promising at first sight, but the shortcomings surfaced in no time, while re-planking and re-fastening the undersides of a 34 ft motor-cruiser.

I eventually had to do it in two passes, with one drill fitted with a countersink and a drill bit of the diameter of the screw shank, followed by a tapered drill-bit with stop-collar (adjusted for screw length) fitted on a second drill.

boylesboats
03-16-2009, 07:39 PM
And don't forget beewax. Coating screw threads with beewax help screw turn easlier, also keep screw cool as you driving it...

StevenBauer
03-16-2009, 07:54 PM
I think MP&G have Fuller custom grind drill bits to match their screws. If you are doing a major refastening job it makes sense.


Steven

rbgarr
03-16-2009, 10:02 PM
And don't forget beewax. Coating screw threads with beewax help screw turn easlier, also keep screw cool as you driving it...

Was it Greg Rossel who wrote about his method of using a commode wax ring for holding and greasing screws?? What a great idea.

Bruce Hooke
03-16-2009, 10:17 PM
I was taught that the screw is there to hold pieces already in place, held and/or clamped together, not to pull pieces together by the screwing action of the fastener.

Ideally, yes, I'd say the pieces of wood should be at least in contact when the screw is installed, but I think it is still reasonably to want the the screw to exert a bit of force on the top piece of wood (the plank for example) to pull it up truly snug against the bottom piece (the frame). Unless you are going to carefully clamp each and every joint before screwing it together, you are not going to get a nice solid joint without the screw pulling the joint tightly closed. That's my opinion anyway.

By the way, there are various places that make stepped drill bits for countersinking screws. The only ones I have seen and used are a little limited since the depth of the clearance hole is not adjustable, but they do pretty darn well. I think they are FAR superior to the silly Fuller bits which are all the wrong shape for a proper screw hole.

Bruce Hooke
03-16-2009, 10:19 PM
An excellent source of information on the proper use of screws is WoodenBoat magazine, Nos. 54-55, in an article by Ed McClave, "A Close Look at Wood Screws."

Your pilot hole should be the length of the screw or a little more. "Bottoming out" can cause excessive torque on the screw, increasing breakage. The diameter of the pilot hole can depend on what type of wood you are screwing into. Other variations can come into play: If, for example, you are screw-fastening a plank to a frame, the bore through the plank should equal the shank diameter, and the pilot hole in the frame should just about match the root diameter.

In my shop I always have a copy of the chart from this article that shows the proper size pilot & clearance holes to drill for different size screws and situations (dry hardwood, dry softwood, wet oak, end grain). I use it all the time...

David G
03-16-2009, 10:24 PM
This will probably be the "newbie" question of the month, but when I'm drilling countersunk holes should I be drilling the hole to a depth that matches the length of the screw? Should I drill it less so that the tip bites into the wood or drill it a little deep (longer than the screw)? I'm using the fuller countersink, if that makes any difference. Thanks!

We seem to have wandered into a bit more general discussion, though I'm sure it'll be illustrative (even if only obliquely) for you.

First, let's get the terminology. Countersinking is what you do so that the head of the screw ends up flush with the face of the wood - or just under-flush. It is accomplished with a conical bit called - interestingly enough - a countersink. Pre-drilling is what you do to allow room for the shank of the screw (in the first layer, like the planking) and to allow room for the root of the screw thread (in the second layer of wood, like the ribs). Counterboring is when you want the head of the screw WAY under-flush, but you didn't ask about that.

To answer your particular question - I can state unequivocally... it depends. It depends partly on what size screws you'll be sinking. It depends even more on what metal the screws are. And it's almost as important what species you'll be drilling through and into. The stronger the screw (harder metal, and larger size) and the softer the wood species... the less important it is to be absolutely precise with your pre-drilling and countersinking.

Example #1: say you are fastening western red cedar planks onto douglas fir ribs with #12 steel screws (you wouldn't likely use steel, or screws that fat, but this is just an illustration). You might use one of the combo bits mentioned above - or even just an awl - to locate a starter hole, and maybe start a shallow countersink. You'd allow the strength of the screw to drive itself into the soft fir and embed itself into the even softer cedar. If you were to go ahead and pre-drill, I'd pick drill bits that were undersized - esp. for the root. If you count on only the portion of the rib that the threads bit into, in this softer wood, it'll too-easily pull out or strip out. Sometimes, with this quick & dirty (no pilot hole) approach, you end up with layer 1 and layer 2 held apart by the thickness of a couple of screw threads - not flush. The quick remedy is to back the screw out quickly until it is only in layer 1, and the two layers can be squeezed together. Then reinsert the screw.

Example #2: at the other end of the spectrum, say you're fastening iroko planks onto ipe ribs with #8 brass screws. Again - a bad combo, but a good illustration. Ipe is so hard and dense, it's almost like machining aluminum, so you'd best be absolutely sure you've drilled the pilot hole for your threaded portion big enough to accomodate the root, or unthreaded core of the threaded length of the screw, and slightly longer than you need, as noted above. You want the exact diameter, or just ever-so-SLIGHTLY larger. Likewise, you want a shank clearance hole that's the same diameter or just slightly larger than the screws shank. The depth of countersink needs to also be precise. Once the head of the screw bottoms out in the conical countersunk hole, It Stops!. There's very little give to Iroko. All of this - in this example - is compounded by the fact that your brass screws are so soft, that they'll twist right off when they encounter any but the slightest resistance. In fact, many people do all of the above, then sink a matching steel screw first to clear the way... then remove it and gently insert the brass screw.

Lubrication helps too. Paraffin is what I use, on those rare occasions when I can't do without it. Beeswax works. Some pro shops buy the wax rings used to seal a toilet to the floor and stick a bunch of screw into it and pull them out as they're needed. There's a specialty product called Ackempucky, which works quite well, but is more expensive. Just don't use soap. Most soap is hydrophilic. That is - it attracts water, which isn't what you want soaking into your boat, or on your fasteners.

So... all that said, would you like to share the specifics of your task, and get more precise recommendations?



"After an access cover has been secured by 16 hold-down screws, it will be discovered that the gasket has been omitted" -- De la Lastra's corollary

GWB
03-18-2009, 03:24 PM
Do you know if this chart is avilable in electronic format? I will soon be mounting my teak handrails.....my boat is FB but I'm wondering what size screws to use....and pilot hole sizes.

Thanks for any help

In my shop I always have a copy of the chart from this article that shows the proper size pilot & clearance holes to drill for different size screws and situations (dry hardwood, dry softwood, wet oak, end grain). I use it all the time...

ChaseKenyon
03-18-2009, 03:58 PM
I use two screw guns, one with a double bit for the shank size and the countersink, and a second one with a Vixx bit for doing door hinges that has a drill bit the size of the root diameter. The counter sink has a v'd bottom as most do. That makes it perfect to use the self centering vixx type bit to drill for the root of the threads. and I use regular Zest (never leaves a film) soap. I have had problems with bungs from wax residue. Zest washes away clean with just water and no film left. I usually set bungs with thickened shelac BTW.