Thread: Removing screws under wooden plugs

Originally Posted by m2c1Iw

I've read a reason for clocking in some applications is for safety as a fastener working loose can be instantly seen.

Not much use if there's a bung or plug sitting over it!
Is there another reason?

Originally Posted by SimonP

Not much use if there's a bung or plug sitting over it!
Is there another reason?

Refers to the non plugged application I reckon.

Peter, I mean no disrespect, I just thought this was over years ago. I too was taught to align slots for various reasons, but then I got two engineering degrees and now know this isn't the wise course of action, regardless of rational.

If you've seen screw slots being cut, you know the slot is ground into the head of the fastener and is a completely separate operation from the threading part of the screw making machine. There is no regard for the location of the threads when the slots are cut, so each has a slot in an arbitrary position. Because of this, each screw will have it's slot in a random location when it's "driven home" fully.

Go out to your car and put random slots on the head bolts on your engine, then align the fake slots. How many miles do you think you'll get before the head gasket takes a dump? This is because the head bolts are torqued to a uniform spec, regardless of where the flats (or slots if they had them) on the bolt heads line up. The exact same logic is applied to wood screws. There is a place where the head is fully "seated" and this is where you stop. If you turn another 1/4 of a turn, to align the slot, 25% of the threads have just been cut (stripped) and if you back it off a 1/4 turn, then it's not "home" and is in fact, loose.

If you entered your boat in a judged "concours" show and aligned the slots on something, they would "ding" you for it, because they know what this means too. I've seen pretty chromed rub rails with carefully vertically aligned slots, on boats and the logic was to let any water drops run out and not rust up in the slot. Seems reasonable on first blush, but it also means very few of those screws (or bolts) where actually "home", meaning rusty slots will be the least of his worries in a few years as moisture gets behind the loose ones.

I preform what I call a "nut and bolt" fairly regularly. The last was a trailer I rebuilt several days ago. What a nut and bolt is and something I blatantly stole from a race car team, is you grab a handful of wrenches and sockets and crawl under whatever, putting a wrench or socket on every stinking nut and bolt you can see, checking for tightness. What this does is assumes I've at some point hit the fasteners with a torque wrench or other wise made each faster tight. What the "nut and bolt" procedure catches is any nut or bolt that may have been missed or come loose for some reason. This is very common for motorcycle owners as they vibrate so much you pretty much have to do this often. On a race car it's a safety issue. It's a tedious operation and usually one of the very last things preformed before a client gets his what ever back. The point of this is to suggest there's a tight fastener and there's something else. I prefer tight fasteners and if I need some sort of alignment on a fastener head, I'll use a button or a cap, which is what they're for (decoration). As far as alignment to have a quick visual check of looseness, well if they're aligned, you can bet some are loose.

Please don't be offended and also look it up in other sources on line. There's a raging debate still, but when pressed, the "aligner's" really can't justify loose or over tightened fasteners, but they usually qualify it with "it looks good", which is nice, but not something I want to rely on when farther from shore then I care to swim back to.

Originally Posted by fraser4syth

I also fold the crap paper!

Well of course, how else would you know how many layers of paper were between your digits and the poo.

Originally Posted by PAR

Peter, I mean no disrespect, I just thought this was over years ago. I too was taught to align slots for various reasons, but then I got two engineering degrees and now know this isn't the wise course of action, regardless of rational.

in my experience aligning the screw slots is called "dressing" the screws, and it's only done for very high quality work -- typically where the screws are highly visible.
I know of situations where the screw is inserted till it is tight, the alignment marked, then the screw removed and a new slot cut so that when reinserted the slots all align
I suppose another "solution" would be to marginally deepen the counter sink.

at least with Phillips heads, it's only a 1/8 turn to align the slots.

If a slot-head screw is driven slightly below surface level it should be in line with the timber grain. This way, it can be painted of filled ,and remain uniform an unnoticeable. If its under a plug , who cares ?

Originally Posted by Kayuwood

This way, it can be painted of filled ,and remain uniform an unnoticeable

Why can't the screw be painted, or filled or remain unnoticeable if it's not aligned with the grain? My contention all along is two fold (again), first the orientation of the slot under a bung or wood filler has absolutely no bearing on the preformance of the filler, visibility under or anything else and secondly, if a screw is over or under tightened to accomplish this silly task, it's either not tight enough or partly stripped. This isn't a debate, it's well documented mechanical understanding. Again as has been previously pointed out, the only way to align slots is to cut new ones or very precisely machine or shim the fastener so it bottoms at it's desired torque setting. Anything less then this, is just kidding yourself on the fastener's holding ability. A torque wrench on several aligned fasteners will quickly show you exactly what I'm saying. They are either torqued to spec or not.

When paint and filler deteriorates over a screw head , the first ones exposed are the ones with the slot not aligned with the timber grain....not a matter for debate, a simple fact.....aligning the slot by driving the screw 1/4 of a turn deeper will not strip wood or screw thread....no need for a torque wrench, unless there is a specific structural engineering requirement for a particular "special" screw that has a purpose beyond the usual requirements of a wood screw. Timber density should be a consideration.....

Nothing personal Kayuwood, but I've restored hundreds of boats over the years and your comments stand on absolutely no rational ground. Not from an engineering stand point, nor from a practical one. There's no documentation you could possible offer to suggest any of your claims are remotely true.

You offer comments such as

When paint and filler deteriorates over a screw head , the first ones exposed are the ones with the slot not aligned with the timber grain

yet you don't explain why, even though you've been previously asked.

Then you follow it with comments such as

aligning the slot by driving the screw 1/4 of a turn deeper will not strip wood or screw thread

any first year engineering student can easily explain why this is clearly not correct. If you over tighten any fastener (regardless of material it's driven into), you have partly (if not completely) stripped it's threads. What do you think those threads are cutting into? Not fresh, unmolested wood, but previously tapped, threaded wood is what is being cut once the head bottoms. So, how is it possible that the next 1/4 turn isn't cutting into the previously cut threads once the head bottoms?

It's not enough to say so, you must offer an explanation, particularly when it's against accepted wisdom. No, not yard wisdom, from a fellow that didn't graduate the 5th grade, but has "30+ years of boat experience" (at doing something incorrectly), but reasonably researched and tested wisdom, such as that shown in texts on the subject, that say an engineering student might need to absorb. In other words, show me one book that says it's okay to apply more torque to a fastener, once it's bottomed in the hole.

In the same vain, explain to me what happens to the putty on a vertically oriented fastener slot (with a horizontal grain), compared to a horizontally oriented one that causes putty demise to occur sooner? And if this is true, I guess you must be all kinds of upset about square and Phillips drives, screwing around with the putty the way it must. So, how do you handle them, make sure the corners of the square are aligned with the grain? How about those Phillips, which must just totally screw up the filler material. Poor filler just can't get a decent break now a days, with all the damn unaligned slots and different drives available now. Gone are the good old days, when the slot were all aligned and love was in the air . . .

Well basically Par , were not talking about square drive or phillips heads are we ?...so why sidetrack ?.....If you were a boat painter doing restoration work , you would understand my point , which is a cosmetic reason for slot heads sitting slightly under the surface to be aligned with the timber grain.....and while we're carrying a tension wrench in our pocket to check optimum screw tightness, we should also have a spec table on hand with the specific densities of all types of wood likely to be encountered , and make sure we know which ones are likely to "strip" the thread of a stainless steel screw and weaken the fastening with a slight extra turn....we also need to establish if the screw positions are pre-drilled and the screw heads driven into a suitably countersunk hole ?.....as I said before , if the screws are covered with a plug , who cares?

There's no side track here, the same logic applies to any fastener head, Phillips, square drive, slotted, what ever, they all exert the same "forces" (imaginary or not) on the filler above it. I've painted hundreds of boats, I've restored more boats then most have seen.

I've never experienced a particular fastener slot orientation issue under putty, unless the putty was soft rosin based, which most have stopped using decades ago, preferring man made stuff now. The old rosin based stuff (bee wax and pine rosin) is heat sensitive and will soften under sunlight, revealing the fastener slot, which is (admittedly) aesthetically more pleasing if left oriented to the grain, but doesn't weaken anything if it isn't. Modern polyester, polyurethane, polysulfide and epoxy fillers don't have this issue. And once again you've failed to describe what about the slot orientation is causing this (I'm calling imaginary) problem, nor suggested any text or reference that says once the fastener head bottoms, you should apply up to a 1/4 more turn. I can offer any number of texts that suggest this is wholly incorrect, on wood, metal, plastics, etc.

Originally Posted by PAR

I can offer any number of texts that suggest this is wholly incorrect, on wood, metal, plastics, etc.

..That would be an interesting read Par , if it's in context , and not refering to screws with a specific engineering requirement beyond the use of wood and woodscrews. ...also the difference between , say W/R cedar and spotted gum would have quite a diference on the outcome....

Ther's no difference from an engineering stand point. A fastener seats and that's it. No one torques small wood screws for obvious reasons, but again once the head bottoms, be this counter sunk or flat bottomed, that's it, she's "home" and any further movement in either direction is defeating the purpose of tightening a fastener. I don't understand how you can't see this quite simple engineering principle.

If a fastener is over tightened and the substrate is firm enough to over come the fastener's elongation resistance, then any over tightening will just stretch the fastener. In metal we call this torque, but in wood, most species will yield at the threads (strip) if the fastener is torqued up past it's bottom out position. Now some woods will easily resit this, past the tensile strength of the fastener, but most will not.

If a fastener is backed off, for what ever reason, it's no longer tight and what's the point of almost tight fasteners.

Originally Posted by PAR

Ther's no difference from an engineering stand point. A fastener seats and that's it. No one torques small wood screws for obvious reasons, but again once the head bottoms, be this counter sunk or flat bottomed, that's it, she's "home" and any further movement in either direction is defeating the purpose of tightening a fastener. I don't understand how you can't see this quite simple engineering principle.

If a fastener is over tightened and the substrate is firm enough to over come the fastener's elongation resistance, then any over tightening will just stretch the fastener. In metal we call this torque, but in wood, most species will yield at the threads (strip) if the fastener is torqued up past it's bottom out position. Now some woods will easily resit this, past the tensile strength of the fastener, but most will not.

If a fastener is backed off, for what ever reason, it's no longer tight and what's the point of almost tight fasteners.

Don't agree Par. I do not believe there is a torque setting for common woodscrew use, and I have pulled the screw head into enough timber ( without a countersink for the head) and never had a problem . It is possible for the scew thread to strip wood , but unlikely unless excessive force is used, which will not happen by simply aligning the slot for cosmetic reasons.