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KeithG:
The modern type of screw for softwood uses no hole at all and is screwed directly into the two pieces thus not really using the force of joining the two pieces very tightly as the thread is put in both pieces... If anything the wood can be forced apart.
But then you can get other designed screws for other applications..... It goes on and on!

MartinR:
Sorry Keith, in the penultimate paragraph you said that was the correct way, but I understood from the previous paragraph you were saying the that modern (post 2000) professional practice is to "the continuous thread screw is driven into the first piece with no drilled hole and so it then grips the piece under it to fix them together, the thing is the pieces of timber are not forced together by the screw but only the pressure on them when the screw is first applied to the piece underneath."  It was this that I was surprised at.

KeithG:
I'm also surprised that you read my post incorrectly!

Read again the next to last paragraph and you will see how to do it properly  ;D

Working with wood it depends what type hard /softwood if you have a tapping thread or not? Also what material the screw is made of even what load the screw has to hold?

These things are gained by experience and not from a book.

MartinR:
I'm suprised that you say that no clearance hole is made first.  I was taught to size the drill  by ensuring that the clearance drill obscured the thread and shank, and that the tapping drill was totally hidden by the core.  If you don't drill the wood correctly IME it splits.  Mind, I've got a bit lazy recently and have installed an old Amazon Fire in the workshop.  It has nice lists of core diameters and clearance for both machine screws and wood screws. :)

KeithG:
I could write a book on fixings but alas on Google lots have beaten me to it!


I did know that the Phillips design screw head was patented in the 1930`s but did not know that it`s design was so that it could let go of the bit during high torque as in practice that does not happen firstly if your actual bit is new or not worn and second if you put a large screw in you do actually push hard so therefore the bit cannot and does not jump out the screw head.


I started my apprenticeship in 1963 and working at the old Kent County Council Medway College of Technology Fort Horsted Chatham now a housing estate!......i was brought up strictly "Old School" in the Maintenance Department so therefore used wooden planes and slotted screws with a hand screwdriver. Even the Yankee spiral screwdriver was out of  bounds.


After about a year we used Phillips and Posidrive head screws but still hand cabinet screwdrivers. Of course as time progresses time is money and also the grades of timber were also worse with knots everywhere, in the 60`s there were hardly any knots in the timber, now we have quick growing whitewood B&Q etc. which is truly awful timber dry as a bone, it is the moisture in the timber that helps give it strength.


These screws with a continuous parallel thread have been produced since 2000 which suits the speed of the more modern worker to make more money with the least effort.......The art of fixing one piece of timber to another has to be used to make the joint as strong as possible, which of course is the idea of construction, but the continuous thread screw is driven into the first piece with no drilled hole and so it then grips the piece under it to fix them together, the thing is the pieces of timber are not forced together by the screw but only the pressure on them when the screw is first applied to the piece underneath.


The proper way to do this is to drill a thread clearance hole in the first piece and then put the screw in the hole and screw it to the other piece of timber thus the screw squeezes together the two pieces under pressure regulated by the maximum amount the correct screw size can give. Yes it can take longer but not much when you have two drills on the go but you end up with a much stronger job.


Talking about fixings, my first job on turning up at work was to put the glue pot on to heat up of course it was the animal glue then most widely used in workshops by the mid `60`s we were on Casco ,not waterproof, and Cascamite, 100% waterproof and then onto the PVA white glue but not waterproof then?

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