Woodscrews

[Graham_Wright]

Is there anything good to be said about cross-point headed woodscrews?
I find that if the driver slips, the head will burr to the extent that it is impossible to drive in or extract to replace.
I believe it is all to do with the angle of the point insertion. In order to locate the driver in the head there is quite a taper on the entry. This seems almost as good at ejecting the driver as it does at accepting it.
The problem is exacerbated with a power driver as, once it starts slipping, a smooth tapered entry is produced in no time especially with stainless which is fairly soft.
At least with a straight slotted-head, there is always a chance at recovering a mishap with a punch and a hammer.

Or have I got it all wrong?

 

[ghost]

a little,
if you have the correct size bit for the screw-( they are not the same and incorrect bit selection will cause you probs) and fair pressure on the back of the driver (cordless, say), as long as you hold the driver straight ie not x degrees off direction of intended screw but dead in line, start off fairly slowly and as soon as the screw does a turn, power on and maintain pressure & power until the torque ratchet clicks,
if you need to screw a tiny bit more, resist simply putting the bit back on the head and powering up - it'll just burr and round off the posi head, try UNDOING the screw and starting again this time until required depth is attained, if after this you still havent got the depth then you should remove the screw and carefully deepen your pilot hole and try keeping your screws in your mouth. you will find that you naturally salivate and this will ease the friction going on during screwing.
On real tough tight hardwood I dab the screw tips into margerine, careful tho, only a very slight amount otherwise you will stain the peice with oily residue, it'll never accept paint etc. But overall - correct bit selection and elbow forearm driver bit and screw all in the same direction, pilot pressure power perfection

 

[ashley]

Buy a couple of proper bits matched to the screws
The ones supplied with the drills are made of soft metals

They will then grip so well they can break the head off the screw rather than slip as i've found!

 

[alanporter]

Do you not have Robertson screws over there ? These have a square hole in the head and there is no risk of the Robertson screwdriver slipping out. You can even put the screw onto the driver before you fit it into the hole in the wood. They are very common here in Canada, although I believe that they are not available in the U.S. Ask at your hardware store

.

 

[aztec]

Hi Graham,

try this...

drill the hole/countersink or whatever.. then use your driver with a steel screw (same size),that way the stonger steel crew will cut the threads for you, back it out and replace with brass/bronze. a little lube on the screw will also help. and as already mentioned make sure you're using the correct end, Pz tips may not suit brass, but phillips might.

good luck, steve.

 

[Graham_Wright]

Yeah;- done all that but when fitting out a boat, it is not always possible to follow the rules, e.g. driver square to the screw.

My point was that a straight slotted screw can, in my experience, always be driven home and looks a lot more boaty.

Some good tips though especially about the pre-threaded hole.

No we don't have square pocketed heads here;- probably been banned by Brussels;-

sounds an excellent Allen screw variant.

 

[DavidGrieves]

Hi Graham

It sounds like you are using the wrong type or size of bit. There are diferent types ie "Pozi drive" and Philips are not the same and using a Pozi bit on a Philips head or vice versa will chew up the head.
Pozi drive heads have a second cross on the head giving it 8 points of contact, the second cross being much smaller. A Philips only has the one +
Now you need to get the right size bit. I think you can get bits as small as "00" then "0", "1", "2", "3" and so on. You will find the most common sizes are 1 and 2 sometimes called number 1 and number 2.
With experiance you will know at a glance what it is, but if in doubt try fitting a screw onto the bit, if it isn't a snug fit it's the wrong one.
Pozies are a great screw, I wouldn't use anything else and a power driver makes them better.

Dave

 

[Ships_Cat]

Despite what others are saying, the cross head screws are a problem and there is no good solution to it - even the professionals find them a pain. I agree with Alan in that the square socket headed screws are the answer and many trades, including boatbuilders, are changing to them to avoid the unavoidable (if not when they are first driven, at least during any other unscrewing/driving of them) mangling problems of the cross head ones.

Only problem with the socket headed ones, just as with the conventional slotted ones, is that they don't look so good if exposed.

John

 

[macca]

Agree 100% with Alan Porter's comment on Robertson screws - they are very good, but as far as I know are unavaialble anywhere except Canada. Don't know why. Are they available in Canada in marine materials?

 

[Ships_Cat]

They are widely available here in New Zealand (even in ordinary hardware stores, so not any kind of a special item at all) and in stainless steel. Not just self tappers available but all sorts such as the types used for plasterboard, MDF, etc as well.

John

 

[michael_99]

You can get them here in Australia, they have been used on BETTER HOMES AND GARDEN tv program.

 

[Graham_Wright]

Thanks for the comment.

As a professional engineer running my own sub-contract company for the last 17 years, I am aware of the matching requirements. (Sorry if that sounds pained!).

The problem with all cross head screws lies in the fact that the lead is tapered (presumably to speed engagement and location of the driver in production plants).

The inevitable consequence is that some of the turning force is translated into a repulsion force (simple mechanics). In confined spaces, it is sometimes impossible to achieve perfect alignment of the driver. This exacerbates the problem.

Conversely, a staight slotted head is a plain parallel sided groove. The only repulsion force can result from a tapered screwdriver blade (which should not occur at the tip).

The Robertson screw sounds a wonderful idea;- how miserable would life be without Mr Allen's hexagonal screw head?

Any problem with unsightliness could presumalbly be eased by using a plug, which, because (I assume) the sides of the hole are parallel unlike the Phillips et al, would not be inclined to reject it.

Torx-headed screws also have an advantage but I have never seen those for wood.

Great how a simple question can resulat in so much discussion!

 

[Ships_Cat]

Square drive screws seem to be available in the UK - a quick search turned up http://www.squarescrews.co.uk/catalogue.htm which lists some ss ones (left hand side of page about half way down). No doubt there are suppliers with a wider range.

John

 

[sequena1]

Agree totally with the problem. My solution is to buy my screws from Screwfix who have a reasonable range in both A2 & A4 at very reasonable prices and reckon on a 10 to 15 % wastage rate. Even if the slot strips on the way in, it will usually retain enough grip to get it out when I replace it with another in the now nicely tapped hole. I don't want to teach grandmothers etc., but in hardwoods it's pretty important to get your pilot hole the correct diameter and I find it's worth superimposing the bit over the screw and choose a size equal or even slightly wider than the screw core. Also lots of pressure on the drill/driver. By the way Screwfix also sell what they call an "angle bit" (sad this, isn't it, Knowing your Screwfix Catalogue backwards) which they say "allows driving of screws at angles. No personal experience, but might be worth a look.

 

[spynappels]

Sorry to reply so late, but I've been away. The company I work for has a range of screws with a high torque, easy centre drive. The bits are half way between Pozi and Torx and are guaranteed not to cam out even under extreme torque. Unfortunately they are only available in a yellow passivated finish. Maybe possible to use them if the finished article is covered with a layer of epoxy resin. We only do A2 and A4 screws with Pozi heads.

Stefan.

p.s. I'm not giving the name of the company I work for as I don't want to be accused of advertising, but if you want more info, PM me.

 

[snowleopard]

There are a couple of options to reduce the risk of 'camming out' with cross-point screws: Screwfix among others sells a diamond-coated bit which has minute diamonds embedded in the surface which dig into the screw under load and prevent the blade sliding out. You can also buy a liquid with fine abrasive grit that has the same effect.