Who gives you the best head?

[old man emu]

Slotted head; Phillips head and Torx head are common styles used to engage a screwdriver with a screw, and they each have their disadvantages in the way that the driver engages with them. There is another style, which I am starting to see and that is the square cavity, or it's correct name, the Robertson head.

 

We all remember the VHS -v- Beta conflict of the 1970s. Here's a little bit about the Phillips -v- Robertson war of the 1920s.

 

 

[Marty_d]

Square all the way.

 

Straight are just ridiculous.  Whoever came up with that idea should be strapped to a chair and have his fingers gashed by straight screwdrivers, which is what happens when it slips.

Phillips head #2 are slightly better but strip too easily.

Hex are quite good, I use hex batten screws for anything that needs a serious big-arse screw.

Square cavity (Robertson?) - I use those now in preference to anything else.  My deck has thousands of them in stainless steel and was far easier to screw down than if they'd been phillips.

 

[nomadpete]

Whether straight or cross head, just like other situations in life, success depends upon getting a tight fit.

 

Slotted head screws are good when you grind the screwdriver to fit the slot perfectly.

 

Cross head relies on the driver being ground to fit the screw. So you have to know which standard the screw head was made to, and buy the right driver to fit the screw head.

 

Phillips was one of the first. But the Philips screws are hardly ever seen these days. More common is Japan Industry Standard (JIS). Maybe the Japanese didn't wish to pay royalties to the Phillips patent owner? These have a sharper 'cross" shape. Using a genuine Phillips driver with JIS will probably strip the head. A quick test is to pick up the screw on the end of the screwdriver. If the screw falls off, the driver is not ground to match the screw. 

 

Of course, USA has it's own (incomatible) standard cross head spec, too.

 

Which brings me to Bunnings Aerospace Standard. Seems the Chinese haven't heard of any of these standards. So their screws fail in many ways.

[nomadpete]

I don't buy chinese screwdrivers - they are poor quality in every regard and either strip out the screw head of a fastening, or strip the end off the driver.

[Marty_d]

Screwdriver?  What is this thing you speak of?

If it doesn't have a bit that fits in my rattler, I'm not interested.

[nomadpete]

You young things!

 

Some of the most satisfying jobs are done by hand.

[willedoo]

1 hour ago, Marty_d said:

Square cavity (Robertson?) - I use those now in preference to anything else.  My deck has thousands of them in stainless steel and was far easier to screw down than if they'd been phillips.

The stainless square section have a classy look. Phillips head screws on a verandah deck make it look like a packing crate.

[Marty_d]

Not that we can see them now, with the bi-annual deck oiling they're as brown as the wood.

[old man emu]

Nobody's mentioned Torx screws in all their interesting designs. It seems that Torx screws were designed to prevent tampering by all but the most determined DIY repairer, or to facilitate assembly utilising robotics.

 

Any screw manufactured from decent materials will do its designed task. The main reason the connection between the screw and the driver fails is over-torquing, or to say it another way, using too much force to get the screw into the material. Because the slot for the driver, whatever the design, has a small surface area, applying too much pressure ( force per unit area) will cause the walls of the slot to fail, throwing the driver out of the slot. Coming from the driver side, too much pressure will damage the face/s of the driver's tip.

 

There are some simple steps one can take to prevent butchering the slot of any screw.

1. Always use a screw whose shank diameter is not too thin, nor too thick for the clamping load that is required.
2. Always drill a pilot hole that is equal to the Minor diameter of the shank, and which takes into account the material the screw is going into. The pilot hole will enable the threads of the screw to cut into the material without them splitting the adjacent fibres as the shank goes into it. It is useful to use a combined pilot hole drill/countersink bit when using countersunk screws as this results in the underside of the head to make more contact with the material, and at the same time not damage the surface.
3.   
4. It is useful to lubricate the threads of a screw with a solid lubricant, such as sopa, candle wax, or beeswax. Screws are not "torqued down", so the effect of lubricants on the clamping force is not so critical
        

One thing that can improve the setting of screws and protect both their slots and the driver is to control the force with which they are inserted. Many people use a powered driver, and these now come standard with clutches which disconnect the drive once a desired torque has been reached. The range of desired torques of met by various tools is not constant. Therefore it is necessary to conduct tests to determine which setting for a particular powered driver gives the desired result. This means taking a scrap of the material into which the screw is to be driven and screwing in some screws to find the setting which results in the clutch disengaging when the head of the screw is in the desired position relative to the surface of the material.

 

Putting in screws involves drilling the pilot hole and countersinking, then using a driver bit to drive home the screw. It can be tedious to have to drill the holes; remove the drill, fit a countersink bit and countersink the hole; remove the countersink bit, and then install the driver bit. I found a useful tool which is a changeable tool holder. You simply pull back the black locking collar and insert the other piece so that the end you want is sticking out. I got this at the big green shed with the red hammer logo. The tool is made by Makita.

 

 

 

 

[Marty_d]

I used a similar one for the deck, but it also has a free-rotating collar that prevents you from sinking the countersink too deep.

[old man emu]

That one, and similar ones that are simply the drill and countersink are OK if you have two drills so you can have the driver bit in the other one. Poor people like me can only afford one drill, so the switcheroo one is great.

[facthunter]

The answer is Cosworth and Ducati..   Nev

[Mr.Vegemite]

If you think slotted are bad have a look at these that are used on RAAF Hercules C-130 aircraft.

 

https://waykenrm.com/blogs/aerospace-fasteners/

 

You slide the tool tip into them, the theory being it won't slip out. Invariably they would just sheer the slot off completely. I would have liked a dollar for every one I had to drill one out. 

The aircraft were given an Aircraft Deterioration Service at Qantas back in the 60's 70's so not surprising the screw heads suffered while sitting out at Richmond base year after year.