Phillips vs Pozidrive and portable drills

[Tim StevensParticipant @timstevens64731]

Roberton heads were used on Vauxhall motor cars for the bodywork, in the days when they were made in Vauxhall, London UK (up to about 1928). Or, to be more accurate, until they were taken over by General Motors, at least.

Just in case anyone thought they were 'just Canada'.

Cheers, Tim

Edited By Tim Stevens on 05/07/2019 17:40:31

[Robert Atkinson 2Participant @robertatkinson2]

Posted by Michael Gilligan on 05/07/2019 17:27:24:

Posted by Robert Atkinson 2 on 05/07/2019 17:07:42:

As an aircraft engineer I have also had to deal with Bristol spline

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Do you happen to know of a reasonably priced supplier [to the UK]

… I have a set of small keys, but need a couple of larger ones.

MichaelG.

I use Xcelite which are available from RS Comoponents e.g.

https://uk.rs-online.com/web/p/screwdrivers/2550519417/

but even then they are extended range.

Snap-On sell a set of L type ones but they will set you back about £150

Robert G8RPI.

[not done it yetParticipant @notdoneityet]

Cheap screwdriver tips suck. I just have a couple of each size fro HIS or Sterling bolts and nuts. Good quality ones last ages. An electric screwdriver with variable torque limit is a must, or either the screws or the tips will suffer.

Buy Reisser and see the difference in quality. You won’t go wrong with a decent quality product.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Robert Atkinson 2 on 05/07/2019 19:45:13:

I use Xcelite which are available from RS Comoponents e.g.

https://uk.rs-online.com/web/p/screwdrivers/2550519417/

but even then they are extended range.

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Thanks Robert … I hadn't thought to check RS

MichaelG.

[PlasmaParticipant @plasma]

The impact driver type screwdrivers are great but do go through bits like sh1t through a goose.

Even the bits labelled for impact use seem to suffer wear and tear.

I've just bought a Facom pocket box of bits and a ratchet and the bits are excellent. My old snap on ratchet driver still has the original bit selection and few of them are shot.

Maybe we should all buy a 3foot long yankee driver and bin the Bosch lol

Regards Mick

[Robert Atkinson 2Participant @robertatkinson2]

Mick said " Maybe we should all buy a 3 foot long yankee driver and bin the Bosch lol "

About 15 years ago I used to take machines to trade shows in the USA, The machnes were shipped in crates with lots of screws to open them . Having got fed up with short battery life on the cordless drivers back then and restrictions on carrying spare bateries on aircraft, I bought a yankee. Never goes flat (but you can wear out) and has automatic increased contact pressure with increased torque so hardly ever slips. Numerous people would come over and say " that's great, I'd fogotten about those" or similar. Not cheap but a great tool.

Robert G8RPI.

[Harry WilkesParticipant @harrywilkes58467]

I had a 'Brum' fitter work for me he was good he didn't need a brum screwdriver he oxy/acetylene

H

[HOWARDTParticipant @howardt]

I also still have a Yankee in my tool bag the bits are still good after 45 years of use. But the thing I found with drill driver bits was to test them for fit in the screw being used, some just don’t fit very well.

[Mike PooleParticipant @mikepoole82104]

A friends father was using a Yankee that slipped out of the screw and powered up his nose, ouch!

Mike

[MK_ChrisParticipant @mk_chris]

Here is my “take” / understanding of the difference between Phillips and Pozidrive.

The angle built in to a Phillips head is designed to “cam out” when the torque limit is reached. Hence no shearing of the head due to over tightening. The results can be a bit variable and depend on the pressure exerted on the driver.

Production tools such as air guns, battery tools etc. came with torque adjustment. The tool and not the operator provides the required torque limit. Hence the Pozidrive variation with a different head design was introduced. It retained the quick location of a driver with the pointed target system and the four extra notches added helped with visual identification.

Battery drills almost always have a torque slipping clutch system built in behind the chuck. Usually marked 1 to something and ending with a No slip drill setting. I rarely see anyone use the torque settings on a battery drill : and have met a number of DIY'ers who did not know the purpose of the dial.

Now hoping for more accurate detail from the many knowledgeable on this forum.

Chris.

[egaParticipant @ega]

Posted by JasonB on 05/07/2019 14:15:30:

The most common use of square drive screws in the UK is for pocket hole joinery where "kreg" are the common brand made popular by Norm on NYWS. That's about the only thing I use them for, driver does tend to stay in the hole well.

I got my Kreg outfit from Axminster before they went over to the ujk brand. The Kreg-supplied screws seem to be Robertson and drive very well as long as axial alignment is maintained. The ujk equivalent is T20 where the connection between driver and screw head is perhaps not quite so positive.

When Pozidriv came in I think the idea was that it could be driven with a Phillips driver but not the other way round which may be the answer to the OP's question.

A character in Victoria Wood's classic sitcom, dinner ladies, was asked if he had any real regrets about his life and replied that he blamed himself for failing to appreciate the importance of the cross point screwdriver!

[Michael GilliganParticipant @michaelgilligan61133]

Posted by ega on 06/07/2019 11:34:51:

When Pozidriv came in …

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at last, someone spells the name correctly

MichaelG.

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P.S. this is succinct **LINK**

https://www.pbswisstools.com/en/news/detail/phillips-and-pozidriv-cross-head-screws-explained-in-simple-terms/

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Edit: Back in 2016, Bugbear posted the patent numbers

https://www.model-engineer.co.uk/forums/postings.asp?th=118584&p=1

Edited By Michael Gilligan on 06/07/2019 13:03:33

[VicParticipant @vic]

Almost on topic … An old friend of mine worked at a school as a physics lab technician. One day one of the physics teachers asked him if he could borrow a screwdriver overnight for a job at home. Yes of course was the reply what type do you want, slotted or cross type? “oh I don’t know I’ll have to go home and have a look”! They walk amongst us …

[egaParticipant @ega]

Michael Gilligan:

Thanks for the link and the thumbs up. It's good to know that my recollection was on the right lines.

The linked article mentions colour coding, an excellent idea in the circumstances particularly for bits with tiny markings. I think that Wera used to put a coloured ring on their bits.

[Kiwi BlokeParticipant @kiwibloke62605]

I find it hard to believe that the Phillips drive was designed to 'cam out'. The axial component must be very small, given the very small wedge angle of the drive flanks. Whether the driver 'cams out' or not will depend on the axial force applied by the operator (in my case, often a large proportion of my somewhat excessive weight) and the friction between driver and recess. And if it was an intended feature, the idiot designer didn't think about subsequent removal…

Good old-fashioned screwdrivers for slotted screws (remember them?) are, of course, tapered too. Is this a designed-in torque-limiting feature too? Parallel-tipped drivers are much more secure than tapered tips. Interesting that gun-makers of old often used screws with very narrow and deep slots, designed to be driven by the finely-tapered tips of 'turnscrews'. These fancy-named screwdrivers wedged securely in the slot, making slip-out unlikely. Useful when fixing very expensively-engraved actions into stocks, etc.

I thought that GKN patented Posidriv in the mid-'60s, so it was a late-comer, in competition with long-established Phillips, and the yanks adopted a 'not invented here' attitude. I think the popularity of the different patterns has more to do with commerce than engineering.

The Robertson drive is very common here in NZ. Note that its driver is also tapered, so might be expected to 'cam out', if the Phillips theory is correct. I have driven about 100 in the last few days, without any problem.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Kiwi Bloke on 07/07/2019 09:25:57:

I find it hard to believe that the Phillips drive was designed to 'cam out'.

[ … ]

And if it was an intended feature, the idiot designer didn't think about subsequent removal…

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Why do you find it difficult to believe ?

Rather than 'camming out' … just think of it being like a self-releasing taper on a machine tool spindle. [so much more convenient than the self-locking Morse]

They were designed for use on production assembly lines, and frankly 'the idiot designer' didn't care about convenience of removal.

MichaelG.

[JasonBModerator @jasonb]

Posted by MK_Chris on 06/07/2019 11:06:57:

Battery drills almost always have a torque slipping clutch system built in behind the chuck. Usually marked 1 to something and ending with a No slip drill setting. I rarely see anyone use the torque settings on a battery drill : and have met a number of DIY'ers who did not know the purpose of the dial.

Now hoping for more accurate detail from the many knowledgeable on this forum.

Chris.

A Torque setting works OK in an engineering context where a machine screw is being driven as the thread will have been cut and you then just want to tighten the screw to a specified torque.

However most DIYers and for that matter carpenters will be driving screws into wood which is not consisent, you could set your torque setting so that the tool drives a screw in to the desired depth and then when you come to a bit with a knot in it your clutch will start slipping before the screw is anywhere near driven home. So that is why the torque setting tends to be left high and the electronic brake together with the users reaction will govern how deep the screw is driven, even then it will depend on whether the upper timber has been pre drilled and or CKS or if the woodscrew has additional ribs to help it CSK itself which will require less torque than one with a plain CSK.

As for Phillips heads the main use of these on site is for drywall screws and you don't use a torque setting to sink these correctly. You have a dediated driver or at the very least a specific bit that will act as a depth stop that will sink the screw below the surface of the plasterboard but not far enough to tear the paper. So Torque is left high or on the drill setting so you can bash them in to any hard knots, soft timber, steel studs, etc and the depth stop will do the rest so they all end up at the same depth..

[SillyOldDufferModerator @sillyoldduffer]

Posted by Kiwi Bloke on 07/07/2019 09:25:57:

…

Good old-fashioned screwdrivers for slotted screws (remember them?) are, of course, tapered too. Is this a designed-in torque-limiting feature too? Parallel-tipped drivers are much more secure than tapered tips. Interesting that gun-makers of old often used screws with very narrow and deep slots, designed to be driven by the finely-tapered tips of 'turnscrews'. These fancy-named screwdrivers wedged securely in the slot, making slip-out unlikely. Useful when fixing very expensively-engraved actions into stocks, etc.

I thought that GKN patented Posidriv in the mid-'60s, so it was a late-comer, in competition with long-established Phillips, and the yanks adopted a 'not invented here' attitude…

The Patent for Pozidriv was filed in 1942 and finally approved in favour of the American Screw Company in 1949. Phillips was an american businessman, not an engineer. His drive was actually invented by John P Thompson and Phillips formed a company to market it, very successfully. Later Philiips worked with the American Screw Company to develop Pozidriv as an improved Phillips. Phillips and Pozidriv are close relatives.

The patent gives lots of interesting background. 'Good old fashioned' slotted screwdrivers get a well-deserved kicking for bad behaviour when used under power, and it is also explained why the blades are tapered.

For years following the advent of the wood screw and its companion the machine screw, the conventional coupling between the head of the screw and the bit of a screw-driver was formed by a simple kerf cut entirely across the screw head and adapted to receive the substantially fiat blade of a screw-driver. The walls of the kerf were parallel to each other in most cases since the cutting was done with a small circular saw, but the engaging walls of the driver blade included an appreciable angle, not only to prevent weakening the blade but for convenience in its construction, for the usual blade was flattened from a circular rod to provide additional width and to reduce the thickness. Sharpening, after wear, should normally follow the original surfaces but the tendency was to increase the included angle to reduce the amount of material necessary to be removed in the sharpening operation.

This type of coupling was subject to numerous faults, not the least of which was the lateral slipping of the driver through the open ends of the kerf resulting in the marring of the material to which the screw was being applied. When considerable resistance to the driving of the screw was encountered, the substantial taper of the driver blade and the relatively small contact of the same with the kerf, which in most cases. was considerably wider than the thickness of the blade, resulted in a high throw-out force tending to move the driver axially away from the screw. This again caused slipping and marring. When screws were driven almost entirely by hand, conditions were not so bad, but with the increased use of power screw-drivers they were materially augmented because of the higher speeds of driving and the greater torque applied. Even though greater torque was available for driving, no greater force could be applied manually to the screwdriver to hold the same in the kerf against the resultant increase in the throw-out force.

Having used plain slots, Phillips and Pozidriv, I'd say the most important factor is having a correctly sized screwdriver tip in good condition. I'd rate Pozidriv above Phillips, and Phillips above slot heads but they're all rubbish once the head is chewed. All three systems are horribly abused by careless operators: I am one!

Dave

[Kiwi BlokeParticipant @kiwibloke62605]

Dave (SOD). Wikipedia says 'The Pozidriv was patented by GKN Screws and Fasteners in 1962'. (So you see that I'm just recycling dubious info. found on the web…). I skimmed the patent to which you linked (how does anyone read this stuff?), but wasn't clear that it was put into production.

Michael G. To design a screw/driver combination to 'cam out' at a desired torque seems pretty heroic, given that the applied axial force, let alone the alignment of the driver to the fastener can't be controlled in the field. And then the driver wears and it all goes to hell. The taper of the driving flanks (ignore the point angle) is, to the Mk 1 eyeball, far shallower than a Morse taper, so one might hope that the screw jams onto the driver, rather than it being a self-releasing taper. I just don't believe that the tiny flank 'slope' will produce a big axial force from reasonable torques.

Anyway, for whatever reason, Phillips and Posidriv drivers can 'cam out', although leaning on an unworn driver with sufficient determination seems to be able to frustrate the (Phillips) designer's supposed intention. If the designer really didn't care about the need for subsequent screw removal, then I still would call him an idiot. There's a lot of them about – especially in the auto industry, where dismantling for service and repair is commonly frustrated by lack of thought – or Machiavellianism.

Grinding a bit of the point off drivers is often worthwhile, allowing better driving flank engagement.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Kiwi Bloke on 08/07/2019 07:18:55:

Michael G. To design a screw/driver combination to 'cam out' at a desired torque seems pretty heroic, given that the applied axial force, let alone the alignment of the driver to the fastener can't be controlled in the field.

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That's not actually what I said … but never mind

'Camming out' is the unfortunate collateral consequence of the taper on the flanks of the Phillips screw and its driver … which were put there for assembly-line convenience.

MichaelG.

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Edit: it is interesting to note the claim made by Phillips, at lines 16-24 in the Patent:

https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=2046839A&KC=A&FT=D&ND=3&date=19360707&DB=EPODOC&locale=en_EP

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Edit: I've just found this:

https://www.geniusstuff.com/videos/phillips-screwdriver-video.htm

Edited By Michael Gilligan on 08/07/2019 09:39:17

[Kiwi BlokeParticipant @kiwibloke62605]

Michael: earlier, you asked why I found it difficult to believe that the 'camming out' was designed in. I was answering, not arguing with you. My original scepticism was in response to MK_Chris' post.

Wikipedia suggests that the 'camming out' was not a designed-in feature, and cites references. I think this is another instance of the harder you look, the confuseder you get…

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Kiwi Bloke on 08/07/2019 10:11:03:

Michael: earlier, you asked why I found it difficult to believe that the 'camming out' was designed in. I was answering, not arguing with you. My original scepticism was in response to MK_Chris' post.

Wikipedia suggests that the 'camming out' was not a designed-in feature, and cites references. I think this is another instance of the harder you look, the confuseder you get…

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I also clarified my 'position' [or so I thought] by writing:

Rather than 'camming out' … just think of it being like a self-releasing taper on a machine tool spindle. [so much more convenient than the self-locking Morse]

I suspect we have done this to death now … and we are actually in agreement

MichaelG.

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P.S. for what it's worth … My Dad worked at GKN in the early 1960s, so I had all this Pozidriv vs Phillips stuff almost 'first hand'

[egaParticipant @ega]

Michael Gilligan:

An earlier development in fastening technology was the tapered thread wood screw which I believe was due to GKN or, perhaps, just N.

[Neil WyattModerator @neilwyatt]

My experience is that a 'fail' tends to damage the driver when using Phillips and the screw when using Pozi.

Neil

[Author]

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