Screw Head Drive Types

It probably depends on the relative size of each; if "about equal" my guess would be Torx = stronger.

Torx will. Warning if they can't tighten it down with out stripping the head. If you improve their in ability to do that you mite find them shearing it off.

Based on my experience..................square drive.

I've got a friend that builds furniture and only uses square drive. In my personal experience, I've used lots of square drive decking screws and never had one strip. Not the case with Torx.

You clutch is too big.

The real thing you want to do is to get a torque screwdriver and find what torque you actually need, then select an appropriate assembly screwdriver such as these: http://www.flexibleassembly.com/Products/electric-screwdriver

The low end is like 0.2 in-lbs.

This clutch http://www.smallparts.com/clutch-bore-end-1-000-1-417-length/dp/B0013813M2/ref=sr_1_4?sr=1-4&qid=1316871972 , I believe would work for you based on experience.

Stainless will easily strip and shear.

Torx is very machine/robot friendly. They don't fall off the ends of the screwdriver. Overall Torx is probably a better solution with a screwdriver that has the right range of torque limiting. It would be best to measure the torque required by using a torque screwdriver.

Not sure if a crude measurement is possible using weights and an arm or a spring scale and an arm.

Why not just get the proper installation/removal tool, with a clutch adjustment that can be properly set so it doesn't strip the heads.

2D geometry clearly favours torx. Unfotunately we live in a 3D (or worse) world, so depth matters also, so square bore depth, plus "conical" shape of the thing usally gives better results. Notice also that square type can be more stressfull for the driver (tool) than for the screw, and for demanding apps top quality tools should be used. S.M.

As an old busted arse radio mechanic I've dealt with my fair share of machine screws.

Tait two way radios use a "Taptite" posi drive screws for their assemblies.

www.taptite.net

I suspect they are available in various configurations and materials might be something there to suit you.

I was going to mention Pozidrive, which was used in HP gear. Unfortunately, many times the wrong screwdrivers were used. There is phillips, reed and prince and Pozi-drive and they look almost the same, but with subtile differences.

Pozi-drive had tic-marks on the screw in an X pattern.

For some dumb reason, GM uses tamper-proof Torx on their Mass air flow sensors and some vintage AM radios used a clutch head screwdriver for the screws on a TO-3 package transistor.

Phillips was a littile more "decorative" than slotted, but Torx looks nice too. Phillips was easy to hand assemble because your not wasteing time to find the slot. Torx, I belive, was specifically invented because of robots.

Bristol or spline screws, fortunately don;t show up very often and neither do 12 sided bolts which can be torqued pretty tight.

Stainless shears very easily.

Stainless is very grabby, the thread sides grip and spall -stick and sieze. The screws should come precoated with a dry lube. Screw makers have these screws pre-coated for factory use, but you will not find them at local hardware stores.

The comment about the correct clutch is valid. Hard drive people buy these clutched drivers and also use stainless torx screws, and they use Torz number 1, 2 and 3 a lot.

http://en.wikipedia.org/wiki/Torx

Do you use "Helicoils"-before installing screws?

Please check if the existing thread has too tight tolerance?

Best Regards JKL

My experiences with both aluminum and stainless steel threads: a bit of graphite or white lead prevents the materials from galling thereby providing easy screw installation. Both stainless steel and aluminum materials are great for doing this.

The same applies for cutting stainless steel threads: use white lead as a cutting lubricant.

For assembling aluminum to aluminum threaded parts: use graphite grease.

Dennis

Go to the link below: Provides a good explanation of weird characteristics of stainless steel fastweners.

http://www.estainlesssteel.com/gallingofstainless.html

Dennis

Has anybody even established the actual cause of the failure? Is thread galling a problem, or is it operator error?

From his post, the threads strip before them are fully inserted. This is the typical galling of binding seen with some metals and screws.

From the article by Mr Blu, he may be able to get the task done if he cuts the speed down to reduce the surface welding?

"but they kept stripping the heads" from the OP. Did I miss something?

And the final question, "I'm curious to know which has the greatest resistance to head stripping Torx or Square drive."

The biggest problem with square drive is the limited availability. It originated in Canada WW2, along with phillips in Europe to enable high speed centered driving. Slot had to be shrouded to keep centered. I have always felt square to be better than Phillips, especially for screw retention. But Phillips won the race but square has gradually increased in popularity over the years and can now be found all over the USA.

some links of interest about the merits and reasoning behind various drives.

List of screw drives

cam out

Thanks to all for the spirited dialogues.

Just to make certain I've articulated the situation clearly.

The heads are not snapping off.

The threads are not stripping.

What is happening is that the cold formed depression in the head of the tool deforms under the torque being applied and the insertion tool can no longer tighten the fastener.

I increased the 2-56 screw with a pan head, to a 4 x 40 with a 82 degree flat-head.

I did that so as to be able to use a larger torq or square type head, something better able to transmit the torque without issues.

One of the benefits of asking is that I was reminded of the cold welding caused by the oxidation of stainless. Been there. . . . done that. Learned new cuss words in the process.

I'll switch to coated steel fasteners. Stronger and less likely to cold weld.

Thanks, all of you for your generous support!

Laughing Jaguar

Velcro.

Have you tried better quality driver tips? I have some Torx and #2 Phillips tips from Wera that have proved to be very durable. I got them from Grainger. Good luck.

Are you using Philips screws with a Poxidriv tip or pozidriv screws with a philips tip - either way you will have problems as described - the tip and screw head must be matched in type and size .... In a philips the flutes are tapered, in a pozi the sides of the flutes are parallel

Heed wawaus's advice. Also, reduce the speed of the driving.

Square head or Robertson screws have such a resistance to head stripping that they have a tendency to twist the head off of the screw before they will ever strip. Many of them are heat treated for this very reason. The drawbacks are they are harder to align when starting in an auto feed environment and if the punch is not changed enough during manufacture the screws will stick to the driver after it is driven. I haven't seen a better screw for driver grip.

Elroy

Elroy:

How true. Especially those long wood screws. You really can't strip a wood screw, but you can shear off it's head.