Using torx drive screws instead of phillips

[Zzz]

I do a lot of home improvement projects where I end up framing stuff with lumber, plywood, etc. I've fallen in love with using torx drive construction screws because the drive is just so positive-- you never skip or strip one. I use the drive bits and have a whole torx socket set and screwdriver set. They're especially nice in the micro sizes on electronics.

I'm thinking about using torx drive stainless screws for all my sheet metal fastening on the Bearhawk. I just remember days past, disassembling my Cessna inspection covers, etc and how much attention and pressure I had to apply for those screws. Wouldn't a good torx drive screw be nicer?

The only downside I can think of is that it would be easier to over-torque them since the drive is so positive, but that can be said of any fastener. A phillips just strips the drive head before you can strip the threads (usually.)

It also seems that torx are more plentiful in pan head, whereas truss head are more scarce but seem to give a nicer low-profile finish for sheet metal applications.

[Mark Goldberg]

The only issue might be having "non standard" screws perhaps flying somewhere and you lose your torx head screwdriver. Some local is not likely to have one laying around. Mark

[Craig C.]

The engineers decided to use Torx drive fasteners on the F-35 and shop hates them. If the fastener binds, or your tip is not square in the screw, or it's even slightly worn, you will be drilling them out due to head damage. Lots of "Drive Grit" gets used to keep the bits from caming out. If you travel much, then you have to carry spare bits for whatever sizes you use as well as spare fasteners. Not every hardware supplier around carries Torx. You don't want to get somewhere and then get grounded for days waiting on an order of a couple of fasteners to get airworthy again. If you never land away from home, then using them might be okay.

[Zzz]

I'm not sure in what world a phillips drive would ever be considered harder to strip/damage than a torx, and it's not as if drive bits and screwdrivers are some foreign thing. If a phillips head is slightly stripped or worn, you're in the same situation. I'd reckon a phillips is even less tolerant of off-axis drive than torx.

How many times have you actually found yourself away from home with your airplane but no tools? That seems like an irrational concern to me. Toss a driver or two into the onboard tool kit. Torx drivers and bits are readily available at most tool or hardware stores. If a shop can't support working with torx fasteners, what else are they incapable of?

I do agree on the availability of fasteners though, they are less common that Phillips drive. Luckily the diameter and thread pitch of screws are standardized at 6-32 or 8-32 et al. The drive does not affect that so just replace with whatever is available in a pinch.

[Craig C.]

Zzz: We've found that even with the high grade Apex brand tips, it's way too easy to round off the tips themselves. The biggest problem is the depth of engagement between the tip and the fastener. A T-15 machine screw has less than .045" for engagement. Couple that with the fact that the tips are not flat ground, means even less engagement. To keep from caming out, it requires keeping the tip square to the fastener and keeping sufficient pressure on the driver. With some of the damaged fasteners, even with 300 lbs downward force on a speed handle, we still end up having to drill about 90% of the damaged fasteners.
As to easy availability on tips and drivers....I've twisted and sheared off probably a dozen or more of the ones you can get locally, as my VW uses them. Most don't fit the screws well, or are too soft. At work, we tend to wear the splines down at the end of the tip on the bits, even using hand tools, although I have a propensity for shattering them. Even the Apex's are only good for a couple hundred fasteners before they show enough wear that we change them out.

With Phillips drives, I can often use a cut down tip of the next size to get damaged screws out. 20 years of running the offset-cruciform drive screws in and out on the F-16 gave me lots of practice with honked up screws.

[Zzz]

Ahh you're talking about the driver bits/tips suffering damage, not the head of the fastener itself?

[Zzz]

I come across a lot of Phillips drivers with damaged splines too, but I always figured the damage only occurs when the drive tip slips, which seems less likely with torx, though from what you're saying just regular non-slipping use wears the drive splines?

What is your opinion of socket head cap screws? Not that I use those in this application, but like torx, the hex drive seems quite intolerant of driver sizing. Growing up with bicycles and motorcycles loaded with those, I've stripped more than I'd like, but it was usually due to a mixup of imperial vs metric sizing, or just bad tool fit in general. Phillips seems a little more tolerant of mismatch in driver size due to the steep taper, but not much. It's too bad all phillips are not pozi-drive, which I've used extensively in mounting snow skis over the years. Much better.

[Battson]

Not to make too finer point of it, but if you are stripping screw heads "you're doing it wrong". I learned the hard way.

I used to strip them out to start with, lots of them. That was, until I learned what I was doing wrong (a few different things - using the wrong tool, over torque, not using a clutch every time, poor fitment). I haven't damaged a single head since, and now I can understand why I used to have these problems. Even the cut-price softer headed ones seem to last almost indefinitely if you do it right.

[Zzz]

Not to make too finer point of it, but if you are stripping screw heads "you're doing it wrong". I learned the hard way.

I used to strip them out to start with, lots of them. That was, until I learned what I was doing wrong (a few different things - using the wrong tool, over torque, not using a clutch every time, poor fitment). I haven't damaged a single head since, and now I can understand why I used to have these problems. Even the cut-price softer headed ones seem to last almost indefinitely if you do it right.

I've driven thousands of phillips head screws in my life (construction), and cleanly operated a thousand more in machine applications, and you're partly right. Required torques vary, from driving a sheetrock screw into wood to the light torque required for machine screws. The size of the tool has to be properly mated to the size of the screw head for maximum engagement, and the fact that you can cover a wide range of sizes with a single driver size is sort of the problem. Phillips also requires increasingly heavy axial pressure as the torque increases. So unless you're rather disciplined and you bring your #1, #2, and #3 with you and swap accordingly, it's tempting to just use the tip of the #3 for your #2. If you don't do it, someone else is likely to. Once a screw head starts to round, the axial pressure required to engage increases, making it easier to damage it further.

I like the minimal axial pressure required to engage torx positively. I don't use a power driver on aircraft sheet metal fastening, but overtorque is probably a common culprit regardless. I have a feeling that if we still used flathead drive in aviation, there would be arguments against adopting phillips.

[tailwind]

The downside of stainless is that they tend to gall and twist off.

[jaredyates]

The downside of stainless is that they tend to gall and twist off.

This has proven to be a most-troublesome issue with the single screw that holds my Dynon D-180 in the panel. It's currently secured, but next time I need to remove it I'll have to snap the screw and hope for the best. At least for now it is an effective anti-theft measure.

[Zzz]

The downside of stainless is that they tend to gall and twist off.

Do you use cad-plated steel machine screws instead? I've never had much issue with stainless screws not holding up.

[Battson]

I like the minimal axial pressure required to engage torx positively. I don't use a power driver on aircraft sheet metal fastening, but overtorque is probably a common culprit regardless. I have a feeling that if we still used flathead drive in aviation, there would be arguments against adopting phillips.

Ironically, for me it's been quite the opposite story, I have found a power tool is part of the solution.

I know my clutch's torque settings, and select based on the application (screw size) to ensure I stopped over tightening.

I am also particular with my choice of bits, to ensure the perfect fit - like you say. Having a selection which go with the same tool has helped that problem too.

And probably my biggest one, if it doesn't go easy - don't force it. I always start the thread by hand now. If it locks up too tight, something is wrong. Maybe the nutplate was a reject, or maybe I crushed it, whatever it is. I run one of my taps through it, or realign the hole correctly, etc - the problem never comes back.

[whee]

My snowmobile is put together with torx screws and I cuss the engineers every time I work on it. My experience is much like Craig's; the bit wears then one slip on the screw and it is done, time to get out the drill. I've started swapping them for phillips where I can and where I can't I install a hex. My riding buddies have mostly done the same. The first thing one of my buddies does when he gets a new sled from the dealer is tear it apart to install mods and when he reassembles he tosses all the torx screws. In my opinion phillips screws are more tolerant of off axis drive than a torx and that is why I swap them out on the sled. It seems on mechanical things I never have clear access the to fasteners. On sheetmetal with clear access to the screws where you can ensure your not misaligned I could see using torx.

[Zzz]

Henry F. Phillips was from Portland, Oregon. I kinda feel bad now criticizing his design. Alas, conversion to torx is made difficult by the availability (and rumored quality) of the fasteners themselves.