Best way to use a torque driver?

[ZAxis]

We run a DJI S1000 and with an eye on upcoming changes in UK operating permissions, I've invested in a set of adjustable torque wrenches so that frame components can be tightened in place correctly to defined and recordable values. These values do not yet exist apart from DJI's statement that folding props should be tightened to 0.4Nm. Can anyone suggest what would be appropriate values for the likes of frame components, motor mounts, etc? Of course, items will also be lock tighted as a final action.
On the matter of the 0.4Nm values suggested by DJI it does seem to make the folding props feel much tighter than the factory set tightness. Can any one comment on this?
The wrenches are high quality Wera items sourced from a reputable dealer.

andy

 

[Carapau]

Hi Andy, I have been building helis for a few years now and if lock tight is used then finger tight works very well in my experience. So if torque data is not available I would work out what torque value for finger tight is- or whatever you feel happy with and then use that figure on your screws from there. Well, those are my thoughts at least.

 

[Old Man]

Hopefully you meant Wiha when you referenced Wera? Wiha makes some very, very good torque screwdrivers that more than likely already meet all our needs without reinventing the wheel. They are used in a great many small component situations where larger tools just won't do. Check the published torque values for those items that need secured to determine if the established torque value is a "wet" or "dry" value. If a torque value is was established "dry" the use of a liquid fastening agent such as a thread locker can significantly alter the value the tool provides when set to the published value. That discrepancy is greatest with small fasteners.

Also requiring some understanding is the type of thread lock compound used. Use the wrong type and you will strip out the hex head of most Chinese fasteners long before you break the bond. This happens often when stainless steel fasteners are used for propeller screws on large RC gas engines as well. Recognize that metric fasteners, having a finer thread pitch, can often be secured with compounds that can be applied after being set with a torque value because those particular compounds have the ability to wick into the threads if an open end of the fastener is available for contact.

Anything that is subjected to vibration requires additional security above and beyond a lock washer. Some Nyloc type fasteners benefit as well but they become a one time use nut when a thread lock compound is used on them. For aviation purposes even the Mil Spec Nyloc nuts are typically items used three times or less, even without a thread lock compound. If a safety wire is impractical, use a thread lock compound. If a torque value is provided by a manufacturer, use it.

 

[Tuomas P.]

Havent had my hands on the S1000, but all screws on my fleet are pretty much M3. So I guess the tightening goes along what they can take. For 3D helis I use theadlock all around but in the multis mostly on prop adapter fastening bolts. For specific torque, ok, if the manufacturer has a black on white on them, good. But its basically also common sense, the screws are either tight enough, or fall off...
TP.

 

[ZAxis]

Thanks for the interesting answers guys.
Looks like it's a case of just figuring out a value by trial and error and duplicating it elsewhere to get consistency. Not forgetting to correctly lock tight it as well.

andy

 

[Ronan]

Which loctite do you guys use? I recently moved and can't find my tube. Went to the hardware store and the tubes all look different now! I was using the blue one but there's now 5 blue one's, 5 red one's, and 3 yellow... @_@

 

[Carapau]

Medium strength is the stuff.

 

[ZAxis]

We've been using Loctite 222 (purple), low strength.

 

[Old Man]

Depends on what the fastener is and where it is. Med strength blue is good most of the time but small metric fasteners work very well with the thin green since it wicks in after the screws are tightened. Bear in mind there is a green sleeve lock compound that you never ever use on anything you may want to take apart again without using lots of heat. There are a couple of blue varieties that are very high torque break away as well. Red is usually for high temp installations. I could look up all the part numbers but I'll be lazy and simply say read the label on the bottle!!

Actual screw torque is established by the type of material and size of screw. You can locate that information by Googling "screw torque chart metric" to review and obtain charts that list fastener sizes, type of material they are made of, and torque values. Be advised those torque values are predicated on the screw or bolt itself and do not factor in the material the screw is securing. If you are using a screw with a high torque value to secure a soft material the screw torque may be high enough to compress and/or damage the material is it securing. This has happened a lot with screws used to secure wood propellers, ruining a great many propellers. If in doubt, try a test fit and tighten the fastener on some test material to determine if the torque value would be achieved before compressing the material being secured. If not then the published torque value will not work and a thread lock compound becomes even more important. Only use enough of the stuff to get the last 1/8" to 1/4" of the threaded portion of the screw wet. No need to load the stuff on because it's purpose is to fill the gaps between screw and hole thread pitches. Screws are normally only tight on the tension side of the threads and the compound fills the other side of the threads.

 

[R_Lefebvre]

Wow, some nice tech there Old Man, good stuff. I did an internship in naval engineering, specializing in bolted joints. And then did some at Ford as well. You're right on.

Exactly which product number are you referring to with the green Loctite? I've never heard of that one. I do have green bearing compound though... need to keep it in a special place to avoid mixup.

 

[ZAxis]

This thread is turning in to a mine of information, excellent!
This is a link to the LocTite catalogue, could be useful...http://hybris.cms.henkel.com/medias/sys_master/catalogsync/8802960932894.pdf

 

[Old Man]

Wow, some nice tech there Old Man, good stuff. I did an internship in naval engineering, specializing in bolted joints. And then did some at Ford as well. You're right on.

Exactly which product number are you referring to with the green Loctite? I've never heard of that one. I do have green bearing compound though... need to keep it in a special place to avoid mixup.

Thank you sir. With the Permatex brand the product name is "Threadlocker Green". I'd have to look up the Locktight P/N. Permatex also makes a "Threadlocker Purple", intended for carburetor work, that has a 6inlb breakaway. Works great for m2 sized screws. Your bearing compound is the same as the sleeve lock compound and once dry requires a considerable amount of heat to release. Some of the RC hobby gas engine manufacturers use the stuff to fill the gaps left over from lousy machining tolerances and poorly trained labor. Also works well when assisting retention of taper fit components like propeller hubs to crankshafts.

There are numerous brands of thread lock compounds but the three most effective in their documentation are Locktite, Permatex, and Permabond. They all "color code" their products but the colors are not all similar in their use applications. For instance the Locktite red is intended for high retention strength with large coarse threads or high temp applications while one of the Permabond products that is blue in color is for the same purpose. The Permabond is actually a bit better than the Locktite red because it has broader applicability. Permabond and some of the others have a marked shelf life that one should pay attention to.

That's why reading the label, and even better, visiting a manufacturer's website and reading through the application charts can be extremely useful. Thread lock compounds are tailored to specific applications and color alone won't always be the guide for what should be used. If one is using a thread lock compound on screws that will periodically be removed and re-inserted they need to invest in a bottoming tap and a die to clean the screw and boss threads. Compounds foul threads with the first application and not cleaning things up before replacing a screw blows any tool torque settings out of the water. You will never know what torque value was achieved when setting screws in threads that have been subjected to applications of compound without cleaning between applications.

 

[MombasaFlash]

We run a DJI S1000 and with an eye on upcoming changes in UK operating permissions, ...

Excuse the slight change in direction but .... what changes and where is this info published?
Where are the goal posts going to this time?
Will we ever be able to stay ahead of the ever-changing regulations now that the UAV is firmly within the nanny's grasp?

 

[Carapau]

The CAA are tightening up permissions to fly in urban areas or 'congested areas' (CA) as it is officially known. In short they are wanting operators to provide a much more detailed safety case for the aircraft they wish to use in CAs so that the CAA can better evaluate both the aircraft, AND the operator (for aircraft over 7kg). The actual details are being worked on as we speak so you wont find many details out there bar their information notice which you can find on their web. The reason is twofold- firstly the CAA hasnt got the manpower to deal with the current system whereby every time you want to fly in a CA you have to ask for specific permission. Secondly, the quality of these requests has divebombed as the number of those asking increases. Im actually very pro the CAA as they are genuinely taking a minimalistic and proportional approach to the risks posed by RPAS/UAV/Drones etc.

 

[MombasaFlash]

And this includes screw torques? They may as well outlaw radio connectors whilst they are at it.

I am not against the whole CAA approval. My initial horror was soon replaced by the realisation that it would go a long way towards clearing the skies of idiots but it is clear that there is still a long way to go, given that the basic premise is to treat UAV's almost the same as full size aircraft, not least in matters related to airworthiness.

If all UAV's were homologated factory RTF products, rather than homebuilt, they would be much happier. Although, having said that, I have been quite taken aback to discover the sizable number of MR operators that don't even build the aircraft they fly, relying on builders to assemble their aircraft.

 

[jes1111]

Great info here - @Old Man is right on the money.

If I may add a few of my own observations:

- Totally agree with Wiha tools as the place to go for torque screwdrivers (but then I would, I'm a dealer for them)

- It's worth emphasizing that "material matters" - aluminium, steel, stainless steel, titanium, polycarbonate, nylon, glass-filled nylon - all will have widely different target torque values [EDIT: - and they will require different threadlocking compounds (or none at all)]. Proceed with caution!

- Threadlockers work on metal/metal contact - they do NOT work on metal/plastic or plastic/plastic joints. In fact, great care must be taken with threadlocking compound and plastic - there's a good chance of "incompatibility": the compound can attack the plastic and cause it to go brittle. Best call your nearest Loctite helpline or, if in doubt, stick to a nyloc.

- A good alternative for critical applications is all-metal locking nuts.

- Another good practice is to use a "marker" such as coloured nail varnish - after the joint is torqued, apply a small dab to the screw/nut join. Once dry it will help resist the nut turning but, more importantly, allows an easy visual inspection during your pre-flight - it will be obvious if the nut has moved.

- If the material you are clamping is soft, washers under the screw head and the nut will spread the pressure. This can also be a good time to use two nuts - tighten the first one down as much as you dare onto the soft material, then "lock" that one by torquing the second one onto the first one (held stationary) to the maximum allowed for the screw material (with locking compound for good measure).

- For critical metal/plastic joints, I was given a great tip by a Loctite engineer - some heavy-duty compounds have a "matching" accelerator. Assuming you've checked the compatibility of the compound with the plastic, spray some accelerator into the threaded hole and apply the threadlocker to the screw - the accelerator will cause the compound to harden and fill the non-contact side of the thread (see Old Man's explanation above) and effectively lock it. If you need to undo the joint it requires little additional torque to break up the brittle dried compound. I've done this myself with stainless screws into tapped Delrin (which is highly resistant to anything sticking to it).

- Given the complexities and dangers of using threadlocking compounds, I've stuck to using nylocs and a marker whenever possible - much simpler.

- Final thought - whatever method you use, nothing removes the need for regular inspection

 

[Old Man]

Good info jes1111/ If I might add for the fingernail polish trick. one can purchase "witness paint" AKA "torque stripe", for this task from places like Mcmaster-Carr and other well rounded hardware vendors. It's designed specifically for the task of providing an easy to see verification that fasteners are still secure.

MombasaFlash,

You should, IMO, anticipate that not very far down the road governments are going to mandate our aircraft meet all the same test and safety standards that manned aircraft have to meet to achieve certification. In the U.S. AOPA, the Airplane Owners and Pilots Association, has already made suggestions to this effect in their membership magazine. The price for what we need to fly will become unaffordable at that point. This is something that was also brought up during the original FAA ARC committee discussions back in 2007. Those regulations may occur incrementally or all at once, but I expect the mandates will be upon us eventually.

 

[jes1111]

- "witness paint" - that's the official name I couldn't remember - thanks

Forgot to add one point - as Old Man says, small hex socket screws are prone to rounding out the socket (particularly cheapo China ones and particularly if you use cheap tools). I greatly prefer Torx head fasteners - harder to find the tools (Wiha has a full range) but they take torque much better than hex. If you do the sensible thing and discard the bag of fasteners that comes with a China-made kit, replace them with Torx

 

[MombasaFlash]

... not very far down the road governments are going to mandate our aircraft meet all the same test and safety standards that manned aircraft have to meet to achieve certification....

Of that I have little doubt!

 

[jes1111]

You should, IMO, anticipate that not very far down the road governments are going to mandate our aircraft meet all the same test and safety standards that manned aircraft have to meet to achieve certification. In the U.S. AOPA, the Airplane Owners and Pilots Association, has already made suggestions to this effect in their membership magazine. The price for what we need to fly will become unaffordable at that point. This is something that was also brought up during the original FAA ARC committee discussions back in 2007. Those regulations may occur incrementally or all at once, but I expect the mandates will be upon us eventually.

IMO, there will always be a lower weight limit for this - the authorities will never have sufficient processing capacity (or will) to impose it on all aircraft. There is still opportunity to shape and guide the policy, especially in making sure that it is fair and workable - viz. the recent discussion in this thread on the UK CAA's illogical and inconsistent treatment of weight divisions.