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| Issue 32 (February 2009) |
Words: Jim Innes |
Undesired things occasionally happen in this hobby; helis crash, pilots make mistakes, and components occasionally fail in flight. Stay in the hobby long enough and you will probably experience them all. One of those things that can quickly ruin a flying day is stripping out or busting the head off a bolt or screw. The good news is that, in most cases, a broken fastener can be removed without damaging the heli.
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Stripped bolts are easy
If you only stripped a screw or bolt, you are in luck; these can be easily removed. With a stripped Phillips head screw, your best bet is to either grip the head of the bolt with a set of Vice Grips™ and spin it out, or use the cutting wheel on your rotary tool and cut a slot in the head. You can then use a standard slotted screwdriver to remove the screw.
A stripped hex head bolt can be removed using the above two methods as well. You can also try forcing a slightly larger hex driver into the stripped bolt, for example a 1/16" hex driver works well in stripped out 1.5mm bolts.
As a last resort with stripped bolts and screws, you can choose to drill/cut the head off the fastener and then remove the component it was attached to. This should leave some amount of the threaded portion of the bolt exposed. Use a set of Vice Grips™ (aka locking pliers) to grab this portion and slowly back it out.
So you broke off a screw...
Sometimes the entire head of a fastener will break off, leaving the threaded portion completely inside the component. What are you to do in this situation? Do you just throw away the part and buy a new one? This is certainly an option, and for cheaper parts it may even be the best solution. However, if you want to try and reuse the existing part, there are ways to remove the bolt.
Removal Method One: The screw extractor set or left-handed drill bit
The most common tool for removing broken bolts is called a screw extractor or "easy out". A screw extractor is basically reverse threaded cone that is used to grab the bolt from the inside and back it out. I have found that the Alden Micro Drill-Out extractor set works quite well for the common M3 to M5 sized bolts on most model helicopters. It can be found at Sears, Ace, or other hardware stores.
To use an extractor you must first drill a hole in the center of the broken bolt. The size of the hole made will depend on the size of the extractor used. This step is very crucial, the hole must be well centered and straight down without removing too much of the bolt material. Once the hole is made, insert the extractor into the hole and slowly turn it counter-clockwise to loosen the bolt. Add some heat to loosen any thread lock if needed.
You must be very careful using an extractor. They are made of very hard metal and can be quite brittle. Turn slowly and keep the extractor straight, since any side-to-side pressure could break it. If the bolt will not budge with moderate pressure do not force it. If you break the extractor off inside the bolt, you will probably have to replace the affected part entirely.
There are also a number of left-handed drill bits out there that combine the drilling and extracting tools. You turn the bit counterclockwise into the center of the bolt with your drill. As it drills into the material, the bit grabs the bolt and starts to back it out. I have never personally been able to remove a fastener with just a left-handed drill bit, but have talked with others that have had success with them.
Removal Method Two: JB Weld
If you do not have an extractor set, or if the bolt is in an area where drilling into it may not be feasible, you can try the JB Weld method. Simply take some JB Weld and glue the end of a new bolt to the broken off portion left in the component. Be sure to allow the JB Weld to touch only the bolts, wipe it off the threads or other areas. Set the part aside to dry overnight. Once it is dry, you can use a hex driver to remove the joined bolts. This method only works well on bolts that are not too tight.
Removal Method Three: The Rotary Tool and screwdriver
This is the fast and dirty method of removing a broken off fastener. Take a rotary tool cutoff wheel and grind it down until the wheel is very small in diameter, the smaller the better in the case of a M3 bolt. Now, take that small cutting wheel and cut a slot right into the top middle of the broken fastener. With this method, you may end up cutting into the component a little bit, so only do this where the loss of a little material won't affect the performance of the part. Use a small slotted screwdriver to remove the bolt from the hole. Again, apply heat if needed to free the part first.
If Nothing Works
If you find yourself with a broken bolt still stuck in your heli after trying the above methods, you have a few more options. You could just trash the part, pat yourself on the back for the effort, and buy a new one. If it's an expensive part you could take it to a machine shop to have the fastener removed professionally. As a third option, drill the entire bolt out and install a Helicoil thread repair kit that creates a new set of threads for a bolt to be fastened to. ]
Even better than any of the above methods is doing what you can to minimize the chances of having a broken fastener in the first place.
Avoiding stripped screws and bolts is easy - use the proper tools. Most of the Phillips screws found on model helicopters are not standard Phillips design; they are manufactured to the JIS (Japanese Industrial Standard) specifications. Get yourself a good set of JIS screwdrivers and you will be amazed by how well they fit.
Hex wrenches vary greatly in their true sizes and quality. Buy a good set of wrenches that fit tightly into the bolts, you do not want a lot of play in-between the wrench and bolt. A tightly fitting set of wrenches greatly minimizes the chances of stripping bolts out.
To avoid breaking bolts off remember these four rules:
1. Only tighten things as tight as they need to be to do their job, any more than that just stresses the fastener.
2. If you question the quality of any fastener, replace it.
3. Anytime you crash, check out all the fasteners on the helicopter. Even a slight bend in a bolt greatly weakens it.
4. And last, use the proper type of thread lock for each joint and only use a small amount. Remember that thread lock, in general, is not used to hold the components together; it simply is there to keep the fasteners from backing out.
Conclusion
Chances are that at some point in your RC heli journey you will run into a broken fastener that needs extracting. With a little patience and care, you can get these stubborn bolts to break free from your model without causing any damage. While a broken bolt is never a welcome experience, with the right tools and methods you can make short work of the repair job and get your model back into the air. See you at the field!
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