Heddles attach your shedding device (which raises and lowers warp threads) to your warp. We sell pre-made Texsolv heddles, but you can also make your own. You can learn more about heddles and the Mirrix shedding device here.
The concept of putting on heddles is fairly straightforward, but there are a lot of chances to make mistakes when putting them on. It is important to pay attention to what you are doing and keep checking to make sure you aren't making mistakes, as one mistake can make it so your shedding device does not work properly.
Heddles go on every-other warp thread on the top of your shedding device and then the shedding device is flipped over and heddles are put on the warp threads that do not have heddles (again, going on every other heddle.)
Below we've gone over some common mistakes people make when putting on heddles.
This is probably the most common mistake made by beginners, but one that is easy to prevent. Make sure you do not skip a warp threads that needs a heddle and then go back and put a heddle on out of order. This will cause your heddles to cross.
Heddle on Two Warp Threads
This is an easy one to do if you aren't paying close attention. It is a good idea to go back and check periodically when you are putting heddles on to make sure you haven't accidentally put one heddle around two warp threads. If you do, it will get your heddle placement out of order. For example, if you were supposed to put heddles on warps 1, 3, 5, etc. and you put them on 1, 3 and 4, you will put the next one on warp 6, the even warps, which will be the same as what the other side is doing. It's very easy to make this mistake, so look carefully at each heddle/warp thread before you move on to the next.
Heddle on the Wrong Warp Thread
Sometimes when putting on heddles, you accidentally skip one and continue putting your heddles on incorrect warp threads. This will cause you to have two heddles (top and bottom) on the same warp thread (just like putting one heddle on two warp threads will do.) You may also simply miss putting a heddle on a warp thread, but continue putting your heddles on correctly. Either way, you will need to go back and fix the mistake.
We see this a lot when people are having trouble getting their shedding device to work. You've made sure your heddles are put on correctly, but why are you having trouble getting a good shed? The answer is usually that the heddles are tangled or crossing one another. They need to be facing all in the same direction and not rubbing up against each other. When they are tangled, they can prevent you from getting a good shed.
This is how heddles should look when they are organized. See how all the tails are on the side of the bar facing you? That is where they should be!
The lesson here is simple: Be careful. Don't try to watch television or have a conversation when you're putting on your heddles. Concentrate, and check often that you're doing everything right. If you do that, you won't have any problems and won't have to go back and troubleshoot!