Maintaining your crossbow involves checking for subtle changes in its body that could lead to future damage, as well as waxing the strings and cables and lubricating the rail. Doing so will prevent serious damage to both the weapon and the shooter and will prolong the product's life.
Each time you take out your crossbow for hunting or target shooting, it is recommended to check it for structural changes. These might be:
1. Tiny splinters on the limbs. Run your fingers along the limbs so you can feel any fibers that have popped out or other irregularities. Any of these could be a sign that the limb might crack so do not shoot the crossbow, but take it to an archery shop.
2. Cams - are they properly seeded and is there anything else with them that looks out of place? Do they rotate freely? Cams are a delicate part so if you have a compound crossbow, you'd probably want to pay extra attention to those.
3. Screws that keep the different parts of the crossbow together - are they tight and secure? Pay special attention to the screws that connect the bow (limbs) to the stock and those that connect the stirrup. You don't want the stirrup to pull free while cocking your crossbow!
Needless to say, you need to tighten up any loose screws.
4. Bow strings (and cables in case of a compound crossbow) - look for fraying and other signs of wearing like thinning or snags.
5. That includes the servings as well - these are the covered parts of the strings that come in contact with other parts of the crossbow (rail, cams, etc.). Make sure they are in good condition as well and don't have flattened sections or rips.
6. Is the rail clean and its groove free of dirt and debris?
7. Test the retainer. Does it hold the arrow securely on the rail? Even if you point the crossbow downwards? If it doesn't work like before, just buy a replacement.
8. While at it, you might want to check all of your arrows as well.
Strings are the twisted 2-color material, and the servings are the (usually) black covers that are wrapped over the strings.
Note that you can't do much to improve the condition of a serving, so if you notice they are getting worn out, you should take your crossbow to an archery shop to take it off and replace it.
Every 30-50 shots you should wax the string to keep in in good condition and extend its life. It is put under immense pressure during the time your crossbow is cocked and wax would prevent it from getting stretched.
Also, keeping the string well waxed would ensure consistent performance as a dry string won't behave the exact same way and you may wonder why your shots land a bit off.
Apart from the purely visual inspection, another way to tell if the crossbow string needs waxing is to touch it. Does it feel sticky? If it's dry, then it's time to reapply some wax.
If you notice too much fraying of the fibers in the string just by looking at it, then it's probably time to replace it.
It is best to follow your crossbow manufacturer's recommendations when shopping for string wax. You should be able to find the needed info on their website.
Simply apply some of the product on the string and then rub it in with your fingers. The wax will melt from the heat of your fingers and that would help it "soak" into the fibers and form a protective layer on the surface.
For recurve crossbows, wax the string, including the whiskers - the part where the string is tied to the limbs.
Compound crossbows have "cables" in addition to the main string - make sure to wax them too.
... Unless it's a product, made specifically for servings or the crossbow manufacturer itself recommends doing it. But considering the serving is made of a different type of material, you should be cautious and get yourself informed first.
Also, the center serving goes all the way into the trigger box when the crossbow is cocked and wax most likely doesn't belong there. With time, it would attract dust and dirt and you'd have to clean it as it might start affecting the overall performance of the weapon.
But again - consult with the manufacturer documentation and act accordingly!
The center serving actually gets lubricated when it slides along the rail. Provided you have lubricated the rail beforehand.
Rail is the part of the crossbow on which the arrow slides down when you pull the trigger. The string is in contact with the rail all the time so you would want to lubricate that surface to ensure smooth movement.
If it is dry, the friction between the string and the rail would slow down the string/arrow movement, thus affecting the speed and accuracy in a negative way. Plus, it would wear out the serving quicker.
Products for lubricating ("lubes") usually have an applicator on their top so you just put a dab on each side of the groove. Then simply smooth it over the rail length with your finger.
You can lift up the string and get some lube under the serving too.
Warning! Do not put much of the lubricant and make sure it is well spread. Excess lubricant may build up on the serving and then go onto the arrow nocks and into the shooting mechanism.
Once or twice a year you should thoroughly clean the crossbow. At least do that after the end of the hunting season and before storing it.
Use wipes to remove the dirt and debris from all surfaces - everywhere you can reach. Use compressed air for all the places you cannot reach - the trigger mechanism, the flight groove on the rail, around the scope, etc. Blow out all dust and debris that have accumulated there.
Clean the scope lenses with wipes that are made specifically for that purpose.
After cleaning the crossbow, it's a great idea to oil up all the metal nuts and bolts and all the crannies, including the safety mechanism and the trigger assembly.
Which crossbow oil product to use? Just check what your crossbow manufacturer sells or recommends.
Cams on a compound crossbow are those wheels at the end of the limbs. When you pull the string to cock, the cams rotate until they are stopped by the cables.
It is said that the cams are in sync if they touch the cables at the same time. Some of the modern crossbows have visual indicators to signal when they are out of sync.
The cam timing is set by adjusting the cables.
Can you do that by yourself? No, unless you have a crossbow press. The string and the cables of a compound crossbow are at a considerable constant pressure and you cannot do anything before releasing them.
If you do have a press, then you'd use it to squeeze the limbs until the cables are released. Then you can adjust them.
No press? Take your crossbow to the nearest archery shop.
The arrows can get bent, specially if they are made of aluminum or wood. And bent arrows don't fly straight.
You can check if an arrow is straight by rolling it into an arrow spinner.
Also, you'd want to make sure the arrows are in good overall shape as well. Look for cracks and splinters. Pay special attention to the end of the arrow - the area where the nock is.
If you try to shoot a damaged arrow, it may shatter before it's left the rail, i.e. - in your face.
Check the fletchings (also called "vanes") as well. They can be replaced in an archery shop if they don't look in good condition anymore.
Aside from the listed instructions, the manufacturer of your crossbow may have specific recommendations on how to maintain it. Don't forget to check the product manual and see if that's the case for your model.
And that's basically it about maintaining a crossbow. As they say, take care of your equipment and it would take care of you!