Archery Arrow Nock Tester

Modern archery is a precision activity, yet there exists no non-subjective way of checking the arrow nock fit on the string. This Instructable attempts to address this by describing a gauge to measure nock fit. It is made with mostly recycled materials and a few simple common components.

It can be used during the initial build of arrows and strings to build the best arrows possible, and to monitor them in use.

1. Length of arrow 7mm in diameter, 200mm long
2. Length of arrow 7mm in diameter, 30mm long
3. Length of arrow 6mm in diameter, 200mm long
4. Length of arrow 6mm in diameter, 30mm long
5. Piece of bicycle inner tube 90mm x 30mm
6. Approx 250mm of 3mm shock cord (elastic cord)
7. Approx 60mm paracord

Also simple tools like cutting equipment, glue gun etc

Note that, in general, dimensions are not critical. The arrows can be of any diameter within reason providing that they are straight, that one fits inside the other and slides freely without being too 'rattly', and are not of micro-diameter. The 3mm shock cord (a type of very thin bungee) can in theory be of any elastic material that will fit inside the smaller arrow easily and is of the appropriate elasticity. The paracord can really be any string to hand and less is needed if the wrist loop is not added.

Archery arrows clip onto the bow string with a notch at the back called a nock. Archery is a precision sport which, for good scores demands repeatability. The fit of the nock on the string, and hence the force required for the arrow to release from the string, contributes to this repeatability.

Most modern arrows use a replaceable polycarbonate nock fitted to the back of the arrow. Nocks come in different designs and sizes, as do strings. Manufacturing processes introduce small variations. On top of this, both nocks and strings wear and degrade. This means that nock fit can vary from extremely tight to almost falling off.

The normal way to test nock fit is to fit the arrow to the bow string, point the arrow vertically downwards, and tap the string smartly a few inches away from the arrow. The arrow should release from the string with a smart tap. This is very subjective. We should be able to do better.

This instructable constructs a simple gauge to measure the force needed to release the nock from the string.

What we are doing is building a very weak spring balance with a fitting on the end to attach to an arrow.

The construction is very simple. Two lengths of arrows are used, one sliding inside the other. The diameters are not really important as long as the smaller one slides easily inside the larger without being excessively rattly. In addition, micro-diameter arrows are not recommended as the construction gets too delicate and prone to binding. A diameter of around 7mm seems to work well. The smaller diameter arrow length is placed inside the larger. A piece of elastic is passed through the middle and attached to the smaller arrow at one end and to the big arrow at the other. I found that 3mm shock cord worked well but other elastic would undoubtedly work. The shock cord is attached by jamming it in position using short lengths of arrows; a small piece of arrow inside the large piece and a large piece of arrow outside the small piece. Refer to the construction cross section; the diagram is reduced in length for ease of reference.

The result is two telescoping lengths of arrow with end pieces and elastic running down the middle. And as stated earlier, it is basically a very weak spring balance.

A single length of paracord is attached to one end to attached to the other and a wrist loop to the other. The easiest attachment method is to push the ends of the paracord into the arrow and add a spot of hot melt but it is recommended that a temporary method of attachment is used until calibration is completed (see later) in case the gauge has to be disassembled and adjusted.

A piece of bicycle inner tube is used to attach the arrow to the gauge. The tube should be around 90mm x 30mm with two holes approximately 8mm diameter near the ends. One end of the tube is fed through the opposite hole to form a loop; the other hole is tied to the paracord. As long as the rubber is clean (it should be washed with dish-washing liquid before construction to remove the talc, and occasionally afterwards) the loop will grip an arrow easily.

To use the gauge an arrow should be placed in the inner tube loop and the loop snugged down if necessary.

The arrow should then be fitted to the bow and the arrow nocked to the string.

The arrow should then be pulled from the string by pulling on the gauge gently. The graduations on the gauge should be watched (see calibration section later) and if the gauge is in the red when the nock releases then the nock should be replaced and the old nock discarded. If too many nocks fail then the string centre section should be inspected for wear, or the string and/or nock size reconsidered.

A glove should be used during testing if sharp arrow points are used.

The gauge must be calibrated before first use.

To calibrate, place about twelve evenly spaced, easily visible marks on the inner arrow tube (for example using a paint pen). Then, take a selection of arrows or nocks and test them in turn, recording the number of marks passed before each nock releases.

The pictures show some real calibration results. The bulk of the nocks were in 5 -10. Nocks 4 and below and 11 and above were suspect.

It may be that you are unlucky and your good nocks are not nicely spread in the middle of the gauge. If this is the case then you may need to disassemble the gauge and reassemble it with a little more (or less) tension in the elastic. If this does not work then you may need to try elastic of a different strength.

Once the calibration is complete the gauge can be permanently glued up. If you do glue the paracord inside the tubes be careful not to get glue on the elastic. You can also tidy the ends with shrink-down tubing.

Finally repeat the calibration in case the final glue-up alters the readings of the gauge. You can simply continue to use the calibration marks but I recommend painting the inner arrow tube red in the nock rejection areas (in my case 1-4 and 11-12). In most cases when testing a simple, easy to read ok/fail result is all that is needed.

There are a couple of potential problems to be aware of. If your arrows are too thin or your elastic too thick then binding can occur and the gauge not operate smoothly. A second potential problem is that if cotton covered elastic is used then it has the feature of stretching a certain length and no further; it comes to a hard stop when the cotton is fully extended. If this happens the gauge will misread.

It is undeniable that too tight a nock fit affects arrow flight. If all are too tight then speed is robbed from the arrows and if only some are too tight then these arrows will not group with the others.

The consequences of too slack a nock fit are potentially much worse. If an arrow falls from a string during the shot then the energy in the bow has nowhere to go and can destroy the bow. This has happened to me.

Sudden loose nock fit can also be a warning of cracking nocks.

Archers have been using the string tapping method for many years successfully. If this is you and you are happy with the method then this tool is not for you. If you are looking for a method for assessing nock fit that is less subjective then this tool may be for you. And it won't cost you much - most archers have old arrows and string lying around and the most that it is likely to cost is for a few feet of elastic.