Shear pins are used to temporarily hold sections of the rocket together until the ejection charges within the rocket blow them apart. They are often needed on high power rockets because the sections can separate prematurely due to the air pressure differences within the rocket.
When the rocket is on the ground, the air pressure outside the rocket is equal to the air pressure on the inside. After launch, when the rocket ascends into the sky, the air pressure surrounding the rocket decreases. At this point, the air inside the rocket is greater than the external pressure, and the nose of the rocket wants to pop off. The only thing holding it on is the friction of the shoulder inside the tube of the rocket. This is fine for most rockets.
According to an archive of www.RocketMaterials.org, three of these nylon shear pins in a rocket require a force of 64.24 pounds to cut in half. This force comes from your ejection charge. It pressurizes the rocket pushing the sections apart. Not only does it need to overcome the shear pins, but also the inertia of the sections and any friction of the coupler joining the sections together. When using shear pins, you'll want to use a minimal amount of friction, so that you can more easily determine how much BP to use for the ejection charge.
Assemble your rocket. Using a permanent marker, draw two "witness marks" across the joint where the rocket will separate. These lines will allow you to align the holes easier between flights.
Drill three 1/16-inch diameter holes around the perimeter of the rocket. The holes should go through the outside tube and the shoulder of the mating part.
If the tube and shoulder are made from a hard material, like fiberglass, phenolic, or Blue Tube, you may want to use a #2 tap to create threads in the holes. This will allow you to install the nylon shear pin screws easier.
On paper tubes, like the LOC high-power tubes, put a drop of CA glue in the holes to stiffen up the edges of the hole. Redrill the holes if necessary.
Insert the nylon shear pin screws into the holes, and simply screw them in place.
The shear pins are a one-flight part, and will need to be replaced between launches.
After the flight, you can unscrew the outer portion of the sheared-off nylon screw. The inner portion, stuck in the shoulder of the joining part, will need to be removed by re-drilling the hole.
This video, from our how-to series, will show you how to install a shear pin in a fiberglass airframe.
In the video shown below, you'll see a quick-and-dirty ejection charge test on a high power rocket.
Why perform an ejection charge test?
The main reason is to make sure you have enough black-powder in the ejection charge to separate the rocket and kick out the parachute. A lot of high power rockets use shear pins to hold the rocket together to prevent premature separation while the rocket is still ascending. The ejection charge must be strong enough to break those pins when it is time for the parachute to pop out.
Performing this test also verifies that your electronics is configured properly.
Yes. Shear pins can be used in paper tube rockets. But after some time, the holes may deform. In that case, you will want to repair the holes using the steps shown in the video below.
| Product | P/N | Qty/ Pack | I.D. | O.D. | Length | Dia. | Weight | Capacity. | Material | Fits Part | Price | Buy Now! |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Vacuum-Formed Canopy PNC-56A | 18901 | 1 | -- | -- | 6.625" (16.828cm) |
1.68" (42.7mm) |
0.198oz (5.6g) |
-- | Polystyrene | #20070 | $8.30 |
|
| Large 4-40 Nylon Shear Pins - 20 pack | 29632 | 1 | -- | -- | -- | -- | 0.003oz (0.08g) |
-- | Nylon (White) | -- | $6.37 |
|
| Removable Plastic Rivets | 13076 | 10 | -- | 0.16" (4mm) |
-- | -- | 0.006oz (0.18g) |
-- | -- | -- | $7.78 |
|
| 4-40 Vindicoat Aluminum Fastener Inserts | 13074 | 3 | -- | -- | -- | -- | 0.026oz (0.73g) |
-- | Aluminum | -- | $17.45 |
|
| 6-32 Vindicoat Aluminum Fastener Inserts | 13078 | 3 | -- | -- | -- | -- | 0.047oz (1.33g) |
-- | Aluminum | -- | $19.04 |
|
| 2-56 Vindicoat Aluminum Fastener Inserts | 13094 | 3 | -- | -- | -- | -- | 0.011oz (0.3g) |
-- | Aluminum | -- | $15.86 |
|
| 1/4" Quick Link | 29621 | 1 | -- | -- | -- | -- | 1.273oz (36.1g) |
880 lb (399.2 kg) | -- | -- | $4.69 |
|
| Camera Hood for 2.6"/BT-80 Dia Tubes (WHITE) | 18915 | 1 | -- | -- | 4.3" (10.922cm) |
1.87" (47.5mm) |
0.148oz (4.2g) |
-- | Polystyrene | #10198 #10199 #11013 #10503 |
$5.91 |
|
| 1/8" Quick Link | 29620 | 1 | -- | -- | -- | -- | 0.3oz (8.5g) |
220 lb (99.8 kg) | -- | -- | $4.06 |
|
| Camera Hood for 1.6"/BT-60 Size Tubes (WHITE) | 18911 | 1 | -- | -- | 4.103" (10.422cm) |
1.532" (38.9mm) |
0.162oz (4.6g) |
-- | Polystyrene | #10148 #10141 |
$5.91 |
|
| Helicopter Hinges | 24033 | 3 | -- | -- | 1.065" (27.1mm) |
0.43" (10.9mm) |
0.008oz (0.22g) |
-- | Nylon | #05017 | $4.04 |
|
| Camera Hood for 2.2"/BT-70 Size Tubes (WHITE) | 18913 | 1 | -- | -- | 1.786" (45.4mm) |
4.252" (10.8cm) |
0.148oz (4.2g) |
-- | Polystyrene | #10164 #10168 |
$5.91 |
|
| 1/4" Round Lifting Eye Nut (2/pk) | 29640 | 1 | 0.67" (17mm) |
1.07" (27mm) |
-- | -- | 0.48oz (13.6g) |
-- | Stainless Steel | -- | $11.54 |
|
| Small Screw Eye | 29611 | 10 | -- | -- | -- | -- | 0.026oz (0.73g) |
-- | Steel, Zinc coated | -- | $3.45 |
|
| Camera Hood for 3"/75mm Dia Tubes (WHITE) | 18917 | 1 | -- | -- | 4.2" (10.668cm) |
1.75" (44.5mm) |
0.148oz (4.2g) |
-- | Polystyrene | #10202 #10204 #11017 |
$5.91 |
|
| Threaded Brass Insert - 6 pack | 29613 | 6 | -- | -- | 0.375" (9.5mm) |
-- | 0.073oz (2.06g) |
-- | Brass | -- | $15.32 |
|
| Camera Hood for 4"/98mm Dia Tubes (WHITE) | 18919 | 1 | -- | -- | 4.28" (10.871cm) |
1.77" (45mm) |
0.173oz (4.9g) |
-- | Polystyrene | #11021 #10505 |
$5.91 |
|
| Small Nylon Shear Pins - 20 pack | 29615 | 20 | -- | -- | -- | -- | 0.001oz (0.02g) |
-- | Nylon (black) | -- | $3.70 |
|
| Camera Hood for 2.2"/BT-70 Size Tubes (CLEAR) | 18923 | 1 | -- | -- | 4.242" (10.775cm) |
1.786" (45.4mm) |
0.194oz (5.5g) |
-- | Polyethylene | #10164 #10168 |
$11.81 |
|
| 1/4-inch Forged Eye Bolt | 29623 | 1 | 0.5" (12.7mm) |
1" (25mm) |
3" (76.2mm) |
0.25" (6.4mm) |
1.058oz (30g) |
-- | Steel, Zinc coated | -- | $6.57 |
|
| Camera Hood for 1.6"/BT-60 Size Tubes (CLEAR) | 18921 | 1 | -- | -- | 4.103" (10.422cm) |
1.532" (38.9mm) |
0.162oz (4.6g) |
-- | Clear Polyethylene | #10148 #10141 |
$11.81 |
|
| Altimeter Mounting Posts | 13084 | 1 | -- | -- | -- | -- | -- | -- | -- | -- | $6.03 |
|
| Camera Hood for 2.6"/BT-80 Dia Tubes (CLEAR) | 18925 | 1 | -- | -- | 4.3" (10.922cm) |
1.869" (47.5mm) |
0.194oz (5.5g) |
-- | Polyethylene | #10198 #10199 #11013 #10503 |
$11.81 |
|
| Brass Screws | 13082 | 1 | -- | -- | -- | -- | -- | -- | -- | -- | $1.84 |
|
| Camera Hood for 3"/75mm Dia Tubes (CLEAR) | 18927 | 1 | -- | -- | 4.2" (10.668cm) |
1.75" (44.5mm) |
0.194oz (5.5g) |
-- | Polyethylene | #10202 #10204 #11017 |
$11.81 |
|
| Large Screw Eyes | 29625 | 6 | -- | -- | 1.5" (38.1mm) |
-- | 0.187oz (5.3g) |
-- | -- | -- | $3.76 |
|
| Camera Hood for 4"/98mm Dia Tubes (CLEAR) | 18929 | 1 | -- | -- | 4.28" (10.871cm) |
1.77" (45mm) |
0.173oz (4.9g) |
-- | Polyethylene | #11021 #10505 |
$11.81 |
|
| Eyebolts with Washers and Nuts | 29629 | 4 | -- | -- | 2" (50.8mm) |
-- | 0.885oz (25.1g) |
-- | -- | -- | $5.65 |
|
| Vacuum-Formed Canopy PNC-33A | 18903 | 1 | -- | -- | 2.71" (68.8mm) |
0.92" (23.4mm) |
0.049oz (1.4g) |
-- | Polystyrene | #20068 | $4.70 |
|
| Standard Rail Button (fits 1" Rail - 1010) - 5 SET BULK PACK | 13058 | 1 | -- | 0.38" (10mm) |
0.381" (9.7mm) |
-- | 0.067oz (1.9g) |
-- | Delrin Plastic | -- | $21.26 |
|
| Standard Rail Button (fits 1" Rail - 1010) | 13060 | 2 | -- | 0.38" (10mm) |
0.381" (9.7mm) |
-- | 0.067oz (1.9g) |
-- | Delrin Plastic | -- | $4.46 |
|
| Standard Airfoiled Rail Buttons (fits 1" Rail - 1010) | 13068 | 2 | -- | 0.45" (11mm) |
0.319" (8.1mm) |
-- | 0.095oz (2.7g) |
-- | Delrin-plastic | -- | $8.22 |
|
| Large Rail Button (fits 1.5" Rail - 1515) | 13063 | 2 | 0.313" (8mm) |
0.63" (16mm) |
0.435" (11mm) |
-- | 0.236oz (6.7g) |
-- | Delrin-plastic | -- | $5.99 |
|
| Large Airfoiled Rail Buttons (fits 1.5" Rail - 1515) | 13069 | 2 | -- | 0.64" (16mm) |
1.26" (32mm) |
-- | 0.339oz (9.6g) |
-- | Delrin-plastic | -- | $11.73 |
|
| 1/8" Rail Button Standoff | 13071 | 4 | 0.166" (4.2mm) |
0.38" (10mm) |
0.125" (3.2mm) |
-- | 0.007oz (0.2g) |
-- | Nylon-plastic | -- | $2.99 |
|
| 3/16" Rail Button Standoff | 29641 | 1 | 0.171" (4.3mm) |
0.38" (10mm) |
0.188" (4.8mm) |
-- | 0.011oz (0.3g) |
-- | Nylon-plastic | -- | $3.79 |
|
| 5/16" Rail Button Standoff | 13073 | 4 | 0.14" (3.6mm) |
0.38" (10mm) |
0.313" (8mm) |
-- | 0.017oz (0.49g) |
-- | Nylon-plastic | -- | $2.99 |
|
| 21-lb Ball Bearing Swivel | 14508 | 1 | 0.132" (3.4mm) |
-- | -- | -- | 0.012oz (0.35g) |
Rated at 21lbs pull - Rockets up to 1lb | Stainless Steel | -- | $3.86 |
|
| 40mm Foam Plug | 20062 | 4 | -- | 1.57" (40mm) |
0.75" (19.1mm) |
-- | 0.021oz (0.6g) |
-- | Styrofoam | #19461 #10139 |
$2.50 |
|
| Motor Retainer Screw Kit | 25017 | 1 | -- | -- | -- | -- | 0.37oz (10.5g) |
-- | Brass | -- | $6.55 |
|
| 100-lb Ball Bearing Swivel | 14509 | 1 | 0.2" (5.1mm) |
-- | -- | -- | 0.046oz (1.29g) |
Rated at 100 lbs pull - Rockets up to 4lb | Stainless Steel | -- | $4.40 |
|
| 220# Ball Bearing Swivel | 14510 | 1 | 0.28" (7.1mm) |
-- | -- | -- | 0.148oz (4.2g) |
Rated at 220lbs pull - Rockets up to 10lbs | Stainless Steel | -- | $5.01 |
|
| 275# Ball Bearing Swivel | 14511 | 1 | 0.31" (7.9mm) |
-- | -- | -- | 0.222oz (6.3g) |
Rated at approx. 275lbs pull - Rockets up to 15lbs | Stainless Steel | -- | $6.26 |
|
| 500# Ball Bearing Swivel | 14512 | 1 | 0.41" (10.4mm) |
-- | -- | -- | 0.409oz (11.6g) |
Rated at 500lbs pull - Rockets up to 25lbs | Stainless Steel | -- | $8.77 |
|
| 1/4 - 20 x 9 Threaded Rod (1/pk) | 29633 | 1 | -- | 0.25" (6mm) |
9" (22.86cm) |
-- | 1.46oz (41.4g) |
-- | Steel | -- | $4.64 |
|
| Garage Sale Item - CLEAR Vacuum-Formed Canopy PNC-56A | GS010 | -- | -- | -- | -- | -- | -- | -- | -- | -- | $7.90 |
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