John's Rocket Blog

There is nothing like the smell of ammonium perchlorate in the morning.

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Payload Bay Part 2

Step 10 – Measure 2” from one end of the payload tube on each of the lines. This is where you will drill the shear pin holes. With the nose cone seated properly, drill a single 5/64” hole at one of your 2” marks. IMPORTANT: insert a 2-256 nylon screw into this hole before you rotate the tube for the other 2 holes. Last make an alignment mark on the nose cone and payload tube so you can remember the orientation since the spacing of the shear pins may not be even. Make sure you transfer this mark when you paint the rocket.

My drill and tap set arrived today, so I went back and completed this step.

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I was originally hoping to counter sink slightly in order to make the head of the screw more flush, but the fiberglass walls are so thin, I am probably going to let it sit proud.

Avionics Bay part 1

Step 11 – Mark one of the bulkplates as shown.

Step 12 – Stack the 2 large bulkplates and 2 smaller bulkplates and temporarily secure the plates with a single eyebolt to hold them together. Drill through all 4 bulkplates at the points you just marked with a 1/4” drill bit.

Not applicable to my kit, as it came with the aluminum bulkplates.

Step 13 – Separate the bulkplates and then glue a large bulkplate to a smaller bulkplate while aligning the holes. You will make 2 sets like this. Make sure the bulkplates are centered so that they will go into the ends of the coupler and not interfere with the body tube. You can secure with an eyebolt, nut and washer while these dry. After the epoxy has set, trap the two 14” threaded rods using 2 nuts and two washers each as shown. Use thread lock to make sure these don’t come undone later. Also, remove the nuts on the 2 eyebolts and replace using thread lock. 

Mostly not applicable. But I used thread lock on all the bolts as described.

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Step 14 – DO NOT EPOXY OR USE THREAD LOCK FOR THIS STEP. Place the bulkplate set with the threaded rods on one end of the long coupler. Place the other bulkplate set on the other end of the coupler and secure using a nut and washer on each threaded rods. The larger bulkplates should seat against the coupler edge with the smaller bulkplates going inside the coupler. After you are satisfied with the fit, you can remove for the next steps.


Step 15 – Mount the switch band in the center of the long coupler so 5” of coupler is exposed on each side. Place a thin layer of epoxy in the center of the coupler and slide the switch band over the epoxy while rotating so the epoxy slowly goes under the switch band. Make sure you clean up the edges of the switch band so it seats against the body tube later. After the epoxy sets, you can drill any desired altimeter vent holes and switch holes you need in the switch band.

After applying the epoxy and cleaning up the extra, I set it aside for a few hours to let the epoxy cure.

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After it cured, I stared at it for a long while pondering where I might want to drill the vent holes, and decided to delay that decision until later. I want the vent holes to serve double duty as arming switch access holes. I also want an outward facing video camera. So I need to think long and hard about this before I drill any holes.


Payload bay part 1

Step 8 – Put the shorter payload body tube on the nose cone coupler and transfer the 3 evenly spaced marks to the payload tube. Use a door jam like you did earlier to mark the entire length of the payload tube.

I used my angle iron instead of a door jam.

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Step 9 – Measure to the middle of the payload tube and drill a single 1/8” hole for a vent hole.


Step 10 – Measure 2” from one end of the payload tube on each of the lines. This is where you will drill the shear pin holes. With the nose cone seated properly, drill a single 5/64” hole at one of your 2” marks…..

I spent about an hour with a small file making sure that the nose cone was seated with almost no gap whatsoever.

I measured, but then decided to wait on drilling the holes. I want to have the hole tapped for my 2-56 nylon shear pins, and I could not find my drill and tap set. I’ve ordered a new set from Amazon.


Step 1 – Use the slotted main body tube to mark 3 evenly spaced marks around the shorter coupler tube. I did not get a photo of the process, but here is the result.


Step 2 – Use a door jamb to mark the full length of the coupler. This will help later when marking other tubes. I used a length of angle iron. It worked very well.


Step 3 – Sand the outside end of the coupler and the inside of the nose cone where the coupler and nose cone parts will bond together. Also sand the inside of the opposite side of the coupler where the bulkplate will be bonded.

No photos of me sanding, sorry. I tried to taper the end of the coupler that will go into the nose cone so that it could be inserted deeper and have more surface area in contact.

Step 4 – Mount the eyebolt with a nut and washer and secure with epoxy so it will not come apart later.

I am using West System with the slow hardener and for this particular step, I am using the 404 high density filler since it claims to be the best for attaching hardware.

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Step 7 (done out of order) – Use lock-tite on the nose cone tip to make sure it does not come loose during transportation.

Since the nose cone bolt is not captured in any way, it would be impossible to secure the aluminum tip once the coupler and bulkplate are in place. I felt it would be best to epoxy the bolt in place, and secure the tip permanently.

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Step 5 – Epoxy the bulkplate into the end of the coupler where you sanded the inside. Leave about 3/8” for a fillet. After the epoxy sets, apply a fillet around the inside edge. I applied a fillet to both sides of the bulkplate.

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Step 6 – Drill a 1/8” vent hold in the bulkplate to let the air out while you epoxy the coupler into the nose cone base. Epoxy the coupler into the base of the nose cone and make sure you leave at least 4” of the coupler exposed. Also ensure you get epoxy on the whole area where the coupler and nose cone will contact to ensure a good bond. It is best to put epoxy inside the nose cone and not the outside of the coupler. Make sure you have a clean coupler so as to not interfere with the payload body tube later.

Yeah, not possible to leave less than 4″ of the coupler exposed in my case, the coupler would not fit any deeper.

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The nose cone is done for now.

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Parts Cleaning

I have officially started the build. Step 0… cleaning.

I spent about two and a half hours cleaning all the parts. Getting all the dust and mold release off was easy. The hard part was all the tape goo stuck to the fins. The instructions talked about a mixture of 1 part rubbing alcohol to 3 parts water with a drop of soap. That worked just fine for everything else. But the tape goo would not come off. I tried some “goo gone” but that did not work well, and left a very oily residue. I tried pure rubbing alcohol, I tried acetone. The only thing that worked well was scraping it off with a razor blade.


TAPs Selected

Two fellow members of WAC have agreed to be the TAPs for my level 3 attempt. Thank you Bob and Jim!

I dislike plastic rivets

I’ve not been happy with the plastic rivets I’ve used so far in my other rockets. On my Gizmo, I had to modify the plastic rivet slightly such that it was able to deal with the thicker fiberglass walls on that rocket. I was not happy with that solution, because it required extra prep time every time I needed to replace a rivet. I was also very worried about scratching the paint each time I struggled to remove a rivet. I tried increasing the size of the hole, but that resulted in mysterious missing rivets upon recovery.

I decided that this new rocket will use a technique that I’ve seen used on other rockets that i was very impressed with. Epoxy a nut of some sort on the inside of the rocket, and use a machine screw to keep the two sections of the rocket firmly together.

I just ordered weld nutsmachine screws, and a few other bits from McMaster

New rocket… possible level 3 project

I’ve obtained a new rocket kit, a MadCow Frenzy XL.  I purchased it from Bay Area Rocketry while at F.I.T.S. 2016. It is a 4 inch diameter, all fiberglass, 75mm kit. Preliminary simulations show that it might be a perfect rocket for my home field, as the biggest motor that fits will kiss the waiver. I intend this kit to be my level 3 project. My Gizmo XL could have been that project, but the local TAPs wanted me to get more experience first before considering me for a level 3 certification attempt. So I’ve been flying it on L motors, and it is starting to get a bit beat up.


F.I.T.S. 2016 was a fun event. I flew the Gizmo XL twice. Here is the onboard video from the first flight.

Testing ejection charges

Today I tested the main ejection charges.

I was only able to find Pyrodex locally. It is supposedly volumetrically equivalent to BP if and only if you keep it tightly contained (like in a brass shell casing). The best I can do is tape over the charge canister with duct tape. I will need to use slightly more Pyrodex than I would BP as a result. Thus the reason for this testing.

I don’t have an accurate enough scale to say how many grams or grains I used, but I was careful to measure the volume as best I could. The first test was with 4 scoops, and the second with 6 scoops. I think I am happier with the 6. I was told that the scoop I was using is approximately 1 gram of BP.

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