4" Estes Photon Probe Upscale

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Well-Known Member
Jan 18, 2009
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I was saving this for post #1000, but that isn't going to happen for about two years. So without further delay, unless I have to get up and do something else, here goes.
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If you want to read the last page to see how it ends, go here.
I don't have a garage filled with with shop quality tools like the Rocket Shop of the Apocolypse, but here is my humble table of construction:

Several boxes and a nose cone. Initially it was going to be 3BNC, but I ordered more stuff.
I love how it says “Please do not crush box” right where it looks to have been drop tested.
Here are the parts all out on display:
A “Sandman” 3.9” “AO” style nose cone
Airframe and motor components from Discount Rocketry and Discount Hobby:
3.9” LOC airframe tubing
29mm motor mount tubing
38mm motor mount tubing (I changed my mind)
38mm and 29mm centering rings (Hmm, what can I do with the 29mm stuff?)
3/32” Baltic Birch ply from National Balsa Company
Recovery components from Giant Leap include a nylon shockloop, nomex shock protector, nomex blanket, and a 36” Spherechute (in the little red bag)
38mm motor retainer from Wildman and a 38mm-29mm adapter from Al’s Hobby.
Railbuttons from Railbuttons.com
Various recovery hardware from my nearby Ace hardware.

This rocket will have a number of firsts for me:
1st 4” airframe
1st use of rail buttons
1st 38mm motor mount
1st commercial motor retainer
1st self-slotting of airframe tubing
1st fin can
I started out by doubling up on the plywood to make 3/16” fin stock. I looked at 3/16” stock around the LHS and found most of it with some kind of warp. I found on Info-Central how to deal with that: use two sheets of half-thickness material epoxied together. I laid down waxed paper over my counter-scrap table. Next, I took a steel rule across the material to determine which sides were concave. I had my 6-year-old mark them with an “e” for epoxy. I poured some 30 minute epoxy into an old peanut butter lid and mixed it up with a credit card. It took more than I expected but I was learning as I was going. After slathering both sides, I set them together and compressed them with some blocks I had found around the house.




The plywood was not all uniform in size. When I glued them together I matched up sides as best as possible. For whatever ended up as overhang I rigged up a sanding jig with the humble table and some more scrap plywood as ablation. I used my heavy-duty $10 yard-sale sander to even up the edges. It worked out better than I thought it would.



Next, I traced the patterns onto my stock. Pencil lines might get covered up by the sawdust created by the jigsaw, so I went over the lines again with a fine Sharpie marker. The idea is to freehand as little as possible. I’m going to use scrap one-bys as guides for the jigsaw. After a good day’s work, I’ve got all the fins and strakes cut out.


Here’s an idea I borrowed from the minimum diameter, high velocity, high altitude crowd. I think I first saw it being used by a UK team but I found the best “how to” guide on Team Vaatas Rocketry’s site. It seems it’s best to use a chop-saw, but not having one of those either I used a combination square and my aluminum angle guides again. For spacing, I set a piece of 3/32 ply, before epoxy, against the angle guide and marked a reference line showing the width of the wood. I flipped everything around and marked the opposite side. I check all my angles with a carpenter’s square. It’s close enough for government work. I used a small center punch to mark the intersections of the lines. Next I used a compass to mark 29mm (that was before) and 38mm lines for the motor mount tubes. Then I drilled out a ½“ hole with my electric drill.. (I couldn’t find my spade bits) Finally I took my Dremel tool and drum sander to open up the hole. Did I say, “Finally?” Well, then I switched to my fiberglass cut wheel and cut slots for the fins. It was a long, slow, smelly, dirty affair, but someone had to do it.


It’s time to get some glue going. It in spirit of Art Upton and the Punk Rocketeers from San Diego, I am proudly displaying my brewed beverage of choice. My tube holder is just some scrap 1x6’s clamped to the humble table. To get the basics of everything lined up, I’ve got my retainer and the aft centering ring dry fitted onto the MMT. I did one fin at a time, waiting about an hour between fins. After getting all four fins on, I let everything dry overnight.




The next day I’ve got a nicely formed cruciform fins. The body tube gets a test fit and I found it to be spot on. That makes a nice time to mark the end of the body tube for cutting the fin slots. I used my tried-and-true combination square to find the slot length. Once again the angle iron gets used to mark straight lines as I need all the crutches I can find. I fashioned a mandrel of sorts from a 2x2 and a busted open cardboard box until it was the correct inside diameter. I first tried to use my Dremel again but it just seemed like too much tool to cut the slots. I ended up using a utility knife and a fresh blade and everything worked out just fine. Another dry fit of the parts says so.




Meanwhile, back at the forward end of the rocket, I got the forward centering ring set up with the hardware attachment for the recovery components. The 3/16” screw eye is actually a leftover from my scrapped PML Ariel.

I left the aft CR off to apply internal fillets. Two layers of the TBIII ought to do well.

Now it’s come to the time for the aft CR. I’ve slathered everything I can think of with glue before insertion of the aft CR. Once I’ve got in place, I set it upright so gravity and time can work for me. I left it alone for another day. And the cat still doesn't care.


Next it is time for the secondary fins. I’ve got everything measured (twice or better) and marked. I clamped angles to the main fins to insure everything stayed parallel. Once the fins were in place, I went back and added the rest of the strake pieces. I used the smaller angles to get all of that lined up. I cut the strakes out of ply. On the original model the strakes are actually wider than the fin stock. To complete the effect I cut strips of 1/16” balsa and sandwiched the fin/strake combination between them. This serves to hide the imperfections of the cut and trimmed pieces and adds some strength the flush mounted fins. Not to mention the balsa is much easier to shape than ply.


While the last of the strake pieces set up it was time to trim the other body tube to length. There have been so many threads about the best way to cut body tubes. Micromeister probably has the best rig, but that’s hard to duplicate. I got my idea from www.info-central.com. Now this is not built from scrap. I actually had to got out and specifically purchase a 1x4. The folks at Lowes cut in half for me. Using what I had at home, I screwed the pieces together and formed a stop-block as squarely as I could. Ok, the stop was scrap pieces. I got everything measured and a single-edge razor blade mounted to the forward end. I used that cardboard mandrel again and many, many passes later, I’ve got a very nicely trimmed tube.




Just for the sake of progress I did another dry fitting. Then I remembered a thread about a boat in the basement. As I had not yet glued on the forward body tube, it was time for a reality check: Can you fit a 68” x 4” rocket into the back of a Saturn? Yes, you can.




Who really likes the messy part? Filling grains and spirals yields really nice finishes, but does anyone really like to do it? I like the results but I’m not fond of the process. At least it makes good use of a credit card. I used Elmer’s Carpenter’s Wood Filler in the new tubs. I had read somewhere that it was Fill-n-Finish under a new name but I couldn’t confirm it. With the 100% humidity and working the weekend, anything more would have to wait a week.


Main fin fillets are next. I got this idea from the Sky Pirates. Where they use epoxy and filler, I’m using wood filler and CA. First I put down some protective masking tape. Next comes the glopping of the wood filler into the corners followed by shaping with some ½” CPVC. Scrap, of course. Glop, shape, smooth, sand. Sanding gets done by wrapping sandpaper around the pipe and gently sanding and shaping. Too much pressure results in groves formed in the edges of the fins and surfaces of the body tube. When I got it as good as I could, I dripped some thin CA to harden it all. They came out nicely on my Big Daddy.


Time for primer! Wal-Mart primer is all right I guess. It’s cheap so I use it. Here are all the parts and an initial sanding to knock down the high spots. Before I move on the base coat I’m going to have to sand off a whole lot more primer.

I had the dilemma of how to drill vertical holes in the CR’s without a drill press. It came to me in a nap. I took some scrap pieces of paneling and formed a 3-sided box with one end shaped to the curve of the BT. The sides of the box are wide enough to just fit to the outside of my drill and tall enough to be able to line up with the placement of the drill bit. I sunk a pilot hole using my smallest bit, a 1/64” I think. I stepped up to a 13/64 for the inserts. It worked great for the forward hole but got deflected on the aft. A sharper drill bit would have helped with that but it was all I had. Follow Dr. Sue’s advice and drill the CR’s before assembly. With some generous epoxy in the holes it should do OK. For a first effort, all I need it to be is functional.

Nylon shock cords should have some kind of protection from ejection heat. That usually comes in the form of Nomex or heat shrink tubing. I’m going without because the loop is attached a good 30” or so from the ejection charge. Heat probably will not be an issue. I will use a nomex blanket to protect the parachute though.

It’s time to add permanent length. Generous amounts of TB III get smeared to the upper tube and spread with a craft stick. The upper tube gets placed onto the lower and it is good to go.




When the glue dries it’s time to go work on the body seam. More wood filler and sanding. The cat grows impatient, waiting to be brushed. As I can’t it still for long I decided to put some color of the bottom and on the nose. Once the body seam was filled to my liking I knocked down more of the primer and put some base color on the rocket. After 3 cans the fins are about where I want them except for some runs in the paint. There is still some primer showing on the forward end but I’m out of paint and warm weather.