Questions: Madcow MIM-23B HAWK (FG)

Discussion in 'High Power Rocketry (HPR)' started by Stephen Henderson, Jul 16, 2019.

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  1. Jul 16, 2019 #1

    Stephen Henderson

    Stephen Henderson

    Stephen Henderson

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    I got this kit as my first HPR build. I've already been cautioned by a few people about the kit perhaps not being the best choice, but it's here, so a-building-I-will-go...

    As my first HPR kit, I've been doing mostly research at this point. I've watched Apogee's "Building Your First HPR" videos through, and have dug around on the internet for some better instructions or tips than what came with the kit.

    While I understand the basics, my question is really regarding the tailcone assembly. I purchased the 38P Aeropack Retainer per Apogee's suggestion. When fitting the parts together (motor mount, body tube, tailcone and retainer), I'm not getting a good image of what the finished rocket should look like. Should the retainer be flush with the rear of the tailcone? How much of a gap should there be between the inside of the tailcone and the outside of the retainer when installed?

    I really wish there was a "rear view" diagram of this. I'm a visual learner, so Madcow's instructions are quite vague for me.

    I appreciate any advice I can get here. I'm not going to begin to build the rocket until I understand this better from beginning to end. Please pardon any ignorance on my part - I'm learning!

    Thanks much in advance!
    stevehelium
     
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  2. Jul 16, 2019 #2

    mperegrinefalcon

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    I think you went the right way with FG, but I am entirely biased as I did my L1 on a 2.6" FG ARCAS, and L2 on 2.6" FG Screech (which was later flown on an L935 and survived without any reinforcement). I also hate fixing broken fins from landing. I have flown my 2.6" Delta and it had a main para-wad, landed at like 80 fps and only had chips in the paint. All I did was a thick bead on the fin root with Rocketpoxy, foam the fincan and then Rocketpoxy fillets. RocketPoxy is great for bonding and easy to use (1:1 mix ratio by weight or volume). I haven't really built any cardboard HPR as I like to put the biggest motor I can afford that will fit in the rocket and let her rip.

    Would you post pictures of the components? I would love to help as much as I can. The first thing you need to check is if the outside diameter of the areopack cap fits through the tailcone. I would personally have it sticking out a bit so it lands on the retainer and doesn't crack the polycarbonite. It can be either way.
     
  3. Jul 16, 2019 #3

    Stephen Henderson

    Stephen Henderson

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    Mperegrinefalcon, thanks very much!

    Hope this helps. One image has the parts loosely set apart, the other shows the tailcone section. As I stated, I've not begun the build yet, so nothing has any adhesives on it. I'm trying to understand how far back the retainer should sit in relation to the butt-end of the tailcone.

    When playing around with it, there are a number of choices. The instructions say "Ideally, the aft end of the motor tube should be flush with the aft end of the tailcone to allow easy retainer attachment."

    I'm getting the impression (as I write this), that the inner part of the retainer should be about half in, half out of the tailcone. But, given what I've read, I'm a little skeptical about this (why, I'm not sure).

    What do you think is the right way to go here?

    Hawk_Tail_Assembly_parts.jpg Hawk_Tail_Assembly_parts_assmb.jpg
     
  4. Jul 16, 2019 #4

    rharshberger

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    Just make sure you can get your fingers around the retainer ring with a good grip, sometimes the ring can get a bit tight. Usually I try and keep the cap ring where once its screwed down there is no/little gap between the cap and the tailcone.
     
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  5. Jul 16, 2019 #5

    mperegrinefalcon

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    If you epoxy the motor mount tube in flush with the tail cone it should be fine, as long as the Aeropack can fit on the motor tube fully and you can screw the retainer cap on. you NEED to use JB weld epoxy to attach this. Wait until the rocket is mostly built to epoxy this.

    If you haven't yet, wash all components with warm water and dish soap to get rid of any grease or dust on them. The cleanliness of your surface helps the epoxy bond.
    Any time you are epoxying a component these are the steps you should go through:
    Gloves on (No finger grease allowed)
    wipe down with acetone or rubbing alcohol. Either will work fine, I use acetone as a gallon is ~$15 and lasts a few rocket builds.
    With clean sandpaper, Sand vertically, horizonally, and diagonally. This roughens up the surface for a mechanical bond and activates it. Use 120-220 grit sandpaper. I use 150 usually.
    Then you wipe down with acetone or rubbing alcohol again to get rid of fiberglass dust.
    Now you can bond the components. Make sure everything is aligned and measure twice.

    This is the cliffnotes version of this: https://www.rocketryforum.com/threa...our-government-doesnt-want-you-to-know.58389/
    Amazing post and always at the top of the HPR form for a reason :)

    Steps I go through for motor mounts:
    Get the top centering ring placement, I usually put this just above the top of the slot for fins, but I don't know what the slots/tabs look like on those fins.

    get the rear centering ring placement. I would put this on after the fins are on and just press it against the fin tabs, but I again don't know how this works with this kit.

    Next thing to do is sand the entire motor mount tube, never sand anything before it is cleaned as it just pushes the grease or dirt into the glass fibers. Mark with pencil the location of the forward centering ring, you can wrap a piece of paper around the tube to make sure it is horizontal. Make sure to clean and sand the CR. Check the fit, if it is loose I will put a drop of CA (super glue) in the joint to hold it, then do fillets on both sides of the centering ring, after the CA has cured. The excess CA needs to be sanded after it cures before the fillets. You need just enough to hold the ring in place for the fillets. A gloved finger should work fine for fillets on this part.

    Make sure you have figured out how you will mount the shock cord. For a 38mm mount in 2.6" AF a 1/4" eyebolt fits but is tight and you have to make sure the rotation is correct or you could end up blocking the motor tube. You could also wrap some 1/4" kevlar around the top of the motor tube against the CR, just make sure it wont get in the way of fin tabs, so the upper CR needs to be further forward. The eyebolt will fit, I used one on my 2.6" ARCAS and Delta, both fitting well, I just had to trim the washer and drill it through the fillets. Forged eyebolts are worth the extra money, I have had the non welded or forged ones bend open from overzealous ejection charges before, luckily the recovery harness stayed on and that bolt is not deep inside an airframe. Either way, make sure you have enough shock cord to come to a point you easily can reach attached to the motor mount before it is installed, otherwise it will be impossible to attach. Do not use a granny knot. I use either a figure 8 follow through knot (the standard knot for rock climbers) or a locked half blood knot. I use these because they do not reduce the strength of the line. I use the figure 8 for permanent fixtures like the eyebolt on a motor tube, or just tie one with a loop to use for quick links. I use the locked half blood knot to tie directly to loops as it is easier to untie than the figure 8, but not for the rocket as it is a self tightening knot.

    figure 8 knot:
    Locked half blood knot:

    I use 20 feet of 1/4" kevlar for shock cords on kits this size. It is overkill, but I have never gotten a zipper using this much, and it can be transferred from rocket to rocket.

    Figure out how you will mount rail buttons. I prefer using weld nuts epoxied directly inside the airframe and have the buttons slide on the post and just use a machine screw to hold the button on with a bit of loctite, but a small bit of plywood against the airframe and a wood screw works just as well. If you go with the weld nuts, you need to put them in first and sand a flat side on the upper CR so it slides past. Wait until after the motor tube is in to place your wood block to screw into if you go that route.

    If you haven't worked with epoxy before, use some cardboard or plywood and make some practice fillets. I would recommend a plastic spoon for drawing them. Make sure you mask off anywhere you do not want epoxy. It is a lot easier to remove epoxy with the tape then it is to sand it, also make the fillets as well as you can while the epoxy is wet as it is less work for later. I don't like the epoxy putty Tim Van Milligan uses, it just makes smoothing out fillets more difficult.

    If you need anything else, feel free to PM me :)
    I just mean to offer my experiences and what I found works best for me. There are thousands of ways to build working HPRs, and none of them are necessarily right or wrong. I got lucky and my L1 went off without a hitch. It was my first composite motor, and first rocket I had built since a Fliskits Richter Wrecker at 14 (I did my L1 at 17 as a junior NAR), and boy was I nervous, but I had people on the forums and at clubs to ask questions of who were very helpful and knowledgeable. Take your time to learn with this build, an L1 is not something to rush. I guarantee there is something you will wish you had done differently, and that will be for the next rocket, then the same and so on.
     
    Last edited: Jul 16, 2019
  6. Jul 16, 2019 #6

    Stephen Henderson

    Stephen Henderson

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    Thanks rharshberger & mperegrinefalcon!

    rharshberger: your comment helps confirm what I thought. That's a great help!

    mperegrinefalcon: thanks for the lengthy bit of information! My only question right now is why JB Weld? I have that in my arsenal of adhesives, but I also just ordered Rocketpoxy (never used it before). My understanding is that Rocketpoxy is useful for just about any bond, and is pretty easy to work with. Perhaps I'm in error. ;-)

    Reading through everything you wrote, I may very well end up with questions along the way but, like I said (I believe), I plan to take my time to get this right. I believe the basic instructions that came with the kit have most of the major measurements. Having never built a HPR before, I am just dealing with some new steps and new adhesives, really. Since I started up with the hobby about 3 months ago, I've built three Estes kits and had no problems with them (though I have yet to launch the Star Orbiter). I built tons of the things when I was a kid.

    I'll continue to post to this thread as I move along. I'm planning on only doing the motor mount this week (busy work week). So I'm not going at warp speed, for sure.

    Thanks again to both of you!
     
  7. Jul 16, 2019 #7

    mperegrinefalcon

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    The motor exhaust is really hot, and the aluminum will conduct that heat. If you used something like rocketpoxy for this part it would turn to a gel at the temperature the retainer reaches. The JB weld is able to handle to temperature and keep it's strength.

    Your understanding of RocketPoxy is correct. While you are starting out I would recommend getting a scale that measures to the gram or some plastic mixing cups to measure out the resin and hardener. It is a simple 1:1 mix ratio of resin to hardener. You can use RocketPoxy for just about anything, at least in terms of composite rocket construction.
     
  8. Jul 16, 2019 #8

    Stephen Henderson

    Stephen Henderson

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    Little googling answered my question, but I might not have even thought of it and just made assumptions.

    Rocketpoxy's maximum use temperature: 225°F
    JB Weld's: 500°F

    I've read, also, that Rocketpoxy is good for fillets. I've also seen some information that FIXIT Epoxy Clay is a good route. While I'm not even near that step yet, I have to admit I'd like to avoid having to buy tons of extra materials if a minimal amount will work out just fine. While I understand, of course, that we need "the right tool for the right job", the varying opinions regarding adhesives on all the forums and social media groups is pretty overwhelming, especially when doing one's first build. With JB Weld, Rocketpoxy, Titebond II, and CA (I have Gorilla) already in my stockpile, are there any others you would say are necessary?

    Thanks again for your follow up!
     
  9. Jul 16, 2019 #9

    Nytrunner

    Nytrunner

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    That covers a lot of the bases (unless you're flying high Mach number flights and need high temp stuff to compensate).
    The only other items I have currently are 5 and 30 min epoxy for bonding dissimiler materials without the mix time and cure time delay of rocketpoxy
    (when you get into laminating or tip-tip reinforcement, you'll want a long cure laminating epoxy)

    I personally dislike epoxy clay. I find it brittle for high power stuff that needs it, and heavy for low power stuff.
     
  10. Jul 17, 2019 #10

    pferg

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    Please post more pics of your kit and your build. I’m considering ordering this kit.
     
  11. Jul 17, 2019 #11

    Stephen Henderson

    Stephen Henderson

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    I'll be happy to post pics as I build! Probably learn a lot from the input given the fact that I'm likely to make some errors. Currently awaiting the arrival of the Rocketpoxy I ordered.

    Just spent an hour reading more threads on adhesives and I'm even more confused that I was. I have a Syringe of the JB Weld ClearWeld 5-min Epoxy that I was going to use for the retainer when I get to that stage, but now I'm questioning the purchase. Are ALL JB Weld products rated to 500 degrees?

    I'm getting the strong impression that the retainer is the only location on the rocket where the heat threshold of the adhesive is really important. Perhaps also on the centering rings given their proximity to the engine? I want to make sure I'm using the correct adhesives in the correct locations.

    The other bit I'm trying to work out is the application of Rocketpoxy. 30-40 minutes set time and 6-8 hour cure time. Having not worked with Epoxy much at all, when setting my fins, I'm wondering about the mechanics of making sure they set straight. When working on Estes kits with Titebond, I've used the Estes fin alignment guide pretty much every time. Any suggestions for making sure the fins set straight both along and perpendicular to the AF?

    I think I'll probably be getting to start the build on Saturday. Should have all the information I need by then!

    Again, thanks to mperegrinefalcon for the lengthy "beginners" explanation. Everyone on this forum is most helpful and, more importantly, not at all condescending. I know some of my questions are newbie questions! I mostly just want to get a successful launch out of this rocket so I can build confidence and, thus, build more!
     
  12. Jul 17, 2019 #12

    Nytrunner

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    Not all JB products are temp rated. The JB specified is the original Cold Weld stuff that has steel particles (see pic below) (although folks have used otehr epoxies for their aeropack retainers, JB is recommended)
    Centering rings are fine with normal epoxy. Motor cases are certified to have their outer temperature be below a certain level. It's the retainer which is right next to the nozzzle and exhaust that should get the hottest.

    Aligning fins? Fin alignment guide from payloadbay.com! Print it out, glue it to a foamboard and cut out the guide. 1 is fine for through-the-wall fins, two are needed for surface mount fins

    Just wait! The new member grace period will wear off soon :rolleyes:
    [​IMG]
     
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  13. Jul 17, 2019 #13

    Stephen Henderson

    Stephen Henderson

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    Yeah, the JB Weld site FAQ just says "Original J-B Weld can withstand a constant temperature of 500ºF." That begs the question regarding the thresholds for the rest of their product line. I've googled until my fingers bleed, and cannot find something specific to ClearWeld. Home Depot only had the one 5-minute Syringe available. It was only $7 or something, so if I need to just get a different one, I will. I just wish I could confirm somewhere that ClearWeld is rated for the same temperature. Sigh.

    Print it out... funny, when I first read that, I assumed you were referring to a 3D print for some reason. Then I looked at the site - looks quite useful! Thanks! While I have 2 3D printers in the house, neither are mine, nor I have I ever used them. Sad, I know...

    Given that the AF of the Hawk is pre-slotted fiberglass and the fins are fiberglass, I actually assume that they'll be somewhat easy to get on straight. I'm just pensive about getting things right.

    Saw that Apogee has a Guillotine Fin Jig, but that's spendy. I love using the Estes guide on their LPRs, but find that, even with that, things have shifted unbeknownst to me after I thought they had set.

    And I guess the inevitable condescension will just mean I've reached the point of being truly accepted to the hobby. ;-)
     
  14. Jul 17, 2019 #14

    mperegrinefalcon

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    Rocketpoxy is perfectly fine to bond components right after you mix it. With fillets I wait around 30-40 mins after mixing to put on the rockets. Once you have a good bead of epoxy between the fin and airframe, let it sit for 5 mins before drawing the fillets. This will let air bubbles come out and allow it to flow into all the gaps.

    The reason you let the epoxy sit for those 30-40 mins is to let it firm up so it hold the shape you give it when drawing the fillets. I recommend using a plastic spoon to draw the fillets. It will pick up the excess epoxy as you pull it along. You just have to make sure you keep the angle of the spoon constant to get even fillets. Make sure to mask where you don't want epoxy.

    DO NOT use the Clear Weld, it is an unfilled, non temperature resistant epoxy.
     
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  15. Jul 18, 2019 #15

    dbpeirce

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    Here a couple of photos of the rear ended of my build of the same kit Like mentioned above, make are you can get a good grip on the retaining cap to take it on and off Also make are you get the motor tube prepped to accept the retainer body BEFORE you attach the tailcone upload_2019-7-18_8-50-57.jpeg
    upload_2019-7-18_8-51-27.jpeg
     
  16. Jul 19, 2019 #16

    Stephen Henderson

    Stephen Henderson

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    dbpeirce, Thank you! Given what folks have said, that is exactly what I was envisioning. Now I have confirmation.

    BEAUTIFUL finishing job, btw. How have your launches gone?
     
  17. Jul 19, 2019 #17

    dbpeirce

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    She’s only been up once on an I327DM. It was a great flight.
    upload_2019-7-19_8-3-56.jpeg
     
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  18. Jul 20, 2019 #18

    Stephen Henderson

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    Beautiful photo! Thanks for the photos again, and encouragement!
     
  19. Jul 20, 2019 #19

    Wallace

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  20. Jul 20, 2019 #20

    Stephen Henderson

    Stephen Henderson

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    First Building Session:

    Got started over night here. Just sanding and fitting for the CRs, tail cone, and retainer. No adhesives applied yet. The forward CR was sanded to a pretty tight fit. The rear was sanded slightly loose so I can use it as a spacer when bonding the front CR to the AF. After the bond in the forward CR is finished curing, the rear CR will be removed so I can add a fillets to the inside rear of the forward CR and the fins.

    First time working with FG. It's very slow going with 150 grit sandpaper. I found that for the CRs, this was very appropriate. Took 15 to 20 minutes to get both the inside and outside of both CRs to the fit I wanted. Getting the retainer to fit on the motor mount was more challenging. I went with a 40 grit for little bits at a time, then to 150 to remove the excess created by the 40. Got a very good fit in the end. Took about an hour because I kept thinking the 150 was removing enough material. It was not. The 40 grit got it done fairly quickly, but I'd probably already removed a fair amount of material already.

    The entire motor mount tube was sanded in multiple directions in order to prepare for the fins' fit against the motor mount.

    I started to get the fins fit. Having a little trouble with one of them. (Some advice might be useful here!) I finding it hard to come up with a good method of getting the sandpaper into the slots and get pressure on it. On the outside of the AF, I can get some, but I feel like I'm just taking off the outside edge of the slot (if that makes sense). I felt it get in a bit better. The fins all fit fine in the other three slots. I got it ALMOST in (probably just need a little more sanding), but it rocks a bit from front to rear. Also, the fins line up about 2mm from the rear of the AF. No big deal. As long as they are all the same. I was hoping for them to be flush with the AF, but the slots are, in reality, really long ovals.

    Of note while I was working on it, the advice I've received started to make more sense. With the rear CR sanded in a way that leaves me a little wiggle room, I can easily see how, once the motor mount (front CR only) and fins are bonded, the rear CR should be able to slide in over the motor mount and fit flush against the fin tabs. I project a little muscle to be applied to get it in - probably a light mallet.

    Two photos are included. One shows the basic alignment of the AF, motor mount, tail cone and retainer. The second shows them mostly assembled. There's still a slight issue with getting a better fit with the tail cone. I find the right angle on the portion that goes into the AF (I don't know what the correct term for that is). very hard to sand correctly. The point being, things are lining up just fine.

    If anyone thinks there should be any adjustments, or if I did anything incorrectly (minus the hour using 150 grit sandpaper) please let me know! I did all of this (with a decent temporary work area set up) in bed while watching Bill & Ted's Excellent Adventure. ;-)

    2019072006111_Hawk_Tail_Prep_Allignment.jpg 2019072006111_Hawk_Tail_Prep_Assembled.jpg
     
  21. Jul 20, 2019 #21

    Stephen Henderson

    Stephen Henderson

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    Wallace: Thank you! I actually just discovered Open Rocket yesterday (I think I had found it through google a half year back and forgotten about it). Got the .rkt file for it (easy enough to find) and was able to get a great view of how all the fits bit together.

    The link is very useful. I went to Madcow's site a few days back, but, apparently, didn't spend enough time there.

    It's all a learning process! But the most important thing is I'm having a lot of fun!
     
  22. Jul 20, 2019 #22

    Tim51

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    Thanks for posting your build. You might find using a set of needle files useful for widening fin slots - easier to apply pressure than with sand paper. I find a flat one and a square section one are a particularly good pair to work with.
     
  23. Jul 20, 2019 #23

    Wallace

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    Handy tip: When you open an Rkt. file and mod it/run flight sims, it'll give you the option to save it as an Ork. file. If you do, it will save all of your sims and data. whereas saving it as an Rkt. will not. You'll also discover the 3d rendering does not like crappy graphics cards..
     
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  24. Aug 4, 2019 #24

    Stephen Henderson

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    Tim51: Thank you! I was just working on the shoulder of the nosecone, and my housemate mentioned using a jeweler's file for the angles in that. Your suggestion regarding the slots makes perfect sense!
     
  25. Aug 4, 2019 #25

    Stephen Henderson

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    Second Building Session:

    Not much today. Life has been busy. However (advice is welcome), and please keep in mind this is my first time doing a HPR and my first time working with fiberglass.

    After sanding the nose cone shoulder (60 grit) for about 2 hours, I almost have a good fit. However looking at the photo, you can see the pressure pattern. When I insert the nose cone into the AF, it's getting close to what "feels" right, but a bit tight once the piece is about 5mm from being completely inserted. so I'm having trouble getting the material removed from that area.

    20190803_Nose_Cone_Sanding.jpg

    Hmmm... not the greatest image (sorry), but on the shoulder you can probably see the issue.

    The other question that has come up as I do this is how to determine if the fit is too tight or too loose. I've been told 15psi is an appropriate goal. I've seen folks testing ejecting charges using black powder setups (videos, that is), but I don't have those resources yet. Of course all the LPR kits I've done were pretty willy-nilly as far as t he nosecone it. The rocket is accelerating, so the air resistance will easily keep the nosecone on. I assume the same physics applies here, but what is optimal and what are some ways to determine that fit without getting too crazy.

    I have the same work to do on the tail cone shoulder. I believe that's going to be a bit more challenging (or time consuming I should say) because the shoulder is a lot smaller. Not as much are to work with.

    Thanks for the continued advice!
     
  26. Aug 4, 2019 #26

    Tim51

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    Judicious use of a needle file (or popsicle stick wrapped with sand paper) should help around that last 5mm. The general rule of thumb when not using shear pins is that a nose cone or coupler should be tight to the extent that you can pick up the entire loaded rocket holding said nosecone without it slipping off, but you can still pull it apart using two hands. If it's already looser than that, wrap the shoulder with masking tape to make it a little tighter.
     
  27. Aug 4, 2019 #27

    crossfire

    crossfire

    crossfire

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    A Dremal tool is a fiberglass kit builders best friend.
     

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