Skip to Sidebar Skip to Content

National Association of Rocketry

  • Home
  • Join NAR
  • Site Map
  • Contact Us
  • My Membership
  • About NAR
    • Overview
    • Organization Awards
    • Organization Contacts
  • Donate

Foam Ejection Plugs

« Construction & Techniques

by Andrew Tomasch

Here are a few of my findings regarding the production of foam plugs for ejection wadding and nose cone shoulders. I have produced nose cone bases which are cored out to rings for lightness, and ejection plugs with cored out rear skirts to reduce weight and minimize any tendency to jam in the tube.

Cutters: I needed good cutters for both 40 mm and 30 mm diameter, the latter for coring out the 40 mm parts when required. I laid up tubes from three layers 3.5 oz/yd^2glass cloth on my 40 mm and 30 mm mandrels. Lots of Crown release, both came off fine.

The resulting tubes are very robust. They can be cut on a band saw. Wrap masking tape around the tube where the cut is desired. Push the tubing into the band saw blade until it just breaks through the wall. Now rotate the tubing into the blade using the tape as a guide until it cuts through all around. I used 3″ lengths of both diameters for my cutting tubes. This will cut plugs up to 1 1/2″ thick. My plugs are 1″ thick blue Styrofoam insulation board.

To sharpen: sand the end of the tube with fresh 220 grit wet/dry paper placed ona flat, hard surface. Use a circular motion, just as you would sand the end of any body tube. You’ll find that the end surface of the tube is now a sharp abrasive surface, due to the glass fibers poking out of the epoxy. This actually helps to abrade the foam as the tool passes into the material, eliminating overheating and melting. Once the cutter is spinning in the drill press, a sanding block can be applied to the outside edge at an angle, to further sharpen. Easy does it. This is in fact not really necessary. Experiment.

Mounting in the drill press: purchase a rubber sanding drum for an electric drill, available at any hardware store. The 30 mm cutter uses a 1″ drum, the 40 mm usesa1 1/2″ drum. In each case, wrap black vinyl electrical tape around the drum until it will just slide into the tube. Now tighten the nut on the drum to swell it outward and trap the cutting tube. Drill a 1/4″ hole just past the end of the drum to allow air to be blown into the tool to remove plugs as necessary. I was able to do this with a sharp new machine drill. A step drill (“Unibit”) for sheet metal should also work. Whatever tool you use, it must be sharp!

To Use: Chuck the tool in the drill press, running on slow speed. If it wobbles, loosen the nut, push it slightly and try again. A couple of tries should yield a nice straight running tool. Cover the drill press table with manila folder stock to keep thetool from hitting metal. Plunge the tool smoothly and slowly into the foam. Most of the time the plug starts to fall out of my cutters. If not, a puff of breath in the hole will remove it. If a plug really sticks, push it up into the tube first, then blow.

Here’s a trick that really improves performance: The Crown wax, which coats the inside of the tool produces a very sticky, high friction surface. So put a little talc on your finger and rub the inside surface with it until it is all smooth and slippery inside. This makes a huge difference! The plugs will cut more easily with no tendency to melt, and they will fit the inside of your airframe tubes to perfection. Fresh talc is necessary every 20 or so plugs, or whenever you notice more friction (plugs not releasing easily for example). This really makes a difference when coring out a 40 mm plug with the30 mm cutter. Without the talc, the plug wants to twist out of your hand. With the talc, it glides right through! This also points out how important to coat the inside of your model with talc when prepping for flight. Also, rub some talc into the edge of the plug too. This goes for S6 too, not just S3.

Hollow nose cone shoulders and ejection plugs: To core out a 40 mm plug with the30 mm cutter to make a ring nose cone base, I just hold the plug by hand and eyeball the centering before plunging the tool. With a little practice, this does a nice job. Keep the tool lubricated with talc for best results.

Hollow skirt ejection plugs: Cut a 40 mm plug. Now cut a 1/4″ thick disk off the end with a hot wire cutter. I have a nice home made one with a table and adjustable fence, which functions just like a band saw. I published it in T Minus 5 a while back. I can post a copy on the web site if there is interest. Now core out the 3/4″ thick plug with the 30 mm cutter. Re attach the disk with a bead of UFO CA glue applied to the end of the ring. The 30 mm scrap makes a good nose cone base for a Junior model. This sounds like a lot of work, but it isn’t bad at all. This goes very quickly, and I estimate I could build perhaps 50 of these in an hour.

I tested the hollow skirt plugs and the ring nose cone base this weekend, and both work fine. The 1/4″ thickness stands off the Delta ejection charges easily, in fact,without damage. No problem with melt-through whatsoever. The ring nose cone bases arefine too. They are rigged with a light Kevlar loop tied around the ring before gluing on the cone. The loop is knotted again just past the ring, trapping the ring in a Kevlar loop. I UFO CA’d the Kevlar to the inside of the ring as well.

  • Return to home
  • Join the NAR
    • Home
    • Join NAR
    • Site Map
    • Contact Us
    • My Membership
    • About NAR
    • The American Rocketry Challenge
    • Model Rocket Info
      • The Sport Rocketry Hobby
      • Model Rocket Safety Code
      • Understanding FAA Regulations
    • High Power Rocketry
      • High Power Rocketry Certifications
      • High Power Rocket Safety Code
      • Understanding FAA Regulations
      • Filing for FAA Launch Authorization
      • High Power Resources
        • High Power Technical Reports
        • NAR HPR Certified Member Search
      • The NAR Rocket Science Achievement Award
    • Educational Resources
      • Online Mentoring Resources
      • NARTREK Skills Program
      • The NARTREK Cadet Program
      • 4-H
      • Air Force JROTC
      • Civil Air Patrol
      • Rocket Teacher Certification Program
      • Grants, Scholarships, and Recipients
      • Educator’s Newsletter Archive
    • Find a Launch
      • General Launch Information
      • Launch Calendar
      • Find a Contest
      • Register an NAR Launch
    • Local Clubs
      • NAR Club Locator
      • Find an NAR Club Launch
      • Submit a Local Club / Submit Changes
      • Section FAQ’s
      • Section Guidebook
    • Insurance Questions/Claims
    • Safety
      • Safety Codes
      • Model Rocket Safety Code
      • High Power Rocket Safety Code
      • Radio Control Rocket Glider Safety Code
    • Rocket Motor Information
      • Certified Motors
        • Motor Related Lists
      • NAR Motor Testing
        • NAR Motor Testing Notices
      • Manufacturer Notifications
      • Report a Malfunctioning Motor
    • Contest Flying – NAR Competition
      • National Scoreboard
      • US Team Selection Scoreboard
      • Find a Contest
      • Register an NAR Launch
      • Competition Results Entry
      • Team Registration
      • Teams List
      • Contest Events
      • Competition Meets
      • US National Model Rocket Performance Records – 8/2/19
      • International Competition
      • Competition Guide
      • U.S. Model Rocket Sporting Code
      • Rules Revision Process
    • Sport Rocketry Magazine
      • Magazine Submissions
      • Write It and Get Paid
      • Advertise in Sport Rocketry
      • Sample Issue
      • Contact Sport Rocketry
    • Member Resources
      • Members Only Forum
      • Magazine Archives
        • Sport Rocketry Magazine
        • eRocketeer Digital Editions
        • Member Guidebook Archive
        • American Spacemodeling Magazine
        • The Model Rocketeer Magazine
        • Model Rocketry Magazine
      • NARTREK Skills Program
      • R&D Reports
      • Technical Bibliography
      • NAR Insurance
        • Insurance Questions
        • Proof of Insurance
        • NAR Insurance Claim Form
      • NAR Association Documents
      • Promotional Materials
    • NAR Products
    • Website Fixes
    • Donate
    • What’s My NAR Number?
    • Log out

  • High Power Rocket Certification

    Design and Fly High Power Rocket Vehicles Learn More

  • Local Rocketry Clubs

    Connect with Proven Rocketry Experts Find A Club Today

  • Members-Only Forum

    Engage in meaningful conversations about rocketry topics that matter. Get Connected!

  • Sport Rocketry Magazine

    Six 48 Page Issues a year with NAR Membership!


  • Contact Nar

    National Association of Rocketry
    P.O. Box 407
    Marion, IA 52302

    Call: 319-373-8910

  • Join NAR

    The best way to get more out of the exciting hobby of rocketry is to connect with other flyers. The National Association of Rocketry can get you connected to the cutting edge of the hobby so you can learn how to fly higher, faster, and better. As an NAR member you will get:

    • Access to launch sites through local NAR clubs
    • The bimonthly color magazine "Sport Rocketry"
    • Insurance coverage for your flights
    • Certification for high power rocket flying

    Join Nar

    © Copyright YEAR National Association of Rocketry | Privacy Notice

    • Home
    • Join NAR
    • Site Map
    • Contact Us
    • My Membership
    • About NAR
    • The American Rocketry Challenge
    • Model Rocket Info
      ▼
      • The Sport Rocketry Hobby
      • Model Rocket Safety Code
      • Understanding FAA Regulations
    • High Power Rocketry
      ▼
      • High Power Rocketry Certifications
      • High Power Rocket Safety Code
      • Understanding FAA Regulations
      • Filing for FAA Launch Authorization
      • High Power Resources
        ▼
        • High Power Technical Reports
        • NAR HPR Certified Member Search
      • The NAR Rocket Science Achievement Award
    • Educational Resources
      ▼
      • Online Mentoring Resources
      • NARTREK Skills Program
      • The NARTREK Cadet Program
      • 4-H
      • Air Force JROTC
      • Civil Air Patrol
      • Rocket Teacher Certification Program
      • Grants, Scholarships, and Recipients
      • Educator’s Newsletter Archive
    • Find a Launch
      ▼
      • General Launch Information
      • Launch Calendar
      • Find a Contest
      • Register an NAR Launch
    • Local Clubs
      ▼
      • NAR Club Locator
      • Find an NAR Club Launch
      • Submit a Local Club / Submit Changes
      • Section FAQ’s
      • Section Guidebook
    • Insurance Questions/Claims
    • Safety
      ▼
      • Safety Codes
      • Model Rocket Safety Code
      • High Power Rocket Safety Code
      • Radio Control Rocket Glider Safety Code
    • Rocket Motor Information
      ▼
      • Certified Motors
        ▼
        • Motor Related Lists
      • NAR Motor Testing
        ▼
        • NAR Motor Testing Notices
      • Manufacturer Notifications
      • Report a Malfunctioning Motor
    • Contest Flying – NAR Competition
      ▼
      • National Scoreboard
      • US Team Selection Scoreboard
      • Find a Contest
      • Register an NAR Launch
      • Competition Results Entry
      • Team Registration
      • Teams List
      • Contest Events
      • Competition Meets
      • US National Model Rocket Performance Records – 8/2/19
      • International Competition
      • Competition Guide
      • U.S. Model Rocket Sporting Code
      • Rules Revision Process
    • Sport Rocketry Magazine
      ▼
      • Magazine Submissions
      • Write It and Get Paid
      • Advertise in Sport Rocketry
      • Sample Issue
      • Contact Sport Rocketry
    • Member Resources
      ▼
      • Members Only Forum
      • Magazine Archives
        ▼
        • Sport Rocketry Magazine
        • eRocketeer Digital Editions
        • Member Guidebook Archive
        • American Spacemodeling Magazine
        • The Model Rocketeer Magazine
        • Model Rocketry Magazine
      • NARTREK Skills Program
      • R&D Reports
      • Technical Bibliography
      • NAR Insurance
        ▼
        • Insurance Questions
        • Proof of Insurance
        • NAR Insurance Claim Form
      • NAR Association Documents
      • Promotional Materials
    • NAR Products
    • Website Fixes
    • Donate
    • What’s My NAR Number?
    • Log out