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CDI RAIL BUTTON SMALL (3 PIECE CONSTRUCTION)  
CDI RAIL BUTTON SMALL (3 PIECE CONSTRUCTION)

List Price: $1.25
Price: $0.75

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CDIRAILBUTTONSMALL3

CDI RAIL BUTTONS
FOR 1 INCH RAILS (THREE PIECE CONSTRUCTION)

RAIL BUTTONS FOR LAUNCH RAILS 1 INCH AND 1.5 INCH
RAIL BUTTONS


3 piece rail buttons

RAIL BUTTONS
FOR 1 INCH RAIL

Small buttons fit a 1" rail (three piece Nylon construction) Small buttons fit a 1" rail (one piece Delron construction)
Large buttons fit a 1.5" rail (one piece Delron construction)

Rail Button Installation:
The Basics

I've had a lot of questions about installation, so I thought I'd cover my experiences here. There is no simple answer to "Where should I place my rail buttons, and how many should I use?" Each rocket is unique in geometry, construction, mass, and lift-off profile, so one simple set of instructions is not going to cover all cases. Once you decide on how many and where they go then the "how" of installation is fairly simple.

First off, how many buttons do you need and where do you place them? In any case you will always need at least two buttons. It's typically agreed that one button should be placed as far to the rear of the rocket as possible. As to the forward button, there are all sorts of theories floating about revolving around the CP and CG. But keep this one simple idea in mind: once there is only one button on the rail you essentially lose most or all of your guidance due to the geometry of the buttons.

When your rocket is on the pad, in a standard two-button configuration, the distance from the upper most button to the top of the rail is your effective guidance length. With lighter rockets I usually aim for the two centering rings that are sandwiching the fin tabs. That may seem awfully close together, but I've never had a rocket hang on the rail (yet). The only issue is whether or not the weight of the rest of the rocket has enough leverage to rip your uppermost button out. The greater your launch angle from vertical the more of a problem this can be unless your rockets are fairly light.

However, I highly recommend what has become a standard three-button configuration on most of my larger rockets. Two of the buttons are placed a few inches apart at the very rear and then a third button up closer to the CG (w/motor) plus or minus a caliber or two. This allows positive guidance for the entire length of the rail while the upper button helps support the weight of the rocket while it's sitting on the pad.

In either the two-button or three-button configuration, if you do put a button forward of your most forward centering ring then make sure the button won't interfere with 'chute deployment or piston movement since the screw extends into the interior. For example, in a three-button configuration it is sometimes convenient to place the uppermost button through the electronics bay airframe in a standard mid-body dual-deployment configuration.

So, now you know where you are going to place your buttons. Next you need to drill pilot holes in your airframe to accept the mounting screws. I've found that depending on the airframe material and type of drill I'm using that I need anywhere from a 1/8" to 5/32" bit for the Series 1000 buttons. Do some tests first on a scrap of similar airframe material. You do not want the screw to just push through without engaging the threads. You should be able to screw and unscrew the button just as if a nut were in place. If you're using cardboard then you might want to wick some thin CA into the edge of the hole and let it dry to harden the edge.

If you're installing these during construction and it's convenient then you can simply use a nut and lock-washer on the inside and you're done.However, since I've retro-fitted most of mine I prefer to do the installation after construction. Ideally I try and drill into one or both of my centering rings, but I've found it's not critical if you can't or if you miss.

Rough up the airframe with sandpaper just around the hole and remove any and all paint. Rough up the bottom surface of the button as well. If you've managed to drill into a centering ring, insert a drop or two of epoxy into the hole so it can be wetting the side surfaces. Take the assembled button and smear some epoxy on the exposed threads. Also smear some epoxy on the bottom surface of the button. It doesn't take much!

Now, screw the button into the airframe and check for alignment. If you've used the correct amount of epoxy you should see a small fillet form around the lower lip as you snug down the button. (Do not over-tighten, as you could deform,compress, or crack the button.) As long as the epoxy doesn't extend above the top of the bottom washer you should be okay.

I've flown rockets with buttons installed using this technique (epoxy-only) on everything from D12 to K550 and have never had a button ripped off the airframe. I'm not going to say it's the only way or even the best way. Use some common sense and feel free to experiment. I'd love to hear any new ideas and feel free to contact me with any questions.
CDI RAIL BUTTON SMALL (3 PIECE CONSTRUCTION) 
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