Rail button issues

I've put rail buttons on three high power rockets so far: My LOC-IV, Minie Magg, and Hyperloc 835. I drilled into the centering rings on all three (or tried to). I measured carefully, measured again, and drilled the holes. Got both into the centering rings the first try on the LOC-IV, so thought, "This isn't so difficult." Uh huh, sure it isn't!

On the Minie Magg, I got the first one, but missed the second one. What the heck? I measured and double checked myself just like I had on the LOC-IV. Then when I did the Hyperloc 835 today, I used a square/depth gauge to measure with, that I got at Harbor Freight. I measured the depth from the bottom of the body tube to the surface of the centering ring, making sure the gauge was on the wood and not on the epoxy. I locked the gauge, then used it to mark the depth on the outside of the body tube. Since the centering rings are 1/4" thick, I measured up 1/8" from the mark, thinking that this would be the center of the ring. But when I drilled, it just *barely* caught the top edge of the centering ring, instead of drilling into the center of it. What the heck? So I drilled 1/8" down from there, and it came out inside the rocket just brushing the rear of the centering ring. WHAT THE HECK???

I measured for the front rail button just like I had for the rear, and drilled right into the centering ring. I'm at a complete loss.

More than likely, the centering rings aren't prefectly square in the tube, and you're measuring at a different spot than you're drilling.

-Kevin

I have given up trying to find the centering rings. Now I add a hardwood block to the centering ring where the rail button goes. It adds a little weight and takes a some prior planning, but it gives you a better chance to find wood when you drill later, and gives you some options if you ever strip the hole.

I've started using a pushpin to verify I've located the centering ring after measuring (it'll go through just the body tube pretty easily, but you'll be able to tell when you've hit a ring.) If you're careful with your measuring, you'll only end up with a few pinholes in the airframe, and they can be covered by the rail button itself.

Worst case is you miss and end up with a pinhole you need to fill, which may be better than drilling a larger hole and then finding out you're off.

Then again, I've also just used well nuts without bothering to drill into a ring at all (did that on my LOC IV.)

I know that doesn't help you in this case, but it might help in the future. I think troj is on the right track... sounds like it just might be higher on one side than the other.

EDIT: Ooh, and what SMR said! Just make a bigger target!

troj said:

More than likely, the centering rings aren't prefectly square in the tube, and you're measuring at a different spot than you're drilling.

-Kevin

Click to expand...

I'm measuring to the face of the ring on the same side as I drill. Even if the ring was crooked, I don't see how it could be that far off. Remember, these are 1/4" rings. They fit pretty square on the motor tube.

SMR said:

I have given up trying to find the centering rings. Now I add a hardwood block to the centering ring where the rail button goes. It adds a little weight and takes a some prior planning, but it gives you a better chance to find wood when you drill later, and gives you some options if you ever strip the hole.

Click to expand...

Now THAT'S a good idea!

slogfilet said:

I've started using a pushpin to verify I've located the centering ring after measuring (it'll go through just the body tube pretty easily, but you'll be able to tell when you've hit a ring.) If you're careful with your measuring, you'll only end up with a few pinholes in the airframe, and they can be covered by the rail button itself.the right track... sounds like it just might be higher on one side than the other.

Click to expand...

Now that's a good idea, too!

I use t nuts without the prongs...I put some epoxy on the bases, push them thru. I then put the rail buttons and slide a scrap of rail on them. I then put a broom handle thru the rocket body and hang the rocket horizontally using the broom handle. The rocket will swing around until the rail buttons & scrap rail is pointed to the floor....let it sit and vola! aligned, even buttons every time!

I just drill into the body tube, and screw 'em in with a dab of epoxy. I haven't had any failures. It's worked on cardboard, fiberglassed phenolic, Quantum Tube and G10/G12 fiberglass.

On my rear I always epoxy a nut and a shaped washer on the inside. so that if I want to take it out I can, plus the washer provides more area so the cap screw doesn't pull through(it shouldn't anyway, but better safe than sorry). On the front I do the same only using a acorn nut to prevent anything from catching on deployment(if it is in that area), sometimes it is in the area of the avionics bay so I use a cap screw, washer and nut in there. It seems to work, and make life a little easier.

John

I just use wellnuts into the airframe.

1. Drill 2 properly sized holes into the airframe,
2. Insert the wellnut,
3. Fasten and tighten the railbutton screw.
4. Done.

https://www.mcmaster.com/#catalog/116/3270/=82l1af

Bob

qquake2k said:

I'm measuring to the face of the ring on the same side as I drill. Even if the ring was crooked, I don't see how it could be that far off. Remember, these are 1/4" rings. They fit pretty square on the motor tube.

Click to expand...

On a 1/4" ring, it doesn't take much. Remember, you're using something that likely spans across much of the ring. Put just a small cant on the ring, and if the high side is near the motor mount, you won't hit the ring, and possibly at all, when you go for the lower (outside) edge.

A 1/4" ring can be an amazing amount out of alignment, without any binding. It has zero impact on the rocket, but it does making hitting the ring more difficult.

-Kevin

Rocketman248 said:

I just drill into the body tube, and screw 'em in with a dab of epoxy. I haven't had any failures. It's worked on cardboard, fiberglassed phenolic, Quantum Tube and G10/G12 fiberglass.

Click to expand...

This method has worked fine for all of my rockets up to 7.5" in diameter and up to a K700 motor. I roughen up the body tube where the base of the button lands and the bottom of the button too so that the epoxy grabs.

That's "Rivnut" to you buddy.

Of course, you probably look at the huge display of cans labelled "Orange Soda" and read it as "Orange Tonic".



I'm epoxying in my fins and aft ring tonight. I'm using 1/4 inch fins and 1/2 inch rings above and below the fins with complete contact on all edges of the through-the-wall fin root tabs. I will then drill and tap rail button screw holes in the rings. I assume I'll hit them, but you never know....

I intend to reinforce the holes with CA and do the threading/CA'ing in 2 or 3 steps. If I'm not completely happy with the strength of the threaded holes, I'll just punt and epoxy the screws in.

bobkrech said:

I just use wellnuts into the airframe.

1. Drill 2 properly sized holes into the airframe,
2. Insert the wellnut,
3. Fasten and tighten the railbutton screw.
4. Done.

https://www.mcmaster.com/#catalog/116/3270/=82l1af

Bob

Click to expand...

By the way, for Rivnuts, I like the knurled type.

shreadvector said:

Of course, you probably look at the huge display of cans labelled "Orange Soda" and read it as "Orange Tonic".

Click to expand...

What's "Orange Soda" ??? Never heard of it.

It goes great in a glass with Vanilla ice cream.

tomar said:

It goes great in a glass with Vanilla ice cream.

Click to expand...

Uh, oh. I sense a "milk shake" vs. "frappe" debate approaching.

shreadvector said:

Uh, oh. I sense a "milk shake" vs. "frappe" debate approaching.

Click to expand...

Unless you're in Rhode Island where you would ask for a "cabinet".

shreadvector said:

That's "Rivnut" to you buddy.

Of course, you probably look at the huge display of cans labelled "Orange Soda" and read it as "Orange Tonic".

Click to expand...

Rivnuts and Wellnuts are different beasts. Welnuts are inserts set into rubber which expand when tightened.

Up here we drink "Orange Pop".