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Dumb rail button question

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DeWain

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This is a basic question that has probably already been covered in a dozen or so other threads, but I could not find the info by searching. I am building my first HPR rocket, a Mad Cow Big Fizz, and the instructions say that the rail button should rotate freely after it is mounted. So here is the question: does the rail button *need* to rotate freely (i.e., would a fixed rail button prevent the proper operation of the button/rail interface) or is this just advice to prevent the button from being compressed/distorted too much?

I read the info on railbuttons.com, and it sounds like a common way to mount rail buttons is to epoxy the button onto the tube (and that would certainly prevent the button from rotating freely).

Forgive me for such a basic question, but I am new to HPR. :eek:
 

lkal32

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I have some that can spin freely and others are tight. None have ever given any problems but I will say I believe that those that are locked in position take more wear than those that can spin. I guess the same sides make the most contact with the rail and with friction (or general bumps and scrapes from putting the rocket on the rail) cause the button to take a little more abuse than ones that can spin, which might help avoid some unneeded friction. Just an observation...
 

jcDerRedMax

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I make mine replaceable. #8 screw into a T-nut. I don't do anything to allow them to rotate freely. Having them removeable has saved 1 launch and prevented rework on another. First was a rail that accepted 1 type of button, but didn't accept Matts buttons. I pulled my button's off and used the rail owner's. Another flier couldn't fly because he couldn't remove his. Another rocket showed wear on the button. I suspect that even if they could rotate, they would wear because the button can't rotate fast enough.
 

sylvie369

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I never heard anyone suggest that they need to rotate freely, and none of mine do. If this is a crucial element to mounting rail buttons, my rockets have been flying wrong for at least eight years without my having noticed.
 

DMcCauley

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Rail buttons do not need to rotate freely. There is no more reason for them to rotate as there is for a 1/4" launch lug to rotate.
 

jderimig

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Interesting idea though.

Since the rail button can only touch one side of the rail at time, allowing it to rotate will cause less wear on the button.

Still not a must but maybe a tweak.

--jd
 

als57

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Well if they needed to rotate ; then the linear rail guides couldn't possibly work.

Most of the rail buttons I've installed will not rotate. If it did I'd consider it something that needed to be fixed.

Delrin rail buttons will take quite a bit of abuse before wearing out. Nylon ones seem a bit more sibject to wear. Its best to build so they are easy to replace.

Al
 

quickburst

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Allowed to rotate is OK.
Not allowed to rotate is OK.
Designed to rotate is most likely bunk.

Do as you wish, it doesn't matter.
 

sylvie369

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Can I use a small motor to make them rotate? :p

Which is better, clockwise or counterclockwise?
 

mikec

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I am building my first HPR rocket, a Mad Cow Big Fizz, and the instructions say that the rail button should rotate freely after it is mounted...
I had exactly the same question when I built my Madcow Super DX3. I think what the instructions mean is that the screw shouldn't be torqued down so tight that the button won't rotate *before* the epoxy has set up. I had a nice fillet of epoxy under the button and have had no problems that way. What you want to avoid is making it so tight that it deforms the button plastic.
 

DMcCauley

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This side of earth, clockwise .. like a toilet flushes.
Thats a myth. The water can spin either direction, no matter where on earth you are.

Plus the way a toilet flushes is defined by the jets of water that wash the bowl as they are directional.
 

MarkII

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Thats a myth. The water can spin either direction, no matter where on earth you are.

Plus the way a toilet flushes is defined by the jets of water that wash the bowl as they are directional.
Yes, but in which direction does a dog that lives in the southern hemisphere turn before lying down? :dark: :roll:

MarkII
 

Handeman

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I had exactly the same question when I built my Madcow Super DX3. I think what the instructions mean is that the screw shouldn't be torqued down so tight that the button won't rotate *before* the epoxy has set up. I had a nice fillet of epoxy under the button and have had no problems that way. What you want to avoid is making it so tight that it deforms the button plastic.
I've only been using rail guides and buttons for a few years, but I have to admit, I never heard of using epoxy to glue the buttons to the rocket. I have glued rail guides to the rocket, but never the buttons.
What do you do when they wear and you want to replace them?
 

sylvie369

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Maybe I'm just living right, or the rocket gods like me, but I've never had a rail button wear out. I get mine from Railbuttons.com, and I've never had any reason to replace one. I've epoxied all of them, with no trouble.
 

Handeman

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Sounds like they might be delrin instead of plastic. The ones I got from Ken at Performance Hobbies showed visible wear on the first flight. That was a 12lb rocket on a 1010 rail and a K695 motor though, the smaller rockets don't seem to wear as much.

BTW, do you score the delron before using the epoxy. My experience with delrin has been that very few adhesives will stick to it so you really need to ruffen up the surface to get a good mechanical bond.
 

sylvie369

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I drill a small hole, then put on a dab of epoxy, and then screw the rail button on with a sheet metal screw. I didn't scuff 'em up at all. I guess it's possible that I'm getting no advantage at all from the epoxy - I just know I have had no problem with the rail buttons' attachment (or wear). I just looked at all of my rockets, and see no sign of wear on any of them.

Now I'm generally flying rockets that weigh between about 3 and 7 pounds. I have a 15 pounder that flies on K motors that has 8 flights on it, but on that one the lower rail button is screwed/epoxied into a centering ring, and the upper one has an internal nut holding it in.
 

DeWain

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Thanks for the info folks. I haven't had a chance to respond since first posting the question. I never thought that this would a spawn a discussion about what direction water swirls in a toilet.:confused:

John and Al should see this puppy fly this weekend at the MARS launch. It is naked now but may sport a coat of primer by the launch. It is against my rocket religion to fly a rocket that isn't fully finished, but hey, I'm a LPR guy flying a HPR rocket so I am crossing over to the dark side anyway. :D
 

jderimig

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Thanks for the info folks. I haven't had a chance to respond since first posting the question. I never thought that this would a spawn a discussion about what direction water swirls in a toilet.:confused:

John and Al should see this puppy fly this weekend at the MARS launch. It is naked now but may sport a coat of primer by the launch. It is against my rocket religion to fly a rocket that isn't fully finished, but hey, I'm a LPR guy flying a HPR rocket so I am crossing over to the dark side anyway. :D
Prepare to justify in detail your rail button mounting system to the RSO.
 

DeWain

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Prepare to justify in detail your rail button mounting system to the RSO.
I'll have to show how the Micro Max spin motors work. :roll:

(I drilled a 1/8' hole, epoxied the threads, and epoxied the bottom of the button to the body tube.)
 

als57

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Thanks for the info folks. I haven't had a chance to respond since first posting the question. I never thought that this would a spawn a discussion about what direction water swirls in a toilet.:confused:

John and Al should see this puppy fly this weekend at the MARS launch. It is naked now but may sport a coat of primer by the launch. It is against my rocket religion to fly a rocket that isn't fully finished, but hey, I'm a LPR guy flying a HPR rocket so I am crossing over to the dark side anyway. :D

What dark side? AP is all good. Prepare to spend more money.:y:

It's not naked if there is any paint on it!:neener:

Besides Nat runs a G rated launch anyway.:p

Al
 

DeWain

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Ummm. How precise does the alignment need to be between two rail buttons? I just realized with horror that the bottom rail button (which is screwed into the rear centering ring) is at a slight angle (the screw is not pointing straight toward the center of the motor mount). The upper button (at the target CG) is pointing toward the center,

The two buttons are on a good straight line, but since the lower one is at a radial angle, I am not sure how well the rail will fit through the two buttons.

Normally I am really fussy with the alignment of things on the LPR rockets, so I don't how how I managed to drill the hole for the button at an angle.
 

als57

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Depends on how much radial difference there is. A small ammount should be OK.

So can you give ua an idea of how much we're talkin about?

Al
 

DeWain

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It just looked like too much of an angle to me. It is a good thing that epoxy doesn't stick too well to Delrin. I was able to get the rail button out with the good ole' screwdriver and a fair amount of force. Now the question is whether I should move the button over to a new line that is not centered between the fins (kinda ugly looking), or move the lower button up above the lower centering ring (less strength).
 

Pantherjon

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Unless they are right next to each other, I would move the button you removed to the upper centering ring and call it good..You should still have a good bit of space between the buttons if the upper one is at the CG point..
 

Tom W

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Since we're already talking about rails.

If you tilt the rail (say 5-10 degrees) do you put the rocket on top, the side or underneath?

To me it makes the most sense to put it on top reducing the stress on the mounting screws but don't have any rail experience to speak of.

Thanks,

Tom W
 

Pantherjon

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Since we're already talking about rails.

If you tilt the rail (say 5-10 degrees) do you put the rocket on top, the side or underneath?

To me it makes the most sense to put it on top reducing the stress on the mounting screws but don't have any rail experience to speak of.

Thanks,

Tom W
Actually it would probably be better to put the rocket on the bottom side if you did tilt the rail..Also, if there is wind, placing the rocket on the downwind side of the rail(this was related to me to help keep the rocket from binding on the rail)..
 

spacecadet

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If you look at sounding rockets they're often launched at an angle and they always hang under the rail. That would be good enough for me.
 

MarkII

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If you look at sounding rockets they're often launched at an angle and they always hang under the rail. That would be good enough for me.
Just make sure that you have attached those buttons well! Real sounding rockets may have hung under the rails before being launched, but their lugs were welded on! ;)

MarkII
 
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