Ensuring rail buttons align...

[ewomack]

It's raining newbie questions.

For LPR, I could easily align the launch lugs with my own launch rod and then test the alignment before launching.

For HPR launch buttons, I don't have a test rail. I do see 6ft rails available for about $40. Is that worth it to help ensure good button alignment before launch?

I do have a pencil line up the side of the rocket, which I'll use for drilling button holes, so that should help, but, short of a test rail, does anyone do anything extra to make sure the rocket glides smoothly off the pad? How much give do the rails and buttons have?

 

[G_T]

You can be off by a hair and it won't matter, not with two round buttons. If you use three buttons they need to be colinear, but even then being slightly off axis is not a problem. If you use conformal rail guides they need to be a bit more closely aligned since otherwise they will bind on the rail.

My last rocket THRP-1 had the conformal rail guides slightly off. One could see a slight angle between the rocket and the rail. But it was close enough there was no binding, and the rocket went straight. There was a slight detectable wiggle off the rail, but there would have been anyway. 1010 rail and a 28# rocket running decent acceleration is going to flex the rail. You'll get some whippage and a little bit of rocket oscillation.

You can go to a hardware store and find a piece of angle steel or aluminum that doesn't have twist. No twist is the crucial point. Lay that on your tube and use as a straightedge.

Or do you have a table saw? They have pretty flat tables. Measure a fixed distance off the surface to make your marks for the guides.

If the rocket is small enough, you can use a door jamb.

Lots of options.

And take a little spray can of WD40 to the rail! You'll get more binding from dry crud than from slight misalignment.

Gerald

 

[krislhull]

You can go to a hardware store and find a piece of angle steel or aluminum that doesn't have twist. No twist is the crucial point. Lay that on your tube and use as a straightedge.

This right here is very sage advice! I have a 3ft length of 1” angle aluminum that I picked up at Home Depot several years ago that I have used on basically every one of my builds. It’s a cheap and easy method.

 

[Handeman]

This right here is very sage advice! I have a 3ft length of 1” angle aluminum that I picked up at Home Depot several years ago that I have used on basically every one of my builds. It’s a cheap and easy method.

I have the same thing, although I think mine is 3/4" angle. I use it to put a line on the BT. The secret to getting buttons aligned is to make sure both holes are drilled on that line and are perpendicular to the tube in all directions, especially along the arch. If you are a little off on the top to bottom direction, that isn't as critical. A drill press can work very well as long as the line drawn on the tube is on the very top of the tube when you put it into the drill press. Eyeball alignment will usually work quite well, but if you can mark a line exactly on the opposite side of the tube and extend both to the very end of the tube, you can use a square to make sure the lines are square to the drill. If you don't have a drill press, many of the newer hand drill will have bubble levels on them so you can make sure you are vertical.

bottom line, if you have the line drawing on the tube and you take your time, eyeball alignment of the drill is usually well within what you need.