Rail button questions

I'm at that point where I would like to start building my rockets with rail buttons. I never did before because I didn't have my own rail launch pad and not sure how many of you guys out there actually do, but since I joined ROC I now have access to the nice equipment they use at their launches. I do have a few questions.

What are the common size rail buttons. 1010 and 1515?

In relationship to the rail size what diameter matches to the rail buttons listed above if I'm correct? 3/4" rail or 1" rail etc..

When building rocket is there a guideline to follow for what size rail button to use based on the diameter of the rocket? What size rail button would you use for rockets between 2-4" verse the larger 5-8" rockets.

I know most of you use 2 buttons per rocket, is there ever time when you might need more?

Wheres the best place to purchase the rail buttons? It seems you can get them most anywhere.

One other question - Do you have a particular way that works best for installing the rail buttons?

Thanks again!

Dan

AfterBurners said:

What are the common size rail buttons. 1010 and 1515?

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Yes, "small"/normal and "large". 1010 buttons use #8 screws; 1515 buttons use either #10 or 1/4". East coast clubs also have Unistrut buttons (i.e., "very large").

AfterBurners said:

In relationship to the rail size what diameter matches to the rail buttons listed above if I'm correct? 3/4" rail or 1" rail etc..

Click to expand...

Small (1010) buttons fit the 1010 extrusion (1" x 1", 0.25" slot), and "large" buttons fit a 1515 (1.5" x 1.5", 0.32" slot) rail. At ROC, one of the rails on the "uber pad" is *almost* big enough for 1515 buttons but not quite; IIRC someone was going to buy a 1515 rail to fit it but I haven't flown off that pad in a while, so I'm not sure.

AfterBurners said:

When building rocket is there a guideline to follow for what size rail button to use based on the diameter of the rocket? What size rail button would you use for rockets between 2-4" verse the larger 5-8" rockets.

Click to expand...

As long as the buttons are well secured, 1010s will work anything up to and including 7.5" kits. Most of the rails at ROC are this size. (Even the big Pad 39A (owned by Leslie Seiders) has a 1010 size rail on it.)

I have recently started switching to 1515 buttons on 6" and 8" rockets, just because the clubs I've flown with recently have 1515 rails at the distances to fly M motors. (n.b.: you can fly a 1010-buttoned rocket off of a 1515 rail!)

AfterBurners said:

I know most of you use 2 buttons per rocket, is there ever time when you might need more?

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Not really-- others on this forum will argue that you need three because when the top button leaves the rail, the bottom end is free to pivot. My explanation for only using two is that even with the top button gone from the rail, any deviations from the flight path will occur with the rocket rotating around its CG, which is far ahead the aft button. Therefore, the aft button still constrains the path of motion to the rail until it has departed the guide.

AfterBurners said:

Wheres the best place to purchase the rail buttons? It seems you can get them most anywhere.

Click to expand...

Lately I've been buying them from Wildman because I always forget to install them until I'm on site and he has them for sale. If I actually planned ahead and ordered a bunch, rail-buttons.com or Doghouse Rocketry would be my go-tos.

AfterBurners said:

One other question - Do you have a particular way that works best for installing the rail buttons?

Click to expand...

Small rockets: drill a 1/8" hole and thread 'em into the airframe with a drop of epoxy or CA.

Large rockets (the aforementioned 6"-8"): glue a wood backing plate on to a centering ring and thread them into that. If I plan ahead, I'll put a tee nut in the backing plate for extra pull out strength. qquake2k has some nice photo-illustrated threads logging this process.

Good luck and have fun! ROC was one of the first clubs to adopt rails, since Delta V Rocketry (later blacksky) was the vendor there for a long time. You're continuing a long tradition there

Thanks a bunch for answering all my questions. I didn't realize that ROC doesn't have an actual 1515? I guess I can stick with the 1010's for awhile. I don't foresee myself building any 8" diamter rockets in the near future so I'm good.

One quick question. Just out of common pratice isn't bottom rail botton always mounted near the AFT end of the airframe? Most of the rockets I've seen with rail bottons have them maybe an 1-2" from the aft end

I've been mounting mine to, the aft & forward centering rings...of late I have also put either one 1/4" (ply)block on one side of the centering ring or 1 piece of 1/8" ply on both sides(to give me a larger target when drilling).
Rex

daveyfire's answers are spot-on. As he mentions, some people will argue the finer points of rocket size vs. button size and # of buttons. Having launched many, many of rockets of all sized, organized many very large launches, and RSO'ed at dozens of launches, David is correct on all counts.

"Yes" on near the aft end - convenient place, too, because there is a centering ring down there.

On rocket vs. button size - I have seen many rockets near 50# and over 6" in diameter flown with 2 1010 buttons. If that won't work for you, you have other problems. On the other hand, if you think you need a 1515 button, no problem, use those. Just make sure you have access to a 1515 rail when needed.

--Lance.

You can get some nice airfoil ones from here:

https://www.scpconcepts.com/rocket-accesories.html

I've installed them in 4 rockets so far including my level 1 and potential level 2 - I like them a lot. Always shipped promptly and arriving in good time.

AfterBurners said:

One other question - Do you have a particular way that works best for installing the rail buttons?

Thanks again!

Dan

Click to expand...

I got turned on to captive nuts (aka pem nuts) by kawabunga here on TRF. I mount one button in the aft centering. I install a pem nut just aft of the forward CR and use that for the forward button. This puts the pem nut inside the MMT so no risk of hanging my harness on it.
You can find them at McMaster Carr for less than 25 cents each. There are many sizes of #8 so measure your tube thickness to get the right stuff.
Drill the specified hole, press the pem nut in and epoxy in place. Stay away from the threads or you get to dig out your tap set (don't ask how I know that one)!
Both of my kids and I use this method and have had really good results.
This is an example of many ways to achieve the same result. Work through all of the suggestions and use the one that suits you best. Good luck.