Converting existing MPR to rail buttons

I have 3 existing rockets that have 1/4 launch lugs on them now. They have been flown many times and the existing system works but with bigger motors, the rod whip can be noticeable.

The three main ones I want to convert are a PML Callisto, a PML Black Brant Vb and a Wildman Darkstar Lite.

I am thinking of plugging the launch lugs with 1/4" dowel and then drilling into the launch lugs and mounting the buttons so that the existing lugs are like a stand off.

Anyone else done this or seen this done?

I've added rail buttons, but I kept the launch lugs on the other side of the rocket just in case I wanted to use them again.

Do you have two sections of launch lugs, separated by some distance on the rocket?

Get some of these https://www.mcmaster.com/weld-nuts Click on 'steel or stainless adhesive mount nuts'. Sand off the paint, bend the flange to fit the body tube and epoxy them on. 8-32 fit 10-10 buttons. Leave the lugs on so you can go either way. (Use 1/4-20 for 15-15 buttons.)

Yes I do.

Since the rockets are all finished I was hoping to be able to mount them on the same side as the existing lugs so everything still matches up - hence the idea to mount them on top of the existing lugs. I won't need to still use the 1/4" lugs going forward since I am just finishing building a rail launcher so backwards compatibility doesn't matter.

I have been trying to think of other solutions....

What about a 3D printed piece like the PML Linear Rail Lugs but the base is built to glue on top of the existing 1/4" launch lug?

Easy to retrofit. Scuff up the outside of the lug a bit, epoxy this assembly on top and let set. Would allow you to still use a 1/4" rod if you wanted or a rail.

Thoughts?

I know you want to save the lugs, I also converted to buttons but I removed the lugs and painted over the old spots. Then added mounts on the inside for the buttons. Could try that also as long as you do not need the lugs anymore.

I'm facing the same dilemma, to cut the lugs off and just put buttons over it, or put the buttons on another surface.

I converted this rocket to buttons using well nuts from McMaster-Carr
https://www.mcmaster.com/well-nuts
I haven't had a chance to fly it so I can't swear to positive results, but the whip on the 1/4" rod was pretty severe. Can't imagine it's not an improvement.

Does the button head bind in the rail channel? Also, do you just glue the well nut on the surface?

David Schwantz said:

Does the button head bind in the rail channel? Also, do you just glue the well nut on the surface?

Click to expand...

The rubber part of the nut goes in a drilled hole and expands when the screw is tightened, so no glue. I don't know about the screw binding in the slot. I don't have a piece of rail to try it with. May be an "oh-oh" moment when I get it to the launch

I asked because I had button heads once and it did not work and have gone to using all flat heads now. I thought that maybe you had a trick to using them.

Lowes has weld nuts (flat prongless t-nuts) in their fasteners drawers, I love those things for mounting 1010s

+1 to flat topped screws that recess in the button's countersink

The round head screws are pretty similar to the stock one supplied by Railbuttons.com. Their buttons don't accept a countersunk screw. I have them installed on a Wildman Sport and they are fine

The butttons I get need to be counter sunk also.

The screws used in the last few pics appear to be standard machine screws, most button head machine screws are thinner and less rounded. I use button head machine screws all the time on 1010 buttons and they fo not bind or need to be recessed.

I got my countersunk buttons from doghouse back when he sold the 10 packs.

We’ve had people show up at launches with buttons that wouldn’t fit because their screwheads were too large. Mike Fisher (Binder Design) sells really nice countersunk buttons.

The Apogee components rail buttons also come with countersunk screws that provide nice clearance.