Attaching rail buttons....

I've read the posts I could find here at TRF and out on the net. One thing I didn't find is at what weight a backing plate is needed on the inside of the BT. Is there a known weight that warrants the use of a backing plate?
My current build is using a LOC 4" BT and the weight will come in around 2lbs. loaded. The BT is stock ( no fiberglassing).

tia...

I don't know of an firm answer. The heaviest that I've used standard buttons in paper (with a drip of CA) is a bit over 3 lbs. With the larger buttons, a bit over 8 lbs.

I didn't use a backing plate on my 12 lb. L2 attempt. The buttons held up better than the 1/4" ply/1 layer of 6 oz. glass fins did!

If the airframe and motor mount leave enough room, I use a backing of some kind on all buttons. My RDS Quasar weighs in at 17 pounds when "Dressed to Kill" @ the pad, and should really be upgraded to larger buttons, but last weekend the buttons held just fine. I mounted these with a nut and slightly molded washer, and then reinforced with a nice "glob" of 5-min. epoxy.

The only time I do not back up the buttons, is when I can tap the button into a MMT Centering Ring, or when I use ACME rail guides but they are a non-issue for buttons.

Johnnie Paul

You might get some info here:
Railbuttons.com

I'd suggest to use some sort of backing every time!
A surface mount railguide will be torn off as soon as there is a modest force on the rail.

Check out this picture:
https://www.argoshpr.ch/Images/MIR_2002_Juerg/Juerg_RedFlash.jpg

A surface mount rail guide would have been torn off.
The reason for this heavy work on the rail is most likely the rail base of our italian hosts that was not stiff enough. This caused some binding of the rail guides.

I try to mount the rail guides into bulkheads, using metal insets (wood threads on the outside, metal threads on the inside) and metal screws. This allows to change the rail guide if I'm using other rail systems.

Juerg

I dont use any backing, except for superglueing them in, on my EZI which is about the same size as the rocket you are describing

on my 8lb V2 (I think it is probably 9 by now) I just screwed one into the plastic where the tailcone met the BT. for the tob I just soaked a little peice of carboard in CA and slapped it on the airframe then screwed into that....works awsome!

Stones
under normal circumstances the rail buttons shouldn't have a large amount of force exerted on them
but If you can get to it, sure wouldn't hurt to atleast put a nut and washer on the back than lock it with a little epoxy mabey..

as Juerg mentions ,if something were to go awry,it would certainly hold better than a dab of super glue!