So the last two days has been all about rail buttons. I need them fitted before I prime (despite the fact I’ll be taking them off again when I do actually start laying paint.
Let me say this: rail buttons are a pain in the 4r$e... and I’ll explain why.
The ones that come from AusRocketry don’t have a tee nut and fit an m4 screw. The button is flat on top and bottom and the hole is the same all the way through.
The ones from MadCow that came with this rocket are set up for a countersunk screw and came with a self tapping wood screw that is miles too long for the application.
The ones from apogee components are my favourite, but ONLY if you don’t lose the screw.
View attachment 367404
They come with a tee nut and a countersunk screw and the body of the tee nut actually fits inside the ID of the button. Did I mention, DON’T lose the screw? I’ve found it impossible to figure out what the screw is. It has an OD of 3.4mm and a thread count of 0.8, and I haven’t been able to find them anywhere local.
So back to the rocket:
The upper button is going to be in prime laundry snagging location so there I want to use the apogee button backed by a tee nut with a drizzle of smooth epoxy to make it snagless...
But: there was no room in the fin can for a tee nut without getting in the way of the tail cone, so there I have to drill and tap. (Never done that before, but I’m all about the learning...)
But I can’t use the apogee one on the fin can as I can’t tap it without the right tap, and again, the only taps at the hardware store are metric. I even scrounged through a box of old imperial taps they were throwing out to no avail.
No worries I said: I’ll get me an m4 countersunk screw...
Well... no. Not one single hardware or electronics store or place that was open on the weekend stocks m4 countersunk screws.
So no matching apogee button at the aft end.
Practiced my drilling and tapping in some scrap ply that I soaked the hole with thin CA before tapping. It worked a treat.
So I drilled and taped the FG, opting to go through the BT in the middle of the TC shoulder (more material) and put the decidedly different AusRocketry button on the rocket’s aft end.
(This aggravates my sense of balance and neatness, but I’ll have to find a way to live with it.)
The MadCow buttons: I have ZERO idea who would put a forward rail button into FG tuning with a coarse thread self tapping wood screw. By my calculation, even if I trimmed the screw, you’d only have 1/2 a thread engaged with the FG. And when (not “if”) it failed, I’m sure it you’ll make a lovely mess of the hole on its way out.
As it stands, they’re all in now.
Rather than trying to get epoxy on the back of the tee nut using a syringe on a long stick, I opted instead to drill the BT vent hole exactly opposite the rail button.
I used my heat shrink tube on the end of a syringe trick, combined with my “mix the epoxy in the syringe” trick to drip the epoxy directly on top of the tee nut.
Interestingly, the iPhone 8 camera can take a picture through a 3mm hole and focus on the opposite end of a 66mm BT quite nicely. This was an amazing view of my handiwork:
1x optical zoom
2x optical zoom