TOPIC:

There's a bit more to inserting Helicoils properly than just the proper tool...
I didn't say anything cos you appeared to be wanting to just glue them in.
To insert them properly (into, say, aluminium or plastic) you need:
The proper size tapping drill for the special tap
The proper tap, which has a special thread profile to match the shape of the wire the insert's made from.
The proper tool, which for the smaller sizes is just a rod with a slot in one end & a T-handle at the other end to work it - this isn't difficult to make.

1st you have to drill (Out) your hole with the tapping drill to make it the right size, & this "right size" is critical to be able to put the inserts in properly. If the hole goes oversize or wonky, it can be very difficult to put the inserts in so that they'll work with your fastener (They can jam & break, jump the special thread, tear the thread out etc etc)
Next, tap the hole with the special tap, again being careful that the thread you cut is clean, straight & perpendicular to the top surface of the workpiece. Use lube in materials that require it for clean-cutting (eg WD40 in ally).
Next, load the helicoil onto the tool, ie insert the helicoil "tang" into the slot of the tool, if this is the tool-type you're using (Some have a threaded section at the tip, to pre-expand the thread-pitch of the insert during insertion).
Next, using the tool absolutely perpendicular to the workpiece, screw the insert into your tapped hole. Do it by "feel", if it jams or jumps the threads, stop before you damage the tapping. As you insert the Helicoil, its wire should follow the threads of the tapping & its thread-pitch will expand to match (Helicoils hold themselves in place by trying to contract against the thread-peaks). Insert the helicoil until it's just beneath the surface, then give it a sharp twist in the opposite direction to break the "tang" off. You don't HAVE to remove the tang (& sometimes you can't due to the nature of the material you're putting it in) but leaving it will restrict how much thread you end up with that's usable.
In summary, putting Helicoils in is similar to winding a spring into a hole - it will turn happily into the hole cos you're reducing its diameter by coiling it up as you put it in, but when you stop (Or try to turn it backwards) its diameter gets bigger (Cos you're now trying to uncoil it) & jams it in place. A perfect example of what I'm on about here is the fitting of the body-mount springs on a Wild Willy, Quattro etc - the springs screw easily onto the threaded mount, but you'll have serious difficulty removing them

Glueing just didn't quite work out with these small ones.
I've looked into a complete set to do this but it would be a bit overdone for these crossmembers...
Unless I mass produce them!





But I think I will take the way of liquid metal now...
Or possibly tapped brass inserts.
Even though I'm quite tool crazy.



Btw - I may have to strike the "high tech" from the title 'cause carbon alone's not cutting it.
Maybe hollow titanium filling and helicoils would!

That Helicoil tool is one of the more posh ones with the "pre-expansion" tapping in its nose. The cheapy ones look a bit like a coathanger, but will work perfectly well for the smaller (sub-M8) inserts.

I'd say the expanding brass inserts would probably be your best bet, but they will require a "right size" hole to put them in to work properly. Thinking about it, you'll have to be careful that your "Right size hole" doesn't mean the wall thickness of the carbon tube is too thin, or the expansion of the insert might split it.

Er... what about, cut your carbon tube shorter than you need, glue in M2 STUDS, then use pre-tapped (M2) "stand-offs" (As used for electronics/PCB mounting) as long nuts to give you your M2 female thread? OR just use the studs through your uprights with nuts on the back?

I had that last train of thought as well... but only because I happened to see such computer studs in the same shop the helicoils came from. They only had M3 though. But certainly another option to look into!

Just checking - this is the liquid metal stuff, right? Seems it could be convenient for multiple purposes...
No hurry, there's 98695 left!

Dyed nylon could be an option...



But brass may be better...



I'm leaning towards these now.

Yes, the goob-tubes are the stuff I'm on about. They're advertised "It can fix busted engine crankcase & gearboxes" is a bit far fetched, but it's loads better than other brands, & yes it will hold a tapping as long as the screw isn't under a huge amount of stress (Overtightening WILL strip the thread out).

Going back to expanding brass inserts, you could always pre-expand them then glue them in (With your new JB Weld!)

Already clicked a few of those 5mm (+ 3mm male) brass studs this way.
I could suddenly see it after you mentioned it!
Getting some of that magic metal soon as well. Contemplating on a double portion for a slight "discount" on shipping...

I'm sure the studs will come in handy for something else anyway...
I'm also fairly sure you'll find more uses for, than you have tubes of JB, so why not get extra...

Fantastic thing R+D, makes you buy stuff you don't need but will find a use for!

Broadens the horizon... although I really should stop clicking on stuff for this "little" project.

Yeah I'd go with that... As exciting as it is finding "the answer", it's best to hold off clicking until you're sure you've explored all other possibilities & have decided which is the best option.... hence the head-wobble over wheels etc on the Thunder Dragons!