Fast and long

Personally I would buy a bar that takes aero-bars. But I can see your approach working.

If you do go the DIY route I think you should stress-test whatever you make. Yank hard on the aero-bars. Repeatedly. And bang them with a rubber mallet to simulate potholes. I can see this failing catastrophically (if at all) so it's better to see that happen in your garden rather than on the road.

Alternatively, could there be a way to fix something between the two shifters? It would be sweet if a company made alternative shifter bar clamps (you know, the silver loops) which could then take attachments sideways. You could then mount a piece of bar between the shifter clamps and clamp aerobars to the new piece of bar.

You could achieve this with Problem Solver bar clamps just below each shifter like this but I don't know if it would interfere with hand placement.

You could use a carbon tube with same ID/OD as fork steerer, and then use a steerer expansion bung in each end. The bolts would then go cleanly from clamp to bung. Handlebar tape over the joins. You also gain another bar to mount lights/Garmin to. I would worry about this bar rotating when you lean on the aerobars though!

Basically a DIY hover bar:

are you mad? why are you drilling carbon handlebars?!

I do know a good dentist in India if/when you need.

Yeah this drilling and modifying of bars introduces risk that in my opinion is unacceptable, for basically no gain whatsoever (the aero aspect of the bar being irrelevant compared to the aero aspect of the rider)

Think it's more about muscle fatigue than aero. I'd certainly find some compatible bars rather than modifying the integrated set. DIY carbon is possible and scarlet has some experience, but I don't know that I'd trust even my own work on something critical like the bars.

OK, I have (I think) fixed the design and started the process.

Many thanks to those showing concern for my forthcoming demise; I will try to remember to leave (undrilled) bicycle components to you in my will.

For those particularly concerned with carbon drillium, that's now NOT part of the plan, and I am just bonding to the existing surface. This does mean the additional risk of failure is with the aerobar; although its only a small consolation to know that if the bars themselves fail, it was the manufacturer at fault.

So, here's some photos to get the ball rolling. You'll need to use a healthy dollop of imagination, but it'll get clearer as I break out the box of doom!

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And the aforementioned box. Other people may have a spares box. In moments of, I sense, frustration, these occasionally appear in the classifieds as "take the whole bastard lot, I can't stand the sight anymore".
I hope I'm taking this to a new level; here's a box full of carbon accident, just waiting for a bike to ambush...

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diy carbon is not the sort of sorcery most think it is. kudos to you for "throwing caution to the wind" and taking on this project!

Agree, excite. Workmanship gives confidence. A mate is on his nth diy carbon road shoes, looking forward to some shiny new thing here.

Thanks, @BassoBry, @Yemble
Here's a quick update. I have started epoxying in the fixings and putting a layer of carbon onto the base of the plate. This plate will go on top of the stem, but the base of the fixings has 1mm depth, which could otherwise create a void between the plate and stem. So, I'm just filling this void with anything carbon-y to give me a fighting chance of eliminating too much fresh air. I'll sand it back so the base of the plate is pretty much flat, and mates up well to the top of the stem.

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Not sure if that delivery note you’re using to catch the mess in any way relates to you, but if it does it has personal information on it you may not want to post on a public forum.

Ta @hollow__legs, the offender has been removed. I'll crop the photo and add below, plus progress from today (sanding the base back to flat). Think its ready for bonding to the stem now. Which means taking sandpaper to the stem, gulp.

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Progress! I have epoxied the plate to the top of the stem now. I am really happy with it - the work to get the bottom of the plate flat (to mate with the top of the stem) and the sanding to the stem both resulted in a really good close fit. I spread epoxy to both sides (plate and stem) and then clamped the two together (checking for straightness, which wasn't easy with the clamps in place). It worked! The plate is straight and the bond is really good with no voids obvious from the side.

Next is to wrap the stem and plate in two layers of 240g carbon.

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Looks great. This is encouraging.

Another day, another layer (or two, actually). This wet layup technique is the way I have always done composites; mix the epoxy, paint the base, lay the fibre cloth over and stipple through with epoxy, then wrap tightly in release tape/peel ply as far as possible to eliminate air, then add clamps as far as possible.
I'll add another layer of epoxy before I neaten things up. But having been here before on other projects, this is looking good (to me).

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After showing the bars a bit of sandpaper, here's where I'm up to:
I'm quite pleased with the shape, and most importantly, no holes drilled to the original bar; in fact, added strength over the stem and central section. I think it will look pretty good once its back in matt black.

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Proving the entire forum wrong, hopefully.

I'm really enjoying this. Keep the updates coming.

Heck yeah, tidy.

I still stand by my original comment that this is a heck of a lot of work to attach some aero bars, but I’m in awe of your work!

Haha - thanks for all the comments, everyone. Made me smile! Figuring out the design probably took more time than the carbon work, but I think that's always the case for prototypes and one-offs. And tbh, you can do (some of) the design work with a beer in hand. Which isn't so bad.

The lay-up is time-consuming because of the epoxy cure time (about 3h to set, but ~8-12h before its sandable). So realistically, I can only do one stage per day; sand and shape, mix epoxy, spread epoxy (and fibre, if that's involved) then make a coffee/do life stuff.

The deal with the aerobars... I probably haven't been very clear in what I'm trying to achieve there. Anyways, here goes... This isn't "just" a clip-on aerobar. I really like/want the elbow pads to have proper location at the sides and back. And I want longer pads than are available off the shelf (because it helps massively with comfort). The ones on my red bike are home-made too, and the length of the forearm contact is about 300mm (compared with a standard pad of 125mm).

But if I custom-make it, I can add other stuff into the shape, which again isn't possible off the shelf. Lights? (OK, so you can get Exposure TT brackets, but...) Bottle or gel storage? Garmin mount? Mini-bar? ;-)

I have found a between the arms bottle/gel flask is a game-changer for me; its right there, you drink as you ride, you can see how much you've had, its super-easy and requires much less dexterity when tired. The light is neat too, I'll show that when I get to that stage.

At the end of the day, its a bit of work. It was more work the first time when I was a complete noob; I've done two sets of aerobars plus some other odd "shapes". This time around, its faster. But I think (hope?) the extra functionality is worth it. And I'm hoping I won't need to call on amey's dentist...

This is great, really interested to see how it turns out.

I am still enjoying the thread... but dare I say, going back to square 1... you've filled the holes in again for the headset spacer pins?! ... ... :-)

I am still enjoying the thread... but dare I say, going back to square 1... you've filled the holes in again for the headset spacer pins?! ... ... :-)

I know!! I tried really hard not to get epoxy in the holes, but once the tape and clamps were on, I couldn't see and... At least I've done it once, it can be done again. I'm sorta hoping that as I do a final sand, the holes reappear. But that would be too easy, I think!

Here's progress! I finished sanding, I found all the holes by exploring a little with a pick, and then added 3 coats of primer and 3 coats of satin black. There are some tiny bits of dust visible in the paint; and painting is really not my strength. I have to make up my mind whether to sand these out, and try to put a final (dust-free) coat on, sand out and polish (to avoid further painting!) or just live with...

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This looks about 10x better than anyone was expecting