That's something I have planned as well. I wouldn't bother with trying to use one entire long piece of carbon as the shaft because the lower tall man White's carbon fiber rod is very long and already has the coil mount on it. You're not going to get any lighter than that thing and it's only $10 from Kellyco. Note that I'm not talking about the middle Tall Man Rod for Whites. They sell a lower carbon fiber coil shaft.
I found that with that installed my new upper aluminum shaft was able to be cut WAY down in length. I think it's maybe only around 2 foot or so in length now, but I for sure cut a lot of length off when it no longer had to be the length of the stock upper shaft due to the extra long Tall Man rod.
Anyway, I've got all the exact numbers written down for the build thread I'll be posting in the mods forum. I've been working on that thing in Wordperfect for several days off and on. What I'm saying is that if you are going to go that route I'd just buy the lower Tall Man rod as it's the right dimension to fit in an upper shaft and will be adjustable. Also no need then to track down a coil mount for it.
Minor note: Get the Whites rubber washers when ordering because they don't come with it. I found the Whites coil mount with those rubber washers installed was still a little less wide than a Minelab's coil's mount, so I inserted two plastic washers behind the rubber ones on the Whites rod and it works perfect. A better choice would probably be grabbing a few rubber washers from Home Depot that will fit in there but this setup seems snug regardless.
If you wait a few days I'll have all these numbers posted in the mods forum. You'll know exactly how long the upper shaft needs to be (unless you are taller than me at 6' 2 and 1/2") if you use a Whites Tall Man rod. Even just using thinner gauge aluminum for the upper shaft and then the stock lower GT rod will save you a good bit of weight, so just going carbon for the upper shaft and using the stock lower shaft will drop a good bit of ounces as well (probably about 5 to 6). But, once I post these numbers you can just track down some carbon stock at that length and use that for your upper shaft. Either way, you've got many options even if you are going the carbon route. A single piece for the upper/lower shaft is still a great idea but it might be much more expensive than just buying the length needed for a shorter upper shaft and using the Whites rod. You'd have to check into that as I haven't yet.
In the future I may replace my homemade upper aluminum shaft with a carbon one but the gauge of aluminum I used is so light that it's still saving me a ton of weight so I don't know if I'll do that yet. Have to dig up the weight comparisons to some carbon stock to see how much more weight loss there would be for that to see if it's even worth it.
Remember, the problem with the upper and lower shaft being one piece is that the upper one is larger in diameter than the lower one. Use a smaller diameter for the upper one and now the arm cup/box and most common hand grips won't fit that diameter. The stock diameter is what most bicycles and other grips use. Use a single piece that matches the upper diameter and now your lower end is too wide for the coil maybe, as the stock lower shaft slides into the upper one. Figure all that out before deciding to go the single piece shaft route.
You might want to search the net for a carbon fiber maker that I think is in California. I'll try to dig up a name for you. I've bought carbon tubes from them (Tubes are hollow like the Sovereign shaft. Rod are solid. Don't confuse the terminology when ordering.) in smaller diameter and they were about 1/4th to 1/5th the price of where I normaly bought that stuff. I'm willing to bet they make larger diameters that are just as cheap compared to other sources. Good quality stuff too. In fact, you might want to do a search in RcGroups.com for "cheap carbon tubes" and you'll probably find that company being talked about. They are big in the RC world because of their prices. Be VERY careful drilling your carbon stock. It doesn't like having rough edges and can cause a running split. You'll at least need to put CA or epoxy around the edges of any drilled or cut areas to keep the carbon from shedding apart.
Please keep us informed on your progress. I'm very interested in seeing what you do and how much your new shaft weighs. Watch the mods forum for details.
