I found a great rod for my trolling/DR salmon application, but it isn't available as a blank to build on, so I'm going to modify a few of them off the shelf. It's a Shimano Technium 10-6 medium fwiw. The problem with the stock version is the rear grip is only 8 inches long (cork, changing over to EVA on more recent models), and my single action reels bottom out when I put it in the flush gunnel mount rod holders on my boat; need longer rear grips. I've been screwing around with 3.5" pvc sections in the rod holders to high-chair them up to height, but it's clunky. So I'm going to extend some rear grips by 4", and upgrade the grip material. My idea is to just use 12 inch carbon fiber tubes. I intend to turn the cork grips down to the tubing ID, and my brother gave me the idea of reaming out the composite cork butt cap on the existing grip, to expose the butt-end of the rod blank, then if I'm lucky and careful enough to keep it intact and clean, take a scrap section of old rod blank (I have some glass blank scraps laying around) and telescope it inside the butt section of blank and glue it in there. Then I'd take the exposed 4" blank graft, put some arbors on it that also fit the ID of the tubing, and glue the whole thing together with a new butt cap. Make sense?

I've read TK's extending rod blanks article from the archives a few times, so I understand it, and the section I'm going to mess with will likely not be under any stress (it's in a straight carbon tube, in a rod holder, in a rod that you handle by the foregrip anyways). Does my plan sound like a good one, or am I maybe overthinking it? An alternative would be just turn down the OD of the existing 8" rear grip and slide on the 12" tube and butt cap and call it good, with the rear 4" of rear grip/tubing being totally hollow; but somehow that feels weird to me. Also, the cork rear grips ought to work as bushings it seems, but when I do the same using the EVA underneath, I'm guessing the EVA material wouldn't perform as well as bushing material under the carbon tube as cork, but I've never done it. Any advice there?

Any opinion on the subject? Thanks in advance,

Brian

I extended the grip on one rod. So not a lot of experience but I think it worked well. In my case I cut off the the butt cap. I then took a section of threaded tubing. I used about a inch and a half. I epoxied this in the blank. I then took a section of grip and fitted it and epoxied it on a piece of threaded rod about an inch and a half longer than the grip section. The rod was horribly out of balance so the rod served as weight as well. In essence I created a weighted fighting butt about five inches long. For the transition between the extension and original grip I used a composite cork butt cap. I cut the end off and glued that over the tenon of the original grip. So it looked like trim band between the original grip and the extension. The extension was just a standard off the shelf rear grip with a tenon for a typical butt cap. I used a composite cork to match the trim ring. My intention was to thread it together with epoxy on the threads. I wanted to try it out first so just screwed it together. Never got around to epoxy. Worked great. Was a med heavy spinning rod that saw a ton, literally probable close to it, of carp action. Occasionally I had to tighten the extension but it never failed.

All that said your idea I think is much better despite being more work. It creates a more united grip. Also for a rod going in and out of a rod holder that long section of carbon tube will be nice. Instead of the trouble of extended the blank for the four inches I have a thought. Once you have the tube all glued up to the rod and prior to gluing on the butt cap carefully fill the tube with foam. Use the great stuff expanding foam for windows and doors. It does not expand as violently as the other stuff. I would plug the blank first so your only filling the extension of carbon tube.

Thanks for the reply. That's an interesting idea of going the hollow route, and then filling in the rear tube void with foam. That would eliminate the chance of water getting in there as well. Thank you,

Brian

Pretty simple:
Drill out the butt cap.
Then, just find a piece of rod blank that will fit nicely up into the rod blank and extend it out past the current grip by at least your desired length. Then, just wrap a piece of tape around the replacement blank tight to the end of the existing butt end of the rod.
Use a caliper to measure the outside diameter of the end of the rod blank.

Now, remove the piece of replacement blank from the rod you are modifying.

Now take a piece of masking tape and out several wraps of tape around the new rod end of the extension tight to the piece of tape that you used to mark the end of the current blank.
Then, remove the first piece of tap.

Now you can either leave the butt extension at its current length whatever it is, or you can trim the extension to be its final length. Then, just take a piece of eva grip material that will match the diameter of the current butt end of the rod and slip it over the extension and to check the fit. If necessary, either shim up the extension with tape, or ream out the grip as needed to allow the grip to slip over the extension.
Coat the extension and the inside of the grip with 5 minute epoxy - working quickly and slip the grip down over the extension tight to the end of the current butt end of the rod.
Clean up the epoxy - quickly with DNA before the glue sets, and if you put on an eva grip with an integral butt cap, you are finished.

The entire job from start to finish should take you less than an hour.

============================
If you did not want to use eva, or a premade grip, you could remove the extension from your blank after the initial measure, Do, the masking tape on the inserted part of the extension to mark the point of full insertion and then, just add cork - if that is what you want for the extension grip, or anything else you want for an extension, glue it all up, and then use your lathe if you have one to turn the extension to size, taking frequent measurements to insure a perfect match fit of the butt extension when you do the final installation.
If you want to add a butt cap, leave the extension long enough to add the butt cap after the extension grip has been finished.

Best wishes.

That does sound easier than what I had planned. Thanks for taking the time to type that up Roger,

Brian