Until the early 90's I had always used Staedtler Mars Lumograph wood pencils for my illustration work. I grew increasingly tired of having to sharpen and shape the ends though, so I decided to try mechanical pencils. With not a lot to choose from and my knowledge base limited (this was pre-internet for me) I settled on a Pentel Sharplet 300 that I used with the unwieldy cap / top half removed. It was short but it did the trick.
The first step was to find more of the pencils. Unfortunately Sanford had just stopped producing the pencil! (They later started manufacturing it again under the Papermate brand, but have since stopped producing it again! Apparently the Papermate Apex - with a much thicker barrel and large retracting tip - has replaced it.) After a fruitless search through local and Canadian suppliers I finally found four Technicians and four ProTouches from an art supply firm in the US and bought all their remaining stock.
To customize the Technician I first tried replacing the rubber grip with epoxy glue but this didn't work for me. I then tried hot glue that I let cool and planned to cut / sand to fit. Unfortunately the glue wouldn't sand well so I had to move on.
I removed the rubber grip and replaced it with an appropriate length of barrel from a Pilot Fineliner felt tip pen that I cut to size. I used epoxy to fix it to the existing barrel. I then hand sanded the entire length of the pencil to smooth it out and even the two barrel sizes. I also sanded the slightly-too-sharp-for-my-taste top edge of the pencil where the eraser fits in. Lastly I sanded off about 1/3 of the length of the small metal tip that holds the lead because it stuck out further than I wanted.
Photo - Three of my four back-up Technicians and my four back-up customized Sanford ProTouch II's. The ProTouch is essentially the same as the Technician from the grip up.
Perfection! Eight years of daily use (sometimes 12-14 hours a day in my hand) with no comfort issues, no mechanical problems and no breakages has proven this pencil is the right one for me.
Photo - My five customized Techinicians. The one with the tape on the end holds a slightly harder lead (H instead of F) that I use occasionally depending on the paper I use.