The original reason was different from oval, but I was quick to learn from others that relief from oval turnings was a side benefit.
The original purpose of TBC (and I was calling it "mandrel less" for the first few months) was that I was disgusted with glued on bushings. In particular, oily woods such as ebonies (Japanese persimmon for me) - when breaking the bushings from the blank, the ends of the CA would raise up off of the ebony and look cloudy because of the separation of the CA from the wood. This happened on numerous occasions for me. I asked how this could be prevented. Two guys, mentioned that they had heard of a method from another forum in which the mandrel was not used, and the blank was mounted between centers. After I started using TBC, the CA lifting off the ends stopped for me.
I was living in Japan at the time and did not have quick access to drive centers, so I made my own. I quickly learned that I did not have to fool with dropped nuts rolling under the lathe, nor having to deal with dropped spacers; I also learned that I could take a blank off and inspect it quickly up close far faster than I could take a mandrel off, unscrew the mandrel, take the parts off, inspect closely and then replace all and get started again. The TBC decreased the inspection time by a minute at the least, and I could inspect a delicate segmented blank several times during a turning faster than a single time with a mandrel.
. . . Saying this another way - It is much faster to take a blank off and inspect it with TBC than with a mandrel system. For me, who did segments often, I needed to take a blank off regularly for inspection. TBC saved a lot of time for me.
Also, I found that my accuracy increased as I quit depending on the bushings for sizing and started using calipers.
For others, as mentioned above they found that TBC helped get out of the oval mess.
The original drive center used on this forum and the original TBC blank:
Imported Photo from leehljp. Please edit title and description.
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