I have been playing around with axles as I got an axle kit. First off, I measured each axle stock with a micrometer and they are all in the .519" to .529" range (including the 3 that came with my TMBRs).
On my Baldwin I shaved down the stock Walnut axle down to .455" and I think it is just about where I want it.
In my Turner, I shaved down an oak axle (didn’t want to mess with my purple heart axle just yet) to .5" even and I will probably shave some more off. I’m still trying to find the sweet spot for both the Freemont and Turner and both of them still need to break in a little more. I notice smoothing out from friction and my oils in the wood really seem to make the bigger difference in (less) response compared to axles as I don’t notice hardly any difference in response when changing those out so far. The oak so far gives me the most response but I really have to watch the cotton string because it tears through them fast. I’m sure the oak axle needs to break in some more before it becomes consistent.
Speaking of break-in and string. I was playing with only Kitty string fat because I couldn’t get my TMBR yoyos to respond how I liked. Eventually, the Baldwin surface became smooth from play and I simply could not get the Baldwin to respond, so I switched back to type 8 cotton. Then my Baldwin kept taking flight every 20 min of play because the string kept snapping at the axle. Now I have type 10 cotton and sure hope that ends. So far so good today.
I played for 5 days on one poly string before it looked like it was too melted to trust anymore. I guess my style is hard on cotton, but not on poly. I still plan on making my own cotton string, but just haven’t had the time to research.