What methods do folks use to file out pits in a smooth concave rubs?

A great deal of care as you do not know how thin they can be.

Two ways I can suggest , make a wooden block the profile of the concave and either wrap a piece of emery cloth round it .
Or , take a half round file cut off the tang and adhere it to a block of wood say two inches deep as a handle and use as a float .
Shaped scrapers can also be used but again with caution and some practice .

Round mold makers stones or soft stones work great as well.

Bill. I heat up a chainsaw file to red just ahead of the handle then bend to about a 45. You can now lay the file flat on the rib. I do same with a rod slipped inside some rubber tubing to make a backer for low tack PSA abrasive.

The bent chainsaw file is working great, Mark. I bent it to provide a handle, and also bent the nose up slightly so it doesn’t dig in anywhere.

What is PSA abrasive?

Peel and stick adhesive. (PSA)

SRH

Bill, I just grind a radius on the end to prevent scratching .

Hear is the paper I use. It sticks but does not bond so it removes easily . I also use Norton A275 sheets as well.

https://www.nortonabrasives.com/en-us/a275op-ao-fine-grit-paper-psa-roll

What a great place to hang out. You guys and your willingness to share are truly inspirational.

Many Thanks

Travis

Thanks Mark. I’ve been using various diameters of heater hose, split lengthwise. It will flex nicely as the barrel taper changes. I think that paper would well for that use as well.