Dear Chiff and Fipple: so my left hand thumb nail has caused a slight chip in the outer wood of the thumb hole. the inner circle of the hole appears intact. This has been there for a while and until recently I was able to get clear tones from my upper notes. It may have become slightly worse; I'm not sure but I'm suddenly having trouble hitting upper notes clearly. It could just be a phase--or could the chip be affecting my ability to half cover the bottom hole?

I'm keeping my thumbnail short but that's another question: do people use a short nail of just the flesh when they half cover the bottom hole?

merci in advance.

I used to just use my nail in the thumb hole on all of mine.

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Keith.
Trying to do justice to my various musical instruments.

Thanks; that's what I've intuitively done. did you ever wear a groove or chip one side of the hole?

How about others? is this your technique too?

also: I've played since the post and things sound better; maybe I've just had a few bad practice sessions--in addition I'm playing harder pieces and now that I think about it I've never really practiced the high f before and I'm having trouble with that which may be resulting in issues for other notes.

It's a common repair for recorders to bush the thumb hole with bone (or ivory in the past). Quite standard. I did my own (as I make instruments). You may find a maker able to do that for you.

I only ever created a slight depression on mine, perhaps you are pressing a little too hard.

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Keith.
Trying to do justice to my various musical instruments.

I believe that Kelischek workshop (Susato) will add a bushing to the thumb hole. As mentioned above this is a common repair.

Many recorders come this way at the out set.

Piper Joe

It's hard to re-learn (or un-learn) technique if you have been using it for a long time. I never used my thumb nail in the thumb hole though as the place I get all my recorders specifically warns against it. Rather he recommends rotating the left wrist towards the player and rolling the thumb slightly down from the top of the hole. This is just as precise acoustically as the thumb nail technique, is quicker and does not damage instrument. Most players use thumb nail technique and thus are a souce of continued work for repairers providing thumb hole bushings.
Frank P

I'll just clip my thumbnail short and see how clumsy I am with that.

Happily things have been going better so I haven't damaged the recorder to where it can't sound notes clearly.l I must have just adjusted my thumb position intuitively.

Now that I think about it, as a guitar player I file and shape the nails on my right hand; I'll try rounding the shape of my short left thumbnail and see how that works. With a file you can take the hard and/or jagged edge off the nail.

thanks again for the replies!