Back check distance in an upright?

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Withindale
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Back check distance in an upright?

Post by Withindale » 06 Oct 2011, 15:10

Hallo

The standard for backcheck distance is 5/8" (15 mm) after mf blows. My 1925 German upright seems to require rather less to catch the hammer high enough for the jack to return quickly for repetition. After pp blows in this position the catchers align with the top of the backchecks and the two just come together. This appears to be in line with the geometry or am I missing something. Thank you.

Ian

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Barrie Heaton
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Re: Back check distance in an upright?

Post by Barrie Heaton » 06 Oct 2011, 19:52

the 15mm is only a guide its how the piano feels that counts. Some pianos are set to 12mm to give them more repartition some older V strung pianos were set to 20mm with a 50mm blow

Barrie,
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Withindale
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Re: Back check distance in an upright?

Post by Withindale » 06 Oct 2011, 20:22

On my piano the distance is down to about 6 mm on stronger blows, with after touch set so the jack is at the point of escape as the key reaches the front punching. Que Sera Sera?

Ian
Last edited by Withindale on 07 Oct 2011, 00:46, edited 2 times in total.

Withindale
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Re: Back check distance in an upright?

Post by Withindale » 06 Oct 2011, 20:25

Barrie's point about blow distance of 50 mm on older V strung pianos is interesting to me; I wondered why it's about that, along with a key dip of well under 10 mm, in my recently acquired "project piano" (well used 1922 Ibach 125). The checking distance does not appear to be anything like as much as 20 mm - but all this is another story.

Ian

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Re: Back check distance in an upright?

Post by Withindale » 12 Oct 2011, 22:28

Barrie Heaton wrote:... its how the piano feels that counts. Some pianos are set to 12mm to give them more repartition ... Barrie,
This YouTube movie http://www.youtube.com/watch?v=16zHYs70Yao shows repetition on a Schulze Pollmann 126 after regulation. The sequence around 00:35 to 00:45 shows a back checks after a soft key stroke. Is this ideal or would it also be in order to set the back checks a bit farther back so that the jack slipped under the butt later in the cycle as the key returned?

Ian

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Re: Back check distance in an upright?

Post by Barrie Heaton » 13 Oct 2011, 19:15

Withindale wrote:Barrie's point about blow distance of 50 mm on older V strung pianos is interesting to me; I wondered why it's about that, along with a key dip of well under 10 mm, in my recently acquired "project piano" (well used 1922 Ibach 125). The checking distance does not appear to be anything like as much as 20 mm - but all this is another story.

Ian
The Noches (knuckles) were smaller and the angle of attack was less very much so on the spring and loop action

Barrie
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Re: Back check distance in an upright?

Post by Barrie Heaton » 13 Oct 2011, 19:23

Withindale wrote:
Barrie Heaton wrote:... its how the piano feels that counts. Some pianos are set to 12mm to give them more repartition ... Barrie,
This YouTube movie http://www.youtube.com/watch?v=16zHYs70Yao shows repetition on a Schulze Pollmann 126 after regulation. The sequence around 00:35 to 00:45 shows a back checks after a soft key stroke. Is this ideal or would it also be in order to set the back checks a bit farther back so that the jack slipped under the butt later in the cycle as the key returned?

Ian
any more than 15mm and you will cause problems in repartition also makes the action feel heavy to the player

Barrie

Just so anyone reading this understands 15mm is the distance from the string to the nose of the hammer when in check, not the distance from the check to the Balances hammer (chacher).
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