Practical action geometry question?

[Richard Brekne]

Sounds to me like you had to regulate the jack out quite a bit to meet the
knuckle. 3 mm is quite a lot of difference. I suppose this in effect shortens
both lever arms if you have the spread set so that the jack is at 90 degrees to
the hammer shank at rest. Lots of fun here. Still.... if you set the spread as
above, and adjust key travel / hammer travel  as neccessary to achieve
acceptable dip and letoff parameters you should be able to make it work well
enough.

Getting theoretically correct hammer and key travel might be a bit more
complicated tho. 

RicB

 Brian Trout wrote:

>Hi list,
>
>I've been doing some reading, at least what I
>could find at my fingertips, on action geometry,
>and although I can find a lot of general stuff,
>and a lot of theory, specifics aren't quite as
>easy.
>
>I've changed out the wippens and
>shanks/flanges/knuckles on a well known action. 
>The new parts are Renner and are the closest I
>could get to original dimensions.  However, they
>are NOT identical.
>
>The wippens are shorter in length by about 3mm,
>the variation appearing to be mostly out at the
>jack end of the wippen. When I leave the action
>spread at 4 1/2", as was the original, the jack
>doesn't have room to clear the knuckle before it
>burys itself in the felt stop at the end of the
>wippen.
>
>I can't seem to get a picture in my head of the
>negative effects of shortening the action spread,
>or if I'm doing anything wrong at all.  It's been
>drilled into us tech types that the action spread
>is sacred and NEVER to be messed with.  Well, I
>had to do something, 'cause the way it was, it
>wouldn't work, period.
>
>What has seemed to work in this instance is
>moving the hammer rail forward about 3mm. 
>(Another possibility would have been redrilling
>the hammer rail to put the flanges a few mm
>farther back <towards the back of the keys>). I
>just wanted to run it past someone else who might
>have seen this stuff before just in case I'm
>overlooking a disaster looming on the horizon.
>
>Any insight?
>
>Thanks,
>
>Brian T.
>
>
>=====
>Brian Trout
>Grand Restorations
>3090 Gause Blvd., #202
>Slidell, LA  70461
>985-649-2700
>GrandRestorations@yahoo.com
>
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Richard Brekne
RPT NPTF
Griegakadamiet UiB