Duysen Action Update

[Richard Brekne]

Ok boys and girls. For those of you following this and perhaps having a
good chuckle at this greenhorns first attempt at this kind of thing.. I
thought I would give you a bit more on this, as I am in the final stages
now.

After reading a few posts concerning related themes I started to get a bit
worried that perhaps I had blown it big time in deciding to move the
capstan and whippen cushion in so far. (12mm for the capstan and 9 for the
whippen cushion, the top spread was also moved in by 3 mm so that the jack
center lined up nicely with the knuckle with the hammer at proper rest
distance from the string.)

The origional configuration consisted of the following

Hammer centerline to hammer shank center 131.5 mm,
knuckle center line to hammer shank center 17 mm

Repetition arm length 92 mm
whippen horizontal arm length 68 mm

Key ratio 0.60 - 0.61

This gave if I am not mistaken in my calculations a total vertical hammer
movement of 64.3. which gives a 6.43 to 1 ratio for a key dip of 10 mm.
(grin I am not exactly sure that I have my calculation routine down right..
but I suppose you all will correct me on this... I took 6.0 * (92 / 68) *
(131.5 / 17) for hammer movement)

The new configuration is as follows

Hammer and knuckle centerlines to hammershank center unchanged.

Repetition arm lenght 92 mm
whippen horizontal arm length 77 mm

Key ratio 5.6

useing the same calculation I come to a hammer vertical movement of 51.85
mm or a total action ration of 5.2 to 1.

I havent taken into consideration lettoff distance in all this.


The action regulates well with a key dip of 10 mm and a hammer to string
distance of 46 mm, so I figure my measurements (done with a straight edge
ruler so admitedly suspect) might be a bit off. In any case these two
settings leave the jack nicely "just" clear of the knuckle at a 2 mm
letoff.

I made decisions relating to capstan and whippen cushion movement based on
attempting to get the key ratio and whippen radius weight to multiply out
to as close as 9.0 as I could... thinking I should conform to Stanwoods
charts as best I could. I have heard from a couple that this way of
proceeding is misinformed. At the same time I took pains to moderated this
by insuring that the whippen cushion / capstan contact point lay on the
magic line at half key stroke and insured useing temporary inserts for both
of these peices that the whippen would indeed rise enough to insure letoff
correctly. (which probably saved my butt on this one...grin)

I will have the rest of the hammers bored and mounted, and implemented a
Strike weight in the next few days and will post the Stanwood figures when
I do.

One question stands out in my mind tho.. As I understand things the whippen
I have "constructed" has a pretty off the wall arm length ratio. What, if
any are the implications of a whippen with such a low ratio. (1.2 to 1) ?

Thanks to all who have been discussing the various threads relating to
Terry's questions and this action, and the general insueing discussion on
action analyses.

--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway