Stefan's Florilegium

WB-tuning-FAQ

WB-Tuning-FAQ - 3/27/97

Walk-back tuning of bows.

NOTE: See also the files: archery-books-msg, C-A-handbook-art, arrows-msg,
crossbows-msg, arrow-making-FAQ, arch-hist-FAQ, clout-shoot-FAQ.

************************************************************************
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mark.s.harris@motorola.com stefan@florilegium.org
************************************************************************

From: bblohm@boi.hp.com (Bill Blohm)
Newsgroups: alt.archery,rec.sport.archery,rec.org.sca
Subject: FAQ: Walk-back Tuning
Date: 19 Dec 1996 18:46:10 GMT
Organization: Hewlett-Packard Co.
Summary: This posting contains the alt.archery FAQ section containing
instructions for performing a walk-back tuning of your bow.

This is a section of the FAQ for alt.archery. It is maintained by me at the
following e-mail address: bblohm@hpbs1686.boi.hp.com
Comments, flames, etc. on the FAQ are welcome and should be directed to me.
Comments on the specifics of the section can be addressed to either me or the
person responsible for this section. If addressed to me, I will forward them
to the author of the section. If you wish to see this section cross-posted to
another group, please e-mail me a request to do so. If I can access that
group, then I will so cross-post whenever I post this section.

Bill Blohm
bblohm@hpbs1686.boi.hp.com

*************************************************************************

CREDITS:
Stephan Melin (melin@hlrserv.hlrz.kfa-juelich.de)

*************************************************************************

Arrow selection and tuning FAQ.

by Stephan Melin (melin@hlrserv.hlrz.kfa-juelich.de)

Comments, flames etc. directly to me...

--------------------------------------------------------------------------

Last updated: 21th March 1994

Contents:

A. walk back tuning (Gerhard Gabriel's method)
(should be valid for all types of bows and shooting styles)
B. cushion plunger tuning (also known as the Vic Berger method)
(only for bows with a cushion plunger)
C. paper tuning
(mainly for archers using a mechanical release)

--------------------------------------------------------------------------

Because the subject of tuning the bow is still a bit controversial, I will
give you my philosophy (which I also apply on shooting style):
- the bow is perfectly tuned, if it gives you the tightest grouping
- the goal of tuning is to get a setup which is most forgiving of slight
variations in shooting style (we are no robots!) and other (external)
conditions

--------------------------------------------------------------------------

IMPORTANT NOTE IMPORTANT NOTE IMPORTANT NOTE IMPORTANT NOTE IMPORTANT NOTE

In section A and B I sometimes write something like:
"Shoot an arrow..."
This sloppy writing could be somewhat confusing, what I mean is that one
should shoot a couple of arrows and determine the centre of the group.

IMPORTANT NOTE IMPORTANT NOTE IMPORTANT NOTE IMPORTANT NOTE IMPORTANT NOTE

--------------------------------------------------------------------------

A. walk back tuning (Gerhard Gabriel's method)
==============================================

Most of the stuff should be valid for all types of bows (longbow, target
recurve, compound), all types of arrows with target or field points or
broadheads and for finger as well as for mechanical release shooters.
It is assumed that one starts with an arrow which is not totally wrong
for the bow (look into the arrow selection charts of the manufacturers!)
Everthing else like the string length for example should be
set to a reasonable value (maybe you use the recommended values from the
manufacturer...). If you don't have a cushion plunger just ignore the
remarks about the plunger. If you have an adjustable rest you can apply
the remarks for the plunger.

While the paper tuning test might help you to tune your compound shot
with a mechnical release it might be somewhat misleading when used
only for a single distance as all other single distance "tuning" methods.
All those methods have a major drawback: they will help you to setup
your bow that it is tuned for this distance, but for any other distance
it might be completely detuned. The method described here overcomes this
drawback by shooting at different distances and works for all types of
bows and shooting styles.

The distances given in the following method are just a suggestion.

Preparation:
Get a ruler, a pen, a fletched arrow and an unfletched arrow
(same spine, point, length, etc.) which are _PERFECTLY STRAIGHT_
(read: new arrows).

Make a target face which looks like this (take the back of the biggest
target face available and make this drawing as big as possible):

|
|
|
|
|
|
------------#-----------
|
|
|
|
|
|

You should always aim at the # in the middle of this cross.

Now make several blank diagrams like this:

30m -------+----+----+------
| | |
27m -------+----+----+------
| | |
24m -------+----+----+------
| | |
21m -------+----+----+------
| | |
18m -------+----+----+------
| | |
15m -------+----+----+------
| | |
12m -------+----+----+------
| | |
9m -------+----+----+------
| | |
6m -------+----+----+------
| | |
3m -------+----+----+------
-7 0 7

The x axis gives the distance in cm of the arrow from the horizontal or
vertical (this depends from what you are tuning) centerline.

Set the sight to approximately 30m (if you are a barebow archer, just
remember to aim always in the same way as if the target were 30m away -
regardless how far it is away).

Everything which I describe is valid for a right hand archer (the arrow
is on the left side of the bow if one looks from behind) - for a left hand
archer it is the opposite...

Step 1 (coarse adjustment):
Set your cushion plunger (or Berger button) head so that the arrow is exactly
in the centre, the pressure of the spring should also be set to an
intermediate value. Set the aim so that it is also at the centre (horizontal).
Set the aim vertically to 30m.

Shoot a few fletched arrows at the target and look where the group goes.
If it is left from the centre increase the spring tension, if right
decrease the tension. Repeat this procedure until the group is at the
centre.

The spring tension should be in the intermediate region. If it is much too
weak the arrow is way to stiff, if it is much too strong the arrow might be
not stiff enough, in this case you could try moving the position of the
cushion plunger head a little bit left and decrease the tension, then repeat
step 1 until the group is in the centre.

Step 2 (arrow selection):
Shoot a fletched and an unfletched arrow at all the distances marked
on the chart. You should always aim at the same point. Measure
the HORIZONTAL distance from the VERTICAL centre line and mark these
values in your chart. Now connect the points for the fletched arrow
and connect the points for the unfletched arrow.

The line for the fletched arrow should always be near the 0 line
(if not, look at step 4). Now look at the line for the unfletched
arrow. If the arrow is ok, it should be more or less parallel to the
line for the fletched arrow and you are done with the tuning.

Here are a few deviation patterns:
O denotes the unfletched arrow
X denotes the fletched arrow
* denotes both on the same spot

30m -------+----X----+------
| | |
27m -------+---X+----+------
| | |
24m -------+---X+----+------
| | |
21m -------+----+-X--+------
| | |
18m -------+----+X---+------O
| | |
15m -------+----+-X-O+------
| | |
12m -------+---XO----+------
| | |
9m -------+--OX+----+------
| | |
6m -------+-OX-+----+------
| | |
3m -------+--*-+----+------
-7 0 7
It starts to deviate at distances less than 15m:
This means the arrow is not stiff enough - get the next stiffer one.
If it deviates to the left, it is too stiff - get the next less stiff one.

30m -------+----X----+------
| | |
27m -------+---X+----+-----O
| | |
24m -------+--X-+---O+------
| | |
21m -------+----*----+------
| | |
18m -------+-O--+-X--+------
| | |
15m -------O----X----+------
| | |
12m ------O+-X--+----+------
| | |
9m -------O--X-+----+------
| | |
6m -------+-OX-+----+------
| | |
3m -------+--OX+----+------
-7 0 7
It starts to deviate at distances greater than 15m:
The arrow is not stiff enough - cut it a little and/or get a lighter point.
If it deviates to the left, it is too stiff - get a heavier point and/or
choose a longer one.
If both lines intersect: your setup of the cushion plunger is wrong...

30m -------+---X+O---+------
| | |
27m -------+----*----+------
| | |
24m -------+---OX----+-----
| | |
21m -------+--OX+----+------
| | |
18m -------+---XO----+------
| | |
15m -------+----XO---+------
| | |
12m -------+----OX---+------
| | |
9m -------+---X+O---+------
| | |
6m -------+----XO---+------
| | |
3m -------+----+*---+------
-7 0 7
The setup is OK.

30m -------+----+X--O+------
| | |
27m -------+--X-+--O-+------
| | |
24m -------+OX--+----+------
| | |
21m -------+----+-X-O+------
| | |
18m -------+--X-+O---+------
| | |
15m -------+--O-X----+------
| | |
12m -------+----+-XO-+------
| | |
9m -------+--OX+----+------
| | |
6m -------+---O+X---+------
| | |
3m -------+---X+O---+------
-7 0 7
Although within the tolerances, you might want to change something in
your setup: use a heavier arrow, adjust the cushion plunger, change the
string length, change the stabilization...

Step 3 (nocking point):
Shoot a fletched and an unfletched arrow at all the distances marked
on the chart - just like in step 2. But now measure the vertical distance
from the HORIZONTAL centre line and mark these values in your chart.

How to interpret the curves:

30m -------+----+---*+------
| | |
27m -------+----*----+------
| | |
24m -------+-*--+----+------
| | |
21m -------*----+----+------
| | |
18m ------*+----+----+------
| | |
15m -------*----+----+------
| | |
12m -------+*---+----+------
| | |
9m -------+--*-+----+------
| | |
6m -------+----*----+------
| | |
3m -------+----+-*--+------
-7 0 7
Both curves are parallel - the nocking point is OK.

30m -------+----+--X-+------
| | |
27m -------+----X----+------
| | |
24m -------+-X--+----+------
| | |
21m ------X+----+----+--O---
| | |
18m -----X-+----+--O-+------
| | |
15m ------X+----+O---+------
| | |
12m -------X----O----+------
| | |
9m -------+-X--+O---+------
| | |
6m -------+---X+-O--+------
| | |
3m -------+----+X-O-+------
-7 0 7
The nocking point is too high.

30m -------+----+---X+------
| | |
27m -------+----X----+------
| | |
24m -------+-X--+----+------
| | |
21m -------X----+----+------
| | |
18m O ------X+----+----+------
| | |
15m --O---X+----+----+------
| | |
12m -----O-X----+----+------
| | |
9m -------+OX--+----+------
| | |
6m -------+--OX+----+------
| | |
3m -------+----OX---+------
-7 0 7
The nocking point is too low.

Source:
Gerhard Gabriel "Pfeilflug wie auf Schienen"
If you can read german, this is very nice little book about tuning
and a few other aspects about practise and tournaments.

--------------------------------------------------------------------------

B. cushion plunger tuning (also known as the Vic Berger method)
===============================================================

This step can be skipped if you everything went fine with the method
of section A. It also can be used for a quick retuning of the bow.

Here you only need to use fletched arrows.
Shoot the arrows at the different distances and measure the HORIZONTAL
deviation from the VERTICAL line. Fill these points into your chart.

Everything is for a right handed archer, left handed archers should
invert all advice.

a) Setting the position of the head (I hope that this is the right
term!!!):
If it looks like this:
30m X
X
X
X
X
X
X
3m X
move the head of the plunger a little in the right direction until it
becomes a straight line. If the curve is oriented in the other direction
move the head of the plunger a little to the left. Repeat this procedure
until you get a straight line.

b) Setting the spring tension:
If the line looks like this:
30m X
X
X
X
X
X
X
3m X
decrease the spring tension until the line is perfectly vertical.
If the line is oriented in the other direction increase the spring
tension...

--------------------------------------------------------------------------

C. paper tuning
===============

The method I describe here should work best, when using a mechanical release
- however I am willing to accept otherwise.

Preparation:
Put a sheet of paper into frame and fix this frame in front of sufficient
back stop - but far enough away so that the arrow can pass through completly.

Now start at about 1m (0.9m = 1 yard) distance from the paper and shoot your
arrow at the paper.

Inspect the hole it made, the advice given is for a right handed archer, the
left handed ones should invert the advice where appropiate:

1.a #
*
*
*
*
*
#
/ \ <- these are the vanes
/ \
/ \

your nocking point is too low

1.b \ /
\ /
\ /
#
*
*
*
*
*
#

your nocking point is too high

2.a \
\
#******#
/
/

either the arrow is too soft, or the spring tension of the
cushion-plunger should be increased
(left handed archers

2.b /
/
#******#
\
\

either the arrow is too stiff, or the spring tension of the
cushion-plunger should be decreased

Of course any combination of 1 and 2 can occur.
Repeat until the hole looks like this:

\ /
\ /
\ /
#
|
|
|

Now the arrow is perfect for this distance.

This test should be repeated in about 1m steps until 5m distance from the
paper. If everything is ok, repeat these tests on a larger distance - until
you find the best compromise.

--------------------------------------------------------------------------

As ever: mail your comments to

Stephan Melin (melin@hlrserv.hlrz.kfa-juelich.de)

I would be happy to get some feedback, especially if you have the tuning
method which improves the scores by at least 1 point :-)

<the end>