Extenders

[JohnK]

I've made a 6in Beiter extender for myself by cutting down a longer rod and adding tuners. Works very well.

[robbo]

out of interest how did they show u to do this??

It would be wrong of me to give a detailed explanation as I have only seen this once and felt I didn't get all the info, hence I may give incorrect info myself, but here's what I remember:

He turned the bow upside down and balanced it on his finger inside the bridge part of my riser. I can't remember exactly where the point of balance should be, but my bow rocked backwards which meant that the weight was too far toward the rear of the riser. The bow needs to be front heavy so I added some spare mid weights I had to the long rod, this made it front heavy.

After adding these weights I do feel that the bow behaves better immediately after the shot, it moves forward in a straight line then tips forward nicely. This is apparently what is supposed to happen.

[Wrexham Exile]

thats sounds ok, may give it a go

but where do you mean by the bridge of the riser? is this the arrow shelf or by the grip?

cheers Al

[robbo]

no, don't forget that I shoot the W&W expert riser that has the carbon bridge which sticks out the front of the standard riser by some 3 inches so my point of balance will be in a different place to yours.

This is the info i'm lacking, i don't know where the point of balance on a standard type riser should be measured from, I would quess that it should be checked at the point where your long rod or extender screws into the riser, but that is just a guess.

[Wrexham Exile]

ah ok, no worries robbo and thanks for the info,

i will have a play later on today i think.

[geoffretired]

Thanks Joe.
I sort of follow the maths from my school days? In my simple terms, am I correct in thinking the extender allows longer back rods to be used while giving the same c.o.g. and longer rods are better for vibration damping?
Would I be right in thinking that as there is more mass on the sight window side of the riser, there is a need for some extra mass on the opposite side to reduce the dynamic torque that shooting will put into the system? I see that a long rod will inhibit the torque(horizontal) caused by the extra mass on one side. But extra weight to give a balance will almost eliminate the tendency in the first place.Or am I wrong? Fixing the long rod over to one side of the riser would do both jobs with no extra mass;or wouldn't it?

[robbo]

Would I be right in thinking that as there is more mass on the sight window side of the riser, there is a need for some extra mass on the opposite side to reduce the dynamic torque that shooting will put into the system?

I have W&W short rods, and whether by design or shear good luck one of them is slightly longer than the other. I have noticed that when I put the slightly longer one on the opposite side to the sight, the bow moves in a straighter line. Put it on the sight side and the bow leans that way after the shot.

Anyone else noticed a difference in their short rod lengths?

[geoffretired]

To find where a bow(Or anything) balances you hold it lightly, in different places, so it can hang free. The nocking point is a good place and the sight bar is another. You could use a hole in the riser or a wheel on a compound. Three is a good number to use as they cross reference each other.
Each time you let the bow hang free, you imagine a line vertically down through the point where you suspend the bow. It helps to get the right idea if you draw a sketch of the bow. turn the sketch round to match the way you held the real one and draw the line on the sketch, vertically down from the place where you held it. After three hangings, you will have three lines on the sketch. Where they cross is the balance point of your bow.
If the sketch is too inaccurate the lines will cross making a small triangle near the balance point. Make a better sketch and repeat. If you want to be very accurate you would use a plumb line to indicate the vertical lines on the real bow and use a full size photo to represent the bow. James Park says he likes the lines to cross just in front of the throat of the grip.
When you suspend the bow a few times it is easy to get an eye for it and you can just imagine the lines and where they would cross. Double check by holding the bow where the lines appear to cross and it should feel in balance there.

[joetapley]

In my simple terms, am I correct in thinking the extender allows longer back rods to be used while giving the same c.o.g. and longer rods are better for vibration damping?

Difficult to explain this as you've got several balls in the air at the same time. Bottom line is you mustn't overtress the extender as you loose dynamic stabilisation. By putting the twin weights in the plane of the grip they have nominally zero impact on rotation around the horizontal axis through the pivot point. If the weights are forward of the grip this increases the stress on the extender (bad); if the twin weights are behind the grip then you reduce the gravity torque on the bow (bad).

The archer damaging vibrations are the high frequency ones. With no TFC the longer the rod and/or the heavier the end weights the lower the vibration frequency. Given the extender length (for long rod stabilisation) the twin rod length is defined by the geometry and the end weights for balance. Rods can be too long (lower vib frequency) so practical result is flat or fairly low angle down for twins.

Would I be right in thinking that as there is more mass on the sight window side of the riser, there is a need for some extra mass on the opposite side to reduce the dynamic torque that shooting will put into the system? I see that a long rod will inhibit the torque(horizontal) caused by the extra mass on one side. But extra weight to give a balance will almost eliminate the tendency in the first place.Or am I wrong?

This imbalance is so small compared with other factors that most archers don't bother with it - granted some do. Preference is for a rigid V bar unit rather than an adjustable one - one less thing to go wrong.

Fixing the long rod over to one side of the riser would do both jobs with no extra mass;or wouldn't it?

Some bows have offset riser bushings. As above effect is minor and having a central rod for alignment purposes, to me anyway, seems much more useful.

ps A quick way to get bow COG (two dimensions is to use the long rod). Balance the bow with finger on riser so that long rod hangs vertically. Balance the bow with finger on extender so that the long rod is horizontal. This gives you the two lines for COG position.

There is no real optimimum cog position. The further in front of the grip the better. Also the lower the cog is below the grip the better. There are practical limits to both these positions re strength, weight etc. Historically there is a lot of bad info around about this from standard coaching opinion based on no understanding of the mechanics putting the COG at the grip or level with the grip (GNAS coaching manual (I think) and Archery Anatomy are examples).

[wingate_52]

I was told that if you upend the bow, the point of balance should be 1 inch away from the riser with your finger underneath the extender or longrod.