three under tuning

[Rusty in Fla.]

I normally shoot my Martin Vision using split fingers and everything is OK. My son has tried the same bow using three under and it sounds like there is a loud TWANG when the arrow releases. Is this something that cane be tuned out if I shoot three fingers under on a routine basis?

[McDave]

I am in the process of retuning my bows for three under. Generally, I find that the nock point needs to be set anywhere from 1/8" to 1/4" higher for three under than for split fingers.  The TWANG you hear is probably the arrow shaft rebounding off the shelf or the riser.

If my nock height for split fingers was 3/8" - 1/2", it didn't seem to be too much trouble to retune for 3 under.

OTOH, for a bow where the nock point was already high for split fingers, say 5/8" or higher, sometimes the bare shaft results were squirrelly when I tried to retune for 3 under.  It was difficult for me to get good bare shaft arrow flight for 3 under when the nock point has to be 7/8" or 1".  One reason is that when the nock point is that high, raising the nock point seems to affect the spine of the arrow as well as the nock height, so you sort of have two things going on at once.  Or, you think you're getting nock high at 3/4" and you move the nock point down a little to try to eliminate it, but it doesn't, because you're really not getting a true nock high, you're just seeing the effects of rebounding off the shelf.

This is no doubt why bowyers ask whether you're going to shoot split fingers or 3 under when they make the bow, because the ones I had trouble with all had positive tillers of 1/4" or more, whereas bows tillered for 3 under are closer to even tiller.

My advice would be to start at about 1/2" above where you're nocked for split fingers, so you are sure you're getting a true nock high reading, and then move down in very small increments from there, maybe 1/16" at a time, no more than 1/8".  Make sure that each time you move the nock point down, you see less nock high when you shoot the bare shaft, so you know your bare shaft hasn't started rebounding off the shelf.

You may find that when you think you have the nock in the right place, you start getting a nock right, showing a stiff spine, which seems to happen as you move the nock point up.  When you try a weaker shaft, you may find that you need to adjust your nock point again.  Some of my bows, I've played around with for 2-3 days, trying different spines and moving the nock point up and down.  Others took less than a half hour to retune, and I only had to move the nock point once or twice and it was perfect.

[Rusty in Fla.]

Thanks Dave, I'll try moving the nock point a bit and see what happens tomorrow when I shoot.

[McDave]

One thing that would probably work, although it wouldn't be perfect, would be to put another nock a little above the nock you use for split fingers so that the arrow nock has enough clearance at full draw to fit in between the two string nocks.  Then nock between the nocks for 3 under and below the bottom nock for split fingers.

[tj69]

I was shooting a Martin Vision for a year and I had the same problem with switching from split to 3 under.
The bow was extremely loud.Exchange the Martin original string for a new endless one,nockpoint a bit higher and silencers.
That was the solution.