Very short bow tillering.

[Craftsman]

Ok, a sneaky one!

I'm not satisfied with the performance of my crossbow prod.

How would you bowyers find the exact 'centre' of the prod to ensure that when in the stock, each 'limb' is pulling the same weight?

The recurve prod is made of moulded and pressed fibreglass, with a nominal centre marked, and then is clamped into a hole through the 30mm wide stock.

I have moved it laterally mm by mm both ways but I'm not sure I'm making much difference, accuracy wise.

So I though I would pick your collective brains, even though it is not your normal medium for working with.

Any (constructive) ideas? (The destructive ones I can think up for myself!)

Brian.

 

[geoffretired]

I am not a bowyer, but I am still interested in the question.

What I would do( rightly or wrongly) Is hang the strung prod, from the centre of the string. Hang a heavy weight on a longish rope, from the centre of the prod and see how it shows up.Just thinking aloud.

 

[Deleted member 7654]

mark the geometric centre.
Clamp it or support it on a tiller at that point. Winch/pull the sting from it's geometric center.
View the curve of the bow.
Adjust the curve of the bow by adjusting the width of the limb, removing material from the lower edge.
(On the assumption you are making it with the top edge straight and all the taper on the underside of the prod).
Here's a wooden one on the tiller. The tips are actually upswept to avoid excessive downward pressure on the track/table/stock whatever we are calling it today.
Bowyer's Diary: Crossbow Prod
Of course most modern Xbows have individual limbs, mounted so that they are effectively centre shot.
Del

 

[Craftsman]

Thanks, now I have to build a tiller, but then again it was something I was gonna have to do anyway if I decide to build/shape my self bow!

At least I have a method to try out.

 

[geoffretired]

Hi Craftsman,Guess who forgot that you were building the Xbow? I thought you had bought one and wanted to check it out!!

 

[Craftsman]

Already built but not happy with the performance yet.

All bolt-shafts cut and weighed, similarly piles all measured and ground down to same weight.

Fletchings attached, flat knocks stuck in,,,,,the only thing I can't control is the fixing glues weight but that appears to be negligible.

I can get 4-5 to group together with the other a flyer but it isn't always the same bolt, (numbered).

So I'm looking at a possible unequal prod limb variance.

I use the same sequence for drawing the string, I have even shot it bench-rested, but something is eluding me,,,,,,grrrr!

 

[Deleted member 7654]

Pictures would help. It the trigger mechanism ggod and solid with no sideways play.
How do the bolts sit on the track?
Is the string contacting the back of the bolt on the centreline?
Are the sights secure?
With it cocked, you should be able to look through one string nock loop, across the top of the track and through the other loop.
What is the brace height? Is it enough to avoid the bow tryling to flip/twist?
Del

 

[Craftsman]

Ok, the trigger unit is solidly mounted but it's not a 'fine' trigger, but having done all my own firearm 'smithing' for 30-odd years, it's about as good as I can get it
I have had to re-mount my 'scope since destroying my rear sight, but it is secure. (Leupold 4xcompact)
The bolts sit partially in the track and as near as I can tell, the string is central and there is full clearance for the fletchings.
When cocked, I can see through the nock loops, but only the top half due to the construction of the stock.
Brace height is what it is and the bow is not twisting as far as I can see and the string is at 90deg to the stock when at rest..