Saturday, 9 February 2013

Catleg Bow Full Draw

The bow has now had 60 arrows through it and has had a little scraped off here and there. It's now pulling about 48# at 26 which is probably just about right.
You can see at full draw the ripples and deflex kick in the limb are still visible.
Later I might add a composite pic with the two shots overlaid so the deflection at each point along the limb is visible, but there's tea and toast to be had...
A pic is worth a thousand words.

I've done the composite pic, and was about to jump to half arsed conclusions but managed to stop myself in time.
It would be easy to look at the composite pic and say the left limb tip has moved a lot further than the right, therefore that limb is too weak... Ah but in the words of a well known comedy character yeah but no but.
The way I set it up on the tiller allows it to pivot as the string is drawn back, due to the fact that the bow is supported pretty much central but drawn at the nocking point. If you flip rapidly between the two pics (you may have to copy them onto the desk top) you will see the grip remains relatively static... yeah, but I just said it's free to rock! (I can't have my cake and eat it too). So Is the lower limb weak? Is the whole tiller the lower limb stiff a myth, do I trust my eye rather than measurements? Can I be bothered to clamp it rigid and repeat the test?
Well no, there comes a point where over analysis adds to the confusion rather than clarifying it.
Measurement and analysis is a guide, a tool, same as maths... no good throwing a load of maths at something if the answer doesn't match reality or help your understanding.
One has to remember that the deflection at any one point is very difficult to see, we get the overall curve, but if you try to look at the bend over a 6" section you will be lucky to see anything.
One could always make a bend meter that you can clamp to a point on the limb with a dial gauge that presses on the limb say 3" further along, that way you could get loads of data and plot lots of nice graphs. But why would you? It was all done many years ago by Clarence N Hickman when he made the first scientifically designed bows. If that's what I wanted, surely I'd be shooting a modern recurve.
There is always a tension between buying fancy tools to make the job quicker and easier, but at the risk of destroying the process which I do for the love of it (sobs into mug of tea).

So, whats the conclusion?
I shall do very little, but if I do any more minor adjustments, they will probably be with a scraper and to the upper (right limb), as it is probably just a whisker stiff. Note, this is pretty much in line with what I've been saying earlier during the tillering process. I do have a few pounds of draw weight to play with still as I'm looking to be between 45 & 50# at 26".
Interestingly, If you hold a CD up to the pic you'll see I've pretty much hit my usual arc of a circle tiller and if you compare it to the pics from one of the earlier posts you'll see it looks much better. Sometimes the changes are quite subtle, and going back to the earlier pics allow me to see the changes.

I've given the upper limb a good going over with the scraper and shot it some more, it's about midway between 45 and 50 now, I'm reluctant to say 47 1/2 # as you just can't measure that accurately.
It's now had 75 arrows though it and has drawn blood! One of my poor attempts at a left handed shot scored my right hand with a fletching, but at least I hit the back stop.
Just down to the cosmetics now, I might do the arrow plate this afternoon.

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