Force Draw Plotter Working

The video is a bit brief and shows a spurious line plotted as I let the bow down, this is because the return spring on the vertical pen travel and the horizontal slide are both a bit slow.
This next video shows the movements separately.

Base Plate and Vertical Travel

You probably can't quite see how it works yet, I have enough trouble visualising it myself!
The horizontal section is now mounted to the base plate, free to slide up and down on two steel tubes. The only thing holding it down (other than gravity) is the spring from the spring balance.
As the bow is drawn the spring will stretch and the horizontal section will lift slightly, this lift will be linked to the pen to draw the vertical displacement onto the graph.
If you don't follow that, just trust me I'm an engineer! If you look closely at the first pic you'll see the spring has come off it's lower mounting (whoops).

Horizontal Travel Mechanism

The mechanism is built with wood, screws and bent wire coathanger, this is so that it can be taken to bits and re-made in a better and more reliable fashion, this is just the mk1, or to use modern engineering parlance a 'proof of concept model'. I prefer the good old fashioned term 'prototype' myself but one has to keep up to date (cough, splutter). Got a bit more done this evening,

It works ok, but the string needs to attached carefully at one side of the roller to get it to track correctly and the plate which will hold the graph paper will need a top guide as it gets kicked off at the slightest provocation.
The wire hook will hook over the bow between your hands as you pull the bow upwards, 28" of travel makes the graph plate slide along about 10".

I've mounted the spring and fitted two lengths of 16mm diameter steel tube to a plate of 1"ply to become the base. Hopefully I'll have some sort of basic working arrangement soon.

Hickman's Bow Weighing Machine

Clarence N Hickman the Father of Scientific Archery, is the title of a book I've had for many years. He was a prolific inventor of all sorts of things* and designed the first modern recurves.
He built a machine which would draw the graph of draw weight vs draw length automatically.
You stood on a plate to hold the machine down, hooked the bow string onto it and pulled the bow upwards. As you pulled up, a plate with a sheet of paper was pulled across, and as the draw weight increased a pen linked to a spring balance moved up drawing the graph.
I'm trying to build myself such a machine just for the fun of it, rather than the serious research he did it for.
Essentially there are two parts, the horizontal travel where the 28" draw becomes about 12" of movement of a sheet of paper, and the vertical travel where the movement of the spring scale is translated into about 8" of pen travel.
The spring balance is a vital part of the machine, and because I recently bought a new dial balance for measuring draw weight, my old spring balance is now available to be recycled into the machine.
I'll post some pics once the first bit (horizontal travel section) is complete. It will be a bit rough and ready as I'm designing it as I go along and it's mostly wooden construction.

* High speed photography, rocketry, acoustics. He was also an amateur magican.
The book is ISBN 0-9613582-003 for anyone interested.

More Scavenging

I went back and tidied up the last badly sawn Hornbeam and took a scrawny length of the bit which had been cut down. One whole side of it had been chaffed away, with no bark and was rotting. You wouldn't think it was worth picking up, but a few minutes with the axe chopping away the bad stuff has given me a stave to make a quick primitive bow with a D shaped back.
It will allow me to have a try with the Hornbeam as it will season quickly. I painted the ends of all the timber with PVA builders adhesive to stop it drying too quick at the ends and splitting (checking), I've read that Hornbeam is prone to checking. I also picked up a nice fat bit of Hazel, a bit of rot has started at one end, but there should be a stave in there.
The beauty of picking up stuff like this is that you can try it out without the worry of working some carefully glued up stave or a precious bit of Yew which you've been seasoning for a year, it's also good to dry different woods.

Tidying the Woodland

I walked up to the town centre via the woodland, there were at least 3 Hornbeam trees which had been sawn down badly at about 2-3 feet from the ground, with a cut which had split down the stump.
I returned later with my saw and tidied up two of them cutting them at about 45 degrees about 10" from the ground, hopefully they'll sprout up next spring.
A guy was passing walking his dogs and said he'd seen a party of school kids from the secondary school the other side of the wood doing clearing and tidying of the pathways and he though a couple of the kids had strayed from the supervision and got a bit saw happy. I'm in no position to criticise, have done done my share of daft things as a kid.
Anyhow I managed to salvage a nice length of hornbeam from the one in the pic' which will hopefully give me a nice pair of billets to splice together into a decent length stave. It's 51/2" diameter and 56" long (whoops I originally put 5'6").
I've not spliced billets before, when I get round to it I'll post the pics.
It weighed a ton and I was sweating like a pig by the time I got home with it across my shoulders like a yoke. Second pic shows how I left it. I also cut a skinny stave from one of the branches, it might make a little primitive bend through the handle bow. I'd rather pick up a stave and then find it's no good later rather than sit at home wishing I'd picked it up.

Odds & Ends

I've been busy doing the fascia and guttering on the front of the house, so the garage now looks like a building site with no room to work on bows.
I've still been busy thinking about bows and a guy in the USA kindly offered to ship me some Osage as I've never used it. It turns out that the cost of shipping is rather high, but oddly, it seems cheaper to ship it the other way!
I had a bit of Yew left too short for a longbow which I though I would ship to him as a sort of trade, I was a bit disappointed as a small knot in one end actually ran along under the sapwood for almost 3" reducing the stave from a respectable 63" to a miserly 58". The guy is a hugely experienced bowyer so I'm sure he'll make use of it.

A while back I posted a picture of some Yew I was hoping to cut next year, I got in touch with the forestry commission as it is on their land. The forester responsible for that area said it would be acceptable to cut it as it's just a side branch, we have to agree on a price first.
Yews are part of a rare and endangered habitat so obviously they don't want people felling trees or taking wood in an irresponsible manner.
I shall offer a good price to compensate for the similar piece I cut without permission many years ago!