Monday, 19 April 2021

Lever Bow Test... lessons learned

 Working on the lighter weight lever bow showed up some really useful points.
Best to watch this Youtube video first to understand what I'm going on about!
https://www.youtube.com/watch?v=Arsk7Kt4vXM



1. Before the string lifts off the levers the bow acts as a short bow with no levers... thus:-
2. The bow, without the levers, needs to be able to be braced and drawn up to the point when you want the string to lift off the levers, This has several benefits.
a) Temporary nock grooves will also come in handy when trying to string the finished bow.
b) The bow is much easier to handle, work on and tiller without the levers.
c) It can be tillered to the desired draw weight and length required at the point string is required to lift off the string bridges.

3. The levers need to have sufficient width to allow string line tracking/adjustment and will probably need guides/bridges to ensure the string is guided correctly onto the levers as the bow is loosed or let down. They also need to be constructed so that they can be shimmed out or rasped to adjust the angle/draw length at which the string lifts.
Note:- they don't need to be very bulky in their finished state, not really any bigger than the tips of a 100# Warbow. The levers on many commercial "horsebows" are ludicrously bulky, mainly because they are made from straight grained timber for reasons of cost!
4. The ratio of lever length to limb length will probably determine the ratio of draw weight per inch once the string has lifted vs when it hasn't.
5. Before proceeding with the heavy bow, I need to have a target draw weight/length for both before and after the string lifts.
You can see in the force draw curve, the string maybe lifts off a bit late? This test bow is too light but if I interpolate the graph to continue without the string lifting off it would probably be 54# @ 28" rather than the 43# @28" which it actually is... Now if we just double those figure, that would give 108# without levers, which I couldn't manage, vs 86# @ 28" with levers which I could ! If the levers lifted a tad earlier, that could come down to a nice manageable 80# @28".
Anyhow, I hope that makes some sort of sense and gives an idea how and why it's a good idea to experiment rather than just diving in and hoping!






Thursday, 15 April 2021

Boo, Hickory, Boo

 One of the guys at the club, Don, wanted me to have a look at a bow he'd been making, he's new to bow making and had got a bit lost, not knowing how to proceed.
He'd done a good job of the glue up and had sensibly made it very long 79". I think he'd rounded the belly too much and put some horn nocks on it, not sure if he'd actually had it on the tiller much, but it had taken a little set, so presumably he had.


The taper in the outer 1/3 wasn't really there which contributed to the weak points where the set was.
Anyway, I videoed it on the tiller, and the lower limb was weak, however sawing 4" off that and marking a new centre restored some balance. It was just a matter of tapering the outers and easing off the rather stiff inner limbs. Removing material from the belly almost took me down to the Hickory core, anyhow, it turned out Ok and made just shy of 50# @28".
Videos here:-
https://www.youtube.com/watch?v=pKb7GIVUrAY
https://www.youtube.com/watch?v=6SPt7j3Rao8
https://www.youtube.com/watch?v=rfQSsqA91QI
https://www.youtube.com/watch?v=uWaoAUhddzI


Sunday, 11 April 2021

Shooting Again!

 


I went over to Boyton Cross for a bit of roving with the gents. I took the recently finished reflexed Walnut bow, as it's not too heavy and I want to see how it performed. The first 3 shots were impressive but on the 4th it went BANG spectacularly.
A very symmetrical break, about 10" either side of the grip.  I suspect the sapwood broke where there is a small knot, but there are also some slight compression cracks showing so maybe the belly collapsed. It's hard to know without some really high speed video.
One of the guy lent me a bow to shoot, it was one made of Yew billets that I'd made for him some time back so it was good to shoot it again... mind I

was understandably nervous at full draw each time I shot!
It was brilliant to get out shooting again, a bit nippy, but some sunshine and good company, plenty of skylarks on the field too.




Saturday, 3 April 2021

Stuff and a little progress

 


I got the Yew heartwood backed with bamboo and glued up with about 1 3/4" of deflex. I've cut in temporary nocks on the sides so I can see how it flexes. I've pulled it to about 110# with the tips barely coming back to brace. Bearing in mind that if I add 10" levers to each end, that will substantially reduce the poundage... I'm not sure how to accurately calculate it, but if I assume a 20" working limb and a 10"

lever, that will give me some idea,  so 110 should become about 73# 2/3. Another guestimate would be that removing an inch off each end of a bow gains 5#... so presumably adding an inch reduces poundage by 5#... so 10" should take off 50# which would give 60#.
So maybe it would become somewhere between 60 and 73#. Of course it was only pulling back a few extra inches on the long string, so I can loose some weight, which is fine especially as there is some pith showing on the belly which would be nice to get past. This is only very early in the build, so I have plenty of bulk to play with!

Meanwhile I'v had to change the 3-way valve in the central heating, as the radiators were getting hot even when the thermostat was turned right down (the water should only be going to the heat the hot water supply, but it was going to the radiators as well). Now I  can fit a new one without draining the system, as I have appropriate shut off valves, but I still needed to move a lot of stuff, including my little milling machine... well, to be honest, I didn't really, but I thought it was a good idea to flush out the hater heating coil in the hot water cylinder, as that had got clogged up before. A rather messy job, but worth doing, even if it just reassured me that it wasn't too clogged. I also cleaned out the magnetic sludge catcher, which certainly needed cleaning. So a job well done, and it gave me some much needed exercise.
I've also been repairing the Deer sculpture that I made my wife 15 years ago for a "big" birthday... doesn't seem possible that it's that long ago, mind it's stood up to the weather quite well.

Thursday, 25 March 2021

Whatever Next...Experimental Bamboo Backed Yew Lever Bow?

 Having finished the 2 Walnut bows... what next?

There is always a dilemma It's fun to experiment, but I don't want to waste premium wood on experiments... but then if you don't use decent materials, can you draw sensible conclusions from the experiment? So I've sorted through some of my Yew and found a reasonably decent piece of Yew heartwood that is too short for a normal bow and not wide enough to become a pair of billets. It's got a few knots and it's cut at a slight angle to the centre of the trunk/limb that it came from. What I mean is that the stave is approx rectangle 40x30mm. The central pith is midway along the long side viewed from one and it's at the edge of the long side viewed from t'other end. 

Anyhow, I'm toying with the idea of a heavy (80-90#) bow, deflexed at the grip with rigid narrow levers angled toward the back. I' thinking that some form of string bridges can allow the outer end of the levers to come into play at about 50% draw length. The hard thing with this sort of bow is to avoid it flipping on the tiller, getting it stable and in line and tillering it in the early stages. To avoid some of this I may try to make the levers very deep so they can effectively be inline with the limbs for early tillering and then re-shaped to become more backset later.
This sort of idea is something I've been tinkering with over the years and the closest I've really come is the Hazel primitive with flipped tips a tryout with Monkey Bow and the horn bow project that I took over from another bowyer.

Relatively wide limbs should help stability and resist some twist exerted by the levers, the deflex at the grip and a fairly high brace should also help. I'm thinking, maybe laminate the levers as a sandwich of yew and bamboo in a V cross section. I may build up the riser and cut away the arrow pass, I'm hoping for a fast bow for flight/roving. It won't win any flight competitions though as it would probably have to compete in a recurve class against glass/carbon faced bows

Oddly I've been doing so much more as video on Youtube, but these early stages are more abouts thoughts and ideas than action, so I find the blog is a better tool.
So fear not dear reader... the blog is still alive!

Saturday, 20 March 2021

Got the Walnut mk2 Finished.


 It shoots nicely, it took a bit of fiddling and fettling to adjust the arrow pass to give clean flight with my standard arrows. I took some video of me shooting it, had to do the vid' 4 times in total as the first two attempts cropped 1/2" off the top limb... 3rd attempt was too far away with loads of dead space. Got it right eventually but could really feel it on my shoulders.... it's only 50#, but that the result of lockdown!
It certainly looks handsome.
link to the video here:-video

Update:- just tested it through the chrono 177fps with a regular arrow 186 with a 27" test flight arrow. That's about what I expected, it would be interesting to try it with a 28" flight arrow, but I don't want to risk it with one of my decent ones, as they may possibly smash when they hit the backstop (an old duvet rolled up in a bag hanging up in front of the back stop netting) 







Tuesday, 16 March 2021

Walnut Bow Is a right Pain!

 It's been driving me to distraction, even slight changes seem to make the tiller shift from one limb stiff to the other limb stiff and back and forth. I've take it slow steady and methodical, I think one problem has been that any heat treating has allowed the bow to try and return to its original shape.
Anyhow it's virtually there now, but even just taking out the tool marks with the scraper on each limb seemed to cause a bit of shift... I'm almost dreading putting on the horn nock overlays.
I've been videoing it as I've done the work and made a Youtube playlist... it dawned on me it's rather long, but then it need patience to make a bow so a bit of patience may be needed to watch the process!
Can't seem to get anything right on this bow! I cut the nock grooves in the wrong nocks... grr... I had


enough bulk on one to re-shape it, but had to re-do the top nock to accommodate a stringer groove.