Monday, 28 May 2012

Club Shoot

We had a scorching hot day for the club NFAS Friendly shoot, a good turn out with plenty of people visiting from other clubs. I shot my favourite Yew primitive 'Twister' and was just about hitting everything first arrow until I got cocky when asked how it was going and promptly missed a rubber Turkey at close range with all 3 arrows. The course was 15 targets (all 3D rubber critters), going round twice, so I got another go at the damn Turkey... couldn't believe I dropped the first arrow just under him but I got him 2nd arrow much to my relief.
After the shoot some of us were shooting on the field and trying each others bows, a couple of guys had a go with Twister, never having shot a Yew bow before. They were favourably impressed.
I was pleasantly surprised to find I'd won the shoot, but was a slightly concerned that I'd counted a shot which was in the horn of the deer on one target. No one could give a clear ruling on if we were counting hooves and horns as hits. I didn't loose any sleep over it as it was a long shot for the first shot. The peg for the second shot was much closer and broadside on to the deer and I knew I'd have got a second shot wound easily. It was nearing the end of the shoot, we were all hot and tired and the next group of archers was waiting to shoot that target so I couldn't be bothered to walk back and take the second shot. Anyway a '2nd shot wound' have dropped 4 points against the 'first shot wound'. In fact I think I'd have won even if I'd missed with all three!
For those field archers who are interested the score was 456 and there were mostly longbows shooting with a sprinkling of recurves, horsebows and American flatbows, so my twisted Yew stick did pretty well :) .
 Hmmm, that sounds a bit obsessive, but I'd much rather loose fairly than win by being considered to have bent the rules or indulged in any gamesmanship. That's why I tend to shun formal competition, I'm happy enough just shooting against myself and enjoying the company.
I got home pleasantly tired and hungry enough to enjoy a Sunday roast.

In the evening I got stuck into my DIY, drained the central heating and ripped out carefully removed the old gas boiler, bloomin' heavy those old cast iron jobs. The cast iron core of the boiler is very cleverly designed, it's 5 sections held together with 4 long threaded rods with a nut on each end. Imagine 5 big books side by side (as they would be on a book case) with a long bolt going through at each corner.
I undid the nuts and it just fell apart, I was expecting to have to persuade it with a sledge hammer! The water channels are sealed with 'O' rings where they go from section to section across the top and bottom, each bit is pretty heavy, but at least I can get it into the boot of the car and take it to the tip. The modern replacement is supposedly a 'one man lift', let's hope so.

Friday, 25 May 2012

Easing Down and Tidying Up

I've just about finished the Yew longbows for this season, although I have a skinny stave left from sawing out the last but one. I'm roughing it down for a kids bow for one of the youngsters at the club. I need to find the height, draw length and weight of the recipient. The girls Mum approched me at the Beltane festival at the club, but I've not seen her since. I'm hoping she'll be able to manage 30# as I don't want to make anything much less than that. Mind if I go for 30 at 28" she can grow into it a bit. We have our end of month club shoot at the weekend, I'll take the stave along and mabe see them there.
The little primitive Hazel has changed it's tiller a bit with the lower limb looking a bit weak now, I've eased off the top limb and maybe I'll heat treat it. It seems to be the shorter flat bows which can suffer from the lower limb easing off, this shows that the 'make the lower limb stronger' school of thought has some merit. I think it only really applies to highly stressed shorter bows though.
I got a nice letter from the guy who had my last bow, he wanted a bow which would reach 180 yards for clout shooting. He said it made the distance easilly and he came 2nd in the club clout shoot with the bow's first outing, excellent.
Ridgeback will be going to it's new home tommorrow, I've signed and named it this morning, once that's dry, a little clear varnish over the lettering and wipe of beeswax polish, once that's dry and it's good to go.
I'll be restricted to some tinkering with stuff for a week or so as I'm tidying up and preparing for some DIY. I've ordered a new gas boiler, the fitting of which should occupy me for a week or so as I'll be re-furbishing the whole central heating ready for next winter. We'll still have hot water while the heating is off as I made some solar hot water panels a while back which work pretty well.

Monday, 21 May 2012

Ridgeback Finished Pics (well nearly)


I took Ridgeback and the little Hazel primitive to the club on Sunday, I had one of those days where I pretty much hit what I pointed at. I tried the Ridgeback for range and made 216 yards slightly down hill with a bit of tail wind and later coming back up the hill the wind had freshened and it still made about 190yards. This seemed pretty good so I shot both bows through the chrono' when I got home.
Ridgeback 164, 170, 172 fps with the 11/32" arrows and 100gn point. (177.8 with a light arrow).
170 fps = 116mph
The little Hazel managed 143, 143,144 fps which is respectable for it's weight.

The bow just needs a few more coats of Danish oil (DO) (2 each day for a few days) and then a wipe with beeswax polish.
People often ask how I get such a good finish as if there is some magic ingredient. It's just patience and repetition,. As an example, this morning the bow had already been thoroughly gone over with file, scraper and fine wet & dry paper and had a wipe of DO. I inlaid the arrow plate smoothed it all down and gave it another wipe over with DO, left it 10 minutes to wipe off any surplus and buff it up.
I noticed some sanding marks near the grip where I'd done the arrow plate, so I took them out with wet & dry, wiped it with DO and left it another 10 mins. When I came to buff it up, I spotted some more marks on the other side near the grip, so I took them out, more DO another 10 mins, wiped it down. Then noticed some little patches of discolouration and faint sanding marks on the back, I took them out going right down to 400 grit wet & dry, more DO and a wipe down after 10 mins. That was about 3 hours ago. By the end of the week it will be a little bit shinier, but not a high gloss, I don't like a deep high gloss finish.
Then I took the pics. The pic lower right shows the ridge of heartwood peeking through the back of the upper limb.
So you can see there is nothing magical about the process, it's just about being stubborn enough to sand off the finish you've already applied and take out any marks. When you get to the point where you can't tell if it's a tool mark or the grain you know it's pretty good. It seems counter productive to sand off the finish, why not get it perfect before applying the DO in the first place? Ah, but often the marks aren't visible until you apply the finish, once you accept the mind numbing repetition it's a doddle ;)

I checked the final draw weight, 58# at 28", I was happy to have lost a few pounds as I didn't want it over 60, having originally been asked for 55# but having forgotten! I also briefly wound it back to 30", it felt like it would have come back further, but 30" is plenty. In the pic I'm drawing a 29" arrow and it looked to me like I had it right back to my knuckle, but you can see I'm a tad short of absolute full draw. Mind it's madness to risk overdrawing as you can drive the point of the arrow into the belly of the bow and cause the arrow to shatter when loosed (Not done it myself, but I've been at a shoot where someone did).

Friday, 18 May 2012

Nocks, Tweaks and Test Shots

 
On the last full draw pic, I had a sneaking suspicion that the left limb looked longer, so now I've got the nocks on I remeasured the centre and it was about a quarter of an inch out. Where I'd adjusted the string it had also moved the tape marking the point on the string where it should be drawn from. These errors were small and the minor work I've done near the tips makes the tiller look even better now.
Since these pics were taken I've taken a whisker off the right limb by that knot just right of the grip as it looks a tad stiff there and the right limb looks a little stiffer than the left. These are real subtleties now, as when an ellipse is drawn on it in 'Paint' it looks very good. I'm now trying hard not to tinker with it any more.
At the primitive meet last weekend I saw a bow with really slim nocks, they were antler which is much harder than horn, but I though I'd go for a slimmer style of nock, narrower than my normal and with the string groove limited to the back of the bow rather than extending round the sides. The white Waterbuffalo horn is translucent and you can see the grain of the heartwood through it at the sides.
When I first started doing horn nocks I didn't much like it and found it very time consuming. Now I've become more adept and honed my technique I rather enjoy it as they have a sculptural quality and can have some individuality. These days I drill the horn, shape the tip and glue the horn onto the bow before I do any shaping of the horn. With the horn glued in place it's much easier to shape and the bow provides a long handle to guide it carefully under the bandsaw to rough out the shape of the nock, this saves a good deal of laborious rasping. It's a bit nerve wracking the first time as a bandsaw can runaway from you if you blink! Of course a good deal of care is required to avoid rasping the bow limb and careful holding of the bow is essential. I use a piece of old woollen carpet draped over the vice jaws which I have slightly open to rest the bow in or to lightly clamp it. The other end of the bow rests on my trusty cushion and sometimes my plastic tool cady is rested on top of it to stop it waggling about.
You can see the heartwood is fairly pale, it will be a bit darker when the Danish oil is on it and the whole bow will have some nice honey tones.
I've really just got the string to make, the arrow plate, some finishing and shooting in before it's finished. This bow won't have a leather grip as it's fairly large and comfortable to hold.
Test shots:-
Wow, it certainly slams home the arrows. I've had a stiff neck for a few weeks and shooting the 5/16" 100grain point arrows was jarring the back of my neck. It was grouping fairly well. I tried a 125grain point, not much different.
I then went for the 11/32" 100 grain ones, smooth as silk, tighter group, hitting the scrap of paper that was on the target with 2 out of 4 arrows.
Weather permitting I'll take it to the club tomorrow and get it shot in. It'll be interesting to shoot it through the chrono' as it seems quick to me. Looks handsome too in an understated way.

Thursday, 17 May 2012

Ridgeback at Full Draw

I went over the belly with a file, scraper and 180 grit wet & dry paper getting it cleaned up. I sawed off 1/2" from each tip where the stringer grooves were (they will be reinstated on the horn nocks) and narrowed the tips. It's back to 60# at 28".
It turns out that 55# was the target, but that's fine as a somewhere between 55 and 60 is fine and will allow me a bit more tweaking.
Talking of abrasives and finishing, I find wet & dry is much longer lasting and less clogging than sand paper. I generally use 180 and finish with 400 grade. (I just went mad and bought some 120 and 240 as well, I had to have a lie down to get over the shock of opening my wallet).
The Bahco rasp I use is a medium rasp on one face and a file on the other (I think it's described as a cabinet rasp). The file side is great for taking out the rasp marks and with a draw filing technique it will give a good fine finish too. Draw filing is where you have a hand on each end of the file and push it along the wood like a drawknife or spoke shave. It gives a much finer finish as the teeth are all cutting at a very oblique angle and the gaps between then are no longer seen as file marks (google it if you want to see some vids of it). First time I came across it was when I was a nipper and I saw my Brother doing it, I thought he was mad until he explained.
It seems to have picked up a tad overnight and is more like 60# @ 27" but such are the vagaries of bows.
the left limb looks to have a slight kink about half way along, but that's more of a ripple in the heart sap boundary than a real bend. It's looking nicely rounded, I'm easing off the left limb a wee bit, but I'll get on to doing the horn nocks next, that will involve easing off the last 1/4 of each limb and rounding the profile.
I couldn't resist plinking an arrow out of it too.

The other shot shows my new tillering string, the last one was getting rather frayed as it was two old Dacron strings joined together by threading through the loops. I've made a nice new shiny Aluminium allow string shortener too. The string is 10 strands of Angel Majesty with nice big well served loops and a very long centre serving, hopefully it will do for tillering most bows, I can use an old longbow string which I made the wrong length for any short primitives.

Wednesday, 16 May 2012

Serious Progress with 'Ridgeback'

A few days of thoughtful tinkering has eased it back to a low brace with out too much sideways bend or twist, and I've had it back to 60# at about 22". I think we are aiming for 60# at 28" with some overdraw to 30" or so for longshots, warbow style shooting and clout etc.
It would have been good to take some pics of the sideways bend, but I didn't want to leave it on the tiller for long in that state. The main cure has been moving the nock on the upper limb sideways by about 1/4" and easing off the belly on the stiff side. If you picture the bow as square cross section with the back of the bow as the top (e.g Like it is on the tiller) I've been shaving away at the bottom corners as appropriate. At one stage I had a bend one way at mid limb and t'other way near the tip.
It's a bit of a catch22 situation as you don't want to bend it back too far while it's missbehaving, but bending it back at a decent brace height will help it come back straight.
As an example a reflexed stave braced to just an inch or so can easily try and flip up the other way on the tiller and whack your knuckles, but once it's pulled back about 10" it will sit happily.
video
I've been cleaning up the back before proceeding and I couldn't resist polishing up the ridge area to see how it will look. Rather striking, in fact it looks a bit as if the top limb has been hit by lightning.
It's now back to 60# at 24" and you can see how it flexes in the video, there's a nice bend over the middle portion but the outer limbs are stiff. Hopefully now it's coming back straight I can reduce the outer limbs without it all going sideways on me.
Update:- Blimey it's hard work, taken a good amount off the outer third of each limb and shortened the string to full brace, it's now 60# at 25" and the curve is looking better, but I've had to work to keep that upper limb from wandering.
Bit of a breather now, but I expect I'll have it back to full draw by tomorrow

Sunday, 13 May 2012

Spine Tester & Matching Arrow to Bow


Before rushing in and reducing the arrow thickness I thought I should measure the spine (flexibility) of the arrow before I started. There are various slightly different definitions for spine measurement, but basically you support the shaft at it's two ends, hang a weight in the middle and measure how much it bends.
I've seen stuff saying the supports should be 28" 23" or 26" apart. I went for 26" as it is convenient for my arrow length. Two nails in my shelving and a small steel angle bracket (adjustable for different thickness arrow shafts) to act as a reference point does the job. A 2lb weight from the kitchen scales put in a plastic bag and hung onto the arrow with a piece of bent coat hanger and the job's a good 'un.
If you divide the distance between the supports (in inches) by the deflection (in inches) it gives a figure for the spine (or thereabouts). The reading with the unmodified arrow gave a spine of 31, I scraped along the central 20" of shaft with my scraper and then spun it up in the electric drill whilst rubbing sandpaper along it. The drill grips onto the point and the nock end was supported in a block of  wood with a hole in which was clamped in the vice.
I measured the spine again and it was down to 26.
The test shot, ok, it's just a single arrow but I had a good feel for the bow and I also know how to hit the spot at 10 paces. I took care to aim dead straight, no allowance for the kick... thwack the arrow thumped home about an inch left of centre.
A very obvious improvement, as yesterday I was having to aim way off right on every shot.
It's nice when the experiment does actually tie in with all the theory, normally my bows aren't to sensitive to spine, but the combination of low draw weight and very wide grip made the Hazel hypersensitive.

Measuring the arrow, it is 8.05mm diameter where I haven't reduced it and 7.45mm in the middle where it's been thinned. Not a vast amount, but enough to make a difference, the arrow is under a huge acceleration as it is loosed so I suppose it doesn't need much to have an effect.

It didn't take long to do two more arrows to be similar, (I didn't go mad looking for perfection). The results speak forthemslves, maybe a tad left still, but a vast improvement. I might take 'em down a bit more, but for now it's gardening weather.

Saturday, 12 May 2012

Primitive Meet 2012

A great day out meeting up with on-line friends and old faces, some of whom I couldn't fit the name to! One exchange ran a bit like this.
Hey Bob, is your Dad here?
My Dad?
Yeah, that guy we shot with last year.
You mean Bob, he's not my Dad.
Are you sure? ( LOL)
There was a great atmosphere and plenty going on. I set up a couple of chairs, a rack for my bows and my tiller rig. I took a few of my unwanted rather twisted staves which I left for anyone who might want them

There were 3 primitive crossbows this time, two made by another Bob! We shot them at the big atl atl* target, so that people could have a go.
There was a group of young girls who had been trying the atl atls, who obviously wanted a go. I offered them a try and the youngest stood up. I hadn't realised how small she was, and I was worried she wouldn't manage it. I carefully explained how to shoot it safely and that with her cheek on the stock and the point of the bolt on the big black spot of the target she should hit it.
Click..thud.
Smack in the middle! Her sisters managed very well too, but she was a natural and kept coming back for more. I was impressed how well they did and how well behaved they were, no pestering or squabbling and they collected the bolts.  She dragged her Mum and Dad along to have a go too.
A young lad had also had ago and I saw him later throwing axes with great skill. One of the youngsters was also getting stuck in preparing rabbits for the pot. Great to see the kids enjoying themselves and joining in with enthusiasm.
One chap had a fine collection of native bows and arrows from around the world, it was great to see them close up and to be able to handle them, very inspiring, last year he'd been there with horn/sinew composites he was making.

There was a table covered in catapults (slingshots) Some were crafted from exotic woods, laminated and riveted. My favourite was like some Art Deco sculpture, you can tell I have exquisite taste, as that one wasn't for sale!
I set up my tiller rig and tinkered with the ridgeback Yew bow but mostly I was strolling about and chatting, all very informal and friendly. I shot round the practice course with Evan, the guy I've been E-mailing and 'Crossbow Bob' who was shooting one of his primitives made of Holly. I shot the new Hazel bow (very badly due to the kick left) Evan shot an Ash Mollegabet which he'd made. We managed to break and loose a few arrows. Later we shot some of the other bows I'd brought along and I had a go with the Mollegabet which thew an arrow with some authority.
I only attended for the one day, but I'm sure the proceedings and competition on the second day will be just as good.
My thanks to Wally the organiser and the people doing the yummy food. Beef burger with a fried egg on top, lemon drizzle cake and a cup of tea, bliss.

Not to mention the strange man try to make dead chickens dance ;)

After some musing about my Hazel bow I've decided to take some of my old arrows which have already lost a point once and waist the shafts to make 'em more flexible. I'll just scaper the shafts down over the centre third, of maybe grip the point in an electric drill and hold some sandpaper round them, I'll try and get them matched up to the bow. It's not something I've done before and it will be interesting to see if all my pontificating is correct and I can get them to fly straight from that bow. The other alternative is to build up the grip in thickness and narrow it to make it more centre shot, I feel that would detract from the whole point of the bow.
I'll report back.

*Atl atl, is like a huge long arrow thrown with a throwing stick.

Friday, 11 May 2012

Shooting the Hazel D Bow & the Archer's Paradox

I made a decent string for the bow, using just 6 strands of Angel Majesty. That's the thinnest string I've made as I wanted it as light as for maximum performance. I bulked up the nocks and centre serving with a few extra strands, but kept the serving down to a minimum. I've kept the brace height fairly low for maximum length of power stroke. Some find this rather counter-intuitive, thinking that a higher brace height and thus higher tension at brace will give give more power, yes it increases the early draw weight a little but reduces the length of actual draw (e.g 28"- 5.5" brace is 22.5" power stroke whereas  28"- 7" brace is 21" power stroke) .
To be honest I haven't done actual tests to prove this and I'm really just quoting from the Traditional Bowyer's Bible, but my experience tends to indicate that cranking up the brace height in an attempt to raise draw weight and power doesn't achieve what one might expect.
In fact scrabbling round trying to gain extra draw weight is fraught with problems, the two most effective ways are heat treating the belly or shortening the bow.
Shooting into the garage at about 10 paces I could see the white scrap of paper I was shooting at but couldn't see where the arrows were landing as it was rather dark in there and bright sunshine outside (yes it's finally stopped raining!) It shows the arrows are a bit stiff for the bow as it's only about 35-40# draw weight and is very wide at the grip. They are all kicking off left, due to the archer's paradox but the group is ok-ish considering I haven't shot it before. There is a little bit of wrist slap too (due to the low brace height).
Those are my lightest arrows (70grain points on a 5/16" shaft).
With bows everything is inter-related, so I may actually twist the string up a bit to raise the brace height, but I'd do it to hopefully reduce the wrist slap and it might also reduce the kick left as the arrow will leave the string a little sooner and won't be exerting so much bending force.
I'll be getting all my stuff together to go to the Primitive Archery meet tomorrow, and this little bow will get some serious shooting, so I'll spend a little time trying to tune it up a bit. (I'll post some pics when I get back).

Archers Paradox:-
videoThe paradox is, why doesn't the arrow shoot off to the left when it can be seen that it points that way at brace height?
You can see at the start of the video the arrow is pointing to a place vertically above the knuckle of my left hand, but by the time I have let the string down to brace height it's pointing way off left. Assuming there is a target in the bushes, it's now pointing to a spot about a yard left.
So why doesn't the arrow go left?
Because it flexes around the bow, during the early part of the release it is going fairly fast and straight and the relatively heavy point has inertia which tries to keep it going straight. The back end of the arrow is also going fairly straight, but there is some flexibility in the string and some oscillation as the string slips off the fingers, this starts the arrow flexing and the laws of physics do the rest. So an arrow which is too stiff for the bow will kick a little left, one which is too flexible can be seen waggling in flight.

I get inordinately irritated by people who shoot compounds and modern target bows talking about archers paradox when their bows are 'centre shot', e.g The arrow points straight at the target at brace height.
The effect they are discussing are arrow tuning, and matching the arrow to bow and the method of release. As the string slips off your fingers it is deflected sideways and causes oscillations and flexing in the arrow/string and even the bow limb. That's not a paradox.
If you took the same two pics with a modern target bow with a cut away sight window, the arrow would be pointing the same way in both.
There are some good slo-mo videos on YouTube showing arrows flexing in flight. http://www.youtube.com/watch?v=WzWrcpzuAp8
I'm sure some people would wish to argue with the above, but Ha! That's the beauty of a blog I can indoctrinate you all into making primitive bows and put my view unimpeded. (exit stage left cackling wildly and rubbing hands in glee)

Wednesday, 9 May 2012

Full Draw Video 28"

I spent some time cleanining it up and fine tuning the tiller, eventually I plucked up courage and took it back to 282 draw.
It still has some reflex, pretty impressive for a sliver of Hazel.
video

Tuesday, 8 May 2012

Bow in a Day Details

It's made of Hazel 63.5" nock to nock.
47mm wide at widest, tapering to 13mm at the tips. narrowing to about 40mm at the grip (this will prob' get reduced further).
Lying flat on the floor the tips still show 2" of reflex, but I haven't taken it beyond 24" draw yet.
The thickness tapers from 19mm at the thickest point of the grip down to about 11mm at the thinnest.
You can see there's not much wood there !
Its the first time I've made a fully bend through the handle bow and as it hasn't taken any set yet I think it will probably come back to 26" maybe 28" which I'd really like so that I could shoot it in my usual style. I shall give it a good going over before I take it back further though.
I've spent an hour on it this evening and added horn overlays to the tips (just roughed out), this has allowed me to narrow them and adjust the string line, which you can see in the pic of it hanging up on a nail, you can see the natural waggle in the stave which I've utilised in the grip, you can see the string is biased towards the right (we are looking down the upper limb) to favour a right handed archer as the arrow pass will be on the right.
I shall try buffing up the bark and going over it with Danish oil to see if it will stay on. If it comes off I may add some abstract decoration of maybe a leaf and grass motif, it's fun to play with a quickie bow as I won't be scared stiff of messing it up.

Monday, 7 May 2012

Woodland Workshop

The weather wasn't too bad, but I set up a tarpaulin over my shave horse which kept the odd squalls of rain off me. I lashed my portable tiller tree to a big old Hornbeam and set to making a bow from a skinny piece of Hazel split from a log in January. I managed to get it finished and shooting by the end of the day, I only tested it to about 24" (~32#) as I didn't want to blow it on the tiller.
It's retained a little reflex which is pretty good, I'd had it seasoning strapped up with a few inches of reflex and being the skinnier half of the log it felt as if it had seasoned reasonably. The bow has it's back left completely intact with the bark left on, it's the first time I've managed this as previous bows have ended up being de-crowned.
Considering the weather we were quite busy and I'd set up shop near the entrance which drew a fair bit of interest.

I'd learnt from last year and only had one bow strung for people to look at, my big 75 pound Yew longbow. The reasoning being that not many people, and certainly no kids, could over draw it.
I'll tidy up the little Hazel bow at my leisure and hopefully tease it back to 26" or maybe even 28" I'll be going to a primitive archery meet next weekend, so I may take it along..
I've just had a contact on my website from a guy wanting to make his first Hazel bow, so I'll post more pictures and meaurements as I finish and fettle it.

The archery club had set up a 'hunting zone' have-a-go where people could shoot at 3D targets, there was also an archery 'clay pigeon' style shoot, aiming at foam discs with big blunt arrows from low poundage bows which was fun.
I didn't get to see round the rest of the festival as I was so busy, but everyone seemed to be in good spirits despite the odd downpour.

Footnote:-
I'd seriously discourage anyone from trying to make a bow in a day, I took this on half expecting to fail, and just doing it to demonstrate the process. If it went bang on the tiller, it would have just been a crowd pleaser.
By all means get it roughed out and onto a long string in a day, but save the real tillering until you are fresh.
Do it little and often with plenty of exercising of the bow as it is worked.
What I learned from the exercise is that it's just experience that teaches you that vital point at which to really slow down and how much wood to remove as it begins to bend.
Hazel is plentiful however and it's a relatively knot fee, clean working wood to to try out. Be warned though, a draw knife can stil tear out deep gouges when try to take off too much. I rapidly moved to my spokeshave set fairly fine which gave a nice surface on the belly.
So have a go, there's nothing to loose and plenty of experience to gain.

Sunday, 6 May 2012

Back to the Ridge Back Bow

I've picked up the Yew stave with the weird ridge and it's begining to get back to brace heigh, it seems like good wood and relatively stiff considering the extra length I've left on it.
I made up a stringer in an attempt to get it braced. I got it to almost brace but could see it was trying to bend sideways. It's a bit panic making when a bow tries to do that, but with some careful adjustment of the cross section and the string line it can be tamed. The extra length is handy too as it allows some shortening and sideways adjustment of the nock positions. I've glued on some scraps of Yew to let me file temorary nocks in the back and to reduce one side of the bow at the tips to help bring it in line.

I'm hoping the weather will be kind tomorrow as it's the Beltane festival at the club and I'll be taking my shave horse and portable tiller tree to do some bow making demo's. I've even drilled another hole in the shave horse so the foot lever can be moved forward so kids can work it. Last years event was great fun, just hope we don't get washed out.

Tuesday, 1 May 2012

Comparing Two Longbows

I've got two bows finished, 55# and 60#.
Well is the 60# any faster? With some trepidation I shot it through the chronometer and averaged the 6 results getting a respectable 173.7 feet per second (fps) average.
I then strung the 55#, would it be just as fast? Again 6 shots and average, 168.9 fps.
I'm happy with those results and it's a bit of a relief to find the 60# is faster (I shot the same 3 arrows with each bow, 5/16" shaft 100gn point). I took a pic once I'd finished as I happened to get a nice group with the last 3 arrows from the 55#, you can see the reading on the chrono'.

I take the arrow speed divided by the draw weight as a sort of "efficiency" indicator. The 55# bow gives 3.1 whereas the 60# gives 2.9 implying the 60# bow is somehow less "efficient". I think the reason for this is light arrow favouring the lighter bow. If I repeated the test using my 11/32" arrows with the 100 grain points I expect the 55# bow would loose more speed than the 60 and the "efficiency" figures would even out or swing the other way. The arrows used for the test feel fine with the 55#, but the 60# definitely feels happier with the slightly heavier arrows.
Out of interest my best speed/draw weight figures tend to be the primitive style flat bows with 'Twister' my Yew primitive (45#) giving a figure of 3.7 Of course the longbow is designed for delivering energy rather than velocity as is better matched to a heavier arrow.
Figures need treating with caution of course and reducing the weight of the arrow will always give increased speed, but it's about matching the arrow to the bow rather than pure speed, unless you are into flight shooting where you are after maximum range with little interest in smoothness or longevity of the bow.
Explain more? Not sure what to explain really, I put "efficiency" in quotes as it's not really a measure of efficiency as it doesn't take into account the arrow weight, but it gives some sort of comparison.
These 2 posts explain more about velocity/energy/ speed and power.
http://bowyersdiary.blogspot.co.uk/2011/11/mass-velocity-and-energy.html
http://bowyersdiary.blogspot.co.uk/2011/10/graingram-scales.html
The chronometer has two photo cells which detect as the arrow passes over it. I've stuck thin pieces of cane in to show the active area which I have to shoot over. (The chronometer comes with metal rods which get severely bent when hit by an arrow so the thin cane is better!) I have two100w incandescent lights which hang down above it to give suitable illumination (fluorescent lamps flicker and can confuse it) Sometimes it's tricky to get reliable readings as the arrows can be flexing at short range as they leave the bow, I generally shoot at about 5 paces and take several reading to make sure I'm getting reproducible results. A chronometer is the only way to really tell how a bow is performing, as they can feel quite different and with the 2 bows I tested here it would be hard to tell which was shooting faster with out the chronometer.