Friday, 30 December 2011

Back to the Longbow

I couldn't resist getting back to work on the longbow.
The feel of seasoned Yew under the drawknife is lovely, the crisp heartwood and the waxy firm sapwood.
I couldn't help musing what one of the bowyers of the Mary Rose bows would have made of my efforts. I imagined I could feel the hand of history resting on my shoulder.
I'd like to think he'd have smiled at my efforts, motioned me to one side and sat at the shave horse with a nice clean stave of Spanish Yew and shown me how it should be done.
I expect they had to churn 'em out pretty quick to earn a living, mind I think the electric lighting and the bandsaw would have made him a tad suspicious!
Enough reverie, here's some pics of how its progressing.

The bow is roughly square in section at the moment, and in the first two pics you can see dark knots which show on the corner of the stave, these will probably disappear as the stave is worked down a little more. The last pic shows a raised mound left round a pin knot, this will doubtless get worked down a bit.
The sapwood is about down to thickness and some of the knots have disappeared, you can see some of the problem areas and features, maybe my imaginary medieval bowyer would have scoffed at the quality of the stave and handed me something better to work on.

Thursday, 29 December 2011

Surprise!

My Birthday is over the holiday period.
We were down near Portsmouth where my parents live. My daughter organised a surprise visit to the Mary Rose collection, my brother drove me there, and it was only when we arrived at the dockyard gates that I dared to think I was going to get to see the bows.
The family had all chipped in and made me a 'Patron of the Mary Rose' which allows access to the private collection, but the people there had gone above and beyond the call of duty and opened up specially on a holiday.
Andy who showed us round was brilliant, he was enthusiastic, knowledgeable and funny. I couldn't stop grinning as he showed us round the artefacts culminating with the bows.
It was great to see them close up and even hold a couple (wearing latex cloves of course).
I was particularly interested in seeing the bows with knots and ripples in, as the more perfect ones are those usually exhibited.
The bows just looked and felt 'right', they were a fair bit longer and fatter than those I usually make with a more graceful taper than the rather straight tapered laminated bow we tend to see today.
My head was reeling, and Andy urged me to take as many pics as I wanted which was great, as I can now pore over them at my leisure.



The book of the collection 'Weapons of Warre' is superb and I've been avidly studying that too, and, not just the bow section.
The whole day flew by and there was a surprise family pub lunch after the trip... I was pretty much stunned and grinning for the next 48 hours.
The trip has given me a better feel for how I want to make the 90# bow I'm working on and it's bolstered both my confidence and enthusiasm.

All in all the best birthday ever!

Monday, 19 December 2011

Last of the Year

I've been busy over the last week refubishing the back door to my garage as it had been flapping about in the high wind. There was a lot of rot along the bottom and it turned into a major job.
It still needs a drip edge adding to the bottom and another coat of paint, but at least I can shut and lock it now and it keep it a bit warmer in there.

A chap called Robin came over today to discus his longbow and have a look at my stuff. He was worried that his Yew longbow was warped a bit.
We'd made contact via the Archery Interchange website where he'd posted a question about his bow.
It was a nice enough bow which he'd bought second hand, however he'd been missinformed about the wood! It was laminated Hickory and another wood (Lemonwood?). Once he'd seen my Yew bows he could see the difference.
We popped the bow up on the tiller and took it back to a nice safe 26" (He draws about 29) There was the slightest hint of a sideways bend in one limb over the last third of the limb, but barely perceptible and certainly in acceptable limits. The string was sitting slightly to one side where the bowyers knot was and it sat slightly skewed on the other nock.
I said it was fine and that if I'd been making it, I'd maybe spend a minute with a needle file on the nock, but that was all.
We shot a variety of my bows and I shot a few arrows from his, which performed fine.
After much talk of bow woods and such like we went over to the local wood to see some wood in it's raw state, as luck would have it there was a 'camp' made by the kids which had a nice straight bit of Hazel built into it.
It was too good to pass over so we took it home and hacked the back off to help it season a bit quicker. I gave Robin a few bits of Waterbuffalo horn to make an arrow plate for his bow and some Dacron which unfortunately got left on the bench!
Robin gave me two bottles of wine for which was a most welcomed and very generous.
He can pick up the Dacron some other time when the Hazel has had time to season and he's back from Uni' again.

So that's about it for this year.
Seasons greetings to one and all, see you in the new year.
Derek

Monday, 5 December 2011

Bandsaw Woes

Hmmm, I havn't made a very good job of ripping down my Yew, the log isn't that big so there's not much margin for error. I worked out where I wanted the cut to give me a good half and a bad half. As I was sawing I wandered over a bit towards the good side at exactly the point where I'll need most wood e.g. the middle of the stave where a bow will be fattest.
I expect it will be ok, worst case would be if it's too skinny then I can cut it in half reverse the two bits, and splice it back together so the thin bit is now the tips of the bow. Or maybe it will be ok for 40# bows rather than heavier ones.
Anyhow, it'll be seasoning for a year and may not look quite so bad when I come to view it again and the bark and excess wood has been removed.
It's always tricky knowing how much wood you dare rough off or how how many staves you can try and squeeze out of a stave.
When you start one is often too cautious and it takes forever to get down to the right dimensions, however impatience and cockiness can lead to removing too much too quickly. I find the right amount is usually enough to make me wince and think 'have I over done it?' Usually I've got it about right... let's hope that's what I've done here.
To add insult to injury I could hear this cracking noise and smell this hot oily electrical smell as I was finishing the cutting.
The capacitor on the electric motor has dark grey goo bubbling out of it. Still that's much cheaper to replace than a burnt out motor. (You can see the capacitor on the pic in the previous post, it's the light grey cylinder, mounted just right of the black connection box on top of the motor)
Maybe I should have stayed in bed all weekend, as I also contrived to drain the transmission fluid of my car instead of the engine oil... mind it was pretty dirty, so probably needed changing. Automatic Transmission Fluid is rather expensive though.
Just to confess all my sins, I also managed to snag the bandsaw blade and jam/kink it. I wrestled it free and after a bit of fettling in the vice and some judicious tap tap taps with a small hammer it's running ok again.
Hey Ho, mustn't grumble, the sun is shining and I've seasoned staves to play with!

I've been reducing the stave for the 90# bow, it's still pretty huge and has a row of knots up the belly, oddly some are quite big (about the size of a pencil) but they don't appear on the back of the bow or the sides... dunno what happens to 'em inside the stave, I shall lay out the bow keeping them dead centre and if I'm unsure I can always carefull drill into them to investigate their extent. Knots on the belly aren't too much of a problem as they are generally harder than the surrounding wood and are in compression. The sapwood on the back of the bow looks good and clean. I can only just get my hand round the middle of the stave and if I lean it against the wall and put my whole body weight into it I can just about feel a hint of give.
Having taken about 10" off the length it's now about 74" long and has a hint of deflex in one limb. I'm still undecided about any straightening or heat treatment as I don't want to risk disturbing the knots. I shall keep working it down slow and steady before I make that decision, the policy is "when in doubt, don't". If only I'd applied that to sawing the Yew log...

Sunday, 4 December 2011

Wheely good idea

I've fixed some wheels onto the base of my bandsaw which will make it easier to manoeuvre. Hopefully it will still be stable.
The steel legs were cut down to keep the overall height the same as it was originally. I shall try it out ripping down that Yew log I harvested last week.
The tray arrangement underneath will be handy for mounting a dust extraction system which I'm hoping Santa might bring me!
In the pic the heavy cast iron table part of the bandsaw hasn't been refitted yet.
Once I've ripped the Yew I shall start on the 90# longbow, deciding whether I should heat straighten/temper it.

Tuesday, 29 November 2011

Update

I phoned the vet' this morning and they said the Woodpecker had died.
At least it wasn't got by a dog, fox or squirrel, it was an adult bird so maybe had just reached the end of the line, happens to us all eventually, and in fact I'm off to a funeral this afternoon.
Oh well, carry on.
I've put up another two shelves for my staves, I was rather pleased that I got the shelf brackets free. Last time I was at the Council rubbish tip I noticed a chap heading towards the scrap metal skip with a plastic bag full of shelf brackets, I caught his eye, nodded at the open boot of my car and said "lob 'em in there", he grinned and lobbed 'em in.
Recycling at it's best!

Monday, 28 November 2011

Green Woodpecker

I was walking in the woods going to collect some fallen Hawthorn and Maple which I'd spotted earlier. As I approached a huge recently fallen Oak with a big hollowed out base I saw a green woodpecker flutter around the base. It didn't fly away, and as I crept closer I realised it something wasn't right, as I went round the back it went round the other side and eventually down inside and hid down in a root cavity. I took my fleece off and laid it on the ground and gently reached in and cupped my hand round him and lifted him out (dunno if it was a him, it just seems right!) I wrapped him up in the fleece, warm dark and cosy.
I'm aware that well meaning amateurs can do more harm than good, so I phoned my wife and asked her to phone the RSPCA for advice and to ring back.
They said that if I could pick it up, it probably wouldn't survive anyway, but if we took it to a vet' they treat wild animals free of charge.

Once home we put him in a box, the pic shows what a handsome fellow he is.
I drove him up to the vets where they said they'd phone one of their bird specialists to come and collect him later. I was tempted to give my phone number so I could follow up and see how he did, but decided against it.
It was a good day for wildlife as I spotted a kingfisher by the brook on the way back too. Here's a pic of the logs I collected, the big one is the Maple. I used my wheeled dolly to drag it out of the woods.

Sunday, 27 November 2011

Tidying Up and a Wasp

I'm running out of room for my logs and staves so I've put up another couple of shelves.
The work entailed clearing out a load of gardening tools, pots, netting, string canes etc amongst which was a dopey wasp settling down for winter. The stripey git stung my finger and it's still feeling a bit itchy 2 days later.
I've got my timber all up out of the way on shelves now, a lot of it isn't the finest quality, but a stave on the shelf is worth two in the woods.
I'm also planning on fitting two wheels onto my badsaw and some sort of third wheel which can be dropped down with a lever to enable me to move it easilly.
I'd love to have a nice big workshop or double garage to work in, but I manage pretty well so I shouldn't grumble, there's plenty of people with no facilities at all.
The sun's out and it's lovely and mild, a bit windy though, I'll drive up to the club and have a bit of a shoot as I havn't been up there for about 3 weeks.
Once everything is all tidy I will start thinking about that 90# Yew longbow.... mmmmm Yew longbow.

Monday, 21 November 2011

Dead wood?












There is much discussion about wood that is dead, standing dead, fallen etc. Some people condemn it outright.
I always say, when in doubt collect it.
As I still had the roof rack on the car I went to see a dead standing Yew near where I live. It wasn't how I remembered it. It was totally unsuitable, so tall that if I did cut it, there was no room for it to fall, it had too many branches and the sapwood was all gone and it was full of splits.
From the base of the tree there were green shoots sprouting, so was it dead or not?
I think a bowyer's recollection of a branch or tree is over optimistic somewhat akin to a fisherman's recollection of the fish that got away!
I had a look round the other trees and spotted a limb sticking out horizontally about 6-7' long broken off at the end with no shoots on it at all. It was about 7' off the ground and I expect kids had tied swings to it. It certainly wasn't a live branch, but the tree itself was certainly still live.
I sawed it down and found the upper surface which I couldn't see had lost all it's sap wood and was pretty manky, however the under surface was fine and the cut face revealed nice thin sapwood and fairly dark heartwood. Definitely worth trimming up and seasoning.
There were plenty of other branches left for the kids to swing on as was evidenced by some rope and old blankets tied to one tree.
I've run it through the bandsaw to cut off the bad half and sealed the ends, I'm pretty sure there is a bow in there.

By the way, the little dolly I made the other day was very handy for moving the long log on my own, I just slipped it under one end and easilly dragged the log from the other end, whereas it had taken two of us to get it on and off the roof rack.

Sunday, 20 November 2011

Yew Log

I harvested a Yew log at the weekend, with some help from my wife.
I'd organised the harvest/purchase with the Forestry Commission. I made initial contact with them by E-mailing a picture of me pointing out the piece of wood I wanted.
They were very helpful and allowed me vehicular access to the woodland, which was handy as it would have been a fair way to drag the wood otherwise. The weather was lovely and my parents came along for the ride too!
You can see the piece I cut is just a side branch, Yew woodland is a protected environment so one wouldn't be allowed to cut a whole tree.
The yew isn't quite as good as I'd remembered, but the heartwood is nice and dark and I think I should get at least one longbow and one shorter primitive out of it, possibly a pair of billets to splice together for a third bow.
I cut the log as long as I could, I shall have to study it carefully before I saw it any further to maximise the use of the wood.
Driving around the woodland elicited some odd looks from the dog walkers, I took the trouble to tell them that I had permission as I didn't want to create any consternation.

Monday, 14 November 2011

Log Dolly

I'm over my cold at last so I've got back to making stuff. I built a two wheeled dolly to transport the Yew log I'm hoping to harvest on Saturday. I just hope I can find it again!
Originally I was going to use the wheels off my roofing ladder, but when I put them on the dolly and put my weight on it the M6 coachbolts holding the wheels bent...
Back to the drawing board. I borrowed the wheels of one of those horrid heavy cheapo sack barrows which we have in the garden shed, they are a bit heavy, but should do the job.
I made the axle from some 1/2" ID steel tube with some stubs of 12mm stainless steel bar epoxied into each end, this makes a lightweight but strong axle. I had the materials lying around from my old electric golf trolley which I made yonks ago. Here's a link to a blog I did about it on an engineering website http://cr4.globalspec.com/blogentry/6416/DIY-Electric-Golf-Trolley


I shall strap the dolly to the log with rubber straps and hopefully it should save my shoulders from having lug a wet Yew log 1/4 of a mile.

Saturday, 12 November 2011

Low Enery Activities

Just beginning to shake off my cold, the irritating cough is easing off so I can get some decent sleep at last.
I've been pottering about refurbishing my target foam in the garage, it was getting rather shot through. I sawed it in half and reversed the pieces so the edges are now in the middle, it should last for a fair while now. I used polyurathane wood glue to put it back together.
I also had a look at my website and found some of the pics had mysteriously vanished, so I tidied that up. I reloaded some of the pics at reduced resolution to save memory usage.
Now I'm feeling perkier I'm hoping to go down South next weekend and harvest a Yew log, gotta get the paperwork from the forestry commission sorted first and make a little 2 wheeled cradle which will strap onto the log to help drag it the 1/4 mile out of the woods.
I'll blog it all up with some nice pics.

Friday, 4 November 2011

Mass Velocity and Energy

I've had a bit of a cold all week, so I thought I'd make do with some gentle experimentation.
The title says it all, how exactly does projectle mass effect speed and energy?
I made a crossbow bolt which I could add weights into by glueing some thinwall steel tube onto a short bolt. A rubber blunt head was then put over the end. I wanted to test for even higher weights and ended up sticking a long M8 coach bolt with several M10 nuts on it into my test bolt. For lower weights I cut down a bolt until it was just about 5" long with no point added. The very low weight bolt actually broke the 200 fps barrier (best shot 202.9 feet per second) .
Pretty obviously the lighter the bolt the faster it goes, what is less obvious is that the maximum energy isn't when the bolt is at it's fastest.
In fact the energy levels off despite the ever increasing weight of the bolt. The real point is that if you want to get maximum range and maximum energy then there is an optimum weight.
For this particular bow you can see it's about 12-15 grams. As the mass increases beyond that the energy doesnt get much higher and the velocity (and thus range) drops off rather a lot.
The text on the graph isn't too clear, so here's a description.
Vertical scale and blue line:- Velocity in m/s
Red line is Bolt Energy (multiplied by 4 to get it to sit nicely on the graph for comparison).
Horizontal scale Bolt mass in grams.
A bit more explanation: (I noticed the 'explain more' box is ticked).
You can only get out of the bow the energy you put into it, or a little less. That accounts for the energy of the bolt not getting any higher once it has levelled off on the graph.
I was slightly surprised that it didn't drop off a bit as bolt mass increased, but there is no real reasn why it should until you make the bolt so heavy that the bow can't push it or friction becomes significant, but presumably that would be at a silly weight, say a couple of pounds.
The energy put in to cock the bow is used up accelerating the bow limbs, the bolt and the string. With the very light bolt more of the energy is staying in the bow limbs and string and less in the bolt. As the bolt gets heavier most of the energy stays with the bolt.
The tips of the bow move faster than the rest of the bow limbs, but even they don't move as fast as the bolt! That's because the string pulls back about 120mm but the bow tips only move back 40mm! That's one of the remarkable things about the simplicity of a bow, a simple piece of string effectively gives you 3:1 leverage.
Anyhow the string and bow tips both return to rest at the same time so the bolt must go 3 times faster than the actual bow tips.
The modern compound bow takes this to extremes by adding extra wheels (like a block and tackle) and cams to make the centre of the string where the arrow is nocked travel much faster than the bow tips. This allows short, stiff, fast limbs to propell an arrow very fast... but at the cost of complexity.

Monday, 31 October 2011

Crossbow Workout

The crossbow got a good work out yesterday at the Celtic Harmony Samhain Festival.
We were running an archery have-a-go. The bow shot nicely, but at one point the string flew off, I added a few twists to effectively shorten it and increase the bracing height and re-fitted it.
A few of the club members had a go with it and found it easy to handle. One of our ladies in period costume had a go, I should really have taken a pic but didn't have my camera to hand.
Experimenting at home shooting through the chronometer shows it's not particularly fast and the actual kinetic energy imparted to the bolt is similar to the last Yew bow I made.
E.G 80# at 12.5" ends up about the same as 40# at 28".
For those who like figures the kinetic energy is calculated as 1/2 x mass x Velocity squared.
The figures need to be in kilograms, and metres per second to give an answer in Joules.
personally I dislike units like Joules as they mean nothing to me , can anyone tell me what a Joule feels like? An old fashioned imperial unit like a horse power at least give you some feel, as you know what a horse looks like.
The figures below are in 'grains' which is what arrows are usually weighed in and feet per second which is what arrow speeds are usually measured in. You can see it's a weird mix of units and if you haven't heard of 'grains' before, a grain is about the weight of a grain of barley.
The heavy bolt (11/32") in the picture is 440gn @ 125fps = 20.7 Joules of kinetic energy.
A light bolt (5/16") 150gn @ 170fps = 13.0 Joules of energy.
The heavy bolt goes pretty slow, but being 4 times heavier ends up having much more energy.
It would be interesting to plot loads of different weights and see which actually gives most energy.
Here's a couple of extra pics. The front view shows how the string sits level, it also shows how I was a bit sloppy making the prod as the left end curves up a bit more abruptly than the right. Still it was just a quick experimental bow to try out the Laburnum, the other pic shows the bolt clip which is Ash and looks a bit 16th century in style.

Saturday, 29 October 2011

Crossbow Finished Pics




Here's a pic of it cocked and some showing the early stages of binding on the prod.

Friday, 28 October 2011

Crossbow Test Shot

Before binding on the prod I wanted to test the bow, but first I needed to make a groove for the bolt to run in. Some crossbows have a groove, others have a small piece of horn or somesuch with a notch for bolt at the end of the 'runway' 'track' 'barrel' 'channel' (or whatever you want to call it) with the back end of the bolt being held by the trigger mechanism.
The trigger mechanism I'm using doesn't actually hold the bolt, so I need a shallow groove, the advantage of a groove is that it lowers the bolt slightly so the string is then pushing the bolt on it's centre-line rather than it's bottom edge, which can cause the string to go under the back of the bolt or the bolt to bounce upwards.
I made a shallow square groove using a plough plane which has a very narrow blade. My Brother gave me the plane for my Birthday many many years ago specifically for that purpose. I rounded the groove using an arrow shaft with fine sandpaper wrapped around it. This wasn't working particularly well so I took a 7.5mm drill and ground the butt end of it at a slight angle on my small grinding wheel, this made an excellent scraper/chisel for working along the groove.
The prod was temporarily bound on with some rubber strip (cut from EPDM roofing sheet, but old inner tube is much the same) I cocked it and put the bolt on, making sure the back of it was just in front of the string, so that the string didn't pop up and knock the bolt off the runway.
THWACK... it smacked into the target at very close range, the trigger pull was smooth and easy, there was no real kick and the bolt was buried up to the flights in the target. Excellent!
I'm now working on the detail. I'm adding a sliver of Ivory (from an old piano key blank) at the front face of the trigger slot which retains the string when the bow is cocked. This will effectively block off the groove in which the bolt rests, stopping it from being pushed back too far. A clip of Ash will also reach over the top of the trigger slot and press lightly on the bolt to stop it falling off or bouncing about, I may incorporate a back sight into the retaining clip. The clip also stops the trigger peg coming out the top of the stock. I shall probably just glue it in place with hide glue. One advantage of hide glue is that it can be undone with heat and humidity, whereas epoxy is rather permanent.
Once I've done these few bits I can bind the prod in place and really test it.
Pics tomorrow.

Monday, 24 October 2011

Trigger Mechanism Try Out

I've cut out the trigger mechanism, drilled a hole for peg (11/32") and used a bit of arrow shaft as the peg.
I've dry assembled it and cocked it just to check it holds. There is tons of work slimming down the stock, shaping it nicely and binding the prod into place.
(Excuse the camera strap flapping about in the first pic)



The trigger mechanism will doubtless need some fine tuning too.
There is a fair bend on the bow, I don't really want to risk more, if I did want to work it any harder I'd take 1/2" off each limb tip.
Once it's finished I will be able to use it to test other prods.
I hope the pics are self explanatory.

Saturday, 22 October 2011

A prod in the right direction

I've been feeling a bit coldy today but I've had a couple of little dabbles with the bow. I made a string, braced to about 3" (90 strands of fine linen thread).
I pulled it back to 12" 70# on the tiller. I then put it on the stock where I've cut the mounting slot and heaved it back to 13" !
Dunno how far I dare push it. Pulling it on the stock gives me the position for the trigger groove.

Friday, 21 October 2011

Crossbow Progress





Here's the prod with the rawhide bound on tight with string, one limb has been unwrapped to show the before and after. It will need to dry out some more and be cleaned up before I continue tillering it, I shall leave some of the grooved finish showing as I think it looks good.
I decided against Oak for the stock as it isn't seasoned, I have a nice chunk of Ash I'm using instead. The last pic shows roughly how it will work. The area I'm not sure of is the trigger, do I make it as part of the stock allowing it to hinge at a selectively weakened point at the front, (see the pencilled in arrow beneath the front of the trigger) or do I make a separate trigger pushed into a slot as a pivot it and bound on with twine? (Click on the pic to enlarge it and you will see how the trigger will push the rod upwards to push the string out of the groove)
Hmmm I'll have to think about it. The stock as drawn on the block of Ash looks horrible, to manufactured and not 'primitive', so it won't end up looking like that.
In the second pic you can see the butt end of the stock bends a litte to the left, this will make it more comfortable to shoot, it will probably drop down about half an inch too. I'm torn between making it shoot well and look primitive. Most shotgun stocks have a little cast to make them point correctly, with a dead straight stock it's hard to get your eye in line with the barrel or bolt in case of a crossbow.
I shall experiment with some offcuts of the Ash to get a feel for the necessary trigger dimensions.

Thursday, 20 October 2011

Crossbow Prod

The prod is still pretty stiff so I checked the thickness and took it down some more, going 1.5mm thinner for each 3" along the bow from the centre.
It still seemed rather stiff, expecially in the centre so I took another 3/16" off the lower edge. I then adjusted the thickness taper from the tips which seemed about right increasing thickness by just 1mm for every 3" this time.
The pics show it on the tiller, but bear in mind it's not braced, the string is just slipped on and the bit of curve is natural deflex. It certainly is bending near the middle now and I'll probably work the tips and mid limb a bit more next.
It's going to have to bend a fair bit more yet, so I've glued some rawhide on the back using hide glue, as in this previous post. http://bowyersdiary.blogspot.com/2010/04/glueing-up-ashcherry-bow.html

The rawhide is a huge bone shaped dog chew from a pet shop soaked in warm water to unknot it. It's pretty slippy stuff to handle and gluing it on and binding it with string until it sets is a messy job. The glue gels quickly and it feels like it's not going to stick, but a waft with a hot air gun when it's finished helps to re-liquify the glue. You can see from the chalk marks on the wall that it is bending about as much as my other bows, so I'm not sure it can take much more.

The last pic shows how the upward curve of the bow moves the string line so that it won't press down too hard on the stock and waste power. The down side of this is that the bow tries to twist on the tiller.
It also shows some of the dark streaks on the belly of the prod, these are shallow cracks which hopefully won't be too much of a problem as they are longitudinal. There was also a knot which I filled with sawdust/epoxy mix.
I believe the stock of a medieval crossbow was called the tiller, being long and straight, maybe it was reminiscent of a boats tiller, and maybe then got applied to a tiller stick used for pulling back the string of a long bow when checking the curve of the limbs.

Wednesday, 19 October 2011

Grain/gram Scales, Crossbows, Speed and Power

I've just bought myself some digital scales for weighing arrows and suchlike. As I've started making a crossbow prod from Laburnum my thoughts strayed to the comparative speed and power of the crossbow vs the longbow.
there is a lot of daft speculation on the subject and it's largely irrelevant as the two weapons are/were so different.
In medieval times crossbows with wooden and composite prods were out ranged by the longbow, the introduction of the steel bow gave the crossbow extra range and power but at the expense of weight and speed of shooting, thus it became a defensive weapon or effectively a snipers weapon.
Doubtless there will be plenty who will argue with this synopsis.
Anyhow I shall illustrate with some facts and figures using my 75# longbow and my 275# crossbow (both on the website)
The Longbow shoots an arrow weighing 28.93 grams at 166 feet per second.
The Crossbow shoots a bolt weighing 54.55 grams at 158.7 feet per second, (the slower speed may surprise you).
Because the crossbow prod has heavy steel limbs it is slightly slower and shooting a lighter bolt doesn't increase the speed much.
If I convert the figures to kilograms and metres/second to get a figure for kinetic energy in recognised units (Joules) I get 37 J for the arrow and 63 J for the bolt.
(Using the formula 1/2 x mass x velocity squared)
You see the bolt is going slightly slower, and will have less range* but has almost twice the energy when it hits home.
Of course the crossbow is only a representation of a 'light sporting bow' and my longbow isn't a full 'Warbow' but it illustrates that range and power aren't necessarily the same and that you have to match the weigh of the projectile to the bow to maximise the energy as well as the range, it also shows the limitation of the crossbow.
To get real long range from a crossbow they had to go to immense draw weights.
E.G. Sir Ralph Payne-Gallwey refurbished a siege crossbow, draw weight 1200 pounds (that's over half a ton!) It would shoot a bolt 460 yards.
The other factor of course is draw length, the crossbow having a much shorter draw. In the above example the string only came back 7".

The point of all this is the primitive crossbow I'm going to make is hopefully going to be about 70-80# draw weight, pulling back about 8-9" but it will doubtless be less fast and less powerful than my longbow.
The prod is made with the tips curving up slightly to help the string lift up over the stock, I've also used a bit of wood with a natural deflex, this will help to avoid over straining such a short bow, and allow me to get a bit more draw length.
This is all just done by guesswork/experience, so I fully expect it to explode the the tiller, especially as I haven't used Laburnum before.

Update:-
Blimey I've trimmed about 3/16" off the width and put a loose string on it. It winched back to 70# on the tiller very quickly at just a few inches deflection, it looks scary as hell.
I think I'll clean it up and maybe glue some rawhide or leather onto the back for extra safety before doing too much more. I thnk it could gould go bang rather spectacularly.
It looks odd having such a short bow on the tiller. I'll post a pic in a day or so.

*As a point of interest a crossbow bolt is a bit more aerodynamic than an arrow. there is an optimum ratio of length to diameter and a short bolt is closer to this. There was a 'Scientific American'article on this many years ago. This shows the cover of the relevant issue (Jan 1985).

Sunday, 16 October 2011

Oak & Apple Explain More

Not quite sure which bit requires further explanation. The primitive crossbow will be explained further when I get round to building it!
It will have a wooden bow (prod) held onto the stock with a binding similar to the repro' mediaeval bow on my website. The trigger mecanism will be a groove across the stock which the string pulls back and drops into. A wooden peg will press up through the stock to push the string up out of the groove, the peg being pressed up by a long wooden trigger beneath the stock
The apple scratter was inspired by this link http://www.sentex.net/~mwandel/press/apple_grinder.html and there is tons of stuff on Youtube about building apple scratters (grinders) and presses.
To cover more about gathering apparently rotten Oak, I went back and took a couple of pics from where I'd cut it. You can see from the Ivy growth and rot that it has been down for a fair time. The fresh cut face has now started to split as it has had a week to dry out, but you can see the heart wood is sound.

Saturday, 15 October 2011

Longbow Fever

The other night I couldn't get off to sleep, longbows were going round in my head.
One of the guys I made a 60# bow for last year wants one of 90#. This could be really nice for me as 90# is probably about the most I'm going to manage to draw.
The Yew which was cut last November (From Audley End House by a tree surgeon) has been reduced to staves. I've picked out the longest 7'1" which gives me a bit of elbow room to find a decent bow in there, I've reduced it's dimensions a bit more and a couple of knots on the edge have been cut away now, so it's looking good.
I get a few people asking how long to season staves, so these pics will help show how work down a stave as the seasoning progresses.
Originally the log was quartered, a month or so ago it was debarked (that is somewhere in the blog). Now I'm reducing it further, including chopping away some of the excess sapwood, the pictures will give some idea of the size at this stage. The chippings on the floor give you an idea of how much I've removed, a bit at a time, with plenty of thinking in between is the way to work on bows. I'm sometimes aghast by beginners diving in and working too fast at the critical part of the process (the tillering)
I'm not sure when I'll start serious work on it but it almost certainly won't get any real flexing until the new year. This stave has a bit of natural deflex which I may possibly take out and heat treat the belly at the same time, although I might just leave it as is.
The guy who wants the bow isn't very tall and a 90# bow needs a reasonable length, I'll read up on the dimensions of the Mary Rose bows and make it about the length of the shortest of those. I don't like bows looking too tall for the archer, but conversely I don't want to over stress the bow and end up with a lot of set (permanent bend) in the bow, that's why I'm toying with the idea of the heat treatment. You can see I've still left plenty of sapwood which will stay on there if I do any heat treatment, as it will protect the actual layer of sapwood which will eventually become the back of the bow. the Yew is a good colour with clearly defined heart/sap wood, the rings aren't particularly tight, but it's similar to the Yew I was using at the start of this year which yielded some lovely bows.
I also need to be thinking about cutting a Yew limb for 2013, I have permission to cut it, but the paperwork hasn't come through yet.

Friday, 14 October 2011

Primitive Arrow, man make fire!

Ages ago one of the guys from Archery Interchange sent me some bits of Cow horn, antler and some Greylag Goose feathers. I finally got round to using some of the feathers on some of the Hazel shafts I'd cut ages ago. I've only done one for now.
I scraped off the bark, straightened it over a gas ring (they become quite pliable with heat) and stuck the flights on.
I cut the narrow end at the right diameter to fit a regular 5/16" point. The nock is cut with a saw and filed to a sort of keyhole shape so the string is a firm fit to push on, but sits loosely on the string once it is on there e.g the nock has a narrow entrance and is opened out at the bottom. This probably helps to avoid splitting, but that won't be an issue on a 40# bow.
Despite not being dead straight it flies straight enough.
there was a discussion recently on Archery Interchange amongst target archers about whether a bare shaft spins on not... what a load of overthink! Good old natural feathers induce spin because they are curved and one face is much smoother than the other. This is useful in helping to stabilise imperfect arrows. The modern target archer has virtually perfect shafts and puts symmetrical plastic vanes on which he then has to deliberately put on at an angle to generate spin, or to buy fancy 'spin wings' or some such, I even saw a plastic nock with the arrow slot cut on a spiral to induce spin and tiny stub vanes on it too. It just goes to show that sometimes simple and natural is sometimes best. (Of course, these guys doubtless shoot more consistently than I do and I'm just representing my opinion here, so apologies to any target archers reading this!)
My wife didn't like the smell of scorched Hazel in the kitchen, so I got an old saucepan from the garage, and bent some tabs out from the bottom. This making air holes and legs at the same time. I burned some offcuts of assorted bow wood in it. A very cheery conflagration which lasted long enough for me to straighten the other shafts.
The fire in a saucepan amused me rather so here's a pic.

Sunday, 9 October 2011

Oak & Apples

For a while I've been toying with the idea of a primitive crossbow, the short wooden bow would allow me to experiment with off cuts of timber and suchlike.
A crossbow stock wants to be heavy and stable, sounds like Oak to me. I went down to the woods and found a nice big fallen Oak limb, it looked much too big and much too rotten with the undergrowth established over it. The bark just crumbled off all black and manky, the sap wood was a white spongy mass, but I could see where the limb had split conveniently along the length the heart wood was solid as ... a chunk of Oak. I mean we used to build ships, barns and all sorts out of the stuff.
I sawed a 3' length, and took it home on my shoulder (it was getting heavier with every pace).
The bandsaw soon shaped it into two nice blanks for use at some future date.
Working the Oak also reminded me of project I'd been mulling over for a while, a machine for chopping up apples to make apple juice and cider. Another piece of that Oak soon became the roller for the machine, Oak works nicely when wet (and makes less dust). You can see from the pic that it's a nice chunk of Oak, cut from a quarter of the log so that the centre isn't in the block so hopefully it won't split as it dries. The roller has loads of stainless steel screws protruding from it to mash up the apples as it spins round, powered from an old 12V Dc motor I have lying around.
Anyhow here are a few pics rather than writing a load.

Monday, 3 October 2011

Video

Here's a short video of the bow in action, it's a bit bleached out, I might to get a better sequence.

Friday, 30 September 2011

Finishing

The final finishing, minor tiller adjustments, sanding and narrowing the tips and shooting it in with 50 arrows or so has lost a few pounds draw weight so it's nearer 40# now.
Some of that may be due to my shaping the handle which allows it to sit a bit lower on the tiller (I havn't bothered to adjust the rule).
It seems to be shooting sweeter now and grouping really well, normally if I group the first 3 arrows I then loose it, but this bow just keeps banging them in the same spot.
I'll shoot it at the club on Sunday and post a few more pics.