Saturday, 23 September 2017

Boo, Purpleheart, Yew Progress

I've got the purple heart tapered and joined with a short scarf joint. The Yew belly billets have been tapered, a short Z splice cut, they have then been heat treated and glued.
I've got to plane up the boo and the glue it all up. I've asked on Primitive Archer whether I'm bette roff gluing all 3 at once or gluing the Yew to the purpleheart first. There's a hint of deflex in one half of the yew still and maybe gluing it up to the Purple heart would pull that out. Mind I'm thinking of gluing the whole thing up with a hint of reflex / backset, maybe just an inch or so, although it probably won't take much set during tillering.

Monday, 18 September 2017

More Thicknesser Development

It's almost finished now, here's a pic with the power plane missing, but it's sole plate is screwed to the top to give alignment as it is all built up.
I've put feet across the bottom spaced so that can be clamped on to the workmate. The adjust wheel is more central now, slightly less convenient, but better mechanically, the screw that pushes upwards bears against a bit of steel plate. I've made lots of improvements to take out slop. The biggest factor is probably the thickness of the table which rides up and down smoothly with no real room to twist.
The only problem is I don't know where I'll have room to store it, maybe I need another major sort out.
Most of the wood is off-cuts from shelving that I've been doing and bits that were hanging around.
Just added a pic with it all finished and set up with a length of Purpleheart in there for tapering.

Update:- It works a treat, no perceptible ripple, bit noisy of course and you have to take the cut in stages, con't just rip a great big taper off in one go. An advantage over a sander style thicknesser is it produces chippings rather than dust. The chips are much easier to collect/sweep up. It does throw 'em out of the front with some force so you can feel 'em pinging onto the back of your hand.

Friday, 15 September 2017

Improved Taper Sled and Thicknesser

The thicknesser was made a while back from an old power plane. One fault was the adjustable plate was hinged at the back and didn't come up parallel to the sole of the plane. I've improved this by hinging both ends so it moves parallelogram fashion, being pushed up by an adjusting screw under the front edge.
The other problem was the taper sled which was wooden and not very stiff or flat. I bought some aluminium U channel and made a better sled, it is still somewhat flexible over a 3' length... but then, so is almost anything unless you go to box section steel.
I gave it a quick try out on a strip of Ash, I set it to quite steep taper and a deep cut. It did the job but with some chattering.
I learned a few things.
1. Stick the whole lamination down with double sided tape.
2. Only take a fine cut, and/or maybe gradually increase the taper.
3. don't try to pull it back out with the plane running. It will take other cuts and spoil the work

I'll have another try on a bit of scrap and report further.
Some of these taper/thickness machines that people make use a drum with sandpaper on, I reckon they must take an age to run through if you are taking off any amount of material, though they doubtless give a better finish. I imagine using this for rough taper, then running the lamination over the belt sander.
We'll see how much wood I ruin before resorting to working staves ;-)

Update:- I've given it a go with finer cuts and it works well, there are still some improvements to make as the parallel motion doesn't work at low angles and there isn't enough height for thicker billets. The wooden adjustable plate wasn't flat, but a few strokes of the plane have improved that.
I'll work at the design to try and make it good and rugged and versatile. It looks promising.


Saturday, 9 September 2017

Next Project

I'm working towards making a tri-lam ELB for a woman who already has a couple of my bows. Laminated bows are something I'm not particularly into but I happen to have the necessary materials.
I've recently bought some more bamboo and my mate Matt from Cambridge longbows gave me a purpleheart lamination some time back.
I'm thinking Yew belly, Purpleheart core Bamboo back.
With a view to improving my Thicknesser/Taperer that I made from an old power plane I've bought some channel section aluminium to make a stiffer adjustable taper sled.
For those of you who have no idea what I'm talking about:- A taper sled is like a tapered plank, you clamp or stick a lamination onto it and run the whole thing through a planer/sander etc and it comes out with the lamination tapered to same angle that you set the sled up to. E.G The lamination and sled together come out parallel, thus if the sled was tapered the lamination now has the equal and oposite taper to make the overall pair of  'em parallel. Anyone who still doesn't get it, draw a long thin rectangle with a diagonal line from corner to corner, label the lower portion "sled" and the top portion "lamination"...  you can colour them in too if you like ;-)
I'll post some pics of the tapering sled and thicknesser when it's finished... mind it may be some time as I've a load of shelving to build (so I'm reliably informed ;-) )


Meanwhile back at the story, the woman in question likes her pink arrows and pink fletchings, so I thought I'd make a very "girly" bow and I've experimented with some coloured acrylic for nocks. The acrylic is sold as pen blanks. I quite like the effect but it is deemed not to comply with the rules for longbow which specifies Horn Nocks... that's NFAS and AGB. All a bit silly really as that doesn't allow bone or antler either of which would have been used.
I did a quick try out putting a nock on an off-cut of Yew.
It turns out she wants horn anyway and like how I do my nock at the moment. Still it was a bit of fun and the pen blank only cost a fiver (enough for 3 nocks)

Wednesday, 6 September 2017

Update on the Crossbow

I tried the prod on the tiller and it was just over 100#, but I probably didn't get it quite back to full draw, I didn't want to risk over-straining it. I plucked up courage and had half a dozen test shots and then tried it 3 times through the chrono' (with the heavier commercial bolts), average was about a disappointing 170fps. I then tried the old prod with patched and repaired belly, using the same bolts of course and it was about 5fps faster!
The new prod took a hint of set so that it needed very little flexing to get the string on. The old prod required a little more flexing despite being about 2 " shorter.
My conclusion is that the Yew is a better belly than the bamboo... of course this may only apply to this particular yew and this particular boo (I don't think it's Tonkin boo, which is considered to be the best).
It also illustrates the dilemma of crossbows, trying to get decent performance from a manageable short prod whilst maximising the draw length, without resorting to bolts that are really too light and risk damaging the prod.
I've added a pic, showing brace and drawn superimposed so I can see how it flexes.
I'll probably re-visit this at some time, and if I can get up to 200fps I'll invest in a scope and try it at a field shoot. It's not that much faster than a good primitive at the mo', after all Twister has been clocked at 166fps (prob' a bit slower these days).
One of the Guys on Facebook was suggesting heat treating the inner faces of the boo, but if you've been following this project you'll realise I've gone through enough experiments for now!

Any how onwards and upwards onto my next project which is...

Tuesday, 5 September 2017

Prod Testing


The crossbow prod looks and feels pretty good, it's about 1/2" short of the full brace height and I haven't actually cocked it yet.
The nocks have been made much more substantial than the previous ones and have been reinforced and shaped by binding with fine linen thread which is soaked with low viscosity superglue as it is bound on. The glued thread is quite solid and can be filed and glued again.
I've videoed it being drawn so that I can look at the tiller.
I will tidy it up, enlarge the shoot through hole to take the larger fletchings of the commercial crossbow bolts, increase the brace height by twisting up the string and then eventually shoot it, with some trepidation.
Oh, yes, I must remember to glue on those horn string catchers that I'd put on the previous version, I'm sure they are a good thing.

In the pic where you can see the whole prod, you can see the line along the centre where I have put two slats together to give a flatter belly.





Monday, 4 September 2017

Bamboo Belly for Crossbow Prod

I'm still messing with the crossbow prod and the bamboo as I've just bought a new batch of boo slats.
I get a decent batch and go halves with my mate Matt from Cambridge Bows.
He came over on Saturday to collect his half and we had a good natter, I later checked up on some of his Youtube videos and his website... excellent.
I wanted to get the bamboo to be as wide and flat as possible for the belly but without loosing the strongest fibres which are in the outer layers. By sawing the bamboo slat down the middle and planing the two bits individually, I could then put them back together side by side to give a flatter pied like  B rather than a D, the pic shows what I mean. I don't know if this is really worth while bu it does give a more even thickness and I can stagger the nodes slightly too.
I've got one side glued up and will do the other today, I'm a tad worried that it will be too high a draw weight, but it's all good fun

Meanwhile I went out shooting with JT and some others, they were lobbing warbow arrows at a flag, but I made a target from an old duvet that was being thrown out loosely rolled and put into a woven rubble sack. I was shooting at it from shortish ranges varying from about 10 to 40 yards trying to get my eye back in with Twister my field bow. The target was excellent, it stopped the arrows nicely without getting shot up, being light it tended to move a bit and absorb the impact, hicghly recommended as a quick cheap target.
One of the guys who was shooting was very taken with the coarse ringed warbow I'd made a while back. I had intended to keep it as a specimen bow, but what's the point of a bow that doesn't get shot? So I decided to let him buy it and he was grinning from ear to ear. he was telling me that there is no comparison in the feel of the Yew as against his laminate. I knew I'd made the right decision to let it go, as I still have an off cut of the wood and it's blogged up on here for future reference.
Just added the pic of my old Yew longbow to illustrate that you don't need to follow a growth ring, this is a response to a question asked on one of my Youtube videos.

Monday, 28 August 2017

New Arrows, Bolts and Stuff

I went to a 3D shoot at Aurora on Sunday with Mick the blacksmith, gorgeous weather,excellent shoot in good company with great catering. I was worst in our group of 5 only just scraping 406 over 40 targets, but my tennis elbow had flared up and I also felt like I had a 6" nail lodged under my left shoulder blade (note to self... please please use a stringer when making heavy bows). Feel free to use these excuses yourselves...
There was plenty of good natured banter... on one target I was up first, a longish shot with a big tree limb diagonally across about 6 foot in front of me. I thought the trajectory would be flat enough to just go under it... thud... the arrow smacked into it in spectacular fashion sticking in nicely, there was a suitable amount of cussing and witty remarks. I stepped forward and hit the target with the next arrow. Mick stepped up (he's a better shot, but his bow maybe has a slightly softer trajectory as he has a shorter draw)... I though he'd judge it right... nope... "thwack" he buried his first arrow right next to mine, and on digging them out we found a third arrow point buried in there between ours!
One other strange occurrence was on a relatively innocuous wolf target at a shortish range, Mark who was shooting in a very controlled and consistent manner proceeded to demolish 3 arrows by putting them all just over it and smashing them into the coppice of sweet chestnut just behind the target, he was as nonplussed as the rest of us.
I improved slightly near the end of the shoot, but just couldn't seem to get that confident feel of distance/trajectory that one has on a good day. I also managed to smash the points off 4 of my new arrows grrrrr.
Mick uses very long two part screw in points which seem to survive better (mind he misses less too!)

Meanwhile I've still been tinkering with the crossbow, I bought 10 commercial bolts (Aluminium alloy shafts, screw in points, plastic fletchings) and modified the crossbow to take them. I had to deepen the slot in the bow mounting for the cock feather and widen the slot in the nut of the trigger mechanism. The fingers of the nut are aluminium alloy, so I clamped it up tight and put it under the pillar drill with an 8mm bit in the chuck. Taking the drill down very very slowly I managed to mill it out, and a bit of work with needle files completed the job. A test shot showed it worked fine and it felt a bit smoother with the heavier bolts.
Talking of crossbows, a lady at the shoot on Sunday kindly let me have a shot with her Jandao crossbow (90# draw weight) it was good to try one with tele' sights and I made sure not to hit her bolts.
" 9 o'clock in the red" I said to her and promptly shot the bolt just there. I forgot to take the safety off initially, I didn't know where the damn thing was, and if you have to wave the bow around whilst looking for it, it is rather unsafe! She was about as old and grumpy as me and I don't think she really understood that I knew what I was talking about when I was saying I didn't think safety catches were really necessary (maybe some readers won't understand my view either). Anyhow that makes it even more kind of her to let me try it.

Thanks to all at Aurora for putting on an excellent shoot and importing the lovely weather.

Tuesday, 22 August 2017

Finishing off A Part Made Bow

Finishing someone else's work is always interesting, it's nice to see the job completed, but on the other hand it can be slightly frustrating.
Mind it saves time as the mistakes have already been made for you and all that's left to do is to correct them ;-)
This stave is handsome Yew, nice colour, fine grain, sapwood thin enough so that it doesn't need reducing.
The problems are:-
1. Some slight lateral bend which has one edge dead straight and all the width taper on the other side. Fortunately there is just about enough tip width to rasp away the straight side to improve the alignment.
2. There are some seriously thin spots where the belly seems to have been taken down even and straight ignoring dips in the back. One of these near the grip is thinner than much of the mid limb section!
3. The belly has been shaped to almost a semicircle... people make the mistake of thinking a "D" is like a Norman arch or a semi circle. If you look at this actual "D" as if it's a bow the sides of it are flat. If a bow is shaped rectangular section and the corners taken off you are pretty much there, it also leaves room for some minor adjustment. A little cosmetic rounding can be done as part of the finishing.
4. There are tears and gouges at various points where an edged tool has dug in against the grain.

Basically the overall effect is a bow that, at a quick glance looks basically ok on the tiller but I was only happy to draw to about 24", it's bending relatively evenly on each limb but most of the bend in in the middle. That's fine by me 'cos that's how I start the tillering process, however I think this bow was seen as being nearer the end of the process.
First job, was to rasp the tips to improve the string line (I did this before even putting it on the tiller).
next I marked all the thin areas with a big "L" for leave, then it was reducing all the thick areas and getting the limbs tapering down from the thin point near the grip.
I've put horn nocks on now and it's looking good now but isn't going to make the 100# initially requested. Mind when I first put a low brace string on it, I immediately commented "That won't make 100 pounds ", because there's no way I can string a 100# bow even at low brace.
I've got it back to 30" at full brace now and it's about 70# (allowing for the scale being about 1/2" out)
The right (upper limb) is stiff, so I have reshaped the nocks and reversed it having the stiffer limb as the lower now.
The nocks are a nice chocolate colour with pale streaks.
Video here:-
https://youtu.be/sAEdK26SWec

Saturday, 19 August 2017

Messing with Bamboo

I've been reading around heat treating bamboo, and like a lot of stuff it's all rather confused and poorly defined with conclusions ranging from, it makes it worse, to it makes it better.
Well I have an off cut from my crossbow prod making which is planed to a nice flat one side with the outer surface intact on the other. So I cut this diagonally to make two tapered limbs I did some bend tests with the limbs up either way and messed with some heat treatment, but it was all rather inconclusive.
One problem I think is that simply  hanging a 2# weight on the tip wasn't giving enough bend to be significant. Anyhow here's the question:-
If you were to make a bamboo bow from one piece, would you have the back of the bow as the flat planed inner bamboo or the hard, shiny outer surface?
The received wisdom is that the strength of Bamboo is mostly in the outer fibres and that most materials like wood and bamboo are stronger in tension than compression. Now this would suggest that you's want the stronger side on the belly.
Of course I could just look at a Youtube video of how a Batak native guy makes a bamboo bow, but I do like to check out stuff for myself.

So, I glued and bound the two pieces together to form a bow flat faces meeting together for a few inches in the middle, made simple nocks by binding thread round the tip and letting low viscosity superglue soak in (V quick and effective). I put a string on and pulled it which immediately showed it as much stiffer in one limb than the other. The hard glossy outer bamboo to the belly was the stiffer limb. The preference for having it this way round is also shown by the fact that the other limb (glossy outer as the back of the bow) took a bit of set.
Now, here's the supplementary question for a bonus point:- How will the flat planed bamboo surface hold up as the back? Will it splinter at the nodes?
What is the point of all this?
Well if you have a bamboo slat and want to make a V quick simple boo bow maybe the counter-intuitive shiny side as the belly is the way to go.
Just in case you didn't watch the video, yup, that's the way he did it :-)

Still dunno if the heat treating made any difference... so many experiments, so little time, and the kitchen still isn't decorated. Slow and steady wins the day ;-)

Monday, 14 August 2017

Coarse Grained Yew Test Shots

I got some video this evening of my mate JT shooting the coarse grained Yew. It seems to shoot pretty crisply, and I left it with JT so he can give it a more thorough work out at his leisure.
https://youtu.be/fplODZVTwgA
Meanwhile I'd been tidying up the garage, finishing some new arrows and spending the day doing my yearly batch of cider 12L this time.
 Once I've got the cider making kit cleaned and put away I can get on with some bows. I had a visitor last week who brought a partly finished bow from a friend of his to be finished and one from a well known bowyer that was a bit stiff in the lower limb. I rasped a little off the belly while he was here and had it up and down on the tiller a few times to check it was better.
I took care not to over do it, he can shoot a good load of arrows and see ho it settles down. It's always better to proceed with caution else you can take off too much and next thing you know you've gone from a 80# bow to a 40# bow!
I like to do small jobs immediately rather than have a stack of jobs which can easily get forgotten amongst the clutter of the garage.

Friday, 11 August 2017

Coarse Grained Yew gets to Full Draw

It's back to nearly 100# at 30" still at a slightly low brace, but I'll let it get shot in rather than stress it on the tiller.
It looks very weird but that's a reflection of the unbraced shape. The wood certainly looks handsome and I can't wait to see how it shoots at the weekend.

It's looking good now, I don't know if it will loose weight or take set but it's pretty much felt like almost any other bit of Yew, silky smooth in places, grain tearing in others and needing the rasp, creamy waxy sapwood. Almost no knots or problems except a few pins and one small dark patch in one ring which didn't seem to go very far.
The waggle is a bit extreme and I used heat to take some of the bend out, but one can't expect to completely straighten something that severe. The heat was also used to stiffen that area a bit as the bend tends to be a weak point.



Monday, 7 August 2017

Coarse Grained Yew Warbow

I've started on a warbow using the Yew harvested in July last year, the ring count is as low as 3 or 4 rings per inch in places. It's often stated that fast grown Yew is "unsuitable"for bows, but I'm of the opinion that there is a huge variation in Yew that can't be directly attributed to where it was grown, altitude it was grown at, ring count, colour appearance of the bark or age of the tree.
I've had good Yew and poorer Yew in all shades and from all sorts of places.
This Yew certainly disproves any idea that fast grown lowland Yew is pale with poor heartwood/sapwood definition. I have 3 billets, so I roughed them all down and picked the best two to splice into a warbow, (I don't feel the world is ready for the three limbed warbow, but I expect some wag has made a 3 limbed bow!) I'm aiming for a fairly modest 100# at 31".
You'll see there is a nice waggle in the further limb.
I've also been sorting out my old arrows and making some new ones. The old ones have been mended so many times and I had more with broken off point than whole ones. I've turned all the old ones into a set of slightly shorter arrows and won't bother to repair any further breakages.





Friday, 4 August 2017

Fun Day

The crossbow project has wound it's way to a conclusion. The prod was a bit weak in one limb as demonstrated by the sting not being at right angles to the stock at brace. I eased off the other limb by removing a little from it's lower edge especially from the glass fibre lamination. Finally plucking up courage to cock and shoot it first with the 100gn point on the bolt 141fps and finally with the 70 gn point 151.7 fps . Excellent!After a couple more shots the nock partially sheared off one limb, this adequately demonstrates the problem of searching for greater and greater projectile speed, it simply leaves more energy in the limbs and thus modern compounds and crossbows and up being noisy brutes with shock absorbing buffers built in.
I could go back to the Boo/Yew prod, but I'm not that fussed about shooting, the best speed I got was 244fps from the natural materials and 251 with the glass belly. I've learned a lot and I now have a good design for a shoot through prod mounting and a usable crossbow prod test bed.

Shock horror probe! Del buys a bow! Well I couldn't resist, its a 1950s Accles and Pollock take down steel bow, it's a bit scruffy but for £25 quid i had to have it. I've put a string on it at low brace and drawn it. The lower limb looks weak, but maybe just needs a little judicious bending. I'll probably make a decent string and try shooting it, I can't imagine it will fail as it's steel.
Update:- I've had many people on Facebook warning me that these have a reputation for breaking and rusting from the inside. I'll probably draw it to full draw on the tiller, don't know if I'll make a proper string for it.

Talking of Facebook, there are some odious idiots on there.
A nice woman archer who I know posted her new English Longbow on there... then some bloke asks "what makes it an English Longbow"
I (and the woman in question) replied at some length in good faith assuming he doesn't know that there are various definitions and a difference between a Victorian target bow and a warbow.
Anyhow it turns out he's well aware of the differences and was just Trolling for an argument, complete tosser.
He tried to sucker me in by saying "don't you want to discuss things with people who have different opinions?"
What...? No I don't!
a) He didn't offer any opinion.
b) He asked a question under false pretenses as he already knew the answer.
c) He accused me of arguing, when I was merely answering the question which was originally posed.

My pet hate is people who ask questions when they don't actually want the answer and are aren't interested in it...


Wednesday, 2 August 2017

Bottle Job


I rasped the Yew belly on the crossbow prod down to about half its original thickness and glued on the fibreglass lamination. Gut feel and experience being used rather than extensive computer simulations and calculations!
The first limb went fine, but the second somehow contrived to be a dodgy glue up, not sure how as I'm pretty meticulous, anyhow the excess fibreglass at the tip got snagged on the bench and popped the glue line at the tip... hmm I was V irritated, but I got it all cleaned up and did it again. It seems ok this time, but is very stiff so I've taken about 4mm off the lower edge of each limb and I'm slowly working it towards full brace and being cocked.
Note I'm using the longest string of the 3 that have been made for the various versions of this prod, which is looped through the string adjuster.
 I'll add the string catchers too as there will be a lot of energy in this bow and I don't want to risk it going over center.
It's hard work to cock it, gotta be about 100# .The actual numbers are a bit irrelevant, but if it settles down to be a reliable prod I'll doubtless measure it on the tiller at some point. The pictures show low brace and cocked, I was hoping to see if the tiller looked even but it's hard to see without carefully lining up the camera, it's also tricky with a crossbow as it's possible to pull the string back off centre forcing it to be on the skew, similarly you can force it back dead straight and it will look true as the string won't slip sideways on the latch.
Dunno if that makes sense... on the tiller rig, the string is being pulled buy a long rope and hook, and the bow is supported so that it can rock, this lets you see how it settles under tension, it's not being forced one way or the other. In comparison, on the crossbow, the prod is tightly clamped and the string catches solidly onto the latch.
Just had it on the tiller, still hard to see how even it is, maybe a hint stiff on the right limb, but that looks contrary to the pic above, I took it to 90# and it wasn't full draw, so I reckon it is pretty much 100#
Anyhow I'm basically rather scared of getting to full brace and cocked without making sure everything is as good as possible. I'm even considering some linen binding at a few strategic points along the limb in case it shatters. What worries me is that now the belly is stronger than the back the failure mode could be an explosion of bamboo splinters which would be at eye level (it will be  a safety glasses job). With the previous configuration the likely failure mode would be a graceful collapse of the Yew belly with chrysals and a deterioration of performance.
I am getting a tad jaded as well as scared but do want to see it through, I'm pining to make a longbow or warbow, and there's decorating to do and we want to put some small windows in the summer house as it's a tad dark in there (good for a crafty cat nap tho' !)
Could also do with a holiday, but that will wait until the school holidays are over.
August already, and we've had blackberry and apple pie, the woman next door is leaving me her windfalls for cider making... the year is rolling by, seems like the Summer months all only have about 15 days.


Friday, 28 July 2017

Last Throw of the Dice


Sometimes I'm my own harshest taskmaster and I was beginning to feel I'd had enough of the crossbow project. It's actually performing ok having settled down to about 215fps with the MkI prod, but I'm not really happy with ok.

I realize there are no deadlines, there isn't a spec', there is no boss or customer to satisfy. On the other hand I don't want to plough in vast amounts of time money or effort, so what materials do I have to hand that would beef up the belly? It would be nice to hit 250fps reliably.

Ah, there's the old horsebow which I smashed by overdrawing, I could use the fibreglass laminations off that, that would give them their third outing! What about adhesive? Some of the specialised bow making epoxies are ludicrously expensive but I've got the epoxy resin left from when I made the glass fibre socket for the take down bow. As a rough guide to dimensions (mainly thickness) I have the glass fibre/rockmaple prod which exploded at the start of this project.
So a plan is coming together... Boo back Yew core glass fibre belly, what's not to like?
I've already split/peeled the glass lam's off the belly of the horse bow and started rasping down the belly of one limb of the prod.
Here's a pic of the chrysal and the various prods/bows/lams I'll be working with.
Just out of interest, I reckon that with the two Boo Yew prods being re-worked at different lengths I've gone through about 7 iterations of prod. A lot of work, but you never get anywhere if you are too keen to quit. Of course it helps if you enjoy what you are doing and you've only got yourself to please... mind I'm reliably informed that there is some decorating that needs doing (Yes Dear!)

I'm feeling a bit more cheerful about the performance I've been getting, it's better than the cheaper split limb (centre shot) 90# crossbows and only just slower than the more expensive ones. The bows that are up in the 240 - 300 fps range are much higher draw weights and have 36" prods and longer power strokes.

PS:- For anyone who can't spot the chrysal or doesn't know what they are looking for. It's a silvery hairline fracture travelling up and left from the lower edge of the limb, just above where you can see a pencil lying on the bench.

Wednesday, 26 July 2017

Crossbow Development

I think I'm homing in on the optimum prod length etc.
Having shortened the prod to about 34.5" after the nock shearing off the performance has stayed pretty much the same as it's taken more set. I've found what I consider a sensible brace and I think I spotted why I got a couple of misfires (putting aside the whole "fire" misnomer for now). I think what has happened is that I've pushed the bolt back, but it has stopped up against the fingers of the latch rather than going snugly between them and onto the string, this has allowed the string to impact the very top edge of the bolt, scrape off a very thin sliver and propel the bolt in a haphazard manner. (making a nasty noise and scaring the crap out of me in the process)
To prevent this happening again I've slapped myself around the head with a rolled up copy of the D G Quicks catalogue, I've also opened out the fingers of the latch slightly and tidied up the back of the bolts.

I think the optimum prod length for this bow is 36", but before rushing in and cutting down the mkII prod, I have first heat treated it.
I did that last night. The pic shows the set up, with the side cheeks clamped on to keep the heat off the glue line and the back. I put copious layers of masking tape over the back and sides fbefore clamping up. I've strung it this morning (with some difficulty). It has certainly raised the draw weight and I haven't quite mustered up the bottle to cock it yet!
I'm leaving it strung for a while and I'll give it some exercise before plucking up courage to test it through the chrono.

This project is beginning to pall a tad, but it's good to persevere and get to a conclusion. The rear sight I made looks really good. Dunno what I'm going to do for a front sight, let's see if the crossbow works decently first.

Update:- I had to re-make the string catchers as the heat treating had weakened the glue and burnt the horn.
It shoots fine with the speed about 219fps, which is reasonable being an increase on the un-heat treated version. I'll now take 1" off each tip and hopefully it will be about optimum.
I'm now using the 14" bolts, 5/16" cedar with 70 gn points as my "standard". The lighter bowpistol bolts don't gain much speed and may be too light for the bow.
The bolts slide home into the latch better now too.
Update 2:-
Bit of a downer, the MkII prod always seemed slower than the MkI. Shortenning it by an inch has done nothing and it's showing a slight chrysal where there is an "island" of growth rings on the belly. It shot 120fps, but has dropped back to 110, I may stick on a fresh belly lamination ('boo? Horn? more Yew?) or go back to the MkI or maybe shoot it, or maybe have a break and do a warbow. It seems like I've pretty much pushed the wood as far as a can, shame I'd have liked to get to 250 fps, but we can't always get what we want.
There's been a lot of work in there, mind the trigger mechanism is working well, so maybe it will get an outing some time.

Sunday, 23 July 2017

Crossbow Capers

Well it's good news and bad news. I took the crossbow up to the Cloth of Gold field archery club as a visitor of my mate Mick the blacksmith.
The test shots went fine and he took some video of a shot.
https://youtu.be/peWs7J-h0-o
I then tried one shot at 10 yards to check the sighting and it kicked like a mule... the bolt was in the target about an inch low, the string was nowhwere to be seen and the right nock had sheared clean off.
My guess is that the brace height was a tad low and the string had gone over the bow taking the right nock with it. The string had then pivoted on the left nock and flown off to my left and slightly behind me, as that is where it was found.
Well it wasn't a disaster as I'd taken good old Twister with me as a back up.
Twister shot like a dream as if to say "you don't need to mess with crossbows!" I hit some great first arrow long shots, and I could tell that even with sights on a crossbow, it's all about distance estimation.
Mind I did manage to smash the points off 6 arrows! It is rather stony at Cloth of Gold. It was showering off and on and I was pretty tired, so after 30 targets I took my leave with Mick and Rob shooting on.

I shall take 1/2" inch or so off each tip and try the crossbow again, all these small changes will eventually be applied to the MkII prod.
From a structural standpoint I think I made a mistake by over doing the sanding on the back of the bow at the tip where the horn overlay is glued on. Sanding it flat makes it possible to glue on the horn but removes some of the strength of the bamboo. This time I'll flatten it much less  as the bamboo has more strength than the Yew. I'll also glue some horn to the belly and file the string grooves into that (rather than gouging into the Yew belly), as a sort of string bridge/string catcher. I'll also take care to mark the minimum brace height on the track of the crossbow so that I can easily check if the string needs a few extra twists.

I've also been making a better rear sight with a sliding sight block of horn with a bit of spring wire holding it in a steel frame. I can file sight marks into the frame so that the block will slide up and click into place.

Thursday, 20 July 2017

Good Improvement

I've taken 1" off each tip of the MkI prod and made a new string, I can feel some increase in draw weight, but I'm not keen to try and fiddle about weighing it on the tiller.
It is certainly faster:-
212 fps using the 230 grain 14.5" bolt  (100gn point).
244fps using the lighter 156 grain bow pistol bolt which is only 12" long with a 50gn point (NFAS rules state 14" minimum).

It would be nice to get upto 250 fps, I don't expect to reach the maximum allowed 300fps
I'm pleased with the 244 for now but will experiment further.
Hoping to try it out on some 3Ds at the weekend, I have some 70gn field points, so I'll make up some 14" bolts with those and some low profile fletchings that should arrive today. Got to make a trigger guard too so that it is NFAS compliant. (Update:- done it!)
It will be interesting to see how far I can push the boo/Yew, I may take a tad more off the mkII or try heat treating the belly.
The bow is still comfortable to cock simply putting the butt against my belly and heaving, no need for a stirrup, which I've often thought a recipe for a pulled back. I think the optimum would be a stirrup of a suitable length so you can use your legs rather than bending your back. Too easy to twinge your back.
It's still slightly nerve wracking have such a highly stressed bow up at face level, but I think the failure mode would be relatively a benign collapse or de-lamination rather than the explosion you get with self Yew.

Wednesday, 19 July 2017

New Prod, Old Prod...

Would you Adam and Eve it?
The MkII prod is actually a whisker slower than the MKI ! Am I despondent? Well just a little.
First problem is the draw weight is lower than I wanted, that's because once I got it braced (which was a nightmare) I could see one limb was stiffer, so I had to ease it off which lost some weight of course.
The good thing is that I now have two similar prods that I can experiment with.
I'm shortening the old one by an inch off each end, which will take it to the original intended length of 36" I'll see if that gains poundage and/or speed. I think I'm maybe near the limit of the materials as the prods have taken a little set (but that's to be expected). I can still heat treat the belly of the MkII if I am careful to keep the heat off the glue line.
I shot the MkI again to provide a reference and it's down to about 195fps, shooting one of my lighter bow pistol bolts takes it up to about 215fps, so that's another area for experimentation.
I'm hoping to maybe test it at a field shoot on Sunday, but we'll see how it progresses, hopefully I'll manage to avoid destroying two prods.
I glued the two 1" off cuts together as a joke and posted it on facebook as an infinite draw weight, zero draw length prod :-)

Meanwhile I bought a quick change toolpost for the lathe. It's only made of Aluminium Alloy and designed for those cheap 7"x 10" Chinese lathes. It's a tad big for my little lathe and looke oout of proportion so I jigged it up and turned 5mm off the top of it, this necessitated making a wooden plug as a steady and also filing the cam on the centre section to suit. The tool holder for a boring bar was also too high, but inverting it and drilling/tapping the holes solved that. It's got a lot of slop in it, but once locked up seems to locate the tools at a reproducible height which is the point of the whole thing.

Saturday, 15 July 2017

The Forgotten Crossbow

By Brother Ian who lives down on the South coast was up this way to buy a banjo (a Gibson Earl Scruggs signature model). He dropped in to visit to look at the crossbow I'm building and have a good talk about trigger mechanisms and stuff. He brought with him a crossbow that I'd made him as a Christmas present over 45 years ago, he wanted to give it back to me as he didn't really have room to store it nicely and he no longer used it. He was a bit worried that I'd be somehow insulted, but felt it would have a better home in my "collection".
To be honest I'd forgotten how good it was and I'd conflated that bow with some of my less successful early attempts. It was joy to see this one again as it has oodles of style with a sort of retro Art Nouveau target crossbow look.
It's only a small bow, basically a scaled up bow pistol with a stock.

My Brother filled me in with the story of its use... at that time he was working for the Natural History Museum in workshops out in Cricklewood. In the heat of summer they'd open the windows high up in workshop but feral pigeons would get in making a mess everywhere and with the very high ceilings there was no easy way to get them out, unless of course you had a light weight accurate crossbow! He says he must have shot more than a dozen easily, but the bolts didn't last long rattling around indoors, so he made blunt ones out of aluminium tube weighted at the and with round head nails (flat end outermost).

Feeling it in my hand again was a joy as the grip had been sculpted perfectly to fit my hand, the Aluminium Alloy prod is about 22" long and the whole bow only 24" long, draw weight is about 45-50# but it's perfect for close range target (or pigeon) work.
The biggest surprise was the trigger mechanism, I'd forgotten that I'd made one of that type and the advantage of it was soon apparent. The string slips down into a groove when cocked, but the groove is slightly angled such that the sting would just slip back out again if not held down by the catch closing above it. The advantage of this is that the upward force on the string as it tries to slip out is only a tiny fraction of the draw weight, so the trigger mechanism isn't subject to the great force that it would normally be and can thus be a more subtle and delicate affair with a nice light pull.
In case that has confused anyone, imagine the slot is sloped at 45 degrees and the pull on the string is 100#, that 45 degrees slope would direct equal amounts of force into the stock and upwards trying to slip the string up and out. If the slot is completely vertical, all the force in into the slot and the string won't pop out on it's own. So you see the angle of the slot controls how much force is on the mechanism. There is always a downside though, and in this case it is that the string isn't constantly touching the bolt like with the more conventional trigger mechanism.
The next day I made a new string and my Son and I had some fun shooting into the garage, although the aperture in the rear sight was a little small for shooting into the relative darkness of the garage. I opened it up by about 0.2mm and this helped, along with the additon of some extra illumination of the target. This opens up a whole area of investigation as there are many types of sights, V U, aperture etc all with pros and cons.
I've also shot it through the chrono and it gave a respectable 165 fps, a lighter bolt would gain some speed if needed, but it's only really meant for short range target work.