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.
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.
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.

Monday, 10 July 2017

MkII Prod

It's a bit scary trying to pull this prod, it feels like a bit of steel girder, but I have to take my own advice and if I want a 100# prod, I'd better pull it to 100#
So I got a string on it, just long enough to slip over the nocks and heaved, I took it back to 100# and it seemed ok, I took some video and gave

it plenty of exercise. I'm working on the principal that if I can get it drawing 100# initially that will allow it to settle down to a usable 95# or so.
I think the left limb looks a tad stiffer but it's hard to say as the lighting isn't square on and even.

Meanwhile I've spliced two of JT's broken flight arrows, one had split at the nock and the other had it's point snap off. A splice near the tip shouldn't be subject to much bending force, so it's a good way of salvaging a flight arrow which would take a lot of work to replace from scratch.

Sunday, 9 July 2017

Crossbow Sights

I've made some quick adustable sights for the crossbow and got it sighted in a 10 yards, made another couple of bolts too for some shooting this morning.
Very strange thing, the two new bolts kick high and left by about 20" at 20 yards whereas the two original ones go straight true and right next to each other. the odd two are made form the same batch of shafts, have the same points and fletchings from the same source although not from the same actual packet. My guess is that the fletchings are interfering with the bow mount, I might try an unfletched bolt.

So, I just used the 2 good bolts and managed to get some idea of trajectory out to 40 yards, and some long shots at 120yds.
My mate JT had a go with the crossbow too and he put 2 bolts withing about 1/4" of each other.
The trajectory was rather disappointing and I think the prod has lost weight. I've since re-weighed the prod on the tiller, it's down to 70# , I s'pose this isn't too surprising as it been exercised now and has had time to settle, the damage to one limb probably hasn't helped either.

I've got the bow mounted on the bench so I can try and work out what's happening with the rogue bolts. First step see if I can repeat the result...
Test 1:-  Shoot one good, one bad bolt. The "bad" bolt is 18" left and high compared with the good one!!!
Test 2:- Trim the fletchings of bad bolt to a low profile. It still flies high and left by about 18".
Test 3:- Remove fletchings of bad bolt. It flies true, striking the target just below the good bolt with a slight nose down attitude.
Conclusion:- it's the fletchings wot dun it guv' and no mistake.

I can't be certain exactly what is happening but my guess is the quill part of the fletching is catching on the 'shoot through' part of the bow mounting, which I shall adjust and then try the second bad bolt.
See results (left) the bad bolts had orange cock feathers, the good bolts had white.
I cleaned up the shoot through aperture, one trick being to reverse the front part and bolt the two together, that showed up any asymmetry and by filing the two together and reversing them back and forth I've enlarged and evened the aperture in the two plates The bow was them bolted back inbetween the plates and the wood rasped to match.

I've also got a few minor issues with the trigger mechanism, so I've ordered two 600 grit diamond needle files off the interweb. They do sets in Toolstation but I have it on good authority that they are 'crap' (prob too coarse for what I need).

Thursday, 6 July 2017

Crossbow Shoots Cleanly

I've got it shooting cleanly now, I twisted up the string to increase the brace height by about 1/4", but I think the stiffer prod mount is also a factor, it was probably moving a fair bit on each shot, that's to say if it put in 2 or 3mm of permanent bend, it must have been moving at least twice that dynamically and that may have been what was throwing off the string. My guess is that I could probably take off the inner string catchers.
I'll probably do more experimentation and development before finishing the MkII prod, after all I want to try to get all the mistakes out of the way on this one.
Now I can take more than one shot I've paid more attention to the feel of the bow and trigger pull, getting lined up for the shot and almost shutting my eyes to concentrate on the feel, the trigger pull is quite hard, but some of that is just feeling the raw edges of the steel, it's also not quite at the right angle to the finger. The bow feel to kick slightly, but again its all nasty corners and an unfinished grip.
It's a good time to strip down the trigger mechanism and examine it. I've been working on it this afternoon as it was rather stiff and is a long pull, I'm ok with the long pull, but some adjustment of the bent (that's the step on the tumbler that the sear engages in) was needed. I jigged it up in the vice so I could use a fine slip stone to just ease it a tad. Trigger mechanisms will wear, some can be adjusted but they will all need some maintenance at some point. A trigger mechanism than can slip could be lethal. A little while back I saw one on a crossbow which had the tumbler made of Aluminium alloy with no steel insert, as I rotated it I could see considerable wear, I mentioned it but was told it was fine and had been round a couple of NFAS courses (I was pretty horrified). We really do need to understand the equipment we use. There was a thread on one of the archery forums about release aids for compound bows. To be frank it was scary and IMO just wrong... here's a quote:-

The problem I had was drawing and getting early misfires. The arrows fly high and long!!!! very scary. Some archers have sorted their draws to the point where they do not expect misfires. I gave up as I could not take the risk... when was the next one going to happen??

To give the guy his due he gave up on that type of release aid and decided not to risk any more misfires, but I find it worrying that there may be others out there who are using triggers and not fully aware of the risks they may be taking. Risks that could be greatly reduced with a better understanding of the need to maintain the equipment and the risks of not doing so.
Over the afternoon I've done more testing and even clamped the crossbow on the bench and measured the trigger pull, it is indeed too heavy at 12 lb !!!! I'll rework it a bit more.

I had a visit last night from a guy with big Yew stave from Salzburg which he'd got from Gunther one of the Austrian contingent at the ILAA Mary Rose shoot the other week. It was a very scruffy bit of wood with some serious damage at one end, one ring that seemed to have turned to black dust for a good few feet and numerous checks and cracks. On the plus side it was big! After much thought, mumbling and head scratching we ran it through the bandsaw to produce a couple of staves. Not quite sure what poundage of bow I'll get from them but hopefully in the 75-110# range. The staves are a "think about it" sort of project, I'll take 'em down further by degrees as the whim takes me.

Wednesday, 5 July 2017

Prod Mount Development

I'm using the MKI damaged prod to experiment and improve the mounting to allow more of a shoot through, with the prod mounted a little higher.
I don't want to risk making a mount that is fine at 80# but explodes when it's tried at 100# especially with the cut out extended down to allow for fletchings.
While making this mount I used the aluminium angle (4x2") up the other way with the 4" as the vertical, this meant the bottom, horizontal leg was too short... I thought I'd try some of that aluminium brazing rod which melts at 300 C (ordered on Ebay)
I could have bought larger angle, or I could have asked my mate Mick the blacksmith to weld it for me, but it's much more fun to try new stuff and where possible do it myself. After all I could buy a whole crossbow for a hundred quid!
. It has worked pretty well, no flux no messing, just a propane torch. the initial try out wasn't all that strong as I'd prepared the joint as you would for a weld. I then read the instructions which said for a butt weld, tin both surfaces and then sweat the parts together, like soldering rather than welding. That worked well, although with hind sight I'd have gone for the slightly harder 400C rods. We'll see how it hold up in use.
Please note :- Any resemblance to an early radio set is purely coincidental !

Update:- It performs better but there are still teething troubles. With the vertical section longer, there is more leverage and the mount has bent forwards slightly, it hasn't helped that I've narrowed the horizontal bit that runs underneath, it looks better but is weaker.
There are plenty of solutions, I could go up to 3/8" thick material or I might add side pieces which can be made from some of the scraps I have.
I did phone Mick the Blacksmith to see
if he could weld in a couple of bracing fillets, but he doesn't have the kit to weld Ali' , no matter, I'm not stuck yet!
Further update:-
See additional brackets in pics:-

Sunday, 2 July 2017

Good Results

I've taken the repaired MkI crossbow prod to full draw and got a Force/Draw curve for it. I've shot it again with the string catchers and a temporary string buffer (see pic) the shot was clean and fast but the string still went over the prod some how, but without damaging the prod! Close inspection of the tips show how the string has ridden up. Presumably the slightly heavier bolt (14" long with 100gn point), the string catchers and buffer all absorbed a good deal of the energy and saved the prod from breakage.
I can now experiment with  string catchers nearer the nocks and moving the string buffer slightly closer to the brace position.
Not much string groove in the belly on that left tip, so maybe that would help.

Meanwhile I've got the Mk II prod glued up and sanded to an even thickness taper ready for nocks.
All in all a very productive time. I'll also be able to try a shot through the chrono'.
Note the MkI has lost a llittle weight due to reshaping the lower edge of the tips and rounding corners. The Mk II is over 1 mm thicker and I'm aiming for about 90-100#

Just shot it through the chrono' 202.6fps, not bad from a 76# bow !
I'd moved the string buffer forward a tad but the string still jumped over the left tip. More development needed, before I get the MkII going.

Friday, 30 June 2017

Prod Development

I've been tinkering with the design and experimenting with the MkI prod whilst building the MkII.
I was pleasantly surprised when the MkI survived being strung and even more surprised when I got it to within a couple of inches of full draw. I thought I'd add some binding over the cracked area to maybe stop it buckling and splitting open. I also added some little horn string bridges or string catchers to hopefully help stop the string popping over the top edge of the bow.
Maybe I'll have the courage to try cocking the bow, if that holds I'll try it through the chrono'

I've also adjusted the stock to get the prod mounting about 3mm higher. In the final design I may go even higher, but the problem with that is it needs more cut away to allow the bolt (arrow) to travel effectively through the prod. I've checked online where I bought that aluminium angle and they have it thicker and with longer sides to the angle, so I could have a much taller vertical section where the bow is mounted and extend it up above the bow to form an arch under which the bolt travels, this would serve several purposes. It would add strength and provide a sight bridge on which I could mount the fore sight. Going up to 3/8" thick section would maintain the rigidity.
None of these changes may be necessary, but one needs to have a game plan for when failure kicks you up the backside... with engineering the time to worry is when you've run out of back up plans and ideas!

Thursday, 29 June 2017

MkII Prod etc

I've been through some of my Yew and found that a load from last year was all but worthless, but I did manage to get two short clean lengths for the crossbow limbs from 4 staves. I'd paid good money for the Yew while it was in the tree, but some you win, some you loose, I've had other stuff for free, so I can't complain.
I'd also gone through my billets too trimming them down and eventually I ended up with 7 potential limbs, from which I chose the best two.
Doing all that has cleared some of my wood storage shelves, so that's a result, I can get some Yew off the garage floor and onto the shelves now.
The new Yew limbs are clear of any knots this time, although it took a bit of careful laying out to achieve that. I've done the Z splice, which is slightly tricky. As the limbs are angled back in deflex they have to be supported at that angle when the splice is cut, I did this by making up a block of plywood and sticking the limb onto it with double sided tape to support it at the right angle as I sawed the splice
Meanwhile I'd glued and clamped the cracked limb and I've actually braced it and pulled it almost to full draw! I may pluck up courage and pull it all the way, but it will just be for curiosity and test purposes, I'll never really trust it.
Hopefully the pics will show what I mean.

I think I can see why the string went up and over the limb. The tip of that limb is bent up very slightly and I think the reason for that is that the lower edge of the limb is thicker than the upper... the reason for that is the bamboo backing being thicker in the middle than the edges. The top edge of the bow corresponds to the edge of the bamboo (thin edge). The lower edge of the limb tapers upwards and as it narrows it goes from the thin edge of the bamboo slat to it's thicker center section.
So the top edge of the limb is say 5mm Yew plus 1mm Bamboo, where the lower edge is 5mmYew plus 3mm Bamboo. This difference causes the limb to twist up slightly towards the weaker top edge.
On the mk II I will try and keep the thickness more even.