Sunday, 20 May 2018

Crossbow Chrono'

I'm back from a weeks holiday on the Dalmation coast of Croatia, gorgeous scenery, lovely warm sea to swim in. A little too much sitting on a coach at a border crossing, but it was all organised so generally very relaxing.

I deliberately hadn't chrono'd the crossbow prior to going as I didn't want any disappointment hanging over me! I finally got round to trying it yesterday evening, it had already had about a dozen shots through it and has had time to settle.
Using a commercial alloy bolt (303gn)
First shot 196.3 fps . I'd been expecting 200 +/- 10 so that seemed about right.
The brace height was a bit higher than I'd used before so I took about 10 twists out of the string and tried again... It was slower, so I then added 5 twists and repeated, and then the same again.
It doesn't take too many twists on a short bow to bring the brace height quite a bit.
Here are the results starting from the slowest where I'd taken off 10 twists.
184.9
186.7 (+5 twists)
190.7 (+5 twists)
195.0 (+5 twists)
192.0 (no change to string)
196.8 (no change to string)
193.4 (no change to string)

I didn't want to twist the string up too much and risk over stressing the bow as it seem to be working within it's comfort zone. But I couldn't resist trying a lighter bolt (198gn)
229.7 fps which is ok. If I take it field shooting I'll use the 303 gn bolts.

 I couldn't resist going on E-bay and ordering a 'scope. I only went for a cheapish one as this is all just a bit of fun. I meant to order one suitable for an air rifle as they for some reason seem to shake scopes worse than fire arms!
In the search for a suitable scope with a decent size lens to let the light in, not too much magnification (x2 is prob enough) and the right mounts, I forgot to check it was suitable for air rifles... I also forgot to check where it was being shipped from.... yup, you guessed China!
 Still I'll find plenty to do around the house and garden while I wait on delivery, and the scope was pretty cheap as it had an 8% discount on it so only £26.03 !
Specifications:
* Reticle Type: Mil-Dot 
* Illuminated Type: Red and Green with 5 level brightness adjustment 
* Magnification: 2-6 x 32mm
* Material: Aircraft-Grade Aluminum Alloy 
* Field Of View(@100yds/@100mm): 15.71-41.96
* Eye Relief(mm): 75.0-95.0 
* Exit Pupil(mm): 4.6-14.0
* Length: 210mm 
* Battery: CR 2032 x 1 (Not Included)
I'll include a link to it just in case anyone is curious, but of course it will expire at some point.
Scope




Tuesday, 8 May 2018

Tidying Up

I spent the morning sorting through the Yew which I got back in January 2017 . I got it all down and trimmed it on the bandsaw, created a whole lot of scrap and ended up with a few decent staves and some marginal ones and possible billets. I put 'em back up on the shelves, most of 'em are spoken for already and one that is otherwise lovely one has a huge sideways bend.
I've been repairing and making some more flight arrows with a bit of weight and stiffness variation. The differences are relatively small, but maybe a little extra weight stiffness and a more forward balance point will fly better in a  head wind... anyhow time will tell.
Pic shows my 28" flight arrows with a regular filed shooting arrow for comparison. (The one at the bottom is being fletched)
It's good to try and re-use ones with broken tips as they are a bit of a fiddle to make.

I haven't had the bottle to test the crossbow through the chrono yet.

Friday, 4 May 2018

Warbow & Crossbow

I've been working once a week mentoring my mate JT while he produces a warbow from a stave of Austrian Yew. He has 2 staves so, as is my wont we worked the worst one first, it had some sideways bend, one big knot and was a tad thin at the grip.
It's progressed nicely and is managing to pull 100# at about 24" . It needs the outers to come round now, but that will happen automatically to some extent when the nocks are fitted and blended in. Video here:-
Mean while the crossbow prod is ready for test... I'll update this post later.... fingers crossed.

The pic shows the string catchers / string bridges, they serve several purposes.
1. The stop the string riding over the top of the prod at the end of the power stroke. This can easily happen with a low brace height, string vibration and stretch.
2. They are made of horn mounted on sheet rubber which will hopefully kill some of the vibration and shock as the string hits home.
3. It improves the force draw curve, increasing early poundage as the bow is effectively shorter until the string lifts off the bridge. Another way of looking at this is that it is effectively allowing a longer string at the brace height. A longer string will pull back further (e.g. In the extreme limit a 30" string pulled back to double up on itself would be 15" long, but a 32" string would come back 16" ).
The Eagle eyed amongst you will notice the aluminium mounting plate has no hole for the bolt to travel through! That's just a blanking plate to allow it to be assembled and tested on the tiller. The actual plate that will be used is mounted on the stock and is an inconvenient angled shape so it can't be used for tiller testing.

The ends of the prod have been bound with carbon fibre/epoxy to prevent the string splitting down the end of the bow. The nocks have been double served, so hopefully it should be ok this time.

Whew, First test shot was good, the draw seemed pretty smooth and the shot didn't seem to clatter or rattle.
I put a load of wax on the track to show how far the string overshoots the brace position when actually shot.
Update:- I took some slo-mo video later to see how the string catchers work. It looks like they do a good job!
https://www.youtube.com/watch?v=LzVH8sQQkVo

... Just saw this little fellow in the garden... not a great pic as it was high up on the bush.

Thursday, 26 April 2018

Another Try at the Crossbow Prod


A while back I bought some nice Maple off Ebay and cut it on the bandsaw to form the core of the prod. Some heat bending got it roughly shaped for glue up on the former. This lay around in the workshop for a while then eventually I cut some Ipe belly laminations and put a bit of shape into them (each limb being a separate lamination). The bamboo was planed up in the usual manner.
Once I'd started the glue up I realised my clamps weren't quite big enough... bugger! Too late to trim down the plywood former to allow the clamps to fit (although I s'pose I could as the pot life of the glue is a couple of hours). Anyhow I pressed on with plenty of rubber strapping. The prod came off the form pretty well, a couple of tiny gaps in the glue line, but they are near the centre where there will be a block glued for the mounting arrangement.
Oh, dear it was too stiff! |When tried on the tiller the draw weight rocketed up towards 150# while the draw was still a bit short. I felt that if I drew further the weight would be too high and it would start to take a set (I was checking that by, putting it back on the former, and I could feel there was a slight change already)
What can I do? I'd narrowed the bow a tad already, I can't take wood off the back without weakening the fibres of the bamboo, and I don't want to take any off the rather thin Ipe belly strip...!

Hmm... I know I'll take it out of middle! What? Eh?
I ran it through the bandsaw cutting along through the centre of the Maple core removing a saw blade's width! This effectively gave me two thin prods, I lightly sanded the two sawn faces and glued them back together now minus the thickness of the saw cut!.
At first sight, this sounds bonkers, but it's actually quite clever. If the saw wanders a bit it doesn't matter because the two halves will still match virtually perfectly! Now the prod is glued back together it is now about 1.5mm thinner, not only that but losing an even amount along the limbs weakens the tips more than the centre which should improve the tiller as it was mostly bending in the middle (1mm removed from a 10mm section is a smaller proportion than 1mm removed from a 5mm section at the tip).

This was all carefully calculated beforehand by sticking a wet finger in the air and going for a fine narrow bandsaw blade. The proof of the pudding is trying it on the tiller and yes, it feels more supple and the weight is down to just over 100# rather than approaching 150# . These figures are at a sort of guess work draw length with a string that will just fit on without flexing the prod.

It looks good enough to proceed with further work.


Saturday, 21 April 2018

Whew What a Scorcher!

Blimey a week ago it was vest,shirt, cardigan, and woolly hat to venture outside. Now it's shorts and now't else.
A couple of hot days and the garden has burst into life so I've been pottering about, putting a new top on the patio table made from cheap decking, putting up a new parasol, dredging the pond and cleaning out the pump to get the waterfall going again.
Chap came over to collect the yew bow yesterday which meant I could go up to Cloth of Gold today and shoot round with my mate Mick the Blacksmith. We were joined by Brian which was just as well because I was smashing arrows at a prodigious rate (it is a bit stony) and he lent me 3 of his old ones.
It was great to shoot in a very relaxed informal manner, often just shooting from the red peg, which gave me practice at the longer shots that I rarely get to take. We didn't bother to score either.
On one very long shot, the Tiger, I used some arrows that had lost their points, that gave me a faster arrow and a flatter trajectory, of course the arrow bounced off the Tigers arse! Quite a noticeable difference going from about 400gn to 300gn whereas going from a 100gn point to a 70gn point makes virtually no difference. The arrows did flirt a little in the air, I shall have to see where the balance point is and see if I can learn anything from that for my flight arrows, mind, they have much smaller fletchings....
I'd been looking forward to trying the moving target, a bear on a zip wire. Mick and Brian kindly let me stay on the peg while they took turns working the rope to draw the bear back and then release it while the other shot. It took me about 9 shots but I eventually hit it. It's very interesting and almost impossible to analyse exactly what one does, it is very liberating not being able to hold and aim as such and IMO encourages an instinctive approach. I tended to draw swing and loose in a fairly smooth movement rather than waiting at full draw. What I found most interesting was that despite shooting poorly prior to the flying bear, the next target I hit nicely first arrow from both A and B pegs (the course is 18 targets with two sets of pegs, A & B for each). I feel I'd become more relaxed and in tune with the bow.

We finished off in the pub with a welcomed pint, ham sandwich and bowl of chips.

On the bow making front I've been running some Ipe through the bandsaw to make tapered laminations for the crossbow prod project and maybe a belly for a laminate flight ELB.

Cheerio! Too hot to do much more!

Tuesday, 10 April 2018

Yew ELB Close to Finished

I've done some more heat correction on the bow to make it overall straight. Although it still has the slight kink it looks much more symmetrical. The horn nocks are done too but not polished up.

I went to a med' soc' 3D shoot in Kent on Sunday, great fun but rather tiring. I shot round with some friends ( in a group of 4) and had a good natter with some of the other folk at lunch time whilst enjoying an excellent Chicken casserole. My shoulder was giving me some gyp, so I dropped down from Twister to my little Hazel bow after lunch. My shooting was the usual inconsistent mix of abysmal and brilliant.
Shot of the day for me was 20yards at a boar which was behind tow trees. From the red peg only about a 1 foot section of it was showing, centred on the kill. No one else had hit it first arrow. I stood and stared at the centre of the kill... and stared some more... then drew and loosed. Plum centre of the inner kill 24 !
The drive back was a bit of crawl with the Sunday traffic and Brands Hatch traffic, but a shower, roast dinner and a glass of beer soon restored my equilibrium.

I also picked up some handy exercise tips and a recommendation of a Thera-Bar flex bar which is apparently V good for curing tennis elbow. I've ordered one from the interweb and I'll report back on how I get on with it.

Thursday, 5 April 2018

Yew ELB WIP


I haven't actually made a bow for a while, been busy refurbing arrows for a 3D shoot on Sunday, tinkering with the lathe, making flight arrows etc.
I've a few bows on the book and thought I'd better get on with one of 'em. These days I find most of my staves are nice quality ones that people have sourced for themselves and have brought along to be made into bows. This arrangement suits me fine as long as I don't get a lorry turn up with a load of staves that someone expects me to turn into bows! I very much pick and choose what I do, mainly because I have my own projects to get on with too.

Anyhow, I was feeling a bit cocky and picked up the Yew stave (Pacific Yew?) and ran it through the bandsaw in short order. I cut it pretty close to my guestimated final size and at one point thought I'd maybe taken off too much. It's fine and has been quick and easy to get back to near final weight. Of course nothing is too easy when you have a rather perfectionist streak. The bow has a couple of deflex dips, the worst being in the lower limb gave it the appearance of an ugly hinge, so I got it jigged up, applied some heat and pulled some of it out. It's virtually impossible to actually completely straighten a dip if it is more like a kink or is concentrated over just an inch or two, but it can be smoothed out to give the limb an overall straight line with the odd undulation. In other words the tips and grip are pretty much in line, which is almost what I achieve. Mind, I may correct it a tad more and induce the merest hint of back set/reflex. We'll see.
I s'pose I should say what I'm aiming for 50-55# at 28" . The draw length will only be 26" but it's wise to take it back to 282 as this will be used for roving where it's easy to stretch for a little extra.
The guy I'm making it for is about my height or a whisker less (5'10") so I'm making it about 70" nock to nock, although it may loose an inch when I put the horn nocks on.
It's a nice clean stave which only had one knot which was on one edge and disappeared as I roughed out the bow. The few dips and undulations still give it some character.