Tuesday, 27 June 2017

One Shot Wonder

I got the bow mount all finished and tested the clamped up bow on the tiller, it was fine and drew to 16" inches with no problem, I briefly flashed it to 18 inches and felt confident that it would be fine,
I got the mount fitted to the stock and plucked up courage for a test shot, I used a bolt which is usually shot from my bow pistol, my heavier bolts are fletched with 2 flights, are larger diameter and wouldn't fit correctly.
The good news was that the trigger held fine and the safety catch worked. The shot seemed fast, but the bow string went over center and one limb smashed. I can't actually be certain how it failed, maybe the shock (or vibration) broke the limb which then allowed the string to go over the top, or maybe the string stretched enough to go up a tad and over centre. If I'd had string bridges or grooves on the belly to catch the string, or maybe buffers like most modern crossbows and compounds have it would have been ok.
The limb failed at the patch, which is predictable as the patch is ok in compression but has no strength in tension if the bow goes past it's unstrung state and flexes the wrong way.

It would be easy to think it's a major failure, but in fact much of the work hasn't been wasted. I still have the form for the bow and the bow mounting, I also now have good dimension for the prod and confidence that it will take the draw length.
Onwards and upwards... with hindsight I'd have fitted string buffers/catchers, but one has to take that test shot at some point and maybe I was just too impatient, although if I'd used a heavy bolt, I could have got lured into a false sense of security and simply had the failure later.
The big shame is that I didn't shoot it through the chrono'.
I may try and mend that limb just so I can do more tests.

Monday, 26 June 2017

Prod Mount

I've been away over the weekend in Lincoln, which is a beautiful city with a nice medieval feel.
I'm finishing off some flight arrow for my mate JT, but while the fletchings are gluing I've been doing more to the crossbow. Last week I made a block which I glued onto the bamboo back to provide a flat surface to clamp it all together when mounted. The block is made of Ash and to match up to the bamboo back it is curved in two planes (you can see in the pic), thist took a lot of fiddling around sawing it rough on the bandsaw and then touching it up repeatedly on the nose of the belt sander, finally a curved scraper smoothed out the irregularities. I had to get a reasonable fit to allow a decent glue line and to allow it to be clamped hard in the vice while the glue cured without splitting the wood or damaging the bow. Hopefully this will give enough strength to allow me to cut away a portion in the centre where the bolt (arrow) will fly through, this will let me mount the prod fairly high to avoid the string bearing down too much on the track.
The pics show the arrangement, note I haven't cut the front plate to accurate size yet, as it is sensible to get the holes correct first, then true up the plate, rather than trying to drill two holes perfectly aligned.
I made it out of aluminium this time mainly because it's easier to work, in fact the bandsaw managed to saw through it using an appropriate blade.

Tuesday, 20 June 2017

Prod Glued Up

I took a lot of time drawing the prod shape onto some ply to make the former, no point getting it wrong. I didn't want too much reflex to over strain the bow, but conversely I wanted a decent draw weight. the compromise was to make the form a bit longer giving an extra inch of reflex to each tip. It's no problem sawing an inch off if I don't need it.
I was a bit worried about pulling the Yew down into the former and damaging it, so I though I'd put in a gentle heat bend and also chamfer the end a whisker to help it pull down without snagging on the rough sawn surface of the ply, (I used the other half of the former for the heat bend).
Note, I covered the former and the face of the bamboo with masking tape, this proved to be well worth while as it still took a bit of tugging to pull it off the form once cured. I clamped it up in the centre and mid limb to hold it in position whilst I strapped it up with rubber strapping, it was then put into the summer house which I'd left closed all day and was nice and hot, that should ensure a really good and quick glue cure, but I still resisted the temptation to unstrap it last night.The bow feels very stiff and looks good, I'll get it cleaned up, put some nocks on and try it on the tiller before worrying about the bow mounting... mind I've been mulling that problem over all week.
Final pic shows the rubber strapping as I've started to unwrap it.

Update:-
I've got nocks on it and with a string that's just taut, taken it back to just over 80#
It's damn scary!


Saturday, 17 June 2017

Can't Keep a Good Man Down

Started on a 'Boo backed Yew prod, I was going to heat treat the Yew but there were a couple of nasty knots that I had to chisel out and fill. I chiselled right through and put in simple rectangular patches, the boo backing will help hold it together and they should be fine with simple square ends as they are in compression. I've spliced the two limbs together with a very short Z splice at a deflexed angle, I'll add the reflex at the glue up stage, I built up the splice area with some Ash before cutting the splices to beef up that area.
I've got the bamboo planed up, might get it glued up tomorrow, but maybe not as it Father's day and we'll be picnicking.
The two limbs were cut from the same billet and one has a bit of sapwood showing, but it will have mostly gone by the time it's ready for the boo back.


:-)

Thursday, 15 June 2017

Crossbow Progress

Hopefully I'll have it ready for some testing later today.
I struggled to get the prod strung to even a low brace last night, but managed to draw it a good way. The bow mounting seems secure, the string sat a few mm above the track, but I'll be able to adjust the bow mount to suit.
I've been working on mounting the trigger mechanism. A big gap is sawn into the stock and the side plates fitted to form a pocket for the mechanism. The stock is slightly wider than the mechanism, but I've milled the side plates to protrude into the hole and take up the slack... the pics show what I mean.
Bear in mind this is only a semi rough try out, it was going to be a really quick dirty try out of plywood, but I found the Ash plank, so it's okish standard. The side cheeks would be of something better than ply in a final version.
Note the method of milling the ply is ... VERY dangerous unless you take small cuts, have a strong grip and a lot of confidence/stupidity. Every man is his own safety officer. You have to make sure that when (not "if") it snatches, it will push your fingers away from the mill and not pull then into it. Not something to do if you are tired or hungry. It would be easy enough to construct a holding tool to do it safely if one was doing more than just a quick try out or milling harder wood (I knew the ply would cut off easily... I would be reluctant to try that with Ash!)

I've found the old bastard string clamps wich are needed to string my repro' medieval light sporting crossbow, I'll use them for stringing this one.

These pics are all with it just dry assembled and roughed out.

Update:- Afternoon, I got it braced using the bastard string and clamps, mighty scary, I feel I may have to take some draw weight off the prod.
The good news is that the trigger mechanism held the strain, mind that's not full draw power yet. I'll make up a suitable string (I'd used one off a very short bow which I'd wound through my string adjuster to give me the right length)
Further Update:-
Got it braced, not sure I've got the strength of bottle to cock it!

BUGGER! It smashed when I tried to cock it, but at least I have a try out stock and trigger mechanism for developing a Boo/Yew prod.
Prob didn't help that it was over 40 years old!
Hopefully it will allow me to design a better bow mounting as I can see where the delamination has propagated from the mounting hole.






Tuesday, 13 June 2017

Trigger Mechanism

Blimey what a lot of fiddling and fettling! I've been at it off and on for about a week.
I forged a small spring to hold the tumbler down after it has been shot to stop it bouncing back. It took a couple of tries and snapped once, all good fun though.
There are 3 springs in total, one to operate the safety catch peg which also acts as a trigger return spring, one small leaf spring (from a bit of clock spring) to operate the little detent pin which gives a nice click to the safety catch and the forged spring to stop the tumbler bouncing back. I've kept the mechanism compact by having the 3 springs sort of overlapping each other. The safety catch is in the centre with the ident spring one side of it and the non return spring running along the other side.
It was built with very little actual measurement, basically it all starts with the nut and trigger made of plywood first.
I'll let the pics speak for themselves.

The pic of the spring shows the one that broke, however I softened it and re-shaped it. This time I heated it red hot and let it cool slowly, it was springy enough, but could be bent, so I didn't bother hardening and tempering a slightly soft spring is going to be more reliable than one which might snap. It was made from a length of silver steel.



Monday, 12 June 2017

A Brief Post

Enjoyed a 3D shoot at Avalon today 4 of us in the group (Scott, James, Mark and myself), some old friends, 2 longbows, a recurve (bare bow) and my primitive, I was last in the group but still hit some good shots (scored 472 over 40 targets). The weather was fine, and it was pleasantly cool in the woods, there was plenty of walking up and down and a series of testing downhill shots from awkward stances I blanked a couple but got a 3 nice first arrow long shots. On one of them, we'd watched two people shooting compound take two shots each to hit the target. Then we shot and three of us got it first arrow and the other got it second!
The styles of shoothing were very varied, James had a nice lean into it stance, full draw medieval look (drawing 60#). Scott's draw was shorter with a more target style, Mark sort of came down on the shot with barely a pause. My style is of course perfect ;-) and my scoring being worst was purely due to random external factors (a list of excuse is available on application).
My fave shot was a long slightly down hill on a tiger, last shot before a much needed lunch break... we'd had to wait for the compounds to finish in front of us. James said, you don't need all that fiddling, just step up and shoot (there may have been a few expletives too), he missed, but got it second arrow. I said, in a mock swaggering West Indian accent... (that's in a spirit of admiration rather than racism... think Usain Bolt) "Dis is how d' man does it honey" and promptly smacked it in first arrow.

One unnerving occurrence was when an arrow exploded when I loosed, it broke in two main halves plus a big splinter, the bits all went about three or four yards, so it must have started to move and flex a fair bit before exploding. It must have had some unseen damage, of course they always say you should flex each arrow and inspect it before use, but how many of us actually do?
Thanks to all at Avalon for an excellent course, organisation and catering.

On the way home I stopped for petrol and bought a pint of milk which I drank straight down whilst standing watching a kestrel which was hovering in the breeze above some long grass.