Crossbow Limb Delamination

I took the crossbow out on Sunday with my new bright yellow bolts with a view to finding at what range the fixed telescopic sight was sighted. That is to say I wanted to find the range at which the bolts hit where the cross hairs were lined up. Then I could find out how many graticule divisions allowance was needed for each 10 yard step up or down from that range.

Well it didn't go according to plan as when I cocked the bow I heard a slight noise. I took the shot and examined the bow. The foggy looking patch on the back of the left limb looked larger. I was pretty sure the patch was where the glass lamination was parting from the wooden core, this was confirmed when I cocked the bow again and heard more noise and could see a slight gap between glass and wood. I took the shot, which was pleasingly only about an inch from the first, this was V good considering the 30mph crosswind which made it very difficult to hold on target.
Once home I peeled off the glass and for the most part it was pulling wood fibres with it, so the glue was doing it's job. Why the glue line had failed at that one point is probably a combination of things.

I'd taken my usual meticulous care over the preparation and glue up. Maybe I'd clamped too hard, maybe there was contamination of one of the surfaces. Nothing obvious was visible when I examined the surfaces. I've just been into the garage again and before I put on the bench light I could see a slight dark patch on the wood where the delamination started, funny how sometimes poor light can show more than good light, it looked like a slight depression in the face of the limb and, sure enough when I put a rule across the limb and slid it back and forth it showed up a depression in that area which was presumably starved of glue. Not conclusive but certainly something to watch out for in future.

  The epoxy adhesive  EA-40 is a bit of a pain for several reasons, it is expensive and hard to obtain in small quantities, it also has a limited shelf life, it also is best cured in a hot box for maximum strength (but will cure at 20degrees C). This isn't a problem if making laminated glass faced bows is your thing, but for my occasional experiments it's not ideal. So with my usual sense of curiosity I've glued up a test piece from the delaminated glass and a scrap of maple using Cascamite/Resintite (my usual wood laminating glue). I cleaned the parts on the belt sander (coarse grit) and glued 'em up last night and when I looked at it this morning I was surprised to see the glue line showed clear through the glass (bottom pic) despite the glue looking opaque beige when either mixed or cured. (see pic above the lowest one ))
The test piece is currently on a radiator to make sure it's thoroughly cured before I do a destruction test later today....
Just tested it and it peeled apart easily, so that's no good. Mind even the epoxy peels apart with a firm pull, but of course in a bow limb it's not in a peel situation.
I've ordered some epoxy adhesive and some acetone from Easycomposites. It's in a 500g size which is handy and at a reasonable cost. The postage was a bit heavy, but not so bad when I lumped in the 500ml of acetone too. The info said it was good for things like laminating snowboards where some flexibility is needed, so it may be just the job for bows. I'll let you know how it turns out.
They do some interesting carbon fibre tube and rod too, if I wanted to make carbon fibre flight arrows, but for the moment I'll stick to my natural materials.

Staves & Splicing Jig Explained

I got the jig for doing 4 point splices made and working. It took a good deal of fiddling and fettling to get it right.

Also been making up some decent crossbow bolts with a view to trying the crossbow on Sunday, although it may well be too cold.

My mate JT has been over and we've been trying to lay out a warbow in a very iffy Austrian Yew stave. we are making some progress after a couple of sessions and a good deal of steam bending and untwisting... mind steam work is quite welcomed on a cold day. I've also sorted through some of my staves and found a nice pair of clean heartwood staves which may make Boo backed flight bows or warbows.

Explain More!
I'm assuming more detail is required on the footing jig, so here you go (extract from an article I've written for Field Archery News online magazine.
The Footing Jig :- I’d been intrigued by 4 point footed arrows for some time and some searching the web found some videos showing how it’s done with an expensive jig. “I can make one of those” I thought and promptly set to. Well, like a lot of things it’s easy in theory, but the devil is in the detail. I used a couple of offcuts of Ash plank and routed in two grooves to clamp the arrow at an angle which was guess work. The first mistake was I made two right handed pieces… I’m sure we’ve all made that mistake! I sorted that and clamped the two parts together with a bit of shaft in the groove to hold it aligned. This allowed me to drill holes for steel alignment pins and a bit of threaded rod for clamping. Once that was done I could square up the faces on the belt sander. For the first try, I guided the jig (with shaft clamped into it) along the table of my mill, with the router bit in the mill rotating at full speed above it and set to take a shallow cut (a pillar drill or router would do the job). I guided the jig against a length of suitable timber to keep it running true, but the router bit cut a rather flat bottomed groove and tended to tear, so I had to carefully grind its tip to a better point. The groove cut along the shaft at rather a steep angle which would give a very short splice so I had to make adjustments by sanding the bottom of the jig to change the angle, of course this gave a splice that was too long! Once it was cutting at a reasonable angle, I could cut the groove depth to just short of centre on the shaft. The shaft was then rotated 90 degrees and another groove cut… this is repeated twice more such that the end of the shaft looks like a cross, which gradually tapers out to nothing, this is the male part. The other half of the splice is much easier. I squared off a scrap of Yew on the bandsaw, and then cut two slots along it, so that looking at the end the slots formed a cross, the female part. The two parts push together nicely, the pics are of the first rough try out just to prove it works. When doing it seriously and gluing the parts one should clamp the female part at the base of the saw cuts to prevent splitting along the shaft. Overall it’s a lot of fiddling about

Boo Yew Test

My friend and test pilot JT gave the BooYew primitive a good work out. It was V windy and shooting a flight arrow down wind made 345yards.
We did some roving too. I noticed the bow looked very slightly weak in the lower limb, but I think some of that is JT 's grip bearing the weight of the heel of the hand (probably typical for warbow weight bows). That shift in where the weight is taken makes a very subtle difference but a little grip re shaping and maybe a tiny scrape off the upper limb will re balance it.
I won't do anything without carefully studying it on the tiller as camera angle and  other factors can sometimes fool the eye.
Video here:-
https://youtu.be/iRDmH-pV8qY




Pics show Twister (45# @ 28") alongside the BooYew (120@31").
The boo Yew at full draw, and, top left shot was me misjudging the tail wind on the final rove shot... Whoops!

Boo Yew Primitive Back to full Draw

The title says it all! It's not finished yet, but is shootable once I've made a string.
I may ease off the outer limbs a tad as they seem a bit stiff and take 1/2" off the tips when I fit horn nock overlays.
Clicking on the pic and holding a CD up to it, makes it look pretty much arc of a circle. I don't think the grip should be flexing much, but the hint of deflex prob' gives it that impression.

Note the scale doesn't line up with the chalk marks on the wall due to the bow having a V deep grip and the scale being moved up a tad to compensate.

Video Here:-
https://youtu.be/qAlCrIft36g

Boo Yew PV on the Tiller

The bow has a nice little hint of deflex reflex. Pic shows it when it was first unwrapped.
I glued on some Elm nocks so that I could get it on the tiller for a first try out. The thickness taper needs some work as the boo isn't a consistent thickness due to the nodes and the thickness taper on the Yew was only roughed on the band saw.
Anyway, the first try out looked pretty good. Youtube video here:- https://www.youtube.com/watch?v=ziP5fI5pDKk&t=13s

I've been working on getting the thickness taper somewhere near even at about 1.5mm every 6" along the limbs and then I'll have another look and maybe pull it a bit harder.
I only took it up to about 90# first time as I could see the outers weren't working.

Boo Yew Primitive Progress

I've glued on a riser block from a off cut of old Yew. The Boo is prepared and I've got the limbs to a reasonable thickness taper buy marking out and very very carefully trimming off the excess from the belly on the bandsaw with a fine cut blade (6 tpi) Using a squared block of timber as a guide to press the back against to ensure a cut parallel to the back.
I need to trim a slight taper to the stave and the boo to help it all line up for gluing, also I have to work out if and how I'm going to glue in any deflex or reflex. I don't have a long enough length of 2x2 to clamp it to for glue up, but I've remembered I have some very long bits of Aluminium extrusion left by the installers of our solar panels from a few years back ... I knew they would come in handy :-)

 I'll hopefully get it glued tonight so it will be cured by the morning, but I won't risk rushing it.
The thickness and taper is all just educated guesswork, hopefully it should be in the right ball park. I had a look at my hickory backed yew 80# @ 32" longbow as a rough guide, but it's a different style bow and the boo will be tougher than the hickory. It will be interesting to get it up on the tiller for the first time in a day or two.
you may notice in the pics, I've found a nice round plastic storage jar which is just right for my face mask. It's my new years resolution to use the mask more as I've had a niggly cough off and on for a while.

Update:-
Got the glue up done, bound with rubber strapping and clamped to give a hint of deflex/reflex.
I also added a thin sliver of Yew (about 4mm) to the back before the glue up just to add a gentler fade and a little extra depth at the grip.
looking forward to unwrapping it tomorrow!

Started on First Bow of 2019

I've been out in the garden burning the greenery from the Christmas wreath and decorations, along with some off cuts of yew. I'm informed it's a lucky thing to do, I put some dry eucalyptus leaves on to the blaze, they burn nicely and give a pleasant smell too. It just about wraps up the festive season, although we still have home made sausage rolls and mince pies in the freezer.

There's been a trend in some roving circles to shooting American Flatbows (what they call "longbows" in the USA), horse bows and other barebows, which are glass faced.
This allows some to use lower poundages and still enjoy the rove, shooting full distances. The bows are more durable (and cheaper) than the self Yew bows. Of course some of these bows out distance the self bows when it comes to the flight contest traditionally held at the end of the rove.

So... I thought maybe a heavy weight primitive of Bamboo backed Yew might give a nod to the trend whilst still being of natural materials, and might even give 'em a run for their money in the flight if matched to a decent flight arrow.

A scaled up version of Twister (45# @ 28") my "go-to" field bow is the basic premise, but at over 100# and about 31" draw.
I happen to have a couple of decent Yew heartwood billets from a log with dodgy sapwood. One is shorter than the other and They don't have any length to spare, consequently I've done a short Z  splice, only 2" long and about an inch wide. The short length should be fine as the Yew belly will be in compression and the bow will have a continuous Bamboo back and it will also have a small riser block glued on the belly. The overall effect will be a very solid join.
The short splice length does conserve maximum length of the two billets and gives me a stave of 76" which is fine. The width mid limb will be about 1 3/4" but the grip will only be about 1" (this has benefits in terms of a clean loose for flight shooting as the arrow will have to flex less to get round the grip
I may glue in a tiny bit of deflex at the grip and reflex at the outers, or leave it dead straight. I don't want to go bonkers and over stress it as it will be a long draw.

It's much easier to do a good accurate splice on billets for a laminated bow as the billets can be cut nice and flat and the two splices cut with the billets taped together.
BTW. The pic shows it dry assembled. I've since glued and clamped it so that it can cure overnight.

If you are not sure how this works, cut a couple of strips of card say 1" by 6". (Mark one face of each piece "back") Tape 'em together with back uppermost on both pieces. Mark out and cut a Z spice with scissors (cutting through both together). Undo the tape, fit 'em together with "back" showing uppermost on both pieces and they should fit together nicely.