Monday, 13 May 2019

Striving For Accurate Measurement

Tricky thing trying to measure accurately. I've patched the belly of the flight bow in the previous post and I'm working it back to 50# at 27" (that's 27" to the belly).
The actual repair patch was heat treated before gluing, you can see the length of the patch compared to the spall that broke off the belly in this pic.
I also took some video of it on the tiller.

I've just got it teased back and taken measurements at 24, 25 and 26". The first reading at 24 was just over 42# but I drew it again and it had settled a whisker.
24" 41.8#
25" 44.2#
26" 46.8#
This gives 2.6# for that last inch and that gives a total of 49.4# @ 27"... ah, but the weight of the scale is hanging on there too, so I weighed that, its an extra 0.37# which I'll round up to 0.4#
That would give a total of 48.8#@27 which is good.

I see some tillering set ups with the scale fixed at the top and the bow hanging down from that. It has one big advantage that if the bow breaks, the scale doesn't come smashing down on to the floor, but it has the disadvantage that the measure of draw length is trickier, as a spring type scale stretches as it is pulled down so the rule needs attaching to the bow string or the hook at the bottom of the scale. Also when measuring the draw weight, the physical weight of the bow is also hanging on there so that needs accounting for if you want an accurate weight. Mind that is all a bit academic except for something like flight shooting as quoted bow weights are often a good bit out once the bow has had a few hundred arrows through it.

Now I've got 3 flight bows all at just under 50# @ 27" I can test 'em through the chrono' and decide which I intend to shoot.... bugger... just realised I'v got to make a string for this one first before I can chrono' it.
Better get on with it then!
Ha! Got the string made... tested it through the chrono... woo!
211.9 fps

Thursday, 9 May 2019

Final Tillering of Flight Bows

My two weights turned up at last, I took them in to the place I used to work and weighed them, they were 10.5 and 10.6 kg. On the way home I stopped at the local post office and checked the 10.5kg weight on their scales, it showed as 10.48kg which was pretty good conformation.
Using those weights to check my scales, showed the digital ones to be accurate and the spring/dial scale to be ok at 45# if zeroed to read 4lb.

I could do the final tillering. The mk3 which is the shortened mk2 was way overweight and despite taking the width down and tapering the riser section down more to give a longer working limb I was struggling to get the draw weight/draw length right. I resolved to use the 26" arrows rather than the 27".
I pulled it to 24" and recorded the weight, pulled to 25" and it went crack , the belly fractured.
It's an interesting failure with a section popping up and out a bit like a geological fault. When I broke off the piece I could see the black central pith of the log dipping from the belly deep into the wood, this was presumably a weak point that contributed to the failure, or at least dictated where it happened. I had assumed that the few pith marks on the belly had been just at the very surface, obviously I would have used better wood if I'd had it to hand.
The main point is that the bamboo back held the bow together. Whereas a failure on the back would result in the bow exploding into shrapnel, this is actually repairable! I could put in a patch or remove about 1/3 of the thickness of the belly and glue on a suitable slat of timber, but that can wait for now.
The bow was very highly stressed and was getting to the point where it was almost as thick as it was wide!

I had better luck with the Boo/Yew/Ipe flight bow (mk4) which is effectively finished now. It's difficult to get accurate poundage readings as when the bow is freshly strung it will read a pound or so heavier than when it's been strung for 15 minutes and exercised.
It's slightly disappointing that the bow had taken a little set, but then it shows it is working hard, and I always say, would you rather have a little set or a smashed bow?

I was anxious about having the bows weighed at the flight shoot, but they explained that they don't take them to full draw, they weight at 1" and 2" less than full draw and use the difference between those as the increase in poundage for the final inch. An example:-
For the mk4:
25"  44.8 lb
26"  47.2 lb              difference between the 2 figures is 2.4lb.
Add the 2.4 lb to the 26" figure to give...calculated figure for 27" of 49.6 lb
Tested it through the chrono' with my test arrow (295 grains)  :-)

Monday, 6 May 2019

A long Wait

My weights still haven't turned up, and Monday is a bank holiday, so even if they do arrive I won't be able to get them accurately weighed until Tuesday... hmmm I'm bored... but not for long!
I put JTs knotty hugely reflexed Austrian yew stave back in the steam and got it much straighter. I filled the steamer to the max and left it to run dry and switch itself off so the stave probably had about an hour. I clamped it up in situ once the steam had been going for about 20mins and left it clamped up over night. It looked very good this morning and it will be interesting to see if the reflex creeps back again like it did last time.
Hmmm, at a loose end again, and then I remembered the crossbow project! That's been on hold for a couple of months now, so I dug out the laminations and epoxy and got the first limb glued up.
the epoxy is from Easy Composites and it will be interesting to see how it performs.
The epoxy has a 2 hour pot life and takes 20-30 hours to cure.
There's always something to tinker with.

Pic shows the knotty Yew stave and one of the troublesome knots... maybe it will never become a bow, but persevering is character forming!

Monday, 29 April 2019

Yew Bow Detail & a Glue Up

I got Jeff's Yew bow finished, the drying crack in the back looks rather horrifying, but other parts look lovely, it has some nice character. Unfortunately Jeff can't shoot it yet as he's getting over a accident and his wrist is still weak, but I shot a few arrow through it for him to see when it was collected.

I've been making the mk5 50# ELB flight bow too!
One reason I'm pressing on with yet another bow is that I can't quite finish the previous one as I can't determine which of my scale is correct. It would be easy to assume the digital one is right, but that's not necessarily so. What I've decided to do is to buy 2 x 10kg weights, I can then take these into the factory where I used to work and get them weighed on some trade approved scales to calibrate them. I'll mark them up and use them as my reference weights. The problem is they haven't arrived yet (inset your own joke about ordering a long weight here)
I had some scraps of Ipe about 30" long so I spliced in a 4" section using scarf joints to make a full length belly for a Boo, Yew, Ipe bow.
I like to use up odd and ends for experimentation. This bow is slightly shorter than the other Boo, Yew flight bows, I took rough limb thickness dimensions at mid limb from the other bows as a guide so that it would be somewhere near the right weight after glue up.
The pic shows it with half the clamps removed after an overnight curing time. Note, I used some rubber strapping as well where the nodes of the bamboo back were making it reluctant to clamp down.
Now it's glued up, I've added a 7" riser/grip piece glued to the belly overlapping the scarf jointed centre section to give a
very secure join.

Tuesday, 23 April 2019

English Yew Bow on the Tiller

This stave was cut by Jeff a tree surgeon who brought it up to me to be worked into a bow. He was in the workshop while we got it sawn from the log, and roughed out to the point where it was flexing on the tiller.
Since then I've taken some twist and sideways bend out with steam and got it coming back further.
Some of the sideways bend had come back and it needed another steam bath. There are some tricky areas and I've had to tease it back working down both the sapwood back and the belly. A big knot on one edge and a twisting undulation have been most problematic as they were rather stiff. It takes some blind faith to rasp down knotty or undulating areas.
Since taking these pictures, the tiller has been improved with the outers flexing more.

Video of it flexing here:-

Next day, got it to full draw now :-)

Sunday, 21 April 2019

Flight Bow Frustration

I got out in the glorious sunshine to test my 2 Boo/Yew flight bows head to head with the same arrows.
The first bow was slightly disappointing, but turns out that by applying all I've learned from the first bow and making minor changes for the second, I've made that one marginally more disappointing!

On the plus side, I didn't  break any arrows and the second bow, being a couple of inches longer can be cut down and reworked.

I had 6 arrows, 4 were pretty similar, about 280 grains with narrow footed tips, one was about 50 grains lighter and one a bit heavier (about 310 grains). The lighter one nearly always the shortest, and the heavier was also one of the shortest.
I shot all 6 from bow mk1, 6 from bow mk2. I then shot 4 from bow mk1 again to see if I'd settled to a better technique, but in fact the first ones were further.

Furthest arrow was a mere 268 yards.
Hey, ho, back to the drawing board, I may re-work the mk2 back to a 26" draw, as I have a set of 26" arrows.

Not much point in pics, I'll allow you to imaging the scene... an empty flat sunny field... some arrows sticking out in a desultory fashion... lone archer plodding disconsolately back and forth ;-)

A couple of the other guys did turn up as I was about to leave, so I had a bit of a natter.

I did have a bit of a mess around with the results by adding the distances achieved by each arrow to see if one performed significantly better, but with only 3 results for each arrow it doesn't mean much.
It did give the best arrows as the one which also had the single furthest distance. The shooting machine would help, but one doesn't want to perform too many tests and shoot out the bow. Mind, once the best bow is found, the second string bow could be used for arrow testing.
basic problem is too many variables.

Friday, 19 April 2019


Hmmm, the bandsaw started squeaking and I noticed that it was stopping very promptly when switched off.
Maybe the blade guides need adjusting or a sliver of wood is jammed in there.
Adjust and clean them.... squeeeeeeak.
Remove upper blade guides.....squeeeeak.
Adjust lower blade guides...... squeeeeak.
Remove blade. ..... squeeeeeak.
Remove the lower wheel, ah, the bearings are seized up.
Rinse 'em out with white spirit, WD40 and much waggling about... got 'em freed up.
Re-fit lower wheel, switch on........ squeeeeak!
Bloody idler wheel bearings (the idler tensions the belt) are similarly seized.
Clean them up.... that's fixed that.
Get online to Bearing Boys and order new bearings, yes I noted the numbers on the bearings before re-fitting everything. Bearing Boys are V good compared with getting the bearings from a bandsaw spares site, and they have several grades of bearing in any give size.
That was about mid day, the new bearings turned up about 11am next day!
Got 'em fitted and it's running much smoother now.
I don't begrudge the bandsaw a bit of minor expenditure and time as it has a pretty busy life.

Meanwhile I'm busy making millions of flight arrows.... well that's what it feels like as they are fairly labour intensive.
I've done some tweaking of the two boo/yew flight bows so that they'll both be shooting 27" arrows at 50#. I hope to do a direct comparison on Sunday if I've got some arrows done and we aren't off on a family jaunt 'cos it's Easter.

My mate JT was over too and he had a relatively new warbow that he felt was iffy and in need of a re-tiller, so we attacked that! Video here.