Wednesday, 22 November 2017

Prod Failure Mode

The experimental crossbow pod is too strong. To reduce weight, improve the tiller and increase draw I've been reducing the width, however it came to a point where the back was too stressed and it popped a splinter with a satisfying "crack!"
Of course the splinter started at a node and I can see that maybe I'd rasped down the node a bit too much. The fibres seem to flow up at the node and as I peeled back the splinter it ran up and out of the bamboo at the next node. This gave me the idea of stripping off the bamboo and re-backing the bow. It might be another iteration of the design before a completely new version. After all it would be good to see how far I can get it back at 120#

I've learned enough from this to make a better version, a tad longer, some built in deflex, a bit less core thickness, and a thicker Yew belly to allow removal of wood from the belly for tillering rather than making it too thin in the limbs.
the final test before it broke got it to a 10" draw (measured from the belly) at 120#  which would extrapolate to about 168# at 14" . Ideally I want 120# at 14" draw at 120#

Now I have a better idea of dimensions I can cut my various components for the prod closer to finished size.
To have the prod still in one piece is hand too as a pattern.
Update:- As I started planing off the bamboo it occurred to me that I could try it again. I'd rasped the limbs such that the back was narrower, and as I planed some off I found the back was returning to it's wider dimension. I sanded it up on the belt sander and gave it another go, getting it back to about 13" at 90# . All very promising, the outer fibres of the bamboo are the strongest, but maybe going down about 1mm still leaves decent material, and maybe the back and belly strength is better matched... mind it could all just mean it performs sluggishly.
Anyhow it's all good dimensional info for the mk2 . I'll clean it up further and try for the 14" draw!

Monday, 20 November 2017

My Project List

I've got lots of stuff on the go and I'm feeling invigorated. A sunny morning lobbing arrows can do that to you. Especially when you realise one of the fields had a decent length for flight shooting.
I'll write it as a list.
1. Yew longbow bow to make for a chap who bought a stave over a few weeks back.
2. Working on a "shoot through" crossbow prod:-
3. Heat treat and re-work an experimental Yew flight bow which was made from dodgy spliced billets which had weird bands of alternating heart and sap wood. It should be good for testing flight arrows.
4. Build a shooting machine for testing flight bows.
5. Build Yew flight bow from a good quality Yew stave, looking at about 90-100# @28" from a short stave. Hard working and fast... in theory.

I've got the prod to a 3" brace now, it needed winching back to 150# on a long string to get it braced! It's been pulled it to 110#, the tiller isn't right yet as it's working most in the centre. If I get the outers coming round I'll increase the draw length at that poundage.
I didn't want to pull it to 120# until I have improved the tiller.
I'm opening out and lengthening the slot between the limbs. There are effectively 4 limbs, so I'm trying to get each one nicely tapered.

Update:- Worked on it a bit as described above, it looks more elegant now, but still needs to work more in the outer limbs.
I've pulled it to 130# thie limbs look more even and it's coming back further. I need to get the string off (not easy!) and see if it's taking any set.
I've certainly learned enough to make a better version already.

On a different subject, I've noticed I seem to be a bit susceptible to dust these days having had two periods of an irritating dry chest cough this year. I can't definitively attribute it to Yew dust, but I'm wearing the face mask when sanding now. I don't bother when using edged tools, but I noticed that just doing a tiny bit of sanding on the crossbow prod kicks up a good deal of dust.
Allergies effect some people more than others and they can switch on or off for no apparent reason. It could just be dust in general and the bout earlier in the year could have been pollen related, but I'm trying to get into the habit of always using the dust extractor when using the bandsaw or belt sander, and using the mask if sanding (especially Yew).

Monday, 6 November 2017

Warbow Tiller Sequence

The bow is virtually finished, and following the comments from the previous post I'll discus it further.
I've added the final pic to the sequence and you can see how once it's braced there isn't much further to pull it back, and yet a little careful work evens up the tiller.
It's frustrating that one guy on a Facebook page got himself to this stage making a warbow, but couldn't seem to follow it through to the finish. I suspect he was taking poor advice that was easy rather than adopting a disciplined approach.
To get that sequence I took at least 7 videos and had it up and down on the tiller about twice that, it isn't quick or easy despite what some will try and tell you. Well, to be fair, maybe with the perfect stave you can get a reasonable tiller straight off doing it by numbers, but it will be at a
random draw weight.

Trying to see how much that reflexed left tip is moving is rather difficult so I taped a spill of bamboo to the limb just inboard of the knot to see how much it moves between brace and full draw.

The final pic shows the overall set, which is very little.

Sunday, 5 November 2017

Horn Nocks On and Improved Tiller

I've got the nocks on, slimmed the tips and improved the tiller it's now coming back a bit further (almost 27"). Not quite full brace yet. I'm starting to scrape out the tool marks and clean off the pinkish under bark where it hasn't popped off on it's own. Doing a little more fine tuning the tiller, get the tips (esp' the left) round a tad more and
It's taken a hint of set from the original stave so it's only slightly reflexed now, it's beginning to look very handsome now.

Saturday, 4 November 2017

Long String On the Tiller

I'm making a 110# warbow from Austrian Yew that I've had waiting for my attention for some months. It's a tricky stave with reflex at one tip and deflex half way along the other.
On one of the Facebook groups there has been someone having trouble tillering a warbow so I thought I'd take regular pictures (captured from video) to help show the progress.
I also wanted to test an observation from one of the hugely respected guys on Primitive Archer (Steve Gardner aka Badger), which is:-

If you have a "long string" that will just slip onto the bow and only dangle down 6" you can read off draw weight and length from that and it will closely tally to the draw weight and length when braced.

It's too easy to take everything one is told as fact, that would be fine if everyone was reliable, the problem is there are a lot of well meaning armchair experts out there. Of course Steve isn't in that category, but seeing is believing, so I did the test.

The top pic shows the stave with no force on it in the upper image, each subsequent image is at 110# on the string that dangles 6".
The final seperate image is with it at a 5" brace pulled to 110#.

It's an absolute pig to get the bow strung and I was having to winch it back to a full 110# on a very long string to give me room to get it braced, and that's where the confusion can lie as the very long string comes back a huge distance because it is dangling down a foot or so.

Right, so in the composite picture, the lowest image shows it at 110# at 24".
I braced it (slightly low about 5") and with some trepidation pulled it back gradually increasing the weight (video running of course)...
At 110# it came back just under 25" which is pretty damn close and very useful.

The moral of the story is:-
1. Make sure you long string only dangles 6"
2. We are all still learning!

There is a slight caveat here, when you have it braced, don't just heave it back to full weight if the tiller isn't good, as the bow will be flexing a bit more than it was on the long string. If you study the pics, you'll see the tips are coming back about an extra inch.
You'll also see that as it's coming back 15" I only have 5 more inches to get the tiller sorted!
That's the rub with a warbow, by the time it's braced you're almost there!
The final pic showing drawn and unstrung together helps to show how it's bending and where I need to take off a little wood. The deflex area middle of the right limb isn't bending enough and the entire right limb is a bits tiff.

Tuesday, 31 October 2017

Roughing Out Some Staves

Had a guy come over on Saturday with a log he'd cut about 4 years ago, I'd made him a bow previously (Ridgeback) and he wanted me to make another. From the pics he'd sent the log didn't look too promising, but once I'd trimmed off the end an had a shufti, I could see one clean face with a bow in it. There is still one iffy knot, but most of that will disappear (see pic)

After he'd gone I ran it through bandsaw and there were some troublesome areas where one growth ring had been damaged/rotted, maybe by fire, lightning, rubbing against another branch or just bad weather. Fortunately it was fairly near the centre and by the time I'd got the save roughed down the bad ring had been cut away.

The other two staves are Austrian Yew cut from a rough half log that was bought at a bargain price by one of my friends in expectation of one good stave and maybe a skinny second. Again there are some splits and shakes, but careful laying out has produced two warbow staves, they are a tad on the short side at 73 and 74" (bearing in mind I like to have a couple of inches spare on a stave), but the bloke isn't very tall and has a 30" draw so they should be ok. It's hard to tell which is actually the best stave so I'll probably work 'em down together and see which is 100-110# and which is good for a bit more.

The paler English Yew stave is prob' going to be about 60# but I've got to discus what's required.
It's good to have a few staves ready to work on, and I've actually got a spliced Yew one as well. I tend to think of this time of year as bow making season, as there's now't much going on in the garden. I'll be thinking of cutting a couple of Hazel staves too with my mate JT, who's going to try his hand at bow making early next year.... I'm sure some beer drinking will also be involved.

I went over to Cloth of Gold as a guest of Mick the Blacksmith on Sunday, had a great shoot around in good company, we weren't scoring and did 18 targets each from two different pegs, so I shot a good few arrows. My shooting seemed back to normal and I made a few decent long shots too. Probably my last outing of the year as it's getting colder, although I might manage the ILAA at Windsor if the weather's good.

Friday, 20 October 2017

Oh Bugger!

It's times like this you wish you hadn't left a tap dripping all yesterday morning!
 I had to spend a good deal of time mopping up the garage floor, fortunately most of the boxes on the floor are plastic rather than cardboard these days. A dustpan and brush got up a good deal of the water, and I have plenty of sawdust to help soak it up.

Next irritation was my bandsaw blade breaking, now this was a 1/4" 4tpi blade with extra set which my mate Stuart had bought as a thanks for the bandsaw usage and stuff. It's a blade configuration I hadn't used and it turned out to be very good, cutting nice and straight. I'd imagined that a wide blade would cut straighter but I found the narrower blade better, also good for following curves. (my other blades are 1/2").
The blade is still pretty new and V sharp so I was reluctant to bin it.

There are plenty of Youtube videos on brazing broken blades. This blade had broken on the weld, but I don't think it was a manufacturing defect, more likely due to me cutting odd shape 1/4 logs freehand.
I had an off-cut of Dexion which made a handy guide to clamp the blade to. I just sawed two slots and bent a section out of the way, cleaned up the sharp corners with a file and the jig was ready... only problem was finding the flux and brazing rod. I really must make another draw for welding and brazing supplies.
The ends of the blade were chamfered on the belt sander, coated with flux and carefully clamped up on the jig.
I think the brazing rod I have is quite a high melting point as it didn't want top flow at first, but once the joint was really glowing bright yellow it suddenly flowed. A bit of careful filing and then I tried it on the bandsaw, it clicked a bit as it went through the guides so I put a small grind wheel in my electric drill and lightly ran it over the sides and back of the join. It now runs lovely and smooth, good job all round, taught me a new trick and I have the jig for next time.
Here's a pic of my G-clamp nest, a couple of old shelf brackets screwed to the wall and it keeps 'em all handy and tidy.