Tuesday, 11 December 2018

Correcting Bad Tiller

I was tempted to call this post "A Tillering Tutorial", but thought that sounded pretentious. The point of it is to show that we all have problems and that a methodical approach will get it sorted.

Target weight/draw length 40# at 28"
The bow is made of spliced billets which can sometimes give a slight miss match to the way the limbs behave if the wood is from two different staves.
To cut to the chase, I've got it at a low brace and pulling to 40# at about 19" or so. Always pull to full draw weight as long as the tiller looks ok.... errr.
I got a shock, the tiller looks hideous, but let's not panic, let's look at it dispassionately as there are several things going on, all of which all work together to make it look awful.
1. There is a slight downward bend in the lower (left) limb just left of the grip.
2. There is a slightly weak point in the left limb at the bend mentioned above.
3. The right limb is stiff.
4. I had it sitting on the tiller slightly too far to the right and was pulling the string a little too far off centre.

I check the simple things first, I re-position it on the tiller and even try it round the other way. It still looks bad. I also unstring it and look at how much of that bend is in the stave (probably a couple of inches).
First fix, I use heat  to remove that bend (15 minutes with a hot air gun and the bow strapped up).
Ah, it looks great unstrung, but still ugly as sin on the tiller.

I take some off the right limb with a rasp, but it doesn't make any difference... it just doesn't seem to want to bend any more. It does have some stiff areas where there are knots, but I want to get some method into the panic.

I compare the thickness of the right and left limbs where that bend is (about 6" from the centre line) using my verniers as a go/no go gauge rather than an actual measurement.
Ah, the stiff right limb is indeed thicker! (despite looking generally thicker, maybe it's just colour variation or heartwood/sapwood difference)
I rasp that area of the right limb until the verniers will just slip over it.
That gives some sort of reference point at the start of the limb. From there I can slide the verniers along the limb, and of course it should become loose as the limb gets thinner. It soon jams on a thick part where there is a knot. Now conventional wisdom tells you to leave some extra at a knot, but how much? I know I have plenty of draw weight still to play with, so if I rasp it down until the verniers only just fit over it, that will still be a little thicker than it should be, (because the limb should have tapered a bit by then). I then check just beyond the knot and the verniers rattle loosely at that point, so I adjust them to be snug and slide them along the limb some more.

I do this along the limb to check that the knots aren't too thick and that there is a gradual taper all along. By the time I've finished I've taken off a good deal of wood with the rasp. I've also taken care to look at the limb from both sides as it's easy to work at an angle giving an uneven thickness across the limb. Having taken some off the belly, the corners where sides meet belly are now a bit sharp, so I rasp these corners off.
Back on the tiller ... groan... the right limb is still stiff... will it never bend. I take the bow in my hand and draw it rapidly back and forth about 20 times, and then decide to try it the other way round with the stiff right (upper) limb as the lower instead.
I re-measure the centre of the bow, mark the new arrow pass 1" above the centre line and put it up on the tiller.
Much better...
Quit while I'm ahead, and decide that writing this up will be a useful post for everyone getting frustrated with limbs that won't bend!

Now I've taken more pics and you can see the improvement.
The main point is that in correcting the tiller the draw has now increased from about 20" to 24", the tiller isn't perfect yet, but it's well on it's way to decent tiller and 28" draw.
Hopefully this shows why you need to get the tiller sorted early.
It's ready for horn nocks now, which will involve tapering the outer limbs too and should get them coming round more.
Youtube video here:-
https://youtu.be/kWaO9K4yko8

I see someone has ticked the "explain more" box. I don't really know what specifically explain. Maybe it's the FAQ about why I have the bow tilting to the right and why reversing the bow on the tiller can make a difference?
To explain briefly, the bow is held at some point roughly in the middle, but the arrow sits above that and the string is pulled in line with the arrow. So the whole thing isn't symmetrical! This doesn't make too much difference on a long bow, but can be very significant on a short bow. If you clamp a bow dead centre, pull the string from dead centre and tiller it like that, when it is held in the hand and shot, the tiller will look slightly off.

Saturday, 8 December 2018

Visitor Bearing Yew

I met a new friend on line who's getting into making bows, he'd been reading the blog and I'd offered some advice on tillering. He'd also offered some Yew, but being an old and lazy git I didn't really feel up to the 90+ minute drive each way and heaving yew around (in my defence there were some home issues too at the time)
Anyhow he volunteered to bring the Yew over and spend some time in the garage, seeing what I get up to.
We had a great time, shot the Chinese repeater and my little crossbow, but most of the time was spent re-tillering a Warbow that he'd bought. It raised some interesting questions about tillering.
The bow was of about 130# and had apparently been tillered to 33" .
There's no way I'm going to heave an unknown bow back to 33" on the tiller, so, what draw weight and length did he actually want? About 100# at 32" was the target.
The dilemma is, do we pull it to 32" and see what it is now for comparison or just pull to 100# and see where we are starting from? Well boys and girls, can you guess which I went for?
Yes, pull to 100# 'cos that's the target weight. Well we didn't even pull it that far straight away as we watched it flex and critiqued the tiller... Which is the stiffer limb? Where is it bending most? Can you see/feel any thick spots?
Anyhow it was 100# at 27" which we could interpolate to the draw weight at 32".
Divide 100# by 27" to give pounds per inch and then multiply that by 32 which gives 118.5 or near as dammit 120# .
This isn't exact but it's gives me a good idea of how much wood I'll be taking off ... (reaches for big rasp)

After reducing the thick spots first, working the belly down and tidying the tips and nocks, it eventually ended up at about 100# @ 30" which was deemed to be close enough, allowing for some subsequent sanding (I'd just finished it with a cabinet scraper), shooting in, etc.
I think seeing how I work and think was quite enlightening, as of course I didn't do all the work at once, it was up and down on the tiller umpteen times. I also did a quick demo of how to put a burr on a cabinet scraper. On the other hand I was, rather rushing and the bow was clattering around with one end resting on my vice with a strip of carpet on it. Normally I'd have clamped it and taken a little more care, working in shorter burst, but we were on a fairly tight time scale. It can get a bit busy trying to show all the processes in a four hour burst (tea and toast breaks of course!)
Once he'd gone I sneaked upstairs for a cat nap, and was out like a light.
Next day (yesterday) I ran the Yew through the bandsaw, wrote the date on it and painted the ends with PVA. The first tidy up through the bandsaw is basically taking the corners off. A half log is semicircle so that gets reduced to more of a D and a Quarter log is pretty much triangular, so the corners are taken off. Anything heavy is reduced in stages, one log was big knots along one side with only a relatively narrow clear strip and I had to take most of the knotty side off first to provide a flat face that would run flat on the bandsaw table for the next cut. I have the far end of the log supported on a roller, but even so it's about at the limit of what I can manage single handed.
The first pics shows the load of Yew with just one piece having been tidied up through the bandsaw.
The final pic shows the 4 good staves (one is barely visible against the garage floor) and a log which didn't really have anything suitable in it, (it may have had a single billet, but you really want billets as pairs, its on the habitat pile in the garden now for the bugs and beetles to enjoy).
The biggest stave may make two bows, but it's best left for now as the position of various knots may mean it's better to have one good warbow stave than two skinny marginal staves. It's the old adage "when in doubt leave it"

Wednesday, 5 December 2018

Visitors and a Good Chat

My old friend Roy from Med' Soc' came over for the Plumb which now has a handsome black leather grip, he brought a friend David along who was interested in having a Yew ELB made.
He was also very interested in flight arrows so we had a good chat and I showed him some of my slo-mo footage of flight arrows being shot from the shooting machine. David was taking about the concept of "centre of effort" which is from sailing, it turned out we mostly agreed with each other but the semantics of describing our thoughts got in the way somewhat!
He'd tested some arrows by dropping them horizontally from a high window and wanted them ideally to fall whilst remaining horizontal or turn  slightly nose down (He can correct me if I'm wrong). I said that my corresponding test was to lob 'em up in the air underarm and I wanted them to arc over at the top of their travel and to fall nose down.
It's an interesting topic as, once the arrow leaves the bow it is falling under the influence of the acceleration due to gravity, BUT if it is shot up at 45 degrees, that angled velocity is superimposed on the fall, and until the downward velocity has increased sufficiently to overcome the upward component it still goes up.
So, is it falling relative to the air or not... or is it just falling on the way down? Do you want it to present as much resistance to downward motion as possible to slow its fall (e.g falling whilst horizontal) whilst having as little resistance as possible to forward travel? Or do you always want it lined up with the direction of travel (feel free to comment... I like comments, it shows me that people read this!).
Much of this has been addressed empirically by Clarence N Hickman using his shooting machine in the early 1900s.
I'm not going to be drawn into venturing an opinion, I'll only say that my flight arrows have their point of balance just forward of the geometric centre by about 3 or 4 % and that I've seen arrows with the balance point too far back fly most erratically turning and diving at right angles!
I use the balance point (centre of gravity) and the geometric centre as these are both easily measured.
Enough of that!
(We also had a go with the Chinese repeating crossbow of course).

Having discussed making a bow it motivated me to sort through some billets one pair looked suitable, a much fatter pair that I will also splice up had some of the dreaded blue grey discolouration (even the good pair had a little). As the billets are cleaned and reduced in dimension the wood looked better, so hopefully any bad stuff is only on the surface. It won't matter too much for a 40 pounder, but for a warbow a clean sound back is critical.
I got the billets for the 40# spliced up and have been working it down to stave that flexes. Mind, it's so long since I made a 40# ELB it's still about warbow weight! Not quite ready for the tiller yet.
Note on the pic of the billets prepared for splicing, they need a nice clean flat surface so that the sit nicely on the bandsaw to give decent straight cuts, also clean flat faces are easier to mark out.

On an unrelated topic... a story was told to me (I try not to report stuff second hand , but this has a purpose).
Someone said that they'd had no joy patching damaged bows, and they'd tried long patches but even those failed.  The other person replied that they'd seen me do it a couple of times and that I spend a lot of time getting a perfect fit, holding it up to the light and repeatedly checking until its a good fit.
The response was words to the effect of "I haven't got time to mess about doing all that!"
What??? How can you have the time to repeatedly do something badly and have it fail, but don't have the time and patience to try doing it right? Bonkers!


Tuesday, 27 November 2018

Awaiting Inspiration

Now't is really grabbing my attention at the mo'.
I'll do a leather grip for the Plum bow and maybe sort through my staves.
I did a little repair for an old friend this afternoon, the bow wasn't one I'd made. It was a Hickory backed Osage ELB, the repair was just a fine linen thread binding over a splinter and it didn't take long. It was good to see him and have a natter tho'.
I've got some more glass coming for crossbow limbs which I may jump onto as I also have some Maple for the core.
I did some testing of the crossbow with the rigid 'scope mount. It shot nicely with the wooden bolt at 20 yards with only about one and a half dots movement on the graticule compared with 10 yards.
I then tried the Ali' bolts and despite being 7 grains heavier they shot about 4" higher! The difference is they are slightly smaller diameter, shorter and have smaller plastic fletchings so ar more aerodynamic. The lesson is that to do any meaningful sighting up one needs well matched bolts (Yeah... I know that's obvious!)
For me the BIG disadvantage of the Ali bolts is that I can't see where they are on the target until I walk up to about 10 yards. So...
I searched the internet and found some Chinese carbon arrows that are bright yellow and 30" long so I'll get 2 bolts from each.
Six of 'em for about £11 which is cheap enough to have a play with.

It's pouring with rain here so I may end up clicking "buy" some more or writing things on my Christmas list.

Sunday, 18 November 2018

Plum Bow Finished.

I got the bow finished, but it didn't seem to group well, a bit of investigation showed my hand was slipping up the grip giving an inconsistent position and effectively making the arrow sit nose up on the string. The grip needed some tweaking, this was mainly due to the upper limb having been shortened and the position of the grip notionally moved down by about and inch.
It didn't need much adjustment and it isn't a heavily sculpted grip, it's just shaped enough so the hand sits in a comfortable consistent position. The other factor is that I haven't shot for ages, so with a bit of tweaking and a few arrows every day, it's now shooting where I point it.







Monday, 12 November 2018

Plum?

After the Elder bow blew I was at a bit of a loose end and in need of a success... but something easy just didn't really appeal. I could have made a hickory and Lemonwood ELB, but then, where's the challenge in that?

So I rummaged through my staves and came across a piece of dark wood with "Cherry/Plum? 2009" written on the end. I'd often looked at this and couldn't decide quite what it was and how to deal with it, so I just ran it through the bandsaw to rough it out and go with the flow. Some comparison with some known Cherry leads me to think it's plum which is supposed to be a good bow wood. I didn't want to go mad and push it too hard so I'm going for my primitive shape at about 40-45# .
The stave has a few small knots, a crack running down the belly of one limb, a sideways kink in the other and a deal of sideways bend in the middle, there's a little deflex in an ugly place too. Other than that it's plain sailing!
I used the hot air gun to do a sideways bend at the grip. I allowed a little too much bend, expecting some spring back which didn't happen, however heating it again let it relax back to where I wanted it. The little ugly deflex was similarly taken out with heat, taking care to keep the heat off the back.

I followed a ring on the back, or at least along the centre of the back, this will get tidied further as the bow progresses. I found that I'd gone a tad tight with the bandsaw and that after following the ring I had a weak point on the upper limb about a foot down from the tip. I marked that area W for "weak" and worked the rest of the bow to match, being careful not to over-stress it on the tiller. After a good deal of work it was still a little weak so I sawed an inch off the tip, this moves the weak area nearer to the tip where the bow will be thinner anyway. Down near the fade on that limb I removed some wood to effectively move the whole limb down towards the grip... that still wasn't quite enough to remove the weak point so I took off another inch and also heat treated the weak area.
That did the trick and actually gives equal length working limbs rather than the more usual slightly shorter lower limb.
All this work didn't happen sequentially, it was a bit of work on the back, a bit of heat work, checking on the tiller and reducing the length etc all slowly moving it along.
The grip is V skinny and not very thick, so I glued on an off-cut of the same wood with the grain running the same way hoping for an almost invisible glue line. I could have used contrasting wood but I don't think it would look so primitive.

It's almost finished now and I think it will be rather handsome (assuming it doesn't go bang on the last inch of draw!)


Sunday, 28 October 2018

Good Day, Bad Day

I got going on the Elder bow and made some good progress, videoing it as it progressed until ...
Well watch this:-
https://youtu.be/UlRuJkeD_5U


I decide to extract maximum fun from the broken bow by doing a destruction test on the other limb!
https://youtu.be/ua0Iwe-AP2U