Thursday, 12 December 2019

Updatey Update Post

JT came round and he did a good deal of work on the bow under my watchful eye. There was the usual panic as the spoke shave or plane dug in and started to tear, but careful use and resorting to the rasp kept things under control.
The bow progressed nicely to about 100# at 20" at a modest brace which is pretty much the amount of work I'd hoped for.
The oddest occurrence was the magic aluminium string adjusting ring breaking whilst try to brace it for the first time! I wouldn't have believed it, had I not witnessed it myself.
Update:- I got an E-mail from my mate Mick the Blacksmith, he said :-
The break is a typical stress fracture and probably started from a small crack sometime ago.
In industry when they test the tensile strength of something by pulling it apart, the fracture is the same as you have on your string thingy.

We took some good video at three stages of the progress.

Previous day my mate Rob came over with some stuff to do. He had a half log of Wych Elm which we ran through the bandsaw laid out as a primitive. The stave has a huge amount of reflex so I though a wide flat design would have less stress than a longbow. He also had a warbow that had over 4" of set... it was pretty obvious why... the bow was over 1mm thinner at the arrow pass than it was for about a foot either side of it! It was obvious to see and to feel, dunno how someone can make a bow like that (he'd paid good money for it). He felt it was no good, so it was worth risking drastic action.
We got the bow strapped down mid limb on one limb (back down). We'd protected the back with multiple layers of masking tape and lightly clamped side cheeks to the bow to keep the heat on the belly. About 5 mins with the hot air gun and we pulled the bow down straight, strapped it down and heat treated the belly over the thin area. After lunch, we had a look and found a series of short transverse cracks had opened up. I recon these were fine chrysals that weren't obvious before, but opened up as the bow was heated and straightened. What to do? Well we rasped out that area of the belly and glued on a patch of heat treat Yew which will allow the bow to be re-tillered with the grip at the correct thickness. Rob left with patch all strapped up (it takes overnight for the glue to cure).
While he was over here we glued some horn tip overlays onto a Yew kids bow he's made for his son.
Heard back from Rob, he's re-shaped the belly where the patch is, and done a bit of scraping here and there to take off some thick areas. The set is now just 3/4" and the draw weight is up from 112# to about 150# ! The tiller looks much better now. Result!

Tuesday, 10 December 2019

Quick Update Post

The Boo/Yew that I've been helping my mate JT to make is ready for some serious work on Thursday, hopefully getting it to low brace and drawing to 20" or more inches... maybe even 26"-28".
Last week JT posted some progress on Facebook (as he does after most our "blokes in a shed" Thursday sessions) but was beset by smart arse comments from people who should know better, bearing in mind they know I'm helping/supervising (and I'm not an idiot). One comment was to the effect that interpolating draw weight from a partly finished bow is pointless and he'd be lucky to get 50# from it. Well to answer the first point, it has been shown to be both reasonably accurate and useful. E.G the bow in it's current state interpolates to about 200# @ 32", well this shows we have plenty of wood and no need to worry about making the target 120-130# draw weight.
If you want more info' read this post:-
The second point? Well time will tell, but I'd be willing to wager £50 that it will end up between 120# and 130# at the target draw length of 31" (all proceeds to charity, if anyone fancies taking the bet!)
There's an unwritten rule that people would do well to abide by... don't offer critique unless asked, and if you really must, at least make sure you are fully aware of all the details. I also try to go by the mantra of "If you can't say something good, don't say anything at all, unless invited".

Anyhow prior to the next instalment which will hopefully be on Thursday, here's the video we took last week, which shows it flexing quite nicely at a very useful draw weight of about will be pulled harder once a little more has been done to adjust the width, fill a small knot and round off some edges.
I could have posted this on the Facebook thread, but it wasn't my thread and I didn't want to get sucked into it.

Bonus update from yesterday (11/12/19). The bow testing rig had it's first real test on a 125# bow:-

Sunday, 1 December 2019

More Belt Sander Fettling

For a while now both the belt sander and the lathe have needed a flick to get them started. I suspected the run capacitor in both cases. Both are small AC induction motors that only have a single capacitor (bigger motors have a separate big start capacitor and a run capacitor). It's difficult to test a capacitor without a specialist meter, some convoluted and cunning measurement* or testing by substitution (or similar) on a live machine.
I happened to have a spare 6uF capacitor but was reluctant to try wiring it in or dabbing it across the terminals and switching on. The lathe motor had been getting increasingly noisy and I'd replaced the bearings recently so I wanted to fix it.
The lathe capacitor is 8uF and I thought if I put the 6uF across that in parallel it would give me an indication if the old one was shagged. I held the cap' in place with one hand with the two wires touching the appropriate terminals (not easy) and switched the lathe on with the other hand... It purred into life, great! That proved that the capacitor was the problem.

While I was on a roll I dismantled the belt sander to see what size cap' was in there so I could order a new one for that whilst I was at it. It was 6uF, ha! (old one is pictured). That's what my brand new spare was, I fitted that and it now starts without a flick. Whilst the belt sander was apart I noticed a lot of fibrous dust had collected in the bottom of the belt guard/case and it was covering the lower half of the motor pulley.
I thought a small hole in the bottom of the guard would be a good idea so that the dust would fall out or could be picked out. A couple of minutes with tin snips, hammer and file made a nice small hole which can't trap a British Standard Finger, but should do the job (indicated by yellow arrow in pic). Note, the underside of the sand belt doesn't have a guard... that's because it is a right pain to remove one when changing belts... (anyone who thinks that this is a hazard should consider that it's no more of a hazard than the top of the belt!)
I ordered a couple of capacitors from Ebay an 8uF and a 9uF just in case a bit of extra oomph was needed. It's not a simple case of more is better and the manufacturers recommended size (+/-10%) should be used. However capacitors are notoriously poor tolerance components so I thought going up to 9uF if necessary should be fine.

While I'm waiting for those to arrive I might add the old tired 6uF in parallel to the old tired 8uF and see how that runs.
I'm keen to get the lathe to start up when switched on, as it almost caused a fire last week!... The switch had been knocked to "on", the lathe cover was over it and the motor sat there stalled humming quietly... I'd noticed the hum and thought it was the central heating pump. It wasn't until my mate JT, who was there, said can you smell something? (Other than my usual farting) that I investigated further.
The motor was too hot to touch and the film of oil and dirt on it was smoking lightly! It was this incident that led to me dismantling the motor and replacing the bearings. Getting it starting correctly should avoid a repetition. Note:- The switch is easily knocked because it is positioned to be accessible for emergency switch off. Of course a fancy latching switch with big red button would do the trick and be less likely to get switched... but IMO the solution is to cure the fault rather than just add more complexity (and cost). If the lathe had actually switched on, it would have been obvious.

I've also been doing more to the bow weighing rig, adding some angle ali' at either end which will provide a way of clamping it to a table. It also adds some extra rigidity.

* For those who are interested I suppose you could measure its capacitance by charging it up to a known voltage and plot how it discharges through a known resistance over time using a digital voltmeter and work it out from there.

Friday, 29 November 2019

Yew Boo Glue Up

My mate JT has been over off and on over the last few weeks and we've been working down a marginal Yew stave, the sapwood was suspect so that came off and it's been gradually worked down as the belly for a boo backed warbow/roving/flight bow.
It's been tricky due to the limitations of the wood, knots, encroaching sapwood etc.
Don't quite know how it will perform or what it will be yet, as it's rather short. Mind it would have been 6" shorter if we hadn't cut out a big knot that ran at a shallow angle through one tip. We actually milled it out as a slot right through the limb on my mini mill (Clarke CMD10). I could have chiseled it out, but it was fun to try a different approach and there was less likelihood of splitting the wood as it was knotty. We fitted a plug about 3" long. The plug being slightly wedge shaped such that, once the Boo back was on it could't possibly pop out (see first pic)

The stave had a fair amount of deflex, and it was glued up on a former with about 1" of reflex. We got it glued up yesterday with clamps and rubber strapping in between for extra belt and braces squeezeosity.

Taking the clamps off this morning the stave sprang back up about 1/2" at the grip making it pretty much straight and putting some nice pre-tension into the Boo backing.
The stave still has some undulations and will have a bit more character than a laminate made up from machined timber. We could have spent more time getting it pre-tapered and even, but our sessions are limited for time and we couldn't resist the temptation of getting the glue up done.
It's that old balance between perfection and pragmatism. :-)

It will be interesting to see how it feels once cleaned up and tried on the tiller... that will have to wait until JT's next vist.

Final pic shows the bow testing rig having a tentative try out with my filed bow. The rig isn't fully finished yet, but it seems like it will work well.

Sunday, 24 November 2019

Bow Weighing Rig

I'm making this portable rig for someone to replace a somewhat heavy and agricultural one.
It gives me an excuse to turn some bits on the lathe and bash some metal.
I bought the crane scale off E-bay for about £19, I've made a nice curved piece to hook onto the bow string and modified the scale slightly, removing some of the bulky case to allow the hook to be fitted better.
I sawed off some of the excess case and used the offcuts to patch the resulting holes, which I then painted with some Humbrol enamel, which gave a remarkably good match.

The scale is rather nice inside, a shaped plate of aluminium has strain gauges mounted to it (these are covered with epoxy) they are wired to the circuit board which has a surface integrated circuit (amplifier) and another mounted directly on the board, potted in epoxy (display driver)? The push buttons are nice discrete switches with good feel (rather than unreliable membrane switches), they sit behind a thin membrane/label which keeps the muck out and protects the display.
It was worth taking it to pieces as I found the internal screws that hold one end of the plate to the case were loose and there was small split pin inside! (it's part of the kit of bits, shackle, hook etc that comes with the scale)
The spine of the rig will be a length of aluminium extrusion which was left over when we had solar panels fitted. The clamp to hold the bow is made of layers of ply, it slides in the extrusion and a simple loop of bungee cord with a nice leather tab holds the bow firmly in position against the larger fixed plywood block. The bungee hooks over a knob turned from lignum vitae (I bought a chunk of lignum off E-bay just for the fun of turning it).
 The winch is also made of plywood glued up and turned on the lathe, it pivots on a turned steel shaft and the handle is turned wood mounted on an aluminium crank. I pretty much copied the dimensions from the original, whilst improving the detail.
I've laid the parts roughly in position to show how it goes together. One nice feature is the measuring tape which slides nicely in a channel along the aluminium extrusion, this will be attached to the sliding block which presses against the back of the bow, thus giving draw length measured to the back.

I'll probably get the rig finished before picking up the next stave, which I expect will be a Pacific Yew Warbow for my mate Rob, not the same Rob who had the Yew primitive...

Thursday, 14 November 2019

Yew PV Finished

I've got the bow finished and taken some video of it being shot.
It's surprisingly difficult to get a good image from the video due to camera angle, lighting and the movement of the bow. In the still taken from video, the upper limb looks much fatter than the lower due to the change in contrast despite the green fabric hanging up to cut some of the back light from the sky.
It shoots very crisply with the arrows waggling a fair bit over the 10 yards, I may ease off the arrow pass a tad, mind the arrows are 35-40 spine and the bow is 50#

Video here:-

Wednesday, 6 November 2019

Multiple Projects

I seem to have swung from nothing much to 4 things on the go!
The Yew primitive needed steam bending to get rid of the side ways bend before it can go on the tiller. First session didn't seem to relax the wood much so I immediately refilled the steamer and have it more time. I pulled it beyond straight and over night it did recover to some extent but was still slightly over corrected. Another steaming allowed it relax back a tad and it looks good now.

While I was waiting for the steaming and allowing time for it to cool I did some roughing out of Rob's Pacific Yew stave, a very nice piece with lovely consistent thin sapwood which won't need any reducing. That will be ready for first try on the tiller soon.

Meanwhile my Pacific Yew stave arrived, not such a nice piece and a less experienced bowyer would have found it very challenging. There was a good deal of deflex and sideways bend, there were muscular ripples running diagonally across the back which told tales of internal stress. I allowed some extra width when doing the first rough out, and as I took a little off the side the thin slice curved itself down towards the belly which is rather unusual.
As I took some off the belly it revealed some nasty worrying black manky stuff where there had been damage as it grew. This will probably be a bow for me and at about 90# maximum so there is still enough good wood, I was a bit concerned that the manky stuff went deep and continued along the whole stave, but it seems ok. The wood was also a bit brittle in parts splitting off too easily for peace of mind. Anyone who had tried to lay a bow out and cut it in one go would have been in trouble... mind there is still plenty of time for me to screw up, but then I like a challenge.
The above is a good illustration of why the buyer needs to beware even when buying from a reputable source and having viewed a video of the stave... no one knows what lurks deep inside the wood.
I blame the fact that it was ordered on Halloween (cue spooky music).

I've also been doing some to the portable bow weighing rig, but I'll post pics of that when it's all finished.

Update:- First video of the Yew Primitive on the tiller here.