Elm Stave

[Richard B]

Got hold of an elm stave. Cut about 18 months ago and dried outside (I think). Moisture content reads about 18%. Nice straight stave with a slight reflex. I debarked it last week and found a couple of things:
1. Where the bark was missing  in the middle (rubbed off after felling?) the surface is stained and slightly scratched.
2. In a number of areas there were small holes through the bark (approx 1mm dia) and the bark was chewed away in a way that suggests infection by the sort of beetle larvae that can carry dutch elm disease. The larvae also chewed about 0.5mm into the outer ring of wood as can be seen in the last photo (the lighting exaggerates the depth).

What do people think? Should I remove the outer ring to get rid of the stained surface (which may have degraded?) and the beetle larvae marks?

[PEARL DRUMS]

Id clean t up by going down a few rings if you can. Im only guessing, but it looks as if it was standing dead when cut.

[TRACY]

Gonna have to chase a ring down to one that is unviolated by cuts and bugs and weather. Pretty straight and looks like a bow is hiding in there

Tracy

[ohma2]

Take it down below  damadge, shape it, take to floor tiller, and let it dry some more.

[Richard B]

Many thanks for the comments. Am scraping away chasing rings. I think that the wood is clean 2 rings in but I'll know when I get to the end.

[Richard B]

Have chased down 2 rings and found sound wood (may go down another ring as there is a little staining still left on one limb). For layout an thinking of a flat bow 69" NTN. 4" handle (centered on bow) with 2" long fades out to a 2" max width. One limb is pretty much knot free, but the other requires some thinking.
I have maintained a 2" width for 12" and then tapered down to 1/2" at the nocks. The photo shows my thoughts on how to work around the knots on the outer, tapered part, of the knotty limb. The middle line represents the string and passes through the center of the handle and the nocks at each end.
This will be my first attempt at a self bow, so would welcome any comments!

[blackhawk]

I'd prob go down another one or two rings until its all fresh white wood...your dimensions sounds fine...if the grain is straight you can draw a straight line for your center line and layout from each side from that..but you should be making your centerline along the top of the crown of the stave faithfully following the grain....it looks like your deviating some from your center line to avoid those knots...its hard for me to see the grain from those pics...but I'm sure the grain flows around those areas..and when laying out the lines on the sides from your centerline you need to follow those as well....now elm might be able to take that subtle violation you have,but when first attempting to build bows it is best to give yourself the best chance at success and follow the grain faithfully to the T...

[Richard B]

Getting close to floor tiller now. One of the knots that I avoided on the back of the bow is still present as a cluster of pin knots down the side and about 2mm into the belly (see photo below). Am concerned that this could act as a weak spot. Any advice?

[wizardgoat]

I'm a firm believer in the water think super glue from lee valley. I give a couple drops in all my knots and pins, and will hit it more when the belly gets worked down more. Just a little insurance

[PEARL DRUMS]

How wide is the blank at that spot?

[Richard B]

Have been slowly reducing the thickness of my stave to start it bending. I am now about 3mm over the thickness that I think will give the target weight (55lbs at 28"), however the varying amount of crown makes calculating section properties a bit tricky. The picture shows the bow tillered on a long string to about 60lbs. The ghosted image is the unstrung shape and the blue and red lines are the predicted tiller for the strung bow ans drawn bow respectively. These curves were developed using David Dewey's spreadsheets for the width profile of the bow and are the same curves that I used to tiller the miniature bow I made from the same stave (see other post).

The back of the bow undulates quite a bit (as does the belly- to give an even taper) so I have drawn a straight pencil line to help me see how the bow is bending. I think it is bending quite evenly, although I wont make the mistake of trying to match the predicted strung curve until I am on the short string (doing that on the miniature bow meant that I ended up removing too much material from the inner parts of the limbs, as the shape changed considerably with the short string).

I think I will remove 1mm along both limbs and see where that gets me. This is my fist go at tillering a full size bow so would be grateful for any advice/comments.

[DarkSoul]

You can paint by numbers, but you cant build a bow by numbers. You're approaching this bow building too technically and too mathematically.
"Moisture content reads about 18%"
"These curves were developed using David Dewey's spreadsheets"
"about 3mm over the thickness that I think will give the target weight"
For me, these are all indicators that you are trying to build by numbers. I understand that you (especially a beginner) need dimensions to get started. But you've surpassed the point where exact measurements no longer work. You can try to lay out the width of the bow very meticulously, but since there are knots and dips in the wood, you need to be creative. You can try to predict a tiller shape with a spreadsheet, but since there are knots and natural variations in the wood, you will have to compromise and create a different tiller in some places. Make sure that you enjoy the process and the woodwork, and you don't have to rely on fixed numbers all the time. If you are enjoying this mathematical approach, then fine. But remember that cavemen didn't have tape measures, spreadsheets and calipers, yet they build fantastic bows.
The bow and tiller is looking good. If the last pic was taken at a draw weight of 60 pounds, you obviously have a lot of wood (thickness) left to remove. As soon as you get a tip deflection (not draw length!) of about 6" at your desired draw weight, you should string the bow to a low brace height. At the moment, you could also shorten your long string, until it is just tight to the handle.

[Richard B]

Fair point, I do sometimes tend to overanalyse. One of the nice things about working with wood is that its properties are too complex to be able to solve the problem by analysis only and you have to feel your way there. The complexities that come with the undulating surface of the back that you get when you follow a ring (which I think are rather beautiful on my elm stave) also make things interesting. But I still enjoy doing the sums and trying to understand what is going on with the physics.
I shall keep scraping away and, hopefully, get to full draw without breaking anything!
One thing I do need to get is a better string. The parachute cord I am using is a bit stretchy.

[zenart]

DarkSoul, thanks for the lesson! 

Richard, what kind of Elm is this?  Also have my first stave (Osage) but yours is definitely more challenging. Wishing you well. I'm following this one.

[Jodocus]

you've surpassed the point where exact measurements no longer work.

Darksoul is right as usual! The only measurement I actually ever take when I make a bow is to find the center with a piece of string I fold in halves. When I help beginners on theirs first steps, they usually find it very hard to accept this...