Had a little play with Maple, ended up with a ripper
Posted: Tue Sep 10, 2019 8:39 am
Aloha,
It's been quite a while since I posted anything I've made. Truth is I haven't made many bows over the last few years. One or two here and there. Mostly I've been teaching bowmaking which has been every bit, if not more fulfilling, than making my own. Especialy two young bowmakers in particular, but that's for another post.
A few months ago I was in the local fancy timber place and happened across a 50 x 150 mm board of Hard Maple, about 2500 mm long. The grain, visible only through the rough-sawn surface, looked reasonable so I grabbed it.
A couple of weeks ago I sawed a stave off it and sanded two sides clean. My heart dropped to start with, as it seemed the grain was too violated to be a viable bow's back.
In reality it turned out to be fine. But to be on the safe side I skewed the centre line of the bow to be slightly diagonal on the board.
I took some bend test data and calculated the dimensions for a 64" longbow pulling 60 lb @ 28". I draw 26, but I have my program calculate everything to 28, except for the warbows which are designed to draw to 30 or 32.
Anyhoo. Out were spat the dimensions. I was a little skeptical actually. The program said it only needed to be 32 mm wide. I was unsure this would be sufficient, and I had used average figures from a range of previous bend tests of other samples. Regardless, I marked and cut out to the dimensions thinking I would be happy with whatever draw weight I could get as long as the tiller shape was good. Here are the dimensions:
When I cut it out I put a short string straight on it, as I was sufficiently confident in my cutting. I didn't take a picture but one limb was a touch stiffer than the other. I didn't do any weight reduction tillering - only tillering to correct the shape of the bending limbs. I didn't take any pictures of the tillering until just over half way through, which we see here:
The tips were still a touch stiff at this point but I knew they'd come around as the draw progressed, and they only needed a tiny whisp taken off at the grinder.
Not long after this I got to my full draw of 26", where it pulled 53#.
I only thought of this just now, but here it is with an overlay of the intended draw shape (which is drawn to 28"):
As it turns out the bow is a touch short at one end, but otherwise the shape is pretty close to the design.
I was quite surprised how close to the calculated draw weight the bow ended up. Below, I've plotted a gross generalisation of a force-draw curve (I know they're not straight lines, thanks) and plotted where this bow sits. It wouldn't quite reach 60 lb at 28", but it's pretty close.
I've never worked Maple before. It was a joy to work with. it grinds much the same as Ironbark or Spotted Gum (on my grinder anyway), and sands easily. It was a funny mind-trick. Historically in my workshop, light-coloured woods are light mass (radiata pine, white cypress, celery-top) and dark woods are heavy (Spotted Gum, Ironbark, Massarabundah). This wood is light coloured and also reasonably dense (haven't calculated it but is probably in the realm of 800 kg/m^3).
When I sanded and waxed it I found this amazing orange horizontal fleck across just one of the limbs. I've no idea what that's about but it looks cool. I don't know if you'll be able to make it out in this picture:
Because it's designed to work, and experience an even stress all along its length, it has absolutely no discernible handle section. I filed in a tiny groove to mark the arrow pass.
Still to do is make the tips outside the nocks look purdy, and make a string to test how well it shoots. I did fling some arrows, but I used the heavy tillering string which still had the vinyl tube I installed to protect it from wear on the tiller stick.
Once unstrung the tips had 1 5/8" and 1 3/8" set, which I think is reasonable and is what I had anticipated from the original calculations. It weighs just a hair under 14 oz. It took me perhaps 3 1/2 hours from faffing about with the initial layout to shooting it.
That's all, folks.
It's been quite a while since I posted anything I've made. Truth is I haven't made many bows over the last few years. One or two here and there. Mostly I've been teaching bowmaking which has been every bit, if not more fulfilling, than making my own. Especialy two young bowmakers in particular, but that's for another post.
A few months ago I was in the local fancy timber place and happened across a 50 x 150 mm board of Hard Maple, about 2500 mm long. The grain, visible only through the rough-sawn surface, looked reasonable so I grabbed it.
A couple of weeks ago I sawed a stave off it and sanded two sides clean. My heart dropped to start with, as it seemed the grain was too violated to be a viable bow's back.
In reality it turned out to be fine. But to be on the safe side I skewed the centre line of the bow to be slightly diagonal on the board.
I took some bend test data and calculated the dimensions for a 64" longbow pulling 60 lb @ 28". I draw 26, but I have my program calculate everything to 28, except for the warbows which are designed to draw to 30 or 32.
Anyhoo. Out were spat the dimensions. I was a little skeptical actually. The program said it only needed to be 32 mm wide. I was unsure this would be sufficient, and I had used average figures from a range of previous bend tests of other samples. Regardless, I marked and cut out to the dimensions thinking I would be happy with whatever draw weight I could get as long as the tiller shape was good. Here are the dimensions:
When I cut it out I put a short string straight on it, as I was sufficiently confident in my cutting. I didn't take a picture but one limb was a touch stiffer than the other. I didn't do any weight reduction tillering - only tillering to correct the shape of the bending limbs. I didn't take any pictures of the tillering until just over half way through, which we see here:
The tips were still a touch stiff at this point but I knew they'd come around as the draw progressed, and they only needed a tiny whisp taken off at the grinder.
Not long after this I got to my full draw of 26", where it pulled 53#.
I only thought of this just now, but here it is with an overlay of the intended draw shape (which is drawn to 28"):
As it turns out the bow is a touch short at one end, but otherwise the shape is pretty close to the design.
I was quite surprised how close to the calculated draw weight the bow ended up. Below, I've plotted a gross generalisation of a force-draw curve (I know they're not straight lines, thanks) and plotted where this bow sits. It wouldn't quite reach 60 lb at 28", but it's pretty close.
I've never worked Maple before. It was a joy to work with. it grinds much the same as Ironbark or Spotted Gum (on my grinder anyway), and sands easily. It was a funny mind-trick. Historically in my workshop, light-coloured woods are light mass (radiata pine, white cypress, celery-top) and dark woods are heavy (Spotted Gum, Ironbark, Massarabundah). This wood is light coloured and also reasonably dense (haven't calculated it but is probably in the realm of 800 kg/m^3).
When I sanded and waxed it I found this amazing orange horizontal fleck across just one of the limbs. I've no idea what that's about but it looks cool. I don't know if you'll be able to make it out in this picture:
Because it's designed to work, and experience an even stress all along its length, it has absolutely no discernible handle section. I filed in a tiny groove to mark the arrow pass.
Still to do is make the tips outside the nocks look purdy, and make a string to test how well it shoots. I did fling some arrows, but I used the heavy tillering string which still had the vinyl tube I installed to protect it from wear on the tiller stick.
Once unstrung the tips had 1 5/8" and 1 3/8" set, which I think is reasonable and is what I had anticipated from the original calculations. It weighs just a hair under 14 oz. It took me perhaps 3 1/2 hours from faffing about with the initial layout to shooting it.
That's all, folks.