First projects out of the heat box
Posted: Sat Oct 18, 2014 6:36 am
I thought the best test to run in the new heat box would be to glue up a couple of staves and see how long it took to set the EA 40.
I had a stave cut out already waiting to go. I also had a stave already backed that had delaminated in one place, and using a knife, I was able to pry the rest of the backing off without tearing the backing or the stave. A sure sign of a bad glue-up, or a bad glue.
I mixed up just over half a disposable cup (maybe 2/3....I can't remember) of Smooth On EA 40. It has a long pot life which meant I didn't have to rush the process. I managed to glue both staves up (quite generously) and had about 1/6 of a full cup of epoxy left over. I wrapped each stave in cling wrap then applied the tire strip binding. The I braced both bows backwards to impart some reflex. One of the bows, a 66" pyramid stave, I put 6" of reverse brace into. The other, a 73" stave, got 9".
I strung them in reverse using nylon. This proved to be a mistake as the strings stretched, I think due to the heat, and so when I got the bows out they were quite a bit lower in brace height.
I used a cheap 24 hour electrical timer set to two hours. I checked the staves at this point and there were still a couple of tacky bits on the belly of the staves (they were put in back-down), so I put the box back on for another hour. All epoxy was rock solid by then. Although, just to see what would happen I put the cup of leftover epoxy in the bottom of the box, where it's coldest, and that was set after two hours.
Wrapping the staves in cling wrap prior to binding meant the rubber strips came off super easy. However I remembered immediately after unwrapping that in my West System epoxy days, I would cover the outside of the boo backing with duct tape to protect it from the globules of excess epoxy. Lesson (re)learned.
The pyramid bow stave turned out okay. It now has about 2" of reflex.
It will take some wrestling in the early stages of tillering, until I get a short string on. No idea what draw weight will come out of this. I think I'd be happy with about 45#.
The longer stave has just over 5" of reflex. However the reflex is unevenly distributed, heavily biased to one limb which almost looks recurved.
Now, trying to tiller this bow with so much reflex would be absurd. It was never my intention to tiller this bow out as-is.
What I plan to do is cut each limb shorter and delfex them, either through gluing to a riser or perhaps a fitting them into a takedown assembly. As an illustration, here I've traced the limb profiles in deflex onto some MDF:
Perhaps what I can do is cut the left limb to length and use it as the upper, and cut the right limb a little shorter and use it as the lower. By cutting the right limb shorter, it will alleviate a little bit of the excess reflex. Or rather, compensate for the lack of reflex in the other limb.
Or perhaps I'm worrying too much.
But in conclusion, I'm very happy with the performance of the Smooth On EA 40 so far. Easy to measure, mix and spread, and with heat....quick to harden.
I had a stave cut out already waiting to go. I also had a stave already backed that had delaminated in one place, and using a knife, I was able to pry the rest of the backing off without tearing the backing or the stave. A sure sign of a bad glue-up, or a bad glue.
I mixed up just over half a disposable cup (maybe 2/3....I can't remember) of Smooth On EA 40. It has a long pot life which meant I didn't have to rush the process. I managed to glue both staves up (quite generously) and had about 1/6 of a full cup of epoxy left over. I wrapped each stave in cling wrap then applied the tire strip binding. The I braced both bows backwards to impart some reflex. One of the bows, a 66" pyramid stave, I put 6" of reverse brace into. The other, a 73" stave, got 9".
I strung them in reverse using nylon. This proved to be a mistake as the strings stretched, I think due to the heat, and so when I got the bows out they were quite a bit lower in brace height.
I used a cheap 24 hour electrical timer set to two hours. I checked the staves at this point and there were still a couple of tacky bits on the belly of the staves (they were put in back-down), so I put the box back on for another hour. All epoxy was rock solid by then. Although, just to see what would happen I put the cup of leftover epoxy in the bottom of the box, where it's coldest, and that was set after two hours.
Wrapping the staves in cling wrap prior to binding meant the rubber strips came off super easy. However I remembered immediately after unwrapping that in my West System epoxy days, I would cover the outside of the boo backing with duct tape to protect it from the globules of excess epoxy. Lesson (re)learned.
The pyramid bow stave turned out okay. It now has about 2" of reflex.
It will take some wrestling in the early stages of tillering, until I get a short string on. No idea what draw weight will come out of this. I think I'd be happy with about 45#.
The longer stave has just over 5" of reflex. However the reflex is unevenly distributed, heavily biased to one limb which almost looks recurved.
Now, trying to tiller this bow with so much reflex would be absurd. It was never my intention to tiller this bow out as-is.
What I plan to do is cut each limb shorter and delfex them, either through gluing to a riser or perhaps a fitting them into a takedown assembly. As an illustration, here I've traced the limb profiles in deflex onto some MDF:
Perhaps what I can do is cut the left limb to length and use it as the upper, and cut the right limb a little shorter and use it as the lower. By cutting the right limb shorter, it will alleviate a little bit of the excess reflex. Or rather, compensate for the lack of reflex in the other limb.
Or perhaps I'm worrying too much.
But in conclusion, I'm very happy with the performance of the Smooth On EA 40 so far. Easy to measure, mix and spread, and with heat....quick to harden.