New bow measurements

[DC]

You just want me to wear out my bow, don't you

of course not, but I do think collecting data at less than full draw is useful and probably not all that much wear once the bow has been shot at the full draw a few times.

You're right, just yanking your chain

[DC]

Wow! Now those are impressive numbers!

Given that this is a backed bow with 5" of reflex and yours is a selfbow with not much reflex I would think your numbers are just as impressive.

[scp]

Without a proper shooting machine, it's too easy to make mistakes in measuring FPS. A while ago I was doing it while drawing almost 3 inches less than my expected 28 inch draw length. I was getting timid while shooting through the chrony. No wonder my better bows were shooting only 140 up to 150. My simplistic shooting machine at that time was also too crude to be reliable. According to it, my control group of fiberglass recurves were shooting only around 160. As I have made the machine a little better and actually simpler, they now shoot around 180. My better bows are around 160 up to 170. If I pull those a couple of inches over my usual draw length, I can probably get 180 out of some of them. But that's very dangerous. I might break them in my eagerness. The simplest way to prevent this is to use only the arrows of proper length. Now I am trying to make my machine shoot faster, instead of trying to make my bows shoot better. So silly of me.

[willie]

Without a proper shooting machine.................. Now I am trying to make my machine shoot faster, instead of trying to make my bows shoot better. So silly of me.

scp-

Don has tried a couple of release methods, and it has been demonstrated that the release matters, if not at a couple of feet to the chrono, at least to the cast of the arrow.
But what about the bow clamp? Can we assume that a bow in a rigid mount shoots the same as a bow held loosely in the hand?

[DC]

Now I am trying to make my machine shoot faster, instead of trying to make my bows shoot better. So silly of me.

All you're trying to do is make your machine more consistent, not faster. it will just take a little work to do that and then it will let you know(or at least give clues) how to make your bows faster. I've got maybe two or three days work into my machine. I consider it time well spent but only if you're a speed freak.

[DC]

Don has tried a couple of release methods, and it has been demonstrated that the release matters, if not at a couple of feet to the chrono, at least to the cast of the arrow.
But what about the bow clamp? Can we assume that a bow in a rigid mount shoots the same as a bow held loosely in the hand?

I think we're going to have to assume that they are similar. I can't think of a way to test the difference. My biggest problem with the clamp is different shaped handles. It holds a Howard Hill type very well but curved belly type sometimes fit, other times they torque.

[sleek]

Try a bean bag between the handle and its clamp?

[bradsmith2010]

thanks DC,, thats great info,,

[DC]

Try a bean bag between the handle and its clamp?

I have a layer of wet suit foam in there now. My machine has automatic release that depends on a pin-in-a-hole trigger so the bow has to be held in the same position every time. A bean bag may not do that. I'll keep it in mind though.
Maybe I went at this the wrong way. Maybe the moveable jaw on the clamp should be against the belly. Then the back(where DL is measured) would be constant. Sounds unsafe though. More thought required.

[DC]

thanks DC,, thats great info,,

It's interesting but is it any use?

[scp]

All you're trying to do is make your machine more consistent, not faster.

I now use a drill press clamp to hold the bow. I use a roller arrow rest, a caliper release, and a hand winch. That way I am holding the bow at full draw for several seconds. I am thinking about an automatic release mechanism. I like the way you used the medieval crossbow roller nut design, but I'm not sure how your automatic release works yet.

My shooter's machining tolerance is terrible, probably more like a quarter inch or so, as I am more of a "2x4 school" of woodworking. But I am good if the consistency margin is less than 5 FPS.

[DC]

I added a post to the Shooting Machine thread. Maybe a little clearer how it works.

[mmattockx]

But what about the bow clamp? Can we assume that a bow in a rigid mount shoots the same as a bow held loosely in the hand?

That's a good question. A loose grip will change how a bow vibrates during the shot, especially with working recurves on R/D bows. Tough to test that, though. Has anyone tried testing using a clicker and a mechanical string release like the compound shooters use? That may be almost as good as DC's machine for consistency.

Is it more important that it is the same as shooting by hand or simply that it is consistently the same for all the bows? I say consistency is king unless we can show the clamp is significantly changing the results.

Maybe the moveable jaw on the clamp should be against the belly. Then the back(where DL is measured) would be constant. Sounds unsafe though.

Why does that sound unsafe to you? The movable jaw does need to be strong enough to not fail, but that shouldn't be an insurmountable problem. I can't criticize your perception, though. You have to stand beside it while full drawn and there is a lot of stored energy in a bow that makes it a bit of a bomb if things go wrong. Whatever feels safe to you is what you should do.


Mark

[DC]

 I'm not sure why it feels unsafe, just a gut feeling. The movable jaw is held by two 5/16" bolts. It's probably stronger than the fixed jaw . I'm at the end of a six foot rope when I shoot it. A nice comfortable way away.

[scp]

Thanks. I saw it but didn't read it. I will check it out soon.

How fast are you pulling the string when drawing a bow in your shooting machine?

After the proper release, the speed of drawing might make all the difference. I was thinking about using a hydraulic piston, but it would be too much of a bother for an occasional hobby.