Lock time?

[Geezerbiker]

I completed a long anticipated project recently to lighten the hammer on a single shot Handi Rifle. The only scale I had that would measure it is my digital kitchen scale and it reports that I took off 4 grams.

Is there any easy way to measure the improvement in lock time?

Tony

 

[MarkCO]

Is there any easy way to measure the improvement in lock time?

Tony

No.

If you have a newer modal Mirrorless camera with 1/8000s (or faster) electronic shutter, and a Pluto trigger for it, you can get close. But it is still an involved and arduous process, and then you have to be able to analyze the video. You can also rent a high speed camera, like 1/100,000 s and faster. They run several hundred dollars a day. But, if you have a bunch of things set up to do at once, you can get a lot of Youtube hits.

A cheaper way, but more precise and still not simple, is a very sensitive accelerometer capable of picking up the vibrations from the release of the sear. Those can be rented from various scientific supply houses.

At one point in time, it was a simple and easy thing for me to do as I could just walk into the lab at my Engineering school and do it. Now it takes scheduling, and Campus police escort and all kinds of other issues.

 

[ballardw]

If you didn't get a measure of lock time BEFORE working on it there really isn't going to be much of a way to determine "improvement" or even just change...

Maybe a bit obvious to say change does not always mean improvement.

 

[44 AMP]

The only scale I had that would measure it is my digital kitchen scale and it reports that I took off 4 grams.

My internet conversion says 4grams = 0.14 ounces.

You might proportion that against the full weight of the hammer originally and use that ratio as a rough estimate of the potential change in lock time.

Not as accurate as actual measurement, of course, but if you don't have any "before" measurements, then the "after" doesn't tell you if what you did actually changed anything, or not.

 

[MarkCO]

You might proportion that against the full weight of the hammer originally and use that ratio as a rough estimate of the potential change in lock time.

Probably closer than one might think. The spring rate and geometry is a complex and frustrating math problem to do by hand. It's mostly done with numerical methods (complex math in computer programs). I hated doing those kinds of problems in school...when direct measurement after a linear approximation was faster and easier in the measurements lab.

 

[Unclenick]

Geezerbiker,

You say you lightened the hammer and expect improved lock time? Generally, "improved" is taken to mean "shortened," but lightening a hammer spring will make it take longer. My mistake; misread as spring lightening.

As far as measurement goes, you may be able to detect the sear break and the hammer impact with a cheap condenser microphone element. Given the hammer is exposed on the Handi Rife, you can also detect both initial movement and impact with the equivalent of a pair of guitar pickups, using fine wire windings around permanent magnets close to the hammer spur in its start and stop positions. Another method is to set up a pair of LEDs and photo-transistors to give you the optical start and stop positions of the hammer spur. None of these may be absolutely exact in their results, but as long as the setup is the same for both the before and after measurements, you can get a percentage-wise change.

 

[mehavey]

I would "think" that Spring constant, F=ma and S=.5at(sq) come into play here.

Simplistically, reduction in lock time being the square root of the % resultant hammer mass.

Ergo (wet thumb) would say: Square root of 20% reduction ~ sqrt(.8) = 0.89 of previous lock time

 

[tangolima]

It can be measured with a microphone and an oscilloscope. But why bother?

-TL

Sent from my SM-N960U using Tapatalk

 

[JohnKSa]

I would "think" that Spring constant, F=ma and S=.5at(sq) come into play here.

Simplistically, reduction in lock time being the square root of the % resultant hammer mass.

Ergo (wet thumb) would say: Square root of 20% reduction ~ sqrt(.8) = 0.89 of previous lock time

Yup. A rough estimate.

---deleted---

The resulting estimate will be a sort of absolute best case scenario. It assumes that every last bit of weight removal happened at the absolute tip of the hammer where it would have maximum effect.

 

[Unclenick]

Ergo (wet thumb) would say: Square root of 20% reduction ~ sqrt(.8) = 0.89 of previous lock time

I misread the OP. For some reason, I thought he was lightening the hammer spring, but on re-read, I see it is the hammer itself. You are correct in your change of time for the different masses to travel the same distance with a proportional change in acceleration. I will just tweak the mass in the next paragraph.

On average, and not counting friction, one would either allow that the hammer spring mass has half the acceleration of the hammer or that half the spring's mass has the same acceleration as the hammer. Using the second method and using weight as a proxy for mass, you need to know the hammer weight plus half the spring weight before lightening, then know the hammer weight plus half the spring weight after lightening to get the portion of mass reduction. Then, as JohnKSa said, take the square root of that ratio to get the portion of the change in time that mass difference makes). In real life, friction will have some effect, as will the viscosity of any lube in there, but the square root of the mass ratio gives you some idea.

 

[MarkCO]

In real life, friction will have some effect, as will the viscosity of any lube in there, but the square root of the mass ratio gives you some idea.

Yep! In engineering school, I often got in arguments with professors in this area. Math, and Engineering, ARE approximations. The level of precision needed is dependent on the use, anticipated misuse, budget and life/safety constraints of whatever system is being evaluated. Factors of Safety and FMEA fall into this realm.

The real world has so many variables, "undergrad studies" have most of those variables removed so that the problems can be solved within the conscripts of a course. Too many engineers lose the forest for the trees trying to get precise. Too many folks "think" they are doing great when precise solutions are, in fact, required. It's the battle and knowing when to apply precision of methods and when the rough calculation is okay.

 

[ballardw]

Math, and Engineering, ARE approximations.

I think you mean "calculation with observed measurements" not Math in that statement.

Math is the A+B part. It takes someone to put values like 0.999999+1.00000 in place of A and B to get "approximately" 2.

For real world applications I tend to say Math is reducing a problem to where any engineer with a calculator can plug in some values and get a result. (slightly cleaned up to reduce likelihood of offense)

 

[mehavey]

The math is exact.
It's the assumptions going in that produce approximation.

But "good enough" is the real art.
(Wet thumb in this case)

 

[MarkCO]

Nah, math is still an approximation. When math can prove you can't stop at a stop sign, but we know you can in the real world, the math is not exact. It's really close in some areas. There are 7 physical laws, those are exact. Our attempt (math) to explain it is an approximation. Maybe a bit philosophical and heady, but it is what it is.

 

[JohnKSa]

When math can prove you can't stop at a stop sign...

If you're talking about the case I think you are, that's not what was proved. What was proved was that an observer in a particular spot could be shown to be unable to detect whether a car stopped at a particular stop sign due to a combination of occlusion and the inability of the observer to detect actual velocity, substituting angular velocity instead.

...math is still an approximation...

Interesting view. I think what you're saying is that math can't always perfectly model complex activities in the real world. I can see some basis for that claim although it can certainly perfectly reflect certain types of activities, such as, keeping track of how many apples one has on hand at any given time. When I say I have 10 apples and someone gives me 3 more and I use math to show that I know have 13 apples, that's not really an approximation. It's an exact value for the number of apples possessed.

On the other hand, if I want to model a non-linear process by assuming that it is linear, the result of the model will be approximations of the real-world process. It might be a good approximation or it might be a bad one, but that's not because the math is imprecise, it's because the model is based on an assumption and it is not actually performing the proper calculation--it is performing a different calculation (very precisely) to provide an approximation of the real-world process.

In this case, the approximation/estimate of lock time based on Newtonian physics will be imprecise because it is based on a number of assumptions. But the math itself is quite precise. If 100 people do the calculation the same, using the same inputs and assumptions, they will all get precisely the same answer.

Math, itself, is generally quite precise (since it was set up to be so, in general) although it can also be used to generate approximations, if desired.

 

[mehavey]

...math is still an approximation...

Math is exact. *
It's one use of it in an "assumed" model that becomes an approximation.




*Unless some gentle reader wants to invoke non-Newtonian/quantum effects.

 

[JohnKSa]

Unless some gentle reader wants to invoke non-Newtonian/quantum effects.

Even then, that is physics (real world science), not actually math. Math is often used to approximate/estimate/model real-world phenomena, including physics, and depending on a number of things, those approximations/estimations/models can be imprecise or very good. But, in either case, the underlying math itself isn't what makes the the approximations/estimations/models good or bad, it's how good of a job the user does when setting up the approximation/estimation/model.

It's sort of the same idea as saying that wrenches are problematic because SAE wrenches won't fit metric fasteners properly. The problem isn't the with the wrenches, it's that how they are being used in that particular case isn't matching up with the real world need properly. In that case it's a user error, and that can be the situation with math as well, but in some cases, it's just a limitation of mathematics--it can't always do everything we want it to. As in trying to use a wrench to solder two pieces of wire together. The wrench just can't do that.

 

[MarkCO]

If you're talking about the case I think you are, that's not what was proved. What was proved was that an observer in a particular spot could be shown to be unable to detect whether a car stopped at a particular stop sign due to a combination of occlusion and the inability of the observer to detect actual velocity, substituting angular velocity instead.Interesting view. I think what you're saying is that math can't always perfectly model complex activities in the real world. I can see some basis for that claim although it can certainly perfectly reflect certain types of activities, such as, keeping track of how many apples one has on hand at any given time. When I say I have 10 apples and someone gives me 3 more and I use math to show that I know have 13 apples, that's not really an approximation. It's an exact value for the number of apples possessed.

On the other hand, if I want to model a non-linear process by assuming that it is linear, the result of the model will be approximations of the real-world process. It might be a good approximation or it might be a bad one, but that's not because the math is imprecise, it's because the model is based on an assumption and it is not actually performing the proper calculation--it is performing a different calculation (very precisely) to provide an approximation of the real-world process.

In this case, the approximation/estimate of lock time based on Newtonian physics will be imprecise because it is based on a number of assumptions. But the math itself is quite precise. If 100 people do the calculation the same, using the same inputs and assumptions, they will all get precisely the same answer.

Math, itself, is generally quite precise (since it was set up to be so, in general) although it can also be used to generate approximations, if desired.

Nope, not that case. There are several mathematical "proofs" that prove you can not stop at a stop sign. In fact, one mathematician got out a traffic ticket by proving such. Simple version, how many points are there between two distinct points on a number line? The answer is infinitely many. Can't divide by infinity...

Yes, for complex problems, anything non-linear of course, it is an approximation. It's a hard concept to grasp, but math is a man-made system used to try and compartmentalize and quantify reality. The 7 Laws are all there really is in the physical realm, and those are phrases. We try to dissect them, as best we can with math. For a "black & white" kind of personality that I have, it was a difficult thing to get there. But being blessed to be able to work alongside a few absolutely brilliant men in my career, I finally got to the point where I understand math is really just very minute shades away from pure white and pure black.

 

[mehavey]

...how many points are there between two distinct points on a number line? The answer is infinitely many. Can't divide by infinity...

That's the old "half the distance with each step" game.
(corollary question: "can you stop on a point?"

But that's (again) not the issue.
Math (the Newtonian F=Ma kind) is exact. *

But it's modeling the physics (which the Gentle Read might remember as originally being called "Natural Philosphy")
Philosophy is always an approximation.
Sorta like modeling a hammer as a point mass acted upon by a lossless spring in a frictionless environment with in a vacuum.

But SQRT(3)= 3.00000 (exact)

Then there's Pi that's got me worried.
(But that's geometry -- another model)

*
Of course we can always argue about a=G=Gravity --> "weight" (varies all over the place)
But that's both physics and geometry....

(and diet)

 

[JohnKSa]

There are several mathematical "proofs" that prove you can not stop at a stop sign.

Well, they either aren't correct proofs or the way they have been applied to the real world is flawed. The fact that there are infinitely many points between any two points doesn't, in any way, prevent one from getting from one point to the other or stopping somewhere in between in the real world or from moving from one point to another on the number line, mathematically speaking.

Yes, for complex problems, anything non-linear of course, it is an approximation. It's a hard concept to grasp, but math is a man-made system used to try and compartmentalize and quantify reality. The 7 Laws are all there really is in the physical realm, and those are phrases. We try to dissect them, as best we can with math. For a "black & white" kind of personality that I have, it was a difficult thing to get there. But being blessed to be able to work alongside a few absolutely brilliant men in my career, I finally got to the point where I understand math is really just very minute shades away from pure white and pure black.

Mixing things.

The math is black and white. That's how it's designed.

When people try to apply it to the real world, in some cases it doesn't fit exactly or our current level of mathematical development doesn't allow exact solutions and then approximations are required.

It's important to understand that the approximation happens, NOT with the math, but in the application of the results to the real world and the disparities that can occur at that point.

For example, when we did the calculation above to estimate lock time reduction, the math itself is precise. If a billion people do the calculation correctly, they will all get exactly the same result. The approximation comes when we take that very precise mathematical result and try to apply it to the real world problem we are trying to solve. It's not the math that's the problem, it's how WE set up the problem and then tried to use the result at the end.