foil will not hold weight with new spring

[finnfence]

Sorry if this has been asked before, but I couldn't find it in the threads: every so often I have a whippy blade that just won't hold the test weight more than one bout no matter how many times I change the spring, no matter whether I rewire, or change the whole tip, or what. I've used that little scrapy tool to make the barrel round, I've tried different batches of springs, and I still can't get these foils to behave. It often happens when I'm using a French blade with a German barrel, tip, and wire.

Any ideas what the problem could be?

[Purple Fencer]

Originally Posted by finnfence

Sorry if this has been asked before, but I couldn't find it in the threads: every so often I have a whippy blade that just won't hold the test weight more than one bout no matter how many times I change the spring, no matter whether I rewire, or change the whole tip, or what. I've used that little scrapy tool to make the barrel round, I've tried different batches of springs, and I still can't get these foils to behave. It often happens when I'm using a French blade with a German barrel, tip, and wire.

Any ideas what the problem could be?

Are the springs and the rest if the point assemblies from the same manufacturer? if so, you MIGHT be running onto a bad batch of springs.

[fencerbill]

Originally Posted by finnfence

Sorry if this has been asked before, but I couldn't find it in the threads: every so often I have a whippy blade that just won't hold the test weight more than one bout no matter how many times I change the spring, no matter whether I rewire, or change the whole tip, or what. I've used that little scrapy tool to make the barrel round, I've tried different batches of springs, and I still can't get these foils to behave. It often happens when I'm using a French blade with a German barrel, tip, and wire.

Any ideas what the problem could be?

Do what everyone else does, stretch the spring.

It is probably due to a melange of not perfectly compatible parts.

I doubt that the "whippy" aspect of the blade has anything to do with it.

The use of a French blade and a German barrel, tip and spring has nothing to do with it.

Does the tip slide smoothly in the barrel? If so, nice work with the "scrapy" tool.

So the spring works at first, then doesn't restore the weight after that. Did you get a real good bargain on that barrel of springs?

The answer is simple, you are not praying to the right gods. From other threads, you may have to resort to switching to Leon Paul components. Or else find new gods to pray to.

[finnfence]

Originally Posted by Purple Fencer

Are the springs and the rest if the point assemblies from the same manufacturer? if so, you MIGHT be running onto a bad batch of springs.

Yup, all the point stuff is from Allstar. It's possible I accidentally used an Uhlmann wire. Would that matter? I thought Uhlmann and Allstar were the same stuff under two different names these days, or at least compatible?

[finnfence]

The tip slides fine - I've also tried exchanging barrels, exchanging tips, using a completely new point assembly, used different batches of springs bought in different countries more than a year apart, and rewiring. Nothing helps. The weird thing is, this has happened before, and I've also seen it happen to other people on occasion, which makes me think there is actually an underlying diagnosable problem, I just haven't been able to figure out what. I do notice that the barrel seems to be sort of offset from center on the blade, so the center of the end of the blade doesn't line up exactly with the center of the barrel. Don't know if that would matter. The other thing that is a little odd is that normally, to get a tip that's beginning to go to hold weight, you pinch the blade between your fingers to straighten it out at the end (without touching the tip...refs frown on that one...) but for these weirdo blades, it helps to pinch the blade so that it curves to the side at the tip. I am really wondering if French barrels are slimmer than German and if the failure of the center point to line up might be the problem. But why that would matter baffles me.

[GypsyScot]

No that's the same wire, my advice is the same, stretch the springs, use a pair of pliers and slowly with one hand stretch them out.

[fencerbill]

Originally Posted by finnfence

The tip slides fine - I've also tried exchanging barrels, exchanging tips, using a completely new point assembly, used different batches of springs bought in different countries more than a year apart, and rewiring. Nothing helps. The weird thing is, this has happened before, and I've also seen it happen to other people on occasion, which makes me think there is actually an underlying diagnosable problem, I just haven't been able to figure out what. I do notice that the barrel seems to be sort of offset from center on the blade, so the center of the end of the blade doesn't line up exactly with the center of the barrel. Don't know if that would matter. The other thing that is a little odd is that normally, to get a tip that's beginning to go to hold weight, you pinch the blade between your fingers to straighten it out at the end (without touching the tip...refs frown on that one...) but for these weirdo blades, it helps to pinch the blade so that it curves to the side at the tip. I am really wondering if French barrels are slimmer than German and if the failure of the center point to line up might be the problem. But why that would matter baffles me.

A situation where the central axis of a point is not congruent with the central axis of the blade is not common but I have seen it. And there was no resultant problem of springs not maintaining strength that you talk about.

I think you are having really lousy luck. Did you step on a crack or something?

[Joe biebel]

Stretch the heck out of them. Your springs are too close to 500 grams. It's not going to cost you as many points to have tips set heavy as it will from penalties for non-conforming equipment. In my test kit, I have a foil weight that I taped four quarters to, to add extra weight. Also, I use Leon Paul components and I find the springs to be very resilient and take a long time to lighten from repeated depressing.

Also, stop whacking the floor and your opponents guard so much, the tips go light much faster that way.

[finnfence]

The thing that's bizarre is, you can take the very same spring that won't hold weight in the problem foil and put it in another foil, and it holds weight fine.

[SJCFU#2]

Originally Posted by finnfence

The thing that's bizarre is, you can take the very same spring that won't hold weight in the problem foil and put it in another foil, and it holds weight fine.

This is sounding more-and-more like a case of mismatched parts.

Unfortunately much of the production is subbed out so you will sometime see variations among parts even when they all come from the same vendor.

[fencerbill]

Originally Posted by finnfence

The thing that's bizarre is, you can take the very same spring that won't hold weight in the problem foil and put it in another foil, and it holds weight fine.

Not really, spring A in Foil #2 may be more compressed, therefore better able to restore the test weight. In other words the compressed length of spring A in Foil #2 is shorter.

We are trusting that there is no friction between the tip and the barrel, after your use of the scrapy tool.

[Beloit Fencer of Old]

Maybe the answer is to stop working on your own weapons.

[Dr Epee]

Sounds like that weapon is jinxed. Consider how much time and money you're spending on that one weapon. You might want to think about reserving that one for practice and get another for competitions. If you feel driven to find out what the underlying problem is, no matter what, they have medication for that.

[the ancient one]

Measure the depth of the contact from the top of the barrel. I bet it is shorter than your "good" points.

If so you probably have "coil lock". Let's say the spring is a helix of perhaps 15 turns and the diameter of the spring wire is A, then the spring when compressed 100% is 15 x A long, which is probably equal or less than the distance from the contact to the second contact on the end of your tip when it is assembled.

The cause is probably that the threaded length of the foil is too long and it is not letting the contact go to its proper depth.

The solution may be to cut your spring a little shorter, and then stretch it if necessay. You can even calculate how much to cut if you make the measurements above. This will make the spring stiffer, but if you take enough off you will not lock the coils.

[DHCJr]

Originally Posted by the ancient one

Measure the depth of the contact from the top of the barrel. I bet it is shorter than your "good" points.

If so you probably have "coil lock". Let's say the spring is a helix of perhaps 15 turns and the diameter of the spring wire is A, then the spring when compressed 100% is 15 x A long, which is probably equal or less than the distance from the contact to the second contact on the end of your tip when it is assembled.

The cause is probably that the threaded length of the foil is too long and it is not letting the contact go to its proper depth.

The solution may be to cut your spring a little shorter, and then stretch it if necessay. You can even calculate how much to cut if you make the measurements above. This will make the spring stiffer, but if you take enough off you will not lock the coils.

I hate to say it but the senile one would be a better description. First there is no "coil lock" as the tip does depress enough to break the circuit of Foil. This is Foil not Epee so the second contact is the barrel. It is always in contact with the first contact on the end of your tip. The spring is not strong enough to push up the spring. Shortening it would weaken not strengthen the spring. I would suggest to check the depth and would expect it to be deeper not shorter.

To show this take a spring at rest and squeeze it just a little. Now have it mostly compressed and sqeeze it the same amount. You will find the latter to be harder to accomplish.

[the ancient one]

Originally Posted by DHCJr

I hate to say it but the senile one would be a better description. First there is no "coil lock" as the tip does depress enough to break the circuit of Foil. This is Foil not Epee so the second contact is the barrel. It is always in contact with the first contact on the end of your tip. The spring is not strong enough to push up the spring. Shortening it would weaken not strengthen the spring. I would suggest to check the depth and would expect it to be deeper not shorter.

To show this take a spring at rest and squeeze it just a little. Now have it mostly compressed and sqeeze it the same amount. You will find the latter to be harder to accomplish.

I think the issue is that the circuit does not re-close under 500g. Your are right to suggest that the barrel is also possibly too deep, but it is still possibly too shallow. If the spring is over-compressed it will bend or shift radially and drag on the inside of an otherwise good barrel.

Springs do get non-linear at their elastic limits, but they are stiffer when shortened in the following sense:
Suppose you have a spring that compresses 2mm under 500 grams.

Now cut it in half. Each piece will now compress 1 mm under 500g.
If you need 2mm compression you will now require 1000g to move the same amount.

Similarly if you stack up 2 of the springs, each spring sees the same 500g and each compresses 2 mm for a total of 4mm under 500g.

Perhaps it seems counter-intuitive, but that is how it is.

[DHCJr]

Originally Posted by the ancient one

I think the issue is that the circuit does not re-close under 500g. Your are right to suggest that the barrel is also possibly too deep, but it is still possibly too shallow. If the spring is over-compressed it will bend or shift radially and drag on the inside of an otherwise good barrel.

Good point about the drag. I forgot about that. I think I was the senile one.

[fencerbill]

Originally Posted by the ancient one

The cause is probably that the threaded length of the foil is too long and it is not letting the contact go to its proper depth.

This is not within my experience. Every Foil and Epee barrel that I have seen has what you might call a ledge of reduced internal diameter near the bottom. The cup and contacts bottom out on this ledge, they are not in contact with the end of the blade itself.

On the hiltward side, next to this ledge you typically have a length of threads and then a length of smooth inside of the barrel. This is specifically required for Foil blades. Furthermore, the inside dimension of the barrel is supposed to equal the outside dimension of the Foil blade hiltward of the threads. The Foil barrel is supposed to have an snug fit onto the blade.

This dimension is not specified IIRC in the rules. Which may be a reason why points and blades from different sources may match more or less well.

Because of this intended interference fit, blades may or may not bottom out, may reach this reduced inside diameter or not.

But because of this ledge, the manufacturer expects his inside barrel dimension, his cup/contact combination, the length of his spring and the length of his tip to result in the compressed spring successfully restoring the contact during a weight test.

Any combination which does not include only his compatible combinations of parts may not result in reliable operation over time. I expect each manufacturer designs in some extra capacity to cope with reasonable ageing of his springs. Not forever, that's why they sell replacement springs.

I have mentioned compatible combinations. As time passes manufacturers may change these compatible combinations - you may not be able to expect compatible combinations of parts sold now milxed with parts sold ten years ago.

If you truly have compatible combinations of parts from reputable manufacturers, you would not be having the problems you complain of.

[the ancient one]

I agree.

If the end of the blade is threaded as it should be, if the mechanical limits are what they should be, there should not be a problem as described. Yet finnfence is having a seemingly irresolvable problem.

It would be illuminating to know accurately the actual depth of the lower contact.

I measured an old Prieur point that happens to be in my desk as well as a few springs. I have attached a drawing.

The point I measured will compress the spring to a height of 4mm when pressed down. To assemble the point you need to compress ( =preload) the spring to 4.6 mm from a nominal length of 8.5mm. If the assembled point resists exactly 500 grams force, the spring constant is roughly 130 grams/mm. When 100% compressed the spring is 3.52 to 3.63mm long, based on my 5 samples.

Now if you follow DCHjrs scenario and you seat the bottom contact 1mm too deep, you are ~130gms too light.

In my proposal if the contact is 0.4mm too high you have 100% compression and the possibility to distort the spring and cause drag or mechanical interference..

SO Fencerbills equally plausible scenario is that mismatched parts will be to blame