I'm looking for an alternative to needle roller bearings (springers)

[vobster]

I ended up using a vlgide piston, which is shorter than the stock 97 one, and a shortened comp tube to suit. The guides a bit on the loose side with a ptfe liner. Rocoil was straighter, I'll fit one in my 25mm 97 and I suspect all my springers, they all get abused by me at some point

[maximus]

do you think that as the gun is cocked the diameter of the spring increases thus reducing the interference on the guide so only during firing does the spring "grab" back onto the guide?
This may allow the rear bearings to work during the firing cycle. Just a thought.

Max

[vobster]

I dunno

[bigtoe01]

do you think that as the gun is cocked the diameter of the spring increases thus reducing the interference on the guide so only during firing does the spring "grab" back onto the guide?
This may allow the rear bearings to work during the firing cycle. Just a thought.

Max

aye that the theory, plus the guides in my TX are:

1 The rear guide is set into the trigger block
2 The front top hat is exact in size both for the spring and on the latch rod without any slop....so there should be no vibration.

[Dr_C]

Put a PTFE 'washer' and a 2mm steel washer into the piston head of my 97 last night. Lubed with Krytox.
Took it to the farm for a plink.
No more twist, hitting the 47yrd bell much more consistantly, able to keep the sight picture the same before/after pulling the trigger, power up a smidge by the end of the evening.

A very simple mod that's worth doing IMO.

C.

[TonyL]

Put a PTFE 'washer' and a 2mm steel washer into the piston head of my 97 last night. Lubed with Krytox.
Took it to the farm for a plink.
No more twist, hitting the 47yrd bell much more consistantly, able to keep the sight picture the same before/after pulling the trigger, power up a smidge by the end of the evening.

A very simple mod that's worth doing IMO.

C.

Excellent. And cheers for the input.

So much about springer tuning is gauged by perceived feel. In his Technical Airgun Series, Jim Tyler actually measures things like recoil and surge on purpose made rigs. It would be very interesting to test a set-up with bearings (either plain or thrust type) and measure the effects. If we could also build in the means to compare twist, that would be most useful.

[Loki_79]

Excellent. And cheers for the input.

So much about springer tuning is gauged by perceived feel. In his Technical Airgun Series, Jim Tyler actually measures things like recoil and surge on purpose made rigs. It would be very interesting to test a set-up with bearings (either plain or thrust type) and measure the effects. If we could also build in the means to compare twist, that would be most useful.

Watch this space!

I have just finished the latest modifications to a home made three-axis accelerometer system that I have been working on. It now can measure acceleration in x, y and z (+/- 250g) and detect the passing of a pellet through a light gate, and log all of this information at a rate of 60kHz for a total duration of around 380ms.

I also now have a load of different thrust bearings, including the 22mm ones that started off this thread. I still don't see how physics can explain the rotation effect (i.e. conservation of angular momentum in a closed system). But, as you suggest, collecting recoil profiles with and without the bearings should be useful in attempting to explain it.

[Shed tuner]

I still don't see how physics can explain the rotation effect (i.e. conservation of angular momentum in a closed system).

Surely it's simply a case of the piston wants to rotate one way, therefore action wants to rotate the other ? No different to piston moving forwards, action moving back ?

Either way, be good to see your data

[Loki_79]

Surely it's simply a case of the piston wants to rotate one way, therefore action wants to rotate the other ? No different to piston moving forwards, action moving back ?

Either way, be good to see your data

It is different to the recoil case because, as you say, the piston may want to rotate, but it cannot.

It would be equivalent to the linear recoil if the piston was free to rotate - the reaction to the rotation of the piston would be for the gun to rotate. But if the piston is constrained, it has no angular momentum to conserve. http://hyperphysics.phy-astr.gsu.edu...er.html#conamo

[bigtoe01]

loki

please sit the gun in a sled, stock, scope gun the whole lot so its free to move so what ever is measured is the whole gun so its what we will feel in the shoulder.

[bigtoe01]

So, shot the TX again this evening, since adding the rear bearing and shooting it in more...I have more power. So now debating whether some off the nose of the tophat or crush a coil on the spring...its still legal (just) but not where i want it to be (765 with exacts)

Very very accurate however, very easy to shoot, no twist, very quick, light recoil, easy to cock.

[Loki_79]

loki

please sit the gun in a sled, stock, scope gun the whole lot so its free to move so what ever is measured is the whole gun so its what we will feel in the shoulder.

If we are interested in measuring twist or rotation, then surely a sled would restrict/prevent these two motions?

[T 20]

do you think that as the gun is cocked the diameter of the spring increases thus reducing the interference on the guide so only during firing does the spring "grab" back onto the guide?

Max

IIRC I measured a compressed spring and found it had expanded by about 1% of the original OD.

I'll check again today if I have time.



All the best Mick

[bigtoe01]

If we are interested in measuring twist or rotation, then surely a sled would restrict/prevent these two motions?

maybe, but measuring recoil and surge would be so much better done this way

[Loki_79]

maybe, but measuring recoil and surge would be so much better done this way

I think that suspending the rifle using a fairly long (>1m?) string is probably best. Ideally the system would also be free to pivot, but perhaps in the interests of safety there should be a minimal restoring force to keep it pointing somewhere down the range!