Impact probe screw failure & solution

Jump to latest Follow Reply
Status
Not open for further replies.
"Pestassassin"
"Jack.K"maybe a temporary fix is to replace the M3x6 grub screw with a M3x8 steel grub screw since the threaded hole on the pellet probe block (feedingpin holder) is deep enough that a longer grub screw can still fit in which will not leave the Hollowed out portion of the screw to take the backward force.

Click to expand...


Temporary fix won't work in this situation, as the probe is bent and unusable. On top of that, I don't want a temporary fix. I want to know that this will never happen again.
Click to expand...
-Pestassassin, 
I was not referring to for you to have a termporary fix for your gun. You should ship it back to get it service. I was mainly saying for the other Impact owners out there to consider the M3x8 steel grub screw as a temporary fix until FX comes up with a solution for this safety issue.
 
Upvote 0
"sharroff"Pestassassin,

Lot's of us have had that probe screw work it's way loose. I complained to AoA about mine coming loose and they didn't have a fix other than replacing the screw and using loc tite

If Ernest is right and that contributes to the shearing, and all you have is a 30 barrel, then I'd use loc tite blue or red depending on that depending on how permanent and 'will never happen again' you want the fix to be. You'll need heat to remove the screw if you use red, and that could damage what you are heating.


Click to expand...
You should be very careful suggesting a fix before knowing what caused the shear really is. Using loctite or other means to make sure the screw doesn't come loose might just postpone the real issue and only solve the (unscrewing)
The constant back blows to this item, could weaken the setscrew as well, regardless of how tight it's set. If the depth of the alen key hole is roughly the same on all of these (assumption) eventually these will fail as the metal become harder as they get worked by the abuse.
 
Upvote 0
Jack.K
"Pestassassin"
"Jack.K"maybe a temporary fix is to replace the M3x6 grub screw with a M3x8 steel grub screw since the threaded hole on the pellet probe block (feedingpin holder) is deep enough that a longer grub screw can still fit in which will not leave the Hollowed out portion of the screw to take the backward force.

Click to expand...


Temporary fix won't work in this situation, as the probe is bent and unusable. On top of that, I don't want a temporary fix. I want to know that this will never happen again.
Click to expand...
-Pestassassin, 
I was not referring to for you to have a termporary fix for your gun. You should ship it back to get it service. I was mainly saying for the other Impact owners out there to consider the M3x8 steel grub screw as a temporary fix until FX comes up with a solution for this safety issue.
Click to expand...


Lol... Naturally. I just assumed you were responding to me.
 
Upvote 0
Windmeister,

The suggestion for loc tite came from AoA to me. I'm sharing the distributors / repair centers recommendation, not making my own.
.
And I'm not saying that is the permanent fix to what happened to Pestassassin. I am saying between now and when FX makes a statement that contradicts what AoA told me to do, having a tight secured probe screw w/ loc tite is better than not loc titing it and it backing out on its own. Unless someone is looking after every shot, you will not know your screw is backing out until you can't load a round. And when you look at why, you will see the probe screw is now jammed on the frame (which is what was happening to me).

I'm not making this up from speculation. I dealt with a lot of Impact issues and eventually returned it. The probe screw issue (and the others) are documented here





 
Upvote 0
As I said in my post, the Loctite cures the unscrewing of the grub screw which in itself is not a big safety issue, since, as someone said before, you cannot cock the gun with it halfway out due to tight tolerances. However, Loctite is not a fix for bolt/grubscrew shearing due to for instance material fatigue, or material not being of adequate strength in the application. 

At this stage it's like Chevrolet having airbags blowing up while standing still, dealerships are not going to assume user error, but let the experts investigate to find the fault. In the meantime, dont drive your Chevrolet.......
 
Upvote 0
WindmeisterAs I said in my post, the Loctite cures the unscrewing of the grub screw which in itself is not a big safety issue, since, as someone said before, you cannot cock the gun with it halfway out due to tight tolerances. However, Loctite is not a fix for bolt/grubscrew shearing due to for instance material fatigue, or material not being of adequate strength in the application. 

At this stage it's like Chevrolet having airbags blowing up while standing still, dealerships are not going to assume user error, but let the experts investigate to find the fault. In the meantime, dont drive your Chevrolet.......
Click to expand...


Thank you! Glad to see someone who understands the actual issue here! My set screw didn't back out. It sheered...
 
Upvote 0
"Pestassassin"
No I cannot. Backing the set screw out at this point will likely damage the threads inside the probe block. My plan is to leave the rifle exactly as it currently is and let the technicians at AOA look it all over.
Click to expand...
Click to expand...
Excellent plan. There are so many clues that can be had from just leaving it exactly as it is. 
I was making those suggestions above for after you get it back form AoA and just general brainstorming. Sorry, I should have mentioned that. It makes perfect sense that a hollow setscrew would shear easier than a solid one. By your pics, it certainly looks like that was the main contributor. 
I'm glad you've got Kip on it as well. That guy truly cares and knows his stuff!
Good luck! I hope you check in with us once you get it back. 
Tom
 
Upvote 0
Go back and take a look at the gunsmiths (Sniperlaybo) post on loose screws and strength. He knows a bit on this from his engineering background. If that screw isn't tight so all the threads are engaged, and the metal pieces are pulled together so that the reciprocal force is distributed along all the connected surfaces then the screw is going to take the brunt of the force vs the whole unit. That will create a shearing force. If the screw is too weak or has a manufacturing defect in the wrong spot (I'm sure FX doesn't do Radiographic or Ultrasonic testing of the stuff) then it will shear. So yea, a screw that is tight could shear on its own, but a loose one has a better chance of doing so. So a loose screw contributes to the safety issue. That is why manufacturers have torque specs on bolts/nuts that bear force (like your cars wheels or engines heads) to ensure things are tight and force is evenly distributed. Please don't try driving around with loose lug nuts to see what happens next. I'd give you a less costly experiment to try with pushing down with a sharp point on a piece of glass laying on a flat table then repeating with the same piece of glass when both sides are only supported by a handful of stacked quarters, but you'd have a mess on your hands; probably literally.

Another safety feature would be to have a mechanism to stop the probe from flying out the back of the gun in the event that it does shear, but that is another design issue, and they are still working on the design. 
 
Upvote 0
Obviously a loose screw have less strength than a tight torqued one. But lets examine the use of the two examples. In the lug nut scenario, the thing that holds your wheel on is the clamping force and resulting friction. On the rifle the grub screw is acting like a removable stop pin, and will always be subjected to shearing forces unlike the lug nut which would only be subjected to shearing forces if all lug nuts where slightly loose.
But yes, your point that a loose screw can withstand less shearing force than a torqued down one is true, but as the picture above shows, the safety margin on this item is simply too small. 
 
Upvote 0
"Windmeister"Obviously a loose screw have less strength than a tight torqued one. But lets examine the use of the two examples. In the lug nut scenario, the thing that holds your wheel on is the clamping force and resulting friction. On the rifle the grub screw is acting like a removable stop pin, and will always be subjected to shearing forces unlike the lug nut which would only be subjected to shearing forces if all lug nuts where slightly loose.
But yes, your point that a loose screw can withstand less shearing force than a torqued down one is true, but as the picture above shows, the safety margin on this item is simply too small.
Click to expand...
Agreed and I would bet at least 2 screws would be needed to meet the 3 to 1 safety margin
 
Upvote 0
"7deuce"This topic made me want to check the new one so I took comparison pics. The new one has seen about 600 shots so far. It looks like it's undamaged. I compared the two and the old one is shorter and possibly a different type of metal. 








Click to expand...
If the new screw is longer (maybe M3x8) and looks like is made with different metal then FX or AOA knows about this problem! Why not lets owners know and replace that screw before someone get seriously injured.
 
Upvote 0
Status
Not open for further replies.
Top Bottom
Back
Home
Forums
Resources
Menu