XS60C PCP Repeater project

[RMM]

Makes me feel good that when I receive my two 60's from Stalwart they are going to be engineered safe.  Keep up the good work gents. 

[stalwart]

Cut the first of the 2K protos... I'm really liking it. Solid. I'm rethinking all this, and given that with a bit more tooling, I can make them quickly enough to make the difference in my costs translate to a great value for the price... and the fact that at 2k, they can be real hitters if needed... they may be a permanent part of my eventual product line.

[PushingPELLETS]

Very good stalwart on the work everything you have been doing looks awesome I'm looking forward to packaging mine up to send for work going to be great

[stalwart]

Thanks, Chris.... welcome to GTA!

Guys, I have decided to go for ChroMoly tubes, across the product line. One of the things I wanted to do with these rifles was to make sure everything I sell can take an accidental overfill (max pressure possible... 4.5K) without danger to the operator. The design, in 1018 steel, can do that... but, would have to be inspected for malformation before refilling. However, in CrMoly...

"The CrMoly tubing is 3.7:1 to yield at 3000 psi.... Two 120K 5mm screws are 3.0:1 in shear (higher tensile would be greater) at 2000 psi.... but only 1.4:1 on bearing area in the tube itself (using just the screw shanks).... Add on the receiver thickness (0.055”?) and you’re at about 2.6:1 at 2000 psi for the bearing load, not an issue.... That would allow a 4500 psi overfill at a safety margin of 1.16:1.... probably just mark the holes from the threads...."

It will cost me (and therefore, you) a *few* more bucks, but I will sleep well knowing they have that margin between us and injury or damage. If you put 4.5K in, it will be up to you to figure out how to get the air back out (drift and big hammer?)... but, you can go right back to shooting the gun.

If anyone wants in on the first short run, holler soon. I will be cutting as soon as the materials and tools arrive. I'll be making only 6 in the first go around (and timing every pass).

[stalwart]

Not much I can add to this, except the R screws will definitely be set into the blocks. A few more bucks yields a 50% increase in margin:

"If you use screws that are 180K tensile, you have a 3:1 safety margin at 3000 psi in shear.... The front screw, with the shank through the tube and receiver, takes a load to yield of 618 lbs. in the tube, plus 332 lbs. in the receiver (based on aluminum at 0.055” thick), for a total of 950 lbs.... The rear screw, with a 5/16” head through the tube and receiver, takes a load to yield of 1278 lbs. in the tube, plus 686 lbs. in the receiver, for a total of 1964 lbs.... so the total for the two screws would be 2914 lbs.... The load at 2000 psi is 872 lbs., so the safety margin would be 3.3:1.... At 3000 psi, it would be 1308 lbs. load, so that is a safety margin of 2.2:1.... (With just the two shanks bearing against the tube and receiver, you have 1237 for the tube and 664 for the receiver, for a total of 1900 lbs.... The load at 2000 psi is 872 lbs, so the safety margin would be 2.2:1).... Setting the rear screw down so that the head takes the bearing load increases the safety factor by just over 50%....
 
Basically, if you use really good screws (180K minimum), and a good fit in both the tube and receiver (so the load is shared by both), the gun would be OK at 3000 psi, for the strength of the tube (3.7:1), the screws in shear (3:1), and even the bearing load (2.2:1).... At 2000 psi, it should be bulletproof, with all three factors being over 3:1.... This assumes a Disco fill fitting, if you use the XS fitting the limit is ~1500 psi / CO2 pressures...."

 

[rsterne]

Note, the key to the above numbers is that the tube and receiver act as one piece, so that the bearing loads of the screws is shared by the total thickness of both parts....

Bob

[stalwart]

[stalwart]

Here's the "twist". Took me quite a few tries, but I got a pic inside the receiver.

The tube threads into the receiver with a 12mm overlap, just behind the R screw. Nothing fancy.... but it's stout. The use of both good threads (past the pressurized area), and pinning with the screws are what gives this the strength.

[stalwart]

Bob... just for fun... how much could this tube take if we put them together with Loctite? We have 4.5" of well fitted overlap. Could we hang a bus from it?

[rsterne]

I don't have the data for steel to aluminum, but Loctite 638 is listed at 4500 psi shear strength for steel to steel.... You are talking over 12 sq.in., so in theory 55,000 lbs.... *LOL*.... Epoxies are typically 3000+ psi, the weakest Loctite I found was 1700 psi.... That is still over 20,000 lbs.... so, yeah, pretty much hang a bus on it.... Once you cover the tube with glue and screw it into the back of the receiver and it sets.... you can treat the assembly as one piece.... The valve screws then do all the work.... and you have more thickness for the screw heads to bear on than just the tube by itself, which is the really kewl part....

Actually, the load limit on pulling the tube out of the receiver will end up being the strength of the tube itself.... Using CrMoly, with a tensile of 97K, and the area of the tube, which is about 0.165 sq.in.... that works out to about 16,000 lbs. load before the tube will break....

Bob

[avator]

Bob... just for fun... how much could this tube take if we put them together with Loctite? We have 4.5" of well fitted overlap. Could we hang a bus from it?

Hey Bob...
Don't you just love how he uses you for his personal calculator..... j/k
You guys amaze me.

[rsterne]

awwwwwwwwww.... he knows what buttons to push is all.... *LOL*....

Bob

[stalwart]

Bob... just for fun... how much could this tube take if we put them together with Loctite? We have 4.5" of well fitted overlap. Could we hang a bus from it?

Hey Bob...
Don't you just love how he uses you for his personal calculator..... j/k
You guys amaze me.

LOL... if you think this is a long process already... without Bob, it would take years!

I've never pretended, even for a moment, that I would get anywhere without this help. Given the dangers if a mistake is made... I'd be afraid to try. You haven't seen the half of it.... I run every dumb idea past Bob, backstage. He's always been kind enough not to laugh (at least, not to my face).

[stalwart]

awwwwwwwwww.... he knows what buttons to push is all.... *LOL*....

Bob

For reasons I haven't quite figured out, you seem to be quite certain you don't want to see me blown up!

All I can say is "whew!".



I'm having so much fun... just love this place.

[avator]

I would give up all my worldly possessions to be able to walk around the shop and watch you guys do what you do.... ok that's a lie... I think I'd like to keep my Silver Streak.... and my Harley... and... and... oh nevermind, I'll just keep on reading about it.

[Sfttailrdr46]

  I think it is Bob's mission in life to drag us all up to his stratospheric level of air gun smarts And Yes Bill that makes two of us I'm convinced that the next time I retire I am going to take some math and mechanical engineering classes 

[avator]

LOL... funny thing is, a couple years ago I bought 5 B2-1 from a wholesale club. I built a spring compressor and took them apart. Filed a little here and sanded a little there, slopped on some heavy tar and moly paste. Painted them black, green, camo and even pink. I got them to shoot quarter size groups at 20 feet and I thought I was a master airgunist...... Thanks Bob and Erik, for poppin that balloon.

[Sfttailrdr46]

LOL... funny thing is, a couple years ago I bought 5 B2-1 from a wholesale club. I built a spring compressor and took them apart. Filed a little here and sanded a little there, slopped on some heavy tar and moly paste. Painted them black, green, camo and even pink. I got them to shoot quarter size groups at 20 feet and I thought I was a master airgunist...... Thanks Bob and Erik, for poppin that balloon.

Bill I remember those posts has it been that long? Yes Bob's esoteric studies tend to leave me scratching my head for at least 2 or 3 readings then I sort of understand kinda 

[avator]

Yep, I think it's been right about 2 years.....
I think I've even thanked Bob a time or 2 for toning things down a bit so I could understand. More often than not, his answers leave me with more questions.

[rsterne]

The kewl thing is I'm still learning.... Somebody asked me today about lightening a hammer to reduce bounce, which led me to explain that hammers always bounced the only bounces that were important were ones that waste air.... which led to talking about plenum size, and then the light went on and I realized that small plenums were more prone to hammer bounce.... Bear with me.... The smaller the plenum is, the more the pressure drops during the shot.... because the regulator can't top the pressure up fast enough.... The more the pressure drops, the easier the valve is to smack open a second time.... Therefore, take two identical guns, one with a larger plenum, and tune them for the same FPE.... The smaller plenum is not only less efficient because the pressure drops faster, that pressure drop also means it is more susceptible to air-wasting hammer bounce.... which amounts to a double whammy on efficiency.... It also means that if you skimp on the plenum, you have to be more concerned about eliminating bounce.... Perhaps this is why guys running minimal plenums tend to use light hammers.... because they have to?....

We now return to our regular insanity errrrrr program....

Bob