XS60C PCP Repeater project

[rsterne]

Makes perfect sense.... If the receiver is on the large side, and the tube in question on the small side, it is a disaster waiting to happen.... Well in this case it didn't wait, I guess, fortunately nobody was hurt.... It makes me glad my FD-PCP has nicely fitting threads, as most probably do.... It also makes me glad the Grizzly has the Thru-tube conversion....

Bob

[Kailua]

Great insight Eric.
So I guess if a threaded tube has some movement it should set off an alarm.
I will need to do some checking.
thanks

[stalwart]

If the tube can still be rocked after about 4-5 turns in, they are already out of quality tolerances. I suspect the enormous amount of part overlap was designed in just to overcome production tolerances.

I'd pay to own that tube. There is a lot of "good" threads left in that receiver. I hope they find it.

[rsterne]

Agreed, the threads are extremely long (3/4"+), if the tube has a lot of movement when fully engaged, something is amiss.... Alarm bells should be ringing at that point.... My son's FD-PCP tube wobbles about 1/10" sideways at the front end when fully engaged, but not tightened against the seal.... loose to be sure, but not enough to worry me....

Bob

[clgraham82]

I degassed and took my .177 apart tonight and the tube wobbles when tightened down but no movement when the flat oring/seal is removed.  It will remain in parts!

[stalwart]

I degassed and took my .177 apart tonight and the tube wobbles when tightened down but no movement when the flat oring/seal is removed.  It will remain in parts!

That's the smart move, unless you are willing to have a new tube cut with an adjustable die, so it can be properly fitted.

edit: Should have looked at your list.

[clgraham82]

I degassed and took my .177 apart tonight and the tube wobbles when tightened down but no movement when the flat oring/seal is removed.  It will remain in parts!

That's the smart move, unless you are willing to have a new tube cut with an adjustable die, so it can be properly fitted.

Is yours an FDPCP, or does it have the stock tube?

It's the FDPCP.

[stalwart]

Thanks for the response... I didn't look at your list.

YGPM

[rsterne]

Eric, it's nice that you have an adjustable die, and a tap to chase the threads, and can supply custom fitted tubes if someone has an oversize receiver.... No reason to scrap a gun that isn't too far out of spec when it just might need a new tube, as I know you have lots of that handy.... Of course if the receiver is way oversize, like you say, it just becomes a candidate for the thru-tube setup....

Bob

[stalwart]

The 2 things that DQ a receiver here are the threads and the extrusion flaw inside at the valve seal. Of those, the flaw is far more often seen. As I posted a long time ago, many of them can be reamed out nicely, keeping the threaded tube... so, there aren't a lot of either DQed here now. I will be reaming out perfectly good receivers for 4.5K, soon.

To properly make precise threads in this stuff takes work. As the tube is oversize OD, it has to be turned down to the receiver's ID, before cutting even begins. If the die is forced to reduce the OD, the effect of "rolling" the excess ahead of the cut is tearing good metal loose, and flowing the now weak metal into the thread's peaks... . This, along with chips rolling under (if the cut isn't reversed regularly, to clear them), can even create what looks like saw teeth along the peaks. They are weak... very weak. At least, that was what I was taught...

The cost of making a fitted tube is high enough here that I have been working toward, and spending some good money on, simply reducing the cost of thru-tubes. I'm getting close enough to a quality threaded tube's cost that I'm planning to ditch the threads for good. At that point, it will either be CO2... or 4.5K... and I'll cheerfully lose some part #s.

[QVTom]

Eric your are correct about making a quality thread is work and what you describe is accurate.  Generally speaking dies are not full profile, meaning they do not cut the crest of the thread but there are exceptions.

Automated threads can be cut with die heads that are progressive.   The first tooth will take a small cut then the next tooth will take a bigger bite and the root depth is usually reach by the 4th tooth.  This prevents all the bad things you described provided the part is cut to the correct major diameter before threading.

Precision threads are usually cut with a single point full profile tool.  Cut depth is progressively deeper using multiple passes.

Tom

[rsterne]

So that means that if a 7/8" (0.875") tube was not turned down prior to threading with a 22 mm (0.866") die the results may not be good....

Bob

[moorepower]

3' of .065 4130 is about $35 shipped. Ream the receiver, cut the slots, and drill the holes, add 2 high strength #10 screws to the valve and you have a 3000psi. gun. ..... And the square o-ring will never leak again, cause it's gone.

[RHytonen]

3' of .065 4130 is about $35 shipped. Ream the receiver, cut the slots, and drill the holes, add 2 high strength #10 screws to the valve and you have a 3000psi. gun. ..... And the square o-ring will never leak again, cause it's gone.

...and make a new "plug"....

[rsterne]

Correct, you also need to deal with the front fill fitting, because the retaining nut/ring on the standard setup is for CO2 pressures only (<1800 psi).... Same applies to the QB78.... The easiest is to thread the tube internally and use a Disco fill fitting....

Bob

[avator]

Correct, you also need to deal with the front fill fitting, because the retaining nut/ring on the standard setup is for CO2 pressures only (<1800 psi).... Same applies to the QB78.... The easiest is to thread the tube internally and use a Disco fill fitting....

Bob

Thank you Bob. This is the first thing I thought of when I read his post. If the threads are the weak points then we need to address both ends of the tube.

[moorepower]

I was figuring a P-Rod front plug. They might be the same part for all I know.

[rsterne]

Properly made, in-spec. threads are fine, but much better of course if the thinner tube wall remaining is not pressurized.... ie the seal is inboard of them.... However, the retaining nut/ring on the front of the XS-60c and QB78 tubes has a rather thin flange on the end that takes all the end load, too thin to use at over ~1800 psi and still have a proper safety margin.... QVTom ran a Finite Element Analysis on it and what he saw concerned him greatly.... It would certainly be possible to make a new nut, out of better material and/or with larger dimensions.... but not a good idea to use the stock one on HPA without a 1.8K burst disc installed....

Bob

[stalwart]

3' of .065 4130 is about $35 shipped. Ream the receiver, cut the slots, and drill the holes, add 2 high strength #10 screws to the valve and you have a 3000psi. gun. ..... And the square o-ring will never leak again, cause it's gone.

Pat, read back a bit.... it's all been figured out, the math has all been checked, and the prototyping is done. I'm currently trying to reduce my costs, to pass the savings on. As you made clear in the explosion thread, you plan to make your own thru-tubes... and that's fine... but, please do so on your own thread. At this point, especially considering the time I spent with you, building your dream 60 (27 emails??)... and considering that when it came time to actually pay me, and start the project.... you vanished... I'm not really interested in teaching you any more about how to take food off of my plate.

[rsterne]

Well stated, Eric....

Bob