Author Topic: XS60C PCP Repeater project (Read 455662 times))

stalwart · « **Reply #1280 on:** December 22, 2015, 02:57:12 PM »

I'll bet your receiver looks a lot like the ones I'll be using. They'll be perfect... glad I didn't pitch mine out (pack rat wins again!). Thanks, Ron. The FDPCP you sent is coded "DT1", in case you want to cheer on it's destruction. It has .017" engagement (.034 difference).

Given some time, I could easily reproduce some pretty bad fits, and try them.

Gertrude · « **Reply #1281 on:** December 22, 2015, 03:07:23 PM »

Quote from: stalwart on December 22, 2015, 02:57:12 PM

The FDPCP ~~you~~ Santa Clause sent is coded "DT1", in case you want to cheer on it's destruction.

AHEM,...

Above quote Edited by Moderator for ACCURACY !

( I'm confident Santa will be watching with great interest ! )

stalwart · « **Reply #1282 on:** December 22, 2015, 03:11:07 PM »

Gotta love that guy! He doesn't ever send me what I think I want.... but, always knows what I need!

stalwart · « **Reply #1283 on:** December 22, 2015, 03:19:47 PM »

BTW... DT2 (FDPCP, as delivered) has only .0095" engagement. The tube rocks even when sealed.

Sfttailrdr46 · « **Reply #1284 on:** December 22, 2015, 03:49:16 PM »

Quote from: stalwart on December 22, 2015, 03:19:47 PM

BTW... DT2 (FDPCP, as delivered) has only .0095" engagement. The tube rocks even when sealed.

that will give us a worst case test right out of the gate awesome

stalwart · « **Reply #1285 on:** December 22, 2015, 04:44:19 PM »

Yup. If not the worst, it is certainly close enough for our purposes.

I'm just glad the thing is out of service.

Guys, I'm not here to make judgements on specs... my task is to provide numbers as clean and accurate as possible... the Big Dogs here can give us the concise determinations... but, I have to say this: Unless your tube can't be rocked after about 6 turns in, you NEED to know the numbers. And, it is not costly or difficult to get them.

Think about it. A cheap set of calipers will give you all you need... even if they are not "dead nuts" capable. If you measure both the ID of the receiver and the OD of the tube with the same undamaged calipers, you have the difference... that's the only number you need to be accurate. You're using the same area of the caliper's scale for both measurements... and if it somehow reads .005 high (for example), it will read both .005 high... and the difference remains the same.

And, I promise you, if you buy a set you will never regret it. Until you own a set, you have no idea how many times it will come in handy.

vigilandy · « **Reply #1286 on:** December 22, 2015, 05:18:02 PM »

Where's the emoticon for cheering?

Thank you Eric (stalwart) for taking this on! I'm looking forward to your results and potential solutions.

rsterne · « **Reply #1287 on:** December 22, 2015, 06:45:20 PM »

I'll be watching these tests with interest.... My son's FD-PCP is barely within specs, with a difference of 0.028" (an engagement of 0.014").... According to the tolerances I found, using the minimum tube OD (0.8580") and the maximum receiver ID (0.8328"), that works out to a difference of 0.0252" (an engagement of 0.0126").... Doing the opposite, with the maximum tube OD (0.8651") and the minimum receiver ID (0.8235"), works out to a difference of 0.0416" (an engagement of 0.0208").... Certainly an engagement of only 0.0095" is way below specified tolerances....

The thing we can't easily measure with calipers is the remaining thickness of the tube wall between the valley of the threads on the tube and the ID of the tube.... If, in fact, the failure was a "spiral failure" following the bottom of the threads in the tube, the OD of the tube could provide a clue if that was likely to happen.... but not definitive proof.... I will be more interested in seeing if any of the failures occur leaving the receiver threads mostly intact and a long spring hanging off the end of the tube.... I wonder if because the water can't expand when the pressure is released if all we will see is a crack (leak) in the tube, at the bottom of the threads, immediately outboard of the receiver....

Bob

stalwart · « **Reply #1288 on:** December 22, 2015, 06:59:42 PM »

Quote from: vigilandy on December 22, 2015, 05:18:02 PM

Where's the emoticon for cheering?

Thank you Eric (stalwart) for taking this on! I'm looking forward to your results and potential solutions.

It's my pleasure, Andy. The newer guns have much tighter tolerances (LOVE my Fusions), but I will always have a soft spot for the runts (Gen1). We need to get them back out there to be beaten (or modded) to death.

Bob, if I made a slug that replaced the valve, and extended it back to include the back mount screws, would that protect the holes enough that we could blow the tube threads out without damaging anything else (allowing a quick 3K conversion afterwards)? That would let me test a bunch of variables without losing a receiver (stretched holes) each time.

stalwart · « **Reply #1289 on:** December 22, 2015, 07:11:36 PM »

BTW... ebay has digital calipers for as low as $5.

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_sop=15&_nkw=digital+caliper&rt=nc&LH_BIN=1

rsterne · « **Reply #1290 on:** December 22, 2015, 07:41:10 PM »

The more screws you pick up with your blanking plug, the less likely to stretch the holes in a receiver.... but you DO need to test one with stock valve screws and a pretty good tube (the one with the 0.017" engagement?) to find out what fails first.... After all, we have no idea what quality those two 5mm screws that hold the valve and backing block are made of, and I was never very happy with those.... The tube threads failing was never really on my radar initially, because I had always assumed them to be within tolerance, and the engagement is huge.... My greatest concerns were for the screws and the reduced tube wall where the threaded portion exits the receiver.... Check out my original post on this matter, from Feb. 21, 2014, Reply #4 in this thread.... http://www.gatewaytoairguns.org/GTA/index.php?topic=62302.0 .... Note that I also missed picking up on the thickness of the flange on the nut retaining the fill fitting, which QVTom suggested was marginal at over (hot) CO2 pressures.... It would be great if you can quantify the failure points of all those items....

Bob

stalwart · « **Reply #1291 on:** December 22, 2015, 08:20:09 PM »

Any FDPCPs sent complete will be stripped to the pressure vessel and tested as delivered. I haven't even touched the screws.

I have also been sent FD tubes. I'm thinking of testing them, using receivers I have slated for 3K conversions, for more data on fit vs strength. I could match them up to any overlap you could imagine... down to nearly zero...lol.

rsterne · « **Reply #1292 on:** December 22, 2015, 09:12:44 PM »

I did a quick drawing for standard ISO Metric threads.... Assuming threads are properly shaped, and perfectly formed (and we know they are not) a set to the tightest tolerance has a shear plane of half the circumference of the pitch circle times the depth of thread engagement.... Using the loosest tolerances listed, the engagement is ~60% of the maximum.... and the shear plane is reduced to ~75% of theoretical.... ie each thread has only 3/4 of the material in shear.... If the threads are more "pointed" it could be even less.... What this means is, that if both tube and receiver were the same material (they aren't), then at best case, a tube/receiver combo on the minimum overlap (0.0126") would be 25% weaker than one at the maximum overlap (0.0208").... The threads are still amazingly strong, particularly considering how loose they are, even at the loosest tolerance specified....

This calculation leads me to suspect even more the wall thickness below the valleys of the threads in the tube as the failure point.... a "spiral" failure....

Bob

rsterne · « **Reply #1293 on:** December 22, 2015, 11:51:17 PM »

Here is a drawing of 22mm x 1mm threads, to scale, as cut into a 0.875" OD x 0.065" wall tube.... The upper horizontal dotted line is where the outer wall would be, if it were not threaded.... The lower horizontal line is the inner wall of the tube....

The black zig-zag line represents both the maximum tolerance for the tube threads and the minimum tolerance for the receiver threads.... They actually clear by a thou or so, but the lines would be superimposed, so I only used one line.... The short horizontal dotted line across the thread is at the pitch diameter, and represents the total shear plane, and therefore the strength of the threads.... It is 0.040" long, half on the tube and half in the receiver....

The Blue zig-zag line represents the minimum tolerance for the tube.... The Red zig-zag line is the maximum tolerance for the receiver.... The short horizontal lines are the shear plane for those, and is a total of 0.029".... You can visually see the gap in the threads which causes the wiggle in the tube, and the roughly 27% loss in shear area that results, even if both components are within tolerance....

The lower dimensions show the thickness of tube wall remaining if perfectly formed threads are cut in the tube.... It is actually slightly less than that, because there is usually a slight radius at the bottom of the valley of the threads.... For a tube with maximum size threads, the wall thickness will be less than 0.039" instead of 0.065".... For a tube with threads at the minimum tolerance, the thickness of the remaining tube will be half what it started at.... If the threads are cut with a pointed threading tool, that comes down to only 0.026"..... It the threads are also pointed on the top, for a tube where the thread OD is right on the minimum tolerance, it could be even less.... For a tube that measures smaller than the minimum tolerance, depending on the shape of the threads, it is quite possible that less than a third of the original tube wall remains.... Of course the reduced overlap would also reduce the amount of material in shear as well....

Please note I am not stating that these conditions exist, or who is responsible for them being that way.... I am only showing you what the threads look like, drawn to scale, on a tube wall of 0.065".... I hope it will give you a visual representation of what the concern is, and why.... I can't state a maximum safe working pressure for the FD-PCP tube is we have no idea what the material is (despite asking Mike numerous times).... A 0.875" OD x 0.065" wall DOM tube made from 1018 steel would have more than a 3:1 safety margin at 3000 psi.... If the wall is a third of that, well you do the math.... Then add stress risers at the sharp corner at the bottom of the threads, and the possibility of striking the pressurized tube when handling the gun (or falling on it) adding more stress to the metal.... well, you get the idea....

Bob

stalwart · « **Reply #1294 on:** December 23, 2015, 06:42:19 PM »

Well, heck!

The last fitting came today, I set it up to pressure test.... and it leaks (weeps, given time. Loses about 100psi per min starting at 9K). Not a lot, but enough that leaving it alone for a while, under pressure, made a nice little mess.

Also, to get the pressure to even 9K requires quite a serious push on the pump handle. I may need to make a longer handle (or, with a rat trap bicycle pedal?)... and a base so that handle doesn't try to flip the pump in use at 15k (gauge limit).

I have decided to make my own stuff.... with good overlap. I changed my mind about feeding from the fill fitting end, and will make an adapter that replaces the valve... which will allow testing the entire system from the foster fitting back.

I'm going to have a lot of time into this before I get to blow anything up... so... I want to blow up everything I can get my hands on. Bring 'em on.

I'm off to enjoy the holiday... Merry Christmas, guys! We'll be roaching guns in '16!

stalwart · « **Reply #1295 on:** December 26, 2015, 09:09:25 PM »

1144 steel, with enough meat to put screw holes for a bunch of different patterns. I'll set it up to test the stock pattern, my 3K and 4.5K designs... and there is enough left to set it up for any other 3/4" patterns (Ron's?).

stalwart · « **Reply #1296 on:** December 27, 2015, 01:06:12 AM »

Well, I just blew something up.

I was using the QD fitting to block off the pump while I took it to 15K, to see if I had to make the handle longer... or, if I could just step on it. Stepping on it works, and I left it pressurized... for about 5 seconds...

The ring blew out in the fitting. Made a cloud of mist about the size of a basketball, and a fairly loud pop. No fireball, no shock wave, no shrapnel (half of the ring is sticking out of the nose).

Now I'm afraid the movies are going to be pretty dull.

rsterne · « **Reply #1297 on:** December 27, 2015, 01:11:29 AM »

You blew up a QD Fitting?.... guess you won't be using those for testing, HUH?.... *LOL*....

Bob

stalwart · « **Reply #1298 on:** December 27, 2015, 01:39:36 AM »

No. LOL... looks like it's going to have to be 1 piece. That's OK, it is a dedicated rig... but, I'm now going to mount the gauge to the pump, instead of the probe. If I don't, I will end up smashing it.

The good news is that the pump and the hose are 15K ready. I'll be able to take the 4.5Ks to 3:1... that was all I needed.

I'm a happy guy, with 1 very shiny shoe.

Sfttailrdr46 · « **Reply #1299 on:** December 27, 2015, 01:59:48 AM »

This place is always an adventure and sometimes it is fun to read about the missteps as long as nobody gets hurt. So now you have a waterproof shoe which isn't all bad either that way when you leak on your shoe your sock will not get wet.

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XS60C PCP Repeater project

Author Topic: XS60C PCP Repeater project (Read 455662 times))