Author Topic: Tale of THREE BRods - .25, .30 and .357 Completed, Page 12 !  (Read 18417 times)

rsterne

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Re: Tale of Two BRods
« Reply #135 on: March 25, 2018, 09:54:23 AM »
Now that I have proved it can be done.... some enterprising guy (like Lloyd did with his .30 cal conversion) could make new wheels, fit them with the appropriate spring, remachine the housing and cover plate (or make a new cover plate) and supply a .35 cal conversion mag. for the MRods.... It won't take a very long bullet, but I think will cover all the weights necessary for a modified MRod.... It will accept the JSB pellets, the EPP-UG, or my 109 gr. BBT, and likely a few others.... If a new cover plate was made with a groove machined in it, and/or the groove in the front of the housing widened, slightly longer bullets could be accommodated....

Certainly it would serve the purpose of having a .35 cal MRod repeater.... It would be a good idea to upgrade the bolt locking lug to stand the much increased force on the bolt from the larger bore.... but that can be done by going to a 10-32 from the stock 8-32....

Bob
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Re: Tale of Two BRods
« Reply #136 on: June 28, 2018, 12:24:33 PM »
I cast up the new NOE pellets today.... The mould comes with 4 sets of RG base pins, and they produce 3 skirted pellets and one solid with a flat base.... They look like this....



The weights in 40:1 lead/tin alloy are 35.0, 37.0, 38.5 and 42.6 gr.... They all chamber perfectly in my .25 cal LW Polygonal barrel, but that is not surprising as I cut the chamber to allow for bullets as well as pellets.... I have my BRod set up with a Cothran valve and the WAR adjustable regulated tank block, set at 1900 psi.... I checked the velocity of all 5 pellets (including the JSBs) and got the following averages for one 8-shot magazine of each....

34.1 gr. JSB = 947 fps (67.9 FPE)
35.0 gr. NOE = 937 fps (68.3 FPE)
37.0 gr. NOE = 919 fps (69.4 FPE)
38.5 gr. NOE = 906 fps (70.2 FPE)
42.6 gr. NOE = 871 fps (71.8 FPE)

I was only shooting inside my shop, with the backstop 20 feet away, and all groups were one ragged hole, with no real difference between any of the pellets.... That is encouraging, because some pellets or bullets can't do that when shooting through the Chrony at that distance.... and those that do usually shoot pretty good at least out to 50 yards....

My summer is taken up with sitting at the Motel reception desk waiting for guests, and we are entering our busiest season now, so it is unlikely I will get to try these at distance any time soon.... but the velocity and energy is right where I want it for testing.... I can't wait....

Bob
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Monkeydad1969

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Re: Tale of Two BRods
« Reply #137 on: June 29, 2018, 05:17:15 AM »
They look good Bob.  Hopefully you'll possibly get a lull in the action at the front desk. Lol

Joe
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rsterne

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Re: Tale of Two BRods
« Reply #138 on: July 03, 2018, 03:02:06 PM »
My parts came in today from Joe at DiscosRUs, and I didn't waste any time whacking the front off the Gen2 MRod stock and grinding it out to fit over the WAR tank block.... Here is what it looks like with the Gen2 trigger installed also, plus a 500 cc 3000 psi aluminum bottle....



I left the stock long enough to cover the tank block and the bonnet section of the regulator.... There is a bulkhead in the stock JUST in front of the front of the tank block when it is mounted in a WAR tube, so about 3/4" ahead of that is where I made the initial cut, and then ground it to fit with my Dremel....

I also purchased a .25 cal MRod receiver and bolt, which I will be modifying as before to fit the .357 cal TJ's 26" twist barrel I have, with a high-modulas CF sleeve glued over it to stiffen it, like I did with the .30 cal barrel.... I already have a modified .25 cal MRod magazine which will give me a 6-shot .357 cal repeater when it is all together.... I probably won't get much done before the winter, but at least I now have all the parts, other than the valve and hammer which I have to make....

Bob
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Monkeydad1969

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Re: Tale of Two BRods
« Reply #139 on: July 03, 2018, 03:29:39 PM »
Keep it coming, Bob.  Looking good.

Joe
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rsterne

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Re: Tale of Two BRods
« Reply #140 on: November 18, 2018, 03:32:38 PM »
Well, the Motel busy season is over for another year, and it's time to hit the shop again.... As promised, the first order of business is to do a .357 version of my BRods…. The parts have been sitting on my bench gathering dust since the Spring.... it's been so long I had to sit down and think about where to start....  ::)

I decided to bore out the receiver for the 0.640" OD Hi-Mod Carbon tubing I used for the sleeve on the .30 cal TJ's barrel, as the .357 liner I have is the same 1/2" OD.... I had a hard time trying to drill it straight, for some reason this receiver just didn't want to run straight in my 4-jaw chuck.... so I drilled it undersize and then held it in my milling attachment, set it up with the bore of the receiver parallel to the ways and lathe C/L, and then used a 5/8" end mill to straighten the hole and move it over so that it lined up with the original 1/2" bore of the receiver.... It took a lot of fiddling, but the result was great, the outer sleeve and the barrel liner both slide into place perfectly.... The counterbored hole for the sleeve is 1.400" deep, so it stops just short of the 4-40 screw holes in the front of the receiver....

I then mounted the receiver across the lathe, in the milling attachment, and centered off the transfer port hole, drilled it out to 9/32" (0.281"), and counterbored it 3/8" x 0.150" deep for the transfer port.... That leaves 0.100" of receiver below the barrel, so the Teflon transfer port will seal against that shoulder with a slight amount of compression against that and the valve.... Travis assures me that you don't need to seal the transfer port against the actual barrel, that the set screw in the receiver that is directly above the barrel port pushes the barrel down against the receiver tight enough to seal OK.... I sure hope he's right about that, as there really isn't enough barrel wall to mill a 3/8" OD flat without hitting the bore.... A .357 barrel with a 1/2" OD only has a 0.070" wall thickness, which is one of the reasons for using the High Modulas CF tubing, to get the greatest stiffness possible for the barrel.... Here is what the receiver looks like at the moment....



The Teflon transfer port will be 3/8" OD x 9/32" ID.... I chose that port diameter because it is 79% of the caliber, which means I don't have to mill an oblong barrel port, I can just drill it.... It should be plenty big for a pellet shooter, IMO.... The plan is to build my own SS valve, with a matching exhaust port, and I'm going to try for a 0.323" throat on the valve (a size "P" drill), which with a 1/8" stem will give be about 12% more throat area than port area.... Using a 3/8" OD PEEK poppet I will have a 0.026" seat margin, which should work OK.... That will allow me to build the same "guts" for this valve as I did for my 6 mm and .257 valves last winter.... which will reduce the development time....

I'm looking forward to progressing on this build as time permits.... It certainly feels good to get back in the shop again.... It's been a loonnngggg summer.... ::)

Bob
« Last Edit: November 18, 2018, 08:13:04 PM by rsterne »
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Re: Tale of Two BRods
« Reply #141 on: November 18, 2018, 10:15:23 PM »
Bob,
good to hear your back in the "Cold" shop once again .... watching this build progress  8)
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rsterne

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Re: Tale of Two BRods
« Reply #142 on: November 19, 2018, 04:59:19 PM »
Two shop days in a row!.... WOO HOO !!!

Today I modified the .25 cal MRod bolt for this .357 cal build.... Two things had to change, the diameter of the bolt and probe, and the size of the lockup pin.... Crosman use an 8-32 SHCS for the bolt lockup in the .25 cal, and at the same pressure the .357 bolt will have twice the load on it.... Through the threads (the weakest point), a 10-32 has about 50% more shear strength of an 8-32, and I will be using only about 2200 psi instead of 3000, so that is what I used.... The bolt is hardened, so I had to heat it to cherry red and let it cool slowly to anneal it.... Once annealed, I could drill and tap the hole out to 10-32 and mill a 1/4" flat for the head to tighten against, and I made a new locking pin from a 1/2" long SHCS with a nut screwed tight against the head to lengthen it.... I turned the head and nut down to 1/4" OD, and shortened it slightly so that it doesn't rub on the tube when the receiver is installed....

To make the larger probe, I used a piece of 3/8" CRS, and drilled it 1/4" to a depth of 3/4" and then shortened the stub of the bolt so that it just slid in full depth.... The OD of the new bolt nose was turned down to 0.356", and I made a longer probe that is 0.125" diameter (which just fits inside a JSB pellet) of the correct length to load the back of the skirt just ahead of the barrel port.... The shoulder between the two diameters I made a 20 deg. taper, which I figured won't restrict the flow, and will slightly reduce the chamber volume behind the pellet.... After taking the photo below of the parts, I installed the new bolt nose with permanent Loctite 638 (green)….



The cocking slot in the receiver needed to be widened a bit for the larger pin, and because I use an 8-32 SHCS as my hammer pin.... The front of the slot on the left side also needed machining wider and deeper, to allow the bigger lock pin to properly lock up the bolt.... You can see those mods in the photo below....



The other job I did today was to shorten the barrel and ream a new chamber.... The barrel was previously used in another receiver, but the barrel port position would not work for this build.... I already had a chamber reamer, so all I had to do was stone the cutting edge with a fine grit diamond file and cut the chamber deeper.... I left the barrel in the lathe because tomorrow I will cut the O-ring groove to seal the bolt before removing it from the chuck.... The photo below shows the completed .357 cal MRod bolt, the chamber reamer, and the tool I will use to cut the groove for the 1 mm x 9 mm O-ring....



With a little luck, I will have the machining done on the barrel tomorrow, including the new barrel port, and be ready to glue on the carbon fibre sleeve....

Bob
« Last Edit: November 19, 2018, 05:44:01 PM by rsterne »
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rsterne

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Re: Tale of THREE BRods - Adding a .357 Version
« Reply #143 on: November 20, 2018, 08:27:36 PM »
Today I finished off the barrel by machining the O-ring groove, drilling the barrel port, and gluing on the CF sleeve.... Here is what the breech end looks like now....



That 9/32" barrel port is pretty huge, and you can see how thin the barrel wall is with a 1/2" OD and a .357 bore.... I had to sand the outside of the CF sleeve slightly to get a nice slide fit inside the receiver, it was just a bit too snug.... There isn't a lot of room between the barrel port and the back of the barrel, another reason I had to use a tiny 1 mm CS O-ring for the breech seal.... I tried the bolt with the barrel installed in the receiver, and it slides into battery perfectly.... It loads a 78 gr. JSB pellet (which has a slightly deeper base cavity than the current 81 gr. version) nicely past the front of the barrel port.... It should also work perfectly with the new NOE Magnum Hunter pellet with the medium base pin (86 gr.).... The skirt of an 81 gr. EunJin pellet does not quite load past the front of the barrel port, so neither would the 81 gr. version of the NOE pellet which uses the deepest base pin.... I could not use a longer loading probe or it would not retract far enough to clear the mag. well.... This .357 build is really pushing the limits of an MRod receiver, the tolerances are virtually non-existent....

Before assembly with the Loctite 638 I sanded the outside of the barrel and the inside of the carbon tube with 100 grit to give them both some "tooth".... I had a nice slide fit, the barrel fell through the sleeve under its own weight.... Tomorrow, after the initial 24 hr. cure at room temperature, I will give the Loctite a post cure at 175*F for 3 hours.... Loctite is designed primarily for gluing metal, and this post cure makes a huge difference in the bond strength to a non-metallic sleeve.... Cured 638 has a shear strength of 4500 psi, which rivals the best epoxies.... While the barrel is curing I plan to make the new rear tube plug and SSG....

Bob

« Last Edit: November 20, 2018, 08:34:37 PM by rsterne »
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Alan

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Re: Tale of THREE BRods - Adding a .357 Version
« Reply #144 on: November 21, 2018, 04:50:03 AM »
No photo!
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rsterne

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Re: Tale of THREE BRods - Adding a .357 Version
« Reply #145 on: November 21, 2018, 08:41:47 AM »
Photobucket was having problems yesterday, I had to wait to upload the photo.... It is working for me, and probably will for you the next time you look....

Bob
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rsterne

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Re: Tale of THREE BRods - Adding a .357 Version
« Reply #146 on: November 21, 2018, 04:26:39 PM »
This afternoon I finished fitting the barrel to the receiver, adjusting the length of the back of the sleeve to stop the barrel in the correct place for the magazine to fit properly.... I use a 1/2" ID O-ring slid over the barrel against the end of the CF sleeve to provide a bit of resistance, so that I have to push it hard into the receiver to seat it, compressing the O-ring.... It will also seal the barrel to the receiver, should there be any slight leak between the barrel port and receiver port.... That won't help much, as any leak will be directed back towards the magazine, but it can't hurt.... I drilled a hole through the carbon fibre sleeve so that the front setscrew tightens against the steel barrel liner.... After fitting the barrel I fed one pellet from my modified MRod magazine into the barrel, and it worked perfectly.... You could feel a bit of resistance the last 1/8" as the pellet engaged the rifling.... Here is what the pellet looked like when pushed back out through the breech....



You can see that the head of the pellet nicely engraves from the lands, but the skirt stops in the parallel portion of the chamber, as intended.... The next job was to make a new rear plug for the tube to hold the SSG I will be making.... This was an exact copy of the one I made for the .30 cal.... Here is a photo.... The bottom grooves are air vents to prevent any vacuum building up behind the hammer on firing....



Tonight, after dinner, I will post cure the Loctite 638, and tomorrow I should be ready to install the barrel in the receiver.... That will complete the work on the .357 upper.... I still have to make a new SS valve, hammer and SSG for this build.... but I am very pleased with the progress so far....

Bob
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rsterne

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Re: Tale of THREE BRods - Adding a .357 Version
« Reply #147 on: November 22, 2018, 03:43:26 PM »
I installed the barrel in the receiver today, and then made a transfer port with a 9/32" ID from a short piece of 3/8" Teflon rod.... I made it to fit the .30 cal lower and accept the .357 cal upper, just for testing purposes.... It sealed up perfectly, and I am delighted to say that Travis was right, it didn't need to seal to the barrel, just between the receiver and valve.... The pressure of the setscrew in the MRod receiver directly over the barrel port presses it down hard enough against the receiver that it doesn't leak when firing, even at 2900 psi.... The valve in the .30 cal lower is an ART-SS Valve with a 0.257" exhaust port, one of the early ones with the 1/4" small end on the poppet, and I am running it with the stock inlet jet, which I believe is a #87.5, or about 0.035".... I have a 51 gr. MDS hammer in place, and the SSG is equipped with an 8 lb/in. spring, with 0.37" of preload (3 lbs)…. Here is what the .30 cal BRod looks like with the .35 cal upper in place....



I tethered the gun at both 1900 psi and 2900 psi, and tested 3 different pellets, all of nearly the same weight, a 77.5 gr. EunJin, the 78.0 gr. JSB (no longer made) and the newer 81.0 gr. JSBs.... At 2900 psi I also tested a 119 gr. BBT-HP and a Lee 154 gr. RF.... The EunJins were indistinguishable from the 78 gr. JSBs, so they are not graphed in the chart below.... The dotted lines are at 1900 psi....



At 1900 psi the velocity is nearly maxed out with a slight gap in the SSG (shown as "0"), so the hammer and spring combination is usable as is.... At 2900 psi the velocity increases somewhat with preload on the spring.... With negative 2 turns of gap (about 4 lbs. of preload on the valve stem) the velocity increases 5% with the pellets and about 10% with the bullets.... so either more spring preload on the SSG or a heavier hammer spring would be necessary to allow proper tuning at that pressure.... Since this is just a preliminary test, with a valve I won't be using, I didn't bother making either change, but it shows what the FPE is that is available with a valve with 1/4" porting and a plenum volume of about 85 cc.... With these results, I feel that the plenum is a bit too small for a .35 cal, there is simply too much barrel volume relative to the plenum volume, and this is limiting the FPE.... On this .357 cal, the plenum volume is less than twice the barrel volume.... On the .30 cal it is nearly 3 times the barrel volume, and in .25 cal it is over 4 times the barrel volume....

I got the following results, testing with this valve....

At 1900 psi
77.5 gr. to 81.0 gr. pellets = 131 FPE Maximum.... 125 FPE with a slight SSG gap

At 2900 psi
77.5 gr. to 78.0 gr. pellets = 173 FPE Maximum.... 158 FPE with a slight SSG gap
81.0 gr. pellets = 176 FPE Maximum.... 162 FPE with a slight SSG gap
119 gr. BBT-HP = 191 FPE Maximum.... 161 FPE with a slight SSG gap
154 gr. Lee RF = 194 FPE Maximum....

As a comparison, I previously used this barrel (though 1" longer) on my Disco Double, running a Cothran valve at 2900 psi.... The Disco Double, however, has a 135 cc plenum.... Here were the results tethered at 2900 psi....

78.0 gr. JSBs = 172 FPE.... and at 1900 psi = 132 FPE
127 gr. BBT-FN = 206 FPE
154 gr. Lee RF = 219 FPE

As you can see, the results with pellets are virtually identical.... However, with bullets, the Cothran valve was able to produce a bit more FPE, but that is probably due to the 60% larger plenum volume.... I am hoping that when I make a new SS valve with a larger throat and ports I can pick up a bit more FPE.... However, that 85 cc Plenum will continue to be a limiting factor to the FPE....

Bob
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rsterne

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Re: Tale of THREE BRods - Adding a .357 Version
« Reply #148 on: November 23, 2018, 03:53:33 PM »
Today I started working on an SS Valve for the .357 BRod…. I couldn't start with an MRod valve unless I wanted to add a longer seat, because the 9/32" port I want would destroy the valve seat, as there simply isn't enough material there.... I looked in my box of used parts, and I found a scratch built valve body that Travis had sent to me where the seat had been moved forward and the port was on an angle.... The threads in the front of the valve were damaged, but I didn't need those, and after some careful measuring I decided I could probably modify it to work....

The ID of the tube I have is a fraction smaller than an MRod tube, so I had to turn down the OD of the valve a few thou to fit.... I then drilled the front of the valve out to 5/8" ID back to just in front of the 4-40 screw holes.... The hole through between those was already just over 1/2", and you can't go to 5/8", it would break through into the threaded holes and the valve would leak.... That 1/2" hole went right back to the valve seat, but I wanted more flow inside the valve, because the thimble of the SS valve will be 7/16" OD.... So, I bored out the back part of the valve ID to 5/8", using an internal threading tool with a 60 deg. point.... Again, I stopped just behind where the 4-40 holes were, but the part behind them, back to the seat, was now 5/8" like the front....

The middle of the valve was still 1/2" ID, however, so I put the valve in the milling attachment on my lathe, and set it up with the 4-40 holes vertical.... I ran a 1/2" end mill down inside the valve and centered it in the hole, and clamped the crossfeed down.... Now, by using the vertical travel on the vice, I could change the round hole into a vertical slot, that was 1/2" wide and 5/8" tall.... This worked perfectly, and now the inside of the valve is 5/8", except for a couple of small bumps on the sides where the 4-40 screws are....

I then drilled the throat of the valve out to a size "P" drill, which is 0.323", and touched up the valve seat by hand with a 1/2" end mill to make sure it was square to the bore.... I then turned a 3/4" ID recess in the front of the valve to a depth of 0.30", to locate the perforated mounting "wheel" which will hold the front of the SS valve thimble.... The last step inside the valve was to machine a snap ring groove to hold that wheel in place.... I tried a thimble, and there is tons of room around it for flow....Here is what the inside of the valve looks like now....



I had to enlarge the port from the 7/32" it was to 9/32".... I centered off the existing port, which was on a 20 deg. angle, and enlarged the hole to 1/4" with an end mill.... It was getting pretty close to the seat, and I still had to go larger, to 9/32, so I reduced the angle to 15 deg. and used a 17/64" end mill to enlarge the port.... That left the top of the port nearly 9/32" fore and aft (because of the angle), so I offset the mill 0.010" higher and lower to make the port oval, but because of the angle it appears round.... I then enlarged the recess for the transfer port from 5/16" to 3/8".... The rest of the port work was done with a Dremel, smoothing the transition of the exhaust port into the throat, and making sure the port was a full 9/32" everywhere.... By the time I was done, I could slide the shank of a 9/32" drill into the port all the way to the throat.... Here is what this huge port looks like.... It is 4 times the area of a .25 cal MRod port....  :o



This valve was made for a Gen1 trigger, and I am using a Gen2 for this build, so I had to mill two more shallow pockets in the bottom to clear the screws.... I had a poppet for an SS valve I built for my 6 mm left over, so I used it to lap the seat, and it looks like it should seal OK.... Tomorrow I plan to make the mounting wheel for the front of the valve, and using the poppet and thimble I have see if I can get it to seal up.... If so, testing should follow shortly.... For now I will use a 105 gr. steel hammer I have left over from the start of the BRod project, before I tried the Cothran and SS Valves.... It may be too heavy, but it will give me a starting point, and I can always borrow the 51 gr. MDS hammer currently in the .30 cal for testing....My gut feel is that I may need something in between, but that will depend on how easy this SS valve opens....

Bob
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Re: Tale of THREE BRods - Adding a .357 Version
« Reply #149 on: November 24, 2018, 06:09:30 PM »
I worked on the inside of the valve today.... I had a poppet and thimble from the first SS valve I made, using the dimensions Lloyd used on his prototype.... The small end of the poppet is VERY hard to machine without breaking it in Delrin, so this one had a brass body with a Delrin overlay.... I have since changed the dimensions, which Travis did too.... in my case to make it easier to machine.... Here is a photo of the parts.... Note the air passage ground into the shaft which vents the area between the O-rings to the exhaust port, that is key to its operation....



Last year I avoided showing any photos of the inside of my SS copy, to protect Travis' investment.... but there have been a few photos posted, and I think most people know what it looks like inside, so I figured there would be no problem sharing what I made myself.... In addition, Travis gave me permission to make a generic drawing of an SS valve to include in the next article I am writing for HAM on balanced valves, thanks Travis.... Here is the completed SS valve.... The valve stem is short enough that the hammer cannot drive the poppet to the end of its travel, which could damage it.... I still have 0.200" of travel....



Here is a photo of the front end, showing how the thimble is mounted, secured by the snap ring.... The way I build the wheel allows a small amount of radial movement for the thimble, so that it can self align with the poppet....



Note the vent hole in the mounting screw.... This allows HPA to enter the front of the thimble, in front of the small O-ring.... The spring only needs to be strong enough to overcome the friction of the O-rings and seal up the valve for initial filling.... Travis uses adjustable jets instead of my fixed 1/16" vent hole, to allow for fine tuning....

Unfortunately, this version didn't work.... The Delrin part of the poppet came loose on the brass rod.... I had another poppet, with a larger front end, that I had made for my 6 mm, but I didn't have a thimble for it.... I made a new thimble, and reassembled the valve.... It STILL leaked.... By this time I was tearing out what little hair I have left....  ::) …. I tried lapping the seat, replacing the O-rings, I even turned the poppet sealing face to re-true it, but the leak got worse and worse, lots of air coming out the exhaust port.... I eventually figured a way to test the O-rings on the poppet, and there was no air leaking out the back of the thimble or through the vent hole, so the only place left was the seat of the valve.... I spun the poppet with a drill to leave a polished ring on the seat, and it was off center, relative to the valve throat.... When I drilled out the throat I guess the drill tended to follow the exhaust port and ended up off center.... Since the sealing margin is so small (0.323" throat and 0.375" poppet) I guess there isn't enough seat on the side nearest the exhaust port, and that must be where it is leaking....  >:(

This is about the hardest thing to fix, unfortunately.... I can either make an entire new valve body, or try to repair the one I have.... Since I have a lot of hours into this one, I'm going to try and fix it.... Tomorrow I plan to make an insert for the back of the valve, with a new throat, seat, exhaust port and valve stem guide hole, and try and get it all straight and centered.... Then I will have to machine out the back of the valve body to install it.... There are a couple of different ways to do this job, I'll be pondering that overnight....

Bob
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