Tale of THREE BRods - .25, .30 and .357 Completed, Page 19 !

[rsterne]

No idea.... If so, can the throat be opened up far enough to produce 10% greater (or even equal) port area to that 0.281" exhaust port, with the very thick (0.175") stem.... and if so, what would that do to the delicate balancing act that is taking place in a Cothran valve?.... The throat required would be 0.346" ID or maybe more to flow around that huge valve stem....

Bob

[YEMX]

Hmmm...  I'll probably just match all my other ports to the Cothran valve.  I'm also only shooting pellets- but I'm aiming for a more sedate 130-ish fpe.   

[rsterne]

You should easily reach that with 1/4" porting....

Bob

[Voltar1]

I know it has been a while since I posted in this thread, but summer is an impossible time for me to work on airguns because the Motel is too busy.... During the winter, I worked with Travis and Jim designing an adjustalbe regulator to go inside their drop down tank block.... I just received one in the mail today, and it is gorgeous....



I got both tank adapters, one for 5/8"-18 UN threads, and one for 18 mm x 1.5 mm threads, so I can use any tank.... The burst disc is on the output side, and is a 3K, as I won't be using more than about 2200 psi.... However, I understand the output can be adjusted higher than that, depending on the Bellevilles installed....



It has room for two gauges, the upper one reads output pressure, and the lower one tank pressure.... The adjusting screw is an allen set-screw on the bottom of the block.... It moves the HP seat towards the piston (CW) to reduce the output pressure and away from the piston (CCW) to increase it.... I can't wait to try it out on the tube I have the Cothran valve installed in.... It will be the perfect arrangement for that, because you must adjust the pressure to adjust the velocity....

Bob

Very cool stuff Bob. A lot of info to digest. This block and reg I cannot follow how the fill and gauge on the block connect to the bottle?
Appreciate any hints
Cheers
Walter

[rsterne]

The lower gauge and the fill fitting are on the input side of the regulator (using a small hole, crossdrilled through the block)…. The regulator is installed vertically (from the top) inside the tank block.... You can see the pressure adjusting screw on the bottom of the block.... Backing that out moves the seat lower, requiring the piston to compress the Bellevilles more before the airflow is shut off.... The bottle threads directly onto the brass adapter....

Bob

[Dairyboy]

Having one on my WARP I have a question...can these reg guts be pulled to shoot unregulated and then reinstalled later to be regulated if wanted? Say slug vs pellet shooter?

[rsterne]

Yes, you could pull out the piston and Bellevilles and leave the seat installed (it is needed to seal the bottom of the tank block)…. and then reinstall the top plug.... You might need something to keep the seat from popping up when fired.... However, the air bleed in the seat is tiny, and so you would still have only the plenum volume of your regulated PCP, the bottle volume would not really participate in keeping up the pressure during the shot like it would if you have large passages through from bottle to plenum.... Between shots, the plenum would reach current bottle pressure, of course, and the gun would be unregulated....

Bob

[Dairyboy]

Didn't even think of that Bob. Looks like it's staying as is. Thanks for the info! By the way these regs you helped design are arguably the best I've ever used. Incredibly consistent and no creep. Thanks for combining your efforts with Jim and Travis to make them happen!

[KnifeMaker]

Nice Work as usual Mr. Bob!


Wish I could see the pics, but as usual, only a blank rectangle. Very typical from Photobucket. 


A LOT easier to post pictures directly from your computer, and much faster!  After all, you have to load them into pb, and it is the same here on the GTA. No middle man needed.


Not to mention anyone on the forum can see them. Not just paid Photobucket subscribers. I will not pay them a single red cent. Period!!!
Knife


Knife

[Voltar1]

The lower gauge and the fill fitting are on the input side of the regulator (using a small hole, crossdrilled through the block)…. The regulator is installed vertically (from the top) inside the tank block.... You can see the pressure adjusting screw on the bottom of the block.... Backing that out moves the seat lower, requiring the piston to compress the Bellevilles more before the airflow is shut off.... The bottle threads directly onto the brass adapter....

Bob

That is very nice design! Who is the machinist on that block? A lot going on there with critical dimensions in such a compact package!
I love it!
Keep up the good work man.
Walter

[rsterne]

Jim Gaska at Marmot Militia.... I did most of the design work when he and Travis teamed up at W.A.R. (Wicked Air Rifles)….

Bob

[Voltar1]

Jim Gaska at Marmot Militia.... I did most of the design work when he and Travis teamed up at W.A.R. (Wicked Air Rifles)….

Bob

Awesome!

[KnifeMaker]

Mr BOB, the pics are now visible on my monitor. Woo-H00!!!


Fascinating thread.


Knife

[rsterne]

Good to hear.... I think your problem was a temporary glitch....

Bob

[rsterne]

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

[triggertreat]

Looks like a great build Bob!  I'm looking hard at the .357 calibers myself, but don't have any machines or your knowledge to build my own.  I'll be following along with interest as you post.

Thanks for the TJ barrel work!  I really, really like the one I have in my .22.  It is so consistent and accurate,  and a real joy to shoot knowing it will hit where I aim if I do my part.

[Dairyboy]

Will continue to follow as well!

[Motorhead]

Bob,
Great to see your at it once more ... "Cold" shop & all ... burrrrr

[rsterne]

Oh it's got heat (providing I remember to turn it up in the morning)…. I keep it at 5*C (40*F) at night.... It is, after all, just a garage....

Bob

[rsterne]

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 am only using 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