Marauder porting greater than .1875" without moving seat forward

[shorty]

Not sure if it's going to work just yet but, the idea seems to be sound.

Bob mentioned to me a few weeks ago in a post that if I find a way to get the porting larger than .1875" without punching through to the seat then I should post about it ( I took this as a challenge and never stopped thinking about it ).

Well I think I figured it out. Should be able to get the equivalent to .22" porting with a stock valve and not punching through to the seat.

I am currently ordering some tooling and a valve to test it out. In the mean time, I have been practicing on some aluminum in the garage. All new machining techniques that I have never done before ( it's looking better the more I practice ).

I made a crude internal punch broach with a 1/8 HSS bit and turned an old drill bit into a bottom out drill bit. I don't have a press or drill press but a hand drill and vise is getting me the practice I need ( I think ).

So how does this work? A square hole?

Since going any more than .205" on the exit part of the valve will break through to the seat, a square exit port will put the flat to the seat without punching through and give you somewhere around 20% to 30% more cross sectional area.
It not only does that, it keeps the alignment through the rest of the porting. This means that a tapered transfer port can be used to channel the squared exit port to the rest of the system.

This also means nearly no modifications to the pressure tube and or the receiver and barrel.

Pretty cool stuff.

[Wayne52]

An EDM would be the perfect thing to make a square hole.

[Motorhead]

I get around this by taking throat deeper, then tilting body and drilling the larger passage on a back slope angle intersecting the throat at the deeper position.  Doing so you don't upset the material between sealing face and transfer hole. *Transfer hole at exit of body still kept centered at OEM position.

FWIW 

[rsterne]

Clever idea, Tim, but the airflow through a square hole doesn't fill in the corners due to turbulence.... You should gain some flow, but not as much as you would with a round port of the same area.... I did mention Scott's idea of angling the port backwards slightly some time ago, but that is still not the ideal solution, because now the air has to turn more than 90*.... Moving the seat ahead, as I did, or in the WAR or Cothran valves, is still the best solution.... Then the MRod valve can be made to flow more like a Disco valve, where there is room to angle the exhaust port forward in a stock valve.... Still, more port area is good in the quest for FPE....

Bob

[shorty]

Pretty clever idea as you said Bob. Thanks.

I think I am still gonna give it a go though and see what happens. I know flow would not be the same but, it's the pressure drop across the orifice "square hole" that I would be looking for.
It's just so short of a port I don't know what to expect.

Who knows until I give it a go. Never seen a square port.

I found an internal punch broach for 40 bucks.
http://www.ebay.com/itm/3-16-Square-Rotary-Broach-Punch-Fits-1-2-Shank-Holders-Made-in-USA-S0189B-/121140286596?hash=item1c34861484:m:mahdYxyEPRUc_qgUw9eOIMQ

[rsterne]

For a one-of, I would try making a "D" shaped port with the front corners of the "D" rounded (~ 1/16" radius), and blended into the front of the throat.... Some careful work with a 1/8" spherical burr in a Dremel should do the job.... If you drill the throat to 1/4", and make the front of the exhaust port the same width (1/8" flat, with rounded corners).... and then enlarge the back of the port to a 1/8" radius, blending into the front radii, you should still be able to get smooth flow.... The area would be (0.125^2) x PI/2 + (0.0625^2) x PI/2 + (0.125 x 0.0625) = 0.0245 + 0.0061 + 0.0078 = 0.0384 sq.in.... That is the equivalent of an exhaust port of 0.221" diameter.... At the top of the port, where it meets the transfer port, it would be 3/16" long by 1/4" wide.... It would take minimal slimming of the poppet stem to flow an equivalent amount of air, or you could drill the throat to 17/64" (0.266"), which would be a good match for it....

If you have access to a mill, you can make a sideways oblong port by using a 3/16" end mill, plunging straight down in line with the port, then move it sideways 0.030" each way to widen the port to 3/16" long by 1/4" wide.... The area would be (0.094^2) x PI + (0.188 x 0.060) = 0.0277 + 0.0113 = 0.0390 sq.in. (equivalent to a round 0.223" port)... The sides would blend into a 1/4" throat, but again it would only be 3/16" long, so would not cut into the valve seat.... Once again, the top of the port, where it meets the transfer port, would be 3/16" x 1/4".... This would be a good way for someone with a shop to make high-flow MRod valves quite easily.... I would use a 0.266" throat in conjunction with it....

Bob

[ackuric]

.201 ports here on the gen 2 mrod valve...hand drilled. I could oval out sideways and get about .21" overall if I wished but doing so would require more throat work on my part that I don't want to do so, .201" I stay...for now! I may take my throat to .23" which would flow enough for .21" ports...hmm. Also haven't tested over 2050 psi...as this is in a regulated marauder.



Drill bit is a .201 drill bit #7 that spins freely with tp installed.

[shorty]

I have my gen2 .22 at .205"/.208" when I did the .357 conversion. It's just too close for comfort.

I just hope my theory sands true with the square vs round orifice. Less of a pressure drop with reduced flow. My hope is that I will be able to hit a high FPE at lower pressures while maintaining the efficiency.

Been trying to figure out plan B and C if it doesn't work as expected and I really like Bib's idea of the D-shape. After he said that I took a .25" HSS boring tool and put a flat on it. Across the flat to the round was .187" and boy the D shape looked cool  when punched through a .1875" hole, but it was  PITA to remove the tool.

I also took the dremel to the square hole and rounded the edges but, it looked horrible by hand.

I am getting nervous with the bottom out drill bits without a drill press. I just can't get it the way it should be. I may weld up a jig to make a milling attachment for my lathe and chuck an end mill into the 3 jaw chuck ( I know that sounds crudy) but, it's all I got.

Lastly,
It looks like the pressure tube needs to be opened to .35" to accept the transfer sleeve. No big deal but, I hate to drill into it.  Ahh, I am sure things will work out.

[shorty]

It will either be a game changer or a complete failure. Doesn't really matter. It's another data point to our craziness.

[shorty]

I got the valve in today. I did the usual for a starting point and figured I would share. Ran some numbers again on the "breaking through" to the high pressure side and for sure it's around .208"/.21" with a wall thickness between TP and high pressure side of around .01".

Sometimes I hate R&D because it costs money that I don't have but, there's always plan B and C.

.19" exit port
Throat .25"
.5" hog to valve seat
.45" valve cap with taper
Custom poppet spring
polish between poppet and poppet seat.

I know it's good for 80FPE plus as is but, it's just so hard to push it further.

Here's the pic's of some of the work

[shorty]

K

[shorty]

K

[shorty]

Well-u'p,
I am not gonna post the next pictures because I said to myself " no guts no glory".

I punched through the exit port with the "D" shaped HSS ground bit. Everything went well until I tried to remove it. The "dang" thing got stuck and broke in the valve.

Mangled the valve pretty good too  . Funny stuff).

[Mark Davis]

Thanks for an honest report.
Here's hoping all goes well next try!

[aceflier]

Good to see the process at any rate. Keep at it!

[rsterne]

I agree with your assessment of how much wall is left between the port and the back inside of the valve, Tim.... What I'm not so confident in, is the ability of 0.010" of aluminum with 3000 psi on one side, and the pressure on the other side varying from 0-3000psi on every shot, to resist fatigue and not crack and fail under use.... If it failed suddenly with a pellet in the chamber, the gun just fired without pulling the trigger....

If people keep trying to get bigger and bigger ports in an MRod valve, IMO it's only a matter of time before we see a failure in service, of a gun that didn't leak initially.... I still think any time guys go over 3/16" they are playing with fire.... That seems to leave about 0.020" of wall remaining at the thinnest point, right?....

Bob

[Motorhead]

While a deepened throat and slightly back sloped transfer passage MAY NOT be optimal for flow ... IT IS SAFE 

[shorty]

After the episode with the stuck and broke HSS D bit in the exit port I tried to do my very best to remove it. That meas boring the entire valve out to .5" .

Today I made my first attempt to plug it, and move the seat forward ( just winging it ). With my skills and tools, this is not a job for me. I made the plug with a .225" exit port and the valve exit port to .343" to accept an oring transfer sleeve.
Plugging really looked like (to me) something that could be real dangerous if not done properly. That plug really needs to be held in place just as strong as the valve.

Plug is way too long with a .225" exit port and be able to seal with an oring to allow use of the stock poppet.

I am thinking of the valve as just a skeleton now. My next hack job is probably going to completely ruin the valve but I am gonna give it a go and part the valve in half ( I think ).

Here's a couple pictures of the failed plugging. This is starting to turn into "what not to do" 

[rsterne]

Yes, if you move the seat ahead, you will need either a longer stem on the poppet, OR you can shorten the back of the valve to allow the hammer to move further before it hits it.... On my valve with the forward seat, I shortened the back of the valve by 0.070" and got enough travel to allow the valve to make 140 FPE at 3000 psi in .30 cal. with a stock poppet....

Bob

[ackuric]

My valve is one of those funny valves that when placed into the air tube has the exit port offset, which leads me to believe my seat is in the normal planned location but exit port hole was drilled around .01-.02" off center... note this was just as off-centered when @ stock porting of .140"...

I measured my wall thickness very, very carefully and it came out to .030"...respectfully..



My poppet has a .020" bevel that you cannot see in this pic that is straight up and down in terms of back/front of valve...which means I have over .020" of wall thickness at an exit port of .201" that goes STRAIGHT down..that subtle taper is NOT the .020" bevel, its .010"+ deeper

Maybe my valve is one of those lucky ones that are fortunate enough to not require much work for just a tad more air flow