Author Topic: made an adjustable piston for the 880 (Read 48524 times))

Rob M · « **Reply #120 on:** October 04, 2016, 12:27:27 AM »

not to assume u dont know, but measure the major thread to the next major thread on an even plane./

Rob M · « **Reply #121 on:** October 04, 2016, 12:38:43 AM »

http://www.mcmaster.com/#steel-pipe-fittings/=14g01ky

ANOTHER IN 1.5

Rob M · « **Reply #122 on:** October 04, 2016, 12:47:59 AM »

MAN THAT will be a lot of extra air , lol.. the gun will sound like a 12 gauge on 25 pumps @ But it will be adjustable when u have it threaded all the way down im sure it will not even double the volume

bhh · « **Reply #123 on:** October 04, 2016, 08:05:09 AM »

Thanks for looking. I'll double check the measurements, but I'm positive it's a 1.0 thread. I used a thread gauge when I measured it.

Rob M · « **Reply #124 on:** October 04, 2016, 12:59:26 PM »

thats really odd man,no one makes anything in 1.0 .. its hard enough to find a tap in 1.0 nevermind a coupler.thats 25.4 threads per inch , super fine thread for that diameter.

Rob M · « **Reply #125 on:** October 04, 2016, 01:02:53 PM »

tap is 8 bux, then ud have to turn the A threads on the lathe.
makes it a big project compared to a wham bam

http://www.ebay.com/itm/M1-M16-Industrial-HSS-Metric-Taper-Plug-Tap-Right-Hand-Thread-Drill-Bits-Set-US-/331769989528?var=&hash=item4d3f084998:m:m7lnSs1coT1LryrDW9vB1Ug

Underdog · « **Reply #126 on:** October 04, 2016, 01:45:45 PM »

I got the piston in the mail yesterday Rob. Thanks! I'm anxious to try it out. (But, it's been so long since I've been into my 880, I've forgotten what all of it looks like. I'll have to get familiar again.)

The threaded rod is a bit off-axis in the bottom of the piston. Will that cause problems? Or will the pivot action in the roll pin connection give me some fudge room?

Rob M · « **Reply #127 on:** October 04, 2016, 01:50:36 PM »

i never noticed apparently.. yes, it should shoot straight due to the natural flex in the entire pump assembly... That was an early proto and all i had left. if you have a 10-24 nut you may wanna put one behind the piston .. With all the designs, even the last one the gains really come from pumps 12-20 ,,. make sure you keep it well oiled , but dont drown it.I can only imagine something was out of spec and thats why it was thrown in the drawer.I probably made 10 designs or more in a month lol

bhh · « **Reply #128 on:** October 04, 2016, 10:57:50 PM »

Quote from: Rob M on October 04, 2016, 01:02:53 PM

tap is 8 bux, then ud have to turn the A threads on the lathe.
makes it a big project compared to a wham bam

Yea, I think I'm just going to machine an all-metal piston, square the valve face, and except what I get. I would rather put my time and money towards building an all-new design with a good receiver and trigger than sink a lot more into the plastic rifle I have now.

Rob M · « **Reply #129 on:** October 04, 2016, 11:16:32 PM »

if i wasnt swamped in projects, id get the gun and see where it goes.i think even with the limited valve volume and a super rigid pump mechanism , based on the numbers you have gotten thus far, that you can crack the 900fps mark no problem! the further you start from scratch , the more headaches, i can promise that.Im still wondering why they used 1mm thread.. The drill and tap valve anlargement idea should still be on the table , its by far the easiest way to gain volume. Heck you could thread in this and triple the volume with 10 minutes and a tap

http://www.aerotechnic.com/store/index.php?main_page=product_info&cPath=6_29&products_id=144

Rob M · « **Reply #130 on:** October 04, 2016, 11:19:41 PM »

or any hollow plug for that matter. But first things first, the piston needs to be all metal and super rigid.. and take any slack out of the pump arm and connection points.

bhh · « **Reply #131 on:** October 04, 2016, 11:59:58 PM »

Hmmm... that threaded reservoir idea has some potential....

But first, I'm going to be sure everything I have now is optimal. Two other potential problems could be scratches in the pump tube and ensure that I have a perfect gland cut. I made a square bottom in my piston and I wonder if it should have been round to hold more pressure? However, I did duplicate the factory piston gland.

Rob M · « **Reply #132 on:** October 05, 2016, 12:06:03 AM »

im not sure.. sqare bottom glands got me to 2200 psi.. slightly more than optimal oring engagement on the wall is always good too , so i usually have the gland about .010 less shallow than suggested/.i might try my 880 in the old configuration again where it sounded like a 22, just to see what the chrony says now having the 24 inch barrel installed.

Rob M · « **Reply #133 on:** October 05, 2016, 03:17:41 PM »

heres my little valve extension with gauge i made. letting the the red thread lock cure in the sun.. it probably adds 4 cc's//

also serves the purpose of having a 3000 psi gauge

bhh · « **Reply #134 on:** October 05, 2016, 08:48:48 PM »

Nice. So you know pressure increase for each pump. How much does it go up from pumps 20 to 23?

Rob M · « **Reply #135 on:** October 05, 2016, 09:00:55 PM »

ive done this before, if you look at old threads on my 880 experiemts.. PUmp 1-10 are about 100 psi per pump with modified piston.. pump 15is about 1600psi and then it declines fast. pump 20 is only 1850 iish , pump 23 hits 2000psi, and 2200 psi was like 26 with the last few pumps being rapid and heated. ( the compression at that point makes the air tremndously hot and also heats the valvve. I havent tested the new setup, because by the time the thread lock set, it was too late to get the chrony outside.. Plus i wanna make a new piston design.. hoping tommor ill try to bust 1000 fps.. BTW the non linear gains had to do with heat accumulation, obviously if i let the air cool after each pump the numbers would have been different

Rob M · « **Reply #136 on:** October 05, 2016, 09:09:16 PM »

I cant find all the details i recall typing , but heres the thread from the old design with perhaps less additional volume

http://www.gatewaytoairguns.org/GTA/index.php?topic=113523.0

Rob M · « **Reply #137 on:** October 05, 2016, 10:06:02 PM »

what cossed my mind is making an insert in the compression tube that will house a smaller piston. still single stage but ill be able to pump to wayyy higher pressure wiith the stock pump arm , granted it will take 40 pumps to get there but even at .500 piston the force required would be half, so getting to 3000psi should be easy

bhh · « **Reply #138 on:** October 05, 2016, 10:55:47 PM »

Yea, one thing I like about this NXG is how easy it is to pump. I'd rather pump it 30 times than my Benji 392 12 times.

Rob M · « **Reply #139 on:** October 05, 2016, 11:11:04 PM »

yep the 880 is very easy too , till i get to 15 ish.. any news on the piston design??

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made an adjustable piston for the 880

Author Topic: made an adjustable piston for the 880 (Read 48524 times))