GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: mata777 on October 25, 2019, 10:33:04 PM
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Hello everyone.
I'm looking to do the 1/4" ice maker tubing mod. From my research I found the the ends have to be pretty much as square as possible, how long should I cut the tubing to get a good seal and ensure that it has the right amount of tension between the tube and barrel? Thanks, I appreciate any help!
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Hi Joe, There is no one-size-fits-all. It depends on the tolerance of the valve counter-bore, how deep you mill your barrel, and the tube and breech wall thicknesses.
On a side note, you will need to (if it hasn't already been done) drill your barrel and valve ports the same... or this mod won't be very effective.
If you feel o.k. with drilling and counter-boring, I've had much better luck going a different route.
Get some 1/4" Delrin tube stock and some 4.5mm (i.d.) x 1.0mm (cross-section) O-rings.
Select the port size from this chart (but don't exceed .172" - 11/64):
(https://i.imgur.com/B14Fg15.gif)
Drill the valve port, Delrin tube stock, and barrel port to your port size.
Counter-bore your barrel port .25" ... a .25" twist drill to start followed by a .25" end mill to square the bottom of the sleeve pocket:
(https://i.imgur.com/pMANhyN.jpg)
Install the barrel in the breech and the valve in the tube. Use a depth gauge (caliper) to get the distance from the tube walls to the c-bore bottoms. Add the two and cut the Delrin stock .050" shorter. It will be about .020" *too* long if you cut it right. The O-rings on both ends add .078" to the length and you want .010" compression... here's a pic:
(https://i.imgur.com/UgslXAh.jpg)
Face cut the delrin so the total length of the delrin sleeve and the two O-rings are long enough that the O-rings will compress about .010" when assembled. Another pic:
(https://i.imgur.com/2DRHO3Q.jpg)
A bit more work, perhaps, but they don't leak even with modest clamping pressure -
Wyo
* edit
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I have some 3d printer transfer ports for a customer easy to do another batch. Printed in PETG so should hold up well.
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@WyoMan
Thank you for the info. When you state to not exceed .172", I'm assuming for .22? I'm looking into building a co2 2550 in the near future and for the power level I'm looking to end up at it seems like .185" would optimal from you chart.
@Insanity
Thanks for the offer, I'll contact you if I end up needing some.
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That's correct, the .172" port is for the .22 cal. The chart suggestions will get you in the ballpark, they're nothing more than that. The .172" port is about 80% of bore diameter and if you exceed that, the pellet head can get clipped because it will tip down into the port. You would probably have to load vertically...
Wyo
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Nice thread. I really enjoyed reading it. Thanks for sharing all that info Wyo.
Bobin WV
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That's correct, the .172" port is for the .22 cal. The chart suggestions will get you in the ballpark, they're nothing more than that. The .172" port is about 80% of bore diameter and if you exceed that, the pellet head can get clipped because it will tip down into the port. You would probably have to load vertically...
Wyo
Thanks again For the info. Last question, I’ve been looking for 1/4 delrin tube stock but have came up short with the exception of one on amazon that’s not in spec according to the reviews. Do you happen to have a source? Thanks again!
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I ended up finding some nylon spacers at ace that should work. Thanks again
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I learn something every day here. Thanks for this.