QB78 DIY Transfer Port... How are you cutting the tubing square?

[imadunatic]

Curious if anyone has came up with a simple method for cutting your own transfer ports from poly tubing? I machined the 1/4" spot faces on the valve and breech and have finally cut one decent section of tubing but man o man what a pain to cut the ends square on a 1/4" diameter x .140" long tube. I'm hoping I am just overlooking the obvious.

[SpiralGroove]

Hey imadunatic,
Cut a section of refrigerator (water supply tubing) with an Exacto knife or one-edge razor blade.  Wrap one layer of electrical tape around the tubing before cutting.  The small section cut off will then be slightly bigger in diameter and fit better.  Also, when looking at the cross section O locate the tubing seam.  Place tubing gasket so that seam faces towards the barrel or butt.

This information is cutesy of Nervoustrigger

[imadunatic]

Hey imadunatic,
Cut a section of refrigerator (water supply tubing) with an Exacto knife or one-edge razor blade.  Wrap one layer of electrical tape around the tubing before cutting.  The small section cut off will then be slightly bigger in diameter and fit better.  Also, when looking at the cross section O locate the tubing seam.  Place tubing gasket so that seam faces towards the barrel or butt.

This information is cutesy of Nervoustrigger

Thanks spiralgroove, I'm gonna give it a shot.  I'm guessing I'm over thinking this.

[Geoff]

i fed the tubing through a copper pipe, then used the end of hte pipe as a guide

[Buldawg76]

I use a 3/16" drill bit and just slide the tubing over it far enough to support the tubing for the length I need for the transfer port , then use a tubing cutter to cut a square straight end over the part that is supported by the drill bit. it gives the tubing a firm backing for the tubing cutter to apply pressure against for a clean straight cut. If you are starting with a new end of the tubing that was an uneven cut from a knife or side cutters just slide it on a make a cut to give you a clean end to measure from to make the transfer port tube.

I will generally measure the recesses of the valve and breech spot faces to determine the length of tubing needed. then cut about .020" longer to allow for compression of the tubing for a perfect tight seal when compressed. Quick, easy, and precise for square ends.

Mike

[imadunatic]

Thanks guys. I ended up cutting one pretty square with the drill bit and tubing cutter.

Once I had a pretty decent seal cut, I decided to start playing with cutting this in the lathe (yeah, should have thought of this first); I chucked up the tubing with a drill bit in the lathe and clamped a razor to the tool holder, this actually produced one of the best seals and allowed me to accurately cut the length (or rather a variety of lengths in .010" increments). Now that I've re-assembled the rifle I realize that this is severe overkill as it squishes down pretty easy and anything +.010" to +.025" would probably work just fine.

I will say that removing the filter from the valve and adding this transfer port mod has really brought the gun alive, I can't believe how much better it breathes now than before and I really haven't done much. I'm not looking to hot rod this, really just get the most efficient bang for my buck. Friday I'm planning to add a bulk fill nipple and still maintain the ability to use Powerlets; shooting off the bottle at the bench is just so much more convenient, especially on a new gun that you just can't shoot enough.

[nervoustrigger]

Hi Kirk, thanks for the shout out but the method I use is more like Mike's.  I do use a turn of tape to establish a cut line when sawing a piece of pipe (like an air tube) so maybe that's what you were thinking of.

I slip the tubing over a drill bit shank (or transfer punch), leaving about 1/8" overhanging the end.  Then I slice through it with the long blade of a box cutter.  The tubing's proximity to the end of the shank keeps it from deforming or collapsing, allowing for a nice clean cut.

Icemaker tubing has an OD that is a loose fit to the opening in the air tube so I wrap one turn of a 0.010" thick Delrin tape around it.  That makes it a snug fit and keeps the tubing centered to minimize the chance of blowby.  I find a length of 0.100" to 0.110" to be optimal.  A length of 1/8" (0.125") is too long and deforms too much but that may have something to do with making the OD a snug fit to the tube. 

[Buldawg76]

Jason

I spot face the valve port and breech at the port holes about .050" deep and use a 3/16" end mill so there is a raised lip around the where the ice maker tubing sits that keeps it centered over the port opening nicely and by making the tubing .020" longer than the length between the two seats in the valve and breech so that when you secure the breech in place it compresses the tubing out against the lip created by the spot face and creates a very good seal.

By making a lipped spot face it serves to not only help center the tubing but causes it to form a perfect round sealing area against the two pieces. I have used this in my QBs, 2240s and Mrods with great success.

Mike

[imadunatic]

How well do these hold up? It seems like it'd be a one and done kind of a deal other than the material just deteriorating over time. Basically just wondering if I need to keep a few spares on hand?

I'd kinda like to do this to the Gasmaster as well as my 2240; the difference over stock on the QB was incredible.

[kj]

i found this and tried it.



peace
kj

[ezman604]

Next visit to the flea market (or yard sales) will be scouting for an old guillotine paper cutter.

I also the drill bit/punch insert way too.

[nervoustrigger]

KJ's mention of a mitre box made me realize I failed to mention that I do use a simple L-shaped fixture made of two wood scraps joined at right angles.  I overhang the tubing off the end and slice through it with the boxcutter blade.  So it's not a mitre box in the sense there is a slot for the blade to ride in.  I considered doing that but it's easy enough to eyeball it and hold the blade square to the edge.

By the way, a serrated blade, even a very fine one, seems to make a mess of the cut.  I much prefer to use a very sharp straight blade.

Dave, my wife is a teacher and has a nice paper cutter but it doesn't do an adequate job cutting poly tubing.

[kj]

there's a groove that fits the tubing perfect. yes the cut is slightlty fuzzy, but a light touch with some sandpaper cleans it up easy. always more ways than one to get the job done, but this makes perfect ones every time. it's also good for teaching my son wood working with his light pine and balsa projects.

peace
kj

[ezman604]

Appreciate that Jason. One of the great things about our family here, you can just about count on is that someone has probably already been there dun dat. LOL
And can save you money or frustration experimenting.

[Buldawg76]

Appreciate that Jason. One of the great things about our family here, you can just about count on is that someone has probably already been there dun dat. LOL
And can save you money or frustration experimenting.

+1 on that for sure.

Mike