Friday, March 5, 2010

A New 2250 Gas Tube

I sort of accumulate parts for airguns. Occasionally, I'll look at the pile and realize I'm but a few pieces away from being able to build a new gun--usually a Crosman 22XX. This time, the key part needed was the gas tube.

A new Crosman 2250 tube--part number #2250-009. Problem was, my steel breech has the "new" breech screw location at the rear of the bolt trough. Actually, that's not the problem--the problem is, though the new gas tube is drilled for both the old and new breech screw locations, only the front hole was tapped with 4-48 threads.

Looked through all my bajillion taps and seems I didn't have a 4-48. Need a 7/32-40? How about a 2-56? Unbelievable. Hit Kromhard's this morning and sourced a plug tap for under $4.

I was mainly concerned with alignment of the threads to get them perpendicular to the tube. With such a thin wall to thread, it would be very easy to cut the threads at an angle. I wondered about just using the existing 4-48 threads that Crosman did cut to align the tube.

With rubber jaws installed in the vise, I gently grabbed the gas tube. Threaded the tap into the existing forward screw location, then brought the drill press table upward until I could chuck the tap. Since the gas tube was held loosely, the tube rotated in the padded vise jaws until the tap was vertical. Snugged down the gas tube, left the tap in the chuck, and centered up on the threadless hole.

Turned the chuck by hand and applied a bit of downward pressure to feed the tap into the hole.

Finished by hand. It's more than accurate enough for the application. Still dragging my feet on the build. Leaning towards .20 cal but waffling on barrel length. I'll need to make a few parts, too, in the coming week. More soon.

No comments: