Bushings for dummies

Kind of learned on the job without any instructions and haven’t made a whole lot of bushings, just five sets. The first ones didn’t work out and were junked, which is why I used the following “results oriented” system.

If I’ve made any errors, point them out to me…they’ve worked great, but am always willing to learn. Need a lathe to make the bushings, but it’s very simple work. Used the lathe to drill out the central hole, bored that hole to a drive fit on the barrel being used.

BUSHINGS FOR DUMMIES:

Think of this as a “How To” without a lot of measureing…aren’t setting up production, just making one set of bushings for one barrel. Have used this to trial a 24” Crosman barrel that got progressively shorter for vel. tests, a second Crosman barrel for accuracy comparisons, a QB barrel that was exceptionally accurate on a QB (and also on a Talon), and an old 177 barrel from a match rifle that’s still in place.

Used black Delrin, settled on 1” wide bushings and are fitted to the barrel press fit tightly (need tubing to lightly drive them into the right spot). Factory bushings are close to 1/2”, but i wanted more contact area (which might have helped…might not have). Only round stock I had on hand was 1 1/4”. the bushings will end up fractionally larger than 1”. How much larger?…have come to believe the frames vary a bit, so that’s going to be an individual difference…but somewhere in the 1.05” to 1.07” area. If I was ordering Delrin rod, would order 1 1/4” stock.

Drill and bore the central (barrel ) first. Want it tight, a light drive fit (tight enough to need to be “urged” into place, not so tight you have to really beat on them to get them there). This kind of tight tends to slightly expand the Delrin. Lathe the bushings for diameter while on the barrel, which will put them true to the bore center, which is what is wanted.

Seem to be “right” when the barrel/bushing assembly will not fall down the frame on it’s own weight but can be pushed in. Double check everything to be sure they are just were they need to be, remove barrel…mark barrel….remove bushings.

Drill/tap a set screws in the bushings. Factory puts all the screws close together, but I’ll put the bushing set screw 180 degrees from the frame screws. Don’t think it makes any difference, it just makes me feel better.

Combination of drive fit, epoxy, and set screws make them pretty much impossible to get back off without destroying them, so really need to be dead sure they’re in just the right spot before driving them, gluing, and set screwing them in place. Remember, the power adjuster/spring assembly’s length is set by the rear of the back bushing, and you want the power wheel to be centered in it’s frame cut out.

Put the barrel/bushing assemble back in, being sure it’s all in just the right spot again. Can run in the frame screws until they contact the Delrin bushings, which will hold it well enough to function test to be sure you’re happy with the placement. Remove each frame screw separately and drill spot the bushings (if you have a sharp pointed set screw in you junk box, works fine for a dead center spot).

Remove all frame screws, remove the barrel, and drill the spotted holes in the bushing.

Put the barrel/bushing assembly back in and run all the frame screws in to contact the drilled holes.

Remove each frame screw separately. HEAT the screw. Run the screw back in just enough for the heat to let you screw it into the bushing by 1 or 2 turns. Do that for all 4 frame screws.

Remove the frame screws and take the barrel/bushing assembly back out. Tap the bushings holes. By running the hot screws in 1 or 2 turns, the tap will follow those threads, and the threads will line up with the frame screw’s threads perfectly. You could chase the frame screws with the tap and then run it into the Delrin. But past bad experiences kind of lead me away from that choice (old lesson: given a choice, work on the cheap replaceable piece).
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Not sure if Delrin has any real disadvantages in this use. Is strong enough, super easy to machine, and strong enough to thread.