Friday, January 30, 2009

Derrick's Trigger Frenzy Part 2

Continuing with my so-called "rocker arm"...

I took it to the bench grinder and got it closer to size. I use a beat-up wheel when grinding aluminum. (Editors Note: It is dangerous to let a grinding wheel load up with aluminum! The aluminum can expand and crack the wheel. Dress the wheel frequently and often stick lube will help prevent the loading.)

Some files and a few minutes really got the shape dialed in.

Sanded the sear contact hump at the rear.

Eyeballed the trigger pivot hole. Needs to be drilled to 0.125". The 100% correct exact hole location is not that important. At this point, I also thinned the piece to 0.163" to nail the width. The soft aluminum really doesn't put up much of a fight.

Drilled the pivot hole just undersized. I'll later take it to the 0.125" with a reamer.

This is where Nick would show you an edge finder. I don't/can't work nearly as precisely as he can/does. I took a caliper and measured the width of the rocker arm. Divided by 2 and dialed the caliper down to that number. Set one jaw against the edge of the piece and slid it down the center, scoring a fine mark. (remember, the piece is just aluminum) Put the caliper on the other side of the piece and repeated. If I'd mis-measured or mis-adjusted the caliper, I would have gotten 2 lines very close to each other and the true center would be halfway between the two. In this case, it retraced the first line. Nice! Drilled a blind hole 2.5mm for the trigger blade's pivot bolt. Why 2.5mm? Soon.

Here's that grooved strip of brass from part uno. Cut more or less to final size.

Clamped it up in the vise with a piece of smooth steel against the face to help prevent gouges. There's some machinisty term for this. A "packing block" maybe? I should just get better vise.

Bent it by hand, by eye, by sheer strength of will. Hey, it's just brass. Chuck Norris could do it by just squinting.

Maybe a bit more.

Bent and flipped. This is the back of the trigger blade.

Used the caliper to find the center. This is just so not critical. Should've, could've, just eyeballed it.

All the precision measurement and I hand file it with a round file to fit against that brass 3/16" tube. See what I mean?

I cut the brass tube down and faced both ends. Forgot to write down the length.

About here, I tapped the aluminum rocker arm with a M3 x 0.5mm plug tap to start, then finished with a bottoming tap. A plug tap is tapered at the tip to start the cut and acts as a guide. The bottoming tap then lets you run full thread to the bottom of a blind hole. When tapping a hole, it's important to first drill the hole to the proper size for a given thread size. A cool feature of metric thread is the ease of calculating the drill size to use for the tap. Take the thread diameter you want to cut--in this case a 3 mm and SUBTRACT the pitch : 0.5mm. So, drill the tap hole to 2.5mm. Neat! If you wanted to tap a M6 x 1.0mm thread, it's 6mm minus 1 so you'd drill with a 5mm bit or the equivalent.

As an aside, imperial threading typically gives a diameter and pitch--in number of threads per inch. IE: 1/4"-20 means that the threading is nominally 1/4" in diameter and there are 20 threads per inch. Metric thread is given as diameter (typically in millimeters) and the "pitch" is how far apart the threads peaks are to each other. The smaller the number, the finer the thread. M10 x 1.0m means it's 10mm diameter with each thread 1 mm apart. A M3 x 0.5mm is a 3mm diameter with the threads each 0.5mm apart.

OK, back to the trigger. Cleaned, fluxed. positioned.

My $8 micro torch to the rescue again!

Soldered. No overflow.

Back to the buffer.

I did some fine shaping with a file here and there to break edges and give it some taper at the top and bottom. Blended it all together on the buffer. Safety note: Try to use the bottom half of the buffing wheel. The work piece is less likely to be grabbed and thrown across the room.

Installed on a Crosman 2300.

There's that hand filing on the trigger blade. Lots of polishing. The M3 screw head contacts the trigger stop. The trigger stop works just as it should. There was some slight resizing of the brass tube along the way to make that happen. Because that's what test fits are for.

Trigger blade is turned about 10 degrees to the right. A huge difference in trigger feel.


JD said...

Hi there! Great job!
I've been reading you for quite a while. You do some awesome tuning!I've never been commenting but this one has great looks!

greetings from Greece!


derrick38 said...

Thank you for your kind words. And greetings to our new friend in Greece!