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.

Tuesday, January 27, 2009

Derrick's on a Trigger Frenzy! Part 1

Derrick here today. Some projects just beget other projects. While working on the wide-bladed brass trigger for the Crosman 2250 last week, I came up with a different trigger idea that I had to work out. As per my usual, I started working without a real plan--and as usual, it's got to have some match gun style.

First, I wanted some better pivot pins for this soon-to-be trigger. Found a piece of hardened 1/8" drill rod and marked off several intervals of 0.410". Might as well make a couple extra.

Used a carbide v-shaped bit to groove each 0.410" section. I didn't bother to cut all the way though. The hardened 1/8" drill rod is incredibly tough stuff. While that's just great for wear resistance and reduction of friction, it's lousy for cutting. I essentially "scored" the rod with the cutting tool. The drill rod then went into a vise and each section was snapped off. Was like breaking a glass rod. Not shown: I then turned on the grinder and ground each pin down to 0.393"---The final length needed for Crosman sized replacement pins.

The soon-to-be trigger blade: I wanted the face of the trigger grooved--just like in the movies! Mounted a piece of 1/2" wide brass in a Taig milling vise. Then bolted that to the horizontal milling attachment for the Taig lathe. (The Taig is all modular. It's pretty ingenious that way) It almost fell apart when I realized (incorrectly at the time) that I didn't have a small enough milling cutter. I ended up making the cut by using the tip of a center drill. My thought was that a center drill is so rigid, and this was soft brass, the tip wouldn't deflect. It worked. Two hours later, I realized there were 10+ suitable cutters in the Dremel kit. Sigh.

I cleaned the grooves up by hand with a needle file and set this aside.

I wanted the trigger blade to be rotational on it's long axis. A 2" long piece of 3/16" brass rod was chucked, faced, spotted and drilled through. I think I used a number 33 drill. The hole just allows clearance for a M3 x 0.5 bolt. I'll cut the brass to length a bit later.

Quack! It's a little aluminum duck! Cut away all the parts that don't look duckish.

Didn't show the first part of this plan: Took the world-renowned Crosman 22XX trigger, transferred the pivot and sear contact locations to this piece of scrap aluminum bar stock. Used a high precision fat tipped Sharpie. Color: Uh, green.

Excel Jeweler's saw. Think "micro coping saw" and you've got it. A great, inexpensive tool for fine precise cuts. Note: Fine precise cuts not shown here.

The Excel people are probably sending someone to repo my saw...

I'll knock it down closer to size on the grinder then go to it with a small file. I wanted some extra material here to work with. The big marker ensured it.

Does this help visualize my dream? The aluminum piece is the trigger pivot and sear contact. Call it a rocker arm.

Sunday, January 25, 2009

Sunday Ramble and Miscellany

I'm tidying up some loose ends with this post. Beyond what you see below I have a Daisy/Milbro 230 rifle and three Crosman 101's in partial process. Not sure how/when I'll have any of them these things go. I'm also working on some other parts, etc. I also have a Gamo 220 that I need to de-Gamo-ify. I bought some Maccari springs and seals to see if I could tame it. I also am learning how to resolder Benjamin barrels that have come unstuck. We'll see if that bears any but humiliating fruit for the blog. Oh yeah, there's a Sheridan C that has an ugly chunk out of the pump arm. Not even sure what's to be done about that.

A Crosman 760 that has a completely jammed barrel and broken parts, an early 1377 pistol that is in pieces and some other 1377 parts left from the carbine conversion and a 2250(?) barrel

Just ugly and worn.

Recutting the 1377 bolt for a larger o-ring.

Less Ugly? Basically just a way to use up some parts and make space. Hey, it shoots!

Some 80/20 aluminum extrusion I got at the scrap yard.

At one end of my shop.

A post that duplicates the mounting of my spotting scope.

Now I can sight guns in, inside the house...and not have to keep walking back and forth to see where the pellets are landing on the target. It stows out of the way when not in use.