Monday, March 30, 2009

Muzzle Weight For Derrick's co-worker Part 1

At the "Toys that Shoot" airgun show in Findlay, OH last year, a cohort bought a .22 cal Hammerli 850 Air Magnum from the nicest guy in the airgun industry, Ron Sauls. As a shooter, the gun is an absolute bell ringer. After scoping the gun and removing the front sight, he wanted a muzzle brake or weight of some sort. My old Beeman ribbed aluminum weight wasn't cutting it. It was too light and the gun's balance point was too far rearward. The Air Magnum is a lightweight gun to begin with, and we both agreed that some additional weight at the business end would allow for a steadier hold.

I started with a piece of 1" diam. drill rod.

Cut off a 5.75" piece. Didn't weigh it. It was easily over a pound of steel.

With the steady rest in place, I faced both ends.

Spotted one end with a center drill.

Note to self: Drilling a 5" hole in a piece of solid steel is really a drag. It would take one heck of a drill press to do this. The lathe spins the workpiece, the tailstock holds the drill bit stationary.

The swarf was piling up.

This was the happiest moment of my day. A 0.250" hole--and it looks on center!

The 0.250" hole will allow a .22 cal pellet to pass through. Now I need to open up one end to fit over the muzzle. A quick call this morning to Joe reminded me that there are several screw holes for the front sight base that I need to cover. Need the bore to be a bit over 2.400" long. The Air Magnum's barrel, by the way, is 0.5905"diameter. (15 mm) Great, that's huge. I don't have a drill bit that large that will fit in the tailstock. I started to drill with a short 1/2" drill bit.

More swarf. I drilled the half inch hole 2.80" into the end.

Then, full stop. I didn't have a 15 mm drill bit and I didn't have a boring bar long enough. This is the fun part of machining--you often need to make tools to use your tools. Yep. Whee!

A not-so-quick side project: a boring bar. Grabbed a piece of 0.250" drill rod from the pile and cut a piece about 4" long.

Faced both ends. I would have done some layout and actually done some measurement, but I was burning daylight. A quick trip to Kromhard Twist Drill Company netted me a small boring bar cutting insert.

I eyeballed the insert's base angle and hand filed it into the end of the drill rod.

What's the worst that could happen? Not shown: I laid the insert into the notch, spotted the center of the hole for the fixing screw, consulted a tapping chart, drilled the tap clearance hole with a #47 drill bit, hand tapped the hole to 3-48, heated the bar to cherry red with a torch , quenched it, and I was in business. No, wait. I don't have a boring bar HOLDER in this size. Gotta make another tool to use the tool.

This is a really handy adapter. It threads directly to the Taig lathe's headstock, and allows attachment of a Jacobs chuck.


I decided to modify an existing tool post to hold the boring bar. I know the boring bar is 0.25" diam. and half of that is 0.125". I dialed out the caliper to a slightly larger number. (Didn't want the edge of the 0.25" hole to come though the side of the holder.) Also had to make sure I didn't drill into the tool post anchor bolt in the center. Settled on 0.150". Set one jaw of the caliper against the aluminum tool post and scratched a reference line. I'll line up the center of my 0.25" hole on this line.

Squared up the tool post on the lathe's cross-slide and bolted it down. Chucked a center drill into the Jacob's chuck, aligned with my scored line, and spotted the hole.

Drilled through with a 0.125" bit...

Followed by a 0.25" bit. I followed this with a chucking reamer to make sure the hole was round and to the correct size.

Spotted 2 holes for 8-32 set screws. Tapping drill #29.

Ran the plug tap in by hand. Lots of cutting oil.

OK, I blued the boring bar.

Back to work. For eyeballing all the angles, the bar worked just fine.

You need a clearance hole for the boring bar to work. Rotated the bar in the holder to get the cutting edge on center. Snugged down the set screws. I used a lot of cutting oil. I bored the hole to just over 0.595". A couple high speed passes just kissing the surface left a nice interior finish.

When I pulled the piece from the lathe, I was astonished to find it still weighed 13.4 oz. I don't think my co -worker had that kind of weight in mind. So, chop. Cut the front end off. Now it's 4.80" OAL and down to 7.62 oz.

I need a metal cutting bandsaw.

Faced the end off using another tool I made a few days ago...

Used the boring bar again to make some cuts into the muzzle end of the weight.

Decided to try out the new live center. Just took a passing cut.

Back to the steady rest again to minimize deflection. To cut a taper on the rear of the brake, I set up the compound slide.

Picked an angle and started with some very light cuts.
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Even the light cuts were pulling the workpiece out of the 3-jaw chuck. I switched to the steel 4-jaw, got out a dial indicator, centered the workpiece.

Slowly cutting the taper.

Another view.

More soon...

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