Saturday, December 3, 2011

Heavy Barrel Sleeve for a BAM B26-2 Part 2

Couldn't leave well enough alone with the shroud--and I guess I wanted some kind of redemption for screwing up the breech project.

Found a suitable ball nose milling cutter--it's a pretty large one at 7/8".  The collet next to it is an R8 type.  R8 collets are normally used to hold tooling.

Another type of collet--a 5C size--fits in a work positioning fixture called a spin index.  Nick sent the index along with a machinist tooling kit-in-a-box gift pack when I bought the mill.  Finding a box from Nick at the mailbox is always a treat--and a spin index was on my short list.  Work can be rotated and positioned in increments as fine as one degree.  Looks like the ticket for making ported muzzle brakes on a mill or drill press.

OK so an appropriately sized collet is installed in the index, then the work is installed into the collet.  What's a collet?   It's a slotted tube that grips around the work and squeezes inward--closing the collet--as the collet is tightened to the tool.  They have tremendous gripping power but a rather small range of useability.  I think the 5C's only collapse about 1/64" or so. 

Due to the length of the shroud, the spin index by itself won't be sufficient to hold the piece for milling.  The plan was to not actually anchor the indexer, but to set the work across the vise jaws and clamp the work in the vise to make a cut.  After making the cut, the jaws are opened and the piece is indexed to the next location, vise is clamped and another cut is made....  I want to mill six flutes, so I'll rotate the shroud 60 degrees after each cut.

...If I ever get that far.  The work is too low in the vise jaws.

A couple 1-2-3 blocks underneath the index gave the height required.  I'll skip pictures of the mind numbing work to get the vise correctly aligned .

A bit ahead of myself, but the 7/8" ball mill was chucked and the head positioned.  The quill was brought down until the tip of the cutter just made contact.

The mill has a digital readout for the spindle depth.  This was set at zero.

Backed off the table and lowered the quill and visually looked at how deep I wanted the cut. 

Noted the reading.  This is the mill to depth.

To make sure the shroud is positioned to the same left/right location each time it's indexed, I made a work stop from an insert vise and a piece of square stock.  When the end of the shroud touches against it, I know it's in the same location as before.

Next, adjusted the table travel stops.  This will ensure the slots are all the same length.

Took a couple passes and worked my way down.

Rotated, and did it again.

And again...

And again...  Eventually, I had six flutes.

Need to add some set screws to attach the shroud to the barrel.  Rotated the work 30 degrees and lined up on a rib.  Switched from the ball mill to a drill chuck.  Spotted for the hole with a center drill.

Drilled through one wall with a #30 bit.

Followed by a piloted tap.  The chuck holds the base of the tap handle perpendicular to the work and the tap handle is manually turned to cut the thread.

Used an M4 x 0.7mm tap.  As is my norm, when the gun is metric, the accessory fasteners are metric.  When the gun is get the idea.   Did this two more times.

Deburred the inside of the shroud.  The set screws need trimmed to length and the shroud needs a finish.

More soon.

Thursday, December 1, 2011

Heavy Barrel Sleeve for a BAM B26-2 Part 1

I've had a piece of steel for this project on hand for some time now.
Not sure as of yet just how far I'll go with it--more on that later.

The old .22 cal BAM B26-2 from a Pyramyd Air open house several years ago.

Aside from maybe needing a new blue job, there was nothing particularly wrong with the existing muzzle brake, just wanted something different.


Barrel band for the sling, too.

Gonna start with a 7/8" OD DOM (Drawn Over Mandrel) steel tube.  The ID is 0.635".

Bought it because it's virtually a perfect fit over the barrel.

Should've bought an even longer tube, though I'd like it to eventually be the same length as the barrel.

I realized that it was slightly too large in diameter at the breech block and would need to be tapered.

Except the tube is longer than the bed of the Taig lathe.

Here's where another inch of length would've helped.  I have about half an inch to chuck.  I'm going to cut the taper just in front of the 3-jaw chuck.  I set a carriage stop as well as set the compound crosslide at the very end of it's travel.  Critical to check clearances to avoid running into the headstock.  Could've easily used a mandrel inside the tube, but I saw that this would work--just barely.

Light cuts--necessary anyway when cutting a taper.

Ground a round-tipped tool bit.  Played with the edge geometry a bit.

The steady rest fingers were greased with moly to help avoid scoring the tube.  Just don't run them dry.

Don't try this at home.  Wiped a file across the taper to blend it in.  Next to the spinning 3-jaw, this is horrible idea.  Seriously, don't do this.

This is also a bad idea--remember, there's very little material chucked in the jaws. 

A quick shine with some 220 grit.  Note the lathe bed is protected with foil from the grit.

Low speed and I kept the work supported.  Un-chucked and cut the stub off the end.

Since it's too long to face down in the lathe, I cut the tapered end off squre using the mill.

Test fit.

Barely too long at the business end--and a bit uneven.

About 0.124" too long.   Could've used that in the chuck...

Scratched a line in the layout blue.  Just provides a witness line to cut to.

Touched the cutter to the end of the work then dialed in 0.118" into the table and made the cut.  Switched to a higher speed and made a couple more passes taking off a couple thousandths each time until I hit the line.

I could just drill and tap for a few set screws, blue it and it's done.  Or maybe I'll lose my mind and try fluting it.  I'll try some test cuts on another piece of steel and see what kind of finish I can get.

More soon.

Wednesday, November 30, 2011

Crosman Breech Attempt--DOA

Well, it was bound to happen sooner or later--abject project failure.  The breech hit the recycling bin a few minutes ago.  I found it impossible to use the small drill press and keep the bit on center when drilling for the barrel.   There's no current plan to make a second attempt.  Sorry 'bout that.  I was really looking forward to this one.  I'll have to regroup and come up with another project.