48.01 Carrier block

This series of threads is intended to document the build of an RRG gat to plans(mostly).  The topics are being separated by drawing number and sub-assembly.  While all comments are welcome please limit the discussion to the print or assembly in question.  Photos and maybe videos (or links) will be added as they become available.

A learning part will be made first in 6061 aluminum.  Dimensions 3\" x 3.125\" (complete material list can be found here.)
Cutting tools are carbide, brushed on lubrication will be used on all cuts.

The learning part will be machined as one piece.  I understand two piece may be the best way to go.

After studying the prints for some time a distinct lack of talent was discovered.  All the dimensions have been sorted save one.  Looking at 48.01 the od on the hex does not seem to be specified.  I located the od to flat dimension and the base circle to peak dimension but cannot determine the base circle (dotted circle) dimension.

Lathe order of operations.
Mount the material in the chuck with about 1.5 inches exposed (should it be turned between centers?)
Face
Center drill
Bore 0.625 hole through piece
Bore 1.000 x 0.125
Turn od to unknown dimension (see above)
Shoulder cut to 1.250
Slot (using cut off tool) 0.090 to depth of 0.150
Reverse piece in chuck
Face to overall length of 3.000
Reduce od to 2.750
Reduce step od to 2.500

Place material in dividing head chuck (hex part facing up)
Use center drill to mark 10 holes on 2.000 diameter
Center drill 0.187 dowel pin hole 0.625 from center inline with barrel hole (press fit)
Bore 10 - 0.275 through holes on 2.000 diameter
Ream to 0.281 (9/32?)
Mill 10 flats on to a depth of 0.375 below od. Top of flat should be even with center of hole.
Reverse material in chuck
Index to dividing head
Bore holes  0.415 to 1.750
Ream to 0.420

That completes this piece.  Please suggest a better (one piece) way to proceed.  Making the assembly in two parts would save boring and reaming a blind hole and a good bit of material.

Just curious about how you are going to bore the .275\" holes before you ream them to .281\".   I drilled and reamed mine as per instructions with the 3 parts sandwiched with the dowel in place.  I had good spots, a good drill and dialed in as close as I could get it.  The bolt circle on the drill exit (2.012\") on the carrier wasn\'t the same as it started. (2.000\").  Every situation could be more or less depending on a lot of factors.  From my understanding, and I\'m a newbie at this, is the barrel plate holes and the .281\" exit holes of the carrier have got to be spot on.

Just finished my barrel assemblies today.  Good luck with your build.

Don

You comments are spot on.  I made the order of operations from the print only.  New plan is being formulated.  Doh!  Guess that is why I posted before cutting.

Guys I made my carrier as a two piece assembly and bored the holes in the two parts and the plates seperately. I used an adjustable lenght carbide boring bar and had the benefit of an accurate CNC Machine to do the work. A link to the boring bar:

http://www.mcmaster.com/#boring-bars/=pof4ho

I found this much easier and more accurate than attempting to keep a drilled and reamed hole straight and on size through the stacked up plates.

nitewatchman

After reviewing the prints AND instructions and many pms and sound posts it has finally gotten through my thick head to make the carries block in two pieces.

See, I can change my alleged mind.  I even manage to listen to sage advice now and then.

Working on the new order of operations.

I really do appreciate all the advice, thanks!

What is the best way to index the two parts of the carrier block?  I am thinking drill a dowel hole though both and pin it.

I used a tight fitting rabbet between the two block halves and the barrel plate and front block half. I then indexed on a 3/16\" dowel pin which I use to control all the parts including the front plate. The master dowel is built into the fixture. The fixture is bolted to the table, faced and then machined to accept a series of 3/8\" shoulder bolts being sure that the shoulder of the bolt enters the fixture about 1/2\" to clamp it in place and align to the reamed or bored holes in the workpiece.

nitewatchman

Wes the tool and die man of our group is also planning to use shoulder bolts in the same way on our group builds.

Later 42rocker