how i make a chamber reamer

How I make chamber reamers

There really isn’t any magic to this. Any well-educated American with a couple of brain cells to rub together should be able to figure this out – heck, I did! But caution is advised. Machining tolerances must be exact or dangerous situations will be produced. Excellent quality chamber reamers are available through multiple commercial sources (e.g. Clymer, PTG, Manson) at very reasonable prices, especially given the time involved in making your own. Despite these caveats I’ve enjoyed spending more time than I should developing the method described. I’ve pulled information from various sources, especially Paul Rodgers (http://www.saubier.com/paulrodgers/reamer.html), so nothing here has been invented. The method described is what I have personally used – I guarantee there are better ways and I hope that suggestions will be shared. If you engage in this activity, do so at your own risk. If you really need a reamer you should buy one commercially – if you’re like me your initial efforts will fail! Step 1: Cut a piece of ½” 01 steel seven inches long. The cheap bandsaw is one of my favorite tools.

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of 1How I make chamber reamers

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Step 2: Face and drill one end of the reamer blank. I use a 3”, four-jaw chuck in my mini-lathe Set-up

Face

Drill for live center

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Step 3: Turn the reamer blank Set-up in four-jaw chuck and live center

Take a cut (to 0.48 – 0.49)

Cut to neck diameter. This blank is for an 8 x 57 AI. Neck diameter = 0.357”. The cross slide is set to 40* for the shoulder.

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Measure the neck

Turn the pilot

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Now its time to set the taper. This was difficult at first and took some practice but is no big deal now. I set the taper by offsetting the mini-lathe tailstock.

Mark the shoulder-to-base dimension

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Use feeler gauges to measure the taper. For the 8 x 57 AI the shoulder is 0.455” and the base is 0.470”, a difference of 0.015”. This difference is in-terms of the diameter of the reamer at these points. The feeler guage measurements reflect differences between the radius of these points. Because the radii are ½ the diameters, we are looking for a 0.0075” difference between shoulder and base. The limit of my feeler gauge precision is 0.001 and so I round down to 0.007. I can set this using a 0.010 gauge at the shoulder and a 0.017 gauge at the base. 0.010” at the shoulder

0.017” at the base

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And cut the taper. Go slow. This is the tricky part. The base diameter is determined by the web of the brass and cannot vary. Make your first cuts light and keep checking. Approach the base diameter slowly. If your taper is correct, when the base diameter is reached the shoulder will be right-on. Focus on hitting the base. OK, now the taper is cut and its time to polish with 400 grit.

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Step 4: Cutting the flutes Cut a piece of masking tape exactly long enough to fit around the unturned end of the reamer blank.

I’ve found that I can fit a total of five flutes around reamers of this size. Measure the piece of tape (which is the blank circumference) and divide by five. Mark the tape and return around the reamer. Mark the reamer. These marks will guide flute placement. Masking tape is cheaper than a dividing head.

Mount the turned blank in V-blocks. Move the end mill down to touch one of the unturned ends. Measure. Because the stock I use is 0.498”, if I go down 0.249” I’ll be at the midline. Machine shop handbooks indicate that reamer flutes are usually at 95*. To simulate this extra 5* without too much drama I just go down an additional 0.005”. It seems to work.

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Cut the first flute

Rotate the reamer until the next mark is TDC and cut the second flute. Repeat until five are cut. Don’t cut too deep – you’ll run out of room and and destroy the edge of neighboring flutes.



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Step Five: Heat treating I use an oxyacetylene torch to heat until non-magnetic, followed by a used motor oil quench. Mounting the reamer in a drill press may help even heating and reduce warpage – I haven’t had a problem yet (knock-knock). Cut-off unturned end proximal to the pilot (how did I live without a band saw?)

Stamp the cartridge information and grind flats for a 7/16” wrench

Mount in a drill press and get everything ready for heat-treat and quenching. That’s used motor oil in the pasta sauce jar, although the sauce would probably get the job done. It might smell better too (but maybe not).

Page 1 of 3Step Five: Heat treating


While turning, heat to non-magnetic

Quickly (and safely) extinguish the torch, and in one smooth movement raise the motor oil to cover the rotating, red-hot reamer and move the press table to support the jar. Stinky! Let the reamer cool in the oil



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Step 6: Relieving and sharpening Stone off the burrs from the cutting edges. Careful! Just take the burr off. Any more will dull the reamer.

I use a Dremel with a grinding wheel to relieve the cutting edges. You only need/want about 1/8-1/16” of a land behind each cutting edge. Much more and the flute won’t cut well. Carefully grind to about this width.

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Page 1 of 1Step 6: Relieving and sharpening


Step 7: Trying it out! Chuck-up a shot-out Mauser barrel

Ream!

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There are some nice chips!

I’ve got this barrel mounted to an action and have fire-formed five nice pieces of 8 x 57 AI brass. Stay tuned for the next episode where I chamber a Mauser take-off in good condition and work-up loads!

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how i make a chamber reamer

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