Single flute chamber reamer?

[pdeal]

I wonder if anybody here can say if this would work. For one of wildcat type projects it would be nice to make my own chamber reamer. It would seem to me that it would be posible to make a single flute chamber forming tool. Think it would work to turn the chamber profile in oil hardening drill rod and cut the flute with neutral or a little negative rake then grind relief on the thing so that it only contacted on the cutting edge and two other points? Seems like it could work. Crazy?l

[GeorgeGaskill]

in the heyday of wildcatting to make "half-reamers" (I've also seen them called D reamers) for their creations. Basically turn a solid version of the desired chamber, harden the piece, then grind away exactly half of the diameter in the areas that you want to cut.

I have made two half reamers; one cut very well, the other was a turkey. I was unable to determine why there was such a great difference in performance. Undoubtedly related to the grinding of the "half" but not obvious as all measurements seemed OK.

You have to be very careful using one that chips don't get caught between the backside of the reamer and the chamber wall so you don't score the chamber walls.

[Rob_Black]

I thought you didn't cut away half - it's actually a little less than half. I've seen a formula, maybe in one of the Machinist Bedside Reader books, that gives it. Also there was an article in American Rifleman on this type of reamer, 1960's era I believe.

I've thought about trying these, but where do you get specs on chamber dimensions anyway?

Well, as usual, I almost know something usefull [img]/ubb/images/graemlins/crazy.gif"%20alt="[/img]

Rob

[pdeal]

I was thinking more along the line of milling a flute into it. Seems this would leave more support to keep the thing from chattering.

[John]

I have made a few "D" reamers over the years and find it just as easy to make one with 4 or 6 flutes. All you need is some way to index, I use a spin jig. You need to be able to grind the outside after it is hardened because it will worp when being heat treated. I mounted my spin jig on a flat bar 1/2" X4" and put an ajustable center on the opposit end. I then clamp the bar in the milling machine vise and use a cup grinding stone in the spindle of the mill. The Bar can be tilted to grind a taper and for puting the throat on the reamer. I have not done any of the bottle neck chambers yet, most strait BP cartridge. A tool and cutter grinder would be great.

[R_Johnson]

As I recall, you grind the D bit under half on the order of .001 per .5 inch of diameter. I have made reloading dies this way. You can find cartridge dimention's in some of the older reloading manuals, such as speer. R. Johnson

[GeorgeGaskill]

SAAMI chamber/cartridge drawings in an appendix. Worth the cost of the manual just for that. It was published about 1980 so it won't have all the newer cartridges in it.

[John]

Pacific tool and gauge sells a book with most of the chamber reamer prints, I think it is about $50. Phone # 541-826-5808. I have one and find it most useful.

[Tel]

..or you can have a look here - they've got a good range of cases fully drawn & dimensioned.

http://www.reloadbench.com/main.html

[Bill W.]

I believe it was the common practice with half reamers to leave a couple of thou over half, to hold the reamer to the chamber while cutting. This was to prevent chips etc. from scoring the chamber. Didn't always work, but this was the theory.

[John Lawson]

Single flute reamers should be made precisely half diameter and releived. They are left about a thou over half, hardened and then stoned to exact size. They cut without chatter either by hand or in the lathe.
If you make six flute reamers, you will have to offset the indexing or they will chatter and ruin the chamber. Boy!. If you can make a five flute as fast as I can make a single flute, you are some gunsmithing whiz! But, I've only been doing it for 60 years.
If you make the half reamer from water hardening drill rod and float a layer 1" thick of heavy oil on a can of salt water, it will harden up without warping. You have to keep it moving as it sizzles. Straight up and down is best. Then into your furnace to draw to a brown color. THEN you stone it. If you grind it from the solid, you will introduce all kinds of strange internal pressures and warps.

[John Lawson]

That didn't come out the way I intended it. I meant to say I'd spot you one flute handicap.
I wrote a complete article on making half reamers in GUNsport in 1969. They were widely used in the late sixties and early seventies. The greatest advantage was that you could try some different shapes without spending your entire inheritance.