Author Topic: Chamber Reamers  (Read 160 times)

rsterne

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Chamber Reamers
« on: February 01, 2019, 04:36:14 PM »
I started on the Chamber Reamers for my new .172 cal and .224 cal TJs barrels today.... The first step was to turn the pilot and chamber sections, and then next was to turn the 1 deg. taper between them, which actually does the cutting.... Here is the .224 reamer, mounted in my lathe, while I was turning the taper....



The taper starts about 0.010" smaller than the pilot, and the taper runs out to the chamber diameter about 1" behind the nose of the reamer.... The actual cutting occurs in the last half of the taper, just before the chamber portion.... After polishing, I milled the flutes, and the turned down the clearance portion between the back of the chamber and the shank.... Here are the two fully machined reamers, ready for heat treating....



Wow, that .172 cal reamer is REALLY tiny, I hope I don't break it when cutting the chamber....  ::)

Bob


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tkerrigan

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Re: Chamber Reamers
« Reply #1 on: February 01, 2019, 11:34:26 PM »
Is the .172 fluted with a 1/8" round end mill and is the .224 3 or 4 flutes?  I am thinking on the .172 that round end might leave a bit more metal to resist breaking and no sharp corners if it can be ran in deep enough to make a cutting edge.  Hard to see for sure.  What is the function of the clearance portion? So you know where to stop?  Chip clearance? Regards, Tom
  • Jefferson, OR

rsterne

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Re: Chamber Reamers
« Reply #2 on: February 02, 2019, 08:18:52 AM »
Both reamers are 3 flute, and I used a 1/4" end mill to machine them.... The end of the reamer machines the cutting edge, so all that using a different diameter reamer does is change the shape of the small radius at the ends of the flutes.... You must start the flute on the taper, where it is smaller than the lands, and end on the clearance portion.... That way the entire length of flute that touches the barrel is a cutting surface....

The pilot on the end is machined 0.002" smaller than the land diameter, and there are no flutes there.... It is a polished surface with slightly rounded corners that just glides over the lands to keep the reamer straight in the bore.... The clearance portion is for chip clearance, and to reduce the drag on the chamber portion once the reamer fully enters the barrel.... if it does, that depends on chamber depth....

Bob
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tkerrigan

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Re: Chamber Reamers
« Reply #3 on: February 02, 2019, 09:32:11 AM »
How do you get 120 degrees between the slots?  Is by guess and by golly close enough for these?  Regards, Tom
  • Jefferson, OR

rsterne

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Re: Chamber Reamers
« Reply #4 on: February 02, 2019, 12:33:39 PM »
I use a 5C collet to hold the shaft of the reamer, with the collet in a Hex block.... I can turn that in my milling vice 1/3 turn per flute.... but yes, eyeballing would be close enough, and there are those that say staggered uneven spacing prevents chatter.... Here is my setup (no collet in place in the Hex block)…. I have a square block as well, really handy for drilling valve screw holes and the port all at 90 deg. to each other....  8)



Here is a photo of the two reamers after hardening....



The .172 cal has been polished, the .224 cal is just the way it came out of the cold water after the hot oil quench.... As you can see, the soap does a pretty decent job of keeping them bright and reducing the scale buildup.... I'll polish the larger one, and then temper them....

Bob

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rsterne

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Re: Chamber Reamers
« Reply #5 on: February 02, 2019, 12:50:11 PM »
I tempered the reamers in my wife's oven at 470*F (I think it is actually 480 at that setting)…. I did the .172 cal for 40 minutes and the .224 cal took 50 minutes to achieve the nice even brown colour I like to see.... In theory, that indicates 500*F, which is on the upper end of the temperature range for reamers (tougher but not as hard)….



I wish I knew more about tempering O1 drill rod.... Hudson steel say 1hr. per inch of thickness, but then turn around and say a 2 hr. minimum....  ??? …. Most guys that use O1 say to temper something the thickness of a knife blade for an hour.... Other places just give a temperature and don't specify a time.... while others say 8 min. per mm of thickness.... which interestingly ended up being what gave me the colour I was after....

Anyone REALLY know how long I should cook reamers when tempering them?....

Bob
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rsterne

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Re: Chamber Reamers
« Reply #6 on: February 02, 2019, 03:13:02 PM »
I chucked up the .224 cal TJ's barrel, blew out any dirt, lubed it and the reamer, and reamed the chamber.... These may just be the best reamers I have ever made....  8) …. They shaved the rifling off like a hot knife through butter.... Once the chamber portion was entering the barrel, after that I only went 0.10" at a time, but the way the reamer was cutting I probably could have done the whole thing at once.... The danger in doing that, of course, is that you collect too many chips, and if one jams, you will shatter the reamer.... Here is a photo of the amount of chips that collect from removing just 0.10" depth of rifling....



The chips are sitting right at the part of the reamer that does all the cutting.... Forward of them, the flutes don't touch the lands, and behind them the reamer is parallel, the diameter of the chamber, so no real cutting occurs there either.... You can see that rather than "dust", these reamers are producing actual "chips" or "slivers" of steel as they cut.... which is why they are cutting so nicely.... For the first time, the barrels were not even getting warm to the touch, another indication that I am shaving off metal, rather than just wearing it away....

The .172 cal reamer cut just as nicely, in fact you could barely feel the reamer bumping as it removed the four shallow lands in that tiny bore.... I am absolutely DELIGHTED in they way these cut, and the smooth finish they left....  8)

Bob
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