Making a Reamers...
Paul Rodgers - How To Make a Reamer This is a short paper describing how I have learned to make my own chamber reamers. These are "half reamer" and is how many of the early wildcats were done. Currently a custom chamber reamer is less than $200 and well worth the money if you have it. The process described below requires expensive machine tools and is labor intensive, if you do not have machine tools or the experience to run them you are probably better off purchasing a custom reamer from a Chamber Reamer manufacturer. As always I advise you that working on firearms is inherently dangerous, you do so at your own risk. Working with wildcat cartridges with no loading data available increases the chances of firearm failure and personal injury, I cannot be held responsible for the work you do or the firearms you work on. I urge you to work carefully and within the limits of your knowledge and skills. The first chamber reamer I made was a "half reamer" and worked without trouble despite missing some key features. I built it from the knowledge gained from various books, magazines and articles, almost no verbal instruction or examples. Since that time I have been instructed by several people who have made many reamers using this method and the results improve with each project. The example here is a .17 Jet die reamer the procedure is the same for a chamber reamer with minor changes. I acquired a barrel for a T/C Contender with some fired brass and nothing else. Reloading dies are not easily obtained and expensive so I made my own starting with this reamer. I start each reamer with a print of the chamber or cartridge, in this case measurements were made from fired cases and a chamber cast. The material used for the reamer is Drill Rod, available from many sources such as MSC Industrial or Enco. I have been most successful with W1 water hardening drill rod, O1 oil hardening seems to be preferred by others but W1 has worked the best for me. Prior to actual reamer cutting I set the shoulder angle on the compound using scrap metal to get the exact angle I want, once set then install your reamer material. Set up your material on center, I use the 3 Jaw chuck and live center, not truly between centers but I get less than .001" taper over 8 inches which is adequate. Use SHARP tools, carbide is good but HSS tool blanks ground and polished work just as well, sharpness is most important. I start with a cleanup cut to get the outside of the material on center then proceed to the pilot diameter, you want this to be no more than .001" smaller than the bore diameter, shoot for .0002-.0005" under. I make the pilot at least .5" long, easy to cut shorter after all the other work is done if you like. The next diameter is the neck, I make this intentionally undersize so I can use the same reamer for FL sizing die and chamber by reaming the final chamber neck to the desired dimension. Then cut the shoulder angle. The way I set up to cut the body taper is by using feeler gages. If you have a taper attachment or can move your tailstock, use whatever method you prefer. I mark where the taper will end measured from the rear of the shoulder/body junction then rotate the compound to about one degree. I determine the RADIAL taper of the body and get two feeler gages that are different by that thickness, in this case it was .004" so I used .016" and .020" feeler gages. Move the compound forward to the rear of the shoulder and dial the cross slide in until the tool touches the BIGGER gage then, using the compound, move the tool to the mark at the rear of
the reamer and check with the SMALLER gage. Adjust the compound until you have the taper you desire, lock it down and cut the body taper. Polish the blank with superfine abrasive paper, I use 600 and 1,000 grit available at auto body supply houses. It should look like the picture below, you can see the mark where the body taper ends.
Now on to the second part, cutting it in half. For the reamer to cut properly it must be cut EXACTLY in half, +/- .0002 or less is the target but you can get acceptable results if you are within .001 of center. Here is how I set it up. Clamp the rear of the reamer in a vise and the front of the pilot in some type of support as shown, leave enough room to get a micrometer in to measure both ends of the reamer, see below. Begin by leveling the blank on center, you will need a micrometer and calculator. Measure the rear diameter of the blank just behind where the body taper ends, you will make all future readings at the same spot here. Measure also the pilot diameter just in front of the neck, measure the neck diameter as well. Record these measurements to the .0001". Calculate the distance between the top of the shank (measurement 1) and the top of the pilot, call this "Z1". Calculate half of each of the measured diameters, write these down. I sketch the reamer profile and write the diameter measurements above the picture and the "half" numbers below. I install a Test Indicator (TI) in a drill chuck and a Dial Indicator (DI) on the column. Bring the head down until the TI reads zero at the rear right where you made Measurement 1, then zero the DI, see picture.
Move the TI over and move the head down until the TI reads zero, DON’T READJUST ANYTHING. Read the distance the head moved on the DI, you want this distance to be exactly "Z1". Gently move the reamer and repeat this back and forth measuring until the DI measurement is exactly "Z1", now you are level on center. Now cut the reamer in half. I use a 4 flute carbide endmill and plenty of cutting oil. You need to cut into where you measured "M1" at the rear and into the pilot where you measured there also. Cut and measure until you have cut about .0005"-.001" ABOVE the center as you calculated earlier. It should look like the picture below.
Clean it off and use a fine hand stone or diamond file to remove the last bit of metal until you are right on center and the flat surface has a nice polished finish, keep your stone/file level as you don’t want to round the cutting edges. You will need to VERY GENTLY remove the burrs from both sides of the flats on the cutting edges, keep your stone square to the flat and don’t dull the cutting edges. I then turn the reamer on it side and carefully file a relief flat under the cutting edges of the body, shoulder and neck. Keep .020-.030" from the cutting edges and I make the flat about .060" wide. Finally I clamp the reamer in the vise backwards and cut two flats at the rear parallel to the cutting flat for a small wrench to hold onto. Make the flats to fit the wrench of your choice. Last step is to harden your reamer. I started with a propane torch but switched to MAPP gas when experiments showed that the propane didn’t get the reamer hot enough for good hardening. Get the body and pilot bright red and hold it there for a couple of minutes moving the reamer back and forth in the flame to keep the heat even. Quench in the appropriate media in a rapid up/down motion with the reamer held straight up and down until it is cool to the touch, a minute or so. Test the hardness with a sharp file on the round bottom of the body near the shoulder. Use light pressure and the file should not cut it, if it does, reharden it but get it a little hotter before quenching.
You can polish the light discoloration off but it isn’t necessary. You can temper it but that also is not necessary if you will only use it a couple of times. Some of my reamers have cut 3 or more chambers without dulling or breaking, use a slow turning speed, a lot of cutting oil and more patience. It took me a few tries to get it right the first time so approach this project with patience and don’t get discouraged if the first couple don’t work out, make another one until you get it right. Here are some tips and observations: If you are making a die, make sure the pilot hole is drilled ALL THE WAY THROUGH. You can pre-drill your chamber to save time, go about 1/16" under shoulder diameter and no deeper than the distance from shoulder to back of pilot. Keep the reamer clean of chips. You may have to wiggle up and down to get the cutting edge to bite depending on how close the pilot fits the bore. In some cases you may have to push the reamer pretty hard to get it to bite. If you can’t get it to cut any other way and the reamer is still sharp you can try to grind a relief on the shoulder all the way around the bottom.