Gavin Gear at the UltimateReloader came to me with the idea of doing a video about chamber reamers. He ended up titling the finished video “All About Chamber Reamers”.
That video is a very complete discussion of chamber reamers, explaining the how and why of these tools. Gunsmiths or hobbyists of all experience levels will likely learn something. With that said, there are things I would have like to cover that would simply have made the video too long for most viewers, so I thought why not cover some of that here.
I am often asked about the difference between solid and live (removable) pilots. We mention this in the video but we did not get into the damage you can cause by ignoring pilot fit to the bore. Pilot fit is a big contributor or fix when it comes to chatter. When the pilot is .0005″ to .001″ smaller than the bore you will be the least likely to have chatter related to the pilot, here is a discussion of why pilots are critical to success.
Reamers work better if they are imperfect. What? How could that be?
If a reamer is perfectly symmetrical that promotes chatter. Reamer makers wisely angle the flutes of the reamer to help avoid this problem. The manufacturing process makes it pretty easy to allow variance in dimensions of the flutes to eliminate chatter. As the grinding stone wears during the cutter grinding process there are tiny changes in the dimensions of the flutes. Not enough change to ruin the chamber dimensions, just enough to help avoid chatter.
Note the end view of a reamer at right, the reamer has been cut off at the middle of the chamber body. You can see that the flutes are not aligned directly with the center point of the reamer. The depth of each cutting flute is slightly different as well.
Chatter is caused or mitigated by many factors. The quality of the barrel steel (yes Virginia it does vary from lot to lot). Various makers may have different alloy recipes. Heat treat of the barrel steel can vary, most rifle barrel run in the lower to mid 30’s on the Rockwell ‘C’ scale. If the barrel is too soft it promotes chatter because the reamer wants to dig into the soft material. If the barrel is too hard it causes undue wear of a High Speed Steel (HSS) reamer. As mentioned before if the pilot is too small it allows the reamer to move around in the bore of the barrel, promoting chatter. If the pilot is too tight it can damage the bore or cause the reamer to break.
Chatter can be mitigated by several things the person reaming has control over. First, adjust feeds and speeds. Once chatter starts the best way to stop it is to slow the RPMs down. Always use plenty of good quality cutting fluid. Experiment with increasing the rate that you feed the reamer or reducing the rate. All these things affect chatter.
Other things you can do to reduce chatter once it starts are to use wax paper wrapped around the reamer, along with normal cutting oil. This will dampen the vibrations and help reduce the chatter. If you are to the point of using one of these fixes, slow down the RPMs and feed rate to get the chatter cleaned up. Another dampening method is to slit a cleaning patch so you can put it on the reamer near the shoulder of the body. If you do detect chatter, then either wrap piece of wax paper around the reamer or cut a small slit in a patch and slide over nose of reamer up to the shoulder. Oil reamer and make a short cut, and when the reamer cuts through the patch. it will remove chatter.
Old time fixes were to load the reamer with thick gear grease or bees wax. These methods work but are much messier than the wax paper or cleaning patch methods. To learn more about chambering rifles check out this book.
Chip welding often leads gunsmiths to think a reamer is dull. Nope, it’s just a build up a steel that has stuck to the inside of the cutting flute. Most commonly at the sharp shoulder at the end of the neck and shoulder on the reamer. But, it can happen all along the cutting edge. Three major factors cause chip welding.
- Quality of the barrel steel
- Quality of the cutting fluid
- Force on the cutting edge
You have no real control over the barrel steel except to buy from known makers who used certified barrel steel in the manufacturing process. But, some steel will have a greater affinity to bond to the surface of the cutting tool. If you see chip welding stop and clear it off with a piece of copper.
Quality of cutting fluid is up to you. Buy cutting fluid that is up to the job. Reamer makers offer suggestions about the right products to use.
The amount of force you apply to the cutting tool is definitely in your control. If you see chip welding and clean it off, the best way to avoid more is to ease off on the feed rate. The harder you push the tool, the more heat is generated at the cutting edge, this forces the cutting fluid away and does not allow it to do it’s job. Feeding too fast will cause tool wear as well as a poor finish in the chamber. The shoulder area is where you will notice the rough finish first.
If you are dealing with an interrupted cut there are simple ways to protect the reamer and prevent chatter from getting started. See this post.
Want to learn more about gunsmithing tools? Check out this book by Fred Zeglin
Below is the video that I mentioned at the start of this post.
GunsmithTalk 