What is chip welding?
The Chamber reamers that we carry at 4D Reamer Rentals LTD are all High Speed Steel (HSS).
When we inspect reamers upon return from rental we look for a few things.
- Obvious damage of any kind. (dings, chips, modifications, burns, rounded edges to name a few)
- Dirt/metal chips from the reaming process
- Oil (in excess)
- Chip Welding
This last one is the point of this post. Chip welding is the result of several possible causes.
- Quality of the cutting oil, when proper cutting oil is used chip welding is greatly reduced.
- Pushing the tool hard when cutting, i.e. high rpm, fast rate of feed or a combination of the two. Naturally this ties back to the cutting oil too.
- Quality or chemistry of barrel steel as well as the heat treat of the barrel can contribute to this.
- The diameter of the chamber, large diameter chambers with big shoulders are very prone to chip welding.
There are probably more, but these are the common and likely causes.
HOW TO AVOID IT…
So #1, use good quality cutting oil. Its getting harder to find these days but sulfur based cutting oils are the best. There are numerous products on the market that work fine. Spectrum cutting oil from Conoco, Brownells Do-Drill, Vipers Venom cutting oil, and in a pinch even Tap Magic will work. This is not an exhaustive list, just a few you can usually find locally or on the Internet. See if you have a local oil distributor, call and ask what they have?
#2 pushing the tool too hard, you can certainly control this one. Having it you’re way and right now is great for fast food, not so much for machining custom firearms. Use plenty of cutting oil, slow down and put some precision and care into your work. Whether you are a hobbyist or a professional this advice will help you build guns that shoot circles around the competition. Your tools will last longer (and so will ours… LOL) and they will produce a better finish in most cases.
#3 large diameter chamber benefit from roughing of the chamber. This can be performed with roughing reamer (which are normally used for production work). Chambers can be roughed with a drill bit and boring bar as well. The boring bar is used to tru up the camber to the bore after drilling. This prevents the misalignment of the chamber to the bore. Because the reamer is not forced to cut so much material in a roughed chamber it is far less prone to metal build up.
Barrel steel: Its certain that all the big name barrel makers use certified barrel steel. Even so lots do vary. All you can really do is watch the tool and make sure it is not getting gummed up with chips welded to the cutting edge. Once the chip weld starts it is a progressive build up. Normally it is of little consequence and can be easily cleaned off with a diamond lap or a stone by someone who understands how the tool works. If you stone the outer periphery of the reamer you are ruining the tool in short order. Never stone the outer cutting edges of the reamer. Only stone on the inside of the flute, if you look at the geometry of the tool you will note that stoning there changes the tool a very tiny amount. When you stone the outside the dimensions are changed instantly and often way too much!
Occasionally we have seen guys test cut in some cheap low carbon steel. This will often chip weld immediately.
If you are at all unsure, Do Not Stone!, we will charge you for having the tool resharpened if you damage the reamer.