Rechambering melonite barrel?

[bobcat trapper]

Ive got a barrel I need to rechamber but its melonited and I can make a reamer even scratch the stuff.I knocked a few threads off and ran a boring bar inside thinking I could cut though it then open up with the reamer no go still can't scratch it with the reamer. I'm worried my next move is to cut the chamber clear out and start over and I don't want to loose that much length.

 

[Pdvdh]

The barrel could be a lost cause. Even if you break thru the surface hardening, the chamber reamer will still be cutting melonited material in the neck/throat/lead area, no?

Your reamer may already be thrashed. Pretty sure you'd need a carbide reamer to have any chance at all. Is it gonna be worth it?

I'm tagging in to follow what advice the gunsmiths and/or machinists might be able to offer ... I'm pessimistic about what you're trying to do, based on what I know it...

 

[bobcat trapper]

That thought crossed my mind as well.

 

[geargrinder]

Carbide reamer is almost the cost of a new barrel.

I vote that it's a lost cause.

 

[shortgrass]

geargrinder and phorwath are both correct. If you've dulled your reamer by trying to cut Melonited steel it can be re-sharpened. Takes carbide to cut treated barrel steel, *or any other treated steel for that matter*.

 

[Trickymissfit]

melonite is nothing but a fancy word for nitriding steel. The case can be anywhere from .005" to .050" deep. Usually Rockwells at 64rc. Yes you can cut it with some grades of carbide, but when your looking at sixty plus RC, your thinking about ceramic's in a heavyduty lathe. Forget hand reaming, as it just won't happen. I've cut a lot of nitrided steel in my life time, and it's kinda scary the first couple time you do it. Chips come off bright red even though they're in a coolant flood. Surface speeds need to be high, and you must really push the metal off fast. Think 1200 rpm to 2000 rpm @ about 10" per minute feed rate for starters. I've seen some steels want a feed rate closer to 24" a minute!

It takes a strong machining system (very rigid with very heavy bearings) just to cut it. I've cut it on Okuma CNC lathes, and it seems that about 1 in five times I ended up in a wreck. Leaving me to completely realigning turret and head stock (one of my least liked jobs!!)

I'd just consider the barrel junk, and start all over.
gary

 

[Deleted member 46119]

melonite is nothing but a fancy word for nitriding steel. The case can be anywhere from .005" to .050" deep. Usually Rockwells at 64rc. Yes you can cut it with some grades of carbide, but when your looking at sixty plus RC, your thinking about ceramic's in a heavyduty lathe. Forget hand reaming, as it just won't happen. I've cut a lot of nitrided steel in my life time, and it's kinda scary the first couple time you do it. Chips come off bright red even though they're in a coolant flood. Surface speeds need to be high, and you must really push the metal off fast. Think 1200 rpm to 2000 rpm @ about 10" per minute feed rate for starters. I've seen some steels want a feed rate closer to 24" a minute!

It takes a strong machining system (very rigid with very heavy bearings) just to cut it. I've cut it on Okuma CNC lathes, and it seems that about 1 in five times I ended up in a wreck. Leaving me to completely realigning turret and head stock (one of my least liked jobs!!)

I'd just consider the barrel junk, and start all over.
gary

Holly cow that's fast.

If you don't push it does it just get harder and abrade the cutting tool?

 

[Gord0]

Holly cow that's fast.

If you don't push it does it just get harder and abrade the cutting tool?

It won't get harder, it will just dull the reamer quick and in a hurry. It'll be rough going with carbide until you break into the softer material. That's a lot of surface area at that hardness to cut. A CNC with a carbide boring bar could break through the skin but you'd still need a carbide reamer.

 

[Trickymissfit]

Holly cow that's fast.

If you don't push it does it just get harder and abrade the cutting tool?

carbide and ceramic tools don't really cut metal as we'd like to think. They push the metal off the surface. Where as a good high speed tool tends to slice the metal off the surface. Carbide's main advantage is it's ability to handle heat, and ceramic will take even more.

A lot of metal work hardening is due to not getting into fresh metal, All metal that has some carbon in it work hardens a little bit. Some more than others due to alloy make up. Steels that are heavy with chrome and nickel work harden faster and easier. All this leads into the term "surface cutting speed." There's a lot going on with that phrase, and the folks that figured it out are a hell of a lot smarter than I am. Plus a major portion is trial & error. You learn that softer metals want a higher surface speed. Metals that are known to be tough and will work harden will want a slow speed with a heavy feed rate. Yet all this changes with the Rockwell and method of cutting. High speed reverts back to the lower rate of speed, but carbide and ceramic was a much faster surface speed. I honestly can't comment on diamond inserts for a couple reasons. I've only used them on pretreat steels and aluminum, and even then it wasn't often. You get into something that has a .025" case at 64RC, and you got to get thru the first .010". The case decreases in hardness as you go deeper. If you only need to remove .008" or less, forget it. You can grind the .008", but that's about it unless it can be honed. Believe me a 64 RC is harder than most tools used. I highly recommend reading the Machinist Handbook for a good start, but there are some better sources. Seems like Valenite has a good manual (maybe Sandvik).

A good rule of the thumb is that a smaller diameter, the faster the rpm. Yet a slower feed rate. But cutting tools simply change everything. Carbide and ceramic want speed to force the chip string off the insert's surface. Two reasons come into play here. First is heat. If the chip stream leaves the cutting surface in a rapid fashion, and doesn't really stay on the insert; then all the heat goes out with the chip, making the part stay cooler and not imparting heat in the insert. It's also a good way to get burnt! Heat will actually harden some steels while cutting, and forget the idea that coolants will fix this. Still some metals don't want any coolant period (Ampco Bronze comes forth here). Ampco will harden so bad that that you can't touch it with a high speed tool, but still cuts better with high speed if done right.
gary