REAMERS Breaking

[Rustystud]

About a two months ago I had my first reamer break. This was a brand new reamer. I have reamed tens of thousands of barrels over the last 45+ years. There is another custom gunsmith in my community and he has had a couple reamers break over the last year or two. I received a call from a good friend and gunsmith for a government test facility. He chambers literally hundreds of barrels every year. Last week the had two reamers break on him in the same day. He has been doing chamber reaming for twenty years or more and these were a first for him. I am not trying to bash any reamer manufacture, but I am curious if any others are having reamer failures. The failures that I am familiar with have been with both the ream, clean, and lube method and the high pressure flush method. All have been HSS reamers. The reamers all have lost a flute in the shoulder area of the reamer. I have noticed the flutes have been thinner and the grooves been wider on larger diameter cases. Curious to hear your responses.

 

[X Ring Accuracy]

So far only one break like I said on your original post. I doubt it is a cost issue of less metal, more of an issue that the maker is cutting the flutes thinner for a more aggressive / faster cut? I'm not saying that's the reason, just guessing. My reamers are from when the known manufacturer was trying to be the top dog and I just have mine resharpened. I wish I had a new versus old one to compare flute width.

 

[Shrek]

I'm betting new steel supplier is the culprit.

 

[Kevin Taylor]

I have done a lot of chambers, thousands, I doubt 10,000. Never had a reamer break. Don't have many new reamers. New steel seems a reasonable problem.

 

[Rustystud]

Don't think it is the steel. The barrel that I was reaming had been stress relieved 4 times. Rockwell 34. Machined very nicely.

 

[carlsbad]

Don't think it is the steel. The barrel that I was reaming had been stress relieved 4 times. Rockwell 34. Machined very nicely.

I think he meant, and I would agree, there is a likelihood that it is the steel supplier for the reamers. It really depends on who is doing the heat treat. Without bashing, is there a commonality to the manufacturer of the reamers? I don't know if reamer manufacturers buy their blanks in the final heat treat state (likely) or if they heat treat them after they receive the steel.

As I'm sure you know, reamers are hardened as hard as possible without being brittle. this sounds like someone is heat treating a little too hard. Could be the alloy, could be the heat treat process.

Could be as simple as the oven temp controller needs to be calibrated.

Your common mode failure analysis should cause the manufacturer to track down the cause of the failures.

--Jerry

 

[skeetlee]

i broke a PTG 30BR reamer once. Not sure why or how. If i were a betting man, and i am not! I would guess it had to do with the pusher i was using. I no longer use pushers and hundreds of barrels later, no issues! I use a lot of PTG reamer and i like them. I love JGS reamers however, and probably prefer them. PTG replaced my reamer no questions asked. Hard to beat that!!! Lee

 

[Shrek]

I was referring to a new steel being too brittle or inconsistent. Steel suppliers are going out of business left and right. New xxxxx steel isn't the exact same as old suppliers xxxxx steel.

 

[shortgrass]

I broke 1 last year. First chambering reamer that I have broken in 25+ yrs. Came from a maker that I'd said I would not buy from any more. Called to see if they would do anything, was told I didn't know what I was doing and it was my fault. I've been machining since '74, attended and graduated from 2yr gunsmithing program (MCC class of '93). Using 'sensibly', about 120rpm, chamber pre-drilled and bored with boring bar, muzzle flush system in use. No bumps, no "wiggles", no "hick-ups", 1 flute just decided it had enough, and snapped. Only had cut about .200" into the new 'chamber' at the shoulder. A new, never used finish reamer, at that. I know for sure now that I won't go back to that maker!

 

[Hal]

He is talking about the area where the flute broke.

Hal

 

[JRS]

He is talking about the area where the flute broke.

Hal

The flute broke, and the reamer remained intact?

 

[Ggmac]

Super glue it ! Well on the serious note , it seems a lot of Reamers have broken lately . I think something has changed in there process . I wish the manufacturer would chime in . I'm sure he doesn't want anymore bad exposure . There's no telling how many barrels COULD have been damaged or even the lost time to both the smith and the client .
I really wish we could hear that it's been fixed .

 

[carlsbad]

Solid carbide is hard, and brittle, but makes up for it in strength. I believe the solid

If being too hard is the issue, one should never buy a solid carbide reamer. I've bought many reamers over the years...some very recently. The only one I've ever broken was MY fault. I was abusing it and it was obvious at the time. Actually, I'm surprised it didn't break much sooner than it did.

If indeed there is an issue, I'd suspect the clearance angle being too steep or the stagger of the flutes being less than ideal.

Hard and brittle aren't exactly the same thing but there is a hardness vs brittle tradeoff for each steel. And it is differnet for each steel. Almost any carbon steel can be heat treated to be brittle. Too steels are allowyed to be hard and stay sharp while stying just inside the brittle region.

I know much less about carbide but clearly it has enough strength to overcome brittleness in most applications but can be broken also. --Jerry

 

[carlsbad]

one thing I've noticed lately is that it is hard to find a reamer with more than 3 flutes cutting. This increases the load on each cutting flute. --Jerry

 

[carlsbad]

Mike,
I agree based on the fracture shape, the failure was overload on that one flute.

So thinking about what you say about only 3 flutes cutting being the design, I can accept this. I've never done tool design but 6 flutes cutting does seem like it would result in unacceptably low feed rate per flute unless you really pushed it hard. So why have the other 3 flutes? I can see their value for centering the tool and cleaning the profile.

--Jerry

 

[TRA]

OR, it could have hit a hard spot in the steel. I wish I could blame a manufacturer everytime my shop breaks high priced tooling. I'm surprised there are not more incidents of breakage due to the methods used in chambering.

 

[carlsbad]

I find hard and soft spots in the metal in cheap Chinese castings but not in $400 barrel blanks. --jerry

 

[TRA]

Steel work hardens, some more than others. Gunsmiths never screw up. It has to always be the manufacturers fault. Just because a bar of steel cost 400.00 does not mean it's perfect either. Because someone drilled, and bored a hole, does not guarantee immunity from tool breakage. I doubt most of these setups are as perfect as believed to be.

 

[shortgrass]

What happens if all flutes cut exactly the same is chatter. Proper reamer design has some offset between flutes contacting the work piece. It may sound counter intuitive but I assure you, it is true. Most work will never be set up true enough to see it consistently either way. Just how does "perfect" simultaneous contact happen, anyway? It doesn't.

There will always be one edge that comes into contact first, with the material. This proves my point, if you think about it.

As for carbide vs hss...HSS is much more "pliable" than carbide. There is a torque on reamers that cause a certain amount of deflection, a lot of which is radial. HSS allows a lot more twisting than carbide. Think about that for a second. Carbide is good at handling heat but is poor at torque or bending. HSS will handle deflection far better than carbide.

The pics above look to me that the feed was too aggressive or the reamer dug in too fast, regardless of material. It shows on one flute but that stress is induced across the whole reamer. Given the exact same problem, I believe the HSS held up better than would solid carbide. There is a yield point that must be met and surpassed before either, or any material will break. Grabbing was probably to root cause of breakage.

I can assure you, I was NOT feeding aggressively. The barrel stayed in the lathe, I immediately ordered a reamer from Manson (like I should have done in the first place!). I examined the 'hole' with the HawkEye, to see what damage may have been done to the barrel,,,, there was very little damage. I checked the set-up again, after the Manson reamer arrived in a few days (Dara had what I wanted on the shelf). No adjustments made to the set up. I started off very, very gently with the Manson reamer. No bobbles what so ever. Mansons reamer went to cutting just as it should have and the chamber was finished like 'clock work'! And , work hardening?! Pre-drilled and bored with the muzzle flush running and properly sharpened tools? Work hardening usually occurs when a tool rubs, which generates heat. My tools did not rub, they cut. And, those tools were always under coolant carrying heat generated from cutting away. I think most of the posts made after the pic I posted are from "arm chair" machinists, mostly self trained or trained by the interdnet, more atune to speculation than actually engaging tool to work. I cut heat treated steels every day (4130 NQT, mostly). After 40+ years machining, making a living at it, seeing the transition from high speed tooling to carbides, the transition from manually operated machine tools to CNCs, after solving hundreds of thousands of tooling related problems on the shop floor or tool room. You can speculate all you want from afar, that's what the interdnet does. I call it a tooling failure that should not have happened. Could have been from the tool being not ground properly, could have been the HS the reamer was made of, could have been the procedure or method used to make the tool. I may not have cut as many chambers as Rusty Stud, but I cut on average 50-60 a year, and have done so for many years now. And I did not learn how by watching YouTube videos or begging for tips on interdnet gun forums, just so I could be "cool" and admired by my friends 'cause I "do my own work".

 

[carlsbad]

Shortgrass,

If you're taking offense to my "overload" diagnosis, that is probably because you interpreted that as overload caused by feeding too fast. There are may causeseof overload.

I'm sure you aren't used to machinists who are also mechanical engineers. I'm the only one I know. There are probably a few more. I've come to the conclusion that many gunsmiths were not machinists before they were gunsmiths which limits their experience. I was lucky to learn from machinists in a nuclear power plant where they generally have minimal budgetary restraints and intolerance for less than perfection. No production mentality. I spent years making precision astronomical equipment before gunsmithing so my focus has always been on precision rather than production. Always prototypes.

Generally in failure analysis there are 3 major categories of root cause of failure of a broken steel part: 1. fatigue 2. material defect 3. overload.

Fatigue is generally characterized by beachmarks. This break surface has none. There is no material defects such as porousity, inclusion, or pre-existing crack visible. Overload is generally characterized by a clean, sharp metallic crystalline face across the entire surface of the failure, which is what I see.

Now I started out talking about about possible causes for a series of reamers breaking, focusing on possible common mode failures. Candidates for root cause of multiple reamers failing in diverse locations included the following. (Don't be offended if I list ridiculous causes. Most standard root cause methodologies list all failure mechanisms that the team can come up with and then start eliminating them.)

1. Bad batch of reamer steel used in multiple reamers.
2. Bad heat treat of reamer steel used in multiple reamers.
3. Change in the design of the reamer by the manufacturer, for example, making flutes thinner.
4. Poor construction of the reamers resulting in one flute taking too much share of the load.
5. Some common training of machinists causing a diverse group to feed too fast (such as a bad youtube video you refernce) .
6. Bad batch of barrel steel with hard spots.
7. Other possible mistakes that cause one flute to take all the load such as binding, misalignment, feeding not along cutting line, etc most of which are unlikely.
8. Common mode failures associated with new lathes such as poor feeding control on the tailstock (assumes all failures on new lathes).
9. Other things that might be common to the batch of reamers that are breaking.
10. There isn't really a change in failure rate. The internet makes it easier to connect multiple failures but reamers have always failed at this rate.

For a single reamer failure you can look at other possible failure mechanisms;

1. Overfeeding.
2. Dull reamer.
3. Impact load from cranking in fast and missing your slow down point.
4. Chatter causing impact loading.
5. work hardening--generally work hardening of 400 series ss is .001" thick or less so taking too light a cut can create a work hardened layer--especially if several passes are made with the cutting tool riding the surface unable to get a bite.
6. More possibliites that I'll probably think of after I've had more coffee.

So the failure was definitely overload based on the fracture surface but machinist error are not likely the cause of the failure. If this were an important part at NASA, this list would be greatly expanded. A root cause on a an important part can result in several man months of invested time.

My money is on 1, 2, or 4 of the top list.

--Jerry