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-   -   Machining (http://www.firearmstalk.com/forums/f33/machining-56201/)

Josh1158 01-24-2012 07:00 AM

Machining
 
Im a machinest I make over engineered medical medical parts every day. I have to hold +/- .00015 all the time. Im having a hard time understanding why so much barrel work is done with reamers. I feel that a normal boring bar would do fine. Can someone please explane this to me.

Axxe55 01-24-2012 08:21 AM

i am going to venture a guess and i could be wrong. a reamer is made to a specific chambering and also centers of the bore via a pilot. a good machinist with the proper machines and bits could probably achieve the same results if they knew exactly what they were doing. some reamers even come in two different types, a rough cut and a finish cut. i do know that on some barrels that can be ordered short chambered and when used with a set of headspace guages, you can do the final chamber cutting with a finish reamer. most times this is done by hand as there is very little material to be removed. now doing it on a lathe with a boring bar, could possibly be done, and maybe is done by some. i have personally never heard it done this way. the the gun makers, such as Remington, Savage, ect., ect. may cut the chambers on a lathe in such a manner. maybe someone else will be able to shed more light on this subject as i am curious about it myself.

hiwall 01-24-2012 01:55 PM

It is many, many times faster and for 99.9% of people it is more accurate to use a reamer.

Josh1158 01-24-2012 05:33 PM

It may be faster but your trusting the accuracy to the guy that made the reamer

Sonic82 01-24-2012 06:07 PM

Quote:

Originally Posted by Josh1158 (Post 687499)
Im a machinest I make over engineered medical medical parts every day. I have to hold +/- .00015 all the time. Im having a hard time understanding why so much barrel work is done with reamers. I feel that a normal boring bar would do fine. Can someone please explane this to me.

I'm no expert. But, the reamiing is only for finishing....the bulk of the work is from drilling. At least according to this; http://www.lasc.us/RangingShotBarrelMakingFeature.htm

Incidently, I operated a CNC machine for 7 years in the medical industry as well, pyrolytic carbon heart valves.

CubDriver451 01-25-2012 01:40 AM

Quote:

Originally Posted by Josh1158 (Post 687499)
Im a machinest I make over engineered medical medical parts every day. I have to hold +/- .00015 all the time. Im having a hard time understanding why so much barrel work is done with reamers. I feel that a normal boring bar would do fine. Can someone please explane this to me.

Josh, I don't know what kind of machine work you do, but here is the skinny on reamers. Straight flute reamers leave a finish that will almost always be better than when using a boring bar. They will also maintain tighter tolerances and reduce work time by a significant amount. A good reamer, used in a rigid machine and setup will easily hold tolerances of .0005 and less if used correctly.

Since you specifically asked about barrel work, I will focus on using a boring bar mounted on the tool post of a lathe. The dials on every lathe I have ever seen are incremented in thousandths. makes it a bit difficult to hold tolerances of less than .001, which a reamer does easily. There is an interesting trick for working in smaller increments than .001 on a lathe though. You can swing your compound feed to either one and a half or three degrees, depending on whether it reads diameter or radius, and set up 10 to 1 ratio by feeding with the compound rather than the crossslide. If you check the setup carefully by using a test indicator that reads in ten thousandths, this method works very well, but it is mind numbingly slow working in such fine increments, and if you are not very careful, tool wear can bite you in the ass.

If you are talking about boring a chamber, it gets even worse. Many, if not most cartridges do not have straight walls, but are a tapered case. Now you have to set up your taper attachment, and carefully indicate it into the proper taper. Another time consuming task. And don't forget abut the shoulders of the bottle neck cartridges. They vary widely in angle and radius at the transition from case body to neck. Your boring bar would have to be carefully ground to match this radius and angle. All this, when a reamer is easily capable of holding dimensional tolerances of .0005 or less. If you would like to take on the challenge, be my guest. I will stick with reamers for all of my barrel chambering and throating needs.

Now let's assume that you want to chamber a rifle barrel for a specific cartridge, and wanted to do it with a boring bar. After all of the previously mentioned setup is done, you carefully install the barrel in your trusty four jaw chuck, and indicate it to perfection. You then proceed to carefully bore the chamber with your custom ground boring bar. When you think you are done, you remove the barrel from the chuck, thread it into the receiver, place a headspace gauge in the newly cut chamber and go to close the bolt, only to find out that you are still just a couple thousandths from the "go" gauge seating with just the slightest hint of pressure. Now you have to reinstall the barrel in the chuck, indicate it to center again, and then try to move the shoulder of you chamber forward that very small amount to make it perfect. If you were using a roughing and finishing reamer set, it would simply be a matter of inserting the finishing reamer and giving it a half turn by hand and then rechecking your headspace, and repeating until you get the proper chamber depth.


Chambering, throating, forcing cone and pretty much any other reamer I have ever tried have always functioned flawlessly for me, leaving a great finish, proper dimensions and proper operation.

JW

Josh1158 01-25-2012 05:41 AM

I see your point when this kind of work is done on a tool room lathe. It would be way easier with a form tool. But if it was done on a cnc I could argue all your points. Use a 3 jaw chuck with soft jaws and bore them to fit the od of the barrel. The run out should then be nonexistent or at least minimal. Even if you take the barrel out and put it back. With your nifty program all the work the reamer does would be cake. I prefer mazatrol and with that programing you could change from caliber to another with only changing maybe 6 numbers. If you use a go/no go gage or maybe a innertest you can check that in the machine. If your still small just run your finish pass again.

Josh1158 01-25-2012 05:47 AM

I guess my next question would be. Why do gunsmiths do things the old school way instead of with modern machines ? I try to work smarter not harder.

Axxe55 01-25-2012 06:30 AM

Quote:

Originally Posted by Josh1158 (Post 688703)
I guess my next question would be. Why do gunsmiths do things the old school way instead of with modern machines ? I try to work smarter not harder.

probably a question of money and availability. how much would a CNC lathe, capable of doing the job your are thinking about doing cost? quite a bit i imagine. a small manual lathe, capable of holding a barrel and a reamer would bee much more cost effective. also not everyone has the access to the type of equipment available to you. possibly for $2500 or less, for a lathe, reamers and tooling, i could chamber and thread a barrel ready to mount into a receiver. reamers generally cost about $100-150, and are usually held to a high degree of precision. plus reamers can also be used by hand to finish cut a chamber. CNC lathes are great pieces of equipment and very capable of extreme precision, but the downside is, they are at a price that the average person can't afford of most gunsmiths don't do enough business to offset the cost of them.

Josh1158 01-25-2012 06:37 AM

Yeah, you totally got me on that. But with all the other parts they could make wouldn't they make there money back in due time? With all the other gun parts they could make they could almost start there own line of gun accessories.


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