Greetings all,
Just a quick question if I may. I was browsing the Clymer Tools site and noticed that in the reamer section reamers are described as "roughers" and "finishers". What's the difference? In chambering a new barrel would you need both to finish a job? Thanks for your help.
Con

A rougher will ream to just underr finished chamber size. Them you go in with the finish reamer to "finish" the chamber. If you are doing a bunch of chambers, the rougher will save wear and tear on your finish reamer. I don't bother with a rougher. I rough out the chamber with a boring bar until almost chamber size and then use the finish reamer.

Bu doing it with the boring bar you are giving up the reason they have pilots on them and leaving yourself open to a chamber that in not concentric to the bore. Her we go!

"feed a stray dog and he becomes a friend. Therin lies the primal difference between a dog and man" Mark Twain.

Better than using a couple of twist drills (as has been done in the past).

I rough every chamber with a twist drill to withing a hundred thousandths or so.

Then the reamer is held in the tailstock chuck and the chamber reamed until the pilot engages.

At that point a mandrel is put in the barrel and concentricty is checked and corrected if needed.

Then the reamer is hand held but supported by the tail stock center at the rear and driven by the tail stock inward in .020 steps until done.

There's a LOT of ways to cut a chamber.

Roughing reamers are great for the factories using turret lathes to thread and chamber. I've never seen one in a gunshop.

wouldn't lathe boring a chamber for "roughing" purposes be MUCH better than using twist drill bits... and at least as good as using a piloted roughing reamer? I would think that if the blank is indicated in on a mandrel in the bore, that boring it would be about as accurate as you could get? I admit I'm not a machinist, but what am I missing here?

I always bore the chamber to the point where the pilot is now in the bore. Of course if the pilot wasn't contacting the bore the chamber might not be concentric. But I thought most folks on this board would know that.
In fact, after I get the chamber bored out to a few thousanths from where I want it to be, I indicate on the area where the neck will be, re center if needed (and it is ALWAYS needed because the bore is NEVER straight) and then clean up the chamber one last time with the boring bar. Now the "prechamber" and the neck area are in perfect alignment. Then I go in with the reamer and finish it up.
My chambers come out as good as I can measure.......

I would think that if you indicate both ends of your bbl blank in the bore and have it running concentric at both ends, your boring bar (if not hogged out) should run true with the bore. Correct me if I'm wrong. I'm not a gunsmith but a retired tool maker. Straight and square is straight and square, always has run true.

You are right, ol crip..........if the bore is straight.

.....and they never are.

Touche' Jack.

There is nothing wrong with roughing out a chamber by step drilling as long as you take measures to true everything up before you ream. Even the lengendary Harry Pope did that. I have a few roughing reamers and I use them but most of the time I use drill bits and drill .050 undersize diameter and stop about .150 short. Then I use a long reach dial indicator and indicate directly on the lands and grooves to within .0002. I then switch to a boring tool and bore the chamber .001 over the diameter of the reamer at the shoulder/body junction. This will guide the reamer very precisely and let it engage the pilot accurately. I use a similar technique when rechambering to guide the reamer in straight untill the pilot takes over.

There are a lot of jobs that don't require roughing the chamber out. For example .458 WM, 45/70, 35 Whelen. By the time you did the calculations and set up you could already have the chamber cut with the finisher. On the other hand if you were reaming the whole chamber for 7MM RUM with just a finish reamer you would have to start mighty early in the morning or else you would miss lunch because you would still be reaming.

>There is nothing wrong with roughing out a chamber by step drilling as long as you take measures to true everything up before you ream.<

I agree. That is the key.

I have fitted and chambered barrels using all kinds of methods and whenever I hear of one that may yield better results I'll give it a try or I'll try variations on the theme.
For the most part a twist drill will follow the hole so near to perfectly that any error will be immeasurable. This if it is a good drill and if it is pushed a bit.
If using a boring bar it works best if the barrel is set up so that the portion containing the chamber and throat is perfectly centered and aligned. It is possible to make a little tool to do this with or Dave Kiff will make one for you. When the barrel is set up this way it is not unusual for the muzzle end to run out considerably if the bore is not particularly straight. Another option is just to dial at the location of the throat and at the muzzle and rough with a boring bar so as not to be influenced by the possibly eccentric breech end.
In standard practice where the barrel is dialled in at breech and muzzle the throat area may not be running concentric depending on the straightness of the bore. In this case the use of a boring bar might not be the best option. This because the boring bar cuts concentric with the axis of the machine (we hope!)rather than following the bore.
In the end I still see no problem with roughing with a twist drill. I use a drill bit about.020" smaller than the shoulder diameter of the reamer and have never had a problem. In fact it is possible to cut closer than that if you want. I will drill in steps though, never going so far that the pilot does not engage.
The common twist drill is often maligned as an inaccurate tool when that is not necessarily the case.
I have drilled a 1/2" hole through 54" long hydraulic cylider rods using common twist drills which I silver soldered onto extensions. I drilled 29" from one end then flipped the rod and drilled to meet the hole from the other end. Often the holes met perfectly and never were they off by more than about .015 or so. I used only straight drills though. If the bit wasn't straight it wasn't used. The rod was run in the steady rest and 4 jaw chuck. The drill was run in about 3/8" at a time. I got pretty tired of dragging that damned tailstock back and forth by the time I finished. I was doing this just because I thought the guys with the gun drills were charging too much.
When a chamber is finished one needs only to inspect the throat to see if the job is concentric with the bore. If the throat portion of the chambering reamer cuts a throat that is .0005 over groove diameter then .0002 of eccentricity is easily seen. In my case not as easily as it might have been 20 years ago. Now I have to use cheaters!
When the barrel is a relatively straight one the job is more easily done than with one that is curved but either can be done well with some thought. I think that often guys obsess to the point they can outsmart themselves and end up with a result that could have been achieved much more easily. Regards, Bill.

Harry Pope ground his twist drill points to a 55 degree included angle, he believed they would follow a bore with the most accuracy at that angle.

Bill I agree with you, there are a lot of twist drills with a lot of runout.

Bill also said more with one sentence than the rest of the entire thread. " often guys obsess to the point they can outsmart themselves "

Set up carefully, use lots of coolant, and clean often. Use the finisher. Why chance a crummy chamber?

Wally

Looks like I got off on the wrong track back at the ending days of WW II. Drills, Yep. BUT these were ground from the solid hardened Hi-Speed
steel blank drills. They were checked to see if they drilled on size and corrected on the point if they did not drill to diameter. I did and still do drill as close to the headstock bearings as I can get, which means in an adjust -tru chuck,
and I do NOT use a gimcrack to hold the muzzle end true. I start the chamber with the reamer and depending on the diameter at the shoulder run it in to about .300 past the shoulder. Often the pilot has some distance to go when the reamer enters its own prepared start. As Jack says ,they aren't as straight as you'd like to believe. When the pilot enters the bore it may bend the reamer until the start and the pilot agree on some compromise. I don't give a damn about their agreement because in the end the chamber will be aligned where it oughter be. The procedure?. I whack the excess off the blank plus one inch over finished (to be length) sometimes at both ends, CAREFULLY recenter for turning betwseen centers, Turn the over the chamber diameter to run true and not yet to desired size, Then chamber deeper than I need, Next I put a slight 60 degree at rear end of chamber, utilise that to turn the taper and contour, (without turning the over the chamber section) Polish the taper and contour to size, Next over the chamber diameter is turned and that is finally threaded In the chuck, If the receiver threads are tapered, tighter as it threads on , I cut the threads on a taper by backing out the tool bit. I like a no wobble fit.
If the muzzle end of the barrel does not run true- looking through it as it spins, and I cannot get it to straighten out, I simply take another cut over the chamber diameter. What do you do if the barrel is one of those Octagon ribbed things and there is no place to grab it. A sleeve of black Iron pipe is made to be stuck in place using chamber cast metal. It is first shimmed close with pieces of wood, one end dammed off and metal poured, then when cooled the sleeve is turned. I like to make it about same size as my barrel vise opening. Guess why? Do I indicate? Well, what the hell for? You have either set the job up properly or you haven't.
Gent's, It has brought real smiles to find that there are many of you using some or all of the methods I use, who am unschooled as a gunsmith and use machinist,toolmaker,gagemaker principles to get the job done, believing that the procedures have got to be the same. One other thing. I use a Jacobs 3/16 to 3/4 capacity chuck for the whole scenario in the tailstock. I cannot remember ever using back gear. I do use loose belt and regulate the RPM with My hand on the body of the 8" buck chuck as a brake. I did do some regrinding of the chuck parts from new, to get the jaws parallel with the spindle bore.
they are solid jaws. The kind now available made with jaw carriers for replaceable or reversible jaws would have been a lot easier. Interesting read. Tells a lot.