Barrel Fitting - Consolidation

I avoid using a steady; the steady I have is from a smaller lathe with a riser I made. It is on the light side. So, as far as possible, I mount barrels through the spindle. Set up once for chambering and threading. I use a spider on the left end of the spindle. Bronze sleeve machined to a push fit on the spindle, with 4 brass tipped clamping screws. On the right end, a 4 jaw chuck with a brass ring over the barrel.
I start off by centering the muzzle end in the spider, the chamber end being supported by the tailstock center. Then I indicate in the bore at the chamber end. Return to the muzzle and indicate it in on the bore. Back to the chamber end, confirm that it is true. I use ground dowel pins in the bore for the indicator to contact, have a selection of gauge pins for the common bore sizes. These do not extend all that far into the bore. Once I am satisfied with the setup, I'll start cutting. If I want to remove metal before reaming, I'll use a boring tool.
I use the same measurements as described above, taking measurements off the GO gauge as the chamber approaches full depth. I ream at low rpms, pulling the reamer by sliding the tail stock, as above, holding it in line. Currently I'm using a cutting fluid "Buttercut", have also used other similar products. I pull and clean the reamer and chamber every tenth of an inch, until the chamber is getting close to depth. I do not polish chambers, just clean them.
I use a commercial reamer holder, feed pressure is applied very much like guntech's system.
Reverse the barrel for cutting, threading and crowning. If I am installing a brake, the threads are cut co-axial with the bore, the brake is installed, and bored to size.
 
Have any of you guys ever had an issue with the bushing not hitting the bore on center when pre drilling and boring? That method has always spooked me as I worry about the potential of my pilot not making it in the bore. Have any of you ever tried the centering fixture for lathes with long headstocks (or short barrels) out of JOHN HINNANTs book - THE COMPLETE ILLUSTRATED GUIDE TO PRECISION RIFLE BARREL FITTING?
 
Robmcleod82 said:
Have any of you guys ever had an issue with the bushing not hitting the bore on center when pre drilling and boring? That method has always spooked me as I worry about the potential of my pilot not making it in the bore. Have any of you ever tried the centering fixture for lathes with long headstocks (or short barrels) out of JOHN HINNANTs book - THE COMPLETE ILLUSTRATED GUIDE TO PRECISION RIFLE BARREL FITTING?
Click to expand...

If the chamber diameter has been bored concentric within 10 thou or so of the reamer, the reamer will follow that without any pilot at all...
 
Leeper said:
No one is unduly concerned about the straightness of the outside of the barrel but barrels are seldom straight inside either (in forty years I think I have see no more than three or four which were close enough to straight to call them that and only one which appeared perfectly straight. As Tiriaq mentioned, one turns a track at the muzzle end which runs true to the bore this is held in the chuck and also serves as an indicator surface. At the breech end the outside is turned true, on centers and this surface then runs in the steady. Some like to thread on centers and run the threads in the steady and this works too.
In a four jaw chuck, a ring of 1/8 to 3/16 brass or soft iron wire works well to allow the barrel to swivel. even then, I like to back off the jaws once I have dialled in the muzzle and reset so as to ensure minimal stress on the barrel.
I'm perfectly willing to give a tutorial on various barrel-fitting and chambering techniques; for production, precision or both but it's necessarily a bit long-winded and most would likely not want to have to struggle through my efforts at technical description.
Click to expand...

I for one would be perfectly willing to sit through a tutorial or spend hours reading said tutorial if you were to publish one.
 
This thread could develop into a tutorial. Perhaps even a photo tutorial.
Here is the muzzle end of a barrel held in a spider:
014.jpg
It has been indicated in, on the bore. Because the muzzle had been turned true to the bore, this surface could have been used to indicate as well.
The cylindrical portion was subsequently removed, and the muzzle crowned.
 

Attachments

  • 014.jpg
    014.jpg
    65.3 KB · Views: 208
I'll skip ahead a bit here before going back to the steady rest system. I also generally chamber in the headstock and also use a pusher much Like Dennis' when the chamber is well started. I also believe in indicating at the throat location. The use of a long indicating rod is the best way to do this and is an adaptation of common machine shop practice. If one is wanting to indicate a spot which is three inches up in the barrel, a twelve inch long rod is supported at the tailstock and, if the dial gauge is set to indicate at a point which is four inches back from the point you want to check, the dial will show a value which is 2/3 of the actual movement. So, if your future throat locations is running out by .009", the indicator will show .006". If you get the indicator to read .0002" TIR, the throat will be .0003" which means it is eccentric by .00015". Now, even if we achieve zero at that point, we are still going to be dealing with some compromises and their are still choices to have been made. The more crooked the bore is, the greater the compromise.
The use of the 2 oz weight is one of the best ways to assure the indicator rod is held against the surface to be indicated. If the throat area is concentric and the chamber is pre-bored, the float built into the pusher doesn't come into pay at all since there is no run out. In this instance the pusher does take any misalignment of the tailstock out of play. If there is still some (though minimal) run out at the throat, the reamer shank will be able to float a bit which will prevent the chamber being oval at the breech end. If a person is going to rough the chamber with a boring bar, the throat run out must be zero in order for the job to be perfect. In reality, it is as close to zero as the operator can make it. Now, I'm going back to the steady rest system but not until after I go out and split some wood for the fire.
 
Regarding the chips "stuck" or "welded" to the cutting edge of the reamer mentioned before....
IMHO the lesser the RPM the less chance of it happening. Reamer deals with tremendous pressure while cutting chamber especially when feed is substantial.
While cutting say 22 Hornet or 223 Rem chamber 120 RPM seams reasonable choice, for any chamber cutting say 308 Win or 338 WM I never exceed 80 RPM
and never have that kind of problem. I have almost 3l in a gallon jug of Nu-Clear left after 20+years of machining that says I am not using it often, it is just mineral oil meant to be used in volume for their big pipe thread cutting machines. Best outcome cutting the chambers IMHO I got is from sulfur based cutting oil like Rapid Tap. I still have old two 16oz cans of it left and use it sparingly with excellent results. I am afraid that newly sold Rapid Tap cutting oil has no sulfur content in them any more....
 
Last edited:
Reamer makers are often recommend even faster speeds but I also don't like to run too fast. Rigid dark has a high sulphur content but, for whatever reason, when I use it, my nose itches! That's why I use the nu-clear. I have also used Sulflo and , as I mentioned, motor oil. People have their favourites and often mix various concoctions which provide the ultimate in performance (or so they like to believe). Not all reamers will pick up metal but many will. Anytime a gunsmith is having to do a lot of polishing, he should be cleaning his reamers instead.
It has occurred to me that I have already written up all of this barrel fitting stuff and even have some illustrations (many of which look like they were done by a slightly challenged six-year-old) and maybe I should just get around to getting it printed up.
 
Maybe already mentioned, but...

If you have a decent lathe with a spindle bore that runs true(not all of them do) and want to do short barrels in a headstock that is too long to grab/dial both ends(or you don't have a steady, or just hate them) Make a bushing about 2" long (I like acetal) that fits the spindle bore with a few tenths slip fit, and snug on the OD of the barrel. It gives it muzzle end support, even if the muzzle end runs out a few thou worse case in a crappy lathe, it won't make a difference so long as the chamber end is done right.
It's only one out of a 100 things that need to come together to make a rifle shoot.
 
You must log in or register to reply here.
Back
Top Bottom