I would like some guidance in the right direction. I am wanting to learn how to chamber, and profile a Barrel. I am wanting to learn this for my own personal satisfaction.
Recently I purchased a few cheap .30 cal barrel blanks that I intent to use for learning, I do not expect to be perfect in my first few attempts. I also have no expectations that I can posibly ever build a barrel that is more accurate than anything commercially available.
I own a Lathe that is adequate for me to learn with. I also know the very basics of using the Metal Lathe. I do have a lot of experience using a wood lathe, and so far my experience with the Metal Lathe is that the big picture concepts between wood and metal are similar, but with metal everything runs at a snails pace in comparison, and your tools are moved with knobs rather than by hand.
So anyway, where to start. I know I need a Chamber Reamer, and a Finish Reamer. I am thinking that I would like to ultimately work with something like .300 AAC Blackout, .30-30, or maybe .308. I don't want to mess with anything larger than .308 though.
I am also thinking it might be best to work with a straight walled case as my first attempts, and then I can always reuse the straight walled barrels to do a tapered round by triming them down some.
Anyway could someone offer some guidance as to what tools I need to buy, and where to start this learning excercise?
I just got started chambering my own barrel, but can tell you it`s not to hard to do. I only buy finish reamers and use a drill bit to hog out most of the metal. I got started chambering for wildcat and simply put together a dumby round to use for a gage. I also only use Savage actions so the head spacing is very simple. Just have at it, it`s fun and really pretty easy.
There are a number of perfectly acceptable ways to set up and fit and chamber rifle barrels. Some methods are more precise than others. Some methods have greater potential for error than others. There are some limitations imposed by the machinery and tooling and some limitations imposed by the material with which you are working.
Methodology has changed slightly in the area of super-precision (benchrest) barrel fitting but even in this arena, there is no solid consensus.
A chapter I have been writing on this seemingly simple task has now run to over twenty single spaced pages and I've produced as many questions as answers. Because there may be some interest in the subject, I will offer a seriously abridged version on this site. This will be contained in more than one posting because I can't take enough time to write it all at once. Also, I don't want to put the whole story out there and kill sales for the book!
I'll start with profiling.
At it's most basic, barrel profiling can be accomplished much as a taper would be cut with a wood lathe. That is, you can turn steps in the barrel to establish the degree of taper then blend the steps with a lathe file. This is workable and, if nothing else, provides the workman with plenty of exercise! A slightly better, though possibly even more labor intensive, method is to turn the steps then blend by draw filing. After draw filing, the lathe file is employed to improve roundness which should be pretty good in any case. By the way, I have employed this method just to see how well it would work and to take a full blank to about a #4 Shilen contour required about four hours and yes, I had blisters by the time I was finished!
A better, and somewhat more professional, method is to offset the tailstock to produce the taper. To do this, you must first establish the amount of taper you want your barrel to have. The Shilen #4 contour posesses about .130" of taper per foot. To set up to cut this taper, you will set up the barrel blank between centers and check that the surface presented is parallel to the axis of the lathe. You will then mark a spot which is 12 inches back from the muzzle and you will offset your tailstock toward you so that the surface presented is angled .065" over that 12 inch distance. Now, when you turn the barrel, you will end up with the desired taper. You will cut this taper to a point approcimately six inches from the breech end.
A word about tooling.
The biggest problem one will encounter when tapering a barrel is a tendency for the work to chatter. To help prevent this, you will need to use a properly shaped tool which is properly set up. The tool is best ground from a cobalt steel blank. It will feature a knife edge withe a "U" shaped groove behind the edge. The lead angle with be about 15 degrees with about five degrees of clearance. The front of the tool will be ground to clear the work (five degrees is enough) and the tool will be set about .020" ABOVE center. With most lathes, turning speed will work well at about 350 RPM and the feed rate about .006" per revolution. I'll usually take about .035 per cut (removing .070 from the diameter).
Use a live tailstock center and drive the barrel with a dog. grease the centers at both ends. The blank is turned until the desired muzzle diameter is reached. Once the blank is tapered, it is necessary to step up to shank size. Most barrel makers produce a concave profile here. This can be accomplished by producing a series of short tapered sections which are then blended to form a curve, by the "step and file" method, or by what Tom Burgess referred to as the "Etch-a sketch" method. I hope these are self-explanatory.
Now that we have produced a contoured blank, it is time to set up to thread and chamber and I'll describe some methods for doing this a little later. Right now, I have to get back into the shop. GD
Just to clarify a little bit on the previous post. The description of contouring a barrel is for those who do not have a copier or a taper attachment for their lathe. The use of either changes things considerably. Also, there are methods one might employ to help control chatter in difficult cases which I won't get into here. Finally, if a barrel blank is not properly stress relieved, it is going to warp when it is turned. There is no excuse for a blank to not be stress relieved. If I get abarrel which is not, I will stress relieve it myself then simply avoid that maker from that point on.
When it comes time to thread and chamber, a time honored method is to set the barrel up between centers with the breech end supported on the tailstock center. Prior to doing this, the centers at each end of thye barrel are re-cut with a piloted center reamer to ensure concentricity. The shank of the barrel is turned so that it is concentric with the bore.
With the barrel between centers and driven with a dog, the barrel tenon is cut. The shoulder is located and a plunge cut taken with a parting tool to form the shoulder. It is reasonable to deliberately make the tenon a few thou too long. It can then be faced to the correct length during the chambering operation.
Establishing tenon length.
The length of the tenon is determined by measuring the action. A depth micrometer is the best tool for this purpose. If the action is a Mauser, the tenon length will be the distance from the face of the receiver to the inner shoulder. Some prefer to make the tenon .002 longer than this measurement while others may want to make it the same amount shorter. Still others will prefer to make it precisely the measurement. There is no wrong answer here. If the action is a Remington, the tenon length will be about .010" less than the measurement from the receiver face to the front of the locking lugs, plus the thickness of the recoil lug. Every action is a rule unto itself as far as dimensions are concerned. The Pre-64 model 70 is about .740 long. This gives sufficient length to allow for the coned breech. Most threads are 60 degree "V" threads. Mausers are a 55 degree "V" while Springfields are a square thread as are P14 Enfields.
Once the proper length is established, you can set up to take the plunge cut mentioned earlier. As I said, I like to make the tenon about ten thou longer then face it to the proper length after threading and prior to chambering.
I use ground high speed steel bits because I think they give a better finish than carbide. 60 degree for most threads, 55 for Mausers. The compound of the lathe is set at thirty degrees for most and 27.5 for Mausers. The tool is advanced with the compound for successive cuts and returned to zero each time with the crossfeed. The threads should be cut to the point that the receiver will just thread on to the barrel by hand.
To chamber, the barrel is held at the muzzle end by the three jaw chuck and the shank of the barrel is run in the steady rest. An alternative is to run the threads in the steady. I prefer to run the shank. More later. GD
Now, before you start chambering, you will want to take some measurements on your reamer. If you are chambering a 308, you will measure the diameter at the shoulder and you will measure the distance from the front of the pilot to the out side of the shoulder. You will be roughing the chamber with a drill bit and you will want select a drill bit about .020 smaller than the diameter of your reamer at the shoulder. Your 308 reamer will measure about .454" so you can use a 7/16 drill bit or, if you wish to be a little more cautious, a 27/64" bit. You will drill to a depth which is about 1/8 of an inch less than the distance from the front of the pilot to the shoulder. This ensures the reamer pilot is supported. To drill the chamber, run the lathe at about 240 RPM and feed the drill rapidly. Hesitate at each revolution of the tailstock wheel just to break the chip. All of my 308 reamers allow me to drill 1 1/8 inches for the first roughing cut.
After drilling to this depth, blow any chips out of the barrel with the air hose. Blow from the muzzle end. I use a long tube with a tapered end which fits in the muzzle end of the barrel and is supported at the rear by a nylon plug which fits into the lathe spindle. You are now ready to start reaming.
I usually run the lathe at 90 RPM to ream a 308. Many advocate reaming at higher speeds but i still have the best results at 90. The reamer is held with a tap wrench and supported on the tailstock center. An alternative is to use one of the floating reamer holders like the one available from Clymer. There are other alternatives as well but I'm trying to keep it simple here.
Oil the drilled chamber liberally with cutting oil (I use Rigid nu-clear) and oil the reamer. Start the machine and introduce the reamer into the roughed hole by holding the reamer on the tailstock center and sliding the tailstock forward.. When the reamer is about to start cutting, lock the tailstock in place and begin feeding with the handwheel. Once the reamer starts cutting, you can either hold the tap wrench with your hand or let it rest on the cross slide or tool post. You can feed the reamer quite rapidly at this point and can feed it in until the neck starts to cut. You will be able to feel this and it will happen at about the 5/8 inch mark. Now, unlock the tailstock and withdraw the reamer. Be sure and hold the reamer against the center as you withdraw and control the reamer. Once again, use the air hose to clear the chips and oil from the barrel. Also, blow the chips off the reamer. Re-oil the chamber and reamer and repeat the performance. This time you will be able to push the tailstock ahead until the reamer makes contact at which point you will lock it down and start feeding. This time you will only reamer about 1/4 inch before you have to pull out and clean. Repeat again, this time reaming about 1/8 inch. One more time for another 1/8 and you should by cutting fully on the shoulder of the reamer.
Time for me to go to work. More later.
By now you will have reamed to a depth of about 1 1/8 inches at the corner of the shoulder. The 308 chamber is just over 1 1/2 inches to this point from the bolt face. Your protrusion, if you are barreling a Mauser, is roughly .110" so you have about .400" to go. Now, you could continue to just feed the reamer in but you can only cut about .060 or so per cut so it makes sense to drill a bit more. If you drill about .325" it will save some work with the reamer and will still leave a sufficient amount to clean up at the shoulder. The thing to do is to speed the lathe up again and drill that .325. After drilling, clean the chamber and start in with the reamer again. You will be able to ream about .200" then you will have to withdraw and clean the chamber and reamer as before. Another .100, clean then ream about 50 thou. Now you will be reaming the full shoulder again and you will be within about .075" or so of final depth. Clean the chamber out, insert your "GO" gauge and, using the depth micrometer, measure the protrusion. Let's assume this measurement is .185". You are now approaching your finished depth. Before starting to ream again, clean the reamer off real well. Run your finger nail along each cutting edge to check for any burrs which the reamer may have picked up. If you feel anything at all, take a short triangular stone and carefully stone the face of each flute. Be sure to hold the stone squarely against the face and stone lengthwise until each cutting edge feels perfectly smooth. Once you have done this, you are ready for the final cuts. For the final cuts, you will feed the reamer more slowly and will cut only about .030 before removing the reamer and cleaning. Check the cutting edges each time and clean with the stone if necessary. For you final cut, you will be cutting only about .015". If your protrusion measures out to be .110" you will want to ream .002 deeper than this. This will allow .002" for compression of the contact surface when the barrel is tightened. This amount works out perfectly with most jobs. So, if your protrusion now measures .125", you will have to ream another .017". Set the tailstock wheel to "zero", oil the chamber and reamer well, start the lathe, and push the reamer in 'til it touches. Lock the tailstock and start feeding the reamer in slowly. For the last .005, ream VERY slowly. Just barely maintain pressure on the reamer. When you have reached the proper depth, allow the lathe to turn a couple of revelutions then withdraw. Clean the chamber for what should be the last time and check with your gauge. The result should be a chamber of perfect depth. There should be virtually no tool marks. You can now break the edge with a 60 degree reamer or a hand held de-burring tool.
The chamber may now be polished but the polishing is just meant to produce a uniform surface finish. There should be no tool marks to remove. To polish, I use a slotted mandrel in an electric drill and a piece of very fine Scotch Brite. Withe lathe running, the drill is run fast and the Scotch Brite introduced into the chamber. About 3 or four seconds of polishing should do the trick. Don't sit in one spot but move the mandrel in and out. Four or five passes should be enough.
The chamber is now finished and the barrel can be installed on the receiver. When I get back to this, I'll give a quick description of setting up to cut and crown and marking the caliber on the barrel. That is, if y'all want to hear it!
This is one method for fitting and chambering and is one which can be used if your lathe is too small to allow you to work through the headstock or if it is too large to allow the barrel to reach through. There are many other ways to skin this cat and, of course, there are variations in methodology dependent upon the action type and so on. There are many refined techniques for dealing with problems which may arise. There are specific techniques for precision chambering. I'm not going to cover every contingency here but will answer specific questions if anyone has any. GD
|All times are GMT. The time now is 12:26 PM.|
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd.