Turning a barrel blank

[Tozguy]

This is the post by spearchucker (Rod Hendrickson) from the link mickri provided.

''Its far more accurate to chamber between centers and that is the way it is usually taught in schools. The steady rest is normally run on the thread extension. The threads are cut on centers so it will run true. Also the brass posts on the steady rest will not harm the steel threads. If you use a steady rest with bearings instead of brass cushions make certain that you put a piece of paper between each bearing and the threads when you set it up to give three thousandths clearance so the metal bearings do not harm the barrel threads. I put a .006 thickness of paper between the steady rest posts and the barrel when I set up a steady rest with brass posts as well. In this way the reamer becomes the rear center. The barrel does not even touch the steady rest posts while the reamer is cutting. (the paper is removed before cutting) The steady rest is really just there to support the barrel when the reamer is removed. Step on the Murphy switch and stop the machine before pulling out the reamer. Insert the reamer just .010 short of cutting before re-starting the machine. Failure to do this can leave a light drag mark on the chamber when you pull out the reamer. This drag mark, if you make it is nothing and can be burnished away with steel wool or 320 wet and dry and kerosene. Some reamers will sing or cry when not supported by the steady rest. Don't confuse this with chatter its simply a slight high pitched vibration that builds up in the barrel during cutting and I have never found it to be harmful. I generally squirt a bit of oil on the barrel and grasp it fairly tightly with my left hand while cutting and that chokes the singing abruptly. I find it annoying like a yowley cat going at it in the back yard when your trying to sleep.''

 

[mickri]

One thing that Rod mentions either further on in the thread I posted or in another thread I saw somewhere is that when he does chambering he locks the carriage in place and then brings the tailstop up against the carriage. This assures that the tailstock is always in the same position so you get consistent measurements on how far you have advanced the reamer into the barrel. Rod has lots of gunsmithing tips posted all over the internet. He uses ER40 collets with a collet chuck to hold the muzzle end of the barrel at the headstock and to hold the reamer in the tailstock. I use ER32 collets. I made a collet chuck for the headstock. Not hard. Just need to be able to cut a 1.50mm metric thread. I purchased an ER32 collet chuck with a MT2 for the tailstock. ER40 collets go up to 26mm and ER32 collets go up to 21mm.

There is a recent thread about using a micrometer reamer stop that you might find helpful. A micrometer reamer stop is at the top of my project list.

 

[cdhknives]

I had never thought about the reamer being the tail center but it makes sense, I was expecting to have to hold the barrel in the 4 jaw through the headstock and use a flat faced (old center) MT2 center as a pusher with something rigged (big tap wrench probably) to prevent reamer rotation. I don't expect to do enough to invest the time/money in a reamer holder. I need to look and see if the chamber reamer is dimpled for a center...that would be too easy. Working this far out from the headstock is kinda a new experience but there should be a lot less wear in the ways!

 

[Tozguy]

My chamber reamers have a centre dimple.

 

[mickri]

What do you use to hold drills, reamers, etc. in the tailstock now? That may be sufficient to hold the chamber reamer.

Do you plan to pre drill most of the chamber so that the reamer only has to cut the last portion of the chamber?

 

[cdhknives]

MT2 arbor w/Jacobs chuck for tailstock drilling...don't think the 3 jaw Jacobs will work well with the 4 flat reamer. I also have a MT2 holder for my QCTP for larger bits if I don't want to use them directly in the tailstock.

I have read both ways, pre-drill to hog out the chamber or use the reamer for it all. I am a bit concerned that drilling out most of the chamber makes the reamer pilot work too hard if it isn't straight...and I am not in production so reamer wear is of little concern. I may do 1 or 2 more with the new reamer and that is all...almost rented a set to be honest. Anything I do is likely less concentric than starting with the reamer for all of it...but I am open to options. No piloted drill bits here...

 

[Tozguy]

drilling out most of the chamber makes the reamer pilot work too hard if it isn't straight.

The drilling has to be followed by a boring operation. This boring operation is done at the same angle as the reamer body. Then the reamer follows this tapered bore. This operation is intended to provide control on the body of the reamer instead of relying on the pilot. Saving reamer wear is secondary.
However with what you have said it would less involved to do it all with the reamer as you have suggested. But you must make sure that the first inch of the bore is in good shape so the reamer starts straight.

 

[mickri]

I have the same concern about pre drilling the blank. I am a newbie at this too and will be doing my first barrels some time this spring. I have thought about first drilling just big enough to get a boring bar in and then doing the rest of the pre drilling with the boring bar. What I have found online is that if you are not pre drilling you should start with a roughing reamer then finish the chamber with a finishing reamer.

 

[cdhknives]

The drilling has to be followed by a boring operation. This boring operation is done at the same angle as the reamer body. Then the reamer follows this tapered bore. This operation is intended to provide control on the body of the reamer instead of relying on the pilot. Saving reamer wear is secondary.
However with what you have said it would less involved to do it all with the reamer as you have suggested. But you must make sure that the first inch of the bore is in good shape so the reamer starts straight.

...and if I understand the geometry correct it has to be concentric and square to the bore (not to mention assuming a concentric bore blank after shaping), all of which are tedious at best to dial in, and problematic on light machines like mine with homemade spider spindle nuts and such, and also indicate strongly to go back to the through headstock setup I would think. It might take me an afternon of pecking at it to clear chips (No power coolant much less through the pilot/center) from the reamer front but I don't trust my skills enough to get all that dialed in!

The bore is visually fine but I didn't cast it before tapping in my center pins. It should be okay for starting the reamer unless it is way out, right? I did mike it with my calipers as best I could to find the narrow/muzzle end and there was a nearly unmeasurable difference in size.

 

[mickri]

If you are turning and chambering between centers there is no dialing in to my understanding. There is some debate like everything whether you should contour the barrel before or after chambering. This how I currently intend to do this between centers.

1. Place barrel between centers with the muzzle end at the tailstock. Take a light skim cut down the length of the barrel to make the OD concentric with the bore. Turn muzzle end down to an OD convenient to fit in an ER32 collet.
2. Swap ends so the chamber end is now at the tailstock between centers. The muzzle end will be held in an ER32 collet at the headstock. The barrel will also be in a dead center at the headstock. The ER32 collet is mostly to drive the barrel and hold the barrel against the dead center.
3. Turn the chamber end down to correct OD and length for the tenon.
4. Thread the tenon.
5. With the barrel still between centers place the steady rest on the tenon with a piece of paper between the threads and the guides.
6. Either cut the chamber with just the chamber reamer or first pre drill and bore with a boring bar before finishing with the chamber reamer. Still deciding on this.
7. Contour the barrel, cut to length and crown the muzzle. Why am I contouring last? Because if I screw something up and have to start over I can still get the contour that I want with the barrel length that I want. I will be using 27" long barrel blanks and want to end up with 24" long barrels. This gives me 3" for mistakes/do overs.

Nowhere in this process do I need to dial anything in.