Question

Ashamed to say, I don’t own a lathe, so haven’t reamed a chamber on a lathe.

Saw this picture. What makes me surprised is how the reamer is held. Looks like the reamer is being pushed in by a dead center on tail stock. It is being kept from spinning by a pair of vise grips! Why not chuck the reamer by a Jacobs chuck on the tail stock for better centering?

The reamer will follow the pilot hole, which is why the floating holder is used. Holding the reamer tool fixed is going to cause either the barrel or the tool to flex. Since the barrel is held by the much stronger chuck jaws my guess would be the tool will. Unless the machine and setup are dead on perfect alignment the hole stands to be out of spec both in size and alignment. But sometimes that is ok and sometimes not enough for anyone to really notice or care. So here is a thought, what do they do to machine all the barrels in production? I can comfortably say I have never seen a floating chamber reamer in a production shop. By the way, I use one! I have also hand reamed some of my chambers. 😀

Comment

A floating holder makes a lot sense when I come to think about it more. The pilot hole should determine the axis of the chamber. That’s exactly what happens when we manually ream the chamber, I reckon.

Just wondering though, is there a divot in the end face of the reamer for the dead center to go in? If there is, then the reamer is not really 100% floating, is it not?

I don’t know the exact origin of the photo. Just grabbed from a google search. It doesn’t look very contemporary though.

Just a side question. What sort of holder do you use to hold the reamer when you do manual reaming? Not necessarily for chamber reaming, but just reaming a hole in general. My first choice is the chuck in drill press. I turn it my hand while applying light pressure on the lever. If needed, I also use T handle chuck for taps.

Comment

The thing to remember is when you ream a hole you are only taking off .001 to .003 of material. (one thousands to three thousands of an inch) The pilot on the reamer will help get the reamer started, but the reamer it self will want to find the center because the walls of the hole you are reaming is applying even force on the cutting edges. When a floating reamer holder is used, it allows the reamer to float to the centerline of the hole in relation to lathe tailstock or milling machine quill. In other words it compensates for the misalignment of the machine, and all machines have misalignment, it is called tolerances.

When I hand ream I typically use either tool holder, (T Handle), collet or the floating holder if required in which ever machine the operation calls for and don’t do it under power. If I am drilling holes on the mill or drill press that requires a reamer fit, I make sure not to move the table until I am done with reaming the hole. Same rule for tapping, do it in one set up. This allows me to know the center line should be the same for the pilot hole and the reaming/tapping process. The other thing that will help is to use a spring loaded center that will keep a light amount of force on the tool. This is a tool that gets chucked up in the machine but has a pointed spring tip with around an inch of travel. The point goes into the center point on the end of your T Handle. This keeps you lined up on center. You should also always use a lot of good cutting oil when you tap, (even more important when you ream), you want to make sure you are floating those chips away from the cutting surface. They also make guides for tapping that can be pretty handy.