J. Randall wrote:
At the risk of looking really studid, oops to late,
, I have to ask:
How does a floating reamer holder get the reamer started on center? If I understand the princiapal of using a floating reamer it is to allow it to bore straight into the chamber and not cant at an angle as one might expect if they were not perfectly aligned for up/down and front/back with the tail stock.
The key word in your post is allow, if you have a true bore and it is dialed in dead nuts, the floating holder and the proper bushing on the reamer allows it to stay straight.
Well, not so much. Dave's question is very spot on, and is proper. In my view, a floating reamer holder is a recipe for chatter and an over size chamber. There are so many opinions on this, but I'll explain mine.
A floater is "supposed" to correct misalignments in a setup. To do that, it must move axially to "follow" a bore. So Dave's question about how can it start off right if it isn't aligned, is valid. A reamer with a pilot bushing has clearances. There is clearance between the bushing and the reamer, it has clearance between the bushing and the bore/lands. While these aren't big clearances, take that short 1/2" long bushing with the clearances inside and out, and place it in the end of a barrel, only as deep as the bushing. Now go to the end of the reamer and see how much wiggle there is. There is always wiggle, you can't have zero wiggle. So again, how is a floater supposed to align this?
The floater goes against every fundamental principal in metal working, which is RIGIDITY! Would you attempt to turn a piece of stock down with your QCTP loose? I doubt it. So why send a reamer in to do the job when it is loose? One problem some smiths have when chambering is chatter. Chatter comes from different things, but most can be related to something loose somewhere. A loose fit between the pilot and the bore is a big problem, which is why a reamer with a bushing pilot is used by the top guys.
One of the top and respected riflesmiths in the Country is Mike Bryant, he has a website. He made a uses what he calls a "pusher". Not really a floater, but it's just a hollow collar that the reamer end fits into, and he pushes the reamer with the "pusher" held in a chuck in the tailstock. It allows some room for movement with the reamer. However, there is more to the story. He does what most BR quality smiths do I believe, which is drill out most of the chamber, reach in and indicate in the bore/grooves, single point bore this drilled hole true. This way, the reamer has a trued hole to follow which is aligned, and the bushing isn't guiding the whole reamer. Plus, he uses a DEAD CENTER in the tailstock to start the reamer and uses it for over half the chamber, then switches to the pusher.
So why switch to the pusher at all? Well, a couple reasons. Once the chamber is established, the reamer will continue to follow, and there is much less chance for problems. There is also the issue of whether the tailstock feed will continue on the aligned path while being extended.
Why do some many people take so many pains to align and indicate in a barrel where they never see a needle move, and never do a thing to get the tailstock aligned as well? That is the first thing I do when setting up my lathe. You have to level the lathe properly, then go through the process of aligning the tailstock with the headstock. This is both fore and aft, and up and down. The check how the tailstock quill travels from in to out. Does it go up or down, or front to back, or run true?
You get your tailstock aligned, and you can use a dead center to drive the reamer, and have a well aligned chamber, a rigid setup, and much less chance of chatter problems. Plus, you can leave the barrel turning while you pull the tailstock back to clean chips from the reamer, where you cannot do this with a floater. Another no-no the floater people do, is use a one sided/handle holder on the reamer. This induces an off center loading on the reamer, and with the floater that can and will move, another chance for an over size chamber. Use a holder that is double handle, equal length on both sides of center, push with a dead center, and you'll be happy with the results.
My opinions here, everyone needs to do what their machine and abilities allow for the end result.