Author Topic: Vertical offset of tailstock (Read 1123 times)

JimInNJ · « **on:** February 06, 2003, 11:49:49 AM »

My tailstock center is about .0005 high relative to my spindle. Is that enough to cause problems when chambering? I could make an adjustable center, but is it worth the bother for half a thousandth?

- Jim

John Traveler · « **Reply #1 on:** February 06, 2003, 12:07:04 PM »

Well, remember that ANY amount of eccentricity registered on your tailstock will be DOUBLED in chamber size when you do a chamber reaming operation. That would total a 0.001" oversize chamber. The same is true for any lateral tailstock offset you might have from turning tapers, or whatever. The tailstock natchurly needs to be as centered as possible with the headstock center.

The way to get around that "oops" is pretty simple:

P.O. Ackley wrote that you ALWAYS do chamber reaming work with the berrel between centers, and drive the muzzle end using a dog. Support the chamber end on a steady rest. You do your rough chambering using the tailstock handwheel to drive in the reamer, with plenty of frequent withdrawls, cleaning, and lubrication, of course. Pressure lubrication from the muzzle is even better. Cut the chamber to say within 0.050" of full chamber depth. After that, use the tailstock center to GUIDE the reamer, but hold it with your hand in a glove.

Chambering this way will assure that you are not cutting the chamber oversize due to headstock/tailstock misalignment.

Joe Kool · « **Reply #2 on:** February 07, 2003, 08:16:23 AM »

Clymer makes a floating reamer holder. Price $90-$95

JimInNJ · « **Reply #3 on:** February 16, 2003, 06:16:25 PM »

Thanks for the helpful replies.

Mr. Ackleys lathe was longer than mine. I am forced to work with the barrel through the headstock and the muzzle end supported by a spider.

I went ahead and made an adjustable center for my tailstock. I will take the advice to use it only as a guide for the last 0.050

- Jim

WLB · « **Reply #4 on:** February 19, 2003, 06:28:19 AM »

Wouldn't it have been much easier and faster to just take the top part of the tailstock off and lightly dress the surfaces with a stone or emory paper wrapped wrapped around something flat?
Bill

John Traveler · « **Reply #5 on:** February 19, 2003, 07:26:34 AM »

Gee,

I guess a really dedicated person could make anything fit anything properly. I'd prefer to leave factory-made machine surfaces well enough alone!

At the dimensional errors we are talking about (0.0005" off-centre height), operator measurement error is most likely a large part of what is perceived as "off centre".

Hobbyist consumer-grade lathes are simply not built with enough precision to worry about that much eccentricity. Lathe centers are not ground accurate enough or fit in the tailstock accurately enough to USE that much accuracy. Proper use of a "floating" chambering reamer will nullify that error.

To compensate for the limited capabilities of modest quality equipment, good machinist technique and procedures must be used.

The late gunwriter/gunsmith Mr. De Haas became famous as "Mr. Single-Shot" for his expertise in gunsmithing singleshot rifles. He also made custom bolt action rifles. He did this over a 40-something year period using little more than an old manual gear-change Sears Atlas lathe and hand tools!.

I've seen many superbly chambered rifle barrels done in a 3-jaw chuck held in the headstock. It's all in the proper technique.

JimInNJ · « **Reply #6 on:** February 19, 2003, 05:22:06 PM »

Bill, that is an interesting option that I just never thought of. But I agree with John Traveler in that I'd prefer to leave factory-made machine surfaces well enough alone. The correct procedure to insure that the surfaces fit properly would be to hand scrape them, and that requires a lot of skill that I have not developed. It is also not reversible.

I was actually surprised to find only .0005" error on my Chinese wonder. I measured this by putting a large chucking reamer between centers and running a DTI along the ground shaft. I do not know how repeatable it would be with the tailstock locked down elsewhere along the bed, or with the quill extended a different amount.

John, I have a copy of "Mr. Single Shots Book of Rifle Plans" and have spent considerable time pondering his designs and construction techniques. I also have a copy of Walter B. Mueller's "Building a Single-shot, Falling-block Rifle Action" which includes plans for an adjustable center that inspired the one I constructed.

I am impressed with the elegance of Mr. De Haas' designs with regard to ease of construction with minimal tooling. I just wish his center fire models were more elegant with regard to appearance. Mr. Mueller on the other hand builds an elegant action, but seems to take delight in the difficulty of is construction.

- Jim