Rebarreling and Home-Shop Machining

# 7 Contour Douglas Barrel

A question was asked on the Long Range Target Shooting Web Site, Gunsmithing section, wether a 17x20 inch lathe is more suitable for barrel work or would and 8 x 36 lathe be better. Although the Shoptask lathe is described as 17 x 20 it will turn a piece of about 8 inch diameter over the carriage so it might also be described as an 8 x 20 with 17 inch diameter work possible to the left of the carriage or in the gap. A gap bed lathe has a space between the bed and the lathe spindle so that larger diameter disks can be turned. The Shoptask lathe has a rotary junction under the milling table which in effect leaves a gap to the left of the carriage allowing 17 inch work to be turned. The Smithy Granite model lathe has similar lathe specs, but is quite different in the milling portion of the lathe. The Shoptask Eldorado has a fifth column to stiffen the mill head and a larger distance between the mill spindle and the lathe spindle flange; this distance was a limitation for me in milling the slotted plate.

            The answer to the question is that a 17 x 20 is suitable for barrel work if you hold the barrel through the spindle for the work. If I had an 8 x 36 lathe I would still choose to do precision rebarreling work through the spindle as the barrel setup is more precise. You need at least a 1.125 inch spindle inner diameter. The only task that is more convenient on the larger lathe is contouring or finishing a barrel blank. Since most Barrel makers offer contoured blanks this is not really a big problem. I finish the blank on my Shoptask by using a temporary center and a rotated milling table using a bandfile that was described previously in this journal. This topic is now on my CD.

            The photo shows a Douglas #7 Contour Barrel Blank setup, ready to start Barrel work. It is 1.225 inch diameter at the breech for three inches and then a straight taper to .875 inch at the muzzle at 26 inch. Notice that I have used a fairly thick but narrow strip of brass at the four jaw chuck to provide a more point contact and space between the inner portions of the chuck jaws and the barrel. This allows precise alignment to the spindle axis. The alignment and the spider holding the other end of the barrel are described in my book “Precision Rebarreling” The lathe was modified to hold this size barrel with no ill effects. The modifications are described in the book as well.

Lathe Rigidity

Monarch Lathe. Rigidity is always an advantage in machining. Heavy headstock and tailstock castings improve rigidity. The Link goes to an example of a very rigid 20" lathe. 3,250 pounds. It won’t do a barrel though because its too short to thread between centers and the spindle ID is too small to thread & chamber through the spindle. Generally a bigger heavier lathe has more rigidity. A Lathe with Babbit bearings in the spindle instead of tapered roller bearings is more rigid, but must run at lower speeds. I have not found high speed to be an advantage in the home workshop. A well setup light lathe may do as good a job as a heavy poorly setup big lathe. A well setup and aligned heavy lathe with1.25 inch to 1.50 spindle ID would be ideal but is likely to be bulky and heavy and expensive.

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