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Posted: 11/28/2006 5:58:22 AM EDT
When it's necessary to index off of the bore [IE: threading chambering etc], how do you keep the other end running concentric if it's too short to reach through the lathe headstock? When I turned my 20" 22cal upper I used a spider on the back side and dial indicated it, but for any thing shorter I'm lost. Do you just indicate the end sticking out and let the rest of the barrel inside the headstock fend for itself? Maybe I worry too much?? Thanks |
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Steady-Rest, or between centers. If its too short to pass through the head-stock (assume you have a 4-jaw chuck on both sides to indicate longer work {oh, you used a spider for this}) and it is too long to be held securely in a 4-jaw chuck you either turn the threads while it is between centers (the best way assuming) or you chuck the end you are not threading into a 4-jaw chuck and the other in a steady rest. The only problem with the 4-jaw chuck method is if the bore axis is not concentric with the outside of the barrel (or other work-piece). It is then difficult to indicate the bore at the head-stock. Something that you can do, is use a spider in the 4-jaw chuck, but you will lose a lot of grip on the work so only very light cuts can be made. You start by mounting the spider on the end that will go in the chuck. Place the work in the lathe so that the steady-rest will hold the spider. You then indicate the bore relative to the o.d. of the spider. Once that is done, then you turn the work around and hold the spider in the 4-jaw chuck and the other by the live center, or steady-rest. I hope this helps. Personally, I prefer turning between centers when possible. ETA. Use copper pads in the jaws of the 4-jaw chuck to prevent marking up the barrel. The pads also allow the work to be bumped around a bit to get the long end indicated. Also, if the o.d. in not concentric with the bore and you want to use a steady-rest, then use a spider at the steady rest also. This will allow you to indicate the bore rather than the outside. Dave. |
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My lathe has a headstock that does not easily allow me to mount a spider on the back. I turn one end of the barrel on the tailstock with a live center with a 3 jaw chuck on the headstock, and then take a finishing cut on a dead center to a diameter I have a collet for. I then put that end in the collet, reinstall the live center, and then turn down the rest of the barrel to whatever profile I am working on. When it is time to cut threads, I install the collet and leave the rest of the barrel hanging in the headstock with maybe 1" of barrel shank sticking out. The collet is solid enough to cut clean crisp barrel extension threads on, and I don't think I am getting that dreaded tapered thread effect. I wrote earlier about having a horrid time cutting threads, and it was due to a slack castle nut thingie adjusting the preload on my tapered bearings. Adjusted it properly, and wow! my threads turn out smooth as silk. Simple as that. |
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