when I engage the half-nut to move the carriage along the work, is their some way to make the carriage stop at exactly the same spot each time? Do I have to manually disengage the half-nut to make the carriage stop where I want to? The compound rest has a graduated dial but working along a longer piece how do I achieve this accuracy? I like to use the power feed as it gives a much smoother finish but I haven't figured out how to stop it at the same spot each time?? Maybe hard to answer without knowing the lathe I am using (it is a lathemaster, import) Thanks-
The WWII era lathe I use most, instead of having a dail on the wheel for the X-axis it has a little caliper type deal that you slide to where you want it, lock it down, and then you can measure off that point (sorry I don't know the lingo and I'm bad at describing) I just slide this to wear I want the carriage to stop and then lock it down real tight and as soon as it hits I disengage the feed. If you keep the feed on it will eventually overpower the little deal and slide it along its track. Sorry, I doubt that helped
on my old south bend, the half nut is for thread cutting, and the friction feed is for normal turning. It take some careful timing to stop at the same spot each time, usually it's better to undercut the ends so it's not critical where you stop.
After you run a certain lathe for a period of time you will get to the point where you will be able to disengage the half nut at the same point every time. It's just a matter of practice, much like everything in life. Frank
Set up the carriage stop, run the carriage up to about 1/8" from the stop, disengage the half nuts and finish the cut with the hand wheel. That's the only way you're gonna get a real precise depth of cut when cutting longitudinally. Depending on how you're doing the cutting you can run the carriage under power up to a particular point sans stop - usually by watching the cutting bit and how close it is to where you're cutting - then open the half nuts. Most times you're cutting a step when you do this and precision can be attained by cutting the other angle on the step with a face cut. [ QUOTE ] If you keep the feed on it will eventually overpower the little deal and slide it along its track. [/ QUOTE ] With all due respect, that's a good way to break the lead screw bearing or worse yet, break a gear in the lathe. Most smaller lathes have a lead screw bearing that's designed to break. (Later versions/models will have a de-clutching device, but it's best not to depend on them to save you.) What happens with the breakable lead screw bearing is; it will get broken, the lathe owner will knock a new one out of aluminum (in most cases) that is much sturdier and figure he's doing good. Next thing that happens is the carriage gets driven - under power - into the tailstock or headstock. The motor will drag down, but most times there's so much torque multiplication due to the feed gear ratio selected that the lathe will break a gear with all the attendant breaking and banging noises and dust floating in the air. They usually let go with a heck of a bang. And yes . . . I did it . . . once. Even the gears on most small lathes are a safety device of sorts. They're made of Sintered metal. Sintered metal is a finely powdered metal that is pressed in a mold under several tons, many times with a binder of some sort and baked in an oven. Cheap to make and they can break easily. The Sintered gears are fairly strong, dependable and a good way to go. Trouble is, try to find a spare one after you break it. You can make a new gear utilizing several methods, but that's a whole other ball game.... Not too difficult though....
cool idea to make a face cut to eliminate the "step" that forms C9...your machining expertise and mine are eons apart...so far I operate this thing like a second grader
[ QUOTE ] [ QUOTE ] If you keep the feed on it will eventually overpower the little deal and slide it along its track. [/ QUOTE ] With all due respect, that's a good way to break the lead screw bearing or worse yet, break a gear in the lathe. Most smaller lathes have a lead screw bearing that's designed to break. (Later versions/models will have a de-clutching device, but it's best not to depend on them to save you.) [/ QUOTE ] That's why I don't leave the feed going And yeah, I'm about as novice as it gets with machining. I'm learning...slowly
[ QUOTE ] C9...your machining expertise and mine are eons apart [/ QUOTE ] Not really. I read a lot - got bunches of machining books and quite a few Home Shop Machinist magazines. Plus, I ain't afraid to try. Thing is to do just like you - and the other guys - are doing. Namely, getting in there and doing it. Each job a little experience is gained and the next similar job is easier. It is surprising what some guys can turn out with just the basics. I've seen very fancy single shot target pistols that were made with drills and files. No lathe, no mill, just the basic hand tools, a vise and some time. One thing you're going to find out is that a high degree of precision is not required on all jobs. The other thing is simply making one thing fit the other thing and to that end having a sample on hand will do the job. That's why the pro machinists ask for the big threaded piece you're working with. They want it so they can fit one to the other and to an extent, tolerances be damned as long as they go together properly. Be careful you don't end up with odd threads or odd sizes. Few years back little brother made his own stainless fuel tank for the front of his Henry J drag racer. He gave me the stainless to cut down to make the threaded weld bungs. For the filler cap, I cut 2 1/4" x 8 threads and made an O-ringed aluminum screw in cap to match. I told him don't lose the cap cuz you ain't ever gonna find anything even close.... Sounds kinda dumb, but the 2 1/4" was the size required and I figured 8 pitch threads would make for a cap that was quick to remove and replace.
[ QUOTE ] is their some way to make the carriage stop at exactly the same spot each time? [/ QUOTE ] Use a Magnetic Base and Dial Indicator,to read the carriage position accurately. Disengage the feed at the same indicator reading each time.
The Jalopy Journal
