|
lathes for a newbie
Archive is at Google.
http://snurl.com/1xor Or, if you prefer: http://groups.google.com/groups?hl=e...indow=1&safe=o ff&group=rec.crafts.metalworking -- Ron Thompson On the Beautiful Mississippi Gulf Coast USA http://www.plansandprojects.com Where did everyone go? Oh, yeah. http://groups.yahoo.com/group/castinghobby/ Y'all come, ya hear? ******* "Zipper" wrote in message news:NJ0Wa.24152$Ho3.4351@sccrnsc03... I was curious if anyone had any advice for a lathe for a complete newbie. I have done a little MIG welding and I'm really enjoying metal working and would like to continue. I've thought about getting a lathe, but I really don't know that much about it. From looking around, I'm not really sure how reasonable getting a lathe is since I don't have a lot of money, but I thought I'd ask. I'm trying not to pay more the a $600 for a lathe, and I realize this won't even buy me a decent one. Any help would be appreciated. Sorry if this question has been asked, but this newsgroup doesn't seem to archive. |
lathes for a newbie
"Zipper" wrote in message news:NJ0Wa.24152$Ho3.4351@sccrnsc03...
I was curious if anyone had any advice for a lathe for a complete newbie. I have done a little MIG welding and I'm really enjoying metal working and would like to continue. I've thought about getting a lathe, but I really don't know that much about it. From looking around, I'm not really sure how reasonable getting a lathe is since I don't have a lot of money, but I thought I'd ask. I'm trying not to pay more the a $600 for a lathe, and I realize this won't even buy me a decent one. Any help would be appreciated. Sorry if this question has been asked, but this newsgroup doesn't seem to archive. For that amount of money you are pretty much limited to Sherline, Taig, or the 7 x 10 lathe Harbor Freight sells. You could fall into the deal of a life time on some used American iron, only used to turn a marshmallow that one time - it happens all the time! (just never happens to me). While both the Sherline and Taig are great little machines, the HF 7 x 10 is a heavier machine with more features for about the same money (under $400)and is pretty hard to beat. Lots of info/support on the web. And still leaves you money for some tooling. I started with one, and then traded it for a quick change tool set for my next lathe, a 9 inch South Bend (I'm still kicking myself). You'll have to clean off all the Chinese ear wax and do a little tweeking, but if you decide to stick with machining you can always sell it, or trade it for some tooling. - just make sure you get what it's worth - damn it! |
lathes for a newbie
|
lathes for a newbie
|
lathes for a newbie
|
lathes for a newbie
You DO NOT want to use ballscrews on a manual machine. With normal
screws, there is enough friction and mechanical advantage to prevent the machine from kicking back when cutting. But with ballscrews there isn't. You need a motor drive holding them. That's why ballscrews are only used on CNC machines. (It is also why trying to convert a CNC machine to manual can be a big expensive problem.) Gary Thanks for the additional information about ballscrews. I guess I can forget about ballscrews until I convert my lathe to CNC then, which won't be for awhile. Michael |
lathes for a newbie
On Fri, 01 Aug 2003 14:27:30 -0400, Gary Coffman
wrote: You DO NOT want to use ballscrews on a manual machine. With normal screws, there is enough friction and mechanical advantage to prevent the machine from kicking back when cutting. But with ballscrews there isn't. You need a motor drive holding them. That's why ballscrews are only used on CNC machines. (It is also why trying to convert a CNC machine to manual can be a big expensive problem.) I don't think this is right, what is meant by "kicking back"? I don't think there is any mechanical reason to not put ball screws on a manual machine. And I seem to recall that it was done on some older high precision manual machines. There should not be any problems with ball screws when cutting with a conventional feed. For climb cutting, the hand turning the feed crank, the weight of the table, cross and compound slides, and properly adjusted gibs, will be enough to keep the cutting forces for overcoming all the other friction and actually turning the screw. If it does not, uncontrolled movement would be limited to the small amount of freeplay in the ballscrew and that eliminates the danger of pulling a chip heavy enough to break a cutter. I can't imagine sustained cutting forces being used on a manual machine converted to ball screws that were heavy enough to overcome all the other friction and drag and drive the hand feed through a ball screw. If that could happen, the operator would feel the lighter or lack of feeding force on the handwheel. They should realize that they are not feeding the material but instead chasing a series of continuous self feeds. That would be a wake up call for me, time to clamp the ways tighter or lighten the cut. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 80,000 Newsgroups - 16 Different Servers! =----- |
lathes for a newbie
On Sat, 02 Aug 2003 17:46:34 -0400, Jack Erbes wrote:
On Fri, 01 Aug 2003 14:27:30 -0400, Gary Coffman wrote: You DO NOT want to use ballscrews on a manual machine. With normal screws, there is enough friction and mechanical advantage to prevent the machine from kicking back when cutting. But with ballscrews there isn't. You need a motor drive holding them. That's why ballscrews are only used on CNC machines. (It is also why trying to convert a CNC machine to manual can be a big expensive problem.) I don't think this is right, what is meant by "kicking back"? A ballscrew has very little friction, so it won't stay where you dialed it against forces acting on the table. In other words, it will allow the table to drive the screw. An ordinary Acme leadscrew has plenty of friction, and won't do this unless cutter forces are extreme. There should not be any problems with ball screws when cutting with a conventional feed. For climb cutting, the hand turning the feed crank, the weight of the table, cross and compound slides, and properly adjusted gibs, will be enough to keep the cutting forces for overcoming all the other friction and actually turning the screw. If it does not, uncontrolled movement would be limited to the small amount of freeplay in the ballscrew and that eliminates the danger of pulling a chip heavy enough to break a cutter. There should be near *zero* lash with a ballscrew. That's not the issue. The problem is that there is so little friction that the table can drive the screw, regardless of whether you are up or down milling. I can't imagine sustained cutting forces being used on a manual machine converted to ball screws that were heavy enough to overcome all the other friction and drag and drive the hand feed through a ball screw. A ballscrew will work in reverse with only a few *ounces* of pressure. Cutting forces are almost always higher than that. If that could happen, the operator would feel the lighter or lack of feeding force on the handwheel. They should realize that they are not feeding the material but instead chasing a series of continuous self feeds. That would be a wake up call for me, time to clamp the ways tighter or lighten the cut. Well, yeah, you could tighten up the gibs to create more drag, but you'd have to tighten them up *a lot* to compensate for the lack of normal leadscrew friction. Remember that the mechanical advantage of the screw multiplies the effects of screw friction. It is also worth noting that ballscrews typically are half or less the pitch of conventional Acme screws, in other words, where you'd normally expect an 8 TPI Acme screw, the equivalent ballscrew would be 4 TPI. So there's less of a multiplier for the little friction that the ballscrew does have. If you disconnect the drives on a CNC machine with ballscrews, you can grab the table and shove it back and forth, while the ballscrew spins madly. Try that with a table that has conventional screws and it is doubtful you could budge it. Gary |
lathes for a newbie
On Sat, 02 Aug 2003 19:28:37 -0400, Gary Coffman
wrote: I don't think this is right, what is meant by "kicking back"? A ballscrew has very little friction, so it won't stay where you dialed it against forces acting on the table. In other words, it will allow the table to drive the screw. An ordinary Acme leadscrew has plenty of friction, and won't do this unless cutter forces are extreme. You seem to be discounting the weight and friction of all the other pieces. This is not my first rodeo. If it does not, uncontrolled movement would be limited to the small amount of freeplay in the ballscrew and that eliminates the danger of pulling a chip heavy enough to break a cutter. There should be near *zero* lash with a ballscrew. That's not the issue. The problem is that there is so little friction that the table can drive the screw, regardless of whether you are up or down milling. You say "near zero", I say small amount, we're taking about the same thing. And again, you seem to be discounting the weight and friction of all the other pieces. I have never seen a situation where fitting ball screws to a manual machine would result in all the weight and moving mass being transferred to the ball screws and all other friction eliminated. A ballscrew will work in reverse with only a few *ounces* of pressure. Cutting forces are almost always higher than that. I say again, you seem to be discounting the weight and friction of all the other pieces. This is a converted manual machine. And the operator still has his hand on the crank. If that could happen, the operator would feel the lighter or lack of feeding force on the handwheel. They should realize that they are not feeding the material but instead chasing a series of continuous self feeds. That would be a wake up call for me, time to clamp the ways tighter or lighten the cut. Well, yeah, you could tighten up the gibs to create more drag, but you'd have to tighten them up *a lot* to compensate for the lack of normal leadscrew friction. Remember that the mechanical advantage of the screw multiplies the effects of screw friction. I think you are overstating the amount of the friction that is derived from the leadscrew. Imagine a properly lubricated hardened and ground leadscrew running in a well fitted bronze nut. Losing some of the friction is not necessarily going to be a bad thing on older machines converted to ballscrews. Don't ignore the presence of the other sources of friction that typically exist in older machines. It is also worth noting that ballscrews typically are half or less the pitch of conventional Acme screws, in other words, where you'd normally expect an 8 TPI Acme screw, the equivalent ballscrew would be 4 TPI. So there's less of a multiplier for the little friction that the ballscrew does have. How about the increased helix angle in the coarser thread? Have you factored that in? And then there is the question of how many angels can dance on the head of a pin. The only machine specifics mentioned in this discussion so far has been $600 lathes and a 7 x 10 minilathe. Those kinds of machines are good candidates for ballscrew conversions and there are ballscrews with finer pitches that can be used on them. And I think we are talking in a venue where people are tinkering with ideas, learning things, trying to make things work, and simply not constrained by the rules and dictums that exist in the full sized CNC machinery world. If you disconnect the drives on a CNC machine with ballscrews, you can grab the table and shove it back and forth, while the ballscrew spins madly. Try that with a table that has conventional screws and it is doubtful you could budge it. Ah! Now I get it. You were thinking of CNC machines with ballscrews already fitted. Aren't there any other sources of friction in those? Are there no resting forces whatsoever? You said "You DO NOT want to use ballscrews on a manual machine." I disagree. There is no good reason to not do that within the framework of the discussion here. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 80,000 Newsgroups - 16 Different Servers! =----- |
lathes for a newbie
Well, yeah, you could tighten up the gibs to create more drag, but you'd have to tighten them up *a lot* to compensate for the lack of normal leadscrew friction. Remember that the mechanical advantage of the screw multiplies the effects of screw friction. It is also worth noting that ballscrews typically are half or less the pitch of conventional Acme screws, in other words, where you'd normally expect an 8 TPI Acme screw, the equivalent ballscrew would be 4 TPI. So there's less of a multiplier for the little friction that the ballscrew does have. If you disconnect the drives on a CNC machine with ballscrews, you can grab the table and shove it back and forth, while the ballscrew spins madly. Try that with a table that has conventional screws and it is doubtful you could budge it. Gary Very true, and something I do everyday, diagnosing machines. Ive given slightly worn ballscrews away, (.0007 backlash), to at least one fellow, (.200 per rev) and he reported he had to put a lock screw in the gib, to keep it from moving when he converted his crossfeed to use the ballscrew. He said it works very well,very accurately, but has to lock the gib everytime he makes a cut, and is not sure it was worth the effort to do the conversion simply because of that. Gunner "What do you call someone in possesion of all the facts? Paranoid.-William Burroughs |
lathes for a newbie
On Sun, 03 Aug 2003 10:11:45 -0400, Jack Erbes
wrote: If you disconnect the drives on a CNC machine with ballscrews, you can grab the table and shove it back and forth, while the ballscrew spins madly. Try that with a table that has conventional screws and it is doubtful you could budge it. Ah! Now I get it. You were thinking of CNC machines with ballscrews already fitted. Aren't there any other sources of friction in those? Are there no resting forces whatsoever? Very very few resting forces. Remove the motor, and they have only inertia for the most part. They are engineered to be as friction free as possible, with the use (generally) of linear ways/cars or box ways/bearings/gibs, with the lube film being accounted for. See my earlier post on a gent whom did a crossfeed conversion. Gunner "What do you call someone in possesion of all the facts? Paranoid.-William Burroughs |
lathes for a newbie
In article , Jack says...
I have some ball screw slides at work, and when the stepping motor is de-energized, it takes very, very little force to move the slide and spin the ballscrew. On manual small lathes or mills? In this case they were crossed slides for some motion control experiments. If the rail was up-ended a bit, the slide would zip to the end, just from gravity. The small stepping motors generated so much linear force that one had to be really, really careful not to get an appendage caught between the slide and the end stop. You guys are going to have to be more careful. You may be stifling genius here. These guys may grow up to be your bosses. :) Heh. Just 'cause he's the boss, that don't make it right! Sometimes the hard part of dealing with the boss, is being tactful when explaining that some part of his plan is technically wrong. Incorrect. Won't actually work. Which is actually one reason why I like my present one. He's right most of the time so I don't have to do that dance, hardly ever. Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
| All times are GMT +1. The time now is 07:51 AM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004 - 2014 DIYbanter