[bmw5002]

hello to all, this is my first post. this looks like an awesome community and i am happy to be a new member of it. maybe you guys could help me out with some recommendations?

I was looking into the sieg sc4 and sc6. i want something to mess around with and learn on, then use it for cnc conversion eventually after i am experienced with manual usage. i looked through some build threads on here, and i saw one guy that converted a lower model of sieg lathe without the power feed options and he put the ballscrew shaft in the area of the powerfeed screw on these models. should i get a version without the power feed for easier conversion? i do like the variable speed and high power of these models though... and i bet with a custom interface to the lathe's controls, the cnc controller could be able to control the spindle speed of these lathes...

let me know what you guys think. and be easy on me, im a total newbie but very interested in cnc. i recently began a new job at a company that builds industrial machines that deal with descrambling and orienting plastic bottles, and we've got a decent size machine shop, with a smaller benchtop lathe, and a giant gearhead lathe, both manual operation. we also have a giant thermwood cnc router that we use to cut mostly plastic, poly and lexan. ive previously done some very novice metalworking with my angle grinder, chopsaw and mig welder at home for automotive stuff, but this new job is a whole new ballpark of fabrication. its cool and i'm learning fast. ive gotten good at using the tig welder for stainless. unfortunately there is not much time for personal stuff, so i would like to get some of my own equipment. also anything cnc is just freaking cool to me so... i hope to be here for a long time to come.

[michaelthomas]

I'm purchasing a Grizzly G0602. It's kind of a medium sized benchtop lathe. It seems to have a fair amount more ability than the 500-600 dollar lathes. There are also a few people doing cnc conversions on here to get ideas from. I was skeptical of buying the smaller lathes, because I was afraid I would grow out of it and want something larger too quickly. It seems like a good middle ground


It really just depends on what you are going to make on them I guess. I do plan on converting mine almost immediately......but I'll have to use it in manual mode to make some parts first.

[sansbury]

The SC4 and SC6 are, if I recall, kind of rare in the US. I think there may be a distributor or two but they are kind of pricey.

FWIW, I have a Sieg 7x10 I got before I knew better (and it was on super-sale so at least the price was right) and I have rarely found myself wishing for a bigger motor. I usually run out of chuck, travel, or rigidity before the motor quits. About the only place where I see a bigger motor really helping would be in drilling larger holes in harder materials. Little Machine Shop and Micro Mark both sell the SC2 in either 7x12 or 7x16 format for $700 and $800 respectively. The SC4 at LMS is nearly $1400, and for that price, you can get a 10- or even 11-inch lathe from Grizzly like the G0602.

Personally, I'd get either the SC2 or the G0602, since the 7x lathes seem to be *very* easy to unload on eBay or Craigslist for a good price, in case you decide you don't need it or want a bigger lathe, while the Grizzly can handle very serious workpieces without taking up half your garage. As to capacity, I've turned 3" cast iron parts on my 7x, though it wasn't much fun, while anything under 1" is. I'm nearly done with a full CNC conversion which helps a bit since the machine doesn't get bored taking eight dozen .001" cuts if that's what the part calls for. I did a ghetto CNC conversion without replacing the screws and for a 7x, I am not sure I'd really bother with much more.

[bmw5002]

looks like the c6/sc6 has 21" between centers. is that the bed length? if so, thats only an inch under the grizzly.

any word on how the spg lathes are?

also im thinking that it would be pointless to get a machine with power feeds because i wouldn't really use it in manual mode, and after conversion, it would probably be useless as well. is it possible to cut threads with these lathes converted to cnc? i guess the lathe would need to be on the lowest speed and the computer would need an rpm speed input from the shaft. then it could calculate exactly how much to move the steppers/servos to cut the right thread. is this correct?

i am also curious about the issue of stepper vs servo. from the little research ive done, ac servos are basically better in every way except price. where i work, our machines use ac servos, but they are no expense spared so...
ac servos are easy to come by used on ebay for less than $100 each. the only hard part is finding the right servo drive since input voltage and power handling capacity differ so much between drives. theres also the issue of compatibility with your setup if you try to mix and match used drives off ebay. how much accuracy is gained by switching from steppers to a servo drive system? or is it really just speed that is gained?

[michaelthomas]

Yep....that's the longest piece that can be turned between the chuck and the tailstock.

You can thread with a cnc conversion as long as you have a spindle input.

The G0602 has a power feed on the z.....which can be used to cnc, or can be replaced with ballscrews or acme screws. See Crevice Reamers G0602 thread.

For small machines, servos are not really necessary. As long as a stepper is not run beyond its means, it is as accurate as a servo.....for our practical purposes. Rather than provide a lengthy comparison......check the Gecko site. They have a lot of information that you will probably find useful.

With a .200 pitch ballscrew and a 1/10th microstepping driver such as the Gecko, that translates to .0001" resolution per step.....which is likely a long way past the sum of the other inaccuracies of this particular lathe. If you don't push steppers beyond their bounds, they won't lose steps.

[blades]

Welcome to the forum, bmw! There's not much I can add regarding the larger of the small lathes, as I've got a 7x10. I guess it all depends on what you plan or forsee needing to turn with it. I chose my 7x because I was looking for a small lathe, only plan on turning small stuff, and needed something lightweight enough to move by myself. The 7x fit all these requirements nicely. If you don't have the aforementioned constraints, a slightly larger lathe will serve you well. A Harbor Freight 8x12 lathe in terms of capacity isn't much larger than a 7x, but it's worlds better because it outweighs the 7x lathe by a factor of 3:1, and that extra bulk always means a more solid and capable machine.

[sansbury]

also im thinking that it would be pointless to get a machine with power feeds because i wouldn't really use it in manual mode, and after conversion, it would probably be useless as well.

If you use the lathe manually, you will use the power feed.

is it possible to cut threads with these lathes converted to cnc? i guess the lathe would need to be on the lowest speed and the computer would need an rpm speed input from the shaft. then it could calculate exactly how much to move the steppers/servos to cut the right thread. is this correct?

Yes, CNC threading is one of the nicest parts of a CNC lathe. Your understanding of how it works is correct. Both Mach and EMC can do this.

i am also curious about the issue of stepper vs servo. from the little research ive done, ac servos are basically better in every way except price.

They're basically a waste on machines this size. In principle they are more precise, smoother, and faster. In practice, you're not going to notice any of that for reasons Michaelthomas mentioned. Hunting eBay for bargain drives is a recipe for wasting a lot of time and sometimes money. I prefer to just buy what I understand and know will work.

[bmw5002]

If you use the lathe manually, you will use the power feed.

ok, mainly i am trying to understand how the power feed would work with a conversion. not sure if i would replace the power feed screw with a precision ballscrew, or if i would mount the ballscrew seperately. then could the power feed still be used in manual mode after conversion? just trying to understand the best way of going about that. maybe it would be less complex to go without keeping the power feed and use the computer to sort of manually jog the servos for manual use....

[michaelthomas]

http://www.cnczone.com/forums/vertic...he_3_step.html

Look this thread over and if it doesn't answer your questions ......post back here.

[sansbury]

Typically conversions are accomplished by replacing the Z-axis screw with a low-backlash ball screw. That said, I did my 7x without replacing the screws, and it works fine so long as you use it properly. On a 10x, I'd probably go for ball screws, but they're hard to fit on a 7x, particularly on the X axis. Even with the plain Acme-style screws, I can get 60IPM rapids which are more than enough for something this small. Threading to a shoulder at >500RPM is kind of exciting...

[bmw5002]

cool, yeah i get it now. check out this lathe:
[nomedia="http://www.youtube.com/watch?v=RJ08LnLnoQ0&feature=related"]YouTube - More CNC Fun[/nomedia]
automatic tool changer, it even automatically unchucks the part in some other videos. what kind of lathe is that? i want it!
i know you guys have probably seen this kind of stuff before, but damn this thing is amazing: [nomedia="http://www.youtube.com/watch?v=5AB_etoHesI&feature=related"]YouTube - GTV-27 Broaching Demo[/nomedia]