FNG question on parts/retro

Hello Gents,
I have a need for CNC control for lathe parts ~ 2" long x 1.75" D. I currently have a southbend heavy 10 and old pulley head bridgeport along with a multitude of tig/mig welders. I can do 90% of what I want to do on the manual but I turn a lot of titanium/17-4 and form tools don't work so hot on either.

So on to the questions
I could do MOST everything I wanted to do by CNC the compound and the cross slide. Obviously no threads with just that but I can thread manually. Is this viable for the occasional use

If I were to build a SMALL CNC instead, I would want to use collets primarily, preferably something with a big enough spindle bore to pass 1.75". I could use 5C Emergencies and cut everything to size first but then would have 2 operations with a part flip instead. I started looking at builds and linear bearings and came across what is essentially pre-built tables with 2 linear rails and a ball screw built in on eBay/my local automation guy. Are these things viable? Can you just mount one on top of the other and go to town? Here is a cheap example of what I'm referring to. I don't think you can buy the piece parts for that?

https://www.ebay.com/itm/200MM-Strok....c100667.m2042

Thanks in advance for the help!

ETA, tolerance required is probably around +/- 0.003. Not super precise like some. Its more I make a lot of similar shapes that have curves making it difficult to turn on a manual (a ball turner wouldn't help)

Added one more concept...2 axis table that can just sit on my ways (or my mill for that matter)

Quite a few have done CNC lathe conversions. Generally the lead screws are replaced with ball screws, so most can't be used manually anymore. Biggest issue with ball screw replacement is that the ball nuts are usually quite a bit larger than acme nuts, so are hard to fit. Most avoid just throwing steppers on the existing screws because the backlash in most of them is too much for CNC.
I don't think you'd be happy with the surface finish you'd get if you added a CNC stage like that ebay one to your lathe or mill. Nowhere near the rigidity you're used to.

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Originally Posted by skrubol

Quite a few have done CNC lathe conversions. Generally the lead screws are replaced with ball screws, so most can't be used manually anymore. Biggest issue with ball screw replacement is that the ball nuts are usually quite a bit larger than acme nuts, so are hard to fit. Most avoid just throwing steppers on the existing screws because the backlash in most of them is too much for CNC.
I don't think you'd be happy with the surface finish you'd get if you added a CNC stage like that ebay one to your lathe or mill. Nowhere near the rigidity you're used to.

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Well that is disheartening. Big machines = rigidity but I lack the space for a craigslist morei seki (sp) even though there is one less than a mile from my house for 4k. I would hate to convert my southbend entirely since a lot of my work is down and dirty 20 min job that would take longer to program than machine. The nature of the product doesn't let me outsource it unfortunately. Maybe I will have to look into making some sort of tracer instead. I have a taper attachment on my lathe so maybe there are some options there.

It is POSSIBLE to CNC a manual lathe without losing any manual capability. You use a ball screw on the cross slide but use the existing carriage drive (not the lead screw) to move the carriage. You control the backlash with an air spring, control the accuracy with linear scales on the axes. CNC threading is no problem, just requires an encoder on the spindle. I designed such a system for my 13x40 but never followed through on it because I bought a CNC lathe.

I think the best solution is going to be just build an appropriately sized CNC lathe. I have all the tools at my disposal to do so. Just a matter of sitting down to design it then build. With as small of a work envelope as I really need I don't think it will get too exorbitant in costs and will be exactly what I want it to be. The trick will be keeping myself limited from trying to go all "live tooling", "tooling turret", micron accuracy on it and realizing what I need it to do is very simple.

16C collet
80mm x 140mm Spindle Bearings?
Servo drive spindle I think?
Ti and my diameter will require quite low RPM - only 400-800 RPM. 17-4 will be under 3000 RPM still.
I think ~10" for Z travel and ~10" for X should suffice? I will need, exterior profiling, interior profiling, drilling and cutoff. May be a bit tight for gang tooling?
~2-3" max stickout
1.75" Diam max for bar, maybe more if I use some emergency collets but unlikely
2 AC bearings on the nose and one radial on the aft end of the spindle.
I think the HSM 1605 standard ball screws will be sufficient especially if I run proper bearings at the fixed end?
Steppers should be fine for the ball screws. This isn't going to be a production machine. Direct drive would be nice but not necessary.


I will have to look into the software/hardware side.

I have the mill and lathe at home already. We have surface grinders at work. This seems like a bit of a difficult project but not over the top.

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Originally Posted by propeine

I think the best solution is going to be just build an appropriately sized CNC lathe. I have all the tools at my disposal to do so. Just a matter of sitting down to design it then build. With as small of a work envelope as I really need I don't think it will get too exorbitant in costs and will be exactly what I want it to be.

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Sounds like a good plan. I would buy the spindle assembly/housing, Ebay has a few of them last time I looked. Maybe buying that CNC lathe that you referenced above would be a good starting point, at least it would have a lot of the hardware that you will need. For $4K it might be worth a look, or you might look around for a less expensive one. If I wanted to build a lathe, that's what I would do.

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The trick will be keeping myself limited from trying to go all "live tooling", "tooling turret", micron accuracy on it and realizing what I need it to do is very simple.

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''Mission creep'' will get you every time :D

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Originally Posted by Jim Dawson

Sounds like a good plan. I would buy the spindle assembly/housing, Ebay has a few of them last time I looked. Maybe buying that CNC lathe that you referenced above would be a good starting point, at least it would have a lot of the hardware that you will need. For $4K it might be worth a look, or you might look around for a less expensive one. If I wanted to build a lathe, that's what I would do.



''Mission creep'' will get you every time :D

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Well now thats a hell of an idea! Finding the right one may take a bit but with the cost of bearings anyways would probably be a net savings.

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Originally Posted by propeine

Well now thats a hell of an idea! Finding the right one may take a bit but with the cost of bearings anyways would probably be a net savings.

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Where are you located? I know of a least one locally that you could buy by the pound. There may be another also.

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Originally Posted by Jim Dawson

Where are you located? I know of a least one locally that you could buy by the pound. There may be another also.

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NW Pennsylvania

A bit far away to get a machine out here. :)

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Originally Posted by Jim Dawson

A bit far away to get a machine out here. :)

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Haha ya just a touch. I'll keep my eyes open here. How about the rest of the list? Does it seem reasonable for what I'm trying to achieve?

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Originally Posted by propeine

Haha ya just a touch. I'll keep my eyes open here.

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I did drive down to Oklahoma to pick up my lathe, 3400 mile round trip.

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How about the rest of the list? Does it seem reasonable for what I'm trying to achieve?

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16C collet

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Max through a 16C is 1 5/8, could go bigger with an emergency collet, but not through.

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80mm x 140mm Spindle Bearings?

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I would just buy a spindle assembly,that way you can get the whole assembly many times including the collet/chuck closer. Here are a few examples from a quick EBay search.

https://www.ebay.com/itm/TSUGAMI-CNC...AAAOSwtfhYnI1D


https://www.ebay.com/itm/TSUGAMI-CNC...sAAOSwCU1YnI6p


https://www.ebay.com/itm/Okuma-LC20-...EAAOSwHPlWdEdk


https://www.ebay.com/itm/Mazak-Quick...wAAOxyfCBSB79I


https://www.ebay.com/itm/Mazak-Slant...kAAOSwm8VU0P7O

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Servo drive spindle I think?

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That would be my choice. I wish I had a C axis spindle on mine, but it's going to get that one day. I have a design for an auxiliary drive system using a 1.8KW servo. A 7.5KW servo is expensive. I've been trying to find a used one at my price.

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Ti and my diameter will require quite low RPM - only 400-800 RPM. 17-4 will be under 3000 RPM still.

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Seems well within normal operation envelope. Don't short yourself on motor power.

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I think ~10" for Z travel and ~10" for X should suffice? I will need, exterior profiling, interior profiling, drilling and cutoff. May be a bit tight for gang tooling?

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That's about what my lathe has, has been adequate for everything that I'm doing. I think my longest part is about 4 inches x 1 1/2 dia. I could easily turn 10 or so inch diameter. Depending on how many tools you need to run with gang tooling,10 inches of X may or may not be enough.

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~2-3" max stickout

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I have been running with 5 inches stickout on the part above, 6061 aluminum, no problems. The stainless parts I run a bit closer, but they are smaller.

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1.75" Diam max for bar, maybe more if I use some emergency collets but unlikely

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As I said above, max through a 16C is 1 5/8, but there is another collet system that goes up to about 3 inches. I haven't priced them but I'm assuming it's not cheap. https://academy.titansofcnc.com/seri...p-collet-chuck

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I think the HSM 1605 standard ball screws will be sufficient especially if I run proper bearings at the fixed end?

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I think my ball screws are 20 or 25mm can't remember which. 10mm lead as I recall.

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Steppers should be fine for the ball screws. This isn't going to be a production machine. Direct drive would be nice but not necessary.

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Steppers would work, but you are really talking about a pretty big lathe, and servos are not that much greater in price unless you are comparing to the cheapest EBay steppers.

I'm using 1.8KW DMM Tech servos on mine, they pretty much match the performance of the original Fanuc servos. https://store.dmm-tech.com/products/...ac-servo-motor

This is not a recommendation, but rather just to get the creative juices flowing. A nice picture of a small slant bed showing the guts. https://hirung.en.made-in-china.com/...-Tool-E35.html

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Originally Posted by Jim Dawson

I did drive down to Oklahoma to pick up my lathe, 3400 mile round trip.



Max through a 16C is 1 5/8, could go bigger with an emergency collet, but not through.




I would just buy a spindle assembly,that way you can get the whole assembly many times including the collet/chuck closer. Here are a few examples from a quick EBay search.

https://www.ebay.com/itm/TSUGAMI-CNC...AAAOSwtfhYnI1D


https://www.ebay.com/itm/TSUGAMI-CNC...sAAOSwCU1YnI6p


https://www.ebay.com/itm/Okuma-LC20-...EAAOSwHPlWdEdk


https://www.ebay.com/itm/Mazak-Quick...wAAOxyfCBSB79I


https://www.ebay.com/itm/Mazak-Slant...kAAOSwm8VU0P7O



That would be my choice. I wish I had a C axis spindle on mine, but it's going to get that one day. I have a design for an auxiliary drive system using a 1.8KW servo. A 7.5KW servo is expensive. I've been trying to find a used one at my price.




Seems well within normal operation envelope. Don't short yourself on motor power.




That's about what my lathe has, has been adequate for everything that I'm doing. I think my longest part is about 4 inches x 1 1/2 dia. I could easily turn 10 or so inch diameter. Depending on how many tools you need to run with gang tooling,10 inches of X may or may not be enough.




I have been running with 5 inches stickout on the part above, 6061 aluminum, no problems. The stainless parts I run a bit closer, but they are smaller.



As I said above, max through a 16C is 1 5/8, but there is another collet system that goes up to about 3 inches. I haven't priced them but I'm assuming it's not cheap. https://academy.titansofcnc.com/seri...p-collet-chuck





I think my ball screws are 20 or 25mm can't remember which. 10mm lead as I recall.




Steppers would work, but you are really talking about a pretty big lathe, and servos are not that much greater in price unless you are comparing to the cheapest EBay steppers.

I'm using 1.8KW DMM Tech servos on mine, they pretty much match the performance of the original Fanuc servos. https://store.dmm-tech.com/products/...ac-servo-motor

This is not a recommendation, but rather just to get the creative juices flowing. A nice picture of a small slant bed showing the guts. https://hirung.en.made-in-china.com/...-Tool-E35.html

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I guess I hadn't considered this being a "large" lathe but as things go you're not wrong. Envelope wise its rather small compared to my Southbend with its little 1hp motor. But I'm asking it to turn the same materials at similar or higher removal rates. I may have to change my budget a bit too. Starts to make the one around the corner look pretty good doesn't it?

That last link is pretty close to exactly what is in my head except for only not from Shenzen :). The fact there are travel axis and approximate weights on there is very helpful so thank you!

Thank you for all your help Jim!

It's my pleasure to help out. :)

Like you I have a nice little tool room lathe, a Jet 13x40 GH, about 1800 lbs or so. Tucks neatly into a corner and uses up minimal floor space. But it takes me forever to make some of my parts on it. It's the tool changes and different setups that are the killer. One particular part that took me about 40 minutes to make on the manual lathe, takes about 4 minutes on the CNC. Spindle HP and rigidity are also a factor.

Yup, I think that CNC lathe around the corner is looking pretty good. All of the hard work is done. And for $4000 you are buying a lot of really expensive hardware if you had to go buy it. The question is do you really want to spend the next year or so building a lathe or would you rather be making parts?

My 30 year old Hardinge Conquest 42 has a smaller work envelope than the Jet, but has a 10 tool turret, w/5 live tool positions. 10 HP spindle motor, weighs in at 10,200 lbs, and has about a 60x90 foot print. I got a pretty good deal on it, basically I bought the 5 live tool holders, the normal tool holders, and a Kitagawa 6 inch chuck and they threw the rest of the lathe in with it, $9000 for all. It ran and made parts when I got it, but I didn't like the way the antique Fanuc controls worked so I ripped out everything that said Fanuc on it and replaced it with my own system. That was a about a month project and I do this stuff for a living.

Like you, my floor space is limited as is my power, but I was able to shoehorn the lathe in there and get it powered up off of a rotary phase converter.

I'll be interested in what direction you decide to go.

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Originally Posted by Jim Dawson

It's my pleasure to help out. :)

Like you I have a nice little tool room lathe, a Jet 13x40 GH, about 1800 lbs or so. Tucks neatly into a corner and uses up minimal floor space. But it takes me forever to make some of my parts on it. It's the tool changes and different setups that are the killer. One particular part that took me about 40 minutes to make on the manual lathe, takes about 4 minutes on the CNC. Spindle HP and rigidity are also a factor.

Yup, I think that CNC lathe around the corner is looking pretty good. All of the hard work is done. And for $4000 you are buying a lot of really expensive hardware if you had to go buy it. The question is do you really want to spend the next year or so building a lathe or would you rather be making parts?

My 30 year old Hardinge Conquest 42 has a smaller work envelope than the Jet, but has a 10 tool turret, w/5 live tool positions. 10 HP spindle motor, weighs in at 10,200 lbs, and has about a 60x90 foot print. I got a pretty good deal on it, basically I bought the 5 live tool holders, the normal tool holders, and a Kitagawa 6 inch chuck and they threw the rest of the lathe in with it, $9000 for all. It ran and made parts when I got it, but I didn't like the way the antique Fanuc controls worked so I ripped out everything that said Fanuc on it and replaced it with my own system. That was a about a month project and I do this stuff for a living.

Like you, my floor space is limited as is my power, but I was able to shoehorn the lathe in there and get it powered up off of a rotary phase converter.

I'll be interested in what direction you decide to go.

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Well the Okuma 15 is being moved OUTSIDE tomorrow. I expect the price to start diminishing rapidly and I have an inside guy. We shall see.