Converting lathe to CNC

[Tom Kitta]

So I am loosing some hope of finding small CNC machines (say under 6000 lbs and under 15hp) and I am looking for small machines to convert to CNC. Parts seem available from China for reasonable price. Results are not "professional" - you cannot turn a 1500 lbs machine into 10000 lbs one but they seem good for hobby use.

I currently have two old 13x40 SB lathes - I am thiking of swapping them for say:
Colchester 10x20 (which I have and missed one on sale)
Hardinge lathe - these are converted professionally as well
Monarch EE
All three and possibly more have high speed spindles at 3000 rpm+ They are small but very heavy build - sturdy. They have no gearing (other then back gear) I think these would be ideal. BUT can I use some "less then ideal" donors? Would a regular engine lathe with gearing with top speed of say 1800 rpm (I know I can push these a bit higher or change bearings) be good enough? Does anyone have a link where some people discuss this topic?

My current 13x40 seem to be bad candidates for conversion to CNC (but I am sure it would look interesting if one did it - controversial for some) because for some reason (supposedly smoothness of operation) SB chose plain bearings not angular or ball. These normally operate at 940 rpm and speed is limited by size of spindle - the larger a plain bearing is the slower it can operate. So it is doubtful I could push them more then say 1200 rpm. Also its threaded spindle. I think bed wear is not that of a big deal as software can compensate for this, can it? There was some talk about changing bearings in SB lathes to quality set that is based on angular contact bearings but there seems to be little info on anyone actually doing this - most people just re-build old bearings and keep lathe original but rebuild. Plus threaded spindle on a CNC would kind of kill any "rapid" reverse or slow down.

I know I should first get a CNC mill but that has same issues as CNC lathe - very hard to find - last time I had a chance was like 3 years ago+.

 

[Janger]

@Alexander has a Syil cnc lathe. I don't know what the max spindle is though. It runs Mach3. Mach3 can manage backlash compensation in software but I don't think there is anything in there for bed wear. On my little lathe (Rockford) I bought this from another member: https://canadianhobbymetalworkers.com/threads/rockford-cnc-lathe-revival.1080/
it has a 3000 rpm spindle. I've been upgrading it to a new centroid control with new servos and software. There is a good forum on facebook on these machines. It's mostly Australians as that is where these machines are from. look for hercus benchtop cnc users.

 

[Johnwa]

I sold and delivered a 10x24 lathe to a guy up on Springbank hill. He had a Southbend 13 that he was planning to CNC —just because.

 

[Tom Kitta]

Yeah I have seen that little CNC lathe - back at the time I thought I will be able to find a decent CNC mill / lathe like Alex has - especially his mill. If I could look into future and see it as dry as it is I would have bough it.

Well I guess I could CNC that SB through I am not sure whatever my skills are up to it - I think it would be quite harder to CNC that then a gear head lathe that is touch more modern. I cannot believe that SB made lathes that feel like WWI up until 1983. In a more modern lathe I just change to ball screws & add two stepper motors + gut all gears & add a large 3ph motor with a VFD speed control. With a SB I have to worry about plain bearings that cannot go too fast as well as threaded spindle.

Yes Syil is an option - especially used one.

 

[kevin.decelles]

Tom, watching this closely! Let the games begin


I’m using LinuxCNC for my mill and I’ve found it great so far as you essentially have the source code and can dig into it. I had to make a small mod to it to support a feature from a hand held pendant I wanted

Just compile and run. Given your line of work this might benefit you


Sent from my iPhone using Tapatalk

 

[Johnwa]

Just came across this conversion on YouTube (4 videos). I watched this 2nd one and learned a lot about threading.

 

[Alexander]

Converting a South Bend to CNC makes sense. It is a good starting platform. Converting anything with significant bead wear sounds like a bad idea. Even on big industrial machines we don't compensate for bed wear in the controller. Instead I break the program down into different segments for each diameter. I compensate for taper using an incremental movement in the finish pass. Backlash is eliminated by feeding to the finish diameter in the same direction each time. I don't have the experience to adjust controller pararameters on someone else's machine. But as a CNC operator I can edit the program to get the parts in tolerance. It is allot easier to get a well adjusted machine set up for production but anything is possible. Start with a machine that has no noticeable taper in the bed the rest will be easy

 

[Tom Kitta]

Yes I was thinking of similar conversion of at least that size of a lathe into CNC (without manual controls). From my research it is not very difficult to do nor very expensive. Yes you still have "issues" with ex manual lathe (such as no auto oiling system or no tool changer) but you can add these features later on. These small CNC converted lathes may be very slow by CNC standard but HUGE upgrade to home shop capability. Same with CNC converted milling machines of say at least 1000lbs grade.

For example I am doing a small run of 18 cam lock pins (as I cannot buy them anywhere) and it takes about 30min per pin on a lathe just to turn it without threading. Then I expect another 10-15 min to thread and another 10 min to cut the cam. Total time is almost an hour -maybe with more jigs can be cut to 30min but that is still a lot. I expect a small CNC lathe would do it in 5 min or less including threading even with manual tool changes. A CNC mill would cut the cam in maybe less then 3 min with setup. So total per part is less then 10min vs. manual at almost an hour - at least 5x speed increase.

 

[Tom Kitta]

I guess I should then check the bed ways on both machines I have Alex. Through a 50+ year old machines that almost never had hardened beds are indeed probably worn. SB simply replaced the whole bed when it was worn out - its a 200lbs plus part.

 

[Johnwa]

I have a beat up Southbend 9C that I was thinking about CNCing, but there is a lot of bed wear so maybe not.

 

[Tom Kitta]

Yeah SB lathes and their soft beds and cone pulley systems in the 80s... My 1960s Colchester has a hardened bedway with little wear (like maybe a thou or so) and modern power train - why SB never changed is a mystery too me - I heard that SB lathes were at they very bottom of the US lathe food chain maybe only above "Atlas". This might explain things.

 

[Janger]

Could the beds be ground on some members surface grinder? Practically speaking is it worth doing?

 

[PeterT]

Modern Tool advertises bed grinding capability but I've never inquired about price vs size. Not even sure if they do it in-house or have a proprietary connection. Dabbler might have some intel on that front. But from watching Jan's videos, you may still not be out of the weeds. Its all the other mating components that go along for the ride. You probably want to get on with cnc conversion, not scraping & fitting.
https://www.youtube.com/channel/UCD1jVjhwma9Ehj8BQqDMPHw/videos

 

[cuslog]

I think Stan-Canada does bed grinding too ? I watched part of a Youtube video of them grinding the bed of what looked to be a huge and quite long lathe bed. Edmonton ? Somehow I'm under the impression that its not cheap

 

[Johnwa]

I think the “owner?” Of Modern Tools has an old planer that he does beds with. I heard it was quite expensive.

 

[Johnwa]

The software for my CNC router allows me to probe the bed to create a height map. Something similar if it exists for a lathe might be able to correct for bed wear.

 

[Dabbler]

Modern Tool advertises bed grinding capability

I did an inquiry about one of the lathes on their floor. With disassembly, grinding, and reassembly, a 47 inch bed large lathe with a veeway and flatway is 4500$ or thereabouts. A 14X40, with it's simpler construction than the old monsters is about 2800$ as of 2 years ago.

They have a genuine gantry grinder worth about 120K$. They purchased it to rebuild machines, and is now run by one of George's sons out at the farm. This is a highly skilled operation, not able to be done by just anybody. It took years of practice to get it right.

 

[Tom Kitta]

I measured the wear and it is around 9 thou maybe 10 (its still wrapped in foil). You can clearly feel the wear with fingernail but its not as much abused as my Indian made 16x75 - which someone hated.

I am 99% sure it is a soft bed so even if re-ground it would not last too long - the lathe comes off the bed and the bed is 5ft long = 60 inches and double V way (i.e. there are 3Vs instead of 2 as on most lathes). With the prices of re-grind in 1000s who actually does it for smaller machines? No one? Apparently if one were to re-grind it the construction allows for easy re-assembly - some lathes are not so easy to put back together and require lots of work after re-grinding.

Anyways I am not dropping 4k or more on a regrind.

There are videos of people building "skateboard" grinder for the ways - seems a lot of work to build one and I am sure results are not perfect (then again with lots of wear I do not see how you can screw up.

I do have a surface grinder and it is 18" maybe total travel is closer to 20? I probably could regrind to make "better" a small lathe bed that was beaten - cannot break it more.

God I am kicking myself for missing that sweet Colchester 10x20 - I would have two and it would make excellent CNC conversion lathe.

 

[Tom Kitta]

I asked on Home Machinist forums whatever it would be all worth the effort - we see what experts say - the cost of converting to CNC is around 2000 CAD plus lots of work. I can sell the machine probably for $2000+- few hundred. I am just wondering whatever the huge effort of conversion would not be wasted too much if I could get a better result from say converting a Colchester 10x20 which I missed for also around 2000.

Also I am wondering whatever there would be a chance of getting a real CNC lathe for say 6000-8000 range.

Anyone made a threaded spindle to D1-3 adapter?

 

[Janger]

You might like the automated lead screw option Tom. @Dabbler knows more about this than me. Maybe he can be enticed to give us a bit of a run down on that option.