Southbend 9A CnC?
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    Default Southbend 9A CnC?

    I have just obtained a 9A. It seems to be in reasonable shape and appears to cut well. The acme screws/nuts are all pretty worn and the halfnut as well. I did a lot of searching but didn't really find that anyone had ever done a CnC conversion on one of these. With the removable gearbox, apron and simple layout it appears like it could be straightforward. I expect that I'd want to turn a good deal of AL with the occasional steel part - custom threaded bolts for antique sewing machines as well as general prototype construction.

    I have some servos, amps and a motion controller that could be adapted with ease.

    I was wondering what advice people have on this idea?

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    Quote Originally Posted by hackish View Post
    I have just obtained a 9A. It seems to be in reasonable shape and appears to cut well. The acme screws/nuts are all pretty worn and the halfnut as well. I did a lot of searching but didn't really find that anyone had ever done a CnC conversion on one of these. With the removable gearbox, apron and simple layout it appears like it could be straightforward. I expect that I'd want to turn a good deal of AL with the occasional steel part - custom threaded bolts for antique sewing machines as well as general prototype construction.

    I have some servos, amps and a motion controller that could be adapted with ease.

    I was wondering what advice people have on this idea?
    It took a long time to reverse engineer my parts for mounting the servo drives. This was an experiment that I now use frequently. Actually more often than I originally anticipated. The control cabinet is a mess but I have relays in there for coolant, tower lights, air blow, ect. It's ran off of 110v ac with (2) 12v dc power centers and has a master switch on the 110v. The Z axis lead screw nut needs work but I can hold .0005" all day in X. My write-up could take forever so I'll leave some pictures and answer questions as I get time. As time and money become available, it will get a vfd and an encoder so I can thread. Right now I have the spindle out to replace the oil wicks.

    Sent from my SM-T900 using Tapatalk

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    That looks pretty cool. I wonder if there is any value in keeping the compound on the lathe since CnC should be able to handle any angles/tapers? What is the max spindle RPM you are running and is it sufficient?

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    Quote Originally Posted by hackish View Post
    That looks pretty cool. I wonder if there is any value in keeping the compound on the lathe since CnC should be able to handle any angles/tapers? What is the max spindle RPM you are running and is it sufficient?
    I left the compound on because I wasn't sure how the machine was going to work. The max rpm right now is 1500 plus or minus. That is why I want to get a vfd for the machine. Then I would put the max at 2k rpm with a 2 hp motor rather than a 1 hp which is what is on the machine currently. It's a 5c collet machine with a D1-3 chuck adapter right on the spindle. It takes a 6" chuck.

    Sent from my SM-T900 using Tapatalk

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    I'm not sure I'd use a 9A (or any other South Bend) as the basis for a CNC "turning center." For the speeds you're thinking about, I'd pick a lathe with an anti-friction bearing headstock which would be much happier with speeds up in the 1500 - 2000 RPM range. And, how about the "slack" in the feed screws and nuts that you mention. Doesn't that make numerical control of the tool position a bit of a problem?

    Also, all those stepper motor add-ons make the lathe a bit crowded for its normal purpose which is manual machining. As the saying goes, "just because you can doesn't necessarily mean you should."

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    Quote Originally Posted by Dobermann View Post
    I'm not sure I'd use a 9A (or any other South Bend) as the basis for a CNC "turning center." For the speeds you're thinking about, I'd pick a lathe with an anti-friction bearing headstock which would be much happier with speeds up in the 1500 - 2000 RPM range. And, how about the "slack" in the feed screws and nuts that you mention. Doesn't that make numerical control of the tool position a bit of a problem?

    Also, all those stepper motor add-ons make the lathe a bit crowded for its normal purpose which is manual machining. As the saying goes, "just because you can doesn't necessarily mean you should."
    This is why I'm asking questions first. The acme screws would be replaced with ball screws so there would be no backlash. I don't know what one would need to spend on a lathe that would be appropriate for CnC, but from looking a while ago it seemed to be in the $5-6k range. I also don't know how much spindle speed is needed cutting with HSS.

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    Stay away from stepper motors if at all possible. You can loose steps, they are noisy and i just dont feel comfortable personally going the cheap route on something that needs to make me money. I put Clearpath servo drives on mine. Worst case if it wouldn't have worked, I could use the servo motors elsewhere. The entire retro was less than $3k. The Masso controller needs some help but it does what I tell it to...
    I wasn't planning on cutting from the chuck back so when I made my acme nut, the threads were cut so they were 95% thread and the nut is about 3" long so as to reduce the chance of backlash. Granted it will eventually happen. I have zero issues starting and repeating my Z location if I cut one way only. I didn't want to spend a lot of $$ for a proof of concept machine kinda thing. To be honest, I make a lot of hydraulic parts on this machine. 4140 ht, 410 ss, 416 ss, 304 ss, and 1018. It cuts it all. Finishes seem to vary from material to material. Hence why I want to get it set up with a vfd. For doing the 1 off type of part, I tend to walk away from it but if I have 2 or more parts to make, then I start looking into running it on that machine. For a 1977ish machine, it cuts beautiful with the retro. I don't use this thing as a manual machine anymore. Strictly cnc.
    Now cutting with HSS tooling, your RPMs will be low. I would have to look at my chart but if my memory serves me correctly, your looking at around 150 sfm for 1018. Aluminum is 300 sfm. Plastic, well let's just say you probably can't get your spindle fast enough for the sfm (600-1000 sfm or higher). I would look at your application and what your plans are for the machine. Make money, play with a cnc, or learn something new? I built mine for both proof of concept and to make money on the parts I didn't have tight tolerances for. Well turns out I can make parts and hold .0005" and make money on it at $45 an hour too. This machine has morphed from nothing to my go-to tool room cnc lathe.

    Just my $.02

    Chips

    Sent from my SM-T900 using Tapatalk

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    Currently i own 4 SB lathes and love them.. and i have been contemplating the same project...

    that being said i will be using a Rockwell 11" lathe for the project. i think the spindle could be run at a much higher speed, the bed ways are hardened, and the carriage and other features of the lathe are much more squared off allowing for easier mounting of brackets and such for the ball screws / servo motors etc...

    my 2c

    Joe

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  12. #9
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    I am thinking about building a new cross slide that is taller and omits the compound. I would then have enough room to put the ball nuts in there without any fuss. I suppose at a point, I'll upgrade to a larger and better machine, so it is important to be able to restore this back to original configuration.


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