Slow Project: "DIY" CNC lathe from Southbend 9 Parts

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Thread: Slow Project: "DIY" CNC lathe from Southbend 9 Parts

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    Default Slow Project: "DIY" CNC lathe from Southbend 9 Parts

    This is going to take a while, so expect rare and intermittent bumps. Mostly because I'm a med student, and also because my workshop is 200 miles away.
    But that won't stop me!

    The goal is to get a CNC lathe up and running, but I just dont like the look and feel of the 7x14's. I used to have a 13" Southbend with a 6 ft bed. Now that was sturdy. But that's another story.

    I have a G540 and some decent ~400oz or so motors sitting about. So not too worried on the electronics side.
    If I end up needing more, well, I'll go nema 34.

    Slow Project: "DIY" CNC lathe from Southbend 9 Parts-g540-jpg

    I also just purchased a Southbend 9 headstock in decent condition, I couldn't get more than a thousandth play with a long lever bar in it.
    I negotiated to get the bed with it for only $10 more. But the ways are beat. And that's where the next part comes in...

    Slow Project: "DIY" CNC lathe from Southbend 9 Parts-head1-jpg

    Slow Project: "DIY" CNC lathe from Southbend 9 Parts-head2-jpg

    I have a couple sets of nice linear rails. Some small... some big.
    For this project I have some THK 45mm rails, only one carriage on each, but the carriage is about 5" long, and already pretty stiff to move (probably needs to be cleaned out or the preload adjusted).
    Pictures of that later.

    Once I get it all in one place and do some measurements I'll see if I can afford to mount the rails directly to the ways, or if I'm going to mount them to the side of the ways (assuming I can make it flat enough or mount flat stock).
    The other option is skipping the bed entirely and mounting some aluminum extrusions to some U channel steel and seeing how rigid that is.

    From there I plan on ordering some of those linearautomation ballscrews, 20mm for the bed, 16mm for the cross slide.

    And either I'll mount an AXA toolpost when I first get it running, or go for a gang lathe approach. I don't think the bed mounting idea will allow me to effectively run a turret, but I might be wrong.

    Any thoughts or ideas for this project?

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    My brother picked up the bed and headstock for me.

    Slow Project: "DIY" CNC lathe from Southbend 9 Parts-20130404_110349-jpg

    Slow Project: "DIY" CNC lathe from Southbend 9 Parts-20130404_110355-jpg

    Looks like a bit of rust or surface crap. But still have to decide if I'm going to use this bed or not. It'd be a big pain to try and carve that ridge off the bed.



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    Hi,if you want to go CNC, then you really want to go to linear rails throughout......with your expertise and facilities anything that resembles recutting and scraping the existing bed just ain't gonna happen.

    However, if you bit the bullet and decided to remove the raised Vees, the only DIY method would be with an angle grinder and lots of elbow grease, but if you know someone or are prepared to send it out to have the bed machined flat on top......this would be highly preferred as you end up with two flat true surfaces to bolt the linear rails directly to.

    Removing the bed raised vees means the carriage (if you have it) is of no use to you, due to the hilly nature of the underside....you don't need the apron or crosslide parts and the new carriage would be better made from a thick slab of aluminium for ease of construction......ball screw drive to the carriage would be best driving up the middle with the stepper motor down at the tailstock end.

    Adding two sets of linear slides in two planes is a straight forward bolt on operation, and you only need to ensure that the new crosslide linear ways are dead square to the axis of the lathe linear slides.......one slider on the rails is not good enough.......two spaced apart longitudinally would be the best way for accurate guidance.

    Next you need to make a new crosslide , again out of a slab of thick aluminium, to run on the linear rails across the carriage to give you sufficient travel across the carriage if you want to go to a gang tool set-up.

    This does give you an exceptionally long crosslide, but if you just went for a QCTP with tool holders for manual tool change the crosslide can be made a lot shorter, as you would be doing bar work mostly.

    Depending on your machining capability, I would scrap the existing headstock and make a new box spindle headstock with angular contact bearings etc, driven from the rear end by a Poly Vee belt and VFD......the job holding can be by 3 jaw chuck or ER 40 collets etc, to give you a 1" bar size through the headstock.

    If you decide to go for the 3 jaw chuck it would pay to have a large bore spindle to allow a fairly large material diam capability.

    This may be beyond your capability, but as the end product will only be as good as it is designed, the making can be sent out to shops with heavier equipment, and you will get something that will function as a true CNC lathe.
    Ian.



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    Well a few things to address.
    I dont have the saddle/apron, never planned on using it. The plan is to mount these HUGE linear rails and use them and make a saddle with cross slide on linear rails, ballscrew up and such.
    I have a manual (non-cnc) X2 manual mill, that's all. So parts limit and funds limit is rather tight.

    Else designing it from scratch and going nuts would absolutely be a better plan... it's just not happening

    For the cross slide I'll have double blocks, but I don't think you realize how BIG the blocks are on the main rails. I'll have pictures soon. But we're talking about 45mm steel rails... not the 15-20mm stuff you normally see on machines here.



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    Hi, huge though the rails may be, you aren't limited by the tool height restrictions of a centre lathe.......no compound slide etc.

    I also suggested that a new headstock/spindle layout would be best......it's a better solution for CNC.

    This gives you the freedom to just mount the rails on the bed, no matter how big they are, and for the bed rails the bigger the better......crosslide rails need to be more "petite", that is smaller so's to get the blocks on and to control the length needed for the crosslide slab of aluminium.

    Basically all you are doing is getting a slab of thick aluminium and adding rails to the top and blocks to the bottom at right angles to one another.

    When you have got to the height with all the rails and blocks assembled and added the tool post, you can then determine the spindle centre height for any tools you want to apply.

    Building the headstock is basically a square box, welded up and machined with two angular contact bearings at the front end and a single or double radial floating ball race at the rear end....the spindle diam will be determined by the material size you want to pass through it, and also this determines the bearing sizes.

    Attempting to use the existing headstock is, in my opinion, a total waste of time.

    I would not be put of or daunted by the amount of "different" work needed to have a CNC lathe....they are very basic compared to the layout of a centre lathe.

    Joking aside, you could practically get a wood turning lathe and add linear ways to the bed rails etc to have what would function to a degree as a CNC lathe, without any re-machining to do....the lighter tubular body of the wood turning lathes currently on EBAY are not very rigid, but as CNC is light cuts and many of them this is not a problem......the more expensive wood lathes have a cast iron bed and better headstock bearings built for high speed.....food for thought....LOL?

    Personally, going from where you are at, I'd have sourced an older wood lathe with a cast iron bed, not the tubular Chinese import crap, and build on that model.....so little machining to get to where you need to go and you still have a very rigid body.

    A wood lathe normally has a gap all along the length of the middle of the bed, and this would be where you would fit your ball screw carriage drive, driving from the tail end.....the headstock (depending on the height) could remain as is, unless it needs to be modified or replaced to give a spindle with a big bore etc.
    Ian.



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    Considering the cost and difficulty of producing a spindle, that may happen on the next iteration, but not for this project.
    The headstock is VERY rigid, has VERY LITTLE runout and play, and appears to be a work of art. Sure it's from the days of slow and deep vs today where we cut fast and shallow, but I'll be building around that.
    Again this is a FIRST lathe for me. The bed is just there for now because I might use it as a way to get more rigidity. The headstock because I can't produce anything similar.



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    Hi, you're quite right, when you have a basis to go forward from sometimes you have to go that direction and progress accordingly.

    Best of luck, don't be afraid to send out the hard bits to improve the build.

    If you intend to build on the solid base of the lathe, I would get the top of the bed machined somehow....it would be the point most people who fabricate a lathe want to arrive at before the add on parts.

    Nothing can beat a base that is flat and true.
    Ian.



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Slow Project: "DIY" CNC lathe from Southbend 9 Parts

Slow Project: "DIY" CNC lathe from Southbend 9 Parts