Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: Why not linear motion style rails on a lathe?

  1. #1
    Join Date
    Dec 2006
    Posts
    4

    Default Why not linear motion style rails on a lathe?

    Hi Guys,

    Newbie here, catching an interest in machine work. I've been reading the posts here and at the practical machinist website trying to learn something about machine work. It started with the desire to build a 3 axis cnc router for woodwork...but then I got to thinking that I might like to build a metalworking lathe too.

    I have bought a couple of instruction books for building lathes: Gingery's "The Metal Lathe", Rama Machines,"Metal Lathe" (Using Truck Pistons?) and Bench Lathe Manufacture reprint from Lindsay's.

    I notice that the carriage on lathes typically run on flat metal ways, but I've been wondering why not use a linear motion setup with bearings or v-guide wheels. Why not? Would would be the reason or reasons that such an arriangement wouldn't be useful on a home-built metal lathe? Not stiff enough? Too much slop? Vibration?

    Thanks,
    Mark

  2. #2
    Join Date
    Mar 2006
    Location
    Yorkshire, England
    Posts
    136

    Default

    Given that traditionally constructed lathes work perfectly well I think you are looking at the cost to achieve a given ridgidity for your answer.
    Regards,
    Nick

  3. #3
    Join Date
    Dec 2006
    Posts
    4

    Default

    That's kind of what I thought the problem might be. I was just toying with the idea anyway. I'd most likely be best served by sticking with what has proven to work.

  4. #4
    Join Date
    Jan 2003
    Posts
    2,900

    Default

    Linear rails are a good method.

    Take a look at the number of new factory made CNC lathes using linear rails, there are quite few. You still need a rigid base to mount the rails on.

    Generally speaking, for a super heavy duty machine conventional way are a bit more rigid.

  5. #5
    Join Date
    Mar 2005
    Posts
    408

    Default Same questions we all have asked or thought about.

    OK, here are my thoughts.
    Lathes have been made for hundreds of years. Many different makers in dozens of countries have come & gone. Don't you think they might have successfully produced a lathe using linear slides, ball bushings etc. if it met all the requirements for economic production, precision, durability, rigidity, simplicity, etc...? Economics is a lot like evolution, not everyone believes in it, but it does seem to work.
    Geometry dictates there are only a few ways to guide a cutting tool along & across a central workpiece. History shows flat bed lathes (ala Atlas etc.), round bed lathes, lathes with round ways, lathes with prismatic V ways. Not many attemps at creating cheap, light weight lathes have worked. Even the Atlas flat bed lathes (cheap & easy to produce, reasonable for light & HSM type use, easily rebuildable, etc.) didn't last. As a means of precision guidance of a carriage, prismatic V ways seem to have won out.
    A rigid structure almost always will be heavy, especially in cast iron which is cheap in bulk, casting is an easy means of rough fabriction of the necessary shapes, has good wearing properties, and good vibration damping characteristics.
    Rigidity & mass are a machinists friend, especially when horsepower goes up as the need/ desire for faster metal removal rates increased. Compare a 12 inch Atlas lathe with a Colchester Student or 13 inch Dean, Smith & Grace lathe. The Atlas would be driven by a 3/4 HP motor, the Colchester or DS&G would like 5 to 7 1/2 HP quite happily and weigh 5 to 6 times as much.
    Even my 13 in. SouthBend weighs something like 4 times what my Dad's Atlas did. It happily handles 2 HP....
    Except for interests sake, there is no point in trying to build a lathe "ala Gingery". As others have said, even a cheap Chicom mini-lathe is better than what you could make at home without other machine tools. Why re-invent the wheel....South Bend did publish plans in their "Machine Shop Projects" series about building an 8 in. bench lathe. Never seen one, though.
    Those are my thoughts. Hope it helps.
    Rick

  6. #6
    Join Date
    Apr 2001
    Location
    Clinton, WA
    Posts
    955

    Default

    Mark,
    My CNC lathe and CNC mills use linear guide ways. They seem to work well. The mill has a 750lb table capacity. This is not a very close up pic but you can kind of see the ways,
    Mark Hockett

  7. #7
    Join Date
    Dec 2006
    Posts
    4

    Default

    Hi Mark,

    It's great to see that someone has used linear rails on a lathe. It kinda gives me hope that my idea wasn't too far fetched. You see, I figure if I build my own lathe one of my biggest problems might be getting the ways true and might even require a trip to the machine shop to have it ground true. If I were to use linear rails I could work out my adjustments in the rails myself. What kind of bearings does the tool carriage on your lathe run on?

    Of course I realize that the base would have to be pretty stout, but even if I stick with the tried and true traditional ways, it would still have to be stout. I was planning on using flat bar stock to build it since I don't think casting iron is within my reach presently and aluminum just doesn't seem like the thing to use.

    Mark

  8. #8
    Join Date
    Nov 2002
    Location
    Kenosha, not the pass the other one
    Posts
    2,448

    Default

    Properly designed they should work quite well. But properly designed they will in likelyhood be more expensive than traditional bed designs. If you are really thinking about building your lathe and want to go with some sort of linear rail design then take a look at this one

    http://www.lathes.co.uk/scinta/index.html

    or any of the other lathes on the Machine Tool Archives site

    http://www.lathes.co.uk/page21.html

    There is one that uses round bars for ways that look to be at least 50mm in diameter. Just can't think of the make off the top of my head. Also for a really good bar lathe you need some way to adjust the guide bushings
    The optimist says the glass is half full, the pessimist says it's half empty. The paranoid in me says somebody put a hole in it.

    Remember pessimists are at heart opptomists. They know things can and will get worse.

  9. #9
    Join Date
    Dec 2006
    Posts
    4

    Default

    Thanks Spin Doctor. I actually found that site just yesterday and have been going through the different lathes trying to get ideas, but I hadn't stumbled on to the one you pointed out yet. I've been considering the potential problem of trash on the rails and what that means to the bearings that ride on the rails, but I suppose I could fabricate a Delrin bushing to ride the rails ahead of the bearings to keep them clean.

  10. #10
    Join Date
    May 2003
    Location
    52N 122W Western Kanuckistan
    Posts
    40,418

    Default

    Here is an example of rails used on a mini CNC lathe. These lathes were constructed as part of the engineering program at Harvey Mudd College. Unfortunately, the web page with the photos and plans has been removed.

    I have plans to build something like this in the near future, after I have finished putting my CNC mill into full operation.

    Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •