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  1. #1

    Lightbulb Manual Lathe to CNC Conversion

    Our company has acquired a very old lathe that we are looking to convert to CNC. There is very little information about this lathe online as the company went out of business many years ago. It's a cool machine with a badge dating back to 1901. It's a 16 foot motor lathe from the Hamilton Machine Company. I've been trying to search across the forum to find the information I need but I haven't been able to find quite all of my answers. Thus, I'm going to ask for all the help I can get in this conversion. I have been running CNC machines for over 10 years but have yet to do a manual to CNC conversion. Biggest questions I have is what size and length ball screw that is needed. Is it the same length as the Acme screw? Here's the information I've been able to gather so far so please correct me if I am wrong or if there is a better direction. This is what I believe I need:
    1. Stepper motors
    2. Limit switches
    3. Slideway to support ballnut
    4. Rotating Ballnut
    5. Ball screw
    6. Software to act as NC controller
    7. Controller to communicate from computer to motors
    Attached Thumbnails Attached Thumbnails 20200902_075136.jpg   20200902_075125.jpg  

  2. #2
    Community Moderator Jim Dawson's Avatar
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    Re: Manual Lathe to CNC Conversion

    That's going to be quite a project. I assume that the machine has babbitt spindle bearings, so is not a high speed spindle.

    You would need a ball screw at least as long as the Z travel that you need, plus extra length for mounting, plus the length of the ballnut assembly. They are available but not cheap in the size you need. I would most likely use a 4040 multistart.

    Normally the existing carriage would support the ballnut. I think you could turn the ballscrew over that length with no problem, would make things a bit easier to set up. I have a 4040 that is 14 ft long that was on my router and turned it at about 500 RPM for rapids, fixed ballnut.

    If you're clever, another way to drive the carriage is using the existing rack & pinion. You could add a pneumatic backlash eliminator and it should work well. Might require linear scales depending on how accurate you want to be.

    On a machine that big I question the use of steppers, servos might be a better choice. You have a lot of moving mass on a machine that size.

    Your BOM seems OK for a start.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3

    Re: Manual Lathe to CNC Conversion

    Quote Originally Posted by KelloggsResearchLabs View Post
    Our company has acquired a very old lathe that we are looking to convert to CNC. There is very little information about this lathe online as the company went out of business many years ago. It's a cool machine with a badge dating back to 1901. It's a 16 foot motor lathe from the Hamilton Machine Company. I've been trying to search across the forum to find the information I need but I haven't been able to find quite all of my answers. Thus, I'm going to ask for all the help I can get in this conversion. I have been running CNC machines for over 10 years but have yet to do a manual to CNC conversion. Biggest questions I have is what size and length ball screw that is needed. Is it the same length as the Acme screw? Here's the information I've been able to gather so far so please correct me if I am wrong or if there is a better direction. This is what I believe I need:
    1. Stepper motors
    2. Limit switches
    3. Slideway to support ballnut
    4. Rotating Ballnut
    5. Ball screw
    6. Software to act as NC controller
    7. Controller to communicate from computer to motors
    You can search the similar size CNC lathe machine, their ball screw length, motor sizes, etc can be your reference.
    It is strongly recommend to use servo motors and drivers, and NC based CNC controller, they will be more reliable and more accurate.
    http://cncmakers.com/cnc/controllers/CNC_Controller_System/CNC_Retrofit_Package.html

  4. #4

    Re: Manual Lathe to CNC Conversion

    Quote Originally Posted by Jim Dawson View Post
    That's going to be quite a project. I assume that the machine has babbitt spindle bearings, so is not a high speed spindle.

    You would need a ball screw at least as long as the Z travel that you need, plus extra length for mounting, plus the length of the ballnut assembly. They are available but not cheap in the size you need. I would most likely use a 4040 multistart.

    Normally the existing carriage would support the ballnut. I think you could turn the ballscrew over that length with no problem, would make things a bit easier to set up. I have a 4040 that is 14 ft long that was on my router and turned it at about 500 RPM for rapids, fixed ballnut.

    If you're clever, another way to drive the carriage is using the existing rack & pinion. You could add a pneumatic backlash eliminator and it should work well. Might require linear scales depending on how accurate you want to be.

    On a machine that big I question the use of steppers, servos might be a better choice. You have a lot of moving mass on a machine that size.

    Your BOM seems OK for a start.
    Thank you for this response as it definitely sends me in the right direction! We went with an inexpensive lathe as we are a start up and trying to reduce some of our costs. The owner figures its a lot cheaper to automate this than to purchase something that might be a bit more than what we really need. Our projected use of the lathe is to wrap Nitinol wire around a mandrel to make springs in high volume. The low speed spindle should work well for this application.

    After reading your response, I took a second look at the machine and see what you mean about the support of the ball screw. That is perfect! We are going to retrofit the carriage to feed the wire instead of feeding a tool. I might have to put some consideration into how accurate we want the carriage to be then.

    When you mention a pneumatic backlash eliminator, is this something a company manufactures or something we would design to work for us? It's an interesting thought and I'm quite curious about this avenue.

  5. #5

    Re: Manual Lathe to CNC Conversion

    Quote Originally Posted by cncmakers001 View Post
    You can search the similar size CNC lathe machine, their ball screw length, motor sizes, etc can be your reference.
    It is strongly recommend to use servo motors and drivers, and NC based CNC controller, they will be more reliable and more accurate.
    That's a good point about looking up similar sized machinery and figuring out what they are using to get a good idea of what we need. I was looking into the controller DriveRack by MicroKinetics. It seems like a decent price for the application we need it for.

  6. #6
    Community Moderator Jim Dawson's Avatar
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    Re: Manual Lathe to CNC Conversion

    A backlash eliminator is simply an air cylinder (air spring) that biases the moving parts in one direction. In the case of a lathe, you would want to bias the carriage against the normal working direction of travel, in other words, towards the tail stock in most cases. With a 1:2 pulley ratio (think block & tackle) the air cylinder need not be longer than the lathe bed.

    Using this method and using the existing rack & pinion, would eliminate several $1000's in the cost of the ball screw. Combine this with linear scales, and you would have very accurate positioning with minimal cost. I'm a real fan of magnetic linear scales, bullet proof, inexpensive, compact, and very accurate. Cost for 16ft of magnetic linear scale, with a resolution of 1 micron, would be in the range of $400.
    Jim Dawson
    Sandy, Oregon, USA

  7. #7

    Re: Manual Lathe to CNC Conversion

    Quote Originally Posted by Jim Dawson View Post
    A backlash eliminator is simply an air cylinder (air spring) that biases the moving parts in one direction. In the case of a lathe, you would want to bias the carriage against the normal working direction of travel, in other words, towards the tail stock in most cases. With a 1:2 pulley ratio (think block & tackle) the air cylinder need not be longer than the lathe bed.

    Using this method and using the existing rack & pinion, would eliminate several $1000's in the cost of the ball screw. Combine this with linear scales, and you would have very accurate positioning with minimal cost. I'm a real fan of magnetic linear scales, bullet proof, inexpensive, compact, and very accurate. Cost for 16ft of magnetic linear scale, with a resolution of 1 micron, would be in the range of $400.
    Very good pieces of advice. Thank you Jim! We are definitely going to run with this idea and see how far it could get us. If I'm understanding this correctly then my motor would drive the pinion along the rack that currently exists on the lathe. The linear scale is to make sure we have locations and accuracy when moving the Z axis. Perfect!

    Now the pneumatic air cylinder would be used just to keep the carriage to have constant bias on one side of the backlash instead of allowing the pinion to move through the backlash when changing directions?

    Doing some quick searches and there is a lot of manufacturers for linear scales. As you have experience working with these, do you have any that you recommend? Also, on backlash eliminators. This would need to be the length of the lathe bed to be able to follow the carriage throughout all of it's range of motions. So it would need to be roughly 16ft?

  8. #8
    Community Moderator Jim Dawson's Avatar
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    Re: Manual Lathe to CNC Conversion

    Quote Originally Posted by KelloggsResearchLabs View Post
    Very good pieces of advice. Thank you Jim! We are definitely going to run with this idea and see how far it could get us. If I'm understanding this correctly then my motor would drive the pinion along the rack that currently exists on the lathe. The linear scale is to make sure we have locations and accuracy when moving the Z axis. Perfect!
    That is correct

    Now the pneumatic air cylinder would be used just to keep the carriage to have constant bias on one side of the backlash instead of allowing the pinion to move through the backlash when changing directions?
    Again, yes

    Doing some quick searches and there is a lot of manufacturers for linear scales. As you have experience working with these, do you have any that you recommend?
    I use both Renishaw LM10 and Ditron DMR200 read heads, and the MS200 magnetic tape. Ditron is a Chinese company that makes DROs and scale systems. sales@dcoee.com

    Here is the X scale on my mill. This is a Renishaw head, but the Ditron head is identical. That has been on there for about 6 years


    A Ditron head



    Also, on backlash eliminators. This would need to be the length of the lathe bed to be able to follow the carriage throughout all of it's range of motions. So it would need to be roughly 16ft?
    It's working length would need to be 16 ft, so would require an 8ft stroke air cylinder at a 1:2 ratio. You would mount the air cylinder on the back of the lathe bed and use a cable/pulley system to attach to the carriage on the front side. I never considered building one with a working length of 16ft, but the same principles apply. With a higher ratio, a shorter cylinder could be used. You don't need over about 100 lbs of tension.
    Attached Thumbnails Attached Thumbnails IMG_1356A.jpg  
    Jim Dawson
    Sandy, Oregon, USA

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