10x7 home made cnc finish problem (linear shafting and bushing not LM guides)


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Thread: 10x7 home made cnc finish problem (linear shafting and bushing not LM guides)

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    Default 10x7 home made cnc finish problem (linear shafting and bushing not LM guides)

    hi everyone,
    After reading a lot and gathering my pocket money, i started building a cnc lathe. Here is what i have

    2 axiz 400oz stepper kit from probotix.com.
    (2) 16mm 5tpi ballscrew (0 backlash).
    16mm linear bushing and shafting from china.
    Zaxis travel is 10 inch and x is 7.
    The base plate is 1 inch and the upper is 1/2 inch steel.
    Here are some pictures attached of the assembly.



    but the first cut made using the Z axis was not finishing and shiny. So i tightened the linear blocks that gave me good results. See the highlighted part of the shaft that was cut after the adjustment to the blocks.

    But the problem is that i am not getting a cnc like finish still.
    I need help before i start making the X-axis. I hope anyone out there can help me.

    The cut was made using 8 inch true chuck with 2HP motor running at 800 rpms with HSS tool. (There are no more pulleys for more speed). The turned shaft is 6/8 inch mild steel.
    I want to know that do I need more rpms and carbide for good finish or the linear bushing is the problem for poor finish. Should I go for LM guides.

    Regards,
    Jasminder singh

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    Attached Thumbnails Attached Thumbnails 10x7 home made cnc finish problem (linear shafting and bushing not LM guides)-assembly-final-jpg   10x7 home made cnc finish problem (linear shafting and bushing not LM guides)-test-copy-jpg  
    Last edited by jasminder; 06-15-2010 at 04:10 PM.


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    I see you have supported rails. Some can have loose tolerances. Use an indicator and see how much looseness is in the Z axis. Push and pull in all directions. What are you usng for a tool? I've seen that finish on 4140 when using High Speed steel and dull carbide cutters, or had the tool height wrong.



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    Quote Originally Posted by MrWild View Post
    I see you have supported rails. Some can have loose tolerances. Use an indicator and see how much looseness is in the Z axis. Push and pull in all directions. What are you usng for a tool? I've seen that finish on 4140 when using High Speed steel and dull carbide cutters, or had the tool height wrong.
    to mrwild,
    the tolerance was around .002 when the blocks were not adjusted. Now it is almost 0. But i can feel the TIC TIC of balls of the blocks when moving it with hand (i mean it is too tight now and after all there is no other way to eliminate the problem).
    May be the shaft will wear faster but at least i will do some precision parts on it and recover the investment.

    thanks,
    jasminder singh


    If your luck wants you to loose, give it a fight. but remember that luck is unbeatable.



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    Member knudsen's Avatar
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    I'd be slappin' a 5 speed pulley on that motor, if you can and the spindle will handle it.

    Wen I was young, I spent most of my money on fast women, slow horses, and cheap booze. The rest of it I just wasted.


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    Lm guides, while ultra-precise and smooth, are not necessarily the best choice for contact machining (as opposed to non-contact, such as plasma, laser, water jet, or wire EDM).
    Vibrations are more readily absorbed and transferred through solid ways, where lm guides are not as capable of passing-through vibrations, hence they tend to show up in your workpiece more so than with solid ways.
    That being said, I believe that lm guides should, overall, work better on a lathe application than on a mill, which has constant interrupted cuts. Placing more resistance or drag on the lm ways may help somewhat.

    Then again, it may just be a tooling issue!

    Late afterthought/edit: if your shaft bushings are true "bushings" and not ball-cage bearings (as i've seen them refered to in the past), then what I've mentioned above is not applicable to your setup, only to ball-supported guides.

    Last edited by blades; 06-18-2010 at 07:15 AM.


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    Hi friends,
    here are the updates of the build,

    I fininshed the XY table, mounted the motors on them and the whole setup was put on a runnning 6FT big lathe to test the precision i can get from my XY table.
    See the pictures.

    Unfortunately, the finish was not as good as a cnc. The slope at the tool's position is arround 0.001 inch approx when checked with a bar. But i guess it should make polish cuts of 0.005 inch atleast. May be beacause i am using HSS tool for cutting.
    Well i just fried my parallel port so i will check the setup with carbide inserts later that i just got from the city.

    jasminder
    if your luck wants you to loose, give it a fight.

    Attached Thumbnails Attached Thumbnails 10x7 home made cnc finish problem (linear shafting and bushing not LM guides)-100_5414-jpg   10x7 home made cnc finish problem (linear shafting and bushing not LM guides)-100_5423-jpg   10x7 home made cnc finish problem (linear shafting and bushing not LM guides)-100_5425-jpg  


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    Quote Originally Posted by blades View Post
    Lm guides, while ultra-precise and smooth, are not necessarily the best choice for contact machining (as opposed to non-contact, such as plasma, laser, water jet, or wire EDM).
    Vibrations are more readily absorbed and transferred through solid ways, where lm guides are not as capable of passing-through vibrations, hence they tend to show up in your workpiece more so than with solid ways.
    That being said, I believe that lm guides should, overall, work better on a lathe application than on a mill, which has constant interrupted cuts. Placing more resistance or drag on the lm ways may help somewhat.

    Then again, it may just be a tooling issue!

    Late afterthought/edit: if your shaft bushings are true "bushings" and not ball-cage bearings (as i've seen them refered to in the past), then what I've mentioned above is not applicable to your setup, only to ball-supported guides.

    dear blades,
    yes they are linear bearings with circulating balls and not the bushing.
    The reason for the slope may be the width of the supported rods that id very less in my design.
    Do you think the slope at the tool can be reduced by increasing the width of the rails? i think i will have a more rigid XY this way.
    see the pic please.

    Attached Thumbnails Attached Thumbnails 10x7 home made cnc finish problem (linear shafting and bushing not LM guides)-submit-jpg  


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    That could potentially help, but I would be careful to not spread them too far apart, so you don't end up not having enough support between the rails.



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    Quote Originally Posted by blades View Post
    Lm guides, while ultra-precise and smooth, are not necessarily the best choice for contact machining (as opposed to non-contact, such as plasma, laser, water jet, or wire EDM).
    Vibrations are more readily absorbed and transferred through solid ways, where lm guides are not as capable of passing-through vibrations, hence they tend to show up in your workpiece more so than with solid ways.
    That being said, I believe that lm guides should, overall, work better on a lathe application than on a mill, which has constant interrupted cuts. Placing more resistance or drag on the lm ways may help somewhat.

    Then again, it may just be a tooling issue!

    Late afterthought/edit: if your shaft bushings are true "bushings" and not ball-cage bearings (as i've seen them refered to in the past), then what I've mentioned above is not applicable to your setup, only to ball-supported guides.
    Dear blades,
    after testing and making a lot of corrections to my design i am finally not getting desired finish from the machine. I am planning to upgrade to thk 25mm lm guides from ebay. But they are used.
    here is the link:

    http://cgi.ebay.com/THK-SR25V-LINEAR...-/250660714779

    i am worried if used linears are not good for precision lathes.

    Do you think it will work?
    i was getting 2 pc 15mm lm guides for really cheap. But again i though it will not be enough for my 6x10 lathe.

    your advice means a lot where my 1200$ investment is not working even.
    thanks,
    jasminder singh



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    Those LM's look really good, like very little use. They're not even dirty. They are also priced very well.

    While smooth and free linear motion is great for some applications, it's not necessarily a good thing for machining, where you really want to have a bit of adjustable drag on the ways. If you can design in some method of introducing friction to the slide, then the LM bearing guides would probably work better. They are certainly rated well enough for a small lathe. In theory, it should work great. But in real-life application it's not always ideal.



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    Quote Originally Posted by blades View Post
    Those LM's look really good, like very little use. They're not even dirty. They are also priced very well.

    While smooth and free linear motion is great for some applications, it's not necessarily a good thing for machining, where you really want to have a bit of adjustable drag on the ways. If you can design in some method of introducing friction to the slide, then the LM bearing guides would probably work better. They are certainly rated well enough for a small lathe. In theory, it should work great. But in real-life application it's not always ideal.
    I have seen double ended air cylinders used for introducing "friction" on lm rails they just had exhaust restrictors and were mounted parallel to the guides. that would definatly give an adjustable amount of "drag" to the guides, not necessarily "friction" per se but will slow the action to what ever you need, just have to find them in the right size for your application

    Nice Work
    JT



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    jasminder, can you show us a picture of the whole lathe? Did you make the lathe? I find it interesting. I was going to ask if it was made in India, butI realized you may have made it yourself, then it would be made in India Also I liked your avitar yesterday. If I were not so ugly, I would do the same:rainfro:

    Wen I was young, I spent most of my money on fast women, slow horses, and cheap booze. The rest of it I just wasted.


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    Quote Originally Posted by knudsen View Post
    jasminder, can you show us a picture of the whole lathe? Did you make the lathe? I find it interesting. I was going to ask if it was made in India, butI realized you may have made it yourself, then it would be made in India Also I liked your avitar yesterday. If I were not so ugly, I would do the same:rainfro:
    dear, knudsen,
    the lathe was aquired from a demolished old GERMAN ship and definately is made in GERMANY. About my picture, i guess a smily like" " will describe me better than my pic. so i removed it.
    To see the lathe, go to the initial pages of the thread. i have some good pics there.

    The one thing positive about me these days is my blood group only.

    jasminder singh

    It is better to die for something than to live for nothing.


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    Quote Originally Posted by blades View Post
    Those LM's look really good, like very little use. They're not even dirty. They are also priced very well.

    While smooth and free linear motion is great for some applications, it's not necessarily a good thing for machining, where you really want to have a bit of adjustable drag on the ways. If you can design in some method of introducing friction to the slide, then the LM bearing guides would probably work better. They are certainly rated well enough for a small lathe. In theory, it should work great. But in real-life application it's not always ideal.
    dear blades,
    i am surprised to know that the "freeness" or smoothness of a lm guide is also a problem for machines, so i will need to add friction to it.
    Then why not just attatch the steppers and ballscrews to my existing lathe made up of casting with ready x and Z. It has a lot of friction too. But i am sure the quality of production will be poor than ever. The few play in the axis will vibrate the tool and eliminating the play will result in jammed axis.

    Can you tell me a sure shot to buld up a good lathe that can machine within 0.001 . But i see everyone here using lm guides. Guldberg, Blight, cnccookbook everyone is using lm guides.

    jasminder singh

    It is better to die for something than to live for nothing.


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    My only experience with using LM guides was years ago, when I made a special machining fixture (for the mill) using the guides. I found that due to the lack of friction, there was a good amount of chatter or vibration while machining. Because of the vastly different nature of milling vs. turning, this may not prove to be an issue so much with a lathe, due to the smooth and constant pressure from the tool.

    Certainly the LM guides would be better than .001, but would require a good, stout carriage assembly.



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    Quote Originally Posted by jasminder View Post
    dear, knudsen,
    the lathe was aquired from a demolished old GERMAN ship and definately is made in GERMANY. About my picture, i guess a smily like" " will describe me better than my pic. so i removed it.
    To see the lathe, go to the initial pages of the thread. i have some good pics there.

    The one thing positive about me these days is my blood group only.

    jasminder singh
    Must be an interesting machine. Was it worn when you acquired it, or still in good shape? Even if worn out, it would be worth rebuilding to perfection.

    My blood group, good or bad, is 1/4 Danish and the rest a mix of British, Irish, Scotts, and who-knows-what. My grandfather came from Denmark as a blacksmith in the early 1900's. I'm not a very good machinist, so I cut myself a lot, and when the blood escapes, it all looks red to me

    Wen I was young, I spent most of my money on fast women, slow horses, and cheap booze. The rest of it I just wasted.


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    Quote Originally Posted by knudsen View Post
    Must be an interesting machine. Was it worn when you acquired it, or still in good shape? Even if worn out, it would be worth rebuilding to perfection.

    My blood group, good or bad, is 1/4 Danish and the rest a mix of British, Irish, Scotts, and who-knows-what. My grandfather came from Denmark as a blacksmith in the early 1900's. I'm not a very good machinist, so I cut myself a lot, and when the blood escapes, it all looks red to me
    dear knudson,
    the lathe is was worn more than 0.010 when purchsed but my dad grinded it well and i am watching it since 10 years and working on it since 4 years. Still it is not going anywhere for next 10 years. It can make more than 100 types of threads (different tpi).

    I am not rebulding the machine, i am using it's spindle and my custom made xz to test.
    But i just acquired a mini collet chuck lathe that will make my cnc lathe. it has 33mm through bore. it also has a lever operated collet closer.
    will post new pictures when my finishing issue is solved. one personal thing from you, what is your age? any projects?

    thanks,
    jasminder singh

    It is better to die for something than to live for nothing.


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    Just a thought...... Your tool holder is quite off-center from your in/out drive screw. If you center the tool holder above the drive screw, you will distribute the cutting forces more evenly to the rails......

    Would be a cheap test to perform......



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    Quote Originally Posted by jasminder View Post
    one personal thing from you, what is your age? any projects?

    thanks,
    jasminder singh
    I am 46 years old. But in hexadecimal, that's only 2E :rainfro:

    I have cheap Chinese made machines, a so called Seig 7 x lathe, a Seig 4" x 5" lathe and an x2 mill.

    Currently I am rebuilding the transmission for our clothes washing machine:



    A new transmission is $200 and a new machine is $600. So if I can make this run for a few months, I'll get a new machine, and the old one can be for oil soaked rags and clothes.

    After I finish that, I plan to start a micro-mill with CNC, but I want to use all parts that were not bought, just parts I have salvaged from junk. Of course, I'll buy the electronics and software, because it just wouldn't be very cost effective to try that on my own.

    If you look at my junk pile thread, you'll see I have a lot of junk to work with. http://www.cnczone.com/forums/showthread.php?t=105904

    I also have a perpetual project, cleaning up and organizing the shop in my garage. It seems every time I get a small area clean, I find some junk to bring home and fill that area, or an emergency project, like the clothes washer comes along, and gets scattered all over the clean spot.

    :rainfro: My wife says I have a "problem." :rainfro:

    I did manage to get my nuts and bolts sorted out pretty good:



    If I may ask, how old are you, sir? Look quite young in your avatar from yesterday.

    Wen I was young, I spent most of my money on fast women, slow horses, and cheap booze. The rest of it I just wasted.


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    Quote Originally Posted by knudsen View Post
    I am 46 years old. But in hexadecimal, that's only 2E :rainfro:

    I have cheap Chinese made machines, a so called Seig 7 x lathe, a Seig 4" x 5" lathe and an x2 mill.

    Currently I am rebuilding the transmission for our clothes washing machine:



    A new transmission is $200 and a new machine is $600. So if I can make this run for a few months, I'll get a new machine, and the old one can be for oil soaked rags and clothes.

    After I finish that, I plan to start a micro-mill with CNC, but I want to use all parts that were not bought, just parts I have salvaged from junk. Of course, I'll buy the electronics and software, because it just wouldn't be very cost effective to try that on my own.

    If you look at my junk pile thread, you'll see I have a lot of junk to work with. http://www.cnczone.com/forums/showthread.php?t=105904

    I also have a perpetual project, cleaning up and organizing the shop in my garage. It seems every time I get a small area clean, I find some junk to bring home and fill that area, or an emergency project, like the clothes washer comes along, and gets scattered all over the clean spot.

    :rainfro: My wife says I have a "problem." :rainfro:

    I did manage to get my nuts and bolts sorted out pretty good:



    If I may ask, how old are you, sir? Look quite young in your avatar from yesterday.
    sir,
    i am 22. But i am surprised to see that your clothes washing machine has a trasmission. is it a commercial washer system?

    jasminder singh

    It is better to die for something than to live for nothing.


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10x7 home made cnc finish problem (linear shafting and bushing not LM guides)

10x7 home made cnc finish problem (linear shafting and bushing not LM guides)