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  1. #1
    Fancy's Avatar
    Lives in Giza, Egypt. Last Activity: 5 Minutes Ago Has been a member for 0-1 years. Has a total post count of 7.
    I was wondering what have you seen achievable out there with DIY machines ? what tolerances were achieved and on what material ? I am asking to have realistic expectations of what is possible.

  2. #2
    Quote Originally Posted by Fancy View Post
    I was wondering what have you seen achievable out there with DIY machines ? what tolerances were achieved and on what material ? I am asking to have realistic expectations of what is possible.
    Can't answer for DIY but my China has a repeat cut tolerance of 0.05mm. Better when running a faster feed

    Sent from my F8331 using Tapatalk

  3. #3
    There are exactly zero limits.
    Dan Gilabert made a 1 micron lathe.

    My lathe has 1 micron mechanical resolution and positioning ability.
    It is not natively accurate to 1 micron, but I can move by 1 micron to any offset size I can measure, using a digital 1 micron dti to confirm relative movement.
    But I use thick ballscrews, 32 mm D, and 10.000 count ac brushless servos of 10Nm peak, 750W cont.
    Lathes are about 10x more accurate, inherently, than milling.

    This is about 800 more for one axis than a typical stepper setup.
    It is not too cheap, but not too expensive either, in context.

    Anyone can make an xy machine with 0.01 mm repeatability, and 0.01 mm resolution.
    A lot better is fairly easy to do by using
    -bigger linear guides (stiffer, more rigid)
    -thicker ballscrews (stiffer, more rigid)
    -better screw mount (stiffer, more rigid) with better bearings.
    -AC servos for more accuracy per rev

    It is not that it is hard, as such.
    But each improvement of those 4 costs about 100 extra for one level and 200-250 extra for 2 levels.
    So for 2 levels or 2 sizes bigger/better you pay about 250 x 4 == 1000 extra.

    So you can get 2 micron resolution for one axis, on a mill or router.
    1 micron if you work more and do "better" in many ways.

    So a 2 micron error, aka +/- 1 micron, is 2x2x2 = 8 microns volumetric local accuracy for milling/routing.
    But screw errors tend to be about 0.1 mm, worst case, on typical 40-800 mm long axis travels.

    So it is nowhere near inherently *accurate* to 0.01 mm (basic one axis), or 0.002 mm (very good axis), since the position is wrong.
    But it can easily repeat to 2 microns, or 0.01 mm worst case, cheap.

    Endless ways to contact probe, map, digital 1 micron dtis, glass scales, so you can offset the position to be accurate to 1 micron or less.
    Granite surface plates, accurate to 2 microns, cost about 300. 640x400 mm.
    Gage blocks to make accurate probing points. Cheap to about 500 mm.
    You can setup optical switches, accurate to about 1-2 microns, for less than 20 each.

    You can calibrate any screw, and map errors out to about 25x more inherent accuracy.
    Thus you can offset the screw error in sw, by adjusting offsets or many ways in gcode, macros, probing, etc.
    You can map the screw error in some controller sw, with various caveats.

    It is not too hard or too expensive to map screws pretty well, more expensive is easier and more accurate.
    Mapping to 0.01 mm positional error, per axis, is pretty easy.

    Making stiffer screw mounts is easy, just make them 2 sizes bigger.

    Example:
    The ballnut mount on my lathe z axis is 120x120x70 mm tool steel. Yes, about 3" thick.
    It was not *hard* to do, but took about 40 hours and 20 in steel.
    It is hard and slow to drill 120 mm deep, 10 mm, in tool steel.
    12xD or 12 diameters deep.

    Most accuracy is mostly making things bigger, thicker, more rigid, in steel.
    After that some 30 bearings, info, and work gets you better results.
    E:
    Like making a fixed-fixed screw, with tension, and a compliant tension mount.
    This means you pull the screw about 500 kgf force, 1200 lbs, with an arrangement that allows the pulling end to move axially.
    It cuts the free length of the screw by half.
    This makes it 8x more rigid.
    A tensioned screw is inherently 2x more rigid.

    A 32 mm D screw == 1400 kgf max thrust, so pull about 500 kgf.

    So you get 16x more rigidity for 60 in materials and 2 days work.


    Quote Originally Posted by Fancy View Post
    I was wondering what have you seen achievable out there with DIY machines ? what tolerances were achieved and on what material ? I am asking to have realistic expectations of what is possible.

  4. The Following 2 Users Say Thank You to hanermo2 For This Useful Post:


  5. #4
    Quote Originally Posted by hanermo2 View Post
    There are exactly zero limits.
    Dan Gilabert made a 1 micron lathe.

    My lathe has 1 micron mechanical resolution and positioning ability.
    It is not natively accurate to 1 micron, but I can move by 1 micron to any offset size I can measure, using a digital 1 micron dti to confirm relative movement.
    But I use thick ballscrews, 32 mm D, and 10.000 count ac brushless servos of 10Nm peak, 750W cont.
    Lathes are about 10x more accurate, inherently, than milling.

    This is about 800 more for one axis than a typical stepper setup.
    It is not too cheap, but not too expensive either, in context.

    Anyone can make an xy machine with 0.01 mm repeatability, and 0.01 mm resolution.
    A lot better is fairly easy to do by using
    -bigger linear guides (stiffer, more rigid)
    -thicker ballscrews (stiffer, more rigid)
    -better screw mount (stiffer, more rigid) with better bearings.
    -AC servos for more accuracy per rev

    It is not that it is hard, as such.
    But each improvement of those 4 costs about 100 extra for one level and 200-250 extra for 2 levels.
    So for 2 levels or 2 sizes bigger/better you pay about 250 x 4 == 1000 extra.

    So you can get 2 micron resolution for one axis, on a mill or router.
    1 micron if you work more and do "better" in many ways.

    So a 2 micron error, aka +/- 1 micron, is 2x2x2 = 8 microns volumetric local accuracy for milling/routing.
    But screw errors tend to be about 0.1 mm, worst case, on typical 40-800 mm long axis travels.

    So it is nowhere near inherently *accurate* to 0.01 mm (basic one axis), or 0.002 mm (very good axis), since the position is wrong.
    But it can easily repeat to 2 microns, or 0.01 mm worst case, cheap.

    Endless ways to contact probe, map, digital 1 micron dtis, glass scales, so you can offset the position to be accurate to 1 micron or less.
    Granite surface plates, accurate to 2 microns, cost about 300. 640x400 mm.
    Gage blocks to make accurate probing points. Cheap to about 500 mm.
    You can setup optical switches, accurate to about 1-2 microns, for less than 20 each.

    You can calibrate any screw, and map errors out to about 25x more inherent accuracy.
    Thus you can offset the screw error in sw, by adjusting offsets or many ways in gcode, macros, probing, etc.
    You can map the screw error in some controller sw, with various caveats.

    It is not too hard or too expensive to map screws pretty well, more expensive is easier and more accurate.
    Mapping to 0.01 mm positional error, per axis, is pretty easy.

    Making stiffer screw mounts is easy, just make them 2 sizes bigger.

    Example:
    The ballnut mount on my lathe z axis is 120x120x70 mm tool steel. Yes, about 3" thick.
    It was not *hard* to do, but took about 40 hours and 20 in steel.
    It is hard and slow to drill 120 mm deep, 10 mm, in tool steel.
    12xD or 12 diameters deep.

    Most accuracy is mostly making things bigger, thicker, more rigid, in steel.
    After that some 30 bearings, info, and work gets you better results.
    E:
    Like making a fixed-fixed screw, with tension, and a compliant tension mount.
    This means you pull the screw about 500 kgf force, 1200 lbs, with an arrangement that allows the pulling end to move axially.
    It cuts the free length of the screw by half.
    This makes it 8x more rigid.
    A tensioned screw is inherently 2x more rigid.

    A 32 mm D screw == 1400 kgf max thrust, so pull about 500 kgf.

    So you get 16x more rigidity for 60 in materials and 2 days work.
    Best response to any questions I have seen in a long time.

    Sent from my F8331 using Tapatalk

  6. #5
    Fancy's Avatar
    Lives in Giza, Egypt. Last Activity: 5 Minutes Ago Has been a member for 0-1 years. Has a total post count of 7.
    Thank you both for replying to the thread. @hanermo2 you wrote a ton of stuff i am gonna need sometime to digest all that. could you elaborate with images preferably on this
    Like making a fixed-fixed screw, with tension, and a compliant tension mount.
    ?? Thanks Guys.

  7. #6
    Let us consider one component, the run out on the collet chuck holding the tool... Standard precision 15-20 microns, Super precision 10 microns, Ultra precision 5 microns

  8. #7
    Fancy's Avatar
    Lives in Giza, Egypt. Last Activity: 5 Minutes Ago Has been a member for 0-1 years. Has a total post count of 7.
    That's sad to know :(

  9. #8
    How many of us amateurs have workshops with sufficient temperature control to prevent thermal movement of both machine and workpiece becoming significant?For that matter,what kind of tolerance do most amateur projects require?It isn't so long since a DRO was an object of lust for most hobbyists.

  10. Anyway, what kind of machine? Over what working area? While the figures quoted might be achievable on a milling machine with the rigidity that goes with it, put those ballscrews on a large working area router and they will hit performance and travel speeds, unless you pair them with massive motors. But that kind of machine is typically cutting wood, and there ain't much point in cutting that to micron accuracy.

    So out of context, talking about achievable accuracy/resolution/repeatability and so on is interesting but not very useful. I think my 1500x750 cutting area router can theoretically achieve something like 3 micron resolution, based on step size and ballscrew pitch, but there is no way I would claim that it is accurate to that degree - and neither does it need to be for its intended purpose, cutting wood. Working to 3 thou, 25 times that theoretical resolution, is probably better than required. Good engineering is about trade-offs and compromise, not throwing money at the problem. Of course, a toolroom lathe or mill is a different question, with different criteria and different priorities - like accuracy over speed.

  11. #10
    Well said Neal. Timber with also change with moisture content from day to day. Plus the fact like a router built out of ali with change dimension as it warms up and cools down.
    ..Clive
    The more you know, The better you know, How little you know

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