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  1. #251
    Gret stuff Joe!
    Having just found out how effective taut wires can be for machine alignment I can really appreciate the value of the new software. Do fishing shops sell stainless steel leader in the UK? It's what I used and may be more stable than nylon.

    One measurement I was completely unable to make on my machine was the straightness of the fixed rails. That may have now changed. I just need to work out a carriage arrangement for the round supported rails.

    Kit
    Last edited by Kitwn; 24-05-2020 at 09:13 AM.
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  2. #252
    Quote Originally Posted by Kitwn View Post
    Gret stuff Joe!
    Having just found out how effective taut wires can be for machine alignment I can really appreciate the value of the new software. Do fishing shops sell stainless steel leader in the UK? It's what I used and may be more stable than nylon.

    One measurement I was completely unable to make on my machine was the straightness of the fixed rails. That may have now changed. I just need to work out a carriage arrangement for the round supported rails.

    Kit
    Hi Kit,

    Yes they do sell steel leader, music wire is also an option. These axis are only 1300mm long so normal lightweight fishing line seems to be perfect, very uniform and black meaning it is easy to resolve in the software. It only flows for around 30s after tension is applied and under the microscope you can see when it stops. The length I put on the machine yesterday hasn't stretched at all over night.

    Some things I noticed that maybe useful:
    1. The microscope (£20) must be focused once at the beginning and then not touched. Turning the focus winder shifts the optical axis which would throw off any measurement. The focus winder is solid enough not to move on its own.
    2. The microscope cable must be tied to the carriage to avoid any force being applied to the back of the scope pushing it off axis.
    3. M6 bolts make perfect wire guides for 0.28mm wire, the wire locks into the V of the thread.

    The depth of field (variation in objective distance where object remains in focus) of the microscope is probably <1mm so you need to get the wire guides to the same height so the wire is not sloped, I set mine level with the top of the epoxy bed using a ruler. The wire is then suspended a few mm outside the epoxy bed.

    If there is enough interest I will share the app, needs a bit of a cleanup first as it was a quick hack.

    Cheers, Joe

  3. #253
    Joe,
    I think it would be well worth sharing the app. I know Johm McNamara shared a lot of very useful info regarding the use of electrical sensing of a wire during the earlier pages of this thread. I was inspired by his work to do my tramming with taut wires alignment a couple of weeks ago which proved very sucessful. But the simplicity and low cost of your solution (who hasn't got a laptop these days?) makes it accessible to everyone. I will have to think about how to make the most use of it AFTER I've spent the next couple of weeks tarting my house up to make it more saleable but I suspect another round of alignment could be on the cards in the future thanks to your efforts.

    Fitting shims is cheap and easy. Working out WHERE to fit the shims is the trick!

    Keep up the good work!

    Kit
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  4. #254
    Hi Joe

    You just made my day.

    Gee using a microscope with your software is a huge step, 3 um = 0.00011811 about a ten thousandth of an inch imperial. accuracy.

    Using wire or fishing line allows the measured line to be accurately positioned. By anchoring each end of the wire to the machine frame precisely you can place the linear rail exactly where you want it. A lot easier than pointing a laser from one end. It also allows you to easily place two rails parallel to each other, by simply measuring the space between the ends.

    I would really like to try your new software. In fact I am quite excited.
    While tweaking it You mentioned that you used black fishing line piano wire is bright and I guess would require a dark background instead of the light background you used to enhance the contrast of the line you used in your experiments.
    Maybe the ability to invert the pixel colour in the contrast discrimination code would be a useful addition.

    Wire or mono filament fishing line? I can think of a number of applications where the the measuring system will need to be left in place for days or weeks when say a large machine installation or While a DIY machine is being built, All plastics will keep creeping and possibly break. Music wire will retain its elasticity indefinitely if it is not loaded above its elastic limit. I use Roslau music wire with great success. Size 0 is .009 Inches in diameter. I never reuse it (From the coil it is perfectly straight you do not want any kinks) a small coil will last for years of hobby use.

    There is another use for this system! A non contact plumb line sensing system or maybe even a pair of plumb lines!!
    Two suspended plumb lines will always remain parallel and perfectly vertical in relation to each other (Ignoring the curvature of the earth that is only measurable at great distances.)

    The two wires define the edges of a rectangular flat plane that in this case is measurable to .0001 inches using wire and your software. I am going to think some more on this....... I have an idea.

    Regards
    John

  5. #255
    Hi John,

    I've put up the first version of the wire app here:
    https://github.com/betzuka/laserleve...uilds/wire.zip

    Extract and run wire.bat, needs java installed as per the laser app. The wire needs to be crossing the rectangular field of view of the sensor in the short dimension, e.g. if your sensor is 640 wide by 480 tall wire should be crossing the sensor from top to bottom.

    It doesn't care whether it is looking at a bright wire on a dark background or vice versa, just needs a decent contrast and the microscope focused so that the wire edges appear reasonably crisp. My fishing line is just black mono filament, super cheap kids stuff that I already had. The main reason for the different algo from the laser is that the objective is lit from the front rather than behind, so it isn't acting like a shadow camera, this means you get lots of reflection off of the surface of the wire which would misslead anything searching for a gaussian, or indeed searching for anything other than the wire edges.

    Your idea of using it to check for planar surfaces is brilliant ! I could stand my machine on end, drop two plumb lines and measure the relative error between the two lines from each respective rail.

    At some point I will integrate it into the laser app so all the other error plotting stuff works. Do you have a microscope to test it with? If not this is the one I'm using, it is also very handy for SMD soldering etc.
    https://www.amazon.co.uk/Microscope-.../dp/B07BF86SRP

    Cheers, Joe

  6. #256
    Hi Joe

    I do have an optical microscope, A cheap student version I used to align my lathe in 2011 using wire. The is a longish post here that discusses lathe alignment and wire, https://www.model-engineer.co.uk/for....asp?th=136771 In this case I lashed up a measuring stage that allowed me to position the wire centrally in a slot by eye using my bio computer then measure off the error using a micrometer. It worked! Page down the thread to see photos.

    In particular note the simple wire positioning stages clamped to the lathe bed made from scrap steel, rock solid.

    Using a USB webcam or microscope with your software is clearly a better solution. It eliminates a number of sources of error.

    I don't have a working USB microscope I will order one! I cant wait to test the software.

    In many ways two cameras will be even more useful, for XY measurement, Ideally using one computer, although old PC's are easy to source for nothing or next to nothing, if two instances of the software could interface to two USB ports on one computer it would be more convenient.

    Regards
    John

    PS stretched wire plumb lines are used to this day by heavy machinery installers, for instance passenger lifts and giant boring mills to align the column. Normally the bob weight is suspended in a container of thick oil to damp out any tendency to sway like a pendulum.
    Last edited by John McNamara; 25-05-2020 at 12:37 AM.

  7. #257
    Quick update,

    I've managed to set the master rail reasonably straight with the setup. It is within +/-5um along the entire length. It was not easy for a few reasons I will outline:
    1. The microscope axis is offset in both X+Y from the centre of the carriage, I did this because obviously it has to be offset in Y as you can't 'see through' the carriage but also in X since I couldn't fit the microscope next to the carriage and remain over the frame. This arrangement is highly non-optimal as you are measuring an offset AND an angle. Eventually you get used to how much adjustment to make, however there must be a better arrangement that avoids this coupling.
    2. Twisting the carriage hard on the rail can induce a few um of error.
    3. Pressing hard on the machine frame and deflect the entire frame a few um.

    The conclusion is that with a machine constructed like mine from 80x80x3 box section over a long dimension of 1300mm aligning to an accuracy of +/-5um is probably the absolute limit and it isn't sensible to try to achieve any greater. Also the frame is unlikely to hold this in actual use due to the deflection under force measured. Still it is good to be able to measure these things to get an idea where the limits are.

    So in conclusion I've managed to align to ~1/2 a thou with a setup that cost a few quid. It is all entirely dependent on the taut wire actually being straight, however if we assume it is then this setup is equivalent to a DIN 874/00 spec straight edge, one of those 1500mm long will cost £2k then you still have to actually align the rail with it.

    Here is a snippet from the alignment:


    Quite pleased, time to get the gantry on now!

  8. #258
    Quote Originally Posted by devmonkey View Post
    2. Twisting the carriage hard on the rail can induce a few um of error.
    To me this says a lot about the quality of your rails and carriages. It also makes the case for a well aligned frame if you want smooth movement without binding.
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  9. #259
    Quote Originally Posted by Kitwn View Post
    To me this says a lot about the quality of your rails and carriages. It also makes the case for a well aligned frame if you want smooth movement without binding.
    I would say it says that standard hiwin rails and carriages are pretty good, would you agree? This is an artificial setup as carriages wouldn't be used singly in a machine. The related interesting fact is that with these 20mm hiwin rails, with a section bolted down hard, moving the microscope 60mm to the next unbolted hole, finger pressure is sufficient to deflect the rail +/-3um although a small contribution will be from frame deflection. As said before everything looks like jelly when you look closely enough.

    Also torquing up the mounting bolts with light pressure on an allen key moves the rail 1-2um, I set the rail at -2um with the bolt snugged down, then tightened it with the allen key that brought it to zero. I've just redone the straightening procedure this way and I'm now +/-2um along the entire length, job done!

    The rail I chose as the master had two 'bends' in it, it was 'S' shaped, with the two ends zero'd there were two intermediate points along the rail which were roughly +/-70um respectively. I verified this wasn't some artifact of the taut wire or the software algo by changing the wire twice, moving the wire guides and changing the end that had the hammer hanging on it.

    This shows that you definitely need to straighten the rail, it is not sufficient to use it out of the box.
    Last edited by devmonkey; 26-05-2020 at 09:50 AM.

  10. #260
    Rails are never straight out of the box they always need to be bolted down. The bolting should be done with a torque wrench for uniformity. If you can get hold of this book or find it at the local library you will see a large section on mounting rails and other components.

    https://www.amazon.com/Precision-Mac.../dp/0872634922

    I got my copy at Foyles many years ago for a lot more, A great book if you build machinery.

    In it he explains the way the rail distorts when tightening it down. Chasing microns is great fun to me! they hide in every corner of your design.

    I would not be concerned about a small amount of movement when you rotate the carriage axially on the rail. If it is a brand name rail you should find the type number engraved on the rail and the bearing blocks. By looking up the manufacturers website you should be able to determine the bearing clearance or preload and accuracy for the particular combination you have. typically around 3 clearance levels may be offered in addition to different accuracy levels. If you are ordering a new rail and bearing set for a project it is tempting to order the maximum preload, this is not necessarily a good idea at all. maximum preloaded bearings are often rated for a shorter life span and more importantly they require more accurate mounting surfaces, using the wrong clearance type can seriously reduce the bearing life and greatly increase the force required to move the bearing placing a high load on the drive system. Fortunately all the bearing manufacturers offer excellent manuals available for free download.

    I ran this Google search today and it yielded some interesting results.

    precision machine design slocomb mounting linear rails

    Or use the link below.

    https://www.google.com/search?rlz=1C...4dUDCAw&uact=5

    Regards
    John

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