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  1. #181
    Quote Originally Posted by devmonkey View Post
    Hi Kit,

    I do have a pack of 105/209 here for this machine, trouble is the temperature in the UK in my unheated uninsulated garage is about 6 degrees, so would have to wait until summer.

    I was also hoping we could improve upon the accuracy of epoxy, from the measurements taken in this thread:

    It appears with epoxy 100um (0.1mm) peak-peak error is possible, I think we can do better than this with the laser and also not have to wait 2 weeks for the epoxy to cure. It might be possible to perform the process I described above in a couple of hours.

    Cheers, Joe
    We're having the opposite problem here. Last night's overnight low was 29C and the days have been up to 46C recently. I'm keeping our epoxy resin (wife and I are making some fancy stuff to sell in the local gift shop) in what used to be a wine fridge.
    Maybe you could pour the resin and then come over to us for a fortnight's tropical snorkeling with whale sharks and manta rays while it cures? Then take your enviable winter tan home and use the laser to guide you hand-scraping the last 100 microns of errors out? Hand scraping resin shouldn't be to hard.
    Engineering is the art of doing for ten shillings what any fool can do for a pound.

  2. #182
    Hmm, so I now have another problem.

    I set laser on the milling machine head, just needs to be attached to something solid, then levelled the laser to the machine frame which is sat on a sturdy bench. The problem is that walking near the laser causes microscopic deflections in the concrete floor, sufficiently large to show up as 10-20um of error 3m away on the machine frame. These are probably amplified by the height of the laser from the floor, about 1.5m as the same doesn't occur walking near the bench.

    I think I will need to move everything directly onto the concrete to stand any hope of getting things stable enough to do any frame levelling. Problem will then be not kicking it during the process.

  3. #183
    Hi All

    Gee who would have thought this thread would have generated so much interest.

    I am tempted to bring up the possibility of automating bed machining using software!

    The following is just first draft of a possible solution. My plan is to level the surface by milling small sections of the bearing surface in an overlapping grid pattern. When finished the surface would look a little like hand scraping. As each "Peck" was made after aligning the cutting head to the laser or stretched wire. Once the cutting cycle is complete the surface flatness would be equal to any errors in the measurement system that we already know is pretty good from the experiments done so far my a number of testers. A final stoning of the machined surface would remove any high spots. Note the cutting head is aligned to the measurement system not the rail it slides on.

    A quite small milling head with a small cutter (5 - 8mm) traversed along the bed using the rails to be later used on the machine itself temporarily fixed to the sides of the in your case 80x80 rail support frame.

    I don't plan on using a high speed spindle just a simple Import

    It would need 4 axis.
    One controlled by the leveling software

    One that rotates the cutter head to vertical (Leveling IC's are cheap) a small stepper. The leveling could be done with 3 steppers for complete control or just one if only levelling transversely across the rail in the x direction. Therefore only one small stepper required.

    One to drive the cutter head down and make a peck. Another small stepper and a simple screw drive ball screw not needed just low backlash.

    One to move the small cutter across the work. the X axis has very limited travel maybe 50mm maximum.

    There would also need to be a longitudinal drive.
    Ideally using the timing belts to keep the cost down.
    This drive could use the drive motor later to be used in the machine.

    So the sequence would be:
    Starting with the cutter head in the up position.

    Move along the rail to the next cutting "peck"
    Level the head

    Find the center point with the alignment software to align the attached cutting head.
    Move the cutter head down #N steps to engage the work.

    Retract the cutter head.

    Repeat cycle.

    The temporarily fitted rails would only need to be roughly aligned. Within say 2mm Ideally 1mm. Not that hard, it can be done with simple measuring tools.

    The accuracy of the system is derived from the measuring system not the supports for the temporary fitted rails.

    I imagine that the mounting face of the Box tubes would be coated with a strip of say 5mm thick and wide enough to fit the rails, to be be machined flat with A mixture of epoxy and metal powder.
    Easier to machine than steel. Thin box sections are often bowed. You don't want to weaken them.

    I posted this a while back. I still run the lathe on the material. Inexpensive to prepare. For non sliding Iron or Aluminium powder alone and epoxy would be fine.

    If a few people are interested I would have a crack at drawing up a design that mainly uses laser cut sheet steel parts ground rod and Asian bearings for the Simple jig needed. Anyone could download the files and send them off for cutting to their local cutting shop. It will be quite small so low cost.

    I am not planning a servo driven XY axis just point to point positioning via steppers,
    An Arduino or similar processor could easily drive all the above.


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  5. #184
    Interesting idea John.

    3 axes may be enough:
    Rotation (few degrees may be enough). Likely the rotation should be clamped after achieving the correct level plane. Rotation adjustment could even be manual.
    Cutter up/down (few mm, accurate depth very important).
    Transverse (~50mm)

    Longitudinal along the rail could be done manually with clamping at each position. This avoids the need for a temporary low backlash longitudinal drive.

    Actually, all the movements could be done manually based on software feedback. Light cuts are expected only.

    An important point is a fixed mounting place for the laser that allows both rails to be machined / aligned. This may be a bracket fixed to the middle of the machine bed, equidistant to the rails.

    (By the way I am keen to see some updates to your epoxy granite mill!)
    Last edited by pippin88; 14-01-2020 at 10:15 PM.

  6. #185
    Hi Pippin

    X and y positioning does not need to be done to CNC milling machine accuracy standards. the pecks cut a small circle and can overlap each other enough to allow for any positioning errors.

    Using a rail that will later be used on the machine (it needs to be a profile rail if only one is used round rails will work but two will be needed) the cutting head will be mounted on one of the rail runner bearings that will later be used on the machine. The cutter head will be small, not a gantry across the machine. At a guess maybe a 250mm cube should be enough to contain the components. made from laser cut and 3d printed parts.

    If the rail used is not ordered a little extra long the cut length will be equal to the length of the rail minus the width of the runner block, not a huge problem the small section at each end could be hand finished. Or the rail could be ordered a little extra long to allow for this.

    How to mount them?

    My plan is to clamp a piece of say 90 x 45mm (4x2" imperial) dressed timber on the side of the frame member to be leveled this would need to be manually straightened to within a mm or so, not hard with simple tools Or better still buy a good straight piece from the local building materials supplier

    I plan to mount the rail on this timber with stout wood screws!

    This is where the laser or wire alignment system comes into play. The rail and cutter head assembly
    only needs to provide solid support for the cutter head. Positioning the cut is done by the measurement system not the frame.

    The X axis is possibly the weakest link in this design, as is as long as a simply flat area is all that is needed it should work fine. If however you wanted to pilot drill the mounting holes it would not be sufficiently accurate without setting up the laser reference or wire reference at 90 degrees.
    Doable at the expense of complexity, probably unnecessary.


    PS: Yes Pippin the epoxy mill begs me to finish it. 2019 was a big year for me work wise with a heavy smattering of other issues. I hope to get back on it soon.

  7. #186
    So I have made a small amount of progress this evening. With the laser mounted solidly to the mill head I was able to map the my machine frame. I clamped the laser solidly then left it well alone. This meant the machine frame had to be adjusted to the laser plane, which is much easier than vice versa. I lifted the frame at 3 points and shimmed each to get the best coincidence of the two planes, this was just done with a steel rule with the end on the frame and reading off where the laser hit it.

    This is the frame and I'm trying to create a planar surface across the top two beams:

    Click image for larger version. 

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    I then mapped the surface, I have about 1mm total peak-peak error, basically each top beam slopes down 1mm from end-end but in opposite directions. This isn't too bad.

    I also took delivery of a little Makita trim router, I think it is the same sort as used on some peoples cnc routers. Anyway for 100 it is a very nice piece of kit, no measurable up-down play in the spindle, I also got a 6mm collet for it.

    The levelling process I'm going to attempt I outlined earlier in the thread, but basically it involves using a trim router and a laser aligned router jig to mill down material fixed to the top the frame to bring it into plane.

    So what material to use? I mixed up some metal polyester filler of the type used to fix leaks on engine castings. This stuff has some nice properties but it is too brittle and I think too soft (definitely softer then unfilled epoxy).

    So what about epoxying an aluminium strip to the top of the steel frame and machining that? Would probably work but more effort, I checked the little Makita is happy milling aluminium and it is fine.

    Whilst I had the router in hand with a 6mm carbide endmill in it, I thought I may as well see what it can do against mild steel, not expecting anything other than chatter and heat. Anyway it cuts it like butter, very cleanly. I only tried 0.5mm and 1mm DOC and it was fine and this is within the range I need for levelling this frame.

    So I will pick up some 30mmx4mm flat bar stock tomorrow and weld it to the top of the frame where the rails will be mounted, then build the laser/router jig and hopefully have a planar frame very soon.

  8. #187
    Quote Originally Posted by devmonkey View Post
    It appears with epoxy 60um (0.06mm) peak-peak error is possible, I think we can do better than this with the laser and also not have to wait 2 weeks for the epoxy to cure.
    Question.!... Why do you need better than 0.06 for a router..? . . . . Answer.! . . . You don't.

    With all the watts of brainpower you've invested in this, you could have heated the garage and built the bloody thing.! . . . Just get on with it and stop overthinking is my suggestion.

  9. #188
    Quote Originally Posted by JAZZCNC View Post
    Question.!... Why do you need better than 0.06 for a router..? . . . . Answer.! . . . You don't.

    With all the watts of brainpower you've invested in this, you could have heated the garage and built the bloody thing.! . . . Just get on with it and stop overthinking is my suggestion.
    Yes I could have done, using maths I even worked out it would cost 84 in electricity ;-)

    I may still use the epoxy if this doesn't work out but this thread is about developing a open source optical metrology system using very cheap components for the benefit of anyone who wants to measure anything accurately to few microns. I thought you'd be well up for that given your pet hate of people quoting accuracy figures they cannot measure.

    Some projects do require better than 60um accuracy, or at least calibration of that level of error. For example I want to use the machine currently under construction or one of its offspring to position high power magnets into a halbach array for a coreless axial flux PMDC EV motor I'm developing, this needs 10um accuracy under quite significant magnetic load.

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  11. #189
    HI All

    Well Put Joe. "Devmonkey"

    This thread "is about developing a open source optical metrology system using very cheap components for the benefit of anyone who wants to measure anything accurately to few microns" The software you have written that forms the cornerstone of the project continues to evolve and mature.

    When I first came across this thread in August 2019 It captured my imagination straight away, It continues to do this now 4 months later. It represents the work of many individuals now, all striving to improve it, by freely sharing their ideas on a world stage. The results will enable many builders and experimenters to achieve measurement accuracy previously only available at great expense.

    Thanks Joe, the best is yet to come!

    Last edited by John McNamara; 16-01-2020 at 09:58 PM.

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  13. #190
    Though the chances of me ever requiring the level of accuracy you are striving for here are minimal I agree with John completely. This remains a valuable and fascinating thread. Have you ever thought of sending your CV to NASA?

    For novice readers who are trying to work out what they should be doing to make a CNC router with performance that is both adequate and practically achieveable your comments are equally valuable.

    Engineering is the art of doing for ten shillings what any fool can do for a pound.

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