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  1. #61
    Quote Originally Posted by Jonathan View Post
    He said 45kHz, so even worse.
    Sorry Jonathan should made it clearer.!..I was refering to a telephone conversasion I had with Steve.






    Quote Originally Posted by Jonathan View Post
    Tension the screw + rotating ballnut = no whipping ? Since that requires a timing belt could gear it up to go even faster anyway. As this is (I think) an 8x4' machine it would help...
    Seriously don't get your fasination with speed jonathan.?. . . The ONLY thing it's usefull for is Rapids and seen as 85% + of the time a machine spends is cutting why go to all the trouble of rotating nut, esp on a machine with twin screws .? . . . I see the bennifit of rotating nut to allow long screws but not extra speed and 10mtr/min rapids is good enough for most machines even an 8 x 4.!

    Let me ask you this.? What do you CUT above 10mtr/min.?? . . .Not much if anything I bet.! . . Also out of the last job (other than mass drilling, which high rapids can help) you cut how much of the overall job cycle time consisted time wise of rapid moves.? . . bet it was easily less than 10% of total cycle time.?

    Thats an awfull lot of extra work and expense incorparating 2 rotating ballnuts into a DIY machine just to gain a few percent saving on cycle times, the Key word being DIY machine where cycle times are usually not an issue. . . .Yes in industry every little bit helps but in DIY it's not worth the expense and trouble just for a few percent.!! . . IF . . normal screw setup can be used.

    Said this before .!!. . .It takes a substancial machine with a powerfull spindle using high quality tooling to cut at high feed rates. . . . High rapids are only usefull on very small percentage of jobs other than that they are just used for bragging.!!
    Also seen as most DIY builders use modified routers usually of the cheaper quality range or spindles like Kress then high cutting feeds with any reasonable depth are simply not achievable anyway.

  2. #62
    Jazz,

    At last a man after my own heart. All this 10,000mm / sec is just dick slapping. Think about it your part is programmed to run at say 600mm / min the only time this high speed comes into effect is on rapid moves and unless you are belting 4 holes into the corner of an 8 x 4 board any long rapids usually means you are not cutting / programming efficiently.

    Even when you ar look at the sceen and see if the actual speed ever gets close to what's' allowed for rapids given that it has to accelerate to speed then slow.
    Most time it never gets close to max rapid given the short distance it has to travel.

    All insane rapids do is wear a machine out, put undue stress on parts probably not capable of handling them and more chances of loosing steps.

    I say dick slapping because a beginners reads all this on here, CNCZone etc and thinks that's what he has to do, most are on small machines that can never, ever reach these speeds and even if they get close how fast can someone get to an Estop ?

    When we were first doing the X3 CNC conversions we tried to see what the max they would run at before loosing steps and it was nearly 5 1/2m /min.
    We then dropped this back to 4 m/min but it was still scary on such a small machine so finished up at 2m /min.

    As a test the machines were sent out with a Sieg Logo badge so the punter could engrave a plate to cover the defunct Z axis handwheel hole as a first job.
    There was 4 seconds difference in running at 4m /min and 2m /min
    John S -

  3. #63
    Quote Originally Posted by John S View Post
    I say dick slapping because a beginners reads all this on here, CNCZone etc and thinks that's what he has to do, most are on small machines that can never, ever reach these speeds and even if they get close how fast can someone get to an Estop ?
    Exactly John and just the reason why I ALWAYS jump on this, It's false and miss leading to new comers and can be very costly and wastefull in both time and money.
    Unfortunatly like you probably do, I see too much of this miss guided route being taken.!!

  4. #64
    Jazz,

    The same with over rating components because of bad advise. Following a conversion at the moment on another form of a Taiwanese 636 milling machine.
    The guy is using 25mm ballscrews and 1640 oz in type 34 motors, unless he can hit that with 10,000 volts it will crawl but bigger is better - yes ?

    End of the day he'll get as much 'useable' power as a 600 oz/in motor and probably twice the speed.
    John S -

  5. #65
    I agree entirely that 10m/min is more than enough and that the difference in machining time between 10m/min and greater is often negligeble. My machine will do at least 15m/min on X and 60m/min on Y, but I leave it at 10-12m/min as it's less likely to go wrong and more time to react should something go wrong. I think the most I've actually cut at is 8m/min.

    The reason I tested the Y-axis up to 60m/min was an experiment to verify my modifications to Irving's motor calculation spreadsheet to include pulleys. I was ascertaining how accurate the calculation was by trying different ratios and comparing the limit to the calculated value.

    I meant that comment to be just pointing out it is probably possible to get round the vibration problem and the feedrate gain is a bonus.

  6. #66
    Quote Originally Posted by John S View Post
    Jazz,

    The same with over rating components because of bad advise. Following a conversion at the moment on another form of a Taiwanese 636 milling machine.
    The guy is using 25mm ballscrews and 1640 oz in type 34 motors, unless he can hit that with 10,000 volts it will crawl but bigger is better - yes ?

    End of the day he'll get as much 'useable' power as a 600 oz/in motor and probably twice the speed.
    Ah ha ye and it was probably the supplier who told him he needed that.!! . . .. . . . The same someone who sold a guy I know 12.5Nm for his Z axis.:whistling:

  7. #67
    Quote Originally Posted by Jonathan View Post
    I meant that comment to be just pointing out it is probably possible to get round the vibration problem and the feedrate gain is a bonus.
    Nah much better to replace the bent screw IMO because after you have gone to all that trouble and expense for what amounts to a very costly and mostly un-usable bonus the screw is still bent.:exclaim:

    RE 60M/min Y axis out of interest how much pulley ratio did you have to use and what sort of accelleration did you achieve.? . . . If you don't mind me asking.!

  8. #68
    Hi All..

    Been out the loop for a couple of days but I note some fascinating posts from you cnc guru's.. Love the one about Mach and kernal speeds, have popped mine back down to 25KHz and it seems fine..

    The sort of speeds you guys are talking about seem more than fanciful to me at the moment.. Have been running my machine at 1.8mts/min max during all these other problems, now that I can achieve more, I still dont dare go above 2.5mts/min due to the bent ballscrew shaking the machine so much.. I did try 4mts/min which the motors seem to easily achieve, but shaking was so severe I thought something was going to rattle off the machine.. Am going to try straightening the ballscrew today, will let you know how I get on..

    Steve..

  9. #69
    Quote Originally Posted by JAZZCNC View Post
    Nah much better to replace the bent screw IMO because after you have gone to all that trouble and expense for what amounts to a very costly and mostly un-usable bonus the screw is still bent.:exclaim:
    True it is quite costly having already bought the bearings etc for rotating the screw. If the nut is rotating and the screw is tensioned (ideally a lot) then the bend should not matter much. As long as the ballnut is precisely on centre (which admittedly is tricky) then there's no radial force on the screw. If the screw is bent and spinning there is a large cyclical radial force which causes it to vibrate... No doubt there's more to it than that but I bet it would be a lot better.
    I'm guessing it's a 25mm screw, what length is it?

    Quote Originally Posted by JAZZCNC View Post
    RE 60M/min Y axis out of interest how much pulley ratio did you have to use and what sort of accelleration did you achieve.? . . . If you don't mind me asking.!
    It was 42:14, but I accidently put 42:12 on the video. See here, post #136:

    http://www.mycncuk.com/forums/showth...outer-building...

    I can't remember what the acceleration was... think it was 2m/s^2, might have been 3. Either way it only hits 60m/min for about 200mm... except if you smash it into the side :whistling:

  10. #70
    Quote Originally Posted by fasteddy View Post
    Just a thought...

    Have been roving around all the cnc forums trying to find another with the same probs... I have seen an awful lot of posts about earthing, but I have to say, as a complete burp at electronics, I ended up more confused than when I started... Cant get my head aound the myriad of different advice being handed out, and much of it was american.. Do they use different terms for all that common,starpoint,earth,neutral,-ve supply/rail,0 volt stuff? Damned if I can work out what they are in English without even more varying terminology.. I ramble..

    Does seem to be a big cure-all for a lot of electronics issues so I was wandering if there is a good post/guide to earthing for us feeble minded noobs? From what I have read, I ought to do this as a matter of course, if only to eliminate several potential problems...

    Steve..
    Hi Mate, are you using Mach3 with a parallel port? If so what kernel speed are you using and what is the maximum velocity for the X and Y axis.

    Mike.

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