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  1. #61
    Square is square.
    Acme is 29 degrees and usually imperial [ not always ]
    Trapezoidal is 30 degrees and always metric

    Let me have a look tomorrow to see what taps I have, definitely got 5/8" x 8 LH Acme but not sure on the rest.
    .
    John S -

  2. #62
    Quote Originally Posted by Ross77 View Post
    My question is how critical is it to completly eliminate backlash or is the compensation in Mach able to overcome it?
    This rather depends on the accuracy you are trying to achieve.

    The software can add extra travel when you reverse direction but that means the slides have to be tight enough to resist side forces from the tool so only the nuts can move them. Once the slides are set tight you have to worry about spring in the system.

    Alternatively use two nuts. If you lock them together then wear becomes your problem. Spring them together with sufficient force to resist the tool pressure and you need monster size motors to turn 'em.

    If it was easy to eliminate backlash with cheap screws nobody would sell expensive screws

  3. My question is how critical is it to completly eliminate backlash...
    40 years ago men were sent to the moon. Most of the machines that built the rocket that got them there had backlash to some extent.

    The critical bit is reducing the backlash/play/give/flex/strain/vibration/call-it-what-you-like it the whole machine down to workable level and working the machine to reduce the effect of the errors.

    If you lock them together then wear becomes your problem. Spring them together with sufficient force to resist the tool pressure and you need monster size motors to turn 'em.
    The important thing it to lock them together with the smallest possible clearance. This can mean that, with a poorly formed lead-screw thread, the nut will be slack in places while tight in others (lapping the thread with a nut and abrasive e.g. metal polish can reduce the tight spots).

  4. #64
    Thanks for all the advice, Taken it all on board. From looking on here and the CNC zone I always planed to use servo motors, linear rails and ballscrews for the main machine, and now I know why.....

    Still all good practice, dont know If I can justify ballscrews for this one. No point in having an ultra precise table if the head flexs all over the place. May be I should just get it working and then if its just the backlash thats an issue, I can sort it then.

    Made the tap tonight and tried it on some plastic I had kicking around. Worked fine but I think the plastic is to springy and the tap wont cut the last bit for clearance, very tight over a 40mm length. Ive tryed tapping fuild and a drill but the end result is a very hot and shiney leadscrew, Still at least I know the best way to polish them now :clap:. I'll have to order some delrin,or try narrower sections.

    Changing the subject, what is the best way to hone the dove tails on the slides? I've got them really smooth, with no play, except for the the first 30mm or so where i can feel an bump, Cant get the oil stone in and dont want to over do it by using a grinder.....If I carry on lapping it will both parts wear and then cause problems over the whole length?

    Thanks again

  5. #65
    Quote Originally Posted by Ross77 View Post
    Changing the subject, what is the best way to hone the dove tails on the slides? I've got them really smooth, with no play, except for the the first 30mm or so where i can feel an bump, Cant get the oil stone in and dont want to over do it by using a grinder.....If I carry on lapping it will both parts wear and then cause problems over the whole length?
    If it is cast iron you scrape it, use engineers blue to find the high spots. I would be very careful about introducing any kind of abrasive unless you are blessed with a Rowlingesque magic wand, "Accio grit"

  6. #66
    Quote Originally Posted by Robin Hewitt View Post
    If it is cast iron you scrape it, use engineers blue to find the high spots. I would be very careful about introducing any kind of abrasive unless you are blessed with a Rowlingesque magic wand, "Accio grit"
    Cheers. whats the best tool to scrap it with? looked in to this when setting up the lathe but looked like a "Black Art

    What is Accio grit? Im sure Ive read that it ok to use abrasive compounds as long as it is properly cleaned with parrifin afterwards...

  7. #67
    Quote Originally Posted by Kip View Post
    Requires manual dexterity
    The famous Mexican bandit :heehee:

  8. You could try just lapping the parts together dry (i.e. degrease it and rub). Cast iron is fairly abrasive stuff so a few dozen cycles should polish the machining marks.

    BTW Use proper 'way oil' e.g. Mobil vactra. (Keep that old can of Duckhams for the car use only ;) )

  9. #69
    If you want to scrape the ways then a scraper is the best way forward....made from an old file or similar.

    Requires manual dexterity and mastery of hand tools....not for the office workers :naughty:
    No need to get personal.:heehee: Office workers can very usefull....making tea, sweeping the floor etc.

    You could try just lapping the parts together dry (i.e. degrease it and rub). Cast iron is fairly abrasive stuff so a few dozen cycles should polish the machining marks.

    BTW Use proper 'way oil' e.g. Mobil vactra. (Keep that old can of Duckhams for the car use only ;) )
    Unfortunatley its not just machining marks, there is a proper lump that needs removing. Still I'll give it try.

    The best tool to scrap it with is a grinder......
    Is that a typo? or did you mean scrap it

  10. #70
    Your typo? my implication :naughty:
    Bugger, thought I had you then. Dont know how that happened! I'm normanally reeelle gurrd @ speiling ;o)

    Ever see the fanboy posts on cnczone where they all went mental and set about knocking the stuffing's out of their dovetails with grit lmao
    No I havent, better find it and have a look, make sure Im not doing the same......

    You got me on the making tea strike.....Can't call em completely useless eh :D
    All this oil is playing havoc with my manicured nails...lol

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