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  1. #81
    What depth of cut, speed, feed, stepover was that? Looks like you took it very gently. Seems a bit of a random place to choose to cut it within the aluminium sheet, but I guess you had your reasons.

    I see you're very generous with the cutting fluid!

    Finished part looks nice, are there any marks in the corners due to backlash. Were you using G64? I think so, but it's difficult to tell in the videos.

  2. #82
    Jonathan,
    I did take it very easy with that cut. Depth of cut was only 0.5mm, step over was 20% which would be just under 1mm and feed speed was 10mm/sec for that cutter was 10mm/sec. The only cutter I was was not new so I did go slowly with it. The alu also has some hard sections in it so that was why the cutting fluid was generously applied. The starting point was a mistake, I for got to set my dxf to 0,0 in cad and I think cut2d picked that up.
    I have had a look at the program file and cant see any G64 codes in it. Youll need to excuse my ignorance in G codes at the moment, I havent got round to learning them yet!!
    Some photos are attched of the cut edge. Quality looks good for an old cutter.

    Click image for larger version. 

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  3. #83
    what would you look for or what would it look like . for backlash??

    James

  4. #84
    James,
    backlash would look like an uneven cut. The finish edge at the corners would be like a wavey line. This happens when there is play in the mechanics of the machine like a set of cogs not meshing together correctly so that when your turn one cog it moves slighlty before the other one moves. In a profiling machine that drives atart to wobble a bit at a change of direction until the machine sort of balances itself out.
    t I have found that the best way the check for backlash is to run your machine at a 45 degree cut so that both x and y axis are travelling at the same time ie cut a square but rotate it to 45 degrees on the bed. The corners should be nice a smooth without any wobble in the cut surface. Cutting at 45 also tells if your speeds are the same in both axis at the same time. If they are not you would have an uneven cut surface all the way along the cut.

    Ian

  5. #85
    Whether or not you get a wavy line/arc depends on the direction of cut (climb/conventional), the cutting force and the friction of the slides. Either way you will get a 'blip' on the corners, or wherever any axis changes direction. Here's an example:

    Click image for larger version. 

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    The corners should be smooth, but as you can see each corner has a line/offset portion where the axis changed direction. For that part it doesn't really matter - it's still shiny

    That was on my milling machine which currently has more than it's fair share of backlash.

    This part was made on my router which has very little backlash, so the corners are smooth with no 'blips':

    Click image for larger version. 

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    Last edited by Jonathan; 19-09-2011 at 12:12 PM.

  6. #86
    Quote Originally Posted by Web Goblin View Post
    Some photos are attched of the cut edge. Quality looks good for an old cutter.

    Click image for larger version. 

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    Hi Ian,

    Congrats on your first Hot Chip's. . . . . . . (Now the BUT.:lol:)
    I think your single spindle mount is causing chatter/resonance looking at the edges I can see chatter lines.!
    I know you say the cutter was old but that does look more like flex chatter..? Also when cutting it sounded ringy more like a resonate ring not a blunt cutter.

    Too little DOC, too slow spend n feed or more importantly wrong chip load can be just as bad for cutter than too much, esp in sticky Ali. Don't be shy give the cutter some work to do as your going far too conservative. . . .Heat is the enemy so send it away with the chip.!!

  7. The Following User Says Thank You to JAZZCNC For This Useful Post:


  8. #87
    Quote Originally Posted by JAZZCNC View Post
    I think your single spindle mount is causing chatter/resonance looking at the edges I can see chatter lines.!
    Just what I was thinking - the vertical lines are a bit of a give-away.

    Definately too low feed and stepover - with only 20% stepover you need to feed much faster to attain the same chipload, look up chip thinning. This explains some of it, though it is aimed at making you buy the program...

    http://www.cnccookbook.com/GWCalcFeedsSpeeds.htm

    Quote Originally Posted by Web Goblin View Post
    The alu also has some hard sections in it so that was why the cutting fluid was generously applied.
    I was joking when I said that was generous!

    Quote Originally Posted by Web Goblin View Post
    I have had a look at the program file and cant see any G64 codes in it.
    Mach3 may have defaulted to it anyway, it depends.
    G64 puts mach3 in constant velocity mode, so that within reason the feedrate remains constant. This means that external corners will become slightly rounded - more if the acceleration is very low.
    G61 puts mach3 in exact stop mode, so it stops once it has got to the point specified by each line of code, then continues. This makes the motion very 'jerky', though depending on the situation it will make the final part more accurate.

    Using constant velocity makes the motion a lot smoother, and a constant feedrate is clearly faster overall and kinder on the cutter. To try it just type G64 at the begining of the program. You'll notice the most difference when a program uses lots of small lines to approximate a curve.
    Last edited by Jonathan; 19-09-2011 at 03:30 PM.

  9. #88
    Hi There,

    How are you finding the High power kinco drives? I can't decide between those and the normal DC powered variety, any reason you chose those?

    Regards

    Andrew

  10. #89
    Quote Originally Posted by andrewbond View Post
    How are you finding the High power kinco drives? I can't decide between those and the normal DC powered variety, any reason you chose those?
    The 2M2280 drivers run on 240VAC they run the motors at a high voltage, not sure if it is actually 230*2^0.5 as that seems a bit much. This get much much higher speed from the motors than the 'normal' 70V (or so) drives, however it will make the motors run hotter. That's not necessarily a problem - as long as the case temperature is not above about 80-90C it's fine.

    I'm thinking of getting a couple to use on either my lathe/mill or router. They're only suitable for Nema 34 (or 42) motors, not 23/24. A Nema 23 motor with high inductance might be ok... but with how much those drivers cost that's probably not the best option.

  11. #90
    Quote Originally Posted by Jonathan View Post
    G61 puts mach3 in exact stop mode, so it stops once it has got to the point specified by each line of code, then continues. This makes the motion very 'jerky', though depending on the situation it will make the final part more accurate.
    Ye Try G61 with an high feed rate/accelleration and watch it turn into a "Darlick on Whiz" as it try's to break dance thru the workshop wall after it's destroyed all in it's path. . .:rofl:

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