Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: jimpinder on January 19, 2008, 03:47:50 PM
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Probably the only reason I have got into CNC is to hear my spindle accelerate as the tool takes a cut across the face of my work piece.
I think I am nearly there. My spindle control is in place (and accurate) with feedback through the index pulse. My X and Z axis are trembling - waiting to step into the new era of the unknown.
BUT - I don't know how to do it. I've looked through all the manuals I have available -
PLEASE - CAN SOMEONE point me in the right direction - is this a G Code thing, and will I have to write a Macro - or has it already been taken care of ???
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Hi Jim,
its all in there just waiting for you to tell it when to move.
Try this code :-
Zero out at some point in fresh air.
G21 (Metric)
G40 (Clear offsets)
G95 (Set feed per rev)
G00 X50. Z0 (Move to start point)
G96 S75 M3 (CSS 75 Metres/min)
G01 X10. F.1 (Feed at .1/rev)
G00 X50. Z1. (Rapid clear)
M30 (End)
Graham.
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Graham - That must be one of the fastest replies on record - I only nipped out to make a cup of coffee !!!
Thanks a lot - I will try that in the morning.
Jim.
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in this example the s75 is the surface feet per minute you want to turn correct?
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Sorry SD this is an old post that has been brought forward.
Yes the 75 is the speed, but note that it is derived from the speed of the spindle and the diameter (or radius it is cutting at) This means it must be told where it is to start (see previous line).
The code Graham has included there works first time. The only problem was that I wanted to cut from the centre outwards - and I couldn't seem to get that to work the same way. I set the thing going as per Grahams program, have it travel in, the cut outward, and it worked perfectly. (up to the speed limit of that set of pulleys)
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Jim,
how do you find CSS at controlling the spindle speed? I tried today and it was very jittery, jumping around about 20 or so rpm even when the X was stationary. I am thinking it may be a SmoothStepper issue but just wanted to make sure it was fine with the PP before I reported it to Greg.
Hood
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Hi Hood,
Till Jim gets back to you.....I used CSS several times on my Homebrew/PP and it worked very well. Didn't notice any abnormalities what so ever.
FWIW,
RC
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Thanks RC, Graham also has smooth operation with CSS and PP so looks like its a SS issue, maybe just with Step/Dir spindle and SS.
Hood
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Please post your findings for future reference.
Or just keep them in that vast mental database of yours.
Thanks,
RC
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yep, its certainly mental in there ;D
Hood
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Mine is vast also........but nearly empty.
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Yep I believe you ;)
Hood
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Hood - Sorry, I was out all day yesterday.
The CSS worked very well, and it seemed to me, very smoothly. The wheels are 6 inches in diameter and I was cutting into the back by about 0.25 to lighten them - they are 1 inch thick. I wanted to start at the centre about 0.5 from the axle hole, and come out to a point about 1 inch from the rim.
I wrote the script that angled into the work, then ran parrallel to the finish. Botched the first one a bit (actually I needed a new tip on the tool) but after that it was a matter of mounting the hweel and pressing cycle start. I did all eight wheels in no time.
I can't really comment, I suppose, becasue the speed is constantly changing as the cut moves, but it seemed alright, and gave a nice finish.
As you know, I don't have a Bob, my index (single pulse) is optical reflector, straight to the computer.
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Thanks Jim,
The speed will jump around even when I dont move the axis.
Its definitely nothing to do with BOB or index or whatever else as it works fine when in normal RPM mode, smooth as silk, doesnt even fluctuate 0.5 rpm, if I tell it to do 2000 rpm it does, tell it to do 2rpm it does, 1562rpm and it does. Issue must be the way Greg has the CSS with the SmoothStepper but as always I am confident he will fix it up, just like all the rest of the problems he has in the past :)
Hood
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Hi Jim,
its all in there just waiting for you to tell it when to move.
Try this code :-
Zero out at some point in fresh air.
G21 (Metric)
G40 (Clear offsets)
G95 (Set feed per rev)
G00 X50. Z0 (Move to start point)
G96 S75 M3 (CSS 75 Metres/min)
G01 X10. F.1 (Feed at .1/rev)
G00 X50. Z1. (Rapid clear)
M30 (End)
Graham.
It is an old post,,,, but it helped me very much.
Could not get any further,, I always got the maximum spindle speed,, until I read your message to zero out in fresh air.
Now I can use Constant Surface Speed. Great.
Thank you very much for this part of code. :D
gr jaja