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Author Topic: Constant Surface Speed.  (Read 7224 times)

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Offline jimpinder

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Constant Surface Speed.
« on: January 19, 2008, 03:47:50 PM »
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 ???
Not me driving the engine - I'm better looking.

Offline Graham Waterworth

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Re: Constant Surface Speed.
« Reply #1 on: January 19, 2008, 03:57:48 PM »
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.
Without engineers the world stops

Offline jimpinder

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Re: Constant Surface Speed.
« Reply #2 on: January 19, 2008, 04:18:50 PM »
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.
Not me driving the engine - I'm better looking.
Re: Constant Surface Speed.
« Reply #3 on: January 31, 2009, 08:13:10 AM »
in this example the s75 is the surface feet per minute you want to turn correct? 

Offline jimpinder

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Re: Constant Surface Speed.
« Reply #4 on: February 02, 2009, 08:28:50 AM »
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)
Not me driving the engine - I'm better looking.

Offline Hood

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Re: Constant Surface Speed.
« Reply #5 on: March 02, 2009, 02:40:46 PM »
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
Re: Constant Surface Speed.
« Reply #6 on: March 02, 2009, 04:54:57 PM »
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

Offline Hood

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Re: Constant Surface Speed.
« Reply #7 on: March 02, 2009, 05:06:54 PM »
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
Re: Constant Surface Speed.
« Reply #8 on: March 02, 2009, 05:10:59 PM »
Please post your findings for future reference.
Or just keep them in that vast mental database of yours.
Thanks,
RC

Offline Hood

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Re: Constant Surface Speed.
« Reply #9 on: March 02, 2009, 05:13:47 PM »
yep, its certainly mental in there ;D

Hood