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Author Topic: Ready to go with CSS - help!  (Read 3959 times)

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Offline jimpinder

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Ready to go with CSS - help!
« on: January 20, 2009, 05:36:45 AM »
I've been busy over the Christmas and New Year -

New computer - to replace the laptop - second hand tower.
Touch screen
Ball Screws fitted
Change everything to metric !!!!!!!!!!!!!!
New pulley system on the spindle drive to give equal steps up the pulleys and get maximum power out of the spindle VFD
Rewire all the auxiliaries (home switches and speed detection)
Wire in removeable touch pad.
Get the spindle speed control working relaibly and accurately.
Video camera in the milling spindle.

READY TO GO  ;D ;D >:(

NOW - I am cutting railway wheels - which means facing across a 6 or 7 inch wheel (3inch radius). If I am using Constant Surface speed, how do I set about it. I know how to get it working - I have "dabbled" a bit with it - but if you are to set up an accurate speed, how do you do it.

Does Mach know that X0 is the centre of the lathe and therefore can calculate the correct speed (given the material) :-\
or - Do I have to set the lathe at a distance from X0 - say X25 - and then do an S command to set the speed at that distance - and Mach will then follow adjusting the speed as I move in or out. :-\
or - Is it something different :-\


HELP  ???





 
« Last Edit: January 20, 2009, 05:40:11 AM by jimpinder »
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Offline Hood

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Re: Ready to go with CSS - help!
« Reply #1 on: January 20, 2009, 07:41:53 AM »
Not messed with CSS yet as I just finally got the big servo on the lathes spindle yesterday. I am not sure how good CSS is at the moment but hope to try it out in the next week or so. I do know Brian is going to be moving to Turn shortly. Should be in the next month but that depends how the comp and display coding goes and turn has been a month away for a while ;)

Hood

Offline jimpinder

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Re: Ready to go with CSS - help!
« Reply #2 on: January 20, 2009, 10:59:50 AM »
Hi Hood -

It works, in that if you set it going , as the tool moves in towards the centre, the spindle speeds up. That's fine, but how do I "calibrate" it. I just tried setting it going at the correct speed for the distance of the tool from the centre, but that is not working.

I am wanting to spin about 200 rpm 50 mm from centre and speed up as I go in (or vica versa, because I am cutting from the centre, outwards). The spindle I am using is max 605 rpm (probably too low, but I need the torque at the low speed).
 
I go G0 X50 - G96 S200 M3 - M1001( macro to call my cutting program) - but all I get is "speed too great for pulley, setting Max" and off it goes at 605 rpm, and it doesn't slow down. I see the CSS led is on with a number isn the DRO but I have no idea what it is.

I'll have another fiddle.

Not me driving the engine - I'm better looking.
Re: Ready to go with CSS - help!
« Reply #3 on: January 20, 2009, 11:52:49 AM »
Hi Jim,
  I tinkered with CSS a little when I first set-up my VFD. My parts are small so I really dont need/use it.
I think it just looks at your X  and S values at the point CSS is turned ON and does the math from there.

The little DRO is METERS per min/FEET per min of material being removed.
A does pretty good with this in the TURN video.
RC
Re: Ready to go with CSS - help!
« Reply #4 on: January 20, 2009, 12:16:21 PM »
HI Jim,
  When I MDI a G96, I am prompted to include an S value before it will "take".
So, looks like all it really needs is 1 event of G96 S*** and a peek at the X DRO at that instant and all is good to go from there...
RC

Offline jimpinder

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Re: Ready to go with CSS - help!
« Reply #5 on: January 20, 2009, 01:30:13 PM »
Yes - thats what I figured as well. G97 is the same and seems to want a "return" value. The only trouble is the value in the little MDI doesn't seem to bear any relationship to the S value I type in.

Still working on it.
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Offline jimpinder

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Re: Ready to go with CSS - help!
« Reply #6 on: January 20, 2009, 01:45:01 PM »
I've found the answer on a previous post that I was the instigator of.

Constant Surface Speed on January 19, 2008.

Graham Waterworth came up with the answer - and code to suit. I will try it tommorrow.


Jim
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Re: Ready to go with CSS - help!
« Reply #7 on: January 20, 2009, 02:31:58 PM »
That's excellent Jim.
Here is the link to that topic:
http://www.machsupport.com/forum/index.php/topic,5503.0.html
Now that you mention it, I remember you posting there.
Thanks,
RC

Offline N4NV

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Re: Ready to go with CSS - help!
« Reply #8 on: January 21, 2009, 09:00:16 PM »
Use some care when running CSS.  At school we had a lathe with a 6000 rpm spindle.  One student put on an 8" chuck with max rating of 3,000 rpm and faced a part.  The spindle went to 6,000 rpm as the cutter neared the center.  The teacher was nearby and hit the big red button.  After that they had the manufacturer come out and disable CSS.

Vince

Offline jimpinder

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Re: Ready to go with CSS - help!
« Reply #9 on: January 22, 2009, 04:35:57 AM »
Thanks for the warning - yes - this is why I was asking if there was any way to calibrate it.

Fortunately I am on a small "hobby" type lathe, and my spindle (on the pulleys I am using) will only do 350 rpm. I need to keep those pulleys becasue the outer diameter is such I am down to 200 rpm - but I need the torque out of my VFD.

Got it running fine now (but see below) and this morning I am facing (to a fairly simple profile) eight wheels. I can confidently set one going, and then come and write of the forum for 20 minutes while it gets done.

I still have one or two questions - if I move to a diameter, then tell the machine to do CSS (G96), then as Vince said, it chuck speeds up as the tool moves in.If I subsequently then make cuts outward, the tool slows down.  What I cannot do, it seems, is set the diameter at a small setting and move the tool out (i.e. slow down) in the first instance. I have also found (I think) that one CSS is selcted, the only way to deselect it is to close the program and restart, G97 has no effect (Have I got the right G Code).

Still we are a fair bit along the way - and I am getting a good consistant finish.

The trouble is now - I need to machine the spokes !!! ???




Not me driving the engine - I'm better looking.