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Messages - stirling

1051
General Mach Discussion / Re: Z home goes past 0.0 to +1.0
« on: January 30, 2012, 09:06:55 AM »
Tom - please don't worry about it. I'm not aware of any rule that says you can't use tinyurl here. I just felt that an awareness of the potential risks should be pointed out to anyone who doesn't know what tinyurl actually does. Remember there's straight visible linking and there's invisible re-directing which is tinyurl's purpose. My apologies if I've offended you - that wasn't my intention. Just trying to help keep this a safe place.

Ian

1052
General Mach Discussion / Re: Z home goes past 0.0 to +1.0
« on: January 30, 2012, 07:20:28 AM »
I um'ed and ah'ed before deciding not to delete the above tinyurl - we're all grown ups right and can make our own decisions. However, if you don't know what tinyurl is then before you click on it you may want to familiarize yourself with the potential risks. This is in no way any suggestion of mal-practice on ttm's part. I'm happy to accept that it re-directs to where he says it does. I do ask myself though why use tinyurl rather than post here?

1053
The outside corners ARE arcs as I suggested in my first post.

N0320 M03
N0330 G01 Z0.0600 F360.0
N0340 G02 X10.5200 Y8.2500 I0.0000 J-0.0200 F200.0
N0350 G01 Y0.0000
N0360 G02 X10.5000 Y-0.0200 I-0.0200 J0.0000
N0370 G01 X0.0000
N0380 G02 X-0.0200 Y0.0000 I0.0000 J0.0200
N0390 G01 Y8.2500
N0400 G02 X0.0000 Y8.2700 I0.0200 J0.0000
N0410 G01 X10.5000
N0420 M05

So I stand by everything I said in my first reply. So back to what you can do about your rounding. Apart from what I said about speed and acceleration, and with specific regards to what I said about CV TUNING you can....

1) Use "Stop CV on angles >" but as ALL your angles are 90 degrees using this with ANY value UP TO and including 89 will do exactly what the label name says i.e. it will turn CV OFF for ALL your angles i.e. you will get the same result as if you use Exact-Stop. Which is what I've been trying to say.

2) Turn on CV Distance and set it to SOME value. Now - you CAN set it to 0.01 if you want but this is saying - don't allow a blend until you're within 0.01 of an inch of each corner. This is really quite harsh and wil again effectively turn CV OFF. I would suggest YOU decide how much rounding is acceptable to YOU and have a play. So for example you might say I can live with 0.25 or maybe 0.1. If so, at least you're allowing CV a chance to work to some extent and you MAY find the results acceptable - you MAY not - it's YOUR call. All I have been trying to suggest is that you attempt to TUNE rather than just "hammer" it from the get go.

3) Take a look at turning on CV Feedrate and entering SOME value. This is a setting that's very rarely mentioned for some reason and when it is it's usually recommended to "hammer" this one as well rather than TUNE it gently to get results that are acceptable to YOU. See http://www.machsupport.com/forum/index.php/topic,20251.msg141302.html#msg141302 where I've attempted to explain its use.

CV TUNING is a bit of an art form - you can tweak it gently or you can smack it so hard you effectively kill it - and that's all I've been trying to say.

In the end though - you can't beat the laws of physics. No machine can change direction *instantly* but *good* acceleration can't be beaten for minimizing rounding.

Good luck and happy TUNING ;D
MODIFIED:ADDED BACKPLOT OF CODE      RICH

EDIT: Thanks RICH

1054
Hi hemi43 - sorry about this. My first post was my best shot and I see there are no outside arcs so I'll have to have a think about it.

1055
Actually, you equated using the CV setting as "hitting the proverbial CV nut with a sledge hammer."
That is NOT what I said at all. If you're going to quote me quote me correctly.

It was ME who said:

You either have to do one or more of these until you're happy. Increase your accel (if you can), lower your feed, tweak CV params (see CV angle, CV distance, CV feed etc.), use exact stop (not good with plasma) or live with it I'm afraid. This is why the often forgotten quest for good accel is every bit as (if not more) important as the more poular quest for speed.

What you said was:

You can either turn on "stop CV on angles" and enter 89 degrees....or turn on "CV distance" and set it to something like .01".

That is the sledge hammer to crack a nut. Get it right.


1056
Although we try not to use any of the CV crutches,
Curious description of tuning parameters

when running at 250IPM+, they work better than exact stop.
250 ipm - you think that's fast?

Running a plasma in exact stop at those speeds just causes the machine to shake.
And what you suggested IS effectively exact stop for anything over 90 degrees.

The "proper" fix would be to (1) increase acceleration until the problem goes away or (2) slow the job way down.  
Which is what I said I believe

Option 1 isn't possible in most cases as it would take accelerations that the machine is not capable of.  Most plasma machines (even the high end industrial machines) are not build for speed and acceleration.
???

When you have a gantry weighing a few hundred pounds traveling at 300IMP, it takes a lot to slow it down.
300 ipm you think that's fast?

Short of rebuilding the machine so you can achieve triple digit acceleration, the CV setting are the next best thing.
Which is more or less what I said.

1057
You can either turn on "stop CV on angles" and enter 89 degrees....or turn on "CV distance" and set it to something like .01".
Well you could but you might as well select exact stop of you're going to hit the proverbial CV nut with a sledge hammer.  ;D

1058
if you want to post your g-code I'll have a look at it.

1059
Hi hemi43

CV will *attempt* to keep your actual feed close to commanded feed by rounding or blending. The higher your feed, the more rounding you get, the higher your accel the less rounding you get. The outside corners are probably square(er) because your CAM will most likely have introduced an arc at each corner with a diameter the same size as your kerf width so unlike an inside corner, the outside path is more CV friendly. (the outside arc is like in milling where the *correct* way to do a corner is to "roll" the tool round it). Your start and end is likely ok because starts and stops are effectively exact stop mode (as opposed to CV).

You either have to do one or more of these until you're happy. Increase your accel (if you can), lower your feed, tweak CV params (see CV angle, CV distance, CV feed etc.), use exact stop (not good with plasma) or live with it I'm afraid. This is why the often forgotten quest for good accel is every bit as (if not more) important as the more poular quest for speed.

1060
General Mach Discussion / Re: Z home goes past 0.0 to +1.0
« on: January 29, 2012, 07:53:26 AM »
I did put full shots of my screen up and config files on a picsaweb page
just in case someone asks to see one I can send them a link
Better if you just post em right here Tom. See the Additional Options link below where you type your reply (not quick reply). Just note they need a name not used here before so just precede each filename with your username or something else that makes them likely to be unique.