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cutting corners off while plasma cutting cv?
« on: November 20, 2009, 12:08:42 AM »
I just installed the newest stable release of mach 3, on my plasma cutter.
I also installed the newest tng sheet cam.
Now that my plasma cutter is up and running again, the corners of my letters seem rounded off.
the files all look fine even in mach, but the end product does not.
see picture. is this a cv setting problem or something else??
does any one have a tried and true screen shot of general configuration, that they would not mind sharing?
I am cutting at 250 in per min, i have a thc-300,

http://www.flickr.com/photos/44766186@N02/4115863090/sizes/l/

Thanks for any help!

Offline lemo

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Re: cutting corners off while plasma cutting cv?
« Reply #1 on: November 20, 2009, 07:45:30 AM »
You have to go slower (I know that might be difficult), not use CV, or change the motor tuning to convince the cv algorithm it does not have to round much.
Lemo
Cut five times and still to short...
Re: cutting corners off while plasma cutting cv?
« Reply #2 on: November 20, 2009, 08:49:16 AM »
 Read through this description of the effects of the various settings.
It should give you a better understanding of how the functions are applied.

http://www.machsupport.com/docs/Mach3_CVSettings_v2.pdf

RC

Offline lemo

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Re: cutting corners off while plasma cutting cv?
« Reply #3 on: November 20, 2009, 09:55:26 AM »
Well.... Mach3 just does not follow that description very well. Good intentions. But it leaves a lot to desire. Angular settings and look ahead are not effective. Maybe on a metal mill with 10-30 ipm but the second you start to go up in speed the model fails for various reasons not all Mach3's "fault". The only salvation is to regulate feed and tune the motors till the results satisfy the need. In a plasma cutter you can adjust the motor tuning much much more aggressive regarding the acceleration compared to a heavy gantry of a larger router. You can fly around the corners like in a bumper car, compared to a semi truck. The more aggressive the acceleration the less the rounding. That together with a reasonable speed will work fine. The look ahead and the angular functions will give you gray hair. Even if the angular function would yield the correct result, it would be nice for a router,cutter, but horribly wrong for a plasma cutter who needs constant velocity to maintain cutting quality. Even in case of a router/cutter a speed change without cutter speed change is a potentially bad thing. But there are limits to Mach3.... understandable limits!

So... long story short, tweak the acceleration as aggressive as you can without loosing steps or stalling the motors and you will be much better off. 
Lemo
Cut five times and still to short...
Re: cutting corners off while plasma cutting cv?
« Reply #4 on: November 20, 2009, 10:55:53 AM »
Thanks Lemo/overloaded..
I bought a new 1600 90 amp esab and its got a need for speed.. Cuts way cleaner then my old one but its min speed recomended for 18ga is 300ipm max is 400

 I designed the plasma table 5x10 for fast travel, nema 23servos with 16 to 1 planetary gear boxes. 72v 15 amps, Is there any control solftwate that works better with plasma?? EMC2?

I have a few more questions, should I be in plasma mode? I tried to cut some 18 ga and I noticed  with it on my machine speeds up alot on straights and slows way down in corners.

When setting motor tuning is there any paticular ramp that Im trying to get? I was told when looking at the grach to set it at a 45deg angle??
Re: cutting corners off while plasma cutting cv?
« Reply #5 on: November 20, 2009, 02:00:00 PM »
I tried turning off all cv setting and cranking up the acceleration   WOW... I think Im going to replace my guides with tank parts, I went from 20 to 150 on the acceleration. What does any one else have theres set to? I spose theres a happy medium

What is screen 1024?

http://www.youtube.com/watch?v=qgdtjHfZcyI

THANKS

Offline lemo

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Re: cutting corners off while plasma cutting cv?
« Reply #6 on: November 20, 2009, 03:53:22 PM »
Sounds like it's "banging"... which means you are a tick to rough on it... but if you need the speed then that's what the setup has to live with. Physics is a bitch. No way to overcome inertia but to kick stuff around. Screw those 'gotta have 45 degree...." advice. You have to adjust to what the setup demands. The shape of the curve is a secondary and totally unrelated result of your adjustments. You do not adjust the TV set to the Oprah show, you adjust it to the reception signal strength. If you receive Oprah... then that's a side effect of proper adjustment.  I pray for you that you will not receive the Opra show with your Plasma Cutter....
Happy adjusting!
Lemo


PS:Watch that you are not loosing steps. And yes.... you have to be in plasma mode. And check your gcode that CV is not switched off by the gcode even if you have it on in the system settings. I think G61 and 64 are responsible... but please, check that. If it slows down... you are not running cv mode. It's supposed to zip around the corners with the same speed but more or less overshoot depending on the tuning (the higher the accelartion is set the more it can 'pull' the corners tight). Till your hardware flies off.... Like a car loosing traction. So.... if part of the machine fly into the office in the shop the acceleration was to hot! If the things sits there and grumbles and just vibrates.... the acceleration was WAY to hot to even start moving.
Cut five times and still to short...
Re: cutting corners off while plasma cutting cv?
« Reply #7 on: November 20, 2009, 11:27:21 PM »
lemo your a hoot!!

 I would never compared my plasma table with operah!

I have servo's with gecko320s. If I were miising steps I would fault. I cranked it all the way up to 800ipm and 200 on the acceleration... It still didnt fault, but I thought it was going rip something loose.
What is a comon setting on the acceleration? I as running it today with the plasma mode off, what does it do?

thanks for the help!

Offline lemo

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Re: cutting corners off while plasma cutting cv?
« Reply #8 on: November 21, 2009, 12:04:14 PM »
Set the feed speed the way you need it, enable CV, look at the overshoot. If it's to large, tighten the acceleration till you can live with the rounding.
There is no generally acceptable acceleration as it solely depends on the mechanical setup. It's all in the inertia. If you need high cutting speed and it still takes your machine apart... then the concept in generally is flawed and you would need a plasma cutting table made in a parallel dimension where other physics are valid. Thinking about that... I think Oprah is from that dimension as well.
Lemo
Cut five times and still to short...