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Mach Discussion => General Mach Discussion => Topic started by: hemi43 on January 29, 2012, 08:57:15 AM

Title: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 29, 2012, 08:57:15 AM
If I try to cut thin material on my plasma table, any inside sharp 90 degree corners end up getting a large radius ( around 3/8 radius), except where the cut starts and stops.
If I cut any ouside 90 degree corners, the corner comes out perfect.
Any ideas?
I've increased my acceleration rate to 40, but the problem persists.
Dan
(http://i1236.photobucket.com/albums/ff451/dantech1/Plasma%20Table/plasmacut.jpg)
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 29, 2012, 10:08:21 AM
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.
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 29, 2012, 10:16:37 AM
Thanks Stirling;
I know for a fact that my CAM is not putting an arc on the outside corners, and that's why I'm confused about this.
There is such a huge difference in radius size between inside and ouside corners at the same speed. I think I will have to learn to cut at slower speeds, but I was hoping not too.
Dan
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 29, 2012, 10:49:09 AM
if you want to post your g-code I'll have a look at it.
Title: Re: corners getting radiused at higher speed on plasma table
Post by: rrc1962 on January 29, 2012, 10:53:53 AM
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".  I agree in that if you're not getting rounding on outside contours, your CAM is probably rolling the tool around the corner.  What CAM are you using?  Post some code of a square with an outside offset.  
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 29, 2012, 11:24:38 AM
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
Title: Re: corners getting radiused at higher speed on plasma table
Post by: rrc1962 on January 29, 2012, 12:16:36 PM
Although we try not to use any of the CV crutches, when running at 250IPM+, they work better than exact stop.  Running a plasma in exact stop at those speeds just causes the machine to shake.  The "proper" fix would be to (1) increase acceleration until the problem goes away or (2) slow the job way down. 

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.  Short of rebuilding the machine so you can achieve triple digit acceleration, the CV setting are the next best thing.
Title: Re: corners getting radiused at higher speed on plasma table
Post by: BR549 on January 29, 2012, 12:40:44 PM
(;-) True industrial machines ARE built for accel AND speed. Ya can't have high speed and not high accel or else you get what the OP is describing.

You can't idle around at 100IPM cutting sheet goods and make money or even get good quality cuts with high power cutters.

One trick is to CHANGE your post to switch back and forth between exact stop and CV ONLY when it is cutting areas that are crutial to a sharp square inside corner.

Ya got to HAUL the mail so to speak, (;-) TP
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 29, 2012, 12:51:24 PM
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.
Title: Re: corners getting radiused at higher speed on plasma table
Post by: rrc1962 on January 29, 2012, 01:18:07 PM
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?

It is when you have a gantry weighing a few hundred pounds and you built the machine using NEMA 23 motors, which is VERY common.
Title: Re: corners getting radiused at higher speed on plasma table
Post by: rrc1962 on January 29, 2012, 01:43:11 PM

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.

[/quote]

Actually, you equated using the CV setting as "hitting the proverbial CV nut with a sledge hammer."

My point was that if you don't have to power to accelerate and decelerate the load at an acceptable rate, you either use the CV settings (which is a workaround to the real issue) or you rebuild your drive system to achieve the speed and acceleration you need.
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 29, 2012, 02:01:27 PM
Thanks guys;

Instead of describing the machine, I'll post a picture. It's not an industrial machine, it's one I built.
I made the gantry from aluminum to keep the weight down. Aproximate weight is probably 50Lbs .
I run dual 960in/lb steppers for the Y axis and one for the X.
The Cad/CAM program I'm using is Dolphin Cad. All my electronics are from CandCNC.

Here is the g-code. I changed the speed to 200IPM from the original 350IPM.
You'll notice that the Post Processor did not program radiuses in the corners.

Thanks for having a look.
Dan


N0000 (Filename: Flight box side.tap)
N0010 (Post processor: MP1000-THCdan.scpost)
N0020 (Date: 29/01/2012)
N0030 G20 (Units: Inches)
N0040 G53 G90 G40
N0050 F1
N0060 (Part: Flight box side)
N0070 (Process: Outside Offset, Layer0, T2: .060 ALUMINUM Jet tool)
N0080 M06 T2 F200  (.060 ALUMINUM Jet tool)
N0090 G00 Z0.5000
N0100 X6.2300 Y2.9800
N0110 Z0.1500
N0120 G28.1 Z0.12
N0130 G92 Z0.0
N0140 G00 Z0.0940
N0150 G92 Z0.0
N0160 G00 Z0.1500
N0170 M03
N0180 G01 Z0.0600 F360.0
N0190 X4.2700 F200.0
N0200 Y0.5200
N0210 X6.2300
N0220 Y2.9800
N0230 M05
N0240 G00 Z0.5000
N0250 X10.5000 Y8.2700
N0260 Z0.1500
N0270 G28.1 Z0.12
N0280 G92 Z0.0
N0290 G00 Z0.0940
N0300 G92 Z0.0
N0310 G00 Z0.1500
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
N0430 G00 Z0.5000
N0440 X0.0000 Y0.0000
N0450 M05 M30


(http://i1236.photobucket.com/albums/ff451/dantech1/DSC04428.jpg)
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 29, 2012, 02:58:25 PM
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.

Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 29, 2012, 03:01:24 PM
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.
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 29, 2012, 03:36:34 PM
Thank-you Stirling !
Any help is greatly appreciated.
I will try and mess around with some of the points you made earlier.
Dan
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 30, 2012, 05:34:53 AM
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 (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
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 30, 2012, 09:00:16 AM
Thanks so much Stirlling !!
I checked the G code for arcs in the small cut out, but never thought of checking the outside corners.  ::)
I understand clearly what you're saying, and I don't have an issue having a small radius on my parts, because this is a plasma machine afterall and not a waterjet.
The radius I have been getting (about 3/8") was just too large and would ruin the part. I would be happy with a 1/8 radius.
I will draw a small sample part today and try some of your recomendations.
I will post back my results.
Thanks again for your time, it's greatly appreciated.
Dan
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 30, 2012, 09:18:43 AM
Hi Dan - There is actually a clue here for you perhaps which may help you in your tuning. If you're happy with the sharpness of the outside corners, that shows that CV is pretty much holding round those small arcs. You could try putting similar size arcs on the inside path. They won't cut as sharp as the outside of course but they may be better than what you have at the moment. One more thing to try anyway.

Ian
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 30, 2012, 09:23:11 AM
Those arc were put there by my CAM, which I forgot to mention is from Sheetcam.
I will check to see if it's possible to create arcs for inside contours.
I'm sure I could manually modify the g-code, but I don't really want to go down that road. ;D
Dan
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 30, 2012, 09:40:47 AM
Yes - most CAMs will "roll" round reflex angles - or at least they should AFAIK. They will not do this for any other angle - they can't because you can't "roll" around those. You will have to create those other arcs yourself in your CAD.

Ian
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 30, 2012, 09:45:44 AM
Ahhhh !! Yeah, that's an easy way to fix the problem !! Why didn't I think of that ?? ;)
I will try that.
Dan
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 30, 2012, 10:01:12 AM
rrc1962 - a peace offering  ;D

Before I first bought Mach I contacted Art and asked how good the CV was because at the time I'd struggled to figure out exactly how to tune it which we all know is not hugely well documented. His answer was the defining reason why I bought the licence and then spent a lot of time tweaking and playing to see what it could do. I'm no expert but I do have a pretty good feel for it and have helped Brian in the past to trouble shoot CV faults and suggested corrections to errors in the CV documentation. I see a lot of posts where folks recommend similar settings to those you've suggested and to me, this is a shame. Not only is CV capable of so much more but settings that work for one person can be useless for others. It so much depends on the individual machine's capabilities. I hope I've helped get accross in this thread why IMHO "one size fits all" harsh settings are doing Mach's CV a big disservice.

Anyway I hope you havn't dropped me off your Christmas card list but if so you arn't the first and I doubt you'll be the last  ;D

Cheers

Ian
Title: Re: corners getting radiused at higher speed on plasma table
Post by: Picengraver on January 30, 2012, 12:58:57 PM
Ian,
Thanks much for the very informative post.  I'm adding you to my card list  :)

Regards,
John Champlain
www.picengrave.com
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 30, 2012, 01:10:28 PM
LOL - Thanks John - you've made my day  ;D
Title: Re: corners getting radiused at higher speed on plasma table
Post by: Picengraver on January 30, 2012, 01:39:11 PM
 :)
Title: Re: corners getting radiused at higher speed on plasma table
Post by: BR549 on January 30, 2012, 03:22:09 PM
I guess yall missed the part where he used an outside offset for and inside cut? That CAN throw a monkey wrench in the way Scam sees and programs a cut.

We use a similar size table and hardware electronics and DO NOT see this problem here.

Just a thought, (;-) TP

Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 30, 2012, 05:23:16 PM
Sorry Tel, it's been a long old day and I'm about to hit the sack but you've lost me there old buddy. He's rightly got kerf to the left so I'm not with you. You want to run that by me again?

Ian
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 30, 2012, 06:39:20 PM
I guess yall missed the part where he used an outside offset for and inside cut? That CAN throw a monkey wrench in the way Scam sees and programs a cut.

We use a similar size table and hardware electronics and DO NOT see this problem here.

Just a thought, (;-) TP


Hmmm !!! I am using outside offset, but only for outside contours. Inside contours automatically get cut on the inside.
Had a busy day and never tried anything on the machine today. :-(
Dan


Title: Re: corners getting radiused at higher speed on plasma table
Post by: BR549 on January 30, 2012, 07:34:19 PM
Look at the posted code. The re is ONLY one operation listed in all the code and that is an OUTSIDE cut.

That tells me that when you cammed it out in Scam you did NOT set up a layer and operation for the inside cut but used the outside offset process to do everything.

So it really did NOT cut where you thought it would.

It would treat an outside cut differently from and inside, MAYBE

Just a thought, (;-) TP


Title: Re: corners getting radiused at higher speed on plasma table
Post by: BR549 on January 30, 2012, 07:57:02 PM
Here is what I would get for the same type cut.

N0000 (Filename: CutSquares.tap)
N0010 (Post processor: MP3000-DTHC-SmlArcFix#3.scpost)
N0020 (Date: 01/30/12)
N0030 G20 (Units: Inches)
N0040 G53 G90 G40
N0050 F1
N0060 (Part: CutSquares)
N0070 (Process: Inside Offset, 1, T3: Plasma, 0.06 in kerf)
N0080 M06 T3 F60  (Plasma, 0.06 in kerf)
N0090 G00 X6.2292 Y4.7488 Z0.5000
N0100 G28.1 Z0.50
N0110 G92 Z0.0
N0120 G00 Z0.1370
N0130 G92 Z0.0
N0140 G00 Z0.1200
N0150 M03
N0160 G04 P1
N0170 G01 Z0.8000 F60
N0180 G02 X6.1332 Y4.8448 I0.0000 J0.0960 F60.0
N0190 G01 X9.1316 F60
N0200 Y2.1095
N0210 X6.1332
N0220 Y4.8448
N0230 G02 X6.2932 Y4.6848 I0.0000 J-0.1600 F60.0
N0240 (Process: Outside Offset, 0, T3: Plasma, 0.06 in kerf)
N0250 M05
N0260 G00 X12.1260 Y12.1260 Z0.5000
N0270 G28.1 Z0.50
N0280 G92 Z0.0
N0290 G00 Z0.1370
N0300 G92 Z0.0
N0310 G00 Z0.1200
N0320 M03
N0330 G04 P1
o549
N0340 X12.1260 Y12.1260
N0350 G02 X12.0300 Y12.0300 Z0.8000 I-0.0960 J0.0000
N0360 G01 X12.0000 F60
N0370 X0.0000
N0380 G03 X-0.0300 Y12.0000 I0.0000 J-0.0300 F60.0
N0390 G01 Y0.0000 F60
N0400 G03 X0.0000 Y-0.0300 I0.0300 J0.0000 F60.0
N0410 G01 X12.0000 F60
N0420 G03 X12.0300 Y0.0000 I0.0000 J0.0300 F60.0
N0430 G01 Y12.0000 F60
N0440 Y12.0300
N0450 G02 X12.1900 Y12.1900 I0.1600 J0.0000 F60.0
N0460 G00 Z0.5000
N0470 X0.0000 Y0.0000
N0480 #650 = 60.473 #651 = 2
N0490 M05 M30
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 30, 2012, 08:45:54 PM
Look at the posted code. The re is ONLY one operation listed in all the code and that is an OUTSIDE cut.

That tells me that when you cammed it out in Scam you did NOT set up a layer and operation for the inside cut but used the outside offset process to do everything.

So it really did NOT cut where you thought it would.

It would treat an outside cut differently from and inside, MAYBE

Just a thought, (;-) TP




Sheetcam automatically cuts inside profiles on the inside, and outside profiles on the outside, when outside offset is selected ( That's a mouthfull )
If what you're saying is correct, then my pieces would not be to size. My pieces are perfect except for the rounded corners.

Dan
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 30, 2012, 09:17:50 PM
OK;
I ran some test pieces, and here's the results.
I hope the picture is clear enough. I tried running the first part at 340 IPM, but it was just too fast.
The second one I turned the CV distance on and set it to 25 units (whatever a unit is , I dunno).Also, I re-drew the part so that the inside corners have a .125 rad.
The third I slowed it to 238IPM. Still no difference.
The last one I checked off the "stopCV ON >0". The results were way better, and something I could live with. It's only thin material that will be an issue anyways.
The machine didn't seem to run any harder than normal.
Dan

(http://i1236.photobucket.com/albums/ff451/dantech1/testpieces.jpg)
Title: Re: corners getting radiused at higher speed on plasma table
Post by: BR549 on January 30, 2012, 09:37:20 PM
We must be running different versions(;-) I'll go back to drinking coffe now.

(;-) TP
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on January 31, 2012, 04:51:33 AM
Took me a while to get my head round your pics at first but then I realized (I think) you've rotated the parts in your pics anti-clockwise by 90 degrees!!! (Your start/end from your code is top-right but in your pics it looks like it's top-left!

The second one I turned the CV distance on and set it to 25 units (whatever a unit is , I dunno).
This is saying it can start rounding when you're within 25 inches (your units) of the corner. Your whole hole is only a couple of inches so your ALLWAYS within 25 inches so this setting is going to have no effect at all. I'd suggest you try a CV distance of 0.25 and work down to 0.125 or so - that sort of range.

The third I slowed it to 238IPM. Still no difference.
Well I wouldn't say NO difference. It's slightly better but I agree still no good. Again your CV distance of 25 inches is going to have no effect. BTW - are your X and Y axis vel and accel the same? The rounding doesn't look symetrical.

The last one I checked off the "stopCV ON >0". The results were way better, and something I could live with. It's only thin material that will be an issue anyways.
The machine didn't seem to run any harder than normal.
Stop CV on > 0 is turning OFF CV - you're effectively cutting Exact Stop. If your happy with this then OK but I'd take this as a clue to trying CV feed starting at say around 50%. Of course if you get down to just a few % your effectively turning OFF CV again.


We must be running different versions(;-) I'll go back to drinking coffe now.
Yeah - but what's in the coffee Tel?  ;D

A vid for our viewing pleasure.
http://www.youtube.com/watch?v=aXEFGmkqvQs&feature=player_embedded (http://www.youtube.com/watch?v=aXEFGmkqvQs&feature=player_embedded)
Title: Re: corners getting radiused at higher speed on plasma table
Post by: BR549 on January 31, 2012, 11:46:04 AM
 ;D  >:D  ;)


It's just hot blonde and sweet with a little extra coolant mixed in.    ::)


Even slower with CV bascially off the cut is a bit rough on the corners and seems to be squirly on the staright cuts BUT that might be the pictures.

It looks as thought the cut height may be too high and the arc is not stable. What are the cut paramaters? Material ?pierc ,cut preset voltage,etc

Are you running with the DTHC active ?  It it maintaining voltage?

(;-) TP
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on January 31, 2012, 03:39:09 PM
;D  >:D  ;)


It's just hot blonde and sweet with a little extra coolant mixed in.    ::)


Even slower with CV bascially off the cut is a bit rough on the corners and seems to be squirly on the staright cuts BUT that might be the pictures.

It looks as thought the cut height may be too high and the arc is not stable. What are the cut paramaters? Material ?pierc ,cut preset voltage,etc

Are you running with the DTHC active ?  It it maintaining voltage?

(;-) TP

All the parameters are by the book, except for the speed that I had to slow down. All the pieces I've been cutting are .060 aluminum. The last piece was steel because I had no more scrap aluminum kicking around. :-)

DTHC was turned on, and maintains a steady pre-programmed 117 volts. My pierce height is .15 and cut height is .060.

Maybe the parts above are a bad example, because I'm very happy with the cut quality.

Dan
Title: Re: corners getting radiused at higher speed on plasma table
Post by: BR549 on January 31, 2012, 09:42:34 PM
Pictures are somtimes very hard to go by If you are happy that is ALL that matters.

Keep um Burning, (;-)TP
Title: Re: corners getting radiused at higher speed on plasma table
Post by: docltf on January 31, 2012, 10:49:51 PM
Hemi

try your start point in the middle of the long X-axis and stay away from the corners.

bill
Title: Re: corners getting radiused at higher speed on plasma table
Post by: rrc1962 on February 01, 2012, 09:01:52 PM
rrc1962 - a peace offering  ;D


No biggie.  I'm kind of in the "build the machine to suit the need" camp rather than the "build the machine and then figure out how to make it work" camp.  We pretty much agree.  The best solution is acceleration...which is a bit confusing.  With 960oz/in motors and a 50 pound gantry, his machine should be able to run some very high acceleration numbers.  Up until this post, I hadn't noticed where he posted his accel numbers.
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on February 01, 2012, 11:42:39 PM
rrc1962 - a peace offering  ;D


No biggie.  I'm kind of in the "build the machine to suit the need" camp rather than the "build the machine and then figure out how to make it work" camp.  We pretty much agree.  The best solution is acceleration...which is a bit confusing.  With 960oz/in motors and a 50 pound gantry, his machine should be able to run some very high acceleration numbers.  Up until this post, I hadn't noticed where he posted his accel numbers.
My very first post stated that I had increased my acceleration rate to 40.
Dan
Title: Re: corners getting radiused at higher speed on plasma table
Post by: hemi43 on February 02, 2012, 09:21:15 AM
I checked the specs on my motors, and they are 620 oz/in NOT 960 !! :)
Title: Re: corners getting radiused at higher speed on plasma table
Post by: stirling on February 02, 2012, 10:20:22 AM
I've built tables with 3Nm (424 oz/in) that get 2500mm/s/s (~100 in/s/s) no problem - in fact that's backed off so I don't jerk the hell out of the things. That gantry looks really light - you MUST be able to get a LOT more accel out of that puppy. What's your power supply, drivers, motors specs, drive ratio?

Ian
Title: Re: corners getting radiused at higher speed on plasma table
Post by: rrc1962 on February 02, 2012, 02:36:24 PM
I missed that.  You should be able to run MUCH higher than that.  We can go over 100 with a 300 pound gantry and 640oz/in motors with 3:1 belt reduction.