Corner problem

[RA Drawing]

Hi All

I’m having a corner problem here.

I’m cutting out MDF letters and when I run at 1500mm per min its good sharp corners. But when I go up to 3000 per min I get some rounding off. This is the same on all letters. This letter is the capital Y Times new roman. You can see that one corner is rounding.

My set up.

Mach 3
5mm down cut cutter.
Cut depth 5mm.
Windows XP
V carve 5.015

Any ideas??
Roger

[cabnet636]

there is a new hardware and software forum at the bottom of the index page!!

could be backlash, cnc is like a car on a road if angle and smoothing settings are not correct the cnc (car) has to compensate or overcompensate when cornering, or in some cases jerking in a curve verses a nice smooth round.

[gravirozo]

hi

in config rolldownmenu, generalsettings... constant velocity exact stop on defined angles....

when you set constant velocity the mach will calculate a speed as it can turn on endpoints of segments... if you uncheck the exact stop on sharp angles (between two vector) the mach will makes a "rounding" around corners... just like a car, to turn in corner need to slow down...
this is the reason for your rounded corners...

thanks
viktor

ps i'm new for mach...and just give a try this as my friends pushed me
they said "viktor you're the last warrior with your dos"

[RA Drawing]

Thanks for your help chaps.
Sorry I didn’t see the hardware forum. Just jumped to VC pro when it came on my screen.

I’m a little bit puzzled here. I can understand how the CV works. But I would like the corners to be sharp. What I can’t understand is, if you look at the pictures, the ends that make up the Y has four corners. But only one corner is rounded. It’s the same pattern all around the letter. If you are going in anti clockwise it’s the third corner.
Wouldn’t it do it on all corners? If not just the 90deg corners.

Apart from that. How low can I set the CV? I would need min.

Roger

[cabnet636]

could it be in the font vector?

jim

[RA Drawing]

I don't think so. If I slow the machine down to 1500mm per min it's purfect.

[cabnet636]

what type of machine,

jim

[RA Drawing]

Home built. XYZ running gear Skate bearings on bright mild steel flats. Motors,300oz steppers running direct on open drive belt.
I thought maybe some play in the bearings or starching belt. So gave it a strip down and service. And it’s very accurate.
If it’s the machine then I would have thought there would have been more corners missing.

Tomorrow after I’ve do I will do three letter, One vertical, one at 45deg and one at 90deg. I’ll run it at 3000mm per min and see what happens. If the letters come out exactly the same then surly this will rule out the machine running gear. This is the same with all fonts with 90 deg ends.
Roger

[gravirozo]

hi

radrawing... on the first picture, DSCF0005.JPG , on the top of letter the Y-s top, as i figured out after a longer straight line it "curved" down... that's why iwas thinking it might be the CV sttings in the mach...
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m cutting out MDF letters and when I run at 1500mm per min its good sharp corners. But when I go up to 3000 per min I get some rounding off. This is the same on all letters. This letter is the capital Y Times new roman. You can see that one corner is rounding

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Wouldn’t it do it on all corners? If not just the 90deg corners.

Apart from that. How low can I set the CV? I would need min.

Roger

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and it's occuring on each corner, but in case the corner coming up after a short segment the error will not be so well visible... that's why you don't see on each corner...
ie on a short segment the machine not accelerated up yet...


as you gave in your post with slower velocity you did not experienced this... if you can post your g-code we can see what is in...
of a picture hard to find out the real problem...
the mach manual contain it, higher speeds settings need to set the exact stop on sharper angles.....

when you turn on mach, on the top, as in windows programs, there are the rolldown menus, click on config, and in the menu click on general settings, and you will see the screen iposted... where's the red square, that is your settings...
this function is working on way... that you setting a minimal degree, i did set 90 and all degree, the mach find on that point the mach turn off the CV and turn back when the angles betwen vectors are fallin outside of this value...

also could help set lookahead option for 60-80 value... this does mean the mach will compute (buffering) 60-80 segment parameters... and calculate more precise feed...

sorry i don't have a good english and very hard to give in simple words these...

i have some experience of computers and drives, and what i understand i might not able explain in english...


summarized, set lookahead for higher number, the winxp will handle it, and set exact stop 90 value...
it will help...

thanks
viktor

[RA Drawing]

Hello Viktor

I don’t think the file will make any difference but here it is. It’s just a standard set up for cutting out letters with a 5mm cutter. I have done a few today and this was the last one. I have messed around with the CV and the look ahead. I can now get up to 2400mm per min. I have changed the speeds in Vcarve then looked at a close up of the 3d image. Don’t know if that would make a difference.

What about micro steps set up? My drives are from motioncontrol and they are MSD542.

Roger

[gravirozo]

hi

in vcarve any sttings won't change the 3d picture...what you make settings speed, that will be write in the nc code..

in mach3 with CV and other settings you can get a "limit" what your machine able to do yet... but for curved corner, in your situation the CV settings was the reason...

i have checked your nc, and 2.5 radius defined, as for 5.0 mm endmill... so that is perfect..
i did not think a minute long the program miscalculate...


my suggestion you, could be, draw a square like 50x50 mm and make test cuts, with different settings...
in mdi mode you can directly overwrite the speed and make it...

and the speed when your router start to make "bad" corners , that is your limit...

also when you raise the speed, the force drastically grow up... 2400 mm/min that's already good that is close 100 ipm... our routers, we use, most people here, they are not industrial routers... these routers not so rigid... not yours, almost all of ours... and the manufacturers of endmill, they recommend settings, you can reach really on industrial routers...
i have also 12x18 with nema23 motors and it can do only 600-800 mm/min....

again, if i can do something or can not that is a big different... if i can make it slower or faster that is a little something...

i hope it helps
viktor

[RA Drawing]

Thank you for your help Viktor.
I have learned a lot from you. I will do many test on squares. It sounds like my machine has work out very well.
6mm depth, 5mm cutter. Well yes, it is too much. That’s one of the reasons I wanted it to go faster. 6mm dose three cut. Were 5mm will do four cuts.
Well thank you again for your time.

Next time I'll post in the right forum.

Regards
Roger

[RA Drawing]

Hi All,
Here is my update.
After Viktor was saying play with my setting I took a look at motor turning in mach3.
Acceleration I have pulled it to 270. This has made it turn corners rapidly. I have just cut a full alphabet set of 150 high Edmunds. Plenty of 90deg corners. I started off at 1500mm per min then pushed it up on each letter. I am cutting at 3000mm per min . With no lost of corners . The cutter is 3mm and the material is12mm MDF. 4 passes @3mm depth. I then pushed it up to 3600mm per min . This just started to miss the odd corner but very slight. I might tighten up the acceleration a bit more tomorrow just to see. Cutting at 3000mm per min the cut is perfectly clean.

Roger

[cabnet636]

bravo love a good solution!!

jim

[gravirozo]

that was easy