G02-G03 calculations

[lseguine]

hello.

i am using mach3, msm pro, mill, xp,parallel port, no plugins.

i'm using a bob c11 from cnc4u. and kl-5056d drivers.

i tried cutting a part that had three holes in it, see attached photo.

the x axis runs through all three holes centerts at y=0 nd origin closr to tyhe middle hole.
when cutting the 5/8 hole and the 1/4 inch holes came up strange.

for some strange reason movement in the y axis stoped befor reaching max y direction by roughly .012" and not at max y value.

once direction changed there was still no movement till further down -x direction then it worked fine till it approach the neg y value but stii a ways from max - value.

i cpou;d see a problem with backlash if things stoped moving at the max y values but to stop .012" short??

any ideas what is going on?

larry

[lseguine]

oooops missed attaching the photo..

Attachments:

[DaveCVI]

Hi Larry,
Mach executes all motion movements whether one is running MSM or another screen set; therefore, if the motion stopped short of where you expected it to go, the first thing I'd think about what could cause mach to do that...

The first mach setting that comes to mind are the soft boundary limits - if you have soft limits on, check where the limits are set.

The second thing that I think of is lost steps - is this a stepper system? Was the lost motion just after a rapid movement? could the system be loosing steps so that it is not ending up physically where mach thinks it is?

Dave

[lseguine]

Dave,

i think i know what your talking about reguardingsoft limits, i'm set at x 11 inch max o min, y 4 max 0 min inch. i'm working out in the middle of the travel for y=0 from wc and the poast processor programmoinmg.

i'm using HSMEXPRESS poast processor software.
there was no rapid movement just 0.5 in/min cutting simi circular cut. starting at x max + y=0 going to max y + then to -x max and again y =0

but for some reason the y axis stops moving when it gets close to something like 15-20 degrees before y= +or- .625 leaving a straight run that is .012" short of .625 the xaxis is giving a clean close .625 +/- .003 ish

so now where do i go??

i have asked on several diferant forums but keep getting the same answer, BACKLASH, but this happens befor the changein direction..
but then i guess i might not under stand backlash.. always seebed that was haow far you moved an axis befor the table actually moved.

i am open to being educated friends help please.....

larry in alaska boonies

[DaveCVI]

Hi,

When a machine does not end up at the expected physical location, it's often good to double check the basics of the machine set up.

The basics fpr setting up mach are in the mach install & config manual - which the "install & config"" button on the MSM reference page will open. The following section #s refer to that manual:

section 5.5.1: covers steps per unit and how to measure if the machine is actually traveling the amount you have commanded.

section 5.6.1 covers soft limits and how they can be used to prevent running into an axis limit.

section 5.6.3 covers backlash
I understanding that a symptom of backlash will be that a circle will not end up round when it's cut. measure the cut circular pockets along different axes to see if this is the case.

If the pocket is round, but not of the expected diameter, check the cutter to see if it is really the diameter than you think it is.

Note: everything I've read re mach and backlash ends up saying that backlash can't really be fixed in software (mach) - it's best to fix the mechanical source of the backlash.

Dave